Method for efficiently degrading pet recycling tpa

Abstract

The present application relates to the technical field of plastic degradation, and in particular to a method for efficiently degrading PET to recover TPA, which comprises the following steps: adding PET waste to be treated into polyethylene glycol aqueous solution containing an alkaline reagent, and performing depolymerization reaction at 70-110 DEG C under normal pressure; and then separating the solid and liquid while hot; wherein the volume ratio of water to polyethylene glycol is 1:1.5-1:9; dissolving the solid obtained by the solid-liquid separation in water, filtering out the residue, adjusting the pH of the obtained solution, and precipitating TPA monomers. The method has the advantages of simple steps, low energy consumption, high degradation efficiency, easy scale-up production, recyclable degradation solution, and good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plastic degradation, in particular to a method for efficiently degrading PET to recover TPA. BACKGROUND

[0002] Polyethylene terephthalate (PET) is a highly applied thermoplastic polyester material, due to its excellent transparency, strength and chemical resistance, it is widely used in plastic bottles, food packaging and textiles and other fields. However, with the rapid increase of PET material use, the resulting waste problem is increasingly serious, which seriously affects the sustainability of the ecological environment. Therefore, the effective recovery of PET has important significance for realizing green environmental protection and sustainable development.

[0003] Currently, the recovery of PET mainly adopts incineration treatment, physical method recovery, chemical method recovery and biological method recovery and other means. Among them, incineration treatment is to directly burn waste PET materials to recover heat energy, although this method is rapid and occupies less space, but the harmful gases and ash produced may cause irreversible impact on the environment. Physical method recovery is to clean, crush and reprocess waste PET materials by mechanical means, this method has significant effect, but when dealing with waste containing other types of impurities or mixed materials, its recovery efficiency decreases significantly. Biological method recovery is to use microorganisms to degrade PET, although this method has broad prospects, but its actual large-scale application is still in the research and development stage, and it cannot realize large-scale commercial application in the short term. In contrast, chemical method recovery is to rely on chemical reaction to degrade PET into lower molecular weight compounds or terephthalic acid (TPA), which can realize higher level of resource recovery, and is the most suitable recovery method for industrial application at present.

[0004] However, the degradation process of PET by chemical method involves complex and harsh process conditions, and a long reaction time is needed to completely degrade PET into TPA. Therefore, it is of great significance to explore more economical and more environmentally friendly PET degradation methods. SUMMARY

[0005] In view of this, the present application provides a method for efficiently degrading PET to recover TPA, which has simple steps, low energy consumption, high degradation efficiency, easy to scale up production, and the degradation liquid can be recycled, and has good industrial application prospect.

[0006] To solve the above technical problems, the present application provides a method for efficiently degrading PET to recover TPA, the steps comprising:

[0007] S1, adding the PET waste to be treated into the polyethylene glycol aqueous solution containing the alkaline reagent, and performing depolymerization reaction at 70-110 DEG C under normal pressure, and then separating the solid and liquid while hot; wherein the volume ratio of water to polyethylene glycol is 1:1.5-1:9;

[0008] S2, dissolving the solid obtained by the solid-liquid separation in water, filtering out the residue, adjusting the pH of the obtained solution, and precipitating TPA monomer.

[0009] The present application uses "alkaline reagent-polyethylene glycol-water" as the degradation solution, which can quickly degrade the PET waste in a short time, greatly improving the degradation efficiency. The inventors analyze that it may be that the hydrogen bond is generated between the hydroxyl ions ionized by the alkaline reagent and the polyethylene glycol, so that the hydroxyl ions can be closer to the PET waste under the "leadership" of the polyethylene glycol, accelerating the degradation of the PET waste. A small amount of water in the polyethylene glycol aqueous solution can accelerate the complete dissolution of the alkaline reagent, thereby accelerating the degradation rate; at the same time, the presence of a small amount of water can also make the terephthalate generated in the degradation to be enriched and deposited at the bottom of the reaction container, which is more conducive to solid-liquid separation. Redissolving the solid obtained by the solid-liquid separation and adjusting the pH of the solution by adding acid can precipitate TPA monomer, which has high purity and high recovery rate.

