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

Abstract

The present invention relates to a monomer composition for synthesizing recycled plastics, which contains an aromatic diol compound, has a ratio of 0.3% or less of an impurity derived from the aromatic diol compound represented by Formula 1, has a melting point of 156.4°C or higher, and is recovered from a polycarbonate resin; a method for producing the same; and recycled plastics and molded articles 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. 10-2023-0098842, filed on July 28, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a monomer composition for synthesizing recycled plastics, which can achieve high purity and excellent color quality despite being recovered by recycling polycarbonate-based resins through chemical decomposition, and which improves the efficiency of the recovery process; a method for producing the same; and recycled plastics and molded articles using the same. [Background technology]

[0003] Polycarbonate is a thermoplastic polymer, a plastic with excellent properties such as excellent transparency, ductility, and relatively low manufacturing costs.

[0004] Polycarbonate is widely used for a variety of purposes, but concerns about the environmental and health impacts of its disposal have been raised.

[0005] Currently, physical recycling methods are being used, but this has led to problems with quality degradation, and research is underway into chemical recycling of polycarbonate.

[0006] Chemical decomposition of polycarbonate refers to the process of decomposing polycarbonate to obtain a monomer, an aromatic diol compound (e.g., bisphenol A (BPA)), which is then used again in polymerization to obtain high-purity polycarbonate.

[0007] On the other hand, in order to purify aromatic diol compounds obtained by decomposition of polycarbonate and ensure high purity, a process of redissolving the compound in an organic solvent such as toluene and recrystallizing it has been conventionally carried out. However, this method has limitations in that it requires many types of solvents and requires careful management due to the toxicity of the solvents. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a monomer composition for synthesizing recycled plastics, which can achieve high purity and excellent color quality despite being recovered by recycling polycarbonate-based resins through chemical decomposition, and which improves the efficiency of the recovery process.

[0009] The present invention also provides a method for producing the monomer composition for synthesizing recycled plastics, and recycled plastics and molded articles using the monomer composition for synthesizing recycled plastics. [Means for solving the problem]

[0010] In order to solve the above problems, the present specification provides a monomer composition for synthesizing recycled plastics, which contains an aromatic diol compound, has a ratio of 0.3% or less of an aromatic diol compound derivative impurity represented by the following formula 1, has a melting point of 156.4°C or more, and is recovered from a polycarbonate-based resin.

[0011] [Formula 1] Ratio (%) of aromatic diol compound derivative impurities = (peak area of ​​aromatic diol compound derivatives measured by liquid chromatography / total peak area measured by liquid chromatography) x 100.

[0012] The present specification also provides a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate-based resin; separating a carbonate-based compound from the depolymerization product; dissolving the depolymerization product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound; and recrystallizing an aromatic diol compound from the dissolved solution.

[0013] The present specification also provides a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate-based resin; dissolving the depolymerized product in a solvent containing a carbonate-based compound; and recrystallizing an aromatic diol compound from the resulting solution.

[0014] Also provided herein is a recycled plastic comprising the reaction product of the monomer composition for synthesizing recycled plastic and a comonomer.

[0015] Also provided herein is a molded article comprising the recycled plastic.

[0016] Hereinafter, a monomer composition for synthesizing recycled plastics according to specific embodiments of the present invention, a method for producing the same, recycled plastics using the same, and molded articles will be described in more detail.

[0017] In this specification, unless expressly stated otherwise, terminology is for the purpose of referring to particular embodiments only and is not intended to limit the invention.

[0018] As used herein, the singular forms "a," "an," and "the" include the plural forms as well, unless the context clearly dictates to the contrary.

[0019] As used herein, "pH" refers to hydrogen ion concentration (pH), a numerical value that indicates the degree of acidity or alkalinity of a substance. It can be calculated by taking the reciprocal logarithm of the dissociated hydrogen ion concentration and is used as a measure of the acidity or base strength of a substance.

[0020] In this specification, a derivative compound means a compound that has been modified from a certain organic compound by introducing a functional group, oxidation, reduction, atomic substitution, etc., within the limits that do not significantly change the structure and properties of the parent compound.

[0021] As used herein, the term "substituted or unsubstituted" means substituted or unsubstituted with one or more substituents selected from the group consisting of deuterium; halogen groups; cyano groups; nitro groups; hydroxy groups; carbonyl groups; ester groups; imide groups; amide groups; primary amino groups; carboxy groups; sulfonic acid groups; sulfonamide groups; phosphine oxide groups; alkoxy groups; aryloxy groups; alkylthioxy groups; arylthioxy groups; alkylsulfoxy groups; arylsulfoxy groups; silyl groups; boron groups; alkyl groups; cycloalkyl groups; alkenyl groups; aryl groups; aralkyl groups; aralkenyl groups; alkylaryl groups; alkoxysilylalkyl groups; arylphosphine groups; or heterocyclic groups containing one or more N, O, and S atoms, or substituted or unsubstituted by combining two or more of the above-mentioned exemplary substituents.

[0022] In this specification, an alkyl group is a monovalent functional group derived from an alkane, and may be linear or branched, and the number of carbon atoms in the linear alkyl group is not particularly limited, but is preferably 1 to 20. Furthermore, the number of carbon atoms in the branched alkyl group is 3 to 20. Exemplary alkyl groups include, but are not limited to, methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methylbutyl, 1-ethylbutyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, n-heptyl, 1-methylhexyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethylpropyl, 1,1-dimethylpropyl, isohexyl, 4-methylhexyl, 5-methylhexyl, 2,6-dimethylheptan-4-yl, and the like. The alkyl group may be substituted or unsubstituted, and when substituted, examples of the substituent are as described above.

[0023] In this specification, a cycloalkyl group is a monovalent functional group derived from a cycloalkane, and may be monocyclic or polycyclic. It has 3 to 20 carbon atoms, but is not particularly limited thereto. According to another embodiment, the cycloalkyl group has 3 to 10 carbon atoms. Specific examples include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, 3-methylcyclopentyl, 2,3-dimethylcyclopentyl, cyclohexyl, 3-methylcyclohexyl, 4-methylcyclohexyl, 2,3-dimethylcyclohexyl, 3,4,5-trimethylcyclohexyl, 4-tert-butylcyclohexyl, cycloheptyl, cyclooctyl, and bicyclo[2,2,1]heptyl. The cycloalkyl group may be substituted or unsubstituted. If substituted, examples of the substituent are as described above.

[0024] In this specification, the aryl group is a monovalent functional group derived from arene, and is not particularly limited. It preferably has 6 to 20 carbon atoms and may be a monocyclic aryl group or a polycyclic aryl group. The monocyclic aryl group may be, but is not limited to, a phenyl group, a biphenyl group, a terphenyl group, etc. The polycyclic aryl group may be, but is not limited to, a naphthyl group, an anthracenyl group, a phenanthryl group, a pyrenyl group, a perylenyl group, a chrysenyl group, a fluorenyl group, etc. The aryl group may be substituted or unsubstituted, and if substituted, examples of the substituent are as described above.

[0025] In this specification, a heteroaryl group includes one or more non-carbon atoms, i.e., heteroatoms, and specifically, the heteroatoms may include one or more atoms selected from the group consisting of O, N, Se, S, etc. The number of carbon atoms is not particularly limited, but is preferably 4 to 20, and the heteroaryl group may be monocyclic or polycyclic. Examples of the heterocyclic group include a thiophene group, a furanyl group, a pyrrole group, an imidazolyl group, a thiazolyl group, an oxazolyl group, an oxadiazolyl group, a pyridyl group, a bipyridyl group, a pyrimidyl group, a triazinyl group, a triazolyl group, an acridyl group, a pyridazinyl group, a pyrazinyl group, a quinolinyl group, a quinazolinyl group, a quinoxalinyl group, a phthalazinyl group, a pyridopyrimidyl group, a pyridopyrazinyl group, a pyrazinopyrazinyl group, an isoquinolinyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a benzimidazolyl group, a benzothiazolyl group, a benzocarbazolyl group, a benzothiophene group, and a dibenzothiophene group. Examples of heteroaryl groups include, but are not limited to, benzofuranyl, phenanthrolinyl, thiazolyl, isoxazolyl, oxadiazolyl, thiadiazolyl, benzothiazolyl, phenothiazinyl, aziridyl, azaindolyl, isoindolyl, indazolyl, purine, pteridyl, beta-carbolyl, naphthyridyl, terpyridyl, phenazinyl, imidazopyridyl, pyropyridyl, azepine, pyrazolyl, and dibenzofuranyl. The heteroaryl group may be substituted or unsubstituted, and if substituted, examples of the substituents are as described above.

[0026] In this specification, an alkylene group is a divalent functional group derived from an alkane, and the above description of the alkyl group is applicable, except that it is a divalent functional group. For example, it may be linear or branched, and may be a methylene group, ethylene group, propylene group, isobutylene group, sec-butylene group, tert-butylene group, pentylene group, hexylene group, etc. The alkylene group may be substituted or unsubstituted, and if substituted, examples of the substituent are as described above.

[0027] In this specification, an arylene group is a divalent functional group derived from arene, and the above description of the aryl group is applicable, except that it is a divalent functional group. For example, it may be a phenylene group, biphenylene group, terphenylene group, naphthalene group, fluorenyl group, pyrenyl group, phenanthrenyl group, perylene group, tetracenyl group, anthracenyl group, etc. The arylene group may be substituted or unsubstituted, and if substituted, examples of the substituent are as described above.

