Method for preparing recycled terephthalic acid without using organic solvent and recycled terephthalic acid prepared thereby
The use of an alkaline catalyst and ultrasonic treatment for depolymerizing waste polyester addresses the need for solvent-free terephthalic acid recovery, enhancing yield and efficiency while minimizing environmental impact and costs.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- TERRACLE CO LTD
- Filing Date
- 2025-10-16
- Publication Date
- 2026-07-23
AI Technical Summary
Existing methods for recovering terephthalic acid from waste polyester require organic solvents, leading to environmental concerns and additional purification processes, and are economically disadvantageous due to low conversion rates.
A method involving the use of an alkaline catalyst and ultrasonic irradiation to depolymerize waste polyester, followed by water addition and acidic treatment to separate and precipitate terephthalic acid, eliminating the need for organic solvents and reducing process time.
This method achieves high-purity terephthalic acid recovery with increased yield and efficiency, reducing energy consumption and process time, making it suitable for commercial-scale recycling.
Smart Images
Figure KR2025016388_23072026_PF_FP_ABST
Abstract
Description
A method for producing regenerated terephthalic acid characterized by not using an organic solvent, and regenerated terephthalic acid produced therefrom
[0001] The present invention relates to a method for efficiently recovering terephthalic acid from waste polyester using an alkaline catalyst and ultrasonic irradiation without using organic solvents. The present invention is a method capable of separating terephthalic acid from waste polyester with high efficiency and high purity, is economical as it does not require a separate impurity removal process by not using organic solvents such as toluene and xylene, and increases the production efficiency of terephthalic acid by accelerating the reaction and promoting uniform decomposition through ultrasonic irradiation.
[0002] Polyester is the most widely purchased and utilized polymer globally, with annual production exceeding 75 million tons. Polyester can be manufactured at a relatively low cost and is used in a wide range of applications, including clothing, carpets, and films, due to its physical, chemical, and thermal properties. Among polyesters, polyethylene terephthalate (PET) is one of the most widely used in various ways, including in single-use applications such as beverage containers. With the commercial success of PET in particular, efforts have been made to recover materials from post-consumption, post-industrial use, scrap, and other sources, and to reuse these materials as an alternative to basic disposal methods such as landfilling. As the annual global volume of plastic waste made from polyester reaches unmanageable levels, interest in recycling waste polyester or regeneration processes utilizing waste polyester is growing.
[0003] Depolymerization technology, one of the methods for chemically recycling waste polyester, is a technology that monomerizes polyester and regenerates it into new products by repolymerizing the monomers produced by depolymerization. This depolymerization technology can be divided into glycolysis, methanolysis, and hydrolysis.
[0004] While pure polyester has a low impurity content, allowing for the easy synthesis of terephthalic acid through depolymerization, waste polyester is highly likely to contain various foreign substances, including heavy metals. Therefore, it requires an additional separation process to remove these impurities, and separation is economically disadvantageous due to the low conversion rate.
[0005] In the case of waste polyester, organic solvents are generally used to effectively dissolve polyester polymer chains and promote decomposition reactions; these solvents selectively bind to terephthalic acid, facilitating separation from other byproducts. However, since the use of organic solvents raises environmental concerns and necessitates additional purification processes, there is currently a demand for methods that do not utilize organic solvents.
[0006] [Prior Art Literature]
[0007] [Patent Literature]
[0008] Korean Registered Patent No. 10-2593219
[0009] The problem that the present invention aims to solve is a method for producing high-purity terephthalic acid with high efficiency by increasing the added value of plastic waste without using organic solvents. The present invention can improve the yield of regenerated terephthalic acid through the use of an alkaline catalyst and ultrasonic treatment, and can provide an economical method for producing regenerated terephthalic acid that is environmentally friendly and significantly reduces process time. Compared to existing methods for recovering regenerated terephthalic acid using organic solvents, it can provide a solution that is more suitable for commercial-scale recycling processes.
[0010] To solve the above problem, the present invention provides a method for producing regenerated terephthalic acid without using an organic solvent, comprising the steps of: mixing waste polyester and an alkaline catalyst; heating the mixture to 80 to 100°C and ultrasonically treating it for 30 minutes to 5 hours at a frequency of 20 to 60 kHz and a power of 100 to 5,000 W under 1 atmosphere conditions; adding water to the ultrasonically treated mixture to separate a metal salt of terephthalic acid; and treating the separated metal salt of terephthalic acid with an acidic solution to precipitate regenerated terephthalic acid. The invention also provides regenerated terephthalic acid produced therefrom.
