Preparation method for recycled terephthalic acid using ultrasonic waves and recycled terephthalic acid prepared thereby

Abstract

The present invention provides a method for preparing purified recycled terephthalic acid and purified recycled terephthalic acid obtained thereby, the method comprising the steps of: treating waste polyester with an alkylated aromatic compound, a polarity control compound, and a solid-phase alkaline catalyst to form a composition comprising a terephthalic acid metal salt; ultrasonically treating the composition comprising a terephthalic acid metal salt; filtering the ultrasonically treated composition comprising a terephthalic acid metal salt to obtain a sludge cake; adding purified water to the sludge cake to obtain a terephthalic acid metal salt from which impurities have been removed; and treating the terephthalic acid metal salt, from which impurities have been removed, with an acidic solution to precipitate terephthalic acid.

Description

Method for producing regenerated terephthalic acid using ultrasound and regenerated terephthalic acid produced therefrom

[0001] The present invention relates to a method for separating terephthalic acid from waste polyester with high efficiency in a short time using a solid-phase alkaline catalyst and ultrasonic treatment. The present invention relates to a method for manufacturing regenerated terephthalic acid that is economical and increases production efficiency by using a solid-phase alkaline catalyst to regenerate terephthalic acid from waste polyester and eliminating the need for a separate separation process since water is not introduced during this process.

[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] While ultrasonic technology is utilized in various fields such as cleaning and medicine, it is not currently applied to the depolymerization of waste polyester. There is a demand to utilize ultrasonic technology for the depolymerization of waste polyester as a cost-effective and environmentally friendly method by reducing the formation of by-products and identifying optimal reaction conditions.

[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 recycling plastic waste by increasing its added value. Specifically, it provides a method that utilizes a solid-phase alkaline catalyst in the depolymerization of waste polyester to shorten the decomposition process and lower the reaction temperature, and uses ultrasound to shorten the reaction time, thereby reducing the cost of producing terephthalic acid.

[0010] To solve the above problem, the present invention provides a method for producing purified regenerated terephthalic acid and purified regenerated terephthalic acid produced therefrom, comprising the steps of: treating waste polyester with an alkylated aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst to form a composition containing a metal salt of terephthalic acid; treating the composition containing the metal salt of terephthalic acid with ultrasound; filtering the ultrasonically treated composition containing the metal salt of terephthalic acid to obtain a sludge cake; adding purified water to the sludge cake to obtain a metal salt of terephthalic acid from which impurities have been removed; and treating the metal salt of terephthalic acid from which impurities have been removed with an acidic solution to precipitate terephthalic acid.

[0011] According to the method for producing purified regenerated terephthalic acid of the present invention, by using an alkaline catalyst in a water-free state, a separate separation process to remove moisture from the metal salt of terephthalic acid is not required, making it economical; furthermore, by using ultrasound for the depolymerization of polyester, the reaction time is significantly shortened. In addition, according to the present invention, since the depolymerization reaction occurs at a relatively low temperature and low frequency is used, energy consumption is very low, resulting in reduced production costs; and high-purity terephthalic acid from which contaminants have been removed can be produced through the cavitation effect of ultrasound.

[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 purified regenerated terephthalic acid according to one embodiment of the present invention comprises the steps of: treating waste polyester with an alkylated aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst to form a composition containing a metal salt of terephthalic acid; treating the composition containing the metal salt of terephthalic acid with ultrasound; filtering the ultrasonically treated composition containing the metal salt of terephthalic acid to obtain a sludge cake; adding purified water to the sludge cake to obtain a metal salt of terephthalic acid from which impurities have been removed; and treating the metal salt of terephthalic acid from which impurities have been removed with an acidic solution to precipitate terephthalic acid.

[0025] The step of treating the waste polyester with an alkylating aromatic compound, a polarity controlling compound, and a solid-phase alkaline catalyst to form a composition containing a metal salt of terephthalate is to chemically swell the structure of the waste polyester sufficiently and monomerize the polymer to increase the conversion rate to terephthalic acid.