[0028] In this specification, the cycloalkylene group is a divalent functional group derived from a cycloalkane, and the above description of the cycloalkyl group is applicable except that it is a divalent functional group. The cycloalkylene group may be substituted or unsubstituted, and if substituted, examples of the substituent are as described above.

[0029] In this specification, the heteroarylene group has 2 to 20, or 2 to 10, or 6 to 20 carbon atoms. The heteroarylene group contains O, N, or S as a heteroatom, and the above-mentioned description of the heteroaryl group is applicable except that it is a divalent functional group. The heteroarylene group may be substituted or unsubstituted, and if substituted, examples of the substituent are as described above.

[0030] 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.

[0031] 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 referred to as a second component, and similarly, a second component may be referred to as a first component.

[0032] 1. Monomer composition for synthesizing recycled plastics According to one embodiment of the present invention, there is provided a monomer composition for synthesizing recycled plastics, which comprises an aromatic diol compound, has a ratio of 0.3% or less of an aromatic diol compound derivative impurity represented by the following formula 1, has a melting point of 156.4°C or more, and is recovered from a polycarbonate-based resin.

[0033] [Formula 1] Ratio (%) of aromatic diol compound derivative impurities = (peak area of ​​aromatic diol compound derivatives measured by liquid chromatography / total peak area measured by liquid chromatography) x 100.

[0034] The present inventors have confirmed through experiments that the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention can achieve excellent color quality of the aromatic diol compound, which is the main target of recovery, and can secure the aromatic diol compound with high purity, even though the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention is recovered by recycling polycarbonate-based resins through chemical decomposition.

[0035] In particular, a monomer composition for synthesizing recycled plastics (second composition) containing a carbonate-based compound such as dialkyl carbonate, which is recovered from a polycarbonate-based resin, can be obtained simultaneously with the monomer composition for synthesizing recycled plastics (first composition) of one embodiment by the method for producing a monomer composition for synthesizing recycled plastics described below.

[0036] In other words, the present invention has the technical advantage that a first composition containing an aromatic diol compound can be obtained with high purity by recycling a polycarbonate-based resin through chemical decomposition, and at the same time, a second composition containing a carbonate-based compound, which is a high-addition by-product, can also be obtained.

[0037] Specifically, the monomer composition for synthesizing recycled plastics according to one embodiment is characterized by being recovered from a polycarbonate-based resin. That is, as a result of recovering the monomer composition for synthesizing recycled plastics according to one embodiment from a polycarbonate-based resin, a monomer composition for synthesizing recycled plastics containing an aromatic diol compound is also obtained.

[0038] The term "polycarbonate-based resin" refers to any homopolymer or copolymer containing a polycarbonate repeating unit, collectively referring to a reaction product obtained by the polymerization or copolymerization of a monomer containing an aromatic diol compound and a carbonate-based compound. A homopolymer can be synthesized by using only one aromatic diol compound and one carbonate precursor to obtain a single carbonate repeating unit. Alternatively, a copolymer can be synthesized by using one aromatic diol compound and two or more carbonate precursors, two or more aromatic diol compounds and one carbonate precursor, or one aromatic diol compound and one carbonate precursor plus one or more other diols to obtain two or more carbonates. The homopolymer or copolymer can include low molecular weight compounds, oligomers, and polymers within a range of molecular weights.

[0039] In addition, the monomer composition for synthesizing recycled plastics according to one embodiment may include an aromatic diol compound. Specific examples of the aromatic diol compound include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, and 1,1-bis(4-hydroxyphenyl)cyclohexane (bis Examples of the aromatic diol compound include 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 2,2-bis(4-hydroxy-3-bromophenyl)propane, 2,2-bis(4-hydroxy-3-chlorophenyl)propane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, and mixtures of two or more thereof. Preferably, the aromatic diol compound in the monomer composition for synthesizing recycled plastics according to the embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0040] The aromatic diol compound is recovered from the polycarbonate-based resin used to recover the monomer composition for synthesizing recycled plastics. In other words, the aromatic diol compound is also obtained as a result of recovery from the polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the present embodiment. Therefore, when a new aromatic diol compound is added externally, separately from the one recovered from the polycarbonate-based resin, to produce the monomer composition for synthesizing recycled plastics of the present embodiment, it is not included in the scope of the aromatic diol compound of the present invention.

[0041] Specifically, the term "recovered from a polycarbonate-based resin" means that the polycarbonate-based resin is obtained by depolymerization of the polycarbonate-based resin. The depolymerization may be carried out under acidic, neutral, or basic conditions, and is particularly favorable under basic (alkaline) conditions. In particular, the depolymerization is preferably carried out in an alcohol, as described below.

[0042] Meanwhile, the monomer composition for synthesizing recycled plastics according to one embodiment may have an APHA Color value, measured according to ASTM D 1209, of 60 or less, or 50 or less, or 40 or less, or 30 or less, or 20 or less, or 10 or less, or 0 or more, or 1 or more, or 0 to 60, or 0 to 50, or 0 to 40, or 0 to 30, or 0 to 20, or 0 to 10, or 1 to 60, or 1 to 50, or 1 to 40, or 1 to 30, or 1 to 20, or 1 to 10.

[0043] The method for measuring the APHA Color of the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and for example, it can be measured using a HunterLab UltraScan PRO Spectrophotometer according to ASTM D 1209.

[0044] APHA Color is a value obtained by comparing the color of colorless water with that of a yellow PtCo solution, with values ​​closer to 0 indicating colorlessness and values ​​closer to 500 indicating yellowness. Therefore, since the APHA Color of the monomer composition for synthesizing recycled plastics according to one embodiment is reduced to 60 or less, transparent color properties can be achieved when synthesizing polycarbonate-based resins using the same.

[0045] On the other hand, if the APHA color of the monomer composition for synthesizing recycled plastics according to one embodiment is excessively increased, such as exceeding 60, there is a limitation in that it becomes difficult to synthesize a colorless and transparent polycarbonate-based resin due to yellowing.

[0046] Meanwhile, in the monomer composition for synthesizing recycled plastics according to one embodiment, the purity of the aromatic diol compound may be 99.6% or more, or 99.7% or more, or 99.8% or more, or 99.9% or more, or 100% or less, or 99.6% to 100%, or 99.7% to 100%, or 99.8% to 100%, or 99.9% to 100%.

[0047] An example of a method for measuring the purity of the aromatic diol compound in the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and may be, for example, 1 H NMR, ICP-MS analysis, HPLC analysis, UPLC analysis, etc. can be used without limitation. Specific methods, conditions, and devices for the NMR, ICP-MS, HPLC, and UPLC can be any of various conventional methods, conditions, and devices.

[0048] As described above, in the monomer composition for synthesizing recycled plastics according to one embodiment, the purity of the aromatic diol compound, which is the main target material for recovery, is significantly increased to 99.6% or more, and other impurities are minimized, thereby enabling the realization of excellent physical properties when synthesizing polycarbonate-based resins using the same.

[0049] Meanwhile, the monomer composition for synthesizing recycled plastics according to one embodiment may have a melting point of 156.4°C or higher, or 156.5°C or higher, or 156.6°C or higher, or 156.7°C or higher, or 156.8°C or higher, or 156.9°C or higher, or 160°C or lower, or 156.4°C to 160°C, or 156.5°C to 160°C, or 156.6°C to 160°C, or 156.7°C to 160°C, or 156.8°C to 160°C, or 156.9°C to 160°C. The fact that the melting point of the monomer composition for synthesizing recycled plastics is higher than 156.4°C is believed to be due to the method for producing the monomer composition for synthesizing recycled plastics, which will be described later.

[0050] The method for measuring the melting point of the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and may be measured, for example, by a differential scanning calorimeter.

[0051] As described above, the melting point of the monomer composition for synthesizing recycled plastics according to one embodiment is higher than 156°C, and other impurities are minimized, so that excellent physical properties can be achieved when synthesizing polycarbonate-based resins using the same.

[0052] Meanwhile, the monomer composition for synthesizing recycled plastics may further contain impurities other than aromatic diol compounds, which refer to derivative compounds of aromatic diol compounds other than the aromatic diol compounds that are the main target substances for recovery in the present invention.

[0053] The derivative of the aromatic diol compound may include one or more compounds selected from the group consisting of monoalkyl carbonate of bisphenol A, bisalkyl carbonate of bisphenol A, and bisphenol A dimer. The monoalkyl carbonate of bisphenol A is a product obtained by reacting a hydroxy group at one end of bisphenol A with a dialkyl carbonate. Specific examples include, but are not limited to, monoethyl carbonate of bisphenol A or monomethyl carbonate of bisphenol A. The bisethyl carbonate of bisphenol A is a product obtained by reacting all of the hydroxy groups at both ends of bisphenol A with a dialkyl carbonate. Specific examples include, but are not limited to, bisethyl carbonate of bisphenol A or bismethyl carbonate of bisphenol A. The bisphenol A dimer is a linear or cyclic product obtained by reacting bisphenol A with bisphenol A.

[0054] That is, the derivative of the aromatic diol compound can include one monoalkyl carbonate of bisphenol A, one bisalkyl carbonate of bisphenol A, one bisphenol A dimer, or a mixture of these two.

