Monomer composition for synthesizing reprocessed plastic, preparation method thereof, and reprocessed plastic and molded product using same

Abstract

The present invention relates to a monomer composition for synthesizing a regenerated plastic, a method for preparing the same, and a regenerated plastic and a molded article using the same. The monomer composition for synthesizing regenerated plastic contains an aromatic diol compound, in which the proportion of aromatic diol compound derivative impurities according to Equation 1 is 0.3% or less, in which the melting point is 156.4 DEG C or higher, and in which the monomer composition is recovered from a polycarbonate-based resin.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0098842 filed in the Korean Intellectual Property Office on July 28, 2023, the disclosure of which is incorporated by reference in its entirety into this specification.

[0003] The present invention relates to a monomer composition for synthesizing recycled plastics, a preparation method thereof, and recycled plastics and molded products using the same, wherein the recycled plastics can achieve high purity and excellent color quality even when recycled by chemical decomposition of polycarbonate resins, and can improve the efficiency of the recycling process. Background Art

[0004] Polycarbonate is a thermoplastic polymer, and is a plastic having excellent properties such as excellent transparency, outstanding ductility, and relatively low production cost.

[0005] Although polycarbonate is widely used in various applications, environmental and health issues in the waste disposal process continue to rise.

[0006] Currently, a physical recycling method is performed, but in this case, a problem of accompanying quality deterioration occurs, and therefore, research on chemical recycling of polycarbonate is being conducted.

[0007] The chemical decomposition of polycarbonate refers to obtaining an aromatic diol compound (eg, bisphenol A (BPA)) as a monomer by decomposition of polycarbonate, and then the aromatic diol compound is used again in polymerization to obtain high-purity polycarbonate.

[0008] Meanwhile, in order to purify the aromatic diol compound obtained by decomposition of polycarbonate and ensure high purity, generally, a process of re-dissolving and recrystallizing the aromatic diol compound in an organic solvent such as toluene has been proposed, but since the types of solvents increase and the solvents are toxic substances, there are limitations that need to be managed. Summary of the invention

[0009] Technical issues

[0010] An object of the present invention is to provide a monomer composition for synthesizing recycled plastics, which can achieve high purity and excellent color quality even when recycled by regeneration through chemical decomposition of polycarbonate resins and can achieve improvement in the efficiency of the recycling process.

[0011] Another object of the present invention is to provide a method for preparing a monomer composition for synthesizing recycled plastics, and recycled plastics and molded products using the monomer composition for synthesizing recycled plastics.

[0012] Technical Solution

[0013] In order to achieve the above-mentioned purpose, a monomer composition for synthesizing recycled plastics is provided herein, wherein the monomer composition comprises an aromatic diol compound, wherein the proportion of impurities of the aromatic diol compound derivative according to the following equation 1 is less than 0.3%, wherein the melting point is above 156.4°C, and wherein the monomer composition is recovered from a polycarbonate resin.

[0014] [Equation 1]

[0015] Ratio (%) of aromatic diol compound derivative impurities=(peak area of ​​aromatic diol compound derivative measured by liquid chromatography / total peak area measured by liquid chromatography)×100.

[0016] Also provided herein is a method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: subjecting a polycarbonate resin to a depolymerization reaction; separating a carbonate compound from the depolymerization reaction product; dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate compound; and recrystallizing an aromatic diol compound from the dissolved solution.

[0017] Further provided herein is a method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the steps of: subjecting a polycarbonate resin to a depolymerization reaction; dissolving the depolymerization reaction product in a solvent containing a carbonate compound; and recrystallizing the aromatic diol compound from the dissolved solution.

[0018] Further provided herein is a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic and a comonomer.

[0019] Further provided herein is a molded article comprising the recycled plastic.

[0020] Hereinafter, a monomer composition for synthesizing recycled plastic according to a specific embodiment of the present invention, a preparation method thereof, and recycled plastic and molded products using the same will be described in more detail.

[0021] Unless explicitly stated herein, the technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the present invention.

[0022] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0023] As used herein, "pH" refers to hydrogen ion concentration (pH), which is a numerical value that indicates the acidity and basicity of a material. pH can be determined by taking the reciprocal of the logarithmic dissociation concentration of hydrogen ions, and is used as a measure of the strength of the acid and base of a material.

[0024] The derivative compound used herein refers to a compound in which, when a certain organic compound is used as a host compound, changes such as introduction of a functional group, oxidation, reduction and atomic substitution are performed within the limit that the structure and properties of the host compound are not significantly changed.

[0025] The term "substituted or unsubstituted" as used herein means unsubstituted or substituted with one or more substituents selected from the following groups: deuterium, a halogen group, a cyano group, a nitro group, a hydroxyl group, a carbonyl group, an ester group, an imide group, an amino group, a primary amino group, a carboxyl group, a sulfonic acid group, a sulfonamide group, a phosphine oxide group, an alkoxy group, an aryloxy group, an alkylthiooxy group, an arylthiooxy group, an alkylsulfoxy group, an arylsulfoxy group, a silyl group, a boron group, an alkyl group, a cycloalkyl group, an alkenyl group, an aryl group, an aralkyl group, an aralkenyl group; an alkylaryl group; an alkoxysilylalkyl group; an arylphosphino group; or a heterocyclic group containing at least one of N, O and S atoms, or unsubstituted or substituted with a substituent in which two or more of the substituents exemplified above are linked together.

[0026] The alkyl group used herein is a monovalent functional group derived from an alkane, and may be linear or branched. The number of carbon atoms of the linear alkyl group is not particularly limited, but is preferably 1 to 20. In addition, the number of carbon atoms of the branched alkyl group is 3 to 20. Specific examples of the alkyl group include 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, etc., but are not limited thereto. The alkyl group may be substituted or unsubstituted, and when substituted, examples of the substituent are the same as described above.

[0027] The cycloalkyl used in this article is a monovalent functional group derived from cycloalkane, which may be a monocyclic group or a polycyclic group, and is not particularly limited, but its carbon number is preferably 3 to 20. According to another embodiment, the carbon number of the cycloalkyl is 3 to 10. Specific examples of cycloalkyl include 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, bicyclo[2,2,1]heptyl, etc., but are not limited thereto. The cycloalkyl may be substituted or unsubstituted, and when substituted, examples of substituents are the same as described above.

[0028] The aryl group used in this article is a monovalent functional group derived from aromatic hydrocarbons, and there is no particular limitation, but the carbon number of the aryl group is preferably 6 to 20, and the aryl group may be a monocyclic aryl group or a polycyclic aryl group. As a monocyclic aryl group, the aryl group may be phenyl, biphenyl, terphenyl, etc., but is not limited thereto. Polycyclic aryl groups include naphthyl, anthracenyl, phenanthrenyl, pyrenyl, peryl, The aryl group may be substituted or unsubstituted, and when substituted, examples of the substituent are the same as described above.

[0029] The heteroaryl group used herein includes one or more non-carbon atoms or heteroatoms, and specifically, the heteroatom may include one or more atoms selected from O, N, Se, S, etc. The carbon number of the heteroaryl group is not particularly limited, but is preferably 4 to 20. The heteroaryl group may be a monocyclic group or a polycyclic group. Examples of heteroaryl groups include thienyl, furanyl, pyrrolyl, imidazolyl, thiazolyl, oxazolyl, oxadiazolyl, pyridyl, bipyridyl, pyrimidyl, triazinyl, triazolyl, acridinyl, pyridazinyl, pyrazinyl, quinolyl, quinazolinyl, quinoxalinyl, phthalazinyl, pyridopyrimidinyl, pyridopyrazinyl, pyrazinopyrazinyl, isoquinolyl, indolyl, benzoxazolyl, benzimidazolyl, benzothiazolyl, benzocarbazolyl, benzothiophenyl, dibenzothiophenyl, benzofuranyl, phenanthrolinyl, thiazolyl, isoxazolyl, oxadiazolyl, thiadiazolyl, benzothiazolyl, phenothiazinyl, aziridinyl, The heteroaryl group may be substituted or unsubstituted. When substituted, examples of the substituents are the same as those described above.

[0030] As used herein, alkylene is a divalent functional group derived from an alkane, and the description of alkyl as defined above can be applied except that alkylene is a divalent functional group. For example, a straight chain alkylene or a branched chain alkylene can include methylene, ethylene, propylene, isobutylene, sec-butylene, tert-butylene, pentylene, hexylene, etc. Alkylene can be substituted or unsubstituted, and when substituted, examples of substituents are the same as above.

[0031] Arylene used in this article is a divalent functional group derived from aromatic hydrocarbons, and except that arylene is a divalent functional group, the description of aryl as defined above can be applied. Examples of arylene include phenylene, biphenylene, terphenylene, naphthylene, fluorenylene, pyrenylene, phenanthrenylene, perylene, tetracenylene (tetracenyl group), anthracene group etc., but are not limited thereto. Arylene can be substituted or unsubstituted, and when substituted, examples of substituents are the same as above.

[0032] Cycloalkylene as used herein is a divalent functional group derived from cycloalkane, except that it is a divalent functional group, the description of cycloalkyl as defined above can be applied.Cycloalkylene may be substituted or unsubstituted, and when substituted, examples of the substituent are as described above.

