Method for producing highly pure terephthalic acid by using polyester depolymerization and highly pure terephthalic acid obtained thereby

Abstract

To produce a highly pure terephthalic acid by using polyester depolymerization.SOLUTION: A method for producing highly pure terephthalic acid comprises: preparing a solvent by mixing an alkaline catalyst with a basic hydrolysis solvent consisting of an alkylated aromatic compound and a polarity adjusting compound; obtaining a polyester depolymerization product by treating waste polyester with the solvent; preparing a sludge cake aqueous solution containing a terephthalate metal salt by filtering the polyester depolymerization product to obtain a sludge cake and adding purified water to the filtered sludge cake; obtaining an aqueous solution containing a terephthalate metal salt by treating the sludge cake aqueous solution with an organic solvent; purifying the terephthalate metal salt aqueous solution by treating the aqueous solution with an adsorbent; and precipitating solid terephthalic acid by treating the purified terephthalate metal salt aqueous solution with an acidic solution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for obtaining high-purity terephthalic acid from waste polyester. The present invention also relates to a method for regenerating high-purity terephthalic acid by improving the conversion rate to terephthalic acid by using an alkylated aromatic compound having a stable structure even under basic conditions to increase purification efficiency and by adjusting the polarity of a solvent to facilitate the swelling process of waste plastics. [Background technology]

[0002] Polyester is the most widely purchased and widely used polymer worldwide, with a mass production of well over 75 million tons per year. Its relatively low-cost production and excellent physical, chemical, and thermal properties allow it to be used in a variety of applications, including clothing, carpets, and films. Polyethylene terephthalate (PET) is one of the most widely used polyesters, with applications including disposable beverage containers. The commercial success of PET, in particular, has led to efforts to recover materials from post-consumer, post-industrial, scrap, and other sources, and to reuse these materials instead of traditional landfill disposal methods. With the annual global generation of polyester-based plastic waste exceeding its capacity, interest in recycling and reclaiming waste polyester has grown. While colorless and transparent PET beverage containers are physically recyclable, colored composite materials, such as those used in automotive interiors and textiles, are difficult to recycle and have traditionally been incinerated or landfilled. For this reason, chemical recycling techniques have been developed to recover waste polyester and replace basic disposal methods such as incineration or landfilling.

[0003] Depolymerization, one of the methods for chemically recycling waste polyester, involves converting polyester into monomers and then repolymerizing the resulting monomers to create new products. Depolymerization techniques are divided into glycolysis, methanolysis, and hydrolysis.

[0004] Glycolysis is a method for monomerizing polyester into bis(2-hydroxyethyl)terephthalate (BHET) through a transesterification reaction using glycols such as ethylene glycol (EG) or propylene glycol (PG) and a catalyst. This is the simplest, oldest, and most readily available process, and many companies are currently developing it. However, glycolysis is very slow unless a catalyst such as a metal salt, zeolite, or ionic catalyst is used, and complete depolymerization of PET to BHET cannot be achieved. Because glycolysis produces a final product containing a significant amount of other oligomers in addition to the BHET monomer, recovery of the BHET monomer, when it is the desired product, is difficult. Because glycolysis requires high temperatures of over 150°C, it presents challenges in terms of energy efficiency and carbon emission reduction. In addition, a pretreatment process is required to remove heavy metals and moisture from the waste prior to the glycolysis reaction, and a considerable amount of activated carbon is required during purification, which makes it less economical.Furthermore, although BHET produced by glycolysis is suitable for synthesizing PET, an additional hydrolysis reaction is required to produce high-value-added polyesters such as polybutylene terephthalate (PBT), which makes it less economical and versatile.

[0005] Methanolysis is a method of depolymerizing polyester with dimethyl terephthalate (DMT) and ethylene glycol through a transesterification reaction using methanol and a catalyst. While it has a similar reaction mechanism to glycolysis, it has the advantage of being able to react at temperatures below 100°C, leading to widespread commercial development. This method has the advantage of being able to produce a variety of polyesters, and the resulting monomer, DMT, is highly versatile. However, methanolysis also requires a pretreatment process to remove heavy metals and moisture from the waste prior to the reaction. Furthermore, purification requires sublimation at temperatures above 200°C, which is both economically and environmentally unfriendly. Furthermore, polyester manufacturing facilities worldwide currently use polymerization facilities using the terephthalic acid (TPA) method, which poses usability issues.