[0055] By applying the method for producing a monomer composition for synthesizing recycled plastics, which will be described later, it is possible to significantly reduce the generation of impurities derived from aromatic diol compounds.

[0056] Specifically, the monomer composition for synthesizing recycled plastics may have an upper limit numerical range of the ratio of derivative impurities of the aromatic diol compound of Formula 1 of 0.3% or less, or 0.25% or less, or 0.2% or less, or 0.12% or less, or 0.1% or less, and a lower limit numerical range of 0.01% or more. The upper limit numerical range and the lower limit numerical range may be combined to satisfy a numerical range from the lower limit to the upper limit. As an example of the numerical range from the lower limit to the upper limit, the ratio of derivative impurities of the aromatic diol compound of Formula 1 may be 0.01% to 0.3%.

[0057] [Formula 1] Ratio (%) of aromatic diol compound derivative impurities = (peak area of ​​aromatic diol compound derivatives measured by liquid chromatography / total peak area measured by liquid chromatography) x 100.

[0058] According to the above formula 1, the unit of the ratio of the derivative impurities of the aromatic diol compound, % means the peak area ratio measured by liquid chromatography, and means area %.

[0059] In the above formula 1, the peak area of ​​the aromatic diol compound derivative measured by liquid chromatography may be the sum of the peak areas of one or more aromatic diol compound derivatives. For example, when the aromatic diol compound derivative is a mixture of three types of bisphenol A monoalkyl carbonate, bisphenol A bisalkyl carbonate, and bisphenol A dimer, it means the sum of the peak areas of bisphenol A monoalkyl carbonate, bisphenol A bisalkyl carbonate, and bisphenol A dimer.

[0060] The method for measuring the weight ratio of the aromatic diol compound derivative impurities in the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and may be, for example, high performance liquid chromatography (HPLC). Specific methods, conditions, and devices for the HPLC may be any of various known methods, conditions, and devices.

[0061] However, as an example, the recycled bisphenol A monomer composition can be dissolved in a methanol solvent at a concentration of 0.5 mg / mL under normal pressure and 20 to 30°C, and then solid impurities in the solution can be removed using a syringe filter (0.45 μm). After that, the content can be measured by UPLC (ultra performance liquid chromatography) using a Capcell Pak C18 (4.6 mm ID x 50 mm L, 5 μm) with a Waters HPLC system (e2695 separation module, 2998 PDA detector). More specifically, the measurement can be performed under the following conditions: (1) Column: Capcell Pak C18 (4.6 mm ID x 50 mm L, 5 μm), (2) Column Temp: 40°C, (3) Injection volume: 10 μl, (4) Flow: Mobile phase A - Acetonitrile / TFA = 100 / 0.1%, B - Water / TFA = 100 / 0.1%, Gradient elution - 0 min A:B = 2:8, 10 min A:B = 100:0, volume = 1 ml / min (total = 10 min), (5) Detector: 275 nm.

[0062] As described above, in the monomer composition for synthesizing recycled plastics according to one embodiment, the ratio of impurities derived from aromatic diol compounds other than the aromatic diol compounds, which are the main target substances for recovery, is significantly reduced, and excellent physical properties can be achieved when synthesizing polycarbonate-based resins using the same.

[0063] More specifically, the ratio of the monoalkyl carbonate of bisphenol A and the bisalkyl carbonate of bisphenol A according to the following formula 2 may be 0.1% or less, or 0.05% or less, or 0% or more, or 0% to 0.1%, or 0% to 0.05%.

[0064] [Formula 2] Ratio (%) of monoalkyl carbonate of bisphenol A and bisalkyl carbonate of bisphenol A = (peak area of ​​monoalkyl carbonate of bisphenol A and bisalkyl carbonate of bisphenol A measured by liquid chromatography / total peak area measured by liquid chromatography) × 100.

[0065] Furthermore, the ratio of the bisphenol A dimer according to the following formula 3 may be 0.3% or less, or 0.2% or less, or 0.13% or less, or 0.12% or less, or 0.1% or less, or 0.09% or less, or 0.01% or more, or 0.01% to 0.3%, or 0.01% to 0.2%, or 0.01% to 0.13%, or 0.01% to 0.12%, or 0.01% to 0.1%, or 0.01% to 0.09%.

[0066] [Formula 2] The proportion of bisphenol A dimer (%) = (peak area of ​​bisphenol A dimer measured by liquid chromatography / total peak area measured by liquid chromatography) × 100.

[0067] In one embodiment, the monomer composition for synthesizing recycled plastics includes a carbonate-based compound as a by-product. The carbonate-based compound includes all compounds containing a carbonate functional group (-OCOO-), including linear and cyclic carbonate compounds. The organic functional group bonded to the carbonate functional group in the carbonate-based compound is not particularly limited, but may include, for example, an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or a combination of two or more thereof.

[0068] More specifically, the carbonate compound may include a dialkyl carbonate or a diaryl carbonate. The dialkyl carbonate has a structure in which two alkyl groups are bonded to both ends of a carbonate functional group, and the two alkyl groups may be the same or different. Specific examples of the dialkyl carbonate are not particularly limited, but include dialkyl carbonates having 3 to 15 or 3 to 13 carbon atoms, such as dimethyl carbonate or diethyl carbonate.

[0069] The diaryl carbonate has a structure in which two aryl groups are bonded to both ends of a carbonate functional group, and the two aryl groups may be the same or different. Specific examples of the diaryl carbonate are not particularly limited, but include diaryl carbonates having 13 to 20 carbon atoms or 13 to 15 carbon atoms, such as diphenyl carbonate.

[0070] In the monomer composition for synthesizing recycled plastics according to the embodiment, the main target substance for recovery is an aromatic diol compound, and therefore the carbonate-based compound can be separated and recovered separately as a by-product from the monomer composition for synthesizing recycled plastics according to the embodiment.

[0071] The monomer composition for synthesizing recycled plastics according to one embodiment can be used as a raw material for producing various recycled plastics (e.g., polycarbonate (PC)) as described below.

[0072] The monomer composition for synthesizing recycled plastics according to one embodiment may further include 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 aromatic diol compounds by depolymerization of polycarbonate-based resins may be used without limitation.

[0073] 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 through various filtration, purification, washing, and drying processes in order to obtain only aromatic diol compounds, which are the main target substances for recovery, in high purity after the depolymerization reaction of polycarbonate-based resin.

[0074] 2. Method for producing monomer composition for synthesizing recycled plastics (1) First manufacturing method According to another embodiment of the present invention, there is provided a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate-based resin; separating a carbonate-based compound from the depolymerization product; dissolving the depolymerization product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound; and recrystallizing an aromatic diol compound from the dissolved solution.

[0075] Specifically, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of depolymerizing a polycarbonate-based resin.

[0076] The term "polycarbonate-based resin" refers to any homopolymer or copolymer containing a polycarbonate repeating unit, collectively referring to a reaction product obtained by the polymerization or copolymerization of a monomer containing an aromatic diol compound and a carbonate-based compound. A homopolymer can be synthesized by using only one aromatic diol compound and one carbonate precursor to obtain a single carbonate repeating unit. Alternatively, a copolymer can be synthesized by using one aromatic diol compound and two or more carbonate precursors, two or more aromatic diol compounds and one carbonate precursor, or one aromatic diol compound and one carbonate precursor plus one or more other diols to obtain two or more carbonates. The homopolymer or copolymer can include low molecular weight compounds, oligomers, and polymers within a range of molecular weights.

[0077] The polycarbonate-based resin may be applied regardless of various forms and types, such as a new polycarbonate-based resin produced by synthesis, a recycled polycarbonate-based resin produced by a recycling process, or a polycarbonate-based resin waste.

[0078] However, if necessary, a pretreatment process for the polycarbonate-based resin may be performed before the depolymerization reaction of the polycarbonate-based resin to improve the efficiency of the process for recovering the aromatic diol compound and the carbonate-based compound from the polycarbonate-based resin. Examples of the pretreatment process include washing, drying, pulverization, and glycol decomposition. The specific method for each pretreatment process is not limited, and various methods widely used in the process for recovering the aromatic diol compound and the carbonate precursor by depolymerization of the polycarbonate-based resin may be applied without limitation.

[0079] The depolymerization reaction of the polycarbonate-based resin may be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions. The type of base is not particularly limited, and examples include sodium hydroxide (NaOH) or potassium hydroxide (KOH). The base is a basic catalyst that acts as a catalyst and has the advantage of being more economical than organic catalysts that are mainly used under mild conditions. More specifically, the depolymerization reaction of the polycarbonate-based resin may be carried out at a pH in the range of more than 8 and less than 12.

[0080] The depolymerization of the polycarbonate resin can be carried out by reacting the base in an amount of 0.5 moles or less, or 0.4 moles or less, or 0.3 moles or less, or 0.1 moles or more, or 0.2 moles or more, or 0.1 to 0.5 moles, or 0.1 to 0.4 moles, or 0.1 to 0.3 moles, or 0.2 to 0.5 moles, or 0.2 to 0.4 moles, or 0.2 to 0.3 moles, per mole of the polycarbonate resin. If the base is reacted in an amount exceeding 0.5 moles per mole of the polycarbonate resin, the increased amount of alkali salt generated increases impurities, reducing the purity of the target recovered material and reducing the economic viability of the catalytic reaction.

