Screening method for regenerating PET (polyethylene terephthalate) and PTA (pure terephthalic acid) by chemical or enzymatic method

Abstract

The invention provides a chemical or enzymic method regenerated PET and PTA screening method, which comprises the following steps: pretreating a PET or PTA sample 1, and measuring the content of p-toluic acid, the content of p-carboxybenzaldehyde and the content of m-terephthalic acid by using high performance liquid chromatography; the method comprises the following steps: pretreating a PET or PTA sample 2, pretreating by using a high-temperature pyrolysis method, and measuring an isotope ratio of oxygen-18 to oxygen-16 by using an isotope ratio mass spectrometer; the method comprises the following steps: calculating a cleanliness index, an oxy-18 index and a bottle flake index by using a formula based on a test result, and classifying PET and PTA samples through a decision tree according to the indexes; combining and mixing the PET and PTA products based on the classification result and the requirements of downstream customers on the regeneration method and the regenerated material content; the method is convenient, accurate and reliable, the classification result is objective, the screening efficiency of PET and PTA regenerated by a chemical or enzyme method can be improved, and the economic cost is saved.

Description

Technical Field

[0001] This invention relates to the field of PET and PTA recycling, and more particularly to a chemical or enzymatic method for screening PET and PTA regeneration. Background Technology

[0002] PET is one of the most widely used plastics in the world, and is widely used in beverage bottles, fibers and packaging materials. With the increasing global awareness of environmental protection and the advancement of the "dual carbon" strategic goal, reducing plastic pollution and promoting the circular economy have become a consensus at home and abroad. Against this backdrop, the market demand for PTA from recycled PET and its intermediate recycled PET has shown explosive growth. Using recycled PET and PTA can not only effectively reduce the consumption of petroleum resources and solid waste, but also significantly reduce carbon footprint, which meets the requirements of sustainable development.

[0003] Although the importance of recycled PET materials has been widely recognized, their large-scale commercial application still faces a key technical bottleneck: the lack of rapid, accurate, and reliable analytical methods to effectively distinguish and screen recycled PET and PTA materials from virgin materials, especially chemically or enzymatically recycled PET and PTA materials, which have low impurity content and very small differences in various performance indicators compared to virgin materials.

[0004] Currently, the industry mainly relies on the following traditional methods for screening and quality assessment of recycled PET and PTA, but these methods all have obvious limitations.

[0005] Supplier declarations and document traceability: This method relies on self-declarations and document records within the supply chain. It is highly subjective, susceptible to human interference, lacks objective and verifiable technical evidence, and is difficult to effectively prevent market irregularities such as false labeling and mislabeling.

[0006] Physical property or chemical impurity testing: Indirect judgment is made by testing physical indicators such as the material's intrinsic viscosity, color value, and melting point, or by testing specific impurities or degradation products, such as acetaldehyde content and diethylene glycol content. However, recycled PET and PTA, which have undergone chemical or enzymatic recovery, are depolymerized and repolymerized at the molecular level. Their physical properties and chemical composition are very close to those of virgin PET, which limits the identification ability of this method and cannot be used as conclusive evidence.

[0007] Tracer technology: A few solutions propose adding chemical tracers during the primary polymerization stage; however, this method requires modifying existing production lines, increasing costs, and depends on the cooperation of the entire supply chain, making it difficult to implement and scale up.

[0008] Therefore, a chemical or enzymatic method for regenerating PET and screening PTA is proposed to solve the above problems. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the defects of the existing technology. The present invention proposes a chemical or enzymatic method for the regeneration of PET and PTA for screening.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for chemically or enzymatically regenerating PET and screening PTA, comprising: After pretreatment of PET or PTA sample 1, the contents of p-methylbenzoic acid, p-carboxybenzaldehyde and m-terephthalic acid were determined by high performance liquid chromatography. After pretreatment of PET or PTA sample 2, the isotope ratios of oxygen-18 and oxygen-16 were determined by high-temperature pyrolysis and isotope ratio mass spectrometry. Cleanliness index was obtained by processing data on p-methylbenzoic acid content and p-carboxybenzaldehyde content; oxygen-18 index was obtained by processing data on the isotope ratio of oxygen-18 and oxygen-16; and bottle / tablet index was obtained by processing data on m-terephthalic acid content. The cleanliness index, oxygen-18 index, and bottle-grade index are compared and analyzed to classify PET or PTA, and then screening is performed based on the classification information.

