Monomer composition for synthesizing recycled plastics, its manufacturing method, and recycled plastics, molded articles, and plasticizer compositions using the same

Abstract

The present invention relates to a monomer composition for synthesizing recycled plastics, which is recovered from a (co)polymer synthesized from a monomer containing terephthalic acid and in which the content of organic impurities such as formic acid and acetic acid has been significantly reduced; a method for producing the same; and recycled plastics, molded articles, and plasticizer compositions each using the same.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0094470, dated July 19, 2021, Korean Patent Application No. 10-2021-0094471, dated July 19, 2021, Korean Patent Application No. 10-2021-0094472, dated July 19, 2021, and Korean Patent Application No. 10-2021-0094473, dated July 19, 2021, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a monomer composition for synthesizing recycled plastics, which can significantly reduce the content of organic impurities and ensure high-purity terephthalic acid when terephthalic acid is recovered by depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid; a method for producing the same; and recycled plastics, molded articles, and plasticizer compositions each using the same. [Background technology]

[0003] Polyethylene terephthalate (PET) is a thermoplastic (co)polymer that has excellent properties such as excellent transparency and heat insulation, and is a plastic that is widely used in wire coatings, household goods, toys, electrical insulators, radio and television cases, packaging materials, etc.

[0004] Although polyethylene terephthalate is widely used for various purposes, environmental and health concerns have been raised during waste disposal. Currently, physical recycling methods are being used, but this can lead to quality degradation, so research is underway into chemical recycling of polyethylene terephthalate.

[0005] Terephthalic acid is a valuable compound used as a raw material for a wide variety of products, including polyethylene terephthalate (PET), polyester fiber, and polyester film for packaging and containers.

[0006] The condensation polymerization of ethylene glycol with terephthalic acid to form polyethylene terephthalate (PET) is a reversible reaction process, and the polyethylene terephthalate (PET) can be depolymerized back to monomers or oligomers.

[0007] Various methods have been proposed for decomposing polyethylene terephthalate (PET) to recover the raw material monomers. The monomers used in the polycondensation reaction to regenerate recycled plastics can be obtained by alkaline decomposition of polyethylene terephthalate (PET) waste.

[0008] For example, the decomposition products of polyethylene terephthalate (PET) under basic conditions include ethylene glycol and the salt of terephthalic acid, which can be further neutralized with a strong acid to produce terephthalic acid.

[0009] However, other organic impurities were detected in the terephthalic acid obtained by the conventional method, and when it was reused as a raw material for manufacturing high-value-added plastics such as PBT / TPEE, there were limitations such as slow reaction times and poor color quality.

[0010] Therefore, it is necessary to develop a method that can significantly reduce the content of organic impurities in the process of decomposing (co)polymers synthesized from monomers containing terephthalic acid, such as polyethylene terephthalate (PET), and recovering the raw monomers. Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention provides a monomer composition for synthesizing recycled plastics, which can significantly reduce the content of organic impurities and ensure high-purity terephthalic acid when terephthalic acid is recovered by depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid.

[0012] The present invention also provides a method for producing the monomer composition for synthesizing recycled plastics, as well as recycled plastics, molded articles, and plasticizer compositions using the monomer composition for synthesizing recycled plastics. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a monomer composition for synthesizing recycled plastics, which comprises terephthalic acid and further comprises one or more organic impurities selected from the group consisting of formic acid and acetic acid, wherein the weight ratio of the organic impurities measured using gas chromatography-mass spectrometry is less than 5 μg per 1 g of the monomer composition for synthesizing recycled plastics, and the monomer composition for synthesizing recycled plastics is recovered from a (co)polymer synthesized from a monomer including terephthalic acid.

[0014] The present invention also provides a method for producing a monomer composition for synthesizing recycled plastics, comprising: depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid to remove a diol component; washing the depolymerized reaction product from which the diol component has been removed with a solvent at a temperature of 20°C to 100°C; and dissolving the washed depolymerized reaction product in water and recrystallizing the resultant product; wherein the step of dissolving the washed depolymerized reaction product in water and recrystallizing the resultant product comprises dissolving the washed depolymerized reaction product in water at a temperature of 200°C to 300°C; and cooling the dissolved solution to a temperature 50°C to 200°C lower than the solution temperature.

[0015] The present invention also provides a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic and a comonomer.

[0016] The present invention also provides a molded article containing the recycled plastic.

[0017] The present invention also provides a plasticizer composition comprising a reaction product of the monomer composition for synthesizing recycled plastics and an alcohol.

[0018] Hereinafter, a monomer composition for synthesizing recycled plastics according to specific embodiments of the invention, a method for producing the same, and recycled plastics, molded articles, and plasticizer compositions using the same will be described in more detail.

[0019] Unless expressly stated otherwise herein, terminology is for the purpose of referring to particular embodiments only and is not intended to be limiting of the invention.

[0020] As used herein, the singular forms "a," "an," and "the" include the plural forms as well, unless the context clearly indicates to the contrary.

[0021] As used herein, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other certain properties, regions, integers, steps, operations, elements, components, and / or groups.

[0022] In this specification, terms including ordinal numbers, such as "first" and "second," are used to distinguish one component from another, and are not limited by the ordinal numbers. For example, within the scope of the present invention, a first component may be called a second component, and similarly, a second component may be called a first component.

[0023] In this specification, the term "(co)polymer" refers to both a polymer and a copolymer, where the polymer refers to a homopolymer consisting of a single repeating unit, and the copolymer refers to a composite polymer containing two or more types of repeating units.

[0024] 1. Monomer composition for synthesizing recycled plastics According to one embodiment of the present invention, there can be provided a monomer composition for synthesizing recycled plastics, which comprises terephthalic acid and further comprises one or more organic impurities selected from the group consisting of formic acid and acetic acid, wherein the weight ratio of the organic impurities measured using gas chromatography-mass spectrometry is less than 5 μg per 1 g of the monomer composition for synthesizing recycled plastics, and the monomer composition for synthesizing recycled plastics is recovered from a (co)polymer synthesized from a monomer including terephthalic acid.

[0025] The present inventors have experimentally confirmed that, although the monomer composition for synthesizing recycled plastics in one embodiment is recovered from a (co)polymer synthesized from a monomer containing terephthalic acid, the ratio of organic impurities (formic acid, acetic acid) is extremely reduced to less than 5 μg per 1 g of the monomer composition for synthesizing recycled plastics, rather than terephthalic acid, which is the main synthetic target substance of the present invention, and that when this is used to synthesize polyethylene terephthalate or high-value-added plastics (PBT, TPEE), the polymerization time can be shortened, polymerization production efficiency can be increased, and excellent physical properties can be achieved in terms of color quality, thereby completing the invention.

[0026] In particular, the amount of organic impurities (formic acid, acetic acid) detected was significantly reduced compared to terephthalic acid recovered from a (co)polymer synthesized from a monomer containing terephthalic acid obtained by a conventional method. This is thought to be because the organic impurities (formic acid, acetic acid) can be effectively removed by the washing step and recrystallization step, which are characteristics of the method for producing a monomer composition for synthesizing recycled plastics, as described below.

[0027] In addition, the present invention does not use toxic organic solvents (e.g., DMAc) or organic acids (e.g., acetic acid) for purification in the method for producing a monomer composition for synthesizing recycled plastics. Therefore, unlike known methods for purifying terephthalic acid, the present invention has the technical advantage of being an environmentally friendly process, as it can be purified using only water and depolymerized using water as a solvent.

[0028] Specifically, the monomer composition for synthesizing recycled plastics according to one embodiment may contain terephthalic acid, which is recovered from a (co)polymer synthesized from a monomer containing terephthalic acid used in recovering the monomer composition for synthesizing recycled plastics.

[0029] That is, terephthalic acid is also obtained as a result of recovery from a (co)polymer synthesized from a monomer containing terephthalic acid to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when new terephthalic acid is added externally, separately from the recovery from a (co)polymer synthesized from a monomer containing terephthalic acid to produce the monomer composition for synthesizing recycled plastics of the embodiment, it is not included in the scope of terephthalic acid of the present invention.

[0030] Specifically, the term "recovered from a (co)polymer synthesized from a monomer containing terephthalic acid" means that the compound is obtained by depolymerization of a (co)polymer synthesized from a monomer containing terephthalic acid. The depolymerization may be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions.

[0031] For example, when the depolymerization reaction is carried out under the basic conditions, a terephthalic acid salt called Na2-TPA and ethylene glycol are primarily produced from the polyethylene terephthalate, and then Na2-TPA is converted to TPA by secondary neutralization with a strong acid, allowing terephthalic acid to be recovered.