[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 forming a composition comprising a metal salt of terephthalate by treating the waste polyester with an alkylating aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst, the alkylating aromatic compound may be one or more compounds selected from the group consisting of toluene, xylene, methylbenzene, dimethylbenzene, trimethylbenzene, tetramethylbenzene, ethylbenzene, diethylbenzene, triethylbenzene, propylbenzene, dipropylbenzene, and butylbenzene. Preferably, the alkylating aromatic compound may be toluene. The alkylating aromatic compound has a structure with high stability against the basic hydrolysis reaction of the polyester. That is, since the alkylating aromatic compound does not have high solubility in alkaline catalysts, it maintains a stable structure even under basic conditions, does not generate pollutants even through chain reactions, and can be reused.

[0030] In the step of forming a composition comprising a metal terephthalate salt by treating the above-mentioned waste polyester with an alkylated aromatic compound, a polarity controlling compound, and a solid-phase alkaline catalyst, wherein the polarity controlling compound comprises methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, tridecanol, tetradecanol, pentadecanol, hexadecanol, heptadecanol, octadecanol, nonadecanol, eicosanol, hen-eicosanol, docosanol, tricosanol, tetracosanol, pentacosanol, hexacosanol, heptadecanol, octacosanol, nonacosanol, triacontanol, polycosanolmethyl, methylpropanol, methylbutanol, ethylene glycol, propylene glycol, and butylene glycol. It may be one or more compounds selected from the group. Preferably, the polarity-regulating compound may be ethanol. The polarity-regulating compound can increase the solubility of a solid-phase alkaline catalyst and promote the chemical swelling of the polyester structure by breaking down the ester functional groups of the polyester. Ultimately, the polarity-regulating compound can promote the monomerization of the polyester and thereby increase fluidity during repolymerization.

[0031] In the step of forming a composition comprising a terephthalic acid metal salt by treating the above waste polyester with an alkylating aromatic compound, a polarity-controlling compound, and a solid-phase alkaline catalyst, the solid-phase alkaline catalyst may be one or more selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide. Preferably, the alkaline catalyst may be one or more selected from the group consisting of sodium hydroxide and potassium hydroxide. The solid-phase alkaline catalyst prevents a portion of the terephthalic acid being produced from acting as an acid catalyst and enables the rapid formation of the terephthalic acid metal salt. Since the alkaline catalyst is in a solid phase, the main solvent in the depolymerization process is ethanol, and thus the depolymerization reaction can be carried out at low temperatures, resulting in an energy saving effect.

[0032] In the step of forming a composition containing a metal terephthalate by treating the waste polyester with an alkylating aromatic compound, a polarity controlling compound, and a solid-phase alkaline catalyst, the solid-phase alkaline catalyst may be in any one form selected from the group consisting of powder, beads, flakes, granules, lumps, pellets, chips, and briquettes. Preferably, the solid-phase alkaline catalyst may be in any one form selected from the group consisting of powder, beads, and flakes. Although an alkaline catalyst in an aqueous solution state has been conventionally used to form the composition containing the metal terephthalate, when an alkaline catalyst in an aqueous solution state is used for polyester depolymerization, it is uneconomical because a separate additional step must be taken to remove moisture or water from the composition containing the metal terephthalate, and there is a possibility that regenerated terephthalic acid may be lost during this process. In the present invention, a separate step of removing water by treating with a solid-phase alkaline catalyst is not included, making it economical, and since the reaction occurs at a low temperature of less than 100°C during subsequent ultrasonic treatment, it has excellent energy efficiency and can obtain regenerated terephthalic acid of high purity.

[0033] In the step of forming a composition containing a metal salt of terephthalate by treating the above-mentioned waste polyester with an alkylating aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst, the solid-phase alkaline catalyst is characterized by not containing a liquid phase, and the solid phase may have a certain crystal structure and be fixed in place while maintaining a certain spacing between constituent particles. When ultrasound is applied to a metal salt of terephthalate composition treated with an aqueous solution or liquid-phase alkaline catalyst, the temperature rises rapidly due to bubbles and pressure caused by the ultrasound, requiring a separate processing device for temperature control, which is uneconomical and causes a problem of reduced terephthalic acid recovery rate. On the other hand, by treating with a solid-phase alkaline catalyst in the step of forming the composition containing the metal salt of terephthalate, the composition containing the metal salt of terephthalate can perform a stable catalytic role without being affected by bubbles generated by ultrasound when ultrasound is subsequently applied to it.