[0011] The method for producing recycled terephthalic acid according to the present invention recovers terephthalic acid from waste polyester through an alkaline catalyst and ultrasonic irradiation without using an organic solvent, thereby enabling the separation of terephthalic acid from waste polyester in a short time with high efficiency. Furthermore, the present invention is economical and shortens reaction time by not requiring a separate impurity removal process since it does not use organic solvents such as toluene and xylene, and has the effect of increasing the production efficiency of recycled terephthalic acid by accelerating the reaction and promoting uniform decomposition through ultrasonic irradiation.
[0012] FIG. 1 is a schematic diagram of a manufacturing method according to one embodiment of the present invention.
[0013] Hereinafter, various embodiments of the present invention are described with reference to the accompanying drawings. The present invention is not limited to specific embodiments and should be understood to include various modifications, equivalents, and / or alternatives of the embodiments of the present invention. In relation to the description of the drawings, similar reference numerals may be used for similar components.
[0014] In this document, expressions such as "have," "can have," "include," or "can include" refer to the existence of the relevant feature (e.g., numerical values, functions, actions, or components, etc.) and do not exclude the existence of additional features.
[0015] In this document, expressions such as “A or B,” “at least one of A or / and B,” or “one or more of A or / and B” may include all possible combinations of items listed together. For example, “A or B,” “at least one of A and B,” or “at least one of A or B” may refer to cases including (1) at least one A, (2) at least one B, or (3) both at least one A and at least one B.
[0016] As used in this document, the expression "configured to" may be replaced, depending on the context, with, for example, "suitable for," "having the capacity to," "designed to," "adapted to," "made to," or "capable of." The term "configured to" does not necessarily mean "specifically designed to."
[0017] The terms used in this document are used merely to describe specific embodiments and are not intended to limit the scope of other embodiments. Singular expressions may include plural expressions unless the context clearly indicates otherwise. Terms used herein, including technical or scientific terms, may have the same meaning as generally understood by those skilled in the art described in this document. Terms used in this document that are defined in general dictionaries may be interpreted as having the same or similar meaning as they have in the context of the relevant technology, and are not to be interpreted in an ideal or overly formal sense unless explicitly defined in this document. In some cases, even terms defined in this document may not be interpreted to exclude the embodiments of this document.
[0018] The embodiments disclosed in this document are presented for the purpose of explaining and understanding the disclosed technical content and are not intended to limit the scope of the invention. Accordingly, the scope of this document should be interpreted to include all modifications or various other embodiments based on the technical concept of the invention.
[0019] Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.
[0020] Therefore, it should be understood that the configurations of the embodiments described in this specification are merely some of the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention, and that various equivalents and modifications that can replace them may exist at the time of filing this application.
[0021] Throughout the specification, when a part is described as "including" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.
[0022] The present invention will be described in detail below.
[0023]
[0024] A method for producing regenerated terephthalic acid according to one embodiment of the present invention, characterized by not using an organic solvent, may comprise the steps of: mixing waste polyester with an alkaline catalyst; heating the mixture to 80 to 100°C and ultrasonically treating it for 30 minutes to 5 hours at a frequency of 20 to 60 kHz and a power of 100 to 5,000 W under 1 atmosphere conditions; adding water to the ultrasonically treated mixture to separate a metal salt of terephthalic acid; and treating the separated metal salt of terephthalic acid with an acidic solution to precipitate regenerated terephthalic acid. Each step is described in detail below.
[0025] The step of mixing the waste polyester with the alkaline catalyst is intended to increase the recovery rate of terephthalic acid by expanding the structure of the waste polyester using the alkaline catalyst and enhancing the bubble permeability effect, which allows microbubbles generated in the subsequent ultrasonic treatment step to penetrate more easily into the polymer.
[0026] The above polyester is a polymer having ester (RO-C(=O)-R') chemical functional groups in its main chain and is also called polyester.