[0006] Hydrolysis is a method of depolymerizing polyester with terephthalic acid and ethylene glycol through hydrolysis using water or a solvent and a catalyst. It can be broadly divided into acid hydrolysis, decomposition hydrolysis, and alkaline hydrolysis. Acid hydrolysis is a reaction in which water and sulfuric acid are heated to 100°C to immediately produce terephthalic acid. This reaction has the advantages of quickly producing terephthalic acid and not requiring an organic solvent, but it is risky to use sulfuric acid of 85% or more, and the immediately produced terephthalic acid must be re-alkalized for purification, making it less economical. While decomposition hydrolysis uses high-temperature steam, terephthalic acid can also be obtained by high temperatures of 200-300°C or by microwave irradiation. However, this method requires specialized equipment and consumes a large amount of energy. Similar to acid hydrolysis, it also requires a re-alkalization process for purification. Alkaline hydrolysis uses an alkaline catalyst and water or a solvent to form the intermediate terephthalate salt, which then undergoes a purification process and acid treatment to finally produce terephthalic acid. Although the reaction conditions and facilities are relatively simple and mild, the purification process requires a large amount of water and solvents, which makes it less economical and environmentally friendly. Furthermore, a large amount of activated carbon is required to remove unspecified impurities such as dyes, and expensive solvents are required for a high conversion rate, resulting in a high unit cost. In other words, hydrolysis requires multiple steps to recover terephthalic acid monomer.

[0007] Therefore, there is a continuing demand for a method for regenerating waste polyester using an inexpensive solvent composition that is easy to recover terephthalic acid, can recover terephthalic acid at high purity, and is highly stable even when used repeatedly. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent No. 10-2462599 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a method for producing terephthalic acid, which can obtain high-purity terephthalic acid from waste polyester, reduce the amount of solvent used in hydrolysis, the energy required for solvent recovery, and production costs, and improve the stability of the solvent. [Means for solving the problem]

[0010] To achieve the above object, the present invention provides a method for producing high-purity recycled terephthalic acid by polyester depolymerization, the method comprising: mixing a basic hydrolysis solvent, which is composed of an alkylated aromatic compound and a polarity control compound, with an alkaline catalyst to prepare a solvent; treating waste polyester with the solvent to obtain a polyester depolymerization product; filtering the polyester depolymerization product to obtain a sludge cake; adding purified water to the filtered sludge cake to prepare an aqueous sludge cake solution containing a terephthalate metal salt; treating the aqueous sludge cake solution with an organic solvent to obtain an aqueous solution containing a terephthalate metal salt; treating the aqueous solution with an adsorbent to purify the aqueous terephthalate metal salt solution; and treating the purified aqueous terephthalate metal salt solution with an acidic solution to precipitate solid terephthalic acid. [Effects of the Invention]

[0011] According to the method for producing terephthalic acid using polyester depolymerization according to the present invention, the conversion rate to terephthalic acid is extremely high, and the recycled terephthalic acid contains almost no impurities, so that high-purity terephthalic acid can be provided. In addition, the amount of solvent used in the conversion to terephthalic acid and the energy required for solvent recovery can be minimized, and the solvent has high stability and can be reused repeatedly. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a graph showing the conversion rate of toluene used in Example 17 of the present invention. [Figure 2] 1 is a graph showing the conversion rate of toluene used in Example 18 of the present invention. [Figure 3] 1 is a graph showing the conversion rate of toluene used in Example 19 of the present invention. [Figure 4] 1 is a graph showing the conversion rate of anisole used in Comparative Example 3 of the present invention. [Figure 5] 1 is a graph showing the conversion rate of MIBK used in Comparative Example 4 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Various embodiments of the present invention will be described below with reference to the accompanying drawings. The present invention is not limited to the specific embodiments, but should be understood to include various modifications, equivalents, and / or alternatives of the embodiments of the present invention. In connection with the description of the drawings, like reference numerals may be used for like components.