[0034] In the step of forming a composition containing a metal salt of terephthalate by treating the waste polyester with an alkylated aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst, the metal salt varies depending on the type of alkaline catalyst, and the metal salt of terephthalate may include one or more selected from the group consisting of potassium terephthalate salt (K2-TPA), sodium terephthalate salt (Na2-TPA), and lithium terephthalate salt (Li2-TPA).

[0035] In the step of forming a composition comprising a metal salt of terephthalate by treating the waste polyester with an alkylating aromatic compound, a polarity controlling compound, and a solid-phase alkaline catalyst, the weight ratio of the waste polyester, the alkylating aromatic compound, the polarity controlling compound, and the solid-phase alkaline catalyst may be 1:0.01 to 10:0.01 to 10:0.01 to 5. Preferably, the weight ratio may be 1:0.05 to 10:0.05 to 10:0.05 to 2. Each of the alkylating aromatic compound and the polarity controlling compound introduced for the basic hydrolysis of the polyester must be able to sufficiently dissolve the solid-phase alkaline catalyst while maintaining stability during the hydrolysis of the polyester. If the weight of the above-mentioned alkylated aromatic compound is less than the above-mentioned numerical range, it may be difficult to maintain a stable structure under basic conditions and it may be difficult to sufficiently react the solid-phase alkaline catalyst; if it exceeds the above-mentioned numerical range, contaminants may be generated by the chain reaction of polyester depolymerization. If the weight of the above-mentioned polarity-regulating compound is less than the above-mentioned numerical range, the conversion rate of polyester to terephthalic acid is low, and the reaction must be carried out under high temperature conditions to increase the conversion rate. If the weight of the above-mentioned polarity-regulating compound exceeds the above-mentioned numerical range, the polarity increases, making it difficult to swell the waste polyester, and thus it may not be decomposed into terephthalic acid monomers. If the weight of the above-mentioned solid-phase alkaline catalyst is less than the above-mentioned numerical range, the metal content derived from the catalyst is low and the yield of terephthalic acid metal salt may be low; if it exceeds the above-mentioned numerical range, the polarity-regulating compound is excessively mixed to dissolve the solid-phase catalyst, which may make it difficult to control the reaction temperature and lower the conversion rate to terephthalic acid.

[0036] The step of treating the composition containing the above-mentioned terephthalic acid metal salt with ultrasound can shorten the time for regeneration into terephthalic acid and increase the recovery rate of high-purity terephthalic acid.

[0037] In the step of treating the composition containing the metal salt of the terephthalic acid with ultrasound, the ultrasound may be characterized by being irradiated for 10 minutes to 10 hours at a frequency of 10 to 100 kHz and an output of 100 to 10,000 w. Preferably, the ultrasound may be characterized by being irradiated for 10 minutes to 5 hours at a frequency of 20 to 70 kHz and an output of 200 to 5,000 w. More preferably, the ultrasound may be characterized by being irradiated for 10 minutes to 1 hour at a frequency of 20 to 70 kHz and an output of 500 to 3,000 w. If the ultrasound is treated at a frequency below the above numerical range during the ultrasound treatment step, it is difficult to purify the terephthalic acid to a high purity due to the presence of a large amount of impurities, and if the ultrasound is treated at a frequency exceeding the above numerical range, the reaction temperature increases, which may lead to reduced economic efficiency due to excessive energy consumption. If the above ultrasound is irradiated with power below the above numerical range, the reaction time becomes long and it is difficult to obtain terephthalic acid with a high yield, and if it is irradiated with power exceeding the above numerical range, there is a problem that the economic feasibility is reduced due to the high energy consumption process. If the above ultrasound is irradiated for a time below the above numerical range, the recovery rate of terephthalic acid decreases, and if it is irradiated exceeding the above numerical range, the structural stability of alkylated aromatic compounds, polarity-regulating compounds, or solid-phase alkaline catalysts decreases, resulting in the production of terephthalic acid with a high impurity content.