[0032] That is, the terephthalic acid recovered from the (co)polymer synthesized from the monomer containing terephthalic acid may contain a base (alkali) decomposition product of the (co)polymer synthesized from the monomer containing terephthalic acid, its acid neutralization product, or a mixture thereof. Specifically, the base (alkali) decomposition product of the (co)polymer synthesized from the monomer containing terephthalic acid may contain Na-TPA, and the acid neutralization product of the base (alkali) decomposition product of the (co)polymer synthesized from the monomer containing terephthalic acid may contain terephthalic acid.

[0033] The molar ratio of the terephthalic acid may be more than 99.15 mol%, or 99.2 mol% or more, or 100 mol% or less, or more than 99.15 mol% and 100 mol% or less, or 99.2 mol% to 100 mol% based on 100 mol% of the total monomer compounds contained in the monomer composition for synthesizing recycled plastics.

[0034] The method for measuring the molar ratio of terephthalic acid is not particularly limited, and examples thereof include 1 H NMR, ICP-MS analysis, HPLC analysis, etc. can be used without limitation. Specific methods, conditions, and devices for NMR, ICP-MS, and HPLC can be various conventional methods without limitation.

[0035] As an example of a method for measuring the molar ratio of terephthalic acid, 5 mg to 20 mg of a monomer composition for synthesizing recycled plastics is collected as a sample under normal pressure and at a temperature of 20°C to 30°C, dissolved in 1 ml of DMSO-d6 solvent, and then analyzed by an Agilent DD1 500 MHz NMR device. 1 H NMR spectra were obtained, and the peaks of all detected substances, such as terephthalic acid (TPA) and isophthalic acid (IPA), were individually assigned and integrated using analytical software (MestReC). The molar ratio (mol%) of terephthalic acid contained within 100 mol% of the total monomer compounds analyzed from the sample was calculated based on the peak integral value.

[0036] As such, the ratio of terephthalic acid, which is the main synthesis target substance in the present invention, is significantly increased to over 99.15 mol% based on 100 mol% of the total monomer compounds contained in the monomer composition for synthesizing recycled plastics. By minimizing terephthalic acid or impurity monomers (e.g., isophthalic acid), excellent physical properties can be achieved when polyethylene terephthalate or high-value-added plastics (PBT, TPEE) are synthesized using this.

[0037] In addition, the monomer composition for synthesizing recycled plastics according to one embodiment may further include isophthalic acid in a molar ratio of less than 0.85 mol % based on 100 mol % of the total monomer compounds contained in the monomer composition for synthesizing recycled plastics.

[0038] The isophthalic acid is recovered from a (co)polymer synthesized from a monomer containing terephthalic acid used in recovering the monomer composition for synthesizing recycled plastics.

[0039] In other words, isophthalic acid is also obtained as a result of recovery from a (co)polymer synthesized from a monomer containing terephthalic acid to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when new isophthalic acid is added externally, separately from the recovery from a (co)polymer synthesized from a monomer containing terephthalic acid to produce the monomer composition for synthesizing recycled plastics of the embodiment, it is not included in the scope of isophthalic acid of the present invention.

[0040] Specifically, the term "recovered from a (co)polymer synthesized from a monomer containing terephthalic acid" means that the compound is obtained by depolymerization of a (co)polymer synthesized from a monomer containing terephthalic acid. The depolymerization may be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions.

[0041] The molar ratio of the isophthalic acid may be less than 0.85 mol%, or 0.5 mol% or less, or 0.1 mol% or less, or 0 mol% or more and less than 0.85 mol%, or 0 mol% or more and 0.5 mol% or less, or 0 mol% or more and 0.1 mol% or less, based on 100 mol% of the total monomer compounds contained in the monomer composition for synthesizing recycled plastics.

[0042] The method for measuring the molar ratio of isophthalic acid is not particularly limited, and examples thereof include 1 H NMR, ICP-MS analysis, HPLC analysis, etc. can be used without limitation. Specific methods, conditions, and devices for the NMR, ICP-MS, and HPLC can be various conventional methods without limitation.

[0043] As an example of a method for measuring the molar ratio of isophthalic acid, 5 mg to 20 mg of a monomer composition for synthesizing recycled plastics is collected as a sample under normal pressure and at a temperature of 20°C to 30°C, dissolved in 1 ml of DMSO-d6 solvent, and then analyzed by an Agilent DD1 500 MHz NMR device. 1 H NMR spectra were obtained, and the peaks of all detected substances, such as terephthalic acid (TPA) and isophthalic acid (IPA), were individually assigned and integrated using analytical software (MestReC). The molar ratio (mol%) of isophthalic acid contained within 100 mol% of the total monomer compounds analyzed from the sample was calculated based on the peak integral value.

[0044] In this way, the ratio of the impurity monomer isophthalic acid, rather than terephthalic acid, the main synthetic target substance in the present invention, is extremely reduced to less than 0.85 mol % based on 100 mol % of the total monomer compounds contained in the monomer composition for synthesizing recycled plastics. Therefore, when using this to synthesize polyethylene terephthalate or high-value-added plastics (PBT, TPEE), excellent physical properties can be achieved.

[0045] In addition, the monomer composition for synthesizing recycled plastics according to one embodiment is characterized in that it is recovered from a (co)polymer synthesized from a monomer containing terephthalic acid. That is, as a result of recovering from a (co)polymer synthesized from a monomer containing terephthalic acid to obtain the monomer composition for synthesizing recycled plastics according to one embodiment, a monomer composition for synthesizing recycled plastics containing both terephthalic acid and isophthalic acid is obtained.

[0046] Regarding the (co)polymer synthesized from the monomer containing terephthalic acid, the (co)polymer means both a polymer and a copolymer, and is a general term for a reaction product obtained by the (co)polymerization reaction of a monomer. The (co)polymer may include low molecular weight compounds, oligomers, and polymers depending on the molecular weight range.

[0047] The (co)polymer synthesized from the monomer containing terephthalic acid can include one or more (co)polymers selected from the group consisting of polyalkylene terephthalate, polyalkylene terephthalate copolymer, and thermoplastic polyester elastomer. That is, the (co)polymer synthesized from the monomer containing terephthalic acid can include one type of polyalkylene terephthalate, one type of polyalkylene terephthalate copolymer, one type of thermoplastic polyester elastomer, or a mixture of two or more types thereof.

[0048] The polyalkylene terephthalate copolymer refers to a copolymer obtained by further reacting an additional comonomer based on alkylene glycol and terephthalic acid, which are monomers for synthesizing polyalkylene terephthalate.

[0049] The (co)polymer synthesized from the monomer containing terephthalic acid may include a reaction product of terephthalic acid and a comonomer, i.e., the monomer containing terephthalic acid may further include a comonomer together with terephthalic acid.

[0050] The comonomer capable of reacting with terephthalic acid is not particularly limited, and specific examples thereof include aliphatic diols, polyalkylene oxides, fatty acids, fatty acid derivatives, and combinations thereof.

[0051] The aliphatic diol may be, for example, one or more of diols having a number average molecular weight (Mn) of 300 g / mol or less, i.e., ethylene glycol, propylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol (1,4-BG), 1,5-pentanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol (1,4-CHDM). Specific examples include 1,4-butanediol, ethylene glycol, 1,4-cyclohexanedimethanol, or a mixture thereof.

[0052] The polyalkylene oxide is a unit constituting a soft segment and may be an aliphatic polyether. Examples of the polyalkylene oxide include one or more of polyoxyethylene glycol, polypropylene glycol, poly(tetramethylene ether) glycol (PTMEG), polyoxyhexamethylene glycol, a copolymer of ethylene oxide and propylene oxide, an ethylene oxide addition polymer of polypropylene oxide glycol, and a copolymer of ethylene oxide and tetrahydrofuran. A specific example is PTMEG, and in particular, PTMEG having a number average molecular weight (Mn) of 600 g / mol to 3,000 g / mol, 1,000 g / mol to 2,500 g / mol, or 1,500 g / mol to 2,200 g / mol may be used.

[0053] The fatty acid may be, for example, one or more aliphatic carboxylic acid compounds excluding terephthalic acid, and a specific example may be adipic acid. The fatty acid derivative is a compound derived from the above-mentioned fatty acid, and for example, may be one or more of fatty acid esters, fatty acid chlorides, fatty acid anhydrides, and fatty acid amides, and a specific example may be adipic acid esters.

[0054] To give a specific example, when 1,4-butanediol, an aliphatic diol, is used as a comonomer that can react with terephthalic acid, polybutylene terephthalate (PBT), a type of polyalkylene terephthalate, is obtained by the polymerization reaction of terephthalic acid and 1,4-butanediol.

[0055] In addition, when ethylene glycol, an aliphatic diol, is used as a comonomer that can react with terephthalic acid, polyethylene terephthalate (PET), a type of polyalkylene terephthalate, can be obtained by the polymerization reaction of terephthalic acid and ethylene glycol.