[0014] In this specification, the terms "have," "can have," "include," or "can include" refer to the presence of a given feature (e.g., a value, function, operation, or component such as a part) and do not exclude the presence of additional features.

[0015] As used herein, phrases such as "A or B," "at least one of A and / or B," or "one or more of A and / or B" can include all possible combinations of the items listed together. For example, "A or B," "at least one of A and B," or "at least one of A or B" can refer to all of the following: (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 herein, the expression "configured to" can be used interchangeably with, for example, "suitable for," "having the capacity to," "designed to," "adapted to," "made to," or "capable of," depending on the context. The term "configured to" does not necessarily mean only "specifically designed to."

[0017] The terms used herein are merely used to describe particular embodiments and may not be intended to limit the scope of other embodiments. A singular expression may include a plural expression unless the context clearly indicates otherwise. Terms used herein, including technical or scientific terms, may have the same meaning as commonly understood by a person of ordinary skill in the art described herein. Terms used herein that are defined in a general dictionary may be interpreted as meanings identical to or similar to the meanings they have in the context of the relevant art, and unless explicitly defined herein, should not be interpreted as having an ideal or overly formal meaning. In some cases, even terms defined herein may not be interpreted to exclude embodiments of the present specification.

[0018] The embodiments disclosed in this specification are presented for the purpose of explaining and understanding the disclosed technical content, and are not intended to limit the scope of the present invention. Therefore, the scope of the specification should be interpreted as including all modifications and various other embodiments based on the technical concept of the present invention.

[0019] Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, the terms and words used in the specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his / her 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 fully represent the technical ideas of the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0021] Throughout this specification, when a part "comprises" a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless otherwise specified to the contrary.

[0022] The present invention will be specifically described below.

[0023] A method for producing high-purity recycled terephthalic acid by depolymerizing polyester according to one embodiment of the present invention may include the steps of: mixing a basic hydrolysis solvent, which includes an alkylated aromatic compound and a polarity control compound, with an alkaline catalyst to prepare a solvent; treating waste polyester with the solvent to obtain a polyester depolymerization product; filtering the polyester depolymerization product to obtain a sludge cake; adding purified water to the filtered sludge cake to prepare an aqueous sludge cake solution containing a terephthalate metal salt; treating the aqueous sludge cake solution with an organic solvent to obtain an aqueous solution containing a terephthalate metal salt; treating the aqueous solution with an adsorbent to purify the aqueous terephthalate metal salt solution; and treating the purified aqueous terephthalate metal salt solution with an acidic solution to precipitate solid terephthalic acid.

[0024] The step of preparing a solvent by mixing the basic hydrolysis solvent consisting of the alkylated aromatic compound and the polarity control compound with an alkaline catalyst is intended to prepare a solvent having a stable structure that can sufficiently swell the polyester structure and increase the conversion rate to terephthalic acid.

[0025] Polyester is a polymer that has ester (RO-C(=O)-R') chemical functional groups in its main chain.

[0026] The polyester may be a polymer formed by condensation polymerization of a dicarboxylic acid and a dialcohol. The dicarboxylic acid may be any one selected from the group consisting of terephthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, trimellitic acid, and pyromellitic acid. Preferably, the dicarboxylic acid is terephthalic acid.

[0027] The dialcohol may be any one selected from the group consisting of ethylene glycol, trimethylene glycol, 1,2-propanediol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, decanmethylene 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 dialcohol may be ethylene glycol.

[0028] The polyester may be any 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 is polyethylene terephthalate (PET).

[0029] In the step of preparing a solvent by mixing a basic hydrolysis solvent comprising the alkylated aromatic compound and a polarity control compound with an alkaline catalyst, the solvent is used for the basic hydrolysis of polyester and can sufficiently dissolve the alkaline catalyst, allowing for repeated use. The alkylated aromatic compound has a structure that is highly stable against the basic hydrolysis reaction of polyester, allowing for the production of high-purity terephthalic acid. The polarity control compound can increase the solubility of the catalyst and easily affect the destruction of the ester functional group. The alkaline catalyst mixed in the step of preparing the solvent forms a terephthalate metal salt and is dissolved in purified water added after filtration, creating an alkaline environment that completely decomposes monoesters and other by-products of the hydrolysis reaction, thereby helping to achieve complete hydrolysis.