[0038] The step of treating the composition containing the metal salt of terephthalic acid with ultrasound may be performed while maintaining a reaction temperature of 20 to 90°C at 1 atm. Preferably, the reaction temperature may be maintained at 25 to 80°C while performing ultrasound treatment. If ultrasound is performed at a temperature below the above temperature range, the reaction time becomes longer, making it inefficient; and if ultrasound is performed at a temperature exceeding the above temperature range, the temperature rises due to heat generation by ultrasound, and terephthalic acid cannot be recovered with high efficiency.

[0039] In the step of forming a composition containing a metal salt of terephthalate by treating the waste polyester with an alkylated aromatic compound, a polarity-controlling compound, and a solid-phase alkaline catalyst, the waste polyester may be in a finely pulverized solid form and have an average particle size of 0.01 to 100 μm. Preferably, the average particle size of the waste polyester may be 0.1 to 70 μm. If the average particle size of the waste polyester is less than the above numerical range, the impurity removal effect may be reduced even by ultrasonic treatment, and since high-frequency ultrasound of 300 kHz or higher must be irradiated, it falls outside the frequency range of 10 to 100 kHz, which is the ultrasonic frequency of the present invention. If the average particle size of the waste polyester exceeds the above numerical range, the reaction time becomes longer, making it difficult to shorten the process time.

[0040] In the step of forming a composition containing a metal salt of terephthalic acid by treating the waste polyester with an alkylating aromatic compound, a polarity controlling compound, and a solid-phase alkaline catalyst, the average particle size of the solid-phase alkaline catalyst may be 0.1 to 200 μm. Preferably, the average particle size of the solid-phase alkaline catalyst may be 0.5 to 150 μm. If the average particle size of the solid-phase alkaline catalyst is less than the above numerical range, it is difficult for sufficient reaction to occur with the waste polyester and the ultrasonic irradiation time may be prolonged, and if the average particle size of the solid-phase alkaline catalyst exceeds the above numerical range, the impurity content of the regenerated terephthalic acid may increase.

[0041] The step of obtaining a sludge cake by filtering the composition containing the ultrasonically treated terephthalic acid metal salt is intended to minimize the impurity content and recover high-purity terephthalic acid. The filtration may be performed using a filter method, but is not limited thereto.

[0042] The step of adding purified water to the above sludge cake to obtain a metal salt of terephthalate from which impurities have been removed is intended to dissolve impurities in the purified water to separate them from the metal salt of terephthalate and to remove contaminants including metallic impurities such as Na, Ca, Mg, Al, Fe, and Mn.

[0043] In the step of obtaining a terephthalic acid metal salt from which impurities have been removed by adding purified water to the sludge cake, the weight ratio of the sludge cake to the purified water may be 1:1 to 20. Preferably, the weight ratio may be 1:2 to 10. If the content of the purified water is below the above numerical range, it is difficult to sufficiently dissolve the sludge cake, and ultimately, regenerated terephthalic acid with a high impurity content may be recovered, and if it exceeds the above numerical range, the recovery rate of the regenerated terephthalic acid may be low.

[0044] The step of treating the metal salt of terephthalic acid from which the above impurities have been removed with an acidic solution to precipitate terephthalic acid is intended to separate the metal salt from the terephthalic acid and recover the regenerated terephthalic acid. The acidic solution may be one or more selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, formic acid, acetic acid, propionic acid, citric acid, and tartaric acid.

[0045] According to another embodiment of the present invention, regenerated terephthalic acid produced by any one of the above manufacturing methods is provided.

[0046]

[0047] 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.

[0048]

[0049] Examples and Comparative Examples

[0050] Example 1

[0051] PET waste was washed and ground to an average particle size of 40 to 50 μm to prepare (S1).

[0052] A composition containing sodium terephthalate was formed by treating 10g of the above-mentioned crushed PET waste with 50g of toluene, 50g of ethanol, and 8g of solid NaOH in the form of beads having an average particle size of 60 to 70μm (S2).