[0033] Heteroarylene used in this article has 2 to 20 carbon atoms, or 2 to 10 carbon atoms, or 6 to 20 carbon atoms. Except that arylene contains O, N or S as heteroatoms and is a divalent functional group, the description of heteroaryl as defined above can be applied. Heteroarylene can be substituted or unsubstituted, and when substituted, examples of substituents are as described above.

[0034] It should be understood that the terms "comprises", "includes", "has", etc. are used herein to illustrate the presence of described features, regions, integers, steps, actions, elements and / or components, but do not exclude the presence or addition of one or more other features, regions, integers, steps, actions, elements, components and / or groups.

[0035] In addition, the terms including ordinal numbers such as "first", "second", etc. are only used for the purpose of distinguishing one component from another component and are not limited by the ordinal numbers. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, or similarly, the second component may be referred to as the first component.

[0036] 1. Monomer composition for synthesizing recycled plastics

[0037] According to one embodiment of the present invention, a monomer composition for synthesizing recycled plastics can be provided, the monomer composition comprising an aromatic diol compound, wherein the proportion of impurities of the aromatic diol compound derivative according to the following equation 1 is less than 0.3%, wherein the melting point is above 156.4°C, and wherein the monomer composition is recovered from a polycarbonate resin.

[0038] [Equation 1]

[0039] Ratio (%) of aromatic diol compound derivative impurities=(peak area of ​​aromatic diol compound derivative measured by liquid chromatography / total peak area measured by liquid chromatography)×100.

[0040] The present inventors have experimentally discovered that although the monomer composition for synthesizing recycled plastics of one embodiment is recycled by regeneration through chemical decomposition of polycarbonate resins, the aromatic diol compound as the main recycling target can achieve excellent color quality and ensure high purity of the aromatic diol compound, and have completed the present invention.

[0041] Specifically, a monomer composition for synthesizing recycled plastics (second composition) containing carbonate compounds such as dialkyl carbonate and the monomer composition for synthesizing recycled plastics (first composition) of the above embodiment can be obtained simultaneously by the method for preparing a monomer composition for synthesizing recycled plastics to be described later, wherein the carbonate compounds are recovered from polycarbonate resins.

[0042] That is, the present invention can have the following technical features and advantages: through the regeneration of the polycarbonate resin by chemical decomposition, a first composition containing an aromatic diol compound can be obtained with high purity, and a second composition containing a carbonate compound as a high value-added by-product can also be obtained.

[0043] Specifically, the monomer composition for synthesizing recycled plastic according to one embodiment is characterized in that it is recycled from a polycarbonate-based resin. That is, this means that as a result of recycling from a polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastic according to one embodiment, a monomer composition for synthesizing recycled plastic containing an aromatic diol compound is obtained together.

[0044] Polycarbonate resin is intended to include homopolymers and copolymers comprising polycarbonate repeating units, and refers to the reaction product obtained by the polymerization reaction or copolymerization reaction of the monomer comprising aromatic diol compound and carbonate compound. When polycarbonate resin comprises a type of carbonate repeating unit obtained by only using an aromatic diol compound and a type of carbonate compound, homopolymer can be synthesized. In addition, when using an aromatic diol compound and two or more types of carbonate compounds as monomers, or using two or more types of aromatic diol compounds and a type of carbonate compounds, or except an aromatic diol compound and a type of carbonate compounds, other glycols of one or more types are also used to comprise two or more types of carbonates, copolymers can be synthesized. According to molecular weight range, homopolymer or copolymer can include all low molecular weight compounds, oligomers and polymers.

[0045] In addition, the monomer composition for synthesizing recycled plastics according to one embodiment may include an aromatic diol compound. Specific examples of aromatic diol compounds 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, 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), 2,2-bis(4-hydroxyphenyl) 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, or a mixture of two or more thereof. Preferably, the aromatic diol compound of the monomer composition for synthesizing recycled plastics of one embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0046] The aromatic diol compound is characterized in that it is recovered from a polycarbonate resin used to recover a monomer composition for synthesizing recycled plastics. That is, this means that as a result of the recovery from the polycarbonate resin to obtain the monomer composition for synthesizing recycled plastics according to one embodiment, the aromatic diol compound is also obtained together. Therefore, in addition to the recovery from the polycarbonate resin to prepare the monomer composition for synthesizing recycled plastics according to one embodiment, the category of the aromatic diol compound of the present invention does not include the case where a new aromatic diol compound is added from the outside.

[0047] Specifically, "recovered from a polycarbonate resin" means obtained by depolymerization of a polycarbonate resin. The depolymerization reaction can be carried out under acidic, neutral or alkaline conditions, and specifically, the depolymerization reaction can be carried out under alkaline (containing alkali) conditions. Specifically, the depolymerization reaction can be preferably carried out in the presence of an alcohol, as will be described later.

[0048] Meanwhile, the APHA color value of the monomer composition for synthesizing recycled plastics of one embodiment measured according to ASTM D 1209 may be 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.

[0049] An example of a method for measuring the APHA color of the monomer composition for synthesizing recycled plastic according to one embodiment is not particularly limited, and for example, it can be measured using a HunterLabUltraScan PRO spectrophotometer device according to the ASTM D 1209 test method.

[0050] APHA color is a value obtained from the color comparison between water having no color and PtCo solution having yellow. A value closer to 0 indicates colorlessness, and a value closer to 500 indicates yellow. Therefore, when the APHA color of the monomer composition for synthesizing recycled plastic according to one embodiment is reduced to 60 or less, transparent color performance can be achieved in the synthesis of a polycarbonate resin using the same.

[0051] On the other hand, when the APHA color of the monomer composition for synthesizing recycled plastic according to one embodiment excessively increases to more than 60 or the like, there is a limitation in that it is difficult to synthesize a colorless and transparent polycarbonate-based resin due to yellowing.

[0052] Meanwhile, the monomer composition for synthesizing recycled plastics according to one embodiment may have the following purity of aromatic diol compounds: 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%.

[0053] There is no particular limitation on examples of a method for measuring the purity of the aromatic diol compound of the monomer composition for synthesizing recycled plastics according to one embodiment. For example, 1H NMR, ICP-MS analysis, HPLC analysis, UPLC analysis, etc. are not limited. As for the specific methods, conditions, equipment, etc. of NMR, ICP-MS, HPLC and UPLC, various known ones can be applied without limitation.

[0054] As described above, in a monomer composition for synthesizing recycled plastics of one embodiment, the purity of the aromatic diol compound as the main recycling target material is significantly improved to more than 99.6%, and other impurities are minimized, thereby achieving excellent physical properties when the monomer composition is used to synthesize a polycarbonate resin.

[0055] Meanwhile, the monomer composition for synthesizing recycled plastic of one embodiment may have a melting point of 156.4° C. or more, or 156.5° C. or more, or 156.6° C. or more, or 156.7° C. or more, or 156.8° C. or more, or 156.9° C. or more, or 160° C. or less, 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 reason why the melting point of the monomer composition for synthesizing recycled plastic is increased to 156.4° C. or more seems to be due to the method for preparing the monomer composition for synthesizing recycled plastic, which will be described later.

[0056] An example of a method for measuring the melting point of the monomer composition for synthesizing recycled plastic according to one embodiment is not particularly limited, and may be measured by, for example, differential scanning calorimetry.

[0057] In this way, the melting point of the monomer composition for synthesizing recycled plastics of one embodiment is increased to 156° C. or more, and other impurities are minimized, thereby being able to achieve excellent physical properties in the synthesis of polycarbonate-based resins.

[0058] Meanwhile, the monomer composition for synthesizing recycled plastics may further contain impurities other than the aromatic diol compound. The impurities refer to all materials other than the aromatic diol compound which is the main recovery target material of the present invention.

[0059] The aromatic diol compound derivative may include one or more compounds selected from the following: monoalkyl carbonate of bisphenol A, dialkyl carbonate of bisphenol A and bisphenol A dimer. Monoalkyl carbonate of bisphenol A is a product obtained by reacting a hydroxyl group at one end of bisphenol A with a dialkyl carbonate, and there is no particular limitation on its specific examples, but monoethyl carbonate of bisphenol A or monomethyl carbonate of bisphenol A may be mentioned as an example. Diethyl carbonate of bisphenol A is a product obtained by reacting two hydroxyl groups at both ends of bisphenol A with a dialkyl carbonate, and there is no particular limitation on its specific examples, but diethyl carbonate of bisphenol A or dimethyl carbonate of bisphenol A may be mentioned as an example. Bisphenol A dimer is a linear or cyclic product obtained by reacting bisphenol A with bisphenol A.

[0060] That is, the aromatic diol compound derivative may include one type of monoalkyl carbonate of bisphenol A, one type of dialkyl carbonate of bisphenol A, one type of bisphenol A dimer, or a mixture of two types thereof.

[0061] By applying the method for preparing a monomer composition for synthesizing recycled plastics, which will be described later, the generation of impurities derived from the aromatic diol compound can be significantly reduced.

[0062] Specifically, the monomer composition for synthesizing recycled plastics may have a ratio of aromatic diol compound derivative impurities according to equation 1, the upper limit range of the ratio is 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 the lower limit range of the ratio is 0.01% or more. The numerical range from the lower limit to the upper limit can also be satisfied by combining the upper limit range with the lower limit range. In an example of the numerical range from the lower limit to the upper limit, the ratio of aromatic diol compound derivative impurities according to equation 1 can be 0.01% to 0.3%.