[0030] In the step of preparing a solvent by mixing a basic hydrolysis solvent consisting of the alkylated aromatic compound and a polarity control compound with an alkaline catalyst, the alkylated aromatic compound may be one or more compounds selected from the group consisting of toluene, xylene, trimethylbenzene, ethylbenzene, diethylbenzene, propylbenzene, dipropylbenzene, and butylbenzene. Preferably, the alkylated aromatic compound may be toluene. The alkylated aromatic compound has a stable structure even under basic conditions, does not generate contaminants through chain reactions, and allows for the reuse of the solvent.

[0031] In the step of preparing a solvent by mixing the basic hydrolysis solvent, which is composed of the alkylated aromatic compound and a polarity control compound, with an alkaline catalyst, the polarity control compound may be one or more compounds selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, ethylene glycol, propylene glycol, and butylene glycol. Preferably, the polarity control compound may be ethanol. The polarity control compound serves to increase the solubility of the alkaline catalyst and adjust the polarity of the solvent, thereby facilitating swelling of the polyester.

[0032] In the step of preparing a solvent by mixing a basic hydrolysis solvent comprising the alkylated aromatic compound and the polarity control compound with an alkaline catalyst, the alkaline catalyst may be at least one selected from the group consisting of potassium hydroxide, sodium hydroxide, lithium hydroxide, potassium oxide, sodium oxide, and lithium oxide. The alkaline catalyst prevents a portion of the produced terephthalic acid from acting as an acid catalyst and forms a terephthalate-metal salt, which is easily dissolved in water.

[0033] In the step of preparing the solvent by mixing the basic hydrolysis solvent, which is composed of the alkylated aromatic compound and the polarity control compound, with the alkaline catalyst, the weight ratio of the alkylated aromatic compound to the polarity control compound may be 1:0.1 to 10. Preferably, the weight ratio may be 1:0.5 to 5. Most preferably, the weight ratio may be 1:0.6 to 3. The solvent used for the basic hydrolysis of the polyester must be able to sufficiently dissolve the basic catalyst, and this is affected by the polarity of the solvent. Therefore, if the weight of the polarity control compound is below the above range, the conversion rate to terephthalic acid is low, and the reaction must be carried out at a high temperature to increase the conversion rate. If the weight of the polarity control compound is above the above range, the polarity becomes high, making it difficult to swell the plastic.

[0034] In the step of preparing the solvent by mixing the basic hydrolysis solvent, which is composed of the alkylated aromatic compound and the polarity control compound, with the alkaline catalyst, the weight ratio of the basic hydrolysis solvent to the alkaline catalyst may be 1:0.01 to 0.5. Preferably, the weight ratio may be 1:0.05 to 0.3. If the weight of the alkaline catalyst is less than the above range, the yield of terephthalic acid may be low due to the low metal content derived from the catalyst. If the weight exceeds the above range, the polarity control compound may be excessively mixed to dissolve the catalyst, thereby reducing the conversion rate to terephthalic acid.

[0035] In the step of preparing a solvent by mixing the basic hydrolysis solvent comprising the alkylated aromatic compound and the polarity control compound with an alkaline catalyst, the basic hydrolysis solvent comprising the alkylated aromatic compound and the polarity control compound is characterized in that the conversion rate of the alkylated aromatic compound after 10 recycles is 90% or more (see Figures 1 to 3).

[0036] The step of treating the waste polyester with the solvent to obtain the polyester depolymerization product is for eluting the terephthalate metal salt, and by treating the solvent, it is possible to produce environmentally friendly terephthalic acid with high purity. The step may involve a saponification reaction in addition to a hydrolysis reaction mediated by water generated by a basic hydrolysis solvent and an alkaline catalyst.