[0010] The present application provides a method for efficiently degrading PET and recovering TPA, which can realize the rapid degradation of PET under normal pressure conditions, without the need for high-temperature and high-pressure depolymerization conditions, thereby improving the safety of the reaction. The degradation method has high specificity for PET components, and when the waste to be degraded contains other components in addition to PET, the method can only degrade the PET component in the waste, while other non-PET components and impurities are distributed in the upper solution, thereby making the terephthalate only deposited at the bottom of the container.

[0011] Preferably, after the depolymerization reaction is completed, the generated terephthalate solid is deposited at the bottom of the reaction container, and the degradation solution can be separated from the terephthalate solid at the bottom of the container by pouring. For a larger scale processing process, the upper solution can be directly pumped out by external power, without the need for a filtering device to realize solid-liquid separation, thereby simplifying the processing steps of the PET waste.

[0012] Preferably, the aqueous solution of hydrochloric acid, sulfuric acid or phosphoric acid can be used to adjust the pH of the solution to less than 3.

[0013] Preferably, the alkaline reagent includes at least one of sodium hydroxide or potassium hydroxide.

[0014] Preferably, the concentration of the alkaline reagent in the polyethylene glycol aqueous solution is 0.04-0.2 g / mL, and more preferably 0.12 g / mL.

[0015] Preferably, the molecular weight of the polyethylene glycol is 200-600, preferably polyethylene glycol 200, polyethylene glycol 400 or polyethylene glycol 600.

[0016] Preferably, the amount of PET waste added per liter of polyethylene glycol aqueous solution dissolving the alkaline reagent is 10-130 grams, further preferably 40-100 grams / liter, and more preferably 70 grams / liter.

[0017] Preferably, the temperature of the depolymerization reaction is 90-100℃, and the reaction time is 2-30 min.

[0018] The method for efficiently degrading PET to recover TPA provided by the present application has different depolymerization times for different forms of PET waste, but according to the method provided by the present application, the PET waste can be completely degraded in 30 min at most, and the degradation treatment efficiency is significantly improved.

[0019] Further preferably, the reaction time of the depolymerization reaction is 10-18 min.

[0020] Preferably, the PET waste includes at least one of plastic bottles containing a PET component, polyester fibers, textiles, bundling tapes or engineering plastic parts, and the method provided by the present application can also be used for PET degradation of other forms of PET waste.

[0021] Preferably, in order to further reduce the processing cost, the liquid phase obtained by the solid-liquid separation of step S1 is recovered, the proportion of polyethylene glycol aqueous solution and alkaline reagent in the liquid phase is adjusted, and then recycled for depolymerization reaction, realizing the recycling of the degradation liquid.

[0022] Preferably, the liquid phase is enriched with ethylene glycol monomers, and when the volume concentration of ethylene glycol monomers in the liquid phase exceeds 10%, the ethylene glycol monomers are distilled and recovered, and the liquid phase after distillation of the ethylene glycol monomers is recycled for depolymerization reaction.

[0023] The application has the advantages that: compared with the prior art, the application uses green and environmentally friendly non-toxic reagents to rapidly degrade PET waste, and the conversion rate of PET is as high as 93% or more, and the highest can reach 99.7%, the yield of the obtained TPA is maintained at 85% or more, and the highest is 95.86%, and the purity of the obtained TPA is maintained at 98.5% or more. The method not only shortens the degradation reaction time and reduces the energy consumption, but also automatically enriches the intermediate product obtained by degradation to the bottom of the container, actively realizes the effective separation of the degradation product and the degradation liquid, omits the cumbersome filtration separation step, and the separated degradation product (terephthalate) only needs to add a small amount of water to be dissolved. Compared with the traditional PET hydrolysis process which produces a large amount of salt-containing wastewater, the degradation method provided by the application greatly reduces the generation of salt-containing wastewater, and the liquid phase after solid-liquid separation can still be used for depolymerization reaction after component adjustment, and a high PET conversion rate and TPA yield can still be obtained; at the same time, the ethylene glycol in the liquid phase obtained by solid-liquid separation can also be recovered when it is enriched to a certain concentration. The degradation method provided by the method significantly improves the economy of the entire degradation process and has great application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The infrared spectrum of the TPA obtained in Examples 1-3 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the application more clear and understandable, the application will be further described in detail below in combination with specific examples. It should be understood that the specific examples described herein are only used to explain the application and do not limit the application.