[0027] The above polyester may be a polymer formed by the condensation polymerization of a dicarboxylic acid and a dialol. The above dicarboxylic acid may be any one selected from the group consisting of terephthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfonadicarboxylic acid, diphenoxyethanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, trimellitic acid, and pyromellitic acid. Preferably, the above dicarboxylic acid may be terephthalic acid. The above-mentioned dialol may be any one selected from the group consisting of ethylene glycol, trimethylene glycol, 1,2-propanediol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, decanemethylene glycol, dodecamethylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, di(tetramethylene) glycol, tri(tetramethylene) glycol, polytetramethylene glycol, pentaerythritol, and 2,2-bis(4-β-hydroxyethoxyphenyl)propane. Preferably, the dialol may be ethylene glycol.
[0028] The polyester may be one or more selected from the group consisting of polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polyglycolide or polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), and Vectran. Preferably, the polyester may be polyethylene terephthalate (PET).
[0029] In the step of mixing the above waste polyester and the alkaline catalyst, the alkaline catalyst can penetrate between the chains of the polyester to hydrolyze the ester bonds and simultaneously weaken the hydrogen bonds between the polymer chains.
[0030] In the step of mixing the above waste polyester with an alkaline catalyst, the alkaline catalyst may be one or more selected from the group consisting of LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2. Preferably, the alkaline catalyst may be one or more selected from the group consisting of NaOH and KOH. When KOH is used as the alkaline catalyst, KOH acts as a strong Lewis base to promote the hydrolysis of ester bonds, and K+ ions form a more effective and stable chelate complex with terephthalic acid compared to Na+ ions, resulting in an excellent chelation effect.
[0031] In the step of mixing the waste polyester and the alkaline catalyst, the weight ratio of the waste polyester to the alkaline catalyst may be 1:1 to 10. Preferably, the weight ratio may be 1:3 to 7. If the alkaline catalyst is below the above numerical range, the hydrolysis of the ester bonds of the waste polyester occurs insufficiently, making it difficult to structurally expand the polyester. Even if ultrasound is applied to the waste polyester that has not structurally expanded, it is difficult for microbubbles caused by ultrasound to penetrate between the polyester structures, and the terephthalic acid recovery rate may be low. If the alkaline catalyst is below the above numerical range, an additional process may be required to separate the alkaline catalyst, which is uneconomical and may reduce the terephthalic acid recovery efficiency.
[0032] The step of heating the above mixture to 80 to 100°C and ultrasonically treating it for 30 minutes to 5 hours at a frequency of 20 to 60 kHz and a power of 100 to 5,000 W under 1 atmosphere conditions is intended to separate terephthalic acid with high purity by additionally ultrasonically treating waste polyester structurally weakened by an alkaline catalyst.
[0033] The above ultrasonic treatment effectively improves the recovery efficiency of terephthalic acid by severing the molecular chains of waste polyester and increasing its surface area, thereby promoting the hydrolysis of the alkaline catalyst. The ultrasound induces cavitation within the liquid, causing the repeated expansion and condensation of microbubbles; when the bubbles collapse, a localized high-temperature and high-pressure environment is formed. Consequently, the ester bonds of the polyester are rapidly decomposed, significantly accelerating the reaction rate. In particular, the localized high-temperature and high-pressure environment formed by the cavitation effect replaces the high energy required for the alkaline hydrolysis process, enabling the depolymerization of polyester at lower temperatures and within a shorter time compared to conventional methods for recovering regenerated terephthalic acid. By utilizing ultrasonic treatment, not only is energy consumption reduced, but the process time is also shortened, thereby enabling the implementation of an economical and efficient process for recovering regenerated terephthalic acid.
[0034] In the step of heating the above mixture to 80 to 100°C and ultrasonically treating it for 30 minutes to 5 hours at a frequency of 20 to 60 kHz and a power of 100 to 5,000 W under 1 atmosphere conditions, if the ultrasonically treated at a frequency below the above numerical range or at a power below the above numerical range, it is difficult for microbubbles caused by ultrasound to penetrate the molecular chains of the waste polyester, and it is difficult to create a local environment of high temperature and high pressure, so the regenerated terephthalic acid may contain a large amount of impurities and the reaction time may be prolonged. If the ultrasonically treated at a frequency exceeding the above numerical range or at a power exceeding the above numerical range, the expansion and condensation of bubbles are excessively repeated, the reaction temperature rises, and economic efficiency may be reduced due to excessive energy consumption. If the ultrasound is applied for a time below the above numerical range, the waste polyester cannot structurally expand sufficiently, making it difficult to obtain terephthalic acid with high purity, and if it is applied for a time exceeding the above numerical range, there is a problem of reduced economic efficiency due to the high energy consumption process. However, depending on the amount of reaction solvent or reaction solute, the ultrasonic power and processing time may increase linearly or non-linearly.