[0053] 100g of a composition containing the above sodium terephthalate salt was irradiated with ultrasound at a reaction temperature of 60 to 65℃, 1 atm, a frequency of 28 to 30 kHz, and an output of 1,000 w (S3).

[0054] A composition containing sodium terephthalate that was ultrasonically treated in step S3 was filtered to obtain a sludge cake (S4).

[0055] 50g of a sludge cake containing the above sodium terephthalate salt was washed with 400g of purified water at a temperature of 50℃ to remove impurities and obtain a metal terephthalate salt (S5).

[0056] 200g of sulfuric acid was applied to the metal salt of terephthalic acid from which the above impurities had been removed to precipitate terephthalic acid (S6).

[0057] Example 2

[0058] The above Example 1 was carried out in the same manner as Example 1, except that in step S2 of Example 1, 0.1g of solid NaOH in the form of beads with an average PET particle size of 60 to 70μm was treated.

[0059] Example 3

[0060] The above Example 1 was carried out in the same manner as Example 1, except that in step S2 of Example 1, 0.5g of solid NaOH in the form of beads with an average PET particle size of 60 to 70μm was treated.

[0061] Example 4

[0062] The above Example 1 was carried out in the same manner as Example 1, except that in step S2 of Example 1, 20g of solid NaOH in the form of beads with an average PET particle size of 60 to 70μm was treated.

[0063] Example 5

[0064] The above Example 1 was carried out in the same manner as Example 1, except that in step S2 of Example 1, 30g of solid NaOH in the form of beads with an average PET particle size of 60 to 70μm was treated.

[0065] Example 6

[0066] The above Example 1 was carried out in the same manner as Example 1, except that in step S3 of Example 1, the frequency was 10 kHz.

[0067] Example 7

[0068] The above Example 1 was carried out in the same manner as Example 1, except that in step S3 of Example 1, the frequency was 20 kHz.

[0069] Example 8

[0070] The above Example 1 was carried out in the same manner as Example 1, except that in step S3 of Example 1, the frequency was 70 kHz.

[0071] Example 9

[0072] The above Example 1 was carried out in the same manner as Example 1, except that in step S3 of Example 1, the frequency was 100 kHz.

[0073] Example 10

[0074] The above Example 1 was carried out in the same manner as Example 1, except that the reaction temperature was set to 10℃ in step S3 of Example 1.

[0075] Example 11

[0076] The above Example 1 was carried out in the same manner as Example 1, except that the reaction temperature was set to 25℃ in step S3 of Example 1.

[0077] Example 12

[0078] The above Example 1 was carried out in the same manner as Example 1, except that the reaction temperature was set to 80°C in step S3 of Example 1.

[0079] Example 13

[0080] The above Example 1 was carried out in the same manner as Example 1, except that the reaction temperature was set to 100℃ in step S3 of Example 1.

[0081] Comparative Example 1

[0082] The above Example 1 was carried out in the same manner as Example 1, except that in step S2 of Example 1, NaOH in an aqueous solution state was used instead of solid NaOH in bead form.

[0083] Comparative Example 2

[0084] The above Example 1 was carried out in the same manner as Example 1, except that in step S2 of Example 1, solid NaOH in bead form with an average particle size of 500 μm was processed.

[0085] Comparative Example 3

[0086] The above Example 1 was carried out in the same manner as Example 1, except that step S3 of Example 1 was not carried out.

[0087]

[0088] Experimental Example 1

[0089] The impurity content (ppm), moisture content (%), and yield (%) of the regenerated terephthalic acid according to Examples 1 to 13 and Comparative Examples 1 to 3 were measured.