[0056] In addition, when the aliphatic diol 1,4-butanediol and the polyalkylene oxide PTMEG are used together as comonomers that can react with the terephthalic acid, a thermoplastic polyester elastomer (TPEE) can be obtained by the polymerization reaction of the terephthalic acid, 1,4-butanediol, and PTMEG.

[0057] In addition, when the aliphatic diol 1,4-butanediol and the fatty acid adipic acid are used together as comonomers that can react with the terephthalic acid, the polymerization reaction of terephthalic acid, 1,4-butanediol, and adipic acid produces polybutylene adipate terephthalate (PBAT), a type of polyalkylene terephthalate copolymer.

[0058] In addition, when the aliphatic diols ethylene glycol and 1,4-cyclohexanedimethanol are used together as comonomers that can react with terephthalic acid, a glycol-modified polyethylene terephthalate (PETG), a type of polyalkylene terephthalate copolymer, can be obtained through a polymerization reaction of terephthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol.

[0059] As a specific example, the polyalkylene terephthalate may include one or more (co)polymers selected from polybutylene terephthalate, polyethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polytrimethylene terephthalate.

[0060] As a specific example, the polyalkylene terephthalate copolymer may include one or more (co)polymers selected from polybutylene adipate terephthalate (PBAT) and glycol-modified polyethylene terephthalate (PETG).

[0061] Meanwhile, the monomer composition for synthesizing recycled plastics may further contain one or more organic impurities selected from the group consisting of formic acid and acetic acid. That is, the monomer composition for synthesizing recycled plastics may further contain organic impurities including one formic acid, one acetic acid, or a mixture of two of these. The formic acid and acetic acid are recovered from a (co)polymer synthesized from a monomer containing terephthalic acid used in recovering the monomer composition for synthesizing recycled plastics.

[0062] In other words, this means that formic acid and acetic acid are both obtained as a result of recovery from a (co)polymer synthesized from a monomer containing terephthalic acid to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when new organic impurities are added from outside, apart from the recovery from a (co)polymer synthesized from a monomer containing terephthalic acid to produce the monomer composition for synthesizing recycled plastics of the embodiment, they are not included in the category of organic impurities of the present invention.

[0063] Specifically, the term "recovered from a (co)polymer synthesized from a monomer containing terephthalic acid" means that the compound is obtained by depolymerization of a (co)polymer synthesized from a monomer containing terephthalic acid. The depolymerization may be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions.

[0064] The weight ratio of the organic impurities, measured using gas chromatography-mass spectrometry, may be less than 5 μg, or 0 μg or more, or 0 μg or more but less than 5 μg, per 1 g of the monomer composition for synthesizing recycled plastics. This is thought to be because, as will be described later, the method for producing the monomer composition for synthesizing recycled plastics includes washing the depolymerization reaction product, from which the diol component has been removed, with a solvent at a temperature of 20°C to 100°C and dissolving the washed depolymerization reaction product in water and recrystallizing it, and the step of dissolving the washed depolymerization reaction product in water and recrystallizing it includes dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 300°C and cooling the dissolved solution to a temperature 50°C to 200°C lower than the solution temperature.

[0065] In the present invention, the weight ratio of organic impurities, formic acid alone, acetic acid alone, or a mixture of these two, rather than terephthalic acid, which is the main target substance for synthesis, is extremely reduced to less than 5 μg, or 0 μg or more, or 0 μg or more but less than 5 μg per 1 g of the monomer composition for synthesizing recycled plastics, so that when polyethylene terephthalate or high-value-added plastics (PBT, TPEE) are synthesized using this, excellent physical properties can be achieved.

[0066] The gas chromatography mass spectrometry method for measuring the weight ratio of the organic impurities is not particularly limited. For example, 0.5 g of a recycled terephthalic acid monomer composition was collected as a sample under conditions of normal pressure and 20 to 30°C, and quantitative analysis was performed using a Headspace-GC / MS (oven temperature: 150°C) device to measure the weight ratio (μg / g) of formic acid (FA) and acetic acid (AA) contained therein, based on 1 g of the sample.

[0067] As described above, the weight ratio of the organic impurities measured by gas chromatography-mass spectrometry in the monomer composition for synthesizing recycled plastics according to the present invention is significantly reduced to less than 5 μg, or 0 μg or more, or 0 μg or more but less than 5 μg per 1 g of the monomer composition for synthesizing recycled plastics. Therefore, when polyethylene terephthalate or high-value-added plastics (PBT, TPEE) are synthesized using the monomer composition for synthesizing recycled plastics, the polymerization time can be shortened, thereby improving polymerization production efficiency, and excellent physical properties can be achieved in terms of color quality.

[0068] On the other hand, if the weight ratio of the organic impurities measured using gas chromatography-mass spectrometry increases to 5 μg or more per 1 g of the monomer composition for synthesizing recycled plastics, the polymerization time will be extended when synthesizing high-value-added plastics (PBT, TPEE), reducing polymerization production efficiency and resulting in poor color quality such as an increase in yellowness index.

[0069] Meanwhile, the monomer composition for synthesizing recycled plastics may further contain one or more aromatic impurities selected from the group consisting of 4-carboxybenzaldehyde, benzoic acid, and p-toluic acid. That is, the monomer composition for synthesizing recycled plastics may further contain aromatic impurities including one of 4-carboxybenzaldehyde, one of benzoic acid, one of p-toluic acid, or a mixture of two or three of these. The 4-carboxybenzaldehyde, benzoic acid, and p-toluic acid are recovered from a (co)polymer synthesized from a monomer containing terephthalic acid that was used to recover the monomer composition for synthesizing recycled plastics.

[0070] In other words, 4-carboxybenzaldehyde, benzoic acid, and p-toluic acid are also obtained as a result of recovery from a (co)polymer synthesized from a monomer containing terephthalic acid to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when new aromatic impurities are added externally, apart from the recovery from a (co)polymer synthesized from a monomer containing terephthalic acid to produce the monomer composition for synthesizing recycled plastics of the embodiment, they are not included in the category of aromatic impurities of the present invention.

[0071] Specifically, the term "recovered from a (co)polymer synthesized from a monomer containing terephthalic acid" means that the compound is obtained by depolymerization of a (co)polymer synthesized from a monomer containing terephthalic acid. The depolymerization may be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions.

[0072] The weight ratio of the aromatic impurities, measured using liquid chromatography (LC), may be less than 100 μg, less than 50 μg, less than 10 μg, less than 1 μg, or 0 μg or more, or 0 μg or more but less than 100 μg, or 0 μg or more but less than 50 μg, or 0 μg or more but less than 10 μg, or 0 μg or more but less than 1 μg. This is thought to be because, as will be described later, a method for producing a monomer composition for synthesizing recycled plastics includes washing a depolymerization reaction product from which a diol component has been removed with a solvent at a temperature of 20°C to 100°C and dissolving the washed depolymerization reaction product in water and recrystallizing the resultant product, and the step of dissolving the washed depolymerization reaction product in water and recrystallizing the resultant product includes dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 300°C and cooling the dissolved solution to a temperature 50°C to 200°C lower than the solution temperature.

[0073] In the present invention, instead of terephthalic acid, which is the main target substance for synthesis, the weight ratio of aromatic impurities such as 4-carboxybenzaldehyde, benzoic acid, p-toluic acid, or a mixture of two or three of these is extremely reduced to less than 100 μg per 1 g of the monomer composition for synthesizing recycled plastics. Therefore, when polyethylene terephthalate or high-value-added plastics (PBT, TPEE) are synthesized using this, excellent physical properties can be achieved.

[0074] The liquid chromatography method for measuring the weight ratio of the organic impurities is not particularly limited. For example, 0.5 g of a recycled terephthalic acid monomer composition is collected as a sample under conditions of normal pressure and 20 to 30°C and analyzed using a liquid chromatography (LC) device. Based on 1 g of the sample, the weight ratios (μg / g) of 4-carboxybenzaldehyde (4-CBA), benzoic acid (BZA), and p-toluic acid (p-TA) contained therein are measured.

[0075] The monomer composition for synthesizing recycled plastics according to one embodiment may further contain small amounts of other additives and solvents. The specific types of additives and solvents are not particularly limited, and various substances widely used in the process of recovering terephthalic acid by depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid may be used without limitation.

[0076] The monomer composition for synthesizing recycled plastics according to one embodiment may be obtained by a method for producing a monomer composition for synthesizing recycled plastics, which will be described later. That is, the monomer composition for synthesizing recycled plastics according to one embodiment corresponds to a resultant product obtained by depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid, followed by various filtration, purification, washing, and drying processes to obtain only terephthalic acid, which is the main synthesis target substance of the present invention, in high purity.