[0063] [Equation 1]

[0064] Ratio (%) of aromatic diol compound derivative impurities=(peak area of ​​aromatic diol compound derivative measured by liquid chromatography / total peak area measured by liquid chromatography)×100.

[0065] According to Equation 1, the unit percentage (%) as the ratio of the aromatic diol compound derivative impurity is a peak area ratio measured by liquid chromatography, and means area %.

[0066] In Equation 1, the peak area of ​​the aromatic diol compound derivative measured by liquid chromatography may be the total peak area of ​​each of the 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 dialkyl carbonate, and bisphenol A dimer, the peak area refers to the total peak area of ​​each of bisphenol A monoalkyl carbonate, bisphenol A dialkyl carbonate, and bisphenol A dimer.

[0067] There is no particular limitation on the example of the method for measuring the weight ratio of the impurities of the aromatic diol compound derivative of the monomer composition for synthesizing recycled plastics according to one embodiment, for example, high performance liquid chromatography (HPLC) analysis can be used. As for the specific method, conditions, equipment, etc. of HPLC, various well-known contents can be applied without limitation.

[0068] However, as an example, after dissolving the regenerated bisphenol A monomer composition in a methanol solvent at a concentration of 0.5 mg / mL under normal pressure and 20-30° C., a syringe filter (0.45 μm) is used to remove solid impurities in the solution, and then the weight ratio can be measured by UPLC (ultra-performance liquid chromatography) using Capcell Pak C18 (4.6 mm ID x 50 mm L, 5 μm) via a Waters HPLC system (e2695 separation module, 2998 PDA detector). More specifically, the weight ratio can be measured under the following conditions: ① column: Capcell Pak C18 (4.6mm ID x 50mm L, 5μm), ② column temperature: 40°C, ③ injection volume: 10μL, ④ mobile: mobile phase A-acetonitrile / TFA=100 / 0.1%, B-water / TFA=100 / 0.1%, gradient elution-0minA:B=2:8, 10min A:B=100:0, volume=1ml / min (total=10min), and ⑤ detector: 275nm.

[0069] In this way, in the monomer composition for synthesizing recycled plastics according to one embodiment, the impurity content of aromatic diol compound derivatives other than the aromatic diol compound as the main target material to be recycled is significantly reduced, thereby enabling excellent physical properties to be achieved when the monomer composition is used to synthesize a polycarbonate resin.

[0070] More specifically, according to the following Equation 2, the ratio of the monoalkyl carbonate of bisphenol A to the dialkyl carbonate of bisphenol A 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%.

[0071] [Equation 2]

[0072] Ratio of monoalkyl carbonate of bisphenol A to dialkyl carbonate of bisphenol A (%)=(peak area of ​​monoalkyl carbonate of bisphenol A and dialkyl carbonate of bisphenol A measured by liquid chromatography / total peak area measured by liquid chromatography)×100.

[0073] In addition, the ratio of bisphenol A dimer according to the following equation 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%.

[0074] [Equation 3]

[0075] Ratio (%) of bisphenol A dimer=(peak area of ​​bisphenol A dimer measured by liquid chromatography / total peak area measured by liquid chromatography)×100.

[0076] Meanwhile, in the monomer composition for synthesizing recycled plastics according to an embodiment, carbonate compounds are obtained as by-products. Carbonate compounds include all compounds comprising carbonate functional groups (-OCOO-), and can include carbonate compounds with linear or cyclic structures. In addition, there is no particular restriction on the type of the organic functional group bonded to the carbonate functional group in the carbonate compounds, for example, it can include an alkyl, a cycloalkyl, an aryl, a heteroaryl or a combination of two or more thereof.

[0077] More specifically, carbonate compounds can include dialkyl carbonate or diaryl carbonate.Dialkyl carbonate has a structure in which two alkyl groups are bonded to the two ends of the carbonate functional group, and the two alkyl groups can be identical or different from each other.The specific example of dialkyl carbonate is not particularly limited, but includes dialkyl carbonates with 3 to 15 carbon atoms or 3 to 13 carbon atoms, such as dimethyl carbonate or diethyl carbonate.

[0078] In addition, diaryl carbonate has a structure in which two aryl groups are bonded to the two ends of a carbonate functional group, and the two aryl groups may be identical or different from each other. The specific example of diaryl carbonate is not particularly limited, but includes diaryl carbonates with 13 to 20 carbon atoms or 13 to 15 carbon atoms, such as diphenyl carbonate.

[0079] Since the main recovery target material in the monomer composition for synthesizing recycled plastics of one embodiment is the aromatic diol compound, the carbonate compound can be separated and recovered separately from the monomer composition for synthesizing recycled plastics of one embodiment as a by-product.

[0080] The monomer composition for synthesizing recycled plastics according to one embodiment may be used as a raw material for preparing various recycled plastics (eg, polycarbonate (PC)) to be described later.

[0081] The monomer composition for synthesizing recycled plastics according to one embodiment may further include a small amount of other additives and solvents. There is no particular limitation on the specific type of the additives or solvents, and various materials widely used in the process of recovering aromatic diol compounds by depolymerization of polycarbonate resins can be applied without limitation.

[0082] The monomer composition for synthesizing recycled plastics of one embodiment can be obtained by a method for preparing the monomer composition for synthesizing recycled plastics to be described later. That is, the monomer composition for synthesizing recycled plastics of one embodiment corresponds to a resultant obtained through various processes of filtration, purification, washing and drying, so as to ensure that only the aromatic diol compound as a main recovery target material after the depolymerization reaction of the polycarbonate-based resin has high purity.

[0083] 2. Method for preparing a monomer composition for synthesizing recycled plastics

[0084] (1) First Preparation Method

[0085] According to another embodiment of the invention, there may be provided a method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: subjecting a polycarbonate resin to a depolymerization reaction; separating a carbonate compound from the depolymerization reaction product; dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate compound; and recrystallizing an aromatic diol compound from the dissolved solution.

[0086] Specifically, a method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of subjecting a polycarbonate-based resin to a depolymerization reaction.

[0087] Polycarbonate resin is intended to include homopolymers and copolymers comprising polycarbonate repeating units, and refers to the reaction product obtained by the polymerization reaction or copolymerization reaction of the monomer comprising aromatic diol compound and carbonate compound. When polycarbonate resin comprises a carbonate repeating unit obtained by only using one type of aromatic diol compound and one type of carbonate compound, homopolymer can be synthesized. In addition, when using one type of aromatic diol compound and two or more types of carbonate compounds as monomers, or when using two or more types of aromatic diol compounds and one type of carbonate compounds, or when also using one or more types of other glycols to comprise two or more types of carbonates except one type of aromatic diol compound and one type of carbonate compounds, copolymer can be synthesized. According to molecular weight range, homopolymer or copolymer can include all low molecular weight compounds, oligomers and polymers.

[0088] The polycarbonate-based resin may be used 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.

[0089] However, if necessary, before subjecting the polycarbonate resin to depolymerization reaction, a pretreatment step of the polycarbonate resin is performed, thereby being able to improve the efficiency of the recovery process of the aromatic diol compound and the carbonate compound. Examples of the pretreatment step may include washing, drying, grinding, glycol decomposition, etc. There is no limitation on the specific method of each pretreatment step, and various methods widely used in the process of recovering aromatic diol compounds and carbonate compounds from polycarbonate resins can be applied without limitation.

[0090] In the process of the depolymerization reaction of the polycarbonate resin, the depolymerization reaction can be carried out under acidic, neutral or alkaline conditions, and specifically, the depolymerization reaction can be carried out under alkaline (containing alkali) conditions. There is no particular limitation on the type of alkali, and its examples include sodium hydroxide (NaOH) or potassium hydroxide (KOH). The alkali is an alkaline catalyst that acts as a catalyst and has economic advantages over organic catalysts that are mainly used under mild conditions. More specifically, in the process of the depolymerization reaction of the polycarbonate resin, the depolymerization reaction can be carried out in a pH range of greater than 8 and less than 12.

[0091] In the process of depolymerization of the polycarbonate resin, the depolymerization reaction can be carried out by reacting a base in an amount of 0.5 mol or less, or 0.4 mol or less, or 0.3 mol or less, or 0.1 mol or more, or 0.2 mol or more, or 0.1 mol to 0.5 mol, or 0.1 mol to 0.4 mol, or 0.1 mol to 0.3 mol, or 0.2 mol to 0.5 mol, or 0.2 mol to 0.4 mol, or 0.2 mol to 0.3 mol relative to 1 mol of the polycarbonate resin. When the polycarbonate resin is reacted with a base in an amount greater than 0.5 mol relative to 1 mol of the polycarbonate resin in the process of depolymerization of the polycarbonate resin, there is a limitation that impurities increase due to the influence of an increase in the amount of generated alkali metal salts, so the purity of the target recycled material decreases, and the economic efficiency of the catalytic reaction decreases.

[0092] In addition, the depolymerization reaction of the polycarbonate resin can be carried out in the presence of alcohol. The present invention can stably obtain bisphenol A as a high-purity monomer by decomposing the polycarbonate resin using alcohol, and has the advantage of further obtaining carbonate compounds with high added value such as dialkyl carbonate as reaction byproducts.