[0011] Preferably, the pretreatment of PET sample 1 involves mixing PET sample 1 with NaOH solution and then reacting the mixture in a hydrothermal reactor to obtain a PET hydrolysis solution.

[0012] Preferably, the pretreatment of PTA sample 1 involves dissolving PTA sample 1 in an alkaline solution.

[0013] Preferably, the alkaline solution is ammonia water, NaOH or KOH solution.

[0014] Preferably, the pretreatment of the PET or PTA sample 2 involves crushing the PET or PTA sample 2 into powder.

[0015] Preferably, PET or PTA is classified into chemical or enzymatic regeneration and non-chemical or enzymatic regeneration based on the cleanliness index.

[0016] Preferably, when PET or PTA is chemically or enzymatically recycled, PET or PTA is classified into products containing bottle flakes and their physically recycled form and products not containing bottle flakes and their physically recycled form, based on the bottle flake index.

[0017] Preferably, when PET or PTA is regenerated by chemical or enzymatic methods, it is classified into enzymatic, hydrolytic, or ethylene glycol or methanol alcoholysis methods based on the oxygen-18 index.

[0018] Compared with existing technologies, the beneficial effects of this invention include: calculating the cleanliness index, oxygen 18 index, and bottle flake index using formulas based on test results; classifying PET and PTA samples according to each index using a decision tree; combining and blending PET and PTA products based on the classification results and downstream customers' requirements for recycling methods and recycled material content; this method is convenient, accurate, and reliable, and the classification results are objective, which can improve the screening efficiency of chemically or enzymatically recycled PET and PTA and save economic costs. Attached Figure Description

[0019] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts. Wherein: Figure 1 The diagram illustrates a flowchart of a chemical or enzymatic method for regenerating PET and PTA according to an embodiment of the present invention. Detailed Implementation

[0020] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0021] Example 1, referring to Figure 1 As one embodiment of the present invention, a chemical or enzymatic method for regenerating PET for screening is provided, comprising: S100: PET sample 1 was mixed with a 2 mol / L NaOH solution (NaOH to PET monomer molar ratio > 2.5), and reacted in a hydrothermal reactor at 200℃ for 3 hours to obtain a PET hydrolysate. The p-methylbenzoic acid content in the PET hydrolysate was determined by high performance liquid chromatography (HPLC). PT , content of p-carboxybenzaldehyde C CBA and the content of iso-terephthalic acid C IPA ; S200: PET sample 2 was crushed into powder with a particle size <250 micrometers. The powder was pretreated using high-temperature pyrolysis and the isotopic ratio δ of oxygen-18 and oxygen-16 was determined using isotope ratio mass spectrometry. 18 O; S300: Calculated based on test results: Cleanliness Index Oxygen 18 Index Bottle Index S400: Comparative analysis of R1, R2, and R3 classifies PET into the following categories: Class I: If R1≥1, R2≤5, and R3≤10, the sample is classified as chemical or enzymatic regeneration, and the recovery method is enzymatic or hydrolytic. The raw material does not contain bottle flakes or their physical regeneration products. Category II: If R1≥1, R2≤5, and R3>10, the sample is classified as chemical or enzymatic regeneration, the recovery method is enzymatic or hydrolytic, and the raw material contains bottle flakes and their physical regeneration products. Category III: If R1≥1, R2>5, and R3≤10, the sample will be classified as chemical or enzymatic regeneration, and the recovery method will be ethylene glycol alcoholysis or methanol alcoholysis. The raw materials will not contain bottle flakes or their physical regeneration products. Category IV: If R1≥1, R2>5, and R3>10, the sample is classified as chemical or enzymatic regeneration, and the recovery method is ethylene glycol alcoholysis or methanol alcoholysis. The raw material contains bottle flakes and their physical regeneration products. Class V: If R1 < 1, the sample is classified as non-chemical or enzymatic regeneration.