[0077] The monomer composition for synthesizing recycled plastics according to one embodiment can be used as a raw material for producing monomers used in synthesizing various recycled plastics (e.g., polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene adipate terephthalate (PBAT), glycol-modified polyethylene terephthalate (PETG), and thermoplastic polyester elastomer (TPEE)) described below, or can be used as a raw material for producing other additives (e.g., dioctyl terephthalate plasticizer) used in processing plastics (e.g., polyvinyl chloride (PVC)).

[0078] 2. Method for producing monomer composition for synthesizing recycled plastics According to another embodiment of the present invention, there is provided a method for producing a monomer composition for synthesizing recycled plastics, the method comprising: depolymerizing a (co)polymer synthesized from a monomer including terephthalic acid to remove a diol component; washing the depolymerized reaction product from which the diol component has been removed with a solvent at a temperature of 20°C to 100°C; and dissolving the washed depolymerized reaction product in water and recrystallizing the resultant product, wherein the step of dissolving the washed depolymerized reaction product in water and recrystallizing the resultant product comprises dissolving the washed depolymerized reaction product in water at a temperature of 200°C to 300°C; and cooling the dissolved solution to a temperature 50°C to 200°C lower than the solution temperature.

[0079] The present inventors have confirmed through experiments that, in the process of recovering terephthalic acid from a (co)polymer synthesized from a monomer containing terephthalic acid, as in the method for producing a monomer composition for synthesizing recycled plastics according to the other embodiment, by applying a washing process and a recrystallization process divided by temperature ranges, not only is the ratio of isophthalic acid, which is another monomer, significantly reduced, but also the detected amounts of organic impurities (acetic acid, formic acid) and aromatic impurities (4-carboxybenzaldehyde, benzoic acid, p-toluic acid) significantly reduced, when this is used to synthesize polyethylene terephthalate or high-value-added plastics (PBT, TPEE), the polymerization time can be shortened, improving polymerization production efficiency, and excellent physical properties can be achieved in terms of color quality, thereby completing the invention.

[0080] In particular, terephthalic acid recovered from a (co)polymer synthesized from a monomer containing terephthalic acid obtained by a conventional method usually contains 1 to 2% of isophthalic acid as an impurity, whereas the present invention has made it possible to almost completely remove isophthalic acid and other impurities by a high-temperature recrystallization step that is a characteristic of the production method of a monomer composition for synthesizing recycled plastics, which will be described later.

[0081] This is because, in the step of dissolving the washed depolymerization reaction product in water and then recrystallizing it, the increased solubility of terephthalic acid allows isophthalic acid and other impurities attached to the crystals or between the crystals to be dissolved in the solvent as much as possible and removed. Since the dissolved terephthalic acid has lower solubility than the impurities, when the temperature is subsequently lowered, the terephthalic acid easily precipitates as crystals due to the difference in solubility.

[0082] In addition, by washing the depolymerization product from which the diol component has been removed with a solvent at a temperature of 20°C to 100°C, the acid component (HCl) and salt components remaining in the depolymerization product from which the diol component has been removed can be removed as much as possible, thereby suppressing corrosion of a reactor and increasing the yield and purity of terephthalic acid.

[0083] Specifically, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid and removing a diol component.

[0084] The (co)polymer synthesized from the monomer containing terephthalic acid can be applied regardless of various forms and types, such as a (co)polymer synthesized from a new monomer containing terephthalic acid produced by synthesis, a (co)polymer synthesized from a monomer containing recycled terephthalic acid produced by a recycling process, or a (co)polymer waste synthesized from a monomer containing terephthalic acid.

[0085] However, if necessary, a pretreatment step of the (co)polymer synthesized from a monomer containing terephthalic acid may be carried out before the depolymerization reaction of the (co)polymer synthesized from a monomer containing terephthalic acid, thereby increasing the efficiency of the step of recovering terephthalic acid from the (co)polymer synthesized from a monomer containing terephthalic acid. Examples of the pretreatment step include washing, drying, pulverization, and glycolysis. The specific method of each pretreatment step is not limited, and various methods widely used in the step of recovering terephthalic acid by depolymerization of the (co)polymer synthesized from a monomer containing terephthalic acid may be applied without limitation.

[0086] The depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid may be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions. More specifically, the depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid may be carried out in water, an alkylene glycol, or an alcohol solvent. A specific example of the alkylene glycol solvent is ethylene glycol, and a specific example of the alcohol solvent is ethanol.

[0087] The depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid can be carried out under basic conditions. The type of the base is not particularly limited, and an example thereof is sodium hydroxide (NaOH).

[0088] The depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid can be carried out by reacting a base in an amount of 2.3 mol or less, or 1 mol to 2.3 mol, or 1.5 mol to 2.3 mol, per mol of the (co)polymer synthesized from the monomer containing terephthalic acid.

[0089] During the depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid, if more than 2.3 moles of base are reacted with 1 mole of the (co)polymer synthesized from the monomer containing terephthalic acid, the solubility of isophthalic acid salts decreases and the amount of alkali salt generated increases, resulting in an increase in impurities such as isophthalic acid and sodium (Na) rather than terephthalic acid, the main synthetic target substance, which are difficult to remove sufficiently even by the washing process described below.

[0090] The temperature at which the depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid is carried out is not particularly limited, and can be, for example, from 25° C. to 200° C., or from 130° C. to 180° C. The time for which the depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid is carried out can be from 0 minute to 3 hours.

[0091] Meanwhile, the diol component can be removed after depolymerization of a (co)polymer synthesized from a monomer containing terephthalic acid. For example, the depolymerization product of polyethylene terephthalate (PET) contains ethylene glycol and terephthalic acid salt.

[0092] Since the main target substance for recovery in the present invention is terephthalic acid, other by-products can be removed by filtration. The filtered by-products can be recycled without separation and purification in the depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid, or can be recycled after separation and purification by conventional distillation, extraction, and adsorption methods as needed.

[0093] Furthermore, since the main target substance for recovery in the present invention is terephthalic acid, in the case of terephthalic acid salts, they can be converted to terephthalic acid by an additional neutralization step with a strong acid, which will be described later.

[0094] As a specific example, the (co)polymer synthesized from the monomer containing terephthalic acid is depolymerized, and the product is cooled to 50°C or less, and then ethylene glycol is removed by vacuum filtration to obtain a terephthalate salt.

[0095] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include washing the depolymerization reaction product from which the diol component has been removed with a solvent at a temperature of 20°C to 100°C.

[0096] As described above, the depolymerization reaction product from which the diol component has been removed may contain terephthalic acid obtained by removing ethylene glycol and neutralizing terephthalic acid salt. However, since various impurities remain during the recovery process of obtaining terephthalic acid, washing may be performed to sufficiently remove these impurities and obtain high-purity terephthalic acid.

[0097] Specifically, the cleaning step may include cleaning with a solvent at a temperature of 20°C to 100°C. The temperature condition refers to the temperature inside a cleaning vessel where cleaning with a solvent is performed, and various heating mechanisms may be used without limitation to maintain a high temperature above room temperature. This effectively minimizes corrosion of the reactor due to strong acid after the neutralization step.

[0098] The step of washing the depolymerization reaction product from which the diol component has been removed with a solvent at a temperature of 20° C. to 100° C. can be repeated at least one time. If necessary, after the step of washing the depolymerization reaction product from which the diol component has been removed with a solvent at a temperature of 20° C. to 100° C., a step of removing the remaining solvent by filtration can be further performed.

[0099] The solvent used in the washing step may be water. Washing using water without an organic solvent can improve environmental friendliness. Furthermore, using an organic solvent such as ethanol instead of water may result in ineffective removal of salt (NaCl), resulting in an increased amount of residual sodium (Na) in the composition.

[0100] The solvent used in the washing step may be used in a weight ratio of 1 to 50 parts by weight, or 5 to 10 parts by weight, based on 1 part by weight of the (co)polymer synthesized from the monomer containing terephthalic acid used in the depolymerization reaction.

[0101] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include dissolving the washed depolymerization reaction product in water and then recrystallizing the resultant.

[0102] As described above, various impurities remain in the recovery process for obtaining terephthalic acid, and recrystallization can be performed to sufficiently remove these impurities and ensure high-purity terephthalic acid.

[0103] Specifically, the recrystallization step may include dissolving the washed depolymerization reaction product in water and then recrystallizing the resultant. By dissolving the washed depolymerization reaction product in water and then recrystallizing the resultant, the solubility of terephthalic acid or a salt thereof contained in the depolymerization reaction product is increased, so that impurities such as isophthalic acid, organic impurities, and aromatic impurities present in the crystals or between the crystals can be dissolved in the solvent as much as possible. Since the dissolved terephthalic acid has poorer solubility than the impurities, when the temperature is subsequently lowered, terephthalic acid crystals can be easily precipitated due to the difference in solubility.