[0081] The depolymerization reaction of the polycarbonate resin may be carried out in the presence of alcohol. The present invention has the advantage that by decomposing the polycarbonate resin into alcohol, the highly pure monomer bisphenol A can be stably obtained, and further, carbonate compounds such as dialkyl carbonates with high added value can be additionally obtained as reaction by-products.

[0082] The number of hydroxy groups in the alcohol is not particularly limited, but may include, for example, a monohydric alcohol, which is a compound having one hydroxy group in the molecule.

[0083] Furthermore, the type of monovalent organic functional group bonded to the hydroxy group in the monohydric alcohol is not particularly limited, but may include organic functional groups having 1 to 10 or 1 to 6 carbon atoms, such as alkyl groups, cycloalkyl groups, aryl groups, heteroaryl groups, or combinations of two or more of these.

[0084] The alcohol may be one type of single compound or a mixture of two or more types. Specific examples of the alcohol are not particularly limited, but include ethanol, methanol, phenol, and mixtures thereof.

[0085] The content of the alcohol may be 5 to 15 mol or 8 to 13 mol per mol of the polycarbonate-based resin. Since the alcohol has good solubility in bisphenol A, an alcohol within the above range must be included. If the content of the alcohol is too low, less than 5 mol per mol of the polycarbonate-based resin, the alcoholysis of the polycarbonate-based resin is difficult to carry out sufficiently. On the other hand, if the content of the alcohol is too high, more than 15 mol per mol of the polycarbonate-based resin, excessive use of alcohol may reduce the economic efficiency of the process.

[0086] The solvent in which the depolymerization reaction of the polycarbonate-based resin is carried out may include one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0087] The organic solvent may include tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0088] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent, there is an advantage that the dissolving property for polycarbonate is improved, thereby improving the reactivity.

[0089] The content of the organic solvent may be 16 to 20 moles or 16 to 18 moles per mole of the polycarbonate resin. The content of the organic solvent may also be 1.5 to 2 moles per mole of ethanol. By mixing the polycarbonate resin, alcohol, and organic solvent within the above ranges, a desired level of depolymerization reaction of the polymer can be achieved.

[0090] Meanwhile, the temperature at which the depolymerization reaction of the polycarbonate resin proceeds is not particularly limited, but may be, for example, 20° C. to 100° C. or 50° C. to 70° C. The time for which the depolymerization reaction of the polycarbonate resin proceeds may be 1 hour to 30 hours or 4 hours to 6 hours.

[0091] Specifically, the above conditions are milder process conditions than the existing pressurized / high temperature process, and stirring under these conditions allows the process to be carried out in a milder process than the existing pressurized / high temperature process. In particular, stirring at 50°C to 70°C for 4 to 6 hours has the advantage of providing the most efficient results in terms of reproducibility and certifiability.

[0092] In other words, the present invention has the advantage that a high-purity aromatic diol compound (e.g., bisphenol A) can be obtained under mild conditions without using an organic catalyst, by adjusting the type and amount of the mixed solvent and the type and content of the base catalyst, and without using a pressurized / high-temperature process. Furthermore, since an alcohol is used as a reactant, a carbonate compound such as a dialkyl carbonate can be obtained as a by-product.

[0093] Meanwhile, an antioxidant may be added to the reaction solution during the depolymerization of the polycarbonate-based resin, allowing the aromatic diol compound recovered by chemical decomposition of the polycarbonate-based resin to have a color level equivalent to that of commercially available reagents or reagents used in PC polymerization.

[0094] Specific examples of the antioxidant are not particularly limited, and various antioxidants that have been widely used in conventional technical fields can be used without limitation, including, for example, sodium hyposulfite, sodium sulfite, erythorbic acid, dibutylhydroxytoluene, butylhydroxyanisole, α-tocopherol, tocopherol acetate, L-ascorbic acid and its salts, L-ascorbic acid palmitate, L-ascorbic acid stearate, triamyl gallate, propyl gallate, disodium ethylenediaminetetraacetate (EDTA), sodium pyrophosphate, sodium metaphosphate, or a mixture of two or more thereof.

[0095] The specific amount of the antioxidant to be added is not particularly limited, but for example, it may be added in a range of 0.1 wt % to 5 wt % or 0.1 wt % to 1 wt % based on the weight of the total reaction solution, at a level that does not affect the physical properties of the monomer composition for synthesizing recycled plastics.

[0096] In addition, during the depolymerization reaction of the polycarbonate-based resin, the depolymerization reaction may be performed under a nitrogen atmosphere.

[0097] More specifically, the step of depolymerizing the polycarbonate-based resin may include a first step of dissolving the carbonate-based resin in an organic solvent, and a second step of adding and stirring a catalyst solution containing an alcohol, a base, and an antioxidant. The alcohol, organic solvent, base, antioxidant, and polycarbonate-based resin in the first and second steps are the same as those described above.

[0098] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may further include, after the step of depolymerizing the polycarbonate-based resin, adding an acid so that the pH of the depolymerized reaction product is 2 to 8. The acid may be a strong acid, such as hydrochloric acid (HCl).

[0099] The salt of the aromatic diol compound contained in the depolymerization reaction product can be converted to the aromatic diol compound by adding an acid so that the pH of the depolymerization reaction product is 2 to 8. The depolymerization reaction is carried out under basic conditions, and the aromatic diol compound produced exists in the form of a salt through a reaction with the base, and is hydrophilic. Therefore, by adding an acid, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted to the aromatic diol compound, thereby making the depolymerization reaction product hydrophobic.

[0100] Therefore, in the step of removing impurities by adding water after the acid addition described below, layers can be separated into an aqueous layer containing impurities and an organic solvent layer containing aromatic diol compounds and carbonate-based compounds. Because the aromatic diol compounds and carbonate-based compounds are hydrophobic, they may be contained in the organic solvent layer between water and the organic solvent, and various water-soluble impurities may be contained in the aqueous layer. This allows for easy separation of the aromatic diol compound, the main product, from the impurities with just a simple process of changing the pH.

[0101] Meanwhile, in the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment, the step of adding water may be further included in the step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8. As a result, in the impurity removal step described below, layers separated into an aqueous layer containing impurities and an organic solvent layer containing aromatic diol compounds and carbonate-based compounds may be formed.

[0102] The order of the acid addition step and the water addition step is not particularly limited, and it is possible to add water after acid addition, or add water after acid addition, or add water and acid simultaneously.

[0103] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include removing impurities after the addition of the acid, where the impurities are hydrophilic substances such as salt compounds, ionic compounds, and acid compounds.

[0104] As described above, after the step of adding an acid to adjust the pH of the depolymerization reaction product to 2 to 8, the step of removing impurities from the depolymerization reaction product after the acid addition is carried out. As a result, the depolymerization reaction product forms layers separated into an aqueous layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate-based compound, and the aqueous layer containing impurities can be separated and removed.

[0105] In the step of removing impurities from the depolymerization reaction product after the addition of the acid, the aqueous layer may be separated from the organic layer, and the impurities contained in the aqueous layer may be removed. Specific separation conditions for separating the aqueous layer from the organic layer are not particularly limited, and various known purification techniques may be applied to specific separation devices and methods without limitation. However, for example, a drain device may be used.

[0106] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include separating a carbonate-based compound from the depolymerization reaction product.

[0107] The carbonate-based compounds include all compounds containing a carbonate functional group (-OCOO-), including carbonate compounds with a linear or cyclic structure. In addition, the type of organic functional group bonded to the carbonate functional group in the carbonate-based compounds is not particularly limited, and may include, for example, an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or a combination of two or more of these.

[0108] More specifically, the carbonate compound may include a dialkyl carbonate or a diaryl carbonate. The dialkyl carbonate has a structure in which two alkyl groups are bonded to both ends of a carbonate functional group, and the two alkyl groups may be the same or different. Specific examples of the dialkyl carbonate are not particularly limited, but include dialkyl carbonates having 3 to 15 or 3 to 13 carbon atoms, such as dimethyl carbonate or diethyl carbonate.

[0109] The diaryl carbonate has a structure in which two aryl groups are bonded to both ends of a carbonate functional group, and the two aryl groups may be the same or different. Specific examples of the diaryl carbonate are not particularly limited, but include diaryl carbonates having 13 to 20 carbon atoms or 13 to 15 carbon atoms, such as diphenyl carbonate.

[0110] The step of separating the carbonate-based compound from the depolymerization reaction product may include evaporating the depolymerization reaction product. Examples of the evaporation conditions are not particularly limited, but as a specific example, the depolymerization reaction product of the polycarbonate-based resin may be evaporated using an evaporator (e.g., a thin film evaporator).

[0111] In addition, the step of separating the carbonate-based compound from the depolymerization reaction product may include a step of distilling the depolymerization reaction product. Although examples of the distillation conditions are not particularly limited, in one specific example, the depolymerization reaction product of the polycarbonate-based resin may be pressurized at a pressure of 200 mbar to 300 mbar and a temperature of 20°C to 30°C, and then depressurized at a pressure of 10 mbar to 50 mbar and a temperature of 20°C to 30°C, thereby performing low-temperature distillation.

[0112] The order in which the evaporation step and the distillation step are performed is not particularly limited, and the evaporation step and the distillation step may be performed simultaneously or sequentially. That is, the evaporation step and the distillation step may be performed simultaneously, or the distillation step may be performed after the evaporation step, or the evaporation step may be performed after the distillation step.