[0026] The molecular weight of the polyethylene glycol used in the following examples and comparative examples is the weight average molecular weight.

[0027] Example 1

[0028] The present embodiment provides a method for efficiently degrading PET and recycling TPA. The PET waste used in this embodiment is PET polyester fiber, and the mass percentage of PET is 100%. The method comprises the following steps:

[0029] 6 g of potassium hydroxide was added to a round-bottom flask containing 50 mL of an aqueous solution of polyethylene glycol 600 (the volume ratio of water to polyethylene glycol 600 was 1:4), heated and stirred to dissolve and mix uniformly, and 3.5 g of PET polyester fiber (denoted as X) was added. The reaction was carried out at 90℃ under normal pressure with stirring at a speed of 400 rpm for 10 min, and the PET polyester fiber was basically completely degraded.

[0030] After the reaction, the potassium terephthalate generated by the degradation of the PET polyester fiber was deposited firmly by enrichment at the bottom of the round-bottom flask, the upper solution was poured into another beaker, 50 mL of water was added to the round-bottom flask to dissolve the terephthalic acid deposited at the bottom of the flask, and the undissolved residues (including undegraded PET raw materials and impurities) were removed by filtration (0.01 g, denoted as Y), the pH of the obtained filtrate was adjusted to less than 3 with an acidic solution to precipitate TPA, and the TPA filter cake was collected by filtration again, washed with water, and dried in an oven at 65°C for 24 h to obtain the monomer product TPA 2.90 g.

[0031] In addition, the upper solution separated was subjected to component adjustment (appropriate addition of polyethylene glycol 600 and potassium hydroxide) and was continuously used for the next PET degradation.

[0032] The conversion rate of PET and the yield of TPA were calculated according to the following formula, and the purity of the obtained TPA was determined by a liquid chromatograph, and the results are shown in Table 1.

[0033] PET conversion rate (%) = (X-Y) / (X x w) x 100.

[0034] Wherein, X represents the initial mass of the PET raw material added into the reactor, in grams in this example; Y represents the mass of the insoluble substances obtained by filtration of the undegraded PET raw materials and impurities; and w represents the mass percentage content of the PET component in the PET raw material.

[0035] TPA yield (%) = actual mass of TPA generated / theoretical mass of TPA that should be generated x 100.

[0036] Wherein, the "actual mass of TPA generated" represents the mass of the monomer product TPA finally obtained, and the "theoretical mass of TPA that should be generated" represents the mass of the TPA that should be generated theoretically from the PET component in the PET raw material (i.e. X x the mass percentage content of PET w).

[0037] Example 2

[0038] The present embodiment provides a method for efficiently degrading PET to recover TPA, and the PET waste used in this embodiment is PET polyester fiber, and the mass percentage content w of PET is 100%, and the method specifically comprises the following steps:

[0039] 5 g of potassium hydroxide was added to a round-bottom flask containing 50 mL of an aqueous solution of polyethylene glycol 400 (the volume ratio of water to polyethylene glycol 400 was 1:9), heated and stirred to dissolve and mix uniformly, 3.0 g of PET polyester fiber was added, and the reaction was carried out at 90°C under normal pressure with stirring at a speed of 400 rpm for 8 min, and the PET polyester fiber was basically completely degraded.

[0040] The steps after the reaction is ended are the same as those in Example 1.

[0041] The conversion rate of PET and the yield of TPA are calculated by the same calculation method as in Example 1, and the purity of the obtained TPA is determined by a liquid chromatograph, and the results are shown in Table 1.

[0042] Example 3

[0043] This example provides a method for efficiently degrading PET to recover TPA. The PET waste used in this example is PET polyester fiber, and the mass percentage w of PET is 100%. The method specifically includes the following steps:

[0044] 8 g of potassium hydroxide is added to a round-bottom flask containing 50 mL of an aqueous solution of polyethylene glycol 400 (the volume ratio of water to polyethylene glycol 400 is 1:1.5), heated and stirred to dissolve and mix uniformly, 0.5 g of PET polyester fiber is added, and the reaction is stirred at 400 rpm under normal pressure at 100°C for 30 min, and the PET polyester fiber is basically completely degraded.