[0104] More specifically, the step of dissolving the washed depolymerization reaction product in water and then recrystallizing it may include the steps of dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 300°C, or 200°C to 250°C, or 205°C to 250°C, and cooling the dissolved solution to a temperature 50°C to 200°C lower than the solution temperature.

[0105] Although the high-temperature range and the cooling temperature range in which recrystallization is performed are relatively mild, the method has the advantage of being able to remove impurities at a high level and increase the recovery efficiency of terephthalic acid. The temperature condition refers to the temperature inside a vessel in which recrystallization using a solvent is performed, and various heating and cooling mechanisms for maintaining high and low temperatures outside room temperature can be applied without limitation.

[0106] Specific examples of dissolution, cooling conditions, apparatus, and method in the recrystallization step are not particularly limited, and various methods widely used in the conventional technical field of recrystallization of terephthalic acid may be applied without limitation.

[0107] In the step of dissolving the washed depolymerization product in water at a temperature of 200°C to 300°C, 1 to 60 parts by weight, or 10 to 50 parts by weight, of water can be used per part by weight of the (co)polymer synthesized from the monomer containing terephthalic acid. If less than 1 part by weight of water is used per part by weight of the (co)polymer synthesized from the monomer containing terephthalic acid, the temperature required to dissolve the terephthalic acid contained in the washed depolymerization product is too high, resulting in poor process efficiency and making it difficult to remove impurities by recrystallization. In contrast, if more than 60 parts by weight of water is used per part by weight of the (co)polymer synthesized from the monomer containing terephthalic acid, the solubility of the terephthalic acid contained in the washed depolymerization product is too high, resulting in a low yield of terephthalic acid recovered after recrystallization and a reduced process efficiency due to the use of a large amount of solvent.

[0108] More specifically, the step of dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 300°C may include dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 220°C, and the amount of water may be 30 parts by weight to 60 parts by weight based on 1 part by weight of the (co)polymer synthesized from monomers including terephthalic acid.

[0109] In addition, the step of dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 300°C may include dissolving the washed depolymerization reaction product in water at a temperature of 240°C to 300°C, and the amount of water may be 1 part by weight to 20 parts by weight, or 5 parts by weight to 20 parts by weight, relative to 1 part by weight of the (co)polymer synthesized from a monomer including terephthalic acid.

[0110] Meanwhile, the step of dissolving the washed depolymerization reaction product in water and then recrystallizing may include the steps of dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 300°C, and then cooling the dissolved solution to a temperature 50°C to 200°C lower than the solution temperature.

[0111] Due to the difference in solubility between terephthalic acid and impurities caused by the cooling, crystallized terephthalic acid can be obtained by filtration or the like, and the impurities can be removed in a state of being dissolved in the solvent.

[0112] The specific cooling conditions for the cooling step are not particularly limited, but for example, the dissolved solution can be cooled to a temperature 50° C. to 200° C. lower than the solution temperature. That is, the difference between the solution temperature and the cooling temperature (the solution temperature minus the cooling temperature) can be 50° C. to 200° C. Therefore, terephthalic acid dissolved in the high-temperature solution is precipitated and recovered due to the difference in solubility between the solution temperature and the cooling temperature.

[0113] The specific cooling conditions for the cooling step are not particularly limited, and may be, for example, cooling to a temperature of 100° C. or less, or 50° C. to 100° C., or 80° C. to 100° C. As for the specific drying apparatus and method used in the cooling step, various conventionally known cooling techniques may be applied without any limitation.

[0114] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a step of neutralizing the depolymerization reaction product from which the diol component has been removed with an acid before the step of washing the depolymerization reaction product from which the diol component has been removed.

[0115] For example, while the alkaline decomposition products of polyethylene terephthalate (PET) include ethylene glycol and terephthalic acid salts, the main target material for recovery in the present invention is terephthalic acid, and therefore, the terephthalic acid salts obtained by the alkaline decomposition can be converted to terephthalic acid by an additional neutralization step with a strong acid. That is, when the depolymerization reaction of a (co)polymer synthesized from a monomer containing terephthalic acid is alkaline decomposition, it can undergo a neutralization step with an acid.

[0116] The acid used in the neutralization reaction can be a strong acid, such as hydrochloric acid (HCl). The neutralization reaction using the strong acid can achieve a pH of 4 or less, or 2 or less, at the end of the neutralization reaction. The temperature during the neutralization reaction can be adjusted to 25°C or higher and 100°C or lower.

[0117] In addition, if necessary, after the neutralization step with an acid of the depolymerization reaction product from which the diol component has been removed, a step of removing remaining impurities by filtration may be further performed.

[0118] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a step of purifying the depolymerization reaction product from which the diol component has been removed, after the step of depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid and removing the diol component.

[0119] The refining can remove remaining impurities, and the specific refining conditions are not particularly limited. Regarding the specific refining apparatus and method, various refining techniques that have been publicly known can be applied without any restrictions.

[0120] For example, the purification step of the depolymerization reaction product from which the diol component has been removed may include a step of dissolving and filtering the depolymerization reaction product from which the diol component has been removed, and a step of adsorbing the depolymerization reaction product using an adsorbent.

[0121] In the step of dissolving and filtering the depolymerization product from which the diol component has been removed, water may be used as a solvent for dissolving the depolymerization product from which the diol component has been removed, and the dissolution temperature may be 25° C. to 100° C. This allows for the removal of a (co)polymer synthesized from a monomer containing residual terephthalic acid that has not reacted in the depolymerization reaction.

[0122] In the adsorption step using an adsorbent, activated carbon can be used as an example of the adsorbent.

[0123] If necessary, the depolymerization reaction product from which the diol component has been removed may be further purified through steps such as extraction, washing, precipitation, recrystallization, and drying, without limitation.

[0124] When the step of purifying the depolymerization reaction product from which the diol components have been removed is performed, the step of washing the depolymerization reaction product from which the diol components have been removed may be performed after the step of purifying the depolymerization reaction product from which the diol components have been removed.

[0125] Furthermore, when the depolymerization reaction is alkaline decomposition as described above, the step of purifying the depolymerization reaction product from which the diol components have been removed may be followed by a step of neutralizing the depolymerization reaction product from which the diol components have been removed with an acid, and then a step of washing the depolymerization reaction product from which the diol components have been removed.

[0126] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a drying step after washing the depolymerization reaction product from which the diol component has been removed. The drying may remove residual solvent, and the drying conditions are not particularly limited, but may be performed at a temperature of 100°C to 150°C. The drying apparatus and method used in the drying may be any of various conventionally known drying techniques.

[0127] 3. Recycled plastics According to yet another embodiment of the present invention, there is provided a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastics of the above embodiment and a comonomer. The content of the monomer composition for synthesizing recycled plastics includes all of the content described above in the above embodiment.

[0128] Examples of the recycled plastics are not particularly limited, and various plastics synthesized using terephthalic acid as a monomer can be applied without limitation. A more specific example is a (co)polymer synthesized from a monomer containing terephthalic acid.

[0129] The (co)polymer is synthesized from a monomer containing terephthalic acid, and the (co)polymer includes both polymers and copolymers, and is a general term for reaction products obtained by the (co)polymerization reaction of monomers. The (co)polymer may include low molecular weight compounds, oligomers, and polymers depending on the molecular weight range.

[0130] The (co)polymer synthesized from the monomer containing terephthalic acid can include one or more (co)polymers selected from the group consisting of polyalkylene terephthalate, polyalkylene terephthalate copolymer, and thermoplastic polyester elastomer. That is, the (co)polymer synthesized from the monomer containing terephthalic acid can include one type of polyalkylene terephthalate, one type of polyalkylene terephthalate copolymer, one type of thermoplastic polyester elastomer, or a mixture of two or more types thereof.

[0131] The polyalkylene terephthalate copolymer refers to a copolymer obtained by further reacting an additional comonomer based on alkylene glycol and terephthalic acid, which are monomers for synthesizing polyalkylene terephthalate.

[0132] The comonomer capable of reacting with the high-purity terephthalic acid contained in the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and specific examples thereof include an aliphatic diol, a polyalkylene oxide, a fatty acid, a fatty acid derivative, or a combination thereof.

[0133] The aliphatic diol may be, for example, one or more of diols having a number average molecular weight (Mn) of 300 g / mol or less, i.e., ethylene glycol, propylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol (1,4-BG), 1,5-pentanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethanol (1,4-CHDM). Specific examples include 1,4-butanediol, ethylene glycol, 1,4-cyclohexanedimethanol, or a mixture thereof.