[0113] The separated carbonate-based compound can be reused without a separate separation and purification process, or can be reused after, if necessary, conventional separation and purification processes such as extraction, adsorption, drying, etc. Specific purification conditions are not particularly limited, and various known purification techniques can be applied without limitation to specific purification devices and methods.

[0114] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound. By adding the solvent containing the separated carbonate-based compound to the depolymerization reaction product from which the carbonate-based compound has been separated, aromatic diol compound crystals contained in the depolymerization reaction product from which the carbonate-based compound has been separated can be re-dissolved in the solvent.

[0115] As a result, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product is increased, allowing the maximum amount of impurities present in the crystals or between the crystals to be dissolved in the solvent. Since the dissolved aromatic diol compound has lower solubility than the impurities, when the temperature is subsequently lowered, the dissolved aromatic diol compound can easily precipitate in the aromatic diol compound crystals due to the difference in solubility.

[0116] In the past, there was a limitation that the efficiency of the process was reduced by using a separate ethanol reagent. However, in the present invention, the carbonate compound separated in the previous step is reused and used as a re-dissolving solvent, thereby significantly improving the efficiency of the process.

[0117] The solvent may contain a separated carbonate-based compound. The separated carbonate-based compound is a product obtained by separating the carbonate-based compound from the depolymerization reaction product, and the solvent may consist solely of the separated carbonate-based compound or may contain the separated carbonate-based compound as a major component with some impurities mixed therein.

[0118] The step of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound may be performed at a temperature of 0°C to 200°C, or 50°C to 150°C, or 50°C to 120°C, or 50°C to 100°C.

[0119] The amount of the solvent containing the carbonate compound added may be 10 parts by weight or more, 40 parts by weight or more, 90 parts by weight or more, 100 parts by weight or more, 200 parts by weight or less, 10 to 200 parts by weight, 40 to 200 parts by weight, 90 to 200 parts by weight, or 100 to 200 parts by weight, based on 100 parts by weight of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate compound was separated. If too little solvent containing the carbonate compound is used, the temperature required to dissolve the aromatic diol compound contained in the depolymerization reaction product from which the carbonate compound was separated may become too high, resulting in poor process efficiency. Furthermore, the temperature difference between the dissolution temperature and the cooling temperature may increase, making it difficult to remove impurities by recrystallization. Furthermore, the solid concentration after recrystallization may be too high, making transportation and solid-liquid separation very difficult, thereby making it difficult to remove impurities.

[0120] On the other hand, if a solvent containing a carbonate-based compound is used in excessive amount, the solubility of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate-based compound has been separated becomes excessively high, resulting in a decrease in the yield of the aromatic diol compound recovered after recrystallization, and the use of a large amount of solvent may reduce process efficiency.

[0121] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include recrystallizing the aromatic diol compound from the dissolved solution, which may result in obtaining an aromatic diol compound with high purity.

[0122] The concentration of the aromatic diol compound contained in the solution may be 90% by weight or less, or 70% by weight or less, or 60% by weight or less, or 50% by weight or less, or 40% by weight or more, or 40% by weight to 90% by weight, or 40% by weight to 70% by weight, or 40% by weight to 60% by weight, or 40% by weight to 70% by weight. The concentration of the aromatic diol compound contained in the solution means the mass percentage of the aromatic diol compound relative to the mass of the total solution.

[0123] If the concentration of the aromatic diol compound in the solution is too high, it is difficult to remove impurities by recrystallization, whereas if the concentration of the aromatic diol compound in the solution is too low, the yield of the aromatic diol compound recovered after recrystallization may decrease.

[0124] In the step of recrystallizing the aromatic diol compound from the solution, the specific example of the recrystallization method is not particularly limited, and various methods widely known as conventional recrystallization methods, such as cooling, evaporation, and flash cooling, can be applied without limitation.

[0125] However, for example, the step of recrystallizing the aromatic diol compound from the dissolved solution may include a step of cooling the dissolved solution. The step of cooling the dissolved solution may be performed at a temperature of 0°C to 40°C, or 5°C to 40°C, or 5°C to 30°C, or 5°C to 20°C. The temperature difference between the step of dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate compound and the step of recrystallizing the aromatic diol compound from the dissolved solution may be 40°C to 100°C, or 40°C to 80°C, or 50°C to 70°C.

[0126] The steps of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound and recrystallizing the aromatic diol compound from the dissolved solution can be repeated two or more times. That is, after performing the steps of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound and recrystallizing the aromatic diol compound from the dissolved solution once, the steps of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound and recrystallizing the aromatic diol compound from the dissolved solution can be performed one or more times again. This allows the aromatic diol compound to be recovered to achieve excellent color quality.

[0127] Meanwhile, the method may further include, between the step of separating the carbonate-based compound from the depolymerization reaction product and the step of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound, a step of adding an adsorbent to the depolymerization reaction product from which the carbonate-based compound has been separated to perform adsorption purification, and then removing the adsorbent.

[0128] In addition, the depolymerization reaction product from which the carbonate-based compound has been separated may be purified by adding an adsorbent thereto, and then the adsorbent may be removed, in which case the adsorbent may be brought into contact with the depolymerization reaction product.

[0129] Examples of the adsorbent include activated carbon, charcoal, or a mixture thereof. Activated carbon is a black carbon material with micropores produced by subjecting raw materials to a carbonization process at about 500°C and an activated carbon process at about 900°C. Examples of the activated carbon include, but are not limited to, various activated carbons, such as plant-based, coal-based, petroleum-based, and waste-based activated carbons, depending on the type of raw material.

[0130] More specific examples of plant-based activated carbon include coconut activated carbon, wood activated carbon, and sawdust activated carbon. Furthermore, coal-based activated carbon includes lignite activated carbon, bituminous activated carbon, and anthracite activated carbon. Furthermore, petroleum-based activated carbon includes petroleum coke activated carbon and oil carbon activated carbon. Furthermore, waste-based activated carbon includes synthetic resin activated carbon and pulp activated carbon.

[0131] The adsorbent may include one or more activated carbons selected from the group consisting of plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon, i.e., the adsorbent may include plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, waste-based activated carbon, or a mixture of two or more thereof.

[0132] More specifically, the adsorbent may include one or more activated carbons selected from the group consisting of palm activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous activated carbon, i.e., palm activated carbon, lignite activated carbon, anthracite activated carbon, bituminous activated carbon, or a mixture of two or more thereof.

[0133] The adsorption purification conditions using the adsorbent are not particularly limited, and various conventionally known adsorption purification conditions can be used without limitation. However, for example, the amount of adsorbent added may be 40% by weight to 60% by weight relative to the polycarbonate resin, the adsorption time may be 1 hour to 5 hours, and the adsorption method may be stirring adsorption or a laboratory adsorption tower.

[0134] If necessary, the method may further include adding a solvent to the depolymerization reaction product from which the carbonate-based compound has been separated, before the step of adding an adsorbent to the depolymerization reaction product from which the carbonate-based compound has been separated and then removing the adsorbent. An example of the solvent is ethanol, which may be added in a ratio of 1 to 20 moles, 10 to 20 moles, or 15 to 20 moles per mole of polycarbonate-based resin. By adding a solvent to the depolymerization reaction product from which the carbonate-based compound has been separated, the aromatic diol compound crystals contained in the depolymerization reaction product from which the carbonate-based compound has been separated can be redissolved in the solvent.

[0135] Meanwhile, the method may further include a step of evaporating the solvent after the step of adding a solvent to the depolymerization reaction product from which the carbonate-based compound has been separated. Examples of evaporation conditions are not particularly limited, but one specific example is that the evaporation may be performed using an evaporator (e.g., a thin film evaporator). After the evaporation step, the depolymerization reaction product from which the carbonate-based compound has been separated may be dissolved in a solvent containing the separated carbonate-based compound.

[0136] Meanwhile, the method may further include a step of recrystallizing the depolymerization reaction product from which the carbonate-based compound has been separated after the step of adding a solvent to the depolymerization reaction product from which the carbonate-based compound has been separated. In the recrystallization step of the depolymerization reaction product from which the carbonate-based compound has been separated, various impurities contained in the depolymerization reaction product from which the carbonate-based compound has been separated can be sufficiently removed to obtain a high-purity aromatic diol compound.

[0137] Specifically, the recrystallization step may include adding water to the depolymerization product from which the carbonate-based compound has been separated to recrystallize the product. By adding water to the depolymerization product from which the carbonate-based compound has been separated to recrystallize the product, the solubility of the aromatic diol compound or its salt contained in the depolymerization product is increased, allowing impurities sandwiched between the crystals or between the crystals to be dissolved in the solvent to the maximum extent. Since the dissolved aromatic diol compound has poorer solubility than the impurities, the difference in solubility allows the aromatic diol compound to easily precipitate into crystals when the temperature is subsequently lowered.

[0138] More specifically, in the step of adding water to the depolymerization product from which the carbonate-based compound has been separated to recrystallize it, 200 to 400 moles or 250 to 350 moles of water can be used per mole of polycarbonate-based resin. If too little water is used, the temperature required to dissolve the aromatic diol compound contained in the depolymerization product from which the carbonate-based compound has been separated becomes too high, resulting in poor process efficiency and making it difficult to remove impurities through recrystallization. On the other hand, if too much water is used, the solubility of the aromatic diol compound contained in the depolymerization product from which the carbonate-based compound has been separated becomes too high, resulting in a reduced yield of the aromatic diol compound recovered after recrystallization, and the use of a large amount of solvent can reduce process efficiency.