[0022] Example 2, refer to Figure 1 As one embodiment of the present invention, a chemical or enzymatic method for PTA regeneration screening is provided, comprising: S100: Dissolve PTA sample 1 in an alkaline solution to a concentration <120 g / L. The preferred alkaline solution is ammonia, NaOH, or KOH. Determine the p-methylbenzoic acid content (C) in the alkaline solution using high-performance liquid chromatography. PT , content of p-carboxybenzaldehyde C CBA and the content of iso-terephthalic acid C IPA ; S200: PTA sample 2 was crushed into powder with a particle size <250 μm. The powder was pretreated using high-temperature pyrolysis and the isotopic ratio δ of oxygen-18 and oxygen-16 was determined using isotope ratio mass spectrometry. 18 O; S300: Calculated based on test results: Cleanliness Index Oxygen 18 Index Bottle Index S400: Comparative analysis of R1, R2, and R3 classifies PTA into the following categories: Class I: If R1≥1, R2≤5, and R3≤10, the sample is classified as chemical or enzymatic regeneration, and the recovery method is enzymatic or hydrolytic. The raw material does not contain bottle flakes or their physical regeneration products. Category II: If R1≥1, R2≤5, and R3>10, the sample is classified as chemical or enzymatic regeneration, the recovery method is enzymatic or hydrolytic, and the raw material contains bottle flakes and their physical regeneration products. Category III: If R1≥1, R2>5, and R3≤10, the sample will be classified as chemical or enzymatic regeneration, and the recovery method will be ethylene glycol alcoholysis or methanol alcoholysis. The raw materials will not contain bottle flakes or their physical regeneration products. Category IV: If R1≥1, R2>5, and R3>10, the sample is classified as chemical or enzymatic regeneration, and the recovery method is ethylene glycol alcoholysis or methanol alcoholysis. The raw material contains bottle flakes and their physical regeneration products. Class V: If R1 < 1, the sample is classified as non-chemical or enzymatic regeneration.

[0023] Example 3, referring to Figure 1 As an embodiment of the present invention, based on the above embodiment, a chemical or enzymatic method for regenerating PET screening is provided.

[0024] S100: Obtain a series of PET slice samples.

[0025] S200: Weigh 5g of PET slice sample, mix with 50mL of 2mol / L sodium hydroxide solution, and add to a hydrothermal reactor. Then, place the hydrothermal reactor in a muffle furnace and heat to 200℃, maintaining the temperature for 3h. After the reaction, cool to room temperature, filter the reaction solution, and wash the hydrothermal reactor and filter residue with deionized water. Dry and weigh the filter residue, and after the filtrate is diluted to a certain volume, determine the concentrations of p-methylbenzoic acid (PT acid), p-carboxybenzaldehyde (4-CBA), and iso-terephthalic acid (IPA) by high performance liquid chromatography. Calculate the contents of PT acid, 4-CBA, and IPA in the PET sample based on the concentrations, filtrate volume, and reactant mass (PET mass - residue mass). The results are shown in Table 1.

[0026] S300: The PET sample was crushed into powder using a crusher, passed through a 60-mesh sieve, and the sieve residue was collected. The crushed PET sample was pretreated by high-temperature pyrolysis and the isotope ratio of oxygen-18 and oxygen-16 was determined by isotope ratio mass spectrometry. The results are shown in Table 1.

[0027] S400: Based on the test results, the cleanliness index, oxygen-18 index and flake index were calculated, and the results are shown in Table 2.

[0028] S500: Comparative analysis of R1, R2, and R3 was performed to classify the PET samples. The classification results are shown in Table 3.

[0029] Table 1. Detection values ​​of various indicators for PET samples Table 2 Calculated values ​​of various indices for PET samples Table 3 PET Sample Classification Example 4, refer to Figure 1 As an embodiment of the present invention, based on the above embodiment, a chemical or enzymatic method for PTA regeneration screening is provided.