[0134] The polyalkylene oxide is a unit constituting a soft segment and may be an aliphatic polyether. Examples of the polyalkylene oxide include one or more of polyoxyethylene glycol, polypropylene glycol, poly(tetramethylene ether) glycol (PTMEG), polyoxyhexamethylene glycol, a copolymer of ethylene oxide and propylene oxide, an ethylene oxide addition polymer of polypropylene oxide glycol, and a copolymer of ethylene oxide and tetrahydrofuran. A specific example is PTMEG, and in particular, PTMEG having a number average molecular weight (Mn) of 600 g / mol to 3,000 g / mol, 1,000 g / mol to 2,500 g / mol, or 1,500 g / mol to 2,200 g / mol may be used.

[0135] The fatty acid may be, for example, one or more aliphatic carboxylic acid compounds excluding terephthalic acid, and a specific example may be adipic acid. The fatty acid derivative is a compound derived from the above-mentioned fatty acid, and for example, may be one or more of fatty acid esters, fatty acid chlorides, fatty acid anhydrides, and fatty acid amides, and a specific example may be adipic acid esters.

[0136] To explain this by citing a specific example, when 1,4-butanediol, an aliphatic diol, is used as a comonomer that can react with the high-purity terephthalic acid contained in the monomer composition for synthesizing recycled plastics according to one embodiment, polybutylene terephthalate (PBT), a type of polyalkylene terephthalate, can be obtained by a polymerization reaction between terephthalic acid and 1,4-butanediol.

[0137] In addition, when ethylene glycol, which is an aliphatic diol, is used as a comonomer that can react with the high-purity terephthalic acid contained in the monomer composition for synthesizing recycled plastics according to one embodiment, polyethylene terephthalate (PET), which is a type of polyalkylene terephthalate, can be obtained by a polymerization reaction between terephthalic acid and ethylene glycol.

[0138] In addition, when the aliphatic diol 1,4-butanediol and the polyalkylene oxide PTMEG are used together as comonomers that can react with the high-purity terephthalic acid contained in the monomer composition for synthesizing recycled plastics according to one embodiment, a thermoplastic polyester elastomer (TPEE) can be obtained by a polymerization reaction of terephthalic acid, 1,4-butanediol, and PTMEG.

[0139] In addition, when the aliphatic diol 1,4-butanediol and the fatty acid adipic acid are used together as comonomers that can react with the high-purity terephthalic acid contained in the monomer composition for synthesizing recycled plastics according to one embodiment, polybutylene adipate terephthalate (PBAT), a type of polyalkylene terephthalate copolymer, can be obtained by a polymerization reaction of terephthalic acid, 1,4-butanediol, and adipic acid.

[0140] In addition, when the aliphatic diols ethylene glycol and 1,4-cyclohexanedimethanol are used together as comonomers that can react with the high-purity terephthalic acid contained in the monomer composition for synthesizing recycled plastics according to one embodiment, a glycol-modified polyethylene terephthalate (PETG), which is a type of polyalkylene terephthalate copolymer, can be obtained by a polymerization reaction of terephthalic acid, ethylene glycol, and 1,4-cyclohexanedimethanol.

[0141] As a specific example, the polyalkylene terephthalate may include one or more (co)polymers selected from polybutylene terephthalate, polyethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polytrimethylene terephthalate.

[0142] As a specific example, the polyalkylene terephthalate copolymer may include one or more (co)polymers selected from polybutylene adipate terephthalate (PBAT) and glycol-modified polyethylene terephthalate (PETG).

[0143] The method for reacting the monomer composition for synthesizing recycled plastics and the comonomer is not particularly limited, and various conventionally known methods can be applied without limitation. However, specific examples of the reaction of the monomer composition for synthesizing recycled plastics and the comonomer include melt condensation polymerization and solid-state polymerization.

[0144] For example, to produce thermoplastic polyester elastomer (TPEE) from recycled plastics, aromatic dicarboxylic acids, aliphatic diols, and polyalkylene oxides are esterified in the presence of a titanium butoxide (TBT) catalyst at 180°C to 250°C for 30 to 210 minutes to produce bis(4-hydroxybutyl terephthalate) oligomers. The TBT catalyst is then reintroduced into the reactor and melt polycondensation is carried out at 200°C to 270°C for 20 to 240 minutes while gradually reducing the pressure from 760 torr to 0.3 torr. After the melt polycondensation reaction is complete, the mixture is discharged from the reactor under nitrogen pressure and pelletized into strands.

[0145] The pellets can then be subjected to solid-state polymerization in a solid-state polymerization reactor or a rotary vacuum dryer at a temperature ranging from 140°C to 200°C for 10 hours to 24 hours under high vacuum and in an inert gas stream such as nitrogen.

[0146] In addition, when producing polyalkylene terephthalate from the recycled plastic, it may be produced by melt-polymerizing an aromatic dicarboxylic acid and an aliphatic diol having a number average molecular weight (Mn) of 300 g / mol or less, followed by solid-state polymerization.

[0147] As a specific example, the polyalkylene terephthalate may be one or more selected from polybutylene terephthalate, polyethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and polytrimethylene terephthalate.

[0148] The polyalkylene terephthalate resin can be obtained by placing low molecular weight pellets obtained by melt polymerization into a solid-state polymerization reactor and reacting them under high vacuum and inert conditions, as described above in the solid-state polymerization of thermoplastic polyester elastomer (TPEE), to obtain a high molecular weight resin.

[0149] The specific method for producing polybutylene terephthalate, polyethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, or polybutylene adipate terephthalate by reacting the monomer composition for synthesizing recycled plastics and the comonomer is not particularly limited, and various processes widely known in the field of conventional recycled plastic synthesis can be applied without limitation.

[0150] The recycled plastic may have a yellowness index of 50 or less, or 5 or less, or 0.5 or more, or 0.5 to 50, or 0.5 to 5.

[0151] If the yellowness index of the recycled plastic is excessively increased to more than 50, the recycled plastic will yellow and have poor color properties. The method for measuring the yellowness index of the recycled plastic is not particularly limited, and various methods for measuring color properties in the plastic field can be applied without limitation.

[0152] However, one example of a method for measuring the yellowness index of the recycled plastics is to use a HunterLab UltraScan PRO Spectrophotometer instrument in reflectance mode.

[0153] The recycled plastic may have a color coordinate b* value of 3 or less, or 2 or less, or 1 or less, or 0.1 or more, or 0.5 or more, or 0.9 or more, or 0.1 to 3, or 0.1 to 2, or 0.1 to 1, or 0.5 to 3, or 0.5 to 2, or 0.5 to 1, or 0.9 to 3, or 0.9 to 2, or 0.9 to 1.

[0154] The recycled plastic may have a color coordinate L* value of 84.5 or more, or 85 or more, or 86 or less, or 84.5-86, or 85-86.

[0155] The recycled plastic may have a color coordinate a* value of −0.3 or less, or −0.4 or less, or −0.5 or less, or −0.6 or less, or −1 or more, or −1 to −0.3, or −1 to −0.4, or −1 to −0.5, or −1 to −0.6.

[0156] If the color coordinate b* value of the recycled plastic is excessively increased to more than 3, the recycled plastic will yellow and have poor color properties. The method for measuring the color coordinates L*, a*, and b* values ​​of the recycled plastic is not particularly limited, and various color property measurement methods in the plastics field can be applied without limitation.

[0157] However, as an example of a method for measuring the color coordinates L*, a*, and b* of the recycled plastic, measurements can be made in reflection mode using a HunterLab UltraScan PRO Spectrophotometer device.

[0158] The recycled plastic may have a melt fluidity index of 5 g / 10 min to 30 g / 10 min, or 15 g / 10 min to 25 g / 10 min, as measured by ASTM D 1238. If the melt fluidity index of the recycled plastic exceeds 30 g / 10 min, the recycled plastic becomes difficult to mold.

[0159] However, an example of a method for measuring the melt fluidity index of the recycled plastic can be measured at 230° C. to 250° C. under a load of 2.16 kg for 4 minutes in accordance with ASTM D1238.

[0160] More specifically, for example, in the case of thermoplastic polyester elastomer (TPEE), it can be measured at 230°C under a load of 2.16 kg for 4 minutes according to ASTM D1238, and in the case of polyalkylene terephthalate, it can be measured at 250°C under a load of 2.16 kg for 4 minutes according to ASTM D1238.

[0161] 4. Molded products According to yet another embodiment of the present invention, there is provided a molded product containing the recycled plastic of the other embodiment. The content relating to the recycled plastic includes all of the content described above in the other embodiment.

[0162] The molded product may be obtained by applying the recycled plastic to various known plastic molding methods without limitation, and examples of the molding methods include injection molding, foam injection molding, blow molding, and extrusion molding.

[0163] The molded article is not particularly limited, and can be applied to various molded articles using plastics without limitation, such as automobiles, electrical and electronic products, communication products, and household goods.