[0093] The number of hydroxyl groups in the alcohol is not particularly limited, but may include, for example, monohydric alcohol. Monohydric alcohol is a compound having one hydroxyl group in a molecule.

[0094] In addition, there is no particular limitation on the type of the monovalent organic functional group bonded to the hydroxyl group in the monohydric alcohol, but may include an organic functional group having 1 to 10 carbon atoms or 1 to 6 carbon atoms, such as an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or a combination of two or more thereof.

[0095] The alcohol may be a single compound of one type or a mixture of two or more types. Specific examples of the alcohol are not particularly limited, but examples thereof include ethanol, methanol, phenol, or a mixture thereof.

[0096] The amount of alcohol may be 5 to 15 moles, or 8 to 13 moles relative to 1 mole of the polycarbonate resin. Since alcohol has good solubility in bisphenol A, it should substantially contain alcohol within the above range. When the content of alcohol is excessively reduced to less than 5 moles relative to 1 mole of the polycarbonate resin, the alcohol decomposition of the polycarbonate resin is difficult to be fully carried out. On the other hand, when the content of alcohol is excessively increased to more than 15 moles relative to 1 mole of the polycarbonate resin, the economy of the process may decrease due to excessive use of alcohol.

[0097] The solvent in which the depolymerization reaction of the polycarbonate-based resin is carried out may include at least one organic solvent selected from the group consisting of tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0098] The organic solvent may include tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0099] More preferably, dichloromethane may be used as the organic solvent. When dichloromethane is used as the organic solvent, there are advantages that solubility in polycarbonate may be improved and reactivity may be increased.

[0100] The content of the organic solvent may be 16 to 20 mol, or 16 to 18 mol, relative to 1 mol of the polycarbonate-based resin. In addition, the content of the organic solvent may be 1.5 to 2 mol relative to 1 mol of ethanol. By mixing the polycarbonate-based resin, alcohol, and organic solvent within the above range, there is an advantage that the depolymerization reaction of the polymer can be performed at a desired level.

[0101] Meanwhile, the temperature at which the depolymerization reaction of the polycarbonate resin is performed is not particularly limited, but for example, the reaction may be performed at 20° C. to 100° C., or 50° C. to 70° C. In addition, the depolymerization reaction of the polycarbonate resin may be performed for 1 hour to 30 hours, or 4 hours to 6 hours.

[0102] Specifically, the conditions are mild process conditions relative to conventional pressurized / high temperature processes, and by stirring under the above conditions, the process can be performed in a mild process compared to pressurized / high temperature processes. Specifically, when stirring at 50° C. to 70° C. for 4 to 6 hours, there is an advantage in obtaining the most effective results in terms of reproducibility and stability.

[0103] That is, according to the present invention, since the type and mixing amount of the mixed solvent and the type and content of the base catalyst are adjusted without using an organic catalyst, there are the following advantages: a high-purity aromatic diol compound (e.g., bisphenol A) can be obtained under mild conditions without using a pressurized / high-temperature process, and an alcohol is used as a reactant, so a carbonate compound such as dialkyl carbonate can be obtained as a by-product.

[0104] Meanwhile, during the depolymerization reaction of the polycarbonate resin, an antioxidant may be added to the reaction solution. Due to the addition of the antioxidant, the aromatic diol compound recovered by regeneration through chemical decomposition of the polycarbonate resin can meet a color level comparable to that of commercially available or used reagents for PC polymerization.

[0105] The specific examples of antioxidants are not particularly limited, and various antioxidants widely used in the prior art can be applied without restriction. However, an example of antioxidants includes sodium thiosulfate, sodium sulfite, isoascorbic acid, butylated hydroxytoluene, butylated hydroxyanisole, alpha-tocopherol, tocopherol acetate, L-ascorbic acid and salts thereof, L-ascorbyl palmitate, L-ascorbyl stearate, tripentyl gallate, propyl gallate or disodium ethylenediaminetetraacetic acid (EDTA), sodium pyrophosphate, sodium metaphosphate or a mixture of two or more thereof.

[0106] There is no particular limitation on the specific amount of the antioxidant added, but as an example, the antioxidant can be added in the range of 0.1 wt % to 5 wt % or 0.1 wt % to 1 wt % based on the total weight of the reaction solution at a level that does not affect the physical properties of the monomer composition for synthesizing recycled plastics.

[0107] In addition, during the depolymerization reaction of the polycarbonate-based resin, the depolymerization may be performed under a nitrogen atmosphere.

[0108] More specifically, the step of subjecting the polycarbonate resin to a depolymerization reaction may include: a first step of dissolving the polycarbonate resin in an organic solvent; and a second step of adding a catalyst solution containing an alcohol, an alkali, and an antioxidant. In the first step and the second step, the details of the alcohol, the organic solvent, the alkali, the antioxidant, and the polycarbonate resin are the same as described above.

[0109] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastic according to another embodiment may further include a step of adding an acid to change the pH of the depolymerization reaction product to 2 to 8. A strong acid may be used as the acid, and examples thereof include hydrochloric acid (HCl).

[0110] In the step of adding an acid so that the pH of the depolymerization reaction product becomes 2 to 8, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted into the aromatic diol compound. Since the depolymerization reaction is carried out under alkaline conditions, the resulting aromatic diol compound exists in the form of a salt when reacting with the base, and thus has hydrophilicity. Therefore, by adding an acid, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted into the aromatic diol compound, thereby making it hydrophobic.

[0111] Therefore, in the step of adding water to remove impurities after adding acid to be described later, a layer can be formed which is divided into a water layer containing impurities and an organic solvent layer containing aromatic diol compounds and carbonate compounds. Since aromatic diol compounds and carbonate compounds have hydrophobicity, they can be contained in the organic solvent layer among the water layer and the organic solvent layer, and various water-soluble impurities can be contained in the water layer. Thus, the main product, i.e., the aromatic diol compound, and the impurities can be easily separated by only a simple step of changing pH.

[0112] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may further include the step of adding water in the step of adding an acid so that the pH of the depolymerized product is 2 to 8. Therefore, a layer separated into a water layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate compound may be formed in the step of removing impurities to be described later.

[0113] The order of the step of adding the acid and the step of adding the water is not particularly limited, and the water may be added after the acid is added, the acid may be added after the water is added, or the water and the acid may be added simultaneously.

[0114] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of removing impurities after adding an acid. Therefore, the impurity is a hydrophilic material, and its example may include a salt compound, an ionic compound, an acid compound, and the like.

[0115] As described above, after the step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8, as the step of removing impurities from the depolymerization reaction product after the addition of the acid proceeds, the depolymerization reaction product forms a layer separated into an aqueous layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate compound, and thus the aqueous layer containing impurities can be separated and removed.

[0116] In the step of removing impurities from the depolymerization reaction product after adding the acid, the aqueous layer may be separated from the organic layer to remove impurities contained in the aqueous layer. There is no particular limitation on the specific separation conditions for separating the organic layer from the aqueous layer. For the specific separation device and method, various known purification techniques may be applied without limitation. However, as an example, a drainage device may be used.

[0117] Meanwhile, according to another embodiment, the method for preparing a monomer composition for synthesizing recycled plastics may include a step of separating a carbonate compound from a depolymerization reaction product.

[0118] Carbonate compounds include all compounds that contain carbonate functional groups (-OCOO-), and can include carbonate compounds with linear or cyclic structures. In addition, the type of the organic functional group bonded with the carbonate functional group in the carbonate compounds is not particularly limited, but can include, for example, alkyl, cycloalkyl, aryl, heteroaryl or two or more combinations thereof.

[0119] More specifically, carbonate compounds can include dialkyl carbonate or diaryl carbonate.Dialkyl carbonate has a structure in which two alkyl groups are bonded to the two ends of the carbonate functional group, and the two alkyl groups can be identical or different from each other.The specific example of dialkyl carbonate is not particularly limited, but can include dialkyl carbonate with 3 to 15 carbon atoms or 3 to 13 carbon atoms, such as dimethyl carbonate or diethyl carbonate.

[0120] In addition, diaryl carbonate has a structure in which two aryl groups are bonded to the two ends of a carbonate functional group, and the two aryl groups may be identical or different from each other. The specific example of diaryl carbonate is not particularly limited, but diaryl carbonates having 13 to 20 carbon atoms or 13 to 15 carbon atoms, such as diphenyl carbonate, may be included.

[0121] The step of separating the carbonate compound from the depolymerization reaction product may include the step of evaporating the depolymerization reaction product. There is no particular limitation on the example of evaporation conditions, but as a specific example, an evaporator (e.g., a thin film evaporator) may be used to evaporate the product of the depolymerization reaction of the polycarbonate resin.

[0122] The step of separating the carbonate compound from the depolymerization reaction product may include a step of distilling the depolymerization product. Examples of distillation conditions are not particularly limited, but in a specific example, the product of the depolymerization reaction of the polycarbonate resin is pressurized at a pressure of 200 to 300 mbar and a temperature of 20° C. to 30° C., and then decompressed at a pressure of 10 to 50 mbar and a temperature of 20° C. to 30° C. and subjected to low-temperature distillation.

[0123] There is no particular limitation on the order of performing the evaporation step and the distillation step, 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, the distillation step may be performed after the evaporation step, or the evaporation step may be performed after the distillation step.