[0035] The step of separating the terephthalic acid metal salt by adding water to the above-mentioned ultrasonically treated mixture promotes the monomerization and hydrolysis of the polyester, and because water is added, water-soluble impurities can be efficiently removed, making it economical as it does not require an additional subsequent purification process. Furthermore, by promoting the crystallization of the terephthalic acid metal salt, the recovery efficiency of pure regenerated terephthalic acid can be increased. The metal salts above vary depending on the type of alkaline catalyst, and the terephthalate metal salts above may include one or more selected from the group consisting of lithium terephthalate (Li2-TPA), sodium terephthalate (Na2-TPA), potassium terephthalate (K2-TPA), rubidium terephthalate (Rb2-TPA), cesium terephthalate (Cs2-TPA), calcium terephthalate (Ca-TPA), strontium terephthalate (Sr-TPA), and barium terephthalate (Ba-TPA).
[0036] In the step of separating the metal terephthalate salt by adding water to the ultrasonically treated mixture, the weight ratio of the ultrasonically treated mixture to water may be 1:0.1 to 10. If the water content is below the above numerical range, it may be difficult to separate the metal terephthalate salt, and if the water content exceeds the above numerical range, the concentration of the metal terephthalate salt may be too low, which may reduce the separation efficiency.
[0037] In the step of separating the metal salt of terephthalate by adding water to the ultrasonically treated mixture, the metal salt of terephthalate may be included in an amount of 10 to 50 weight percent relative to the total weight of the solution mixed with the ultrasonically treated mixture and water. When the content of the metal salt of terephthalate is below the above numerical range, the concentration of the metal salt is too low, which may reduce separation efficiency and dilute the solution, which may increase energy consumption in subsequent processes; when it exceeds the above numerical range, the solubility limit of the metal salt of terephthalate is reached, causing precipitation, and the viscosity of the solution increases, making separation difficult and reducing the efficiency of removing impurities.
[0038] In the step of separating the metal salt of terephthalate by adding water to the ultrasonically treated mixture, the water may be added in an amount of 5 to 15 times the weight of the waste polyester in the step of mixing the waste polyester and the alkaline catalyst. If the water is added in an amount less than the above numerical range, effective dispersion of the alkaline catalyst is not achieved and sufficient solubility of the metal salt of terephthalate is not secured, which may result in reduced separation efficiency. If the water is added in an amount exceeding the above numerical range, the reaction mixture is diluted, the reaction rate slows down, and the efficiency of the process decreases, and the efficiency of the subsequent separation process decreases, making it difficult to recover regenerated terephthalic acid with high purity.
[0039] The step of precipitating regenerated terephthalic acid by treating the separated metal terephthalic acid salt with an acidic solution is intended to precipitate pure regenerated terephthalic acid by separating metal ions from the metal terephthalic acid salt through treatment with an acidic solution.
[0040] In the step of precipitating regenerated terephthalic acid by treating the separated terephthalic acid metal salt with an acidic solution, the weight ratio of the separated terephthalic acid metal salt to the acidic solution may be 1:0.5 to 2. Since the acidic solution causes a change in pH to promote the crystallization of terephthalic acid and enables the recovery of pure terephthalic acid, if the acidic solution is treated below the above numerical range, complete decomposition of the terephthalic acid metal salt may not occur and the purity may be lowered, and if treated above the above numerical range, side reactions may occur and impurities may be generated, and the structure of terephthalic acid may be deformed due to excessive acidic conditions.
[0041] In the step of precipitating regenerated trephthalic acid by treating the separated metal terephthalic acid salt with an acidic solution, the acidic solution may be one or more selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, oxalic acid, citric acid, tartaric acid, maleic acid, and succinic acid. Preferably, the acidic solution may be one or more selected from the group consisting of hydrochloric acid, sulfuric acid, and nitric acid.