[0164] 5. Plasticizer composition According to yet another embodiment of the present invention, there is provided a plasticizer composition including the reaction product of the monomer composition for synthesizing recycled plastics of the above embodiment and an alcohol. The content of the monomer composition for synthesizing recycled plastics includes all of the content described above in the above embodiment.

[0165] Generally, plasticizers are made by adding various additives such as fillers, stabilizers, pigments, and anti-fogging agents to resins such as polyvinyl chloride (PVC) to impart various processing properties, and are then used as materials for a variety of products, including electrical wires, pipes, flooring, wallpaper, sheets, artificial leather, tarpaulins, tapes, and food packaging materials, through processing methods such as extrusion molding, injection molding, and calendaring.

[0166] Typically, plasticizers are prepared by reacting alcohol with polycarboxylic acids such as phthalic acid and adipic acid to form the corresponding esters. In addition, in light of domestic and international regulations on phthalate-based plasticizers, which are harmful to the human body, research is ongoing into plasticizer compositions that can replace phthalate-based plasticizers, such as terephthalate-based, trimellitate-based, and other polymer-based plasticizers.

[0167] The reaction product of the monomer composition for synthesizing recycled plastics and the alcohol according to the embodiment may include a terephthalate-based compound. Specifically, the terephthalate-based compound may be obtained by a direct esterification reaction between terephthalic acid contained in the monomer composition for synthesizing recycled plastics and the alcohol.

[0168] The direct esterification reaction is prepared by adding terephthalic acid to alcohol, adding a catalyst, and reacting under a nitrogen atmosphere; removing unreacted alcohol and neutralizing unreacted acid; and dehydrating and filtering the resulting mixture by distillation under reduced pressure.

[0169] Examples of the terephthalate-based compound are not particularly limited, but include dioctyl terephthalate (DOTP), diisononyl terephthalate (DINTP), diisodecyl terephthalate (DIDTP), and di(2-propylheptyl) terephthalate (DPHTP).

[0170] The terephthalate-based compound can be prepared by a direct esterification reaction in which terephthalic acid reacts with any one alcohol selected from the group consisting of octanol, isononyl alcohol, isodecyl alcohol, and 2-propylheptyl alcohol.

[0171] The plasticizer composition can be applied to the production of electric wires, flooring materials, automobile interior materials, films, sheets, wallpapers, or tubes. [Effects of the Invention]

[0172] According to the present invention, it is possible to provide a monomer composition for synthesizing recycled plastics, which can ensure high-purity terephthalic acid with a low water content and a significantly reduced content of organic impurities when terephthalic acid is recovered by depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid; a method for producing the same; and recycled plastics, molded articles, and plasticizer compositions using the same. DETAILED DESCRIPTION OF THE INVENTION

[0173] The present invention will be described in more detail below with reference to examples. However, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0174] <Example> Example 1 (1) Production of recycled terephthalic acid monomer composition 192g (1 mol) of polyethylene terephthalate (PET) bottle scraps, 1250g (approximately 20 mol) of ethylene glycol (EG), and 82g (2.05 mol) of sodium hydroxide (NaOH) were placed in a 3L stainless steel reactor and stirred in a closed system at 180°C for 2 hours to carry out the PET depolymerization reaction. The product of the depolymerization reaction was cooled to 20-30°C and then vacuum filtered to obtain sodium terephthalate (Na2-TPA).

[0175] The filtrate containing sodium terephthalate (Na2-TPA) was completely dissolved in water and then vacuum filtered again to remove unreacted PET and other solid impurities. The filtrate was then purified by activated carbon adsorption, neutralized with 6M HCl at 20-30°C, and the slurry was reduced to pH 2 or less. The slurry was vacuum filtered again to obtain terephthalic acid (TPA).

[0176] In order to remove NaCl generated during the neutralization process, the PET was washed with 1920 g of water, which is 10 times the mass of the PET used, at 20 to 30°C, and then filtered under vacuum.

[0177] Then, 9600 g of water, which is 50 times the mass of the PET used, was added and heated to 205°C until it was completely dissolved. The TPA aqueous solution was then cooled to 100°C or less and atmospheric pressure to recrystallize the terephthalic acid, and the resulting slurry was vacuum filtered at 20-30°C to recover terephthalic acid (TPA) crystals.

[0178] Thereafter, the mixture was dried in a convection oven at 120°C to produce a recycled terephthalic acid monomer composition from which recycled terephthalic acid (TPA) was recovered.

[0179] (2) Manufacturing recycled plastics 200 g of the recycled terephthalic acid monomer composition obtained in Example 1(1), 200 g of 1,4-butylene glycol, and 125 g of poly(tetramethylene ether) glycol (PTMEG) with a number average molecular weight of 1,000 to 2,000 g / mol were placed in an ester interchange reactor, and 0.1 wt% of TBT catalyst was added. The reaction was carried out for 120 to 180 minutes while maintaining the temperature at 200 to 240°C. The reaction was terminated when the reaction rate (the amount of water effluent from the reaction converted into the reaction rate) reached 90% or more, yielding an oligomer.

[0180] The resulting oligomer was then transferred to a polycondensation reactor and added with 0.1 wt% TBT catalyst, 0.14-0.15 wt% hindered phenol antioxidant, and 0.15-0.2 wt% aromatic amine antioxidant or sulfur stabilizer. The temperature was maintained at 230-250°C, and the pressure was reduced from 760 torr to 0.3 torr for 30 minutes. The melt polycondensation reaction was then continued under high vacuum conditions of 0.3 torr or less until the desired torque was reached. The reaction was terminated and discharged under nitrogen pressure to form strands, which were then cooled and pelletized to produce thermoplastic polyester elastomer (TPEE) resin.

[0181] Example 2 (1) Production of recycled terephthalic acid monomer composition 192g (1 mol) of polyethylene terephthalate (PET) bottle scraps, 1600g of water, and 82g (2.05 mol) of sodium hydroxide (NaOH) were placed in a 3L stainless steel reactor and stirred in a closed system at 180°C for 2 hours to carry out the PET depolymerization reaction. The depolymerization product was cooled to 50°C and then vacuum filtered to remove unreacted PET and other solid impurities.

[0182] The filtrate was then purified by activated carbon adsorption, neutralized with 6M HCl at 20-30° C., and the slurry, whose pH was reduced to 2 or less, was again vacuum filtered to obtain terephthalic acid (TPA).

[0183] In order to remove NaCl generated during the neutralization process, the PET was washed with 1920 g of water, which is 10 times the mass of the PET used, at 20 to 30°C, and then filtered under vacuum.

[0184] Then, 1920 g of water, which is 10 times the mass of the PET used, was added and heated to 250°C until it was completely dissolved. The TPA aqueous solution was then cooled to 100°C or less and atmospheric pressure to recrystallize the terephthalic acid, and the resulting slurry was vacuum filtered at 20-30°C to recover terephthalic acid (TPA) crystals.

[0185] Thereafter, the mixture was dried in a convection oven at 120°C to produce a recycled terephthalic acid monomer composition from which recycled terephthalic acid (TPA) was recovered.

[0186] (2) Manufacturing recycled plastics A thermoplastic polyester elastomer (TPEE) resin was prepared in the same manner as in Example 1-2, except that the recycled terephthalic acid monomer composition obtained in Example 2-1 was used instead of the recycled terephthalic acid monomer composition obtained in Example 1-1.

[0187] Example 3 (1) Production of recycled terephthalic acid monomer composition A recycled terephthalic acid monomer composition was produced in the same manner as in Example 1 (1).

[0188] (2) Manufacturing recycled plastics 300 g of the recycled terephthalic acid monomer composition obtained in Example 1(1) and 300 g of 1,4-butylene glycol were placed in an esterification reactor and 0.1 wt% of TBT catalyst was added. The reaction was carried out for 120 to 180 minutes while maintaining the temperature at 200 to 240°C. The reaction was terminated when the reaction rate (the amount of water effluent from the reaction was converted into the reaction rate) reached 90% or more, thereby obtaining an oligomer.

[0189] The oligomer was then transferred to a polycondensation reactor and maintained at 230-260°C. The melt polycondensation reaction was carried out under high vacuum conditions of 0.3 torr or less, while the pressure was reduced from 760 torr to 0.3 torr for 30 minutes. The torque applied to the stirrer was then increased to the desired value. After the reaction was terminated, the mixture was discharged under nitrogen pressure to form strands, which were then cooled and pelletized to produce polybutylene terephthalate (PBT) resin.

[0190] <Comparative Example> Comparative Example 1 As shown in Table 1 below, a recycled terephthalic acid monomer composition and a recycled plastic were prepared in the same manner as in Example 1, except that the recrystallization step (1) in Example 1 was not performed and secondary washing was performed at a temperature of 20 to 30°C using 3840 g of water, which is 20 times the mass of the used PET.