[0090] Ca(ppm)Al(ppm)Fe(ppm)Moisture Content(%)Yield(%) Example 10 1500 0.19 8.7 Example 2 10 470 1.29 0.1 Example 3 5380 0.59 2.3 Example 4 310 0.39 3.5 Example 5 270 0.39 0.7 Example 6 16430 2.78 9.1 Example 7 740 0 1.58 9.9 Example 8 6350 1.39 1.7 Example 9 5230 2.58 8.2 Example 10 26320 2.98 5.8 Example 11 15250 2.28 7.6 Example 12 200 0.29 1.0 Example 13 180 0.29 1.8 Comparative Example 101802594.7 Comparative Example 2134602081.2 Comparative Example 3334803574.2

[0091]

[0092] Experimental Example 2

[0093] Table 2 shows the time taken to recover the regenerated terephthalic acid according to Examples 1 to 13 and Comparative Examples 1 to 3 above.

[0094] Yield (%) Time Example 198.714 min Example 290.175 min Example 392.349 min Example 493.547 min Example 590.761 min Example 689.186 min Example 789.955 min Example 891.757 min Example 988.260 min Example 1085.890 min Example 1187.652 min - Example 1291.048 min Example 1391.860 min Comparative Example 194.785 min Comparative Example 281.2117 min - Comparative Example 374.2105 min

Claims

1. A step of forming a composition comprising a metal terephthalate salt by treating waste polyester with an alkylated aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst; A step of ultrasonically treating the composition containing the above-mentioned terephthalic acid metal salt; A step of obtaining a sludge cake by filtering a composition containing the above-mentioned ultrasonically treated terephthalic acid metal salt; A step of adding purified water to the above sludge cake to obtain a metal salt of terephthalic acid from which impurities have been removed; and A step of precipitating terephthalic acid by treating the metal salt of terephthalic acid from which the above impurities have been removed with an acidic solution. A method for producing purified regenerated terephthalic acid including 2. In Claim 1, A method for producing purified regenerated terephthalic acid, wherein the above waste polyester is treated with an alkylated aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst to form a composition comprising a terephthalic acid metal salt, wherein the solid-phase alkaline catalyst is one or more selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide.

3. In Claim 1, A method for producing purified regenerated terephthalic acid, wherein the above waste polyester is treated with an alkylated aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst to form a composition comprising a terephthalic acid metal salt, wherein the solid-phase alkaline catalyst is in any one form selected from the group consisting of powder, bead, flake, granule, lump, pellet, chip, and briquette.

4. In Claim 1, A method for producing purified regenerated terephthalic acid, wherein the above waste polyester is treated with an alkylated aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst to form a composition containing a terephthalic acid metal salt, wherein the solid-phase alkaline catalyst does not contain a liquid phase, and the solid phase has a constant crystal structure and is fixed in place while maintaining a constant spacing between constituent particles.

5. In Claim 1, A method for producing purified regenerated terephthalic acid, wherein the step of treating a composition containing the above-mentioned terephthalic acid metal salt with ultrasound, wherein the ultrasound is irradiated for 10 minutes to 10 hours at a frequency of 10 to 100 kHz and an output of 100 to 10,000 W.

6. In Claim 1, A method for producing purified regenerated terephthalic acid, wherein the step of treating the composition containing the above-mentioned terephthalic acid metal salt with ultrasound involves treating with ultrasound while maintaining a reaction temperature of 20 to 90°C at 1 atm.

7. In Claim 1, A method for producing purified regenerated terephthalic acid, wherein the waste polyester is treated with an alkylated aromatic compound, a polarity-controlling compound, and a solid-phase alkaline catalyst to form a composition comprising a metal salt of terephthalic acid, the waste polyester being in a finely pulverized solid form and having an average particle size of 0.1 to 100 μm.

8. In Claim 1, A method for producing purified regenerated terephthalic acid, wherein the average particle size of the solid-phase alkaline catalyst is 0.1 to 200 μm, in the step of treating the above waste polyester with an alkylated aromatic compound, a polarity-regulating compound, and a solid-phase alkaline catalyst to form a composition comprising a metal salt of terephthalic acid.

9. In Claim 1, A method for producing purified regenerated terephthalic acid, wherein in the step of adding purified water to the above sludge cake to obtain a terephthalic acid metal salt from which impurities have been removed, the weight ratio of the sludge cake to the purified water is 1:1 to 20.

10. Purified regenerated terephthalic acid produced by any one of the manufacturing methods of claims 1 to 9.

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