[0042] The purity of the above-mentioned regenerated terephthalic acid can be 98% or higher.
[0043] According to another embodiment of the present invention, regenerated terephthalic acid produced by any one of the above manufacturing methods is provided.
[0044]
[0045] The present invention will be described in more detail below through examples. These examples are intended solely to explain the present invention more specifically, and it will be obvious to those skilled in the art that the scope of the present invention is not limited by these examples according to the gist of the present invention.
[0046]
[0047] Examples and Comparative Examples
[0048] Example 1
[0049] 420 g of PET waste, which had been washed to remove surface impurities and crushed, was mixed with 2,723 g of 45% NaOH aqueous solution (S1).
[0050] The beaker containing the above mixture was placed in a reaction vessel equipped with an ultrasonic generator of 28 kHz frequency and 500 w power, heated to 95°C under 1 atmosphere, and then treated with ultrasound for 90 minutes while stirring at 200 rpm using a mechanical overhead stirrer (S2).
[0051] 5,040 g of water was added to the above ultrasonically treated mixture to separate 628.6 g of sodium terephthalate (Na2-TPA) (S3).
[0052] 450g of sulfuric acid was applied to the above-determined sodium terephthalate salt (Na2-TPA) to precipitate terephthalic acid (S4).
[0053] Examples 2 to 6
[0054] Terephthalic acid was precipitated in the same manner as in Example 1, except that the process conditions for each step in [Table 1] below were changed.
[0055] S1 Step Type of Alkaline Catalyst S1 Step Alkaline Catalyst Content (g) S3 Step Metal Salt of Terephthalic Acid Example 1 45% NaOH Aqueous Solution 2,723 Na2-TPA Example 2 45% NaOH Aqueous Solution 420 Na2-TPA Example 3 45% NaOH Aqueous Solution 1,260 Na2-TPA Example 4 45% NaOH Aqueous Solution 2,940 Na2-TPA Example 5 45% NaOH Aqueous Solution 4,200 Na2-TPA Example 6 45% KOH Aqueous Solution 2,723 K2-TPA
[0056] Examples 7 to 22
[0057] Terephthalic acid was precipitated in the same manner as in Example 1, except that the process conditions for each step in [Table 2] below were changed.
[0058] S2 Step Frequency (kHz) S2 Step Ultrasonic Treatment Time (min) S3 Step Added Water (g) S4 Step Acidic Solution (g) Example 7 15905,040450 Example 8 20905,040450 Example 9 60905,040450 Example 1075905,040450 Example 1128105,040450 Example 1228305,040450 Example 13281205,040450 Example 14281505,040450 Example 1528901,680450 Example 1628902,100450 Example 1728906,300450 Example 1828907,140450 Example 1928905,040250 Example 2028905,040310 Example 2128905,0401,250 Example 2228905,0401,570
[0059] Comparative Example 1
[0060] The above Example 1 was carried out in the same manner as Example 1, except that 2,723 g of 45% NaOH aqueous solution was not treated in step S1 of Example 1.
[0061] Comparative Example 2
[0062] The above Example 1 was carried out in the same manner as Example 1, except that the S2 step of Example 1 was not carried out.
[0063] Comparative Example 3
[0064] The above Example 1 was carried out in the same manner as Example 1, except that in step S1 of Example 1, 2,723 g of 45% NaOH aqueous solution was replaced with toluene, an organic solvent.
[0065]
[0066] Experimental Example 1
[0067] The conversion rate (%) of the recycled terephthalic acid according to Examples 1 to 22 and Comparative Examples 1 to 2 was measured. The conversion rate (%) of the recycled terephthalic acid was calculated as the weight ratio of the recovered terephthalic acid to the input PET waste.