[0037] In the step of treating the waste polyester with the solvent to obtain a polyester depolymerization product, the ester functional groups of the polyester are destroyed by the solvent used, so that even bulk waste polyester that does not undergo a separate pulverization step can be depolymerized. Furthermore, in the process of treating the waste polyester with the solvent and subjecting it to basic hydrolysis, conditions such as temperature and pressure can be applied without any limitations to those applied in previous hydrolysis methods.

[0038] In the step of treating the waste polyester with the solvent to obtain a polyester depolymerization product, the weight ratio of the waste polyester to the solvent may be 1:1 to 50. Preferably, the weight ratio may be 1:5 to 25. Most preferably, the weight ratio of the waste polyester to the solvent may be 1:5 to 20. If the weight of the solvent is less than the above range, the viscosity of the waste polyester treated with the solvent increases, preventing smooth depolymerization. If the weight exceeds the above range, too much solvent is added, which is uneconomical.

[0039] In the step of treating the waste polyester with the solvent to obtain the polyester depolymerization product, the solvent may be added so that the pH of the entire reaction is 7.1 or more.

[0040] The steps of filtering the polyester depolymerization product to obtain a sludge cake and adding purified water to the filtered sludge cake to prepare a sludge cake aqueous solution containing a terephthalate metal salt are intended to remove the solvent and dissolved impurities from the polyester depolymerization product. The filtered sludge cake contains the obtained terephthalate metal salt and non-reactive impurities, and purified water can be added thereto to obtain an aqueous solution containing a primarily purified terephthalate metal salt.

[0041] The metal terephthalate salt is a salt to which an alkali metal derived from a catalyst is bonded, and may be any one selected from the group consisting of dipotassium terephthalate (K2-TPA), disodium terephthalate (Na2-TPA), and dilithium terephthalate (Li2-TPA). Preferably, the metal terephthalate salt may be disodium terephthalate (Na2-TPA).

[0042] In the step of filtering the polyester depolymerization product to obtain a sludge cake and adding purified water to the filtered sludge cake to prepare an aqueous sludge cake solution containing a metal terephthalate salt, the weight ratio of the filtered sludge cake to the purified water may be 1:2 to 20. Preferably, the weight ratio may be 1:4 to 15. Most preferably, the weight ratio may be 1:4 to 10. If the amount of purified water added is less than the above range, the filtered sludge cake will reach a supersaturated state, and if the amount exceeds the above range, it will have an adverse effect on the environment and be less economical.

[0043] The step of treating the aqueous sludge cake solution with an organic solvent to obtain an aqueous solution containing a metal terephthalate salt is performed by adding an organic solvent for purification and performing phase separation.

[0044] In the step of treating the aqueous sludge cake solution with an organic solvent to obtain an aqueous phase solution containing a terephthalate metal salt, the organic solvent may be at least one selected from the group consisting of pentane, hexane, heptane, octane, nonane, decane, and undecane. The organic solvent may be a hydrophobic solvent used alone or mixed with other hydrophobic solvents. In some cases, the organic solvent may be a water-soluble solvent used alone or mixed with a hydrophobic solvent. The organic solvent may be used to remove trace amounts of impurities or reaction solvents present in the aqueous layer after phase separation.

[0045] In the step of treating the aqueous sludge cake solution with an organic solvent to obtain an aqueous phase solution containing a terephthalate metal salt, the weight ratio of the aqueous sludge cake solution to the organic solvent may be 1:1 to 20. Preferably, the weight ratio may be 1:2 to 15. Most preferably, the weight ratio may be 1:2 to 10. If the organic solvent is added in an amount less than the above range, the purity of the finally obtained terephthalic acid may decrease due to an emulsion layer between the aqueous phase and the organic phase. If the organic solvent is added in an amount exceeding the above range, the terephthalic acid may be separated from the organic phase, resulting in a decrease in purity. Furthermore, if a large amount of organic solvent for purification is discarded, it is economically inefficient and may cause environmental pollution.

[0046] The step of treating the aqueous phase solution with an adsorbent to purify the aqueous solution of metal terephthalate salt is for removing trace amounts of impurities and organic solvents.