[0139] After the recrystallization of the depolymerization reaction product from which the carbonate-based compound has been separated, a step of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound may be performed. However, if necessary, after the recrystallization of the depolymerization reaction product from which the carbonate-based compound has been separated, a step of removing remaining impurities by filtration or adsorption may be additionally performed.

[0140] In addition, between the steps of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound and recrystallizing the aromatic diol compound from the dissolved solution, the method may further include the steps of adding an adsorbent to the depolymerization reaction product from which the carbonate-based compound has been separated to perform adsorption purification, and then removing the adsorbent. The description of the step of adding an adsorbent to the depolymerization reaction product from which the carbonate-based compound has been separated to perform adsorption purification, and then removing the adsorbent is the same as described above.

[0141] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a step of washing the depolymerization reaction product from which the carbonate-based compound has been separated, between the steps of separating the carbonate-based compound from the depolymerization reaction product and dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound.

[0142] In the step of washing the depolymerization reaction product from which the carbonate-based compound is separated, the depolymerization reaction product from which the carbonate-based compound is separated may contain an aromatic diol compound. However, since various impurities remain during the recovery process of obtaining the aromatic diol compound, washing may be performed to sufficiently remove these impurities to obtain a high-purity aromatic diol compound.

[0143] Specifically, the cleaning step may include cleaning with a solvent at a temperature of 10° C. to 30° C. or 20° C. to 30° C. The temperature condition refers to the temperature inside a cleaning vessel where cleaning with a solvent is performed, and various heating devices may be used without limitation to maintain a high temperature above room temperature.

[0144] If necessary, after the step of washing with a solvent at a temperature of 10° C. to 30° C., a step of removing the remaining solvent by filtration may be additionally carried out.

[0145] The solvent used in the washing step may include one of water, alcohol, and organic solvents, such as tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0146] The solvent used in the washing step may be used in a weight ratio of 1 to 30 parts by weight, or 1 to 10 parts by weight, based on 1 part by weight of the polycarbonate-based resin used in the depolymerization reaction.

[0147] More specifically, the solvent used in the step of washing with a solvent at a temperature of 10°C to 30°C may be an organic solvent. Preferably, methylene chloride can be used as the organic solvent. In this case, the organic solvent can be used in an amount of 1 part by weight to 10 parts by weight per 1 part by weight of the polycarbonate resin.

[0148] Meanwhile, if necessary, after the recrystallization step of the depolymerization reaction product from which the carbonate-based compound has been separated, a step of removing remaining impurities by filtration or adsorption may be additionally performed.

[0149] Furthermore, if necessary, a drying step may be further included after the recrystallization step. The residual solvent can be removed by the drying, and the specific drying conditions are not particularly limited, but the drying can be carried out at a temperature of, for example, 10°C to 100°C, or 50°C to 100°C. Regarding the specific drying apparatus and method used in the drying, various known drying techniques can be applied without any restrictions.

[0150] (2)Second manufacturing method Meanwhile, according to yet another embodiment of the present invention, there is provided a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate-based resin; dissolving the depolymerized product in a solvent containing a carbonate-based compound; and recrystallizing an aromatic diol compound from the resulting solution.

[0151] For convenience, the method for producing a monomer composition for synthesizing recycled plastics according to the other embodiment will be referred to as a first production method, and the method for producing a monomer composition for synthesizing recycled plastics according to the still other embodiment will be referred to as a second production method.

[0152] The second manufacturing method may include a step of depolymerizing the polycarbonate-based resin, and the details regarding the step of depolymerizing the polycarbonate-based resin may include those described above in the first manufacturing method.

[0153] Meanwhile, the second preparation method may further include, after the step of depolymerizing the polycarbonate-based resin, adding an acid so that the pH of the depolymerization reaction product is 2 to 8. The details of the step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8 may include the same as those described above in the first preparation method.

[0154] The second preparation method may include a step of removing impurities after the addition of the acid, and the details regarding the step of removing impurities may include those described above in the first preparation method.

[0155] The second preparation method may include dissolving the depolymerization reaction product in a solvent containing a carbonate-based compound. The depolymerization reaction product and the carbonate-based compound may be the same as those described above for the first preparation method. By adding the solvent containing the carbonate-based compound to the depolymerization reaction product, the aromatic diol compound crystals contained in the depolymerization reaction product can be redissolved in the solvent.

[0156] As a result, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product is increased, allowing the maximum amount of impurities present in the crystals or between the crystals to be dissolved in the solvent. Since the dissolved aromatic diol compound has lower solubility than the impurities, the difference in solubility allows the aromatic diol compound to easily precipitate into the aromatic diol compound crystals when the temperature is subsequently lowered.

[0157] The solvent may include a carbonate-based compound. The solvent may consist solely of a carbonate-based compound, or may be composed mostly of a carbonate-based compound with some impurities mixed therein. The method for producing the carbonate-based compound is not particularly limited, and any carbonate-based compound obtained by a conventional method for producing a carbonate-based compound may be used without limitation.

[0158] To explain this by citing one example, the polycarbonate resin may be one obtained by a depolymerization reaction of a polycarbonate resin, may be one newly synthesized industrially, or may be one obtained by simultaneously carrying out a depolymerization reaction and a new synthesis.

[0159] The step of dissolving the depolymerization reaction product in the solvent containing the carbonate-based compound may be performed at a temperature of 0°C to 200°C, or 50°C to 150°C, or 50°C to 120°C, or 50°C to 100°C.

[0160] The amount of the carbonate-based compound-containing solvent may be 10 parts by weight or more, 40 parts by weight or more, 90 parts by weight or more, 100 parts by weight or more, 200 parts by weight or less, 10 to 200 parts by weight, 40 to 200 parts by weight, 90 to 200 parts by weight, or 100 to 200 parts by weight, based on 100 parts by weight of the aromatic diol compound contained in the depolymerization reaction product. If too little of the carbonate-based compound-containing solvent is used, the temperature required to dissolve the aromatic diol compound contained in the depolymerization reaction product becomes too high, resulting in poor process efficiency. Furthermore, the temperature difference between the dissolution temperature and the cooling temperature increases, making it difficult to remove impurities by recrystallization. Furthermore, the solid concentration after recrystallization becomes too high, making transportation and solid-liquid separation very difficult, thereby making it difficult to remove impurities.

[0161] On the other hand, if the solvent containing a carbonate-based compound is used in excessive amount, the solubility of the aromatic diol compound contained in the depolymerization reaction product may become excessively high, resulting in a decrease in the yield of the aromatic diol compound recovered after recrystallization, and the use of a large amount of solvent may reduce the efficiency of the process.

[0162] Meanwhile, the second preparation method may include a step of recrystallizing the aromatic diol compound from the dissolved solution, and the details regarding the step of recrystallizing the aromatic diol compound from the dissolved solution may include those described above in the first preparation method.

[0163] Meanwhile, in the second preparation method, the steps of dissolving the depolymerization reaction product in a solvent containing a carbonate-based compound and recrystallizing the aromatic diol compound from the dissolved solution can be repeated two or more times. That is, after the steps of dissolving the depolymerization reaction product in a solvent containing a carbonate-based compound and recrystallizing the aromatic diol compound from the dissolved solution are performed once, the steps of dissolving the depolymerization reaction product in a solvent containing a carbonate-based compound and recrystallizing the aromatic diol compound from the dissolved solution can be performed again one or more times. This allows the aromatic diol compound to be recovered to achieve excellent color quality.

[0164] Meanwhile, the second manufacturing method may further include a step of adding an adsorbent to the depolymerization product for adsorption purification and then removing the adsorbent between the steps of depolymerizing a polycarbonate-based resin and dissolving the depolymerization product in a solvent containing a carbonate-based compound. The details of the step of adding an adsorbent to the depolymerization product for adsorption purification and then removing the adsorbent may be the same as those described above for the first manufacturing method.

[0165] Meanwhile, the second preparation method may further include, between the steps of dissolving the depolymerization reaction product in a solvent containing a carbonate-based compound and recrystallizing the aromatic diol compound from the dissolved solution, a step of adding an adsorbent to the depolymerization reaction product for adsorption purification and then removing the adsorbent. The details of the step of adding an adsorbent to the depolymerization reaction product for adsorption purification and then removing the adsorbent may be the same as those described above for the first preparation method.

[0166] Meanwhile, the second preparation method may further include a step of washing the depolymerization reaction product between the step of depolymerizing a polycarbonate-based resin and the step of dissolving the depolymerization reaction product in a solvent containing a carbonate-based compound, and the details of the step of washing the depolymerization reaction product may include those described above in the first preparation method.

[0167] 3. Recycled plastic 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 plastic according to the above embodiment and a comonomer.

[0168] The content relating to the monomer composition for synthesizing recycled plastics of the embodiment includes all of the content described above in the embodiment.

[0169] Examples of the recycled plastics are not particularly limited, and various plastics synthesized using an aromatic diol compound such as bisphenol A and a carbonate compound such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate as a monomer can be used without limitation. A more specific example is a polycarbonate resin.