[0068] Unreacted PET Fragments (g) Conversion Rate (%) Example 1 1,299.7 Example 2 133,368.3 Example 3 74,582.3 Example 4 21,994.8 Example 5 27,493.5 Example 6 13,896.7 Example 7 7,398.3 Example 8 9,197.8 Example 9 118,271.9 Example 10 148,964.5 Example 11 280,833.1 Example 12 137,267.3 Example 13 1,899.8 Example 14 1,699.6 Example 15 1,899.6 Example 16 1,799.6 Example 17 2,199.5 181.799.6 Example 19299.5 Example 201.799.6 Example 211.999.5 Example 222.399.5 Comparative Example 1419.10.2 Comparative Example 2401.24.5 Comparative Example 3419.70.1
[0069] Experimental Example 2
[0070] The yield of the recycled terephthalic acid according to Examples 1 to 22 and Comparative Examples 1 to 2 was calculated as the weight ratio of the recovered terephthalic acid to the input PET waste, and the purity was measured using high-performance liquid chromatography (HPLC). The results are as shown in [Table 4] below.
[0071] Yield (%) Purity (%) Example 192.399.6 Example 259.797.5 Example 374.298.9 Example 486.498.2 Example 587.897.8 Example 689.498.2 Example 787.294.7 Example 888.396.2 Example 960.197.2 Example 1056.594.8 Example 1118.292.3 Example 1253.594.8 Example 1391.795.6 Example 1490.394.4 Example 1585.698.7 Example 1689.399.0 Example 1792.199.4 1892.299.3 Example 1942.197.8 Example 2060.798.3 Example 2192.198.3 Example 2292.098.0 Comparative Example 100 Comparative Example 22.194.3 Comparative Example 300
Claims
1. A step of mixing waste polyester and an alkaline catalyst; A step of heating the above mixture to 80 to 100°C and ultrasonically treating it for 30 minutes to 5 hours at a frequency of 20 to 60 kHz and a power of 100 to 5,000 W under 1 atmosphere conditions; A step of separating the metal salt of terephthalic acid by adding water to the above ultrasonically treated mixture; and A step of precipitating regenerated trephthalic acid by treating the separated metal terephthalic acid salt with an acidic solution. A method for producing regenerated terephthalic acid characterized by not using an organic solvent containing 2. In Claim 1, A method for producing regenerated terephthalic acid characterized by not using an organic solvent, wherein, in the step of mixing the above waste polyester and an alkaline catalyst, the alkaline catalyst is one or more selected from the group consisting of LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2.
3. In Claim 1, A method for producing recycled terephthalic acid characterized by not using an organic solvent, wherein in the step of mixing the waste polyester and the alkaline catalyst, the weight ratio of the waste polyester to the alkaline catalyst is 1:1 to 10.
4. In Claim 1, A method for producing regenerated terephthalic acid characterized by not using an organic solvent, wherein, in the step of separating the terephthalic acid metal salt by adding water to the ultrasonically treated mixture, the weight ratio of the ultrasonically treated mixture to water is 1:0.1 to 10.
5. In Claim 1, A method for producing regenerated terephthalic acid, characterized by not using an organic solvent, wherein, in the step of separating the metal salt of terephthalic acid by adding water to the ultrasonically treated mixture, the metal salt of terephthalic acid is included in an amount of 10 to 50 weight% relative to the total weight of the solution mixed with the ultrasonically treated mixture and water.
6. In Claim 1, A method for producing recycled terephthalic acid characterized by not using an organic solvent, wherein, in the step of separating the metal salt of terephthalic acid by adding water to the ultrasonically treated mixture, the water is added in an amount of 5 to 15 times the weight of the waste polyester in the step of mixing the waste polyester and the alkaline catalyst.
7. In Claim 1, A method for producing regenerated terephthalic acid, characterized by not using an organic solvent, wherein, in the step of treating the separated metal terephthalic acid salt with an acidic solution to precipitate regenerated terephthalic acid, the weight ratio of the separated metal terephthalic acid salt to the acidic solution is 1:0.5 to 2.
8. In Claim 1, A method for producing regenerated terephthalic acid, characterized by not using an organic solvent in the step of treating the separated terephthalic acid metal salt with an acidic solution to precipitate regenerated terephthalic acid, wherein the acidic solution is one or more selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, oxalic acid, citric acid, tartaric acid, maleic acid, and succinic acid.
9. In Claim 1, A method for producing regenerated terephthalic acid characterized by not using an organic solvent, wherein the purity of the regenerated terephthalic acid is 98% or higher.
10. Regenerated terephthalic acid produced by any one of the manufacturing methods of claims 1 to 9.