[0124] If necessary, the separated carbonate compounds can be regenerated without a separate purification process, or can be regenerated by separation and purification such as conventional extraction, adsorption and drying. There is no particular restriction on the specific purification conditions. For specific purification devices and methods, various known purification techniques can be applied without restriction.

[0125] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include the step of dissolving the depolymerization reaction product from which carbonate compounds have been separated in a solvent containing the separated carbonate compounds. By dissolving the depolymerization reaction product from which carbonate compounds have been separated in a solvent containing the separated carbonate compounds, the aromatic diol compound crystals contained in the depolymerization product from which carbonate compounds have been separated can be dissolved in the solvent again.

[0126] By such a step, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product is increased, and therefore, crystals or impurities interposed between crystals can be dissolved with the solvent to the maximum extent, and further, since the dissolved aromatic diol compound has a poor solubility relative to the impurities, it can be easily precipitated into aromatic diol compound crystals by the difference in solubility when the temperature is subsequently lowered.

[0127] Conventionally, there is a limitation that process efficiency is reduced due to the use of a separate fresh ethanol solution, but in the present invention, the process efficiency can be significantly improved by regenerating the carbonate compound separated in the previous step and using it as a redissolution solvent.

[0128] The solvent may contain separated carbonate compounds. The separated carbonate compounds are products obtained in the step of separating carbonate compounds from the depolymerization reaction product, and the solvent may consist of only separated carbonate compounds, or may be a solvent in which separated carbonate compounds occupy most of the main components and some impurities are mixed therein.

[0129] The step of dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate 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.

[0130] Based on 100 weight parts of the aromatic diol compound included in the depolymerization reaction product of wherein separated carbonate compounds, the addition of the solvent that comprises carbonate compounds can be more than 10 weight parts, or more than 40 weight parts, or more than 90 weight parts, or more than 100 weight parts, or below 200 weight parts, or 10 weight parts to 200 weight parts, or 40 weight parts to 200 weight parts, or 90 weight parts to 200 weight parts, or 100 weight parts to 200 weight parts.If the solvent that comprises carbonate compounds is used with too little amount, the temperature that is used to dissolve the aromatic diol compound included in the depolymerization reaction product of wherein separated carbonate compounds can become too high, and this can cause process efficiency to deteriorate.Along with the temperature difference between solution temperature and the cooling temperature increases, be not easy to remove impurities by recrystallization.In addition, because the solid concentration after recrystallization is too high, transportation or solid-liquid separation become very difficult, therefore may not be easy to remove impurities.

[0131] On the other hand, if the solvent containing the carbonate compound is used in an excessive amount, the solubility of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate compound has been separated becomes too high, which may result in a decrease in the yield of the aromatic diol compound recovered after recrystallization, and the process efficiency may be reduced due to the use of a large amount of solvent.

[0132] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastic according to another embodiment may include a step of recrystallizing the aromatic diol compound from the dissolved solution. The aromatic diol compound can be obtained with high purity through the recrystallization step.

[0133] The concentration of the aromatic diol compound contained in the solution may be 90 wt % or less, or 70 wt % or less, or 60 wt % or less, or 50 wt % or less, or 40 wt % or more, or 40 to 90 wt %, or 40 to 70 wt %, or 40 to 60 wt %, or 40 to 70 wt %. The concentration of the aromatic diol compound contained in the solution refers to the mass percentage of the aromatic diol compound relative to the mass of the entire solution.

[0134] If the concentration of the aromatic diol compound contained in the solution is excessively increased, it is not easy to remove impurities by recrystallization. Meanwhile, if the concentration of the aromatic diol compound contained in the solution is excessively reduced, the yield of the aromatic diol compound recovered after recrystallization may be reduced.

[0135] In the step of recrystallizing the aromatic diol compound from the dissolved solution, there is no particular limitation on specific examples of the recrystallization method, and various methods such as cooling, evaporation and flash cooling, which are well-known conventional recrystallization methods, can be applied without limitation.

[0136] However, as an example, the step of recrystallizing the aromatic diol compound from the dissolved solution may include the 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.

[0137] The following steps can be repeated twice or more: dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate compound; and recrystallizing the aromatic diol compound from the dissolved solution. That is, the following steps can be repeated once or more: dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate compound; and recrystallizing the aromatic diol compound from the dissolved solution. In this way, the aromatic diol compound to be recovered can achieve excellent color quality.

[0138] On the other hand, the method may further include the steps of adding an adsorbent to the separated depolymerization reaction product for adsorption purification and then removing the adsorbent between the step of separating the carbonate compound from the depolymerization reaction product and the step of dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate compound.

[0139] Furthermore, in the step of adding an adsorbent to the depolymerization reaction product from which the carbonate compounds have been separated to perform adsorption purification and then removing the adsorbent, the adsorbent may be brought into contact with the depolymerization reaction product.

[0140] Examples of adsorbents that can be used include activated carbon, charcoal, or a mixture thereof. Activated carbon is a black carbon material having micropores produced by subjecting a raw material to a carbonization process at about 500° C. and an activated carbon process at about 900° C. Examples of activated carbon are not particularly limited, but for example, various activated carbons such as plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon can be applied without limitation depending on the type of raw material.

[0141] In a more specific example, the plant-based activated carbon may include coconut activated carbon, wood activated carbon and sawdust activated carbon. In addition, the coal-based activated carbon may include lignite activated carbon, bituminous coal activated carbon and anthracite activated carbon. In addition, the petroleum-based activated carbon may include petroleum coke activated carbon and oil carbon activated carbon. In addition, the waste-based activated carbon may include synthetic resin activated carbon and pulp activated carbon.

[0142] The adsorbent may include at least one activated carbon selected from the group consisting of plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon. That is, 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.

[0143] More specifically, the adsorbent may include at least one activated carbon selected from the group consisting of coconut activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous coal activated carbon. That is, the adsorbent may include coconut activated carbon, lignite activated carbon, anthracite activated carbon, bituminous coal activated carbon, or a mixture of two or more thereof.

[0144] There is no particular limitation on the adsorption purification conditions by the adsorbent, and various known adsorption purification conditions can be used without limitation. However, in one example, the amount of the adsorbent added may be 40% to 60% by weight relative to the polycarbonate resin, the adsorption time may be 1 to 5 hours, and the adsorption method may be stirring adsorption or an adsorption tower for laboratory use.

[0145] If necessary, before adding adsorbent to carry out adsorption purification and then removing the step of adsorbent in the depolymerization product of carbonate compounds separated therein, the method may further include the step of adding solvent in the depolymerization product of carbonate compounds separated therein. The example of solvent includes ethanol, and ethanol can be added in a ratio of 1 mole to 20 moles, or 10 moles to 20 moles, or 15 moles to 20 moles, relative to 1 mole of polycarbonate resin. The aromatic diol compound crystals contained in the depolymerization product of carbonate compounds separated therein can be dissolved in the solvent again by the step of adding solvent in the depolymerization product of carbonate compounds separated therein.

[0146] Meanwhile, after the step of adding a solvent to the depolymerization product from which carbonate compounds have been separated, the method may further include the step of recrystallizing the depolymerization reaction product from which carbonate compounds have been separated. The example of evaporation conditions is not particularly limited, but as a specific example, an evaporator (e.g., a thin film evaporator) may be used for evaporation. After the evaporation step, the step of dissolving the depolymerization reaction product from which carbonate compounds have been separated in the solvent comprising the separated carbonate compounds may be performed.

[0147] Meanwhile, after the step of adding a solvent to the depolymerization product from which the carbonate compound has been separated, the method may further include the step of recrystallizing the depolymerization reaction product from which the carbonate compound has been separated. In the step of recrystallizing the depolymerization reaction product from which the carbonate compound has been separated, various impurities contained in the depolymerization reaction product from which the carbonate compound has been separated can be sufficiently removed, thereby ensuring a high-purity aromatic diol compound.

[0148] Specifically, the recrystallization step may include a step of adding water to the depolymerization reaction product from which the carbonate compound has been separated for recrystallization. By adding water to the depolymerization reaction product from which the carbonate compound has been separated for recrystallization, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product is increased, and thus, crystals or impurities interposed between crystals can be dissolved to the greatest extent by the solvent, and further, since the dissolved aromatic diol compound has a poor solubility relative to the impurities, when the temperature is subsequently lowered, the aromatic diol compound can be easily precipitated into aromatic diol compound crystals by the difference in solubility.

[0149] More specifically, in the step of adding water to recrystallize in the depolymerization reaction product of wherein separated carbonate compounds, relative to 1 mole of polycarbonate resin, 200 moles to 400 moles or 250 moles to 350 moles of water can be used.When using water with too little amount, the temperature for dissolving the aromatic diol compound contained in the depolymerization reaction product of wherein separated carbonate compounds becomes too high, so this deteriorates process efficiency, and is difficult to remove impurities by recrystallization.On the other hand, when using water with excessive amount, the solubility of the aromatic diol compound contained in the depolymerization reaction product of wherein separated carbonate compounds becomes too high, and therefore, the yield of the aromatic diol compound reclaimed after the recrystallization decreases, and owing to using a large amount of solvents, process efficiency may decline.