[0047] In the step of treating the aqueous phase solution with an adsorbent to purify the aqueous solution of metal terephthalate salt, the adsorbent may be at least one selected from the group consisting of incineration ash, activated carbon, zeolite, silicate, calcium carbonate, calcium oxide, calcium hydroxide, magnesium carbonate, magnesium oxide, magnesium hydroxide, sodium carbonate, sodium hydrogen carbonate, and alumina.

[0048] The step of treating the purified aqueous solution of terephthalate metal salt with an acidic solution to precipitate solid terephthalic acid is intended to obtain terephthalic acid by reacting the metal salt with the acid. The acidic solution may be a strong acid, preferably sulfuric acid, to precipitate terephthalic acid with high purity.

[0049] According to another embodiment of the present invention, the terephthalic acid produced by any of the above methods for producing high-purity recycled terephthalic acid using polyester depolymerization may have a purity of 99.00% or more. Preferably, the terephthalic acid may have a purity of 99.50% or more. The recycled terephthalic acid produced by any of the above methods has an extremely low impurity content.

[0050] The calculation method for the conversion rate of terephthalic acid in the above production method is as follows.

number

[0051] The yield of terephthalic acid obtained by the above production method is calculated as follows.

number

[0052] The present invention will be described in more detail with reference to the following examples. These examples are merely for the purpose of explaining the present invention in more detail, 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.

[0053] Examples and Comparative Examples [Comparison of depolymerization reaction depending on polarity control compound weight] Example 1 A solvent agent was prepared by adding 8.3 g of NaOH to a mixed solvent of 40 g of toluene and 60 g of ethanol in a 250 mL flask (S1).

[0054] 10 g of finely crushed PET waste was added to the solvent prepared in step S1 and stirred at 60°C for 3 hours (S2).

[0055] The PET depolymerization product after stirring was filtered to obtain a sludge cake, and 80 g of water was added to the filtered sludge cake to obtain an aqueous solution in which disodium terephthalate was eluted (S3).

[0056] The above aqueous solution was treated with 20 g of hexane, and after phase separation, only the aqueous layer was recovered (S4).

[0057] The aqueous layer was treated with 0.1 g of activated carbon, stirred for 2 hours, and then filtered to recover the purified aqueous layer (S5).

[0058] The recovered aqueous layer was treated with sulfuric acid to adjust the pH to 3 or less to obtain a white solid, which was then filtered, washed three times with 30 g of water, and dried to obtain white terephthalic acid (S6).

[0059] Example 2 Terephthalic acid was obtained in the same manner as in Example 1, except that 26 g of ethanol was used in the above step S1.

[0060] Example 3 Terephthalic acid was obtained in the same manner as in Example 1, except that 40 g of ethanol was used in the above step S1.

[0061] Example 4 Terephthalic acid was obtained in the same manner as in Example 1, except that 100 g of ethanol was used in the above step S1.

[0062] Example 5 Terephthalic acid was obtained in the same manner as in Example 1, except that 4 g of ethanol was used in the above step S1.

[0063] Example 6 Terephthalic acid was obtained in the same manner as in Example 1, except that 20 g of ethanol was used in the above step S1.

[0064] Example 7 Terephthalic acid was obtained in the same manner as in Example 1, except that 200 g of ethanol was used in the above step S1.

[0065] Example 8 Terephthalic acid was obtained in the same manner as in Example 1, except that 400 g of ethanol was used in the above step S1.

[0066] Comparative Example 1 Terephthalic acid was obtained in the same manner as in Example 3, except that 40 g of anisole was used instead of toluene in step S1.

[0067] Comparative Example 2 Terephthalic acid was obtained in the same manner as in Example 3, except that 40 g of MIBK was used instead of toluene in step S1.

[0068] [Table 1]

[0069] [Comparison of depolymerization reaction by alkaline catalyst weight] Example 9 Terephthalic acid was obtained in the same manner as in Example 1, except that 1 g of NaOH was used in step S1.

[0070] Example 10 Terephthalic acid was obtained in the same manner as in Example 1, except that 5 g of NaOH was used in step S1.