[0170] The term "polycarbonate-based resin" refers to any homopolymer or copolymer containing a polycarbonate repeating unit, collectively referring to a reaction product obtained by the polymerization or copolymerization of a monomer containing an aromatic diol compound and a carbonate-based compound. A homopolymer can be synthesized by using only one aromatic diol compound and one carbonate precursor to obtain a single carbonate repeating unit. Alternatively, a copolymer can be synthesized by using one aromatic diol compound and two or more carbonate precursors, two or more aromatic diol compounds and one carbonate precursor, or one aromatic diol compound and one carbonate precursor plus one or more other diols to obtain two or more carbonates. The homopolymer or copolymer can include low molecular weight compounds, oligomers, and polymers within a range of molecular weights.

[0171] More specifically, in the recycled plastics containing the reaction product of the monomer composition for recycled plastic synthesis and the comonomer according to the embodiment, a carbonate compound can be used as the comonomer. Specific examples of the carbonate precursor include phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl)carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis(diphenyl)carbonate, and bishaloformates.

[0172] The reaction process of the monomer composition and comonomer for synthesizing recycled plastics to synthesize the polycarbonate-based resin is not particularly limited, and various conventionally known polycarbonate manufacturing methods can be applied without limitation.

[0173] However, as an example of the method for producing polycarbonate, a method for producing polycarbonate can be used that includes polymerizing a composition containing a monomer composition for synthesizing recycled plastics and a comonomer. In this case, the polymerization can be performed by interfacial polymerization, which can be performed at atmospheric pressure and low temperature, and allows for easy molecular weight control.

[0174] The polymerization temperature may be 0° C. to 40° C., and the reaction time may be 10 minutes to 5 hours. The pH during the reaction may be maintained at 9 or higher or 11 or higher.

[0175] The solvent that can be used in the polymerization is not particularly limited as long as it is a solvent that is used in the polymerization of polycarbonates in the art. For example, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0176] The polymerization can be carried out in the presence of an acid binder, and examples of the acid binder include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amine compounds such as pyridine.

[0177] Furthermore, the polymerization can be carried out in the presence of a molecular weight regulator to control the molecular weight of the polycarbonate. The molecular weight regulator can be an alkylphenol having 1 to 20 carbon atoms, and specific examples include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol, or triacontylphenol. The molecular weight regulator can be added before, during, or after the initiation of polymerization. The molecular weight regulator can be used in an amount of 0.01 to 10 parts by weight, or 0.1 to 6 parts by weight, per 100 parts by weight of the aromatic diol compound, and the desired molecular weight can be obtained within this range.

[0178] In addition, to accelerate the polymerization reaction, a reaction accelerator such as a tertiary amine compound, a quaternary ammonium compound, or a quaternary phosphonium compound, such as triethylamine, tetra-n-butylammonium bromide, or tetra-n-butylphosphonium bromide, may be additionally used.

[0179] 4. Molded products According to yet another embodiment of the present invention, there is provided a molded product including 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.

[0180] 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.

[0181] The molded products are not particularly limited and may be applied to various molded products using plastics without limitation, such as automobile parts, electrical and electronic products, communication products, daily necessities, building materials, optical parts, exterior materials, etc.

[0182] In addition to the recycled plastic of the other embodiment, the molded article may further contain, as necessary, one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact modifiers, fluorescent brighteners, ultraviolet absorbers, pigments, and dyes.

[0183] An example of a method for manufacturing the molded product may include thoroughly mixing the recycled plastic of the other embodiment and an additive using a mixer, extruding the mixture in an extruder to form pellets, drying the pellets, and then injecting the pellets into an injection molding machine. [Effects of the Invention]

[0184] According to the present invention, there are provided a monomer composition for synthesizing recycled plastics, which can achieve high purity and excellent color quality despite being recovered by recycling polycarbonate-based resins through chemical decomposition, and which improves the efficiency of the recovery process; a method for producing the same; and recycled plastics and molded articles using the same. DETAILED DESCRIPTION OF THE INVENTION

[0185] The present invention will be described in more detail in the following examples, but the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0186] <Examples and Comparative Examples: Production of Recycled Bisphenol A Monomer Composition> Example 1 (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of methylene chloride (MC) and then added to a 3L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH). Sodium hydrosulfite was added as an antioxidant at 0.7 wt% of the total solution, and the atmosphere in the system was replaced with nitrogen. The PC depolymerization reaction was carried out by stirring at 60°C for 6 hours in an inert state.

[0187] (2. pH Adjustment) After the product of the depolymerization reaction was cooled to 30°C or less, the pH of the bisphenol A was adjusted to 8 by adding 10% hydrochloric acid (HCl) and water to the product.

[0188] After (3. Layer separation), when an aqueous layer and a methylene chloride (MC) layer were formed, the organic layer located at the bottom was collected using a drain device at the bottom of the reactor, and the aqueous layer located at the top was discharged and discarded.

[0189] (4. Distillation) Then, the recovered methylene chloride (MC) layer was subjected to low-temperature distillation by reducing the pressure from 250 mbar, 20-30°C to 30 mbar, 30°C, to separate and recover the by-product diethyl carbonate (DEC).

[0190] After (5. Purification step - filtration), the residue from which diethyl carbonate (DEC) was removed was washed with methylene chloride (MC) in an amount twice the mass of the PC used at 20-30°C, and then vacuum filtered to recover bisphenol A.

[0191] (6-1. Further Purification Step - Redissolution Step) 50 g of the recovered bisphenol A and 50 g of diethyl carbonate (DEC) recovered in the distillation step 4 were mixed at room temperature, and then heated to 80°C with stirring to redissolve.

[0192] (6-2. Further Purification Step - Recrystallization Step) The solution was cooled to 20°C to recrystallize bisphenol A, and the resulting slurry was subjected to vacuum filtration at 20°C to recover bisphenol A (BPA) crystals.

[0193] (7. Drying step) After that, the mixture was dried in a convection oven at 100°C to prepare a recycled bisphenol A monomer composition from which recycled bisphenol A (BPA) was recovered.

[0194] Example 2 (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of methylene chloride (MC) and then added to a 3L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH). Sodium hydrosulfite was added as an antioxidant at 0.7 wt% of the total solution, and the atmosphere in the system was replaced with nitrogen. The PC depolymerization reaction was carried out by stirring at 60°C for 6 hours in an inert state.

[0195] (2. pH Adjustment) After the product of the depolymerization reaction was cooled to 30°C or less, the pH of the bisphenol A was adjusted to 8 by adding 10% hydrochloric acid (HCl) and water to the product.

[0196] After (3. Layer separation), when an aqueous layer and a methylene chloride (MC) layer were formed, the organic layer located at the bottom was collected using a drain device at the bottom of the reactor, and the aqueous layer located at the top was discharged and discarded.

[0197] (4. Distillation) Then, the recovered methylene chloride (MC) layer was subjected to low-temperature distillation by reducing the pressure from 250 mbar, 20-30°C to 30 mbar, 30°C, to separate and recover the by-product diethyl carbonate (DEC).

[0198] After (5. Purification step - filtration), the residue from which diethyl carbonate (DEC) was removed was washed with methylene chloride (MC) in an amount twice the mass of the PC used at 20-30°C, and then vacuum filtered to recover bisphenol A.

[0199] (6-1. Further Purification Step - Redissolution Step) 50 g of the recovered bisphenol A and 50 g of diethyl carbonate (DEC) recovered in the distillation step 4 were mixed at room temperature, and then heated to 80°C with stirring to redissolve.

[0200] (6-2. Further Purification Step - Recrystallization Step) The solution was cooled to 20°C to recrystallize bisphenol A, and the resulting slurry was subjected to vacuum filtration at 20°C to recover bisphenol A (BPA) crystals.

[0201] (6-3. Further purification step - redissolution step) 50 g of the recovered bisphenol A and 50 g of diethyl carbonate (DEC) recovered in step 4. distillation were mixed at room temperature, and then redissolved by heating to 80°C while stirring.

[0202] (6-4. Further Purification Step - Recrystallization Step) The solution was cooled to 20°C to recrystallize bisphenol A, and the resulting slurry was subjected to vacuum filtration at 20°C to recover bisphenol A (BPA) crystals.

[0203] (7. Drying step) After that, the mixture was dried in a convection oven at 100°C to prepare a recycled bisphenol A monomer composition from which recycled bisphenol A (BPA) was recovered.

[0204] Example 3 (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of methylene chloride (MC) and then added to a 3L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH). Sodium hydrosulfite was added as an antioxidant at 0.7 wt% of the total solution, and the atmosphere in the system was replaced with nitrogen. The PC depolymerization reaction was carried out by stirring at 60°C for 6 hours in an inert state.

[0205] (2. pH Adjustment) After the product of the depolymerization reaction was cooled to 30°C or less, the pH of the bisphenol A was adjusted to 8 by adding 10% hydrochloric acid (HCl) and water to the product.

[0206] After (3. Layer separation), when an aqueous layer and a methylene chloride (MC) layer were formed, the organic layer located at the bottom was collected using a drain device at the bottom of the reactor, and the aqueous layer located at the top was discharged and discarded.

[0207] (4. Distillation) Then, the recovered methylene chloride (MC) layer was subjected to low-temperature distillation by reducing the pressure from 250 mbar, 20-30°C to 30 mbar, 30°C, to separate and recover the by-product diethyl carbonate (DEC).

[0208] After (5. Purification step - filtration), the residue from which diethyl carbonate (DEC) was removed was first washed with methylene chloride (MC) in an amount twice the mass of the PC used at 20-30°C and then vacuum filtered. The filtered material was secondarily washed with water in an amount twice the mass of the PC used at 50°C.