[0045] The steps after the reaction is ended are the same as those in Example 1.

[0046] The conversion rate of PET and the yield of TPA are calculated by the same calculation method as in Example 1, and the purity of the obtained TPA is determined by a liquid chromatograph, and the results are shown in Table 1.

[0047] Example 4

[0048] This example provides a method for efficiently degrading PET to recover TPA. The PET waste used in this example is a plastic bottle made of PET material, and the mass percentage w of PET is 100%. The method specifically includes the following steps:

[0049] 10 g of sodium hydroxide is added to a round-bottom flask containing 50 mL of an aqueous solution of polyethylene glycol 600 (the volume ratio of water to polyethylene glycol 600 is 1:4), heated and stirred to dissolve and mix uniformly, 6.5 g of PET polyester bottle pieces are added, and the reaction is stirred at 400 rpm under normal pressure at 70°C for 30 min, and the PET plastic bottle is basically completely degraded.

[0050] The steps after the reaction is ended are the same as those in Example 1.

[0051] The conversion rate of PET and the yield of TPA are calculated by the same calculation method as in Example 1, and the purity of the obtained TPA is determined by a liquid chromatograph, and the results are shown in Table 1.

[0052] Example 5

[0053] The embodiment provides a method for efficiently degrading PET to recover TPA, and the PET waste used in the embodiment is an engineering plastic part made of PET, and the mass percentage of the PET is 96%, and the method comprises the following steps:

[0054] 2 g of sodium hydroxide is added to a round-bottom flask containing a water solution of 50 mL of polyethylene glycol 600 (the volume ratio of water to polyethylene glycol 600 is 1:4), heated and stirred to dissolve and mix uniformly, and 0.5 g of the engineering plastic part made of PET is added, and the reaction is stirred at 400 rpm under normal pressure at 110 ℃ for 20 min, and the PET in the engineering plastic part is substantially completely degraded.

[0055] The steps after the reaction ends are the same as those in Example 1.

[0056] The conversion rate of the PET and the yield of the TPA are calculated by the same calculation method as in Example 1, and the purity of the obtained TPA is determined by using a liquid chromatograph, and the results are shown in Table 1.

[0057] Example 6

[0058] The embodiment provides a method for efficiently degrading PET to recover TPA, and the PET waste used in the embodiment is an engineering plastic part made of PET, and the mass percentage of the PET is 96%, and the method comprises the following steps:

[0059] 6.5 g of potassium hydroxide is added to a round-bottom flask containing a water solution of 50 mL of polyethylene glycol 600 (the volume ratio of water to polyethylene glycol 600 is 1:4), heated and stirred to dissolve and mix uniformly, and 3 g of the PET polyester fiber is added, and the reaction is stirred at 400 rpm under normal pressure at 100 ℃ for 2 min, and the PET polyester fiber is substantially completely degraded.

[0060] The steps after the reaction ends are the same as those in Example 1.

[0061] The conversion rate of the PET and the yield of the TPA are calculated by the same calculation method as in Example 1, and the purity of the obtained TPA is determined by using a liquid chromatograph, and the results are shown in Table 1.

[0062] Comparative Example 1

[0063] The comparative example provides a method for degrading PET to recover TPA, and the PET-containing waste used in the comparative example is the same as the PET waste in Example 1, that is, the PET polyester fiber, and the mass percentage of the PET is 100%, and the specific steps comprise:

[0064] 6 g of potassium hydroxide was added to a round-bottom flask containing 50 mL of water, heated and stirred to dissolve and mix uniformly, 3.5 g of PET polyester fiber was added, and the reaction was stirred at 400 rpm at 90 °C under normal pressure for 10 min, and the PET polyester fiber was not completely degraded.

[0065] The reaction solution was filtered to remove the undegraded PET polyester fiber, the pH of the filtrate was adjusted to less than 3 with an acidic solution to precipitate TPA, and after washing with water and drying in an oven at 65 °C for 24 h, the monomer product TPA was obtained.