[0150] After the step of recrystallizing the depolymerization reaction product from which the carbonate compound has been separated, a step of dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate compound may be performed. However, if necessary, after the step of recrystallizing the depolymerization reaction product from which the carbonate compound has been separated, a step of removing residual impurities by filtration or adsorption may be further performed.

[0151] In addition, between the step of dissolving the depolymerization reaction product from which the carbonate compounds have been separated in a solvent containing the separated carbonate compounds and the step of recrystallizing the aromatic diol compound from the dissolved solution, the method may further include the step of adding an adsorbent to the depolymerization reaction product from which the carbonate compounds have been separated for adsorption purification and then removing the adsorbent. The details of the step of adding an adsorbent to the depolymerization reaction product from which the carbonate compounds have been separated for adsorption purification and then removing the adsorbent are the same as described above.

[0152] Meanwhile, between the step of separating the carbonate compound from the depolymerization reaction product and the step of dissolving the depolymerization reaction product from which the carbonate compound has been separated in a solvent containing the separated carbonate compound, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may further include the step of washing the depolymerization reaction product from which the carbonate compound has been separated.

[0153] In the step of washing the depolymerization reaction product from which the carbonate compound has been separated, the depolymerization reaction product from which the carbonate compound has been 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 and ensure a high-purity aromatic diol compound.

[0154] Specifically, the washing step may include a step of washing 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 the washing container when washing with a solvent. In order to maintain a high temperature deviating from room temperature, various heating devices can be applied without limitation.

[0155] In the washing step, after performing the washing step with a solvent at a temperature of 10° C. or higher and 30° C. or lower, a step of removing the residual solvent by filtration may be further performed.

[0156] The solvent used in the washing step may include one of water, alcohol and an organic solvent. As the organic solvent, tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof may be used.

[0157] The solvent used in the washing step may be used in a weight ratio of 1 part by weight to 30 parts by weight, or 1 part by weight to 10 parts by weight, based on 1 part by weight of the polycarbonate-based resin used in the depolymerization reaction.

[0158] More specifically, the solvent in the step of washing with a solvent at a temperature of 10° C. to 30° C. may be an organic solvent. Preferably, dichloromethane may be used as the organic solvent. At this time, the organic solvent may be used in an amount of 1 part by weight to 10 parts by weight based on 1 part by weight of the polycarbonate resin.

[0159] Meanwhile, if necessary, after performing the recrystallization step of the depolymerization reaction product in which the carbonate precursor has been separated, a step of removing residual impurities by filtration or adsorption may be further performed.

[0160] In addition, if necessary, after the recrystallization step, the method may further include a drying step. The residual solvent may be removed by drying, and there is no particular limitation on the specific drying conditions, but for example, the drying may be performed at a temperature of 10° C. to 100° C., or 50° C. to 100° C. For the specific drying equipment and method used in the drying, various known drying techniques may be applied without limitation.

[0161] (2) Second Preparation Method

[0162] Meanwhile, according to another embodiment of the present invention, a method for preparing a monomer composition for synthesizing recycled plastics can be provided, the method comprising the following steps: subjecting a polycarbonate resin to a depolymerization reaction; dissolving the depolymerization reaction product in a solvent containing a carbonate compound; and recrystallizing an aromatic diol compound from the dissolved solution.

[0163] For convenience, the method for preparing a monomer composition for synthesizing recycled plastic according to another embodiment is referred to as a first preparation method, and the method for preparing a monomer composition for synthesizing recycled plastic according to still another embodiment is referred to as a second preparation method.

[0164] The second preparation method may include a step of subjecting the polycarbonate-based resin to a depolymerization reaction, and details of the step of subjecting the polycarbonate-based resin to a depolymerization reaction may include those described above in the first preparation method.

[0165] Meanwhile, after the step of subjecting the polycarbonate-based resin to a depolymerization reaction, the second preparation method may further include the step of adding an acid to change the pH of the depolymerization reaction product to 2 to 8, and details of the step of adding an acid to change the pH of the depolymerization reaction product to 2 to 8 may include the details described above in the first preparation method.

[0166] The second preparation method may include a step of removing impurities after adding the acid. The details of the step of removing impurities may include the details described above in the first preparation method.

[0167] The second preparation method may include the step of dissolving the depolymerization reaction product in a solvent containing a carbonate compound. The details of the depolymerization reaction product and the carbonate compound may include the details described above in the first preparation method. The aromatic diol compound crystals contained in the depolymerization reaction product may be redissolved in the solvent by adding a solvent containing a carbonate compound to the depolymerization reaction product.

[0168] By such a step, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product increases, and therefore, crystals or impurities interposed between crystals can be dissolved to the maximum extent by the solvent, and further, since the dissolved aromatic diol compound has a poor solubility relative to the impurities, it can be easily precipitated into aromatic diol compound crystals by the difference in solubility when the temperature is subsequently lowered.

[0169] The solvent may comprise a carbonate compound. The solvent may consist of only a carbonate compound, or may be a solvent in which a carbonate compound occupies most of the main components and some impurities are mixed therein. There is no particular restriction on the method for preparing the carbonate compound, and all carbonate compounds obtained by the conventional known method for preparing the carbonate compound may be applied without restriction.

[0170] In one example, the carbonate compound can be obtained from a depolymerization reaction of a polycarbonate resin, or can be newly synthesized industrially, or can be obtained by performing a depolymerization reaction and a new synthesis in parallel.

[0171] The step of dissolving the depolymerization product in a solvent containing a carbonate 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.

[0172] Based on the aromatic diol compound contained in the depolymerization reaction product of 100 weight parts, the addition amount of the solvent containing carbonate compound can be more than 10 weight parts, or more than 40 weight parts, or more than 90 weight parts, or more than 100 weight parts, or less than 200 weight parts, or 10 weight parts to 200 weight parts, or 40 weight parts to 200 weight parts, or 90 weight parts to 200 weight parts, or 100 weight parts to 200 weight parts. If the solvent containing carbonate compound is used with too little amount, the temperature for dissolving the aromatic diol compound contained in the depolymerization reaction product becomes too high, which causes the process efficiency to deteriorate. Along with the temperature difference between the dissolution temperature and the cooling temperature increases, it is not easy to remove impurities by recrystallization. In addition, because the solid concentration after the recrystallization is too high, transportation or solid-liquid separation become very difficult, and therefore may not be easy to remove impurities.

[0173] On the other hand, if the solvent containing the carbonate compound is used in an excessive amount, the solubility of the aromatic diol compound contained in the depolymerization reaction product becomes too high, which leads to a decrease in the yield of the aromatic diol compound recovered after recrystallization, and the process efficiency may be reduced due to the use of a large amount of solvent.

[0174] Meanwhile, the second preparation method may include a step of recrystallizing the aromatic diol compound from the dissolved solution, and details of the step of recrystallizing the aromatic diol compound from the dissolved solution may include the details described above in the first preparation method.

[0175] Meanwhile, in the second preparation method, the following steps may be repeated twice or more: dissolving the depolymerization reaction product in a solvent containing carbonate compounds; and recrystallizing the aromatic diol compound from the dissolved solution. That is, after the step of dissolving the depolymerization reaction product in a solvent containing carbonate compounds and the step of recrystallizing the aromatic diol compound from the dissolved solution are performed once, the step of dissolving the depolymerization reaction product in a solvent containing carbonate compounds and the step of recrystallizing the aromatic diol compound in the dissolved solution may be performed once or more. In this way, the aromatic diol compound to be recovered can achieve excellent color quality.

[0176] Meanwhile, between the step of subjecting the polycarbonate-based resin to a depolymerization reaction and the step of dissolving the depolymerization reaction product in a solvent containing a carbonate-based compound, the second preparation method may further include a step of adding an adsorbent to the depolymerization reaction product to perform adsorption purification and then removing the adsorbent. Details of the step of adding an adsorbent to the separated depolymerization reaction product to perform adsorption purification and then removing the adsorbent may include the details described above in the first preparation method.

[0177] Meanwhile, between the step of dissolving the depolymerization reaction product in a solvent containing a carbonate compound and the step of recrystallizing the aromatic diol compound from the dissolved solution, the second preparation method may further include the step of adding an adsorbent to the depolymerization reaction product for adsorption purification and then removing the adsorbent. Details of the step of adding an adsorbent to the separated depolymerization reaction product for adsorption purification and then removing the adsorbent may include the details described above in the first preparation method.

[0178] Meanwhile, between the step of subjecting the polycarbonate resin to depolymerization reaction and the step of dissolving the depolymerization reaction product in a solvent containing a carbonate compound, the second preparation method may further include a step of washing the depolymerization reaction product. Details of the step of washing the depolymerization reaction product may include the details described above in the first preparation method.

[0179] 3. Recycled plastics

[0180] According to another embodiment of the present invention, there may be provided a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic according to one embodiment and a comonomer.

[0181] The details of the monomer composition for synthesizing recycled plastic according to another embodiment include all the contents described in the above-mentioned one embodiment.

[0182] There is no particular limitation on examples corresponding to recycled plastics, and various plastics synthesized from aromatic diol compounds such as bisphenol A and carbonate compounds such as dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate as monomers can be applied without limitation, and a more specific example can be a polycarbonate resin.