[0071] Example 11 Terephthalic acid was obtained in the same manner as in Example 1, except that 30 g of NaOH was used in step S1.

[0072] Example 12 Terephthalic acid was obtained in the same manner as in Example 1, except that 50 g of NaOH was used in step S1.

[0073] [Table 2]

[0074] [Comparison of depolymerization reaction depending on solvent weight] Example 13 Terephthalic acid was obtained in the same manner as in Example 1, except that in step S1, 0.8 g of NaOH was added to a mixed solvent of 3.7 g of toluene and 5.5 g of ethanol to prepare a solvent.

[0075] Example 14 Terephthalic acid was obtained in the same manner as in Example 1, except that in step S1, 3.8 g of NaOH was added to a mixed solvent of 18.5 g of toluene and 27.7 g of ethanol to prepare a solvent.

[0076] Example 15 Terephthalic acid was obtained in the same manner as in Example 1, except that in step S1, 15 g of NaOH was added to a mixed solvent of 74 g of toluene and 111 g of ethanol to prepare a solvent.

[0077] Example 16 Terephthalic acid was obtained in the same manner as in Example 1, except that in step S1, 20 g of NaOH was added to a mixed solvent of 92 g of toluene and 138 g of ethanol to prepare a solvent.

[0078] [Table 3]

[0079] Example 17 A solvent agent was prepared by adding 8.3 g of NaOH to a mixed solvent of 40 g of toluene and 40 g of ethanol in a 250 mL flask (S1').

[0080] In step S1, 10 g of finely crushed PET waste was added to the solvent solution prepared, and then stirred at 60°C for 3 hours (S2').

[0081] The PET depolymerization product after stirring was filtered to obtain a sludge cake, and 80 g of water was added to the filtered sludge cake to obtain an aqueous solution in which disodium terephthalate was dissolved. After obtaining the sludge cake, the solvent filtrate, which was a mixture of toluene and ethanol, was stored for use in the next reaction (S3').

[0082] The above aqueous solution was treated with 20 g of hexane, and after phase separation, only the aqueous layer was collected (S4').

[0083] The aqueous layer was treated with 0.1 g of activated carbon, stirred for 2 hours, and filtered to recover the purified aqueous layer (S5').

[0084] The recovered aqueous layer was treated with sulfuric acid to adjust the pH to 3 or less to obtain a white solid, which was then filtered, washed three times with 30 g of water, and dried to obtain white terephthalic acid (S6').

[0085] The solvent filtrate, a mixture of toluene and ethanol stored in step S3', and 4.5 g of NaOH were added to a 250 mL flask to prepare a solvent. This was then treated with 10 g of crushed PET waste and stirred at 60°C for 3 hours. The subsequent steps from step S3' to step S6' were repeated 10 times (S7'). The toluene conversion rate was plotted as a graph and is shown in Figure 1.

[0086] [Table 4]

[0087] Example 18 Terephthalic acid was obtained in the same manner as in Example 17, except that in step S1, 8.3 g of NaOH was added to a mixed solvent of 40 g of toluene and 28 g of ethanol to prepare a solvent. The conversion rate of toluene was plotted as a graph and is shown in Figure 2.

[0088] [Table 5]

[0089] Example 19 Terephthalic acid was obtained in the same manner as in Example 17, except that in step S1, 8.3 g of NaOH was added to a mixed solvent of 40 g of toluene and 52 g of ethanol to prepare a solvent. The conversion rate of toluene was plotted as a graph and is shown in Figure 3.

[0090] [Table 6]

[0091] Comparative Example 3 Terephthalic acid was obtained in the same manner as in Example 17, except that 40 g of anisole was used instead of toluene in step S1' of Example 17. The conversion rate of anisole was plotted as a graph and is shown in Figure 4.

[0092] [Table 7]

[0093] Comparative Example 4 Terephthalic acid was obtained in the same manner as in Example 17, except that 40 g of MIBK was used instead of toluene in step S1' of Example 17. The conversion rate of MIBK was plotted as a graph and is shown in Figure 5.