[0066] The conversion rate of PET and the yield of TPA were calculated according to the same calculation method as in Example 1, and the purity of the obtained TPA was determined by liquid chromatography, and the results are shown in Table 1.

[0067] Comparative Example 2

[0068] This comparative example provides a method for degrading PET to recover TPA, and the PET-containing waste used in this comparative example is the same as the PET waste in Example 1, i.e. PET polyester fiber, and the mass percentage of PET w is 100%, and the specific steps include:

[0069] 6 g of potassium hydroxide was added to a round-bottom flask containing 50 mL of water, heated and stirred to dissolve and mix uniformly, 3.5 g of PET polyester fiber was added, and the reaction was stirred at 400 rpm at 90 °C under normal pressure for 10 min, and the PET polyester fiber was not completely degraded.

[0070] The reaction solution was filtered to remove the undegraded PET polyester fiber, the pH of the filtrate was adjusted to less than 3 with an acidic solution to precipitate TPA, and after washing with water and drying in an oven at 65 °C for 24 h, the monomer product TPA was obtained.

[0071] The conversion rate of PET and the yield of TPA were calculated according to the same calculation method as in Example 1, and the purity of the obtained TPA was determined by liquid chromatography, and the results are shown in Table 1.

[0072] Comparative Example 3

[0073] This comparative example provides a method for degrading PET to recover TPA, and the PET-containing waste used in this comparative example is the same as the PET waste in Example 1, i.e. PET polyester fiber, and the mass percentage of PET w is 100%, and the specific steps include:

[0074] 6 g of potassium hydroxide was added to a round bottom flask containing 50 mL of ethylene glycol, heated and stirred to dissolve and mix uniformly, 3.5 g of PET polyester fiber was added, and the reaction was stirred at 90 ℃ under normal pressure at a speed of 400 rpm for 10 min, and the PET polyester fiber was not completely degraded.

[0075] The reaction solution was filtered, and the filter cake (the filter cake was undegraded PET polyester fiber, impurities and potassium terephthalate generated by PET degradation) was collected and re-dissolved in water to completely dissolve the potassium terephthalate, and then the undegraded PET polyester fiber and impurities were removed by filtration, the pH of the obtained filtrate was adjusted to less than 3 with an acidic solution to precipitate TPA, and after filtration, the TPA was washed with water and dried in an oven at 65 ℃ for 24 h to obtain the monomer product TPA.

[0076] The conversion rate of PET and the yield of TPA were calculated according to the same calculation method as in Example 1, and the purity of the obtained TPA was determined by a liquid chromatograph, and the results are shown in Table 1.

[0077] Table 1 Determination results of Examples 1-6 and Comparative Examples 1-3

[0078] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 PET conversion (%) 99.71 98.76 99.23 93.16 99.13 97.82 1.04 6.10 29.4 TPA yield (%) 95.86 95.68 94.06 85.86 94.35 92.21 0.70 3.13 24.50 TPA purity (%) 99.48 98.81 98.76 99.05 99.25 99.31 98.74 98.68 99.31

[0079] As shown in Table 1, by using the method for degrading PET provided by the present application, the conversion rate of PET component in PET waste can reach more than 93% within 30 min, and the shortest time is 2 min, and at the same time, the yield of the obtained TPA is maintained at more than 85%, and the purity is maintained at more than 98.5%.

[0080] In Comparative Example 1, only water was used as the degradation solvent, and the obtained PET conversion rate and TPA yield were both low; in Comparative Example 2, a mixture of ethylene glycol and water was used as the degradation solvent, and compared with Comparative Example 1, the PET conversion rate and TPA yield were increased, but still at a low level, which was not suitable for large-scale production; in Comparative Example 3, only ethylene glycol was used as the degradation solvent, and the PET conversion rate and TPA yield were further improved, but still both did not exceed 30%, which indicated that only using ethylene glycol as the degradation solvent could not completely degrade the PET waste into TPA within 10 min.