[0183] Polycarbonate resin is intended to include both homopolymers and copolymers comprising polycarbonate repeating units, and refers to the reaction product obtained by the polymerization reaction or copolymerization reaction of the monomer comprising aromatic diol compound and carbonate compound. When polycarbonate resin comprises a type of carbonate repeating unit obtained by only using one type of aromatic diol compound and one type of carbonate compound, homopolymer can be synthesized. In addition, when using one type of aromatic diol compound and two or more types of carbonate compounds as monomers, or when using two or more types of aromatic diol compounds and one type of carbonate compounds, or when using one or more types of other diols to include two or more carbonates except the one type of aromatic diol compound and the one type of carbonate compound, copolymer can be synthesized. According to molecular weight range, homopolymer or copolymer can include all low molecular weight compounds, oligomers and polymers.

[0184] More specifically, in the recycled plastics comprising the reaction product of the monomer composition for synthesizing recycled plastics according to one embodiment and a comonomer, a carbonate compound can be used as a comonomer. Specific examples of carbonate compounds include phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate, m-tolyl carbonate, dinaphthyl carbonate, bis(diphenyl) carbonate or bishaloformates.

[0185] There is no particular limitation on the example of the reaction process of the monomer composition for synthesizing recycled plastic and the comonomer for synthesizing the polycarbonate-based resin, and various known methods for preparing polycarbonate can be applied without limitation.

[0186] However, in one example of the method for preparing polycarbonate, a method for preparing polycarbonate comprising the step of polymerizing a composition comprising a monomer composition for synthesizing recycled plastic and a comonomer can be used. In this case, polymerization can be performed by interfacial polymerization, and during the interfacial polymerization, the polymerization reaction can be performed at normal pressure and low temperature, and the molecular weight can be easily controlled.

[0187] The polymerization temperature may be 0° C. to 40° C., and the reaction time may be 10 minutes to 5 hours. In addition, during the reaction, the pH may be maintained at 9 or above or 11 or above.

[0188] There is no particular limitation on the solvent that can be used for the polymerization as long as it is a solvent used for the polymerization of polycarbonate in the art, and as examples, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0189] In addition, the polymerization may be carried out in the presence of an acid binder. As the acid binder, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an amine compound such as pyridine may be used.

[0190] In addition, in order to regulate the molecular weight of polycarbonate in the process of polymerization, polymerization can be carried out in the presence of a molecular weight regulator. Alkylphenols with carbon atoms of 1 to 20 can be used as molecular weight regulators, and its specific examples include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol or triacontylphenol. Molecular weight regulators can be added before polymerization initiation, during polymerization initiation or after polymerization initiation. Based on the aromatic diol compound of 100 weight parts, the consumption of molecular weight regulator can be 0.01 weight part to 10 weight parts or 0.1 weight part to 6 weight parts, and the molecular weight desired can be obtained within this range.

[0191] Furthermore, in order to promote the polymerization reaction, a reaction accelerator such as a tertiary amine compound, a quaternary ammonium compound or a quaternary phosphonium compound including triethylamine, tetra-n-butylammonium bromide or tetra-n-butylphosphonium bromide may be further used.

[0192] 4. Molded products

[0193] According to another embodiment of the present invention, a molded product comprising the recycled plastic according to another embodiment may be provided. The details of the recycled plastic include all the contents described above in another embodiment.

[0194] The molded product can be obtained by applying the recycled plastic to various known plastic molding methods without limitation. As examples of the molding method, injection molding, foam injection molding, blow molding or extrusion molding can be mentioned.

[0195] There is no particular limitation on examples of molded products, and it can be applied to various molded products using plastics without limitation. Examples of molded products include automobiles, electric and electronic products, communication products, daily necessities, building materials, optical components, exterior materials, and the like.

[0196] If necessary, in addition to the recycled plastic according to another embodiment, the molded article may further include one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact enhancers, optical brighteners, ultraviolet absorbers, pigments and dyes.

[0197] An example of a method for producing a molded article may include the steps of well mixing the recycled plastic according to another embodiment with an additive using a mixer, extrusion-molding the mixture with an extruder to produce pellets, drying the pellets, and then injecting the pellets with an injection molding machine.

[0198] Beneficial Effects

[0199] According to the present invention, a monomer composition for synthesizing recycled plastics, a preparation method thereof, and recycled plastics and molded products using the same can be provided, wherein the recycled plastics can achieve high purity and excellent color quality even when recycled by regeneration utilizing chemical decomposition of polycarbonate resins, and the efficiency of the recycling process can be improved. DETAILED DESCRIPTION

[0200] Hereinafter, the present invention will be explained in detail with reference to the following examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

[0201] <Examples and Comparative Examples: Preparation of Regenerated Bisphenol A Monomer Composition>

[0202] Example 1

[0203] (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of dichloromethane (MC), and then added to a 3 L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH), sodium bisulfite was added as an antioxidant in an amount of 0.7 wt % relative to the total solution, the atmosphere in the system was replaced with nitrogen, and the mixture was stirred at 60° C. for 6 hours in an inactive state to perform a PC depolymerization reaction.

[0204] (2. pH Adjustment) The product of the depolymerization reaction was cooled to 30° C. or less, and then bisphenol A was adjusted to have a pH of 8 by adding 10% hydrochloric acid (HCl) and water to the product.

[0205] (3. Layer Separation) Thereafter, in a state where a water layer and a methylene chloride (MC) layer are formed, the organic layer located on the bottom side is recovered using a drainage device located at the bottom end of the reactor, and the water layer located on the top side is discharged and then discarded.

[0206] (4. Distillation) Thereafter, the recovered methylene chloride (MC) layer was subjected to low-temperature distillation to reduce the pressure from 250 mbar and 20-30° C. to 30 mbar and 30° C., and thereby diethyl carbonate (DEC) as a by-product was separated and recovered.

[0207] (5. Purification step - filtration) Thereafter, the residue from which diethyl carbonate (DEC) was removed was preliminarily washed with dichloromethane (MC) twice the weight of PC at 20 to 30° C., and vacuum filtered to recover bisphenol A.

[0208] (6-1. Additional purification step - redissolution step) Thereafter, 50 g of the recovered bisphenol A was mixed with 50 g of diethyl carbonate (DEC) recovered in the 4. distillation step at room temperature, and then the mixture was heated to 80° C. with stirring, and redissolved.

[0209] (6-2. Additional Purification Step - Recrystallization Step) The solution was cooled to 20°C to recrystallize bisphenol A, and then the resulting slurry was vacuum filtered at 20°C to recover bisphenol A (BPA) crystals.

[0210] (7. Drying Step) Thereafter, the resultant was vacuum dried in a convection oven at 100° C. to prepare a recycled bisphenol A monomer composition in which recycled bisphenol A (BPA) had been recovered.

[0211] Example 2

[0212] (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of dichloromethane (MC), and then added to a 3 L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH), sodium bisulfite was added as an antioxidant in an amount of 0.7 wt % relative to the total solution, the atmosphere in the system was replaced with nitrogen, and the mixture was stirred at 60° C. for 6 hours in an inactive state to perform a PC depolymerization reaction.

[0213] (2. pH Adjustment) The product of the depolymerization reaction was cooled to 30° C. or less, and then bisphenol A was adjusted to have a pH of 8 by adding 10% hydrochloric acid (HCl) and water to the product.

[0214] (3. Layer Separation) Thereafter, in a state where a water layer and a methylene chloride (MC) layer are formed, the organic layer located on the bottom side is recovered using a drainage device located at the bottom end of the reactor, and the water layer located on the top side is discharged and then discarded.

[0215] (4. Distillation) Thereafter, the recovered methylene chloride (MC) layer was subjected to low-temperature distillation to reduce the pressure from 250 mbar and 20-30° C. to 30 mbar and 30° C., and thereby diethyl carbonate (DEC) as a by-product was separated and recovered.

[0216] (5. Purification step - filtration) Thereafter, the residue from which diethyl carbonate (DEC) was removed was preliminarily washed with dichloromethane (MC) twice the weight of PC at 20 to 30° C. and vacuum filtered to prepare bisphenol A.

[0217] (6-1. Additional purification step - redissolution step) Thereafter, 50 g of the recovered bisphenol A was mixed with 50 g of diethyl carbonate (DEC) recovered in the 4. distillation step at room temperature, and then the mixture was heated to 80° C. with stirring and redissolved.

[0218] (6-2. Additional Purification Step - Recrystallization Step) The solution was cooled to 20°C to recrystallize bisphenol A, and then the resulting slurry was vacuum filtered at 20°C to recover bisphenol A (BPA) crystals.

[0219] (6-3. Additional purification step - redissolution step) Thereafter, 50 g of the recovered bisphenol A was mixed with 50 g of diethyl carbonate (DEC) recovered in the 4. distillation step at room temperature, and then the mixture was heated to 80° C. with stirring, and redissolved.

[0220] (6-4. Additional Purification Step - Recrystallization Step) The solution was cooled to 20°C to recrystallize bisphenol A, and then the resulting slurry was vacuum filtered at 20°C to recover bisphenol A (BPA) crystals.

[0221] (7. Drying Step) Thereafter, the resultant was vacuum dried in a convection oven at 100° C. to prepare a recycled bisphenol A monomer composition in which recycled bisphenol A (BPA) had been recovered.