[0094] Table 8

Claims

1. mixing a basic hydrolysis solvent, which comprises an alkylated aromatic compound and a polarity control compound, with an alkaline catalyst to prepare a solvent; treating the waste polyester with the solvent agent to obtain a polyester depolymerization product; filtering the polyester depolymerization product to obtain a sludge cake, and adding purified water to the filtered sludge cake to prepare an aqueous sludge cake solution containing a terephthalate metal salt; treating the aqueous sludge cake solution with an organic solvent to obtain an aqueous solution containing a terephthalate metal salt; treating the aqueous phase solution with an adsorbent to purify the aqueous solution of metal terephthalate salt; treating the purified aqueous solution of terephthalate metal salt with an acidic solution to precipitate solid terephthalic acid; A method for producing high-purity recycled terephthalic acid using polyester depolymerization, comprising:

2. 2. The method for producing high-purity recycled terephthalic acid by depolymerizing a polyester according to claim 1, wherein in the step of preparing a solvent by mixing a basic hydrolysis solvent comprising the alkylated aromatic compound and a polarity control compound with an alkaline catalyst, the alkylated aromatic compound is one or more compounds selected from the group consisting of toluene, xylene, trimethylbenzene, ethylbenzene, diethylbenzene, propylbenzene, dipropylbenzene, and butylbenzene.

3. 2. The method for producing high-purity recycled terephthalic acid by polyester depolymerization according to claim 1, wherein in the step of preparing a solvent by mixing a basic hydrolysis solvent comprising the alkylated aromatic compound and a polarity control compound with an alkaline catalyst, the polarity control compound is one or more compounds selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, ethylene glycol, propylene glycol, and butylene glycol.

4. 2. The method for producing high-purity recycled terephthalic acid by depolymerization of polyester according to claim 1, wherein in the step of preparing a solvent by mixing a basic hydrolysis solvent comprising the alkylated aromatic compound and the polarity control compound with an alkaline catalyst, the alkaline catalyst is at least one selected from the group consisting of potassium hydroxide, sodium hydroxide, lithium hydroxide, potassium oxide, sodium oxide, and lithium oxide.

5. 2. The method for producing high-purity recycled terephthalic acid by depolymerization of polyester according to claim 1, wherein in the step of treating the aqueous sludge cake solution with an organic solvent to obtain an aqueous phase solution containing a terephthalate metal salt, the organic solvent is at least one selected from the group consisting of pentane, hexane, heptane, octane, nonane, decane, and undecane.

6. 2. The method for producing high-purity recycled terephthalic acid by polyester depolymerization according to claim 1, wherein in the step of treating the aqueous phase solution with an adsorbent to purify the aqueous terephthalate metal salt solution, the adsorbent is at least one selected from the group consisting of incineration ash, activated carbon, zeolite, silicate, calcium carbonate, calcium oxide, calcium hydroxide, magnesium carbonate, magnesium oxide, magnesium hydroxide, sodium carbonate, sodium bicarbonate, and alumina.

7. 2. The method for producing high-purity recycled terephthalic acid by depolymerization of polyester according to claim 1, wherein in the step of preparing a solvent by mixing a basic hydrolysis solvent comprising the alkylated aromatic compound and a polarity control compound with an alkaline catalyst, the weight ratio of the alkylated aromatic compound to the polarity control compound is 1:0.1 to 10.

8. 2. The method for producing high-purity recycled terephthalic acid by depolymerization of polyester according to claim 1, wherein in the step of preparing a solvent by mixing the basic hydrolysis solvent comprising the alkylated aromatic compound and the polarity control compound with the alkaline catalyst, the weight ratio of the basic hydrolysis solvent to the alkaline catalyst is 1:0.01 to 0.

5.

9. 2. The method for producing high-purity recycled terephthalic acid by depolymerizing polyester according to claim 1, wherein in the step of treating the waste polyester with the solvent to obtain a polyester depolymerization product, a weight ratio of the waste polyester to the solvent is 1:1 to 50.

10. The terephthalic acid produced by any one of the production methods of claims 1 to 9 has a purity of 99.50% or more.

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