[0081] Application Example

[0082] This application example is used to illustrate the repeated use performance of the upper solution separated by the method provided by the present application after filtration, and the specific process is as follows:

[0083] An aqueous solution of polyethylene glycol 600 and potassium hydroxide were added to the upper layer solution separated in Example 1 to meet the component ratio required for degradation (the aqueous solution of polyethylene glycol 600 was added based on the volume loss, and the amount of potassium hydroxide added was determined by testing the potassium hydroxide content in the upper layer solution). The resulting solution was then used as the degradation solution again, and the PET polyester fibers were degraded using the same degradation steps and conditions as in Example 1. The conversion rate of PET and the yield of TPA were calculated. The above steps were repeated four times, and the conversion rate of PET and the yield of TPA were calculated after each repetition. The results of each cycle are shown in Table 2.

[0084] Table 2

[0085]

[0086] As shown in Table 2, after the reaction is completed and solid-liquid separation is performed, the liquid obtained from the solid-liquid separation (i.e., alkaline polyethylene glycol aqueous solution) can be adjusted in proportion to meet the component ratio required for degradation and then reused for PET degradation. Moreover, after repeated adjustments and use, a high PET conversion rate and TPA yield can still be guaranteed. This indicates that the efficient PET degradation method provided by the present invention can also realize the reuse of degradation liquid, further reducing the recycling cost of PET.

[0087] Test Example

[0088] Infrared spectroscopy was performed on the degradation products TPA obtained in Examples 1-3 and Comparative Examples 1-3, and the results were compared with those of commercial TPA. Figure 1 As shown, the degradation products obtained in Examples 1-3 and Comparative Examples 1-3 are all TPA.

[0089] In summary, when the solution system composed of "alkaline reagent-polyethylene glycol-water" provided by this invention is not used to degrade PET waste, it is impossible to complete the efficient degradation of PET waste within 30 minutes, and it is also impossible to obtain a high PET conversion rate and TPA yield. This shows that the efficient PET degradation method provided by this invention can significantly improve the degradation efficiency of PET waste; and the liquid obtained after solid-liquid separation can be adjusted and reused multiple times, reducing recycling costs.

[0090] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for efficiently degrading PET and recovering TPA, characterized in that the steps include... include: S1. Add the PET waste to be treated to a polyethylene glycol aqueous solution containing an alkaline reagent, and carry out a depolymerization reaction at 70~110℃ and normal pressure. After the reaction, separate the solid and liquid components while hot. The volume ratio of water to polyethylene glycol is 1:1.5~1:

9. S2. Dissolve the solid phase obtained from solid-liquid separation in water, filter out the residue, adjust the pH of the resulting solution, and precipitate TPA monomer.

2. The method for efficiently degrading PET and recovering TPA as described in claim 1, characterized in that, The alkaline reagent includes at least one of sodium hydroxide or potassium hydroxide.

3. The method for efficiently degrading PET and recovering TPA as described in claim 1, characterized in that, The concentration of the alkaline reagent in the polyethylene glycol aqueous solution is 0.04~0.2 g / mL.

4. The method for efficiently degrading PET and recycling TPA as described in claim 3, characterized in that, The molecular weight of the polyethylene glycol is 200-600.

5. The method for efficiently degrading PET and recovering TPA as described in claim 1, characterized in that, The amount of PET waste added to each liter of polyethylene glycol aqueous solution containing alkaline reagent is 10-130 grams.

6. The method for efficiently degrading PET and recovering TPA as described in claim 1, characterized in that, The depolymerization reaction is carried out at a temperature of 90-100℃ for a duration of 2-30 minutes.

7. The method for efficiently degrading PET and recovering TPA as described in any one of claims 1 to 6, characterized in that, The PET waste includes at least one of the following: plastic bottles containing PET components, polyester fibers, textiles, cable ties, or engineering plastic parts.

8. The method for efficiently degrading PET and recovering TPA as described in claim 1, characterized in that, The liquid phase obtained from solid-liquid separation in step S1 is recovered, the ratio of polyethylene glycol aqueous solution to alkaline reagent in the liquid phase is adjusted, and then recycled for depolymerization reaction.

9. The method for efficiently degrading PET and recovering TPA as described in claim 8, characterized in that, The liquid phase is enriched with ethylene glycol monomers. When the volume concentration of ethylene glycol monomers in the liquid phase exceeds 10%, the ethylene glycol monomers are recovered by distillation. The liquid phase after distillation of the ethylene glycol monomers is recycled for depolymerization reaction.

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