[0209] (6-1. Additional purification step - redissolution step) Then, bisphenol A was redissolved in 16.6 mol of ethanol.

[0210] (6-2. Additional Purification Step-Adsorption Step) Then, lignite activated carbon was added as an adsorbent in a ratio of 50% by weight to the waste polycarbonate, and the mixture was purified by adsorption for 3 hours, and the lignite activated carbon was removed by filtration.

[0211] (6-3. Additional purification step - recrystallization step) Then, 300 mol of water was added to recrystallize bisphenol A, and the resulting slurry was subjected to vacuum filtration at 20 to 30°C to recover bisphenol A (BPA) crystals.

[0212] (7-1. Further Purification Step - Redissolution Step) 50 g of the recovered bisphenol A and 50 g of diethyl carbonate (DEC) recovered in the distillation step 4 were mixed at room temperature, and then redissolved by heating to 80°C while stirring.

[0213] (7-2. Further Purification Step - Recrystallization Step) The solution was cooled to 20°C to recrystallize bisphenol A, and the resulting slurry was subjected to vacuum filtration at 20°C to recover bisphenol A (BPA) crystals.

[0214] (8. Drying step) After that, the mixture was dried in a convection oven at 100°C to prepare a recycled bisphenol A monomer composition from which recycled bisphenol A (BPA) was recovered.

[0215] (Comparative Example 1) A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that (6-1. Further purification step - redissolution step) and (6-2. Further purification step - recrystallization step) of Example 1 were not performed.

[0216] (Comparative Example 2) A recycled bisphenol A monomer composition was prepared in the same manner as in Example 3, except that (7-1. Further purification step - redissolution step) and (7-2. Further purification step - recrystallization step) of Example 3 were not performed.

[0217] <Experimental Example> The properties of the recycled bisphenol A monomer compositions obtained in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1.

[0218] 1.BPA purity The recycled bisphenol A monomer composition was dissolved in methanol at a concentration of 0.5 mg / mL at ambient pressure and 20-30°C. After removing solid impurities from the solution using a syringe filter (0.45 μm), the purity of bisphenol A (BPA) was analyzed using ultra-performance liquid chromatography (UPLC) on a Waters HPLC system using a Capcell Pak C18 (inner diameter 4.6 mm, length 50 mm, particle size 5 μm). Specifically, the peak area ratio (unit: %) of bisphenol A (BPA) was measured relative to the total UPLC peak area (100%).

[0219] The specific UPLC measurement conditions are as follows:

[0220] (1)Column: Capcell Pak C18 (4.6mm IDx50mm L, 5μm), (2)Column Temp:40℃, (3)Injection volume:10μl, (4)Flow:Mobile phase A-Acetonitrile / TFA=100 / 0.1%, B-Water / TFA=100 / 0.1%, Gradient elution-0min A:B=2:8, 10min A:B=100:0, volume=1ml / min(total=10min), (5)Detector:275nm 2. Impurity ratio UPLC analysis was performed in the same manner as in 1. Method for Measuring BPA Purity, and the peak area ratios (units: %) of impurities of BPA derivatives (mono-ethylcarbonate of bisphenol-A (MEBPA; ethyl(4-(2-(4-hydroxyphenyl)propan-2-yl)phenyl)carbonate), bis-ethylcarbonate of bisphenol-A (BEBPA; diethyl(propane-2,2-diylbis(4,1-phenylene))bis(carbonate)), and bisphenol A dimer (BPA dimer) relative to the total UPLC peak area (100%) were determined according to the following formula A:

[0221] [Formula A] Ratio of BPA derivative impurities (%) = (peak area of ​​bisphenol A derivatives measured by liquid chromatography / total peak area measured by liquid chromatography) × 100.

[0222] In the above formula A, the peak area of ​​the bisphenol A derivative measured by liquid chromatography is the sum of the peak areas of MEBPA, BEBPA, and BPA dimer.

[0223] 3.APHA Color The recycled bisphenol A monomer composition was subjected to measurement in the same manner as ASTM D1209 using a Hunterlab UltraScan PRO model device after removing solid impurities from the solution using a syringe filter (0.45 μm).

[0224] 4. Melting Point The recycled bisphenol A monomer composition was measured using a differential scanning calorimeter (DSC2920, manufactured by TA Instrument) at a temperature range of 0°C to 180°C at a heating rate of 10°C / min to obtain a melting point (T m The melting point (T m ) was obtained by peak analysis of the heat flow curve during the first temperature rise, and the average value was calculated by performing three measurements for each sample.

[0225] [Table 1]

[0226] As shown in Table 1, the recycled bisphenol A monomer compositions obtained in Examples 1 to 3 exhibited high purities of 99.75% to 99.91% and high melting points of 156.5°C to 156.9°C. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 to 3 were measured to have a low BPA derivative impurity ratio of 0.09% to 0.25%. In contrast, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 had a purity of 98.82% to 99.57%, which was lower than that of the Examples, and a melting point of 154.8°C to 156.3°C, which was lower than that of the Examples. Furthermore, the recycled bisphenol A monomer compositions were measured to have a high BPA derivative impurity ratio of 0.35% to 0.95%, which was higher than that of the Examples.

Claims

1. Contains an aromatic diol compound, The ratio of impurities derived from the aromatic diol compound represented by the following formula 1 is 0.3% or less, The melting point is 156.4°C or higher, A monomer composition for synthesizing recycled plastics, characterized by being recovered from polycarbonate-based resin: [Formula 1] Ratio (%) of aromatic diol compound derivative impurities=(peak area of ​​aromatic diol compound derivatives measured by liquid chromatography / total peak area measured by liquid chromatography)×100.

2. 2. The monomer composition for synthesizing recycled plastics according to claim 1, wherein the derivative of the aromatic diol compound comprises one or more compounds selected from the group consisting of monoalkyl carbonate of bisphenol A, bisalkyl carbonate of bisphenol A, and bisphenol A dimer.

3. 3. The monomer composition for synthesizing recycled plastics according to claim 2, wherein the ratio of the monoalkyl carbonate of bisphenol A and the bisalkyl carbonate of bisphenol A according to the following formula 2 is 0.1% or less: [Formula 2] Ratio (%) of monoalkyl carbonate of bisphenol A and bisalkyl carbonate of bisphenol A = (peak area of ​​monoalkyl carbonate of bisphenol A and bisalkyl carbonate of bisphenol A measured by liquid chromatography / total peak area measured by liquid chromatography) × 100.

4. 3. The monomer composition for synthesizing recycled plastics according to claim 2, wherein the ratio of the bisphenol A dimer according to the following formula 3 is 0.3% or less: [Formula 3] Proportion of bisphenol A dimer (%)=(peak area of ​​bisphenol A dimer measured by liquid chromatography / total peak area measured by liquid chromatography)×100.

5. The monomer composition for synthesizing recycled plastics according to claim 1, wherein the monomer composition for synthesizing recycled plastics has an APHA Color value of 60 or less as measured by ASTM D 1209.

6. 2. The monomer composition for synthesizing recycled plastics according to claim 1, wherein the purity of the aromatic diol compound in the monomer composition for synthesizing recycled plastics is 99.6% or more.

7. A step of depolymerizing the polycarbonate-based resin; separating the carbonate-based compound from the depolymerization reaction product; Dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound; and recrystallizing the aromatic diol compound from the dissolved solution; A method for producing a monomer composition for synthesizing recycled plastics.

8. The step of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound comprises: The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the reaction is carried out at a temperature of 0°C to 200°C.

9. dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound; 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the amount of the solvent containing the carbonate-based compound added is 10 parts by weight or more relative to 100 parts by weight of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate-based compound has been separated.

10. recrystallizing the aromatic diol compound from the solution, 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the concentration of the aromatic diol compound contained in the solution is 90% by weight or less.

11. The step of recrystallizing the aromatic diol compound from the dissolved solution includes:

8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, further comprising a step of cooling the dissolved solution.

12. Dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound; and 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the step of recrystallizing the aromatic diol compound from the solution is repeated two or more times.

13. between the step of separating the carbonate-based compound from the depolymerization reaction product and the step of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound, 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, further comprising the step of adding an adsorbent to the depolymerization reaction product from which the carbonate-based compound has been separated to perform adsorption purification, and then removing the adsorbent.

14. The depolymerization reaction of the polycarbonate resin is 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the method is carried out in the presence of alcohol.

15. 15. The method for producing a monomer composition for synthesizing recycled plastics according to claim 14, wherein the content of the alcohol is 10 to 15 moles per mole of the polycarbonate resin.

16. 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the carbonate-based compound includes a dialkyl carbonate or a diaryl carbonate.

17. between the step of separating the carbonate-based compound from the depolymerization reaction product and the step of dissolving the depolymerization reaction product from which the carbonate-based compound has been separated in a solvent containing the separated carbonate-based compound, 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, further comprising a step of washing the depolymerization reaction product from which the carbonate-based compound has been separated.

18. A step of depolymerizing the polycarbonate-based resin; dissolving the depolymerization reaction product in a solvent containing a carbonate-based compound; and and recrystallizing the aromatic diol compound from the solution.

19. A recycled plastic comprising the reaction product of the recycled plastic synthesis monomer composition of claim 1 and a comonomer.

20. A molded article comprising the recycled plastic of claim 19.

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