[0191] <Reference example> Reference example 1 A plastic was produced in the same manner as in Example 1, except that a TPA reagent (manufacturer: TCI) that has been commercially available was used instead of the recycled terephthalic acid monomer composition.

[0192] <Experimental Example 1> The properties of the recycled terephthalic acid monomer compositions obtained in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1.

[0193] 1. Terephthalic acid (TPA) and isophthalic acid (IPA) content 5 to 20 mg of the recycled terephthalic acid monomer composition was collected as a sample under normal pressure and 20 to 30°C conditions, dissolved in 1 ml of DMSO-d6 solvent, and then analyzed using an Agilent DD1 500 MHz NMR device. 1 H NMR spectra were obtained. Using analytical software (MestReC), peaks for all detected substances, including terephthalic acid (TPA) and isophthalic acid (IPA), were individually assigned and integrated. The molar ratio (mol%) of terephthalic acid and isophthalic acid contained within 100 mol% of the total monomer compounds analyzed from the sample was calculated based on the peak integration value.

[0194] 2. Formic acid (FA) and acetic acid (AA) content 0.5 g of the recycled terephthalic acid monomer composition was collected as a sample under normal pressure and 20 to 30°C conditions and analyzed using a Headspace-GC / MS (oven temperature: 150°C) device to measure the weight ratio (μg / g) of formic acid (FA) and acetic acid (AA) contained therein based on 1 g of the sample.

[0195] 3. Contents of 4-carboxybenzaldehyde (4-CBA), benzoic acid (BZA), and p-toluic acid (p-TA) A 0.5 g sample of the recycled terephthalic acid monomer composition was analyzed using liquid chromatography (LC) at atmospheric pressure and 20-30°C to measure the weight ratios (μg / g) of 4-carboxybenzaldehyde (4-CBA), benzoic acid (BZA), and p-toluic acid (p-TA) contained in the sample based on 1 g of the sample. The analytical limits (lower limits) for each substance using LC were 20 μg / g for 4-CBA, 80 μg / g for BZA, and 100 μg / g for p-TA. Values ​​below the analytical limits and not detected were reported as ND (Not detected).

[0196] [Table 1]

[0197] As shown in Table 1, 100 mol % of the monomers contained in the recycled terephthalic acid monomer composition obtained in Example 1 was terephthalic acid, and 99.6 mol % of the monomers contained in the recycled terephthalic acid monomer composition obtained in Example 2 was terephthalic acid, and a considerable amount of isophthalic acid, an impurity, was removed. On the other hand, the recycled terephthalic acid monomer composition obtained in Comparative Example 1 contained 0.9 mol % of the monomers contained in the recycled terephthalic acid monomer composition, which was excessive compared to the examples, and it was confirmed that the purification efficiency of terephthalic acid was significantly reduced.

[0198] On the other hand, other impurities, formic acid (FA) 4.0 μg / g to 4.3 μg / g and acetic acid (AA) 0.5 μg / g to 0.6 μg / g, were detected in the recycled terephthalic acid monomer compositions obtained in Examples 1 and 2, but 4-carboxybenzaldehyde (4-CBA), benzoic acid (BZA), and p-toluic acid (p-TA) were not detected, indicating excellent purification efficiency against impurities.

[0199] On the other hand, other impurities such as formic acid (FA) and acetic acid (AA) were detected in the recycled terephthalic acid monomer composition obtained in Comparative Example 1 at 13.5 μg / g and 2.0 μg / g, respectively, which were excessive compared to the Examples, confirming that the purification efficiency for impurities was poor.

[0200] Furthermore, in the TPA reagent (manufacturer: TCI) in Reference Example 1, which has been commercially available, other impurities such as acetic acid (AA) at 299.6 μg / g, 4-carboxybenzaldehyde (4-CBA) at 153 μg / g, and p-toluic acid (p-TA) at 136 μg / g were detected in excess compared to the Examples, confirming that the purification efficiency for impurities was poor.

[0201] <Experimental Example 2> The physical properties of the recycled plastics obtained in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2.

[0202] 1. Polymerization time In producing the thermoplastic polyester elastomers (TPEEs) obtained in the above examples and comparative examples, the oligomer was transferred to a polycondensation reactor, and the time required from the start of pressure reduction to the target torque was measured and evaluated as the polymerization time.

[0203] 2.Melt Flow Index (MFI) The melt fluidity index of the thermoplastic polyester elastomers (TPEE) obtained in the above examples and comparative examples was measured in accordance with ASTM D1238 at 230° C. under a load of 2.16 kg for 4 minutes.

[0204] 3. Yellow index (YI), color coordinates (L*, a*, b*) Injection test specimens (1.5T) were prepared from the thermoplastic polyester elastomers (TPEE) obtained in the examples and comparative examples, and the test specimens were analyzed in reflection mode using a HunterLab UltraScan PRO Spectrophotometer.

[0205] [Table 2]

[0206] As shown in Table 2, the TPEE (co)polymers synthesized from the recycled terephthalic acid monomer compositions obtained in Examples 1 and 2 had a short polymerization time of 122 to 127 minutes, a melt fluidity index of 23 to 24 g / 10 min, a yellowness index (YI) of 1.1 to 3.0, color coordinates L* of 85.0, a* of -0.6, and b* of 0.9 to 1.7, showing excellent color quality.

[0207] On the other hand, in the case of the TPEE (co)polymer synthesized from the recycled terephthalic acid monomer composition obtained in Comparative Example 1, the polymerization time was 183 minutes, which was longer than that of the Examples, and the color quality was poor, with a yellowness index (YI) of 8.7, color coordinates L* of 83.5, a* of 0, and b* of 4.8.

[0208] In addition, in the case of the TPEE (co)polymer synthesized from the TPA reagent (manufacturer: TCI) that has been commercially available in Reference Example 1, the polymerization time was 129 minutes, which was longer than that of the Examples, and the color quality was poor, with a yellowness index (YI) of 6.2, color coordinates L* of 85, a* of 0, and b* of 3.4.

Claims

1. A method for producing a monomer composition for synthesizing recycled plastics, comprising: The monomer composition for synthesizing recycled plastics is a monomer composition for synthesizing recycled plastics containing terephthalic acid, further containing one or more organic impurities selected from the group consisting of formic acid and acetic acid, and the weight ratio of the organic impurities measured using gas chromatography mass spectrometry is 0.5 μg / g or more and less than 5 μg / g per 1 g of the monomer composition for synthesizing recycled plastics, and the monomer composition for synthesizing recycled plastics is recovered from a (co)polymer synthesized from a monomer containing terephthalic acid, a step of depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid to remove a diol component; washing the depolymerization reaction product from which the diol component has been removed with a solvent at a temperature of 20°C to 100°C; and dissolving the washed depolymerization reaction product in water and then recrystallizing the resultant product. The step of dissolving the washed depolymerization reaction product in water and then recrystallizing the same comprises: dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 250°C; and cooling the dissolved solution to a temperature 50°C to 200°C lower than the solution temperature; dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 250°C; A method for producing a monomer composition for synthesizing recycled plastics, which uses 10 to 50 parts by weight of water per part by weight of a (co)polymer synthesized from a monomer containing terephthalic acid.

2. 2. The method of claim 1, wherein the solvent used in the step of washing the depolymerization reaction product from which the diol component has been removed with a solvent at a temperature of 20°C to 100°C is water.

3. washing the depolymerization reaction product from which the diol component has been removed with a solvent at a temperature of 20°C to 100°C; 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein 1 to 50 parts by weight of a solvent is used per 1 part by weight of a (co)polymer synthesized from a monomer containing terephthalic acid.

4. The step of dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 250°C includes: dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 220°C; 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the amount of water is 30 parts by weight to 60 parts by weight per part by weight of the (co)polymer synthesized from the monomer containing terephthalic acid.

5. The step of dissolving the washed depolymerization reaction product in water at a temperature of 200°C to 250°C includes: dissolving the washed depolymerization reaction product in water at a temperature of 240°C to 250°C; 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the amount of water is 1 part by weight to 20 parts by weight per 1 part by weight of the (co)polymer synthesized from the monomer containing terephthalic acid.

6. The depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid is 2. A method for producing a monomer composition for synthesizing recycled plastics according to claim 1, characterized in that the base is reacted in an amount of 2.3 moles or less per mole of the (co)polymer synthesized from the monomer containing terephthalic acid.

7. The depolymerization reaction of the (co)polymer synthesized from the monomer containing terephthalic acid is 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the method is carried out in the presence of water or an alkylene glycol solvent.

8. Before the step of washing the depolymerization reaction product from which the diol component has been removed, 2. The method of claim 1, further comprising neutralizing the depolymerized reaction product from which the diol component has been removed with an acid.

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