[0222] Example 3

[0223] (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of dichloromethane (MC), and then added to a 3 L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH), sodium bisulfite was added as an antioxidant in an amount of 0.7 wt % relative to the total solution, the atmosphere in the system was replaced with nitrogen, and the mixture was stirred at 60° C. for 6 hours in an inactive state to perform a PC depolymerization reaction.

[0224] (2. pH Adjustment) The product of the depolymerization reaction was cooled to 30° C. or less, and then bisphenol A was adjusted to have a pH of 8 by adding 10% hydrochloric acid (HCl) and water to the product.

[0225] (3. Layer Separation) Thereafter, in a state where a water layer and a methylene chloride (MC) layer are formed, the organic layer located on the bottom side is recovered using a drainage device located at the bottom end of the reactor, and the water layer located on the top side is discharged and then discarded.

[0226] (4. Distillation) Thereafter, the recovered methylene chloride (MC) layer was subjected to low-temperature distillation to reduce the pressure from 250 mbar and 20-30° C. to 30 mbar and 30° C., and thereby diethyl carbonate (DEC) as a by-product was separated and recovered.

[0227] (5. Purification step - filtration) Thereafter, the residue from which diethyl carbonate (DEC) was removed was preliminarily washed with dichloromethane (MC) twice the weight of the PC used at 20 to 30° C., and vacuum filtered. The filtrate was secondarily washed with water twice the weight of the PC used at a temperature of 50° C.

[0228] (6-1. Additional purification step - redissolution step) Thereafter, bisphenol A was added to 16.6 mol of ethanol and redissolved.

[0229] (6-2. Additional Purification Step - Adsorption Step) Thereafter, lignite activated carbon was added as an adsorbent in a ratio of 50 wt % relative to the waste polycarbonate, and then purification was performed by adsorption for 3 hours, and then the lignite activated carbon was removed by filtration.

[0230] (6-3. Additional Purification Step - Recrystallization Step) Thereafter, 300 mol of water was added to recrystallize bisphenol A, and the resulting slurry was vacuum filtered at 20 to 30° C. to recover bisphenol A (BPA) crystals.

[0231] (7-1. Additional purification step - redissolution step) Thereafter, 50 g of the recovered bisphenol A was mixed with 50 g of diethyl carbonate (DEC) recovered in the 4. distillation step at room temperature, and then the mixture was heated to 80° C. with stirring, and redissolved.

[0232] (7-2. Additional Purification Step - Recrystallization Step) The solution was cooled to 20°C to recrystallize bisphenol A, and then the resulting slurry was vacuum filtered at 20°C to recover bisphenol A (BPA) crystals.

[0233] (8. Drying Step) Thereafter, the resultant was vacuum dried in a convection oven at 100° C. to prepare a recycled bisphenol A monomer composition in which recycled bisphenol A (BPA) had been recovered.

[0234] Comparative Example 1

[0235] A regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1, except that (6-1. Additional purification step - redissolution step) and (6-2. Additional purification step - recrystallization step) of Example 1 were not performed.

[0236] Comparative Example 2

[0237] A regenerated bisphenol A monomer composition was prepared in the same manner as in Example 3, except that (7-1. Additional purification step - re-dissolution step) and (7-2. Additional purification step - recrystallization step) of Example 3 were not performed.

[0238] <Experimental example>

[0239] The physical properties of the recycled bisphenol A monomer compositions obtained in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

[0240] 1. BPA Purity

[0241] After the regenerated bisphenol A monomer composition was dissolved in a methanol solvent at a concentration of 0.5 mg / mL under normal pressure and 20-30° C., a syringe filter (0.45 μm) was used to remove solid impurities in the solution, and then Capcell PakC18 (inner diameter 4.6 mm, length 50 mm, particle size 5 μm) was used to analyze the purity of bisphenol A (BPA) via UPLC (ultra-high performance liquid chromatography) of a Waters HPLC system. Specifically, the peak area ratio (unit: %) of bisphenol A (BPA) was measured relative to 100% of the total UPLC peak area.

[0242] The specific UPLC measurement conditions are as follows.

[0243] ① Column: Capcell Pak C18 (4.6mm ID x 50mm L, 5μm), ② Column temperature: 40°C, ③ Injection volume: 10μL, ④ Mobile phase: 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

[0244] 2. The proportion of impurities

[0245] UPLC analysis was performed in the same manner as the method for measuring 1. BPA purity, and the peak area ratio (unit: %) of BPA derivatives [monoethyl carbonate of bisphenol A (MEBPA; ethyl (4-(2-(4-hydroxyphenyl)propan-2-yl)phenyl) carbonate), diethyl carbonate of bisphenol A (BEBPA; diethyl (propane-2,2-diylbis(4,1-phenylene))bis(carbonate)), bisphenol A dimer (BPA dimer)] impurities relative to 100% of the total UPLC peak area was measured according to the following equation A.

[0246] [Equation A]

[0247] Ratio of BPA derivative impurities (%) = (peak area of ​​bisphenol A derivative measured by liquid chromatography / total peak area measured by liquid chromatography) × 100

[0248] In equation 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.

[0249] 3.APHA Color

[0250] For the recycled bisphenol A monomer composition, solid impurities in the solution were removed using a syringe filter (0.45 μm), and then measured using a Hunterlab UltraScan PRO model device in the same manner as in ASTM D1209.

[0251] 4. Melting point

[0252] The melting point (T) of the recycled bisphenol A monomer composition was measured from a temperature versus heat flow curve obtained using a differential scanning calorimeter (device name: DSC2920, manufacturer: TA Instruments) in a temperature range of 0 to 180° C. at a heating rate of 10° C. / min. m The melting point (T) is obtained by peak analysis of the thermal curve of the heat flow during the first temperature increase. m ), and three measurements were performed on each sample and the average value was taken.

[0253] [Table 1]

[0254] Experimental results

[0255]

[0256] As shown in Table 1, the recycled bisphenol A monomer compositions obtained in Examples 1 to 3 exhibited high purity of 99.75% to 99.91% and had a high melting point of 156.5° C. to 156.9° C. In addition, 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%.

[0257] On the other hand, the regenerated bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 have a purity of 98.82% to 99.57%, which is lower than that of the examples, and a melting point of 154.8° C. to 156.3° C., which is lower than that of the examples. In addition, the BPA derivative impurity ratio was measured to be 0.35% to 0.95%, which is higher than that of the examples.

Claims

1. A monomer composition for synthesizing recycled plastics, comprising an aromatic diol compound, in, The ratio of the impurities of the aromatic diol compound derivative according to the following equation 1 is 0.3% or less, Wherein, the melting point of the monomer composition is above 156.4°C, and Wherein, the monomer composition is recovered from a polycarbonate resin: [Equation 1] Ratio (%) of aromatic diol compound derivative impurities=(peak area of ​​aromatic diol compound derivative measured by liquid chromatography / total peak area measured by liquid chromatography)×100.

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

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

4. The monomer composition for synthesizing recycled plastics according to claim 2, wherein: According to the following equation 3, the ratio of the bisphenol A dimer is 0.3% or less: [Equation 3] Ratio (%) 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 plastic has an APHA color value of 60 or less measured according to ASTM D 1209.

6. The monomer composition for synthesizing recycled plastics according to claim 1, wherein: The monomer composition for synthesizing recycled plastics has a purity of 99.6% or more of aromatic diol compounds.

7. A method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: Depolymerizing a polycarbonate resin; separating carbonate compounds from the depolymerization reaction product; dissolving the depolymerization reaction product from which carbonate compounds have been separated in a solvent containing the separated carbonate compounds; as well as The aromatic diol compound is recrystallized from the dissolved solution.

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

9. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, wherein: wherein the depolymerization reaction product from which the carbonate compound has been separated is dissolved in a solvent containing the separated carbonate compound, The solvent containing the carbonate-based compound is added in an amount of 10 parts by weight or more based on 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. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, wherein: In the step of recrystallizing the aromatic diol compound from the dissolved solution, The concentration of the aromatic diol compound contained in the solution is 90% by weight or less.

11. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, wherein: The recrystallizing the aromatic diol compound from the dissolved solution includes cooling the dissolved solution.

12. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, wherein: 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 are repeated two or more times.

13. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, further comprising: Between separating the carbonate compounds from the depolymerization reaction product and dissolving the depolymerization reaction product from which the carbonate compounds have been separated in a solvent containing the separated carbonate compounds, an adsorbent is added to the depolymerization reaction product from which the carbonate compounds have been separated for adsorption purification, and then the adsorbent is removed.

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

15. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 14, wherein: The amount of the alcohol is 10 mol to 15 mol relative to 1 mol of the polycarbonate-based resin.

16. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, wherein: The carbonate compound includes dialkyl carbonate or diaryl carbonate.

17. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, further comprising: Between separating the carbonate compounds from the depolymerization reaction product and dissolving the depolymerization reaction product from which the carbonate compounds have been separated in a solvent containing the separated carbonate compounds, the depolymerization reaction product from which the carbonate compounds have been separated is washed.

18. A method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: Depolymerizing a polycarbonate resin; dissolving the depolymerization reaction product in a solvent containing a carbonate compound; and The aromatic diol compound is recrystallized from the dissolved solution.

19. A recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic according to claim 1 and a comonomer.

20. A molded article comprising the recycled plastic according to claim 19.

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