[0030] S100: Obtain a series of PTA powder samples from various manufacturers.

[0031] S200: Weigh 5g of PTA powder sample and add it to a 10 vol.% ammonia solution. Place the solution in an ultrasonic oscillator until the PTA is completely dissolved. Determine the concentrations of p-methylbenzoic acid (PT acid), p-carboxybenzaldehyde (4-CBA), and iso-terephthalic acid (IPA) by high performance liquid chromatography. Calculate the contents of PT acid, 4-CBA, and IPA in the PTA sample based on the concentrations, solution volumes, and PTA mass. The results are shown in Table 4.

[0032] S300: 5g of PTA powder sample was weighed and pretreated by high-temperature pyrolysis and the isotope ratio of oxygen-18 and oxygen-16 was determined by isotope ratio mass spectrometry. The results are shown in Table 4.

[0033] S400: Based on the test results, the cleanliness index, oxygen-18 index and flake index were calculated, and the results are shown in Table 5.

[0034] S500: Comparative analysis of R1, R2, and R3 was performed to classify the PTA samples. The classification results are shown in Table 6. Only PTA of Class I, II, and V were obtained. This is because PTA can only be regenerated by enzymatic or hydrolytic methods. The regeneration products of ethylene glycol hydrolysis or methanol hydrolysis are bis(ethylene glycol) terephthalate (BHET) and dimethyl terephthalate (DMT), respectively.

[0035] Table 4. Detection values ​​of various indicators for PTA samples Table 5 Calculated values ​​of various indices for PTA samples Table 6 PTA Sample Classification Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0036] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for screening chemically or enzymatically regenerated PET and PTA, characterized in that, include: After pretreatment of PET or PTA sample 1, the contents of p-methylbenzoic acid, p-carboxybenzaldehyde and m-terephthalic acid were determined by high performance liquid chromatography. After pretreatment of PET or PTA sample 2, the isotope ratios of oxygen-18 and oxygen-16 were determined by high-temperature pyrolysis and isotope ratio mass spectrometry. Cleanliness index was obtained by processing data on p-methylbenzoic acid content and p-carboxybenzaldehyde content; oxygen-18 index was obtained by processing data on the isotope ratio of oxygen-18 and oxygen-16; and bottle / tablet index was obtained by processing data on m-terephthalic acid content. The cleanliness index, oxygen-18 index, and bottle-grade index are compared and analyzed to classify PET or PTA, and then screening is performed based on the classification information.

2. The method for chemically or enzymatically regenerating PET and screening PTA according to claim 1, characterized in that, The PET sample 1 was pretreated by mixing it with NaOH solution and then adding it to a hydrothermal reactor to react and obtain a PET hydrolysate solution.

3. The method for chemically or enzymatically regenerating PET and PTA for screening according to claim 1, characterized in that, The pretreatment of PTA sample 1 involves dissolving PTA sample 1 in an alkaline solution.

4. The method for chemically or enzymatically regenerating PET and screening PTA according to claim 3, characterized in that, The alkaline solution is ammonia water, NaOH or KOH solution.

5. The method for chemically or enzymatically regenerating PET and PTA for screening according to claim 1, characterized in that, The pretreatment of the PET or PTA sample 2 involves crushing the PET or PTA sample 2 into powder.

6. The method for chemically or enzymatically regenerating PET and PTA for screening according to claim 1, characterized in that, PET or PTA are classified into chemical or enzymatic regeneration and non-chemical or enzymatic regeneration based on their cleanliness index.

7. A chemical or enzymatic method for screening regenerated PET and PTA according to claim 6, characterized in that, When PET or PTA is chemically or enzymatically recycled, it is classified into products containing bottle flakes and their physically recycled form and products not containing bottle flakes and their physically recycled form, based on the bottle flake index.

8. A chemical or enzymatic method for screening regenerated PET and PTA according to claim 6, characterized in that, When PET or PTA is regenerated chemically or enzymatically, it is classified into enzymatic recovery, hydrolysis recovery, or ethylene glycol alcoholysis or methanol alcoholysis recovery based on the oxygen-18 index.

Images