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

Abstract

The present invention relates to a monomer composition for synthesizing recycled plastics, which can achieve excellent color quality and improve the efficiency of the recovery process even though the polycarbonate resin is recovered by recycling through chemical decomposition, a method for producing the same, and recycled plastics and molded articles using the same.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0151487 filed on November 14, 2022 and Korean Patent Application No. 10-2023-0067219 filed on May 24, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a monomer composition for synthesizing recycled plastics, which can achieve excellent color quality and improve the efficiency of the recovery process even though the polycarbonate resin is recovered by recycling through chemical decomposition, a method for producing the same, and recycled plastics and molded articles using the same. [Background technology]

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

[0004] Polycarbonate is used widely for various purposes, but environmental and health concerns have been continuously raised regarding its disposal.

[0005] So far, physical recycling methods have been used, but problems with quality degradation have arisen in this case, and research is underway into chemical recycling of polycarbonate.

[0006] Chemical decomposition of polycarbonate refers to the process of obtaining aromatic diol monomers (e.g., bisphenol A (BPA)) by decomposing polycarbonate, and then using these monomers in polymerization to obtain high-purity polycarbonate.

[0007] Representative examples of such chemical decomposition include pyrolysis, hydrolysis, and alcoholysis. Among these, the most common method is alcoholysis using a base catalyst, but methanolysis has the problem of using methanol, which is harmful to the human body, and ethanol requires high temperature and pressure conditions, resulting in a low yield.

[0008] In addition, an alcohol decomposition method using an organic catalyst is known, but it currently has economic disadvantages. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a monomer composition for synthesizing recycled plastics, which can achieve excellent color quality despite being recovered by recycling through chemical decomposition of polycarbonate-based resins, and improves the efficiency of the recovery process.

[0010] The present invention also provides a method for producing the monomer composition for synthesizing recycled plastics, and a recycled plastic and a molded article using the monomer composition for synthesizing recycled plastics. [Means for solving the problem]

[0011] In order to solve the above problems, the present specification provides a monomer composition for synthesizing recycled plastics, which comprises an aromatic diol compound, has a color coordinate b* of 1.8 or less, and has an APHA Color value of 30 or less as measured by ASTM D 1209, and is recovered from a polycarbonate resin.

[0012] The present specification also provides a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate-based resin; separating a carbonate precursor from the depolymerized reaction product; and purifying the depolymerized reaction product from which the carbonate precursor has been separated, the method including: introducing a hydrophilic reducing agent into the depolymerized reaction product from which the carbonate precursor has been separated; and introducing an adsorbent into the depolymerized reaction product from which the carbonate precursor has been separated to perform adsorption purification, and then removing the adsorbent.

[0013] Also provided herein is a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic and a comonomer.

[0014] Also provided herein is a molded article comprising the recycled plastic.

[0015] Hereinafter, a monomer composition for synthesizing recycled plastics according to specific embodiments of the present invention, a method for producing the same, and recycled plastics and molded articles using the same will be described in more detail.

[0016] In this specification, unless expressly stated otherwise, the terminology used is for the purpose of referring to particular embodiments only and is not intended to be limiting of the invention.

[0017] As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates to the contrary.

[0018] As used herein, the meaning of "comprising" is to embody certain features, regions, integers, steps, operations, elements, components and / or components, and does not exclude the presence or addition of other certain features, regions, integers, steps, operations, elements, components and / or groups.

[0019] In this specification, terms including ordinal numbers such as "first" and "second" are used for the purpose of distinguishing one component from another component, and are not limited by the ordinal number. For example, within the scope of the present invention, a first component may be named a second component, and similarly, a second component may be named a first component.

[0020] 1. Monomer composition for synthesis of recycled plastics According to one embodiment of the invention, there is provided a monomer composition for synthesizing recycled plastics, which comprises an aromatic diol compound, has a color coordinate b* of 1.8 or less, and has an APHA Color value of 30 or less as measured by ASTM D 1209, and is recovered from a polycarbonate resin.

[0021] The present inventors have confirmed through experiments that the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention is recovered by recycling polycarbonate-based resins through chemical decomposition, and that the aromatic diol compound, which is the main target of recovery, can achieve excellent color quality, and that excellent physical properties can be achieved when polycarbonate-based resins are synthesized using the aromatic diol compound, thereby completing the invention.

[0022] In particular, the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention can reduce the amount of organic solvent used in the adsorption purification process and the amount of water used in the recrystallization process, which can be described later, and thus has the technical advantage of being able to achieve excellent color quality while improving process efficiency.

[0023] In addition, the present invention has the technical advantage that a first composition containing an aromatic diol compound can be obtained with high purity by recycling the polycarbonate-based resin through chemical decomposition, and at the same time, a second composition containing diethyl carbonate, which is a high-addition by-product, can be obtained.

[0024] Specifically, the monomer composition for synthesizing recycled plastics according to the embodiment is characterized in that it is recovered from a polycarbonate-based resin. That is, as a result of proceeding with recovery from a polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics according to the embodiment, a monomer composition for synthesizing recycled plastics containing an aromatic diol compound is also obtained.

[0025] The polycarbonate resin includes all homopolymers or copolymers containing polycarbonate repeating units, and is a general term for reaction products obtained by polymerization or copolymerization of monomers containing aromatic diol compounds and carbonate precursors. When it contains one type of carbonate repeating unit obtained by using only one aromatic diol compound and one carbonate precursor, a homopolymer can be synthesized. When it contains two or more carbonates by using one aromatic diol compound and two or more carbonate precursors, two or more aromatic diol compounds and one carbonate precursor, or one aromatic diol compound and one carbonate precursor as well as one or more other diols, a copolymer can be synthesized. The homopolymer or copolymer can include all low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0026] In addition, the monomer composition for synthesizing recycled plastics according to the embodiment may include an aromatic diol compound. Specific examples of the aromatic diol compound include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (bis Phenol Z), 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 of these. Preferably, the aromatic diol compound of the monomer composition for synthesizing recycled plastics of the embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0027] The aromatic diol compound is characterized by being recovered from the polycarbonate-based resin used in the recovery of the monomer composition for synthesizing recycled plastics. In other words, the aromatic diol compound is also obtained as a result of the recovery from the polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when a new aromatic diol compound is added from the outside in addition to the recovery from the polycarbonate-based resin to produce the monomer composition for synthesizing recycled plastics of the embodiment, it is not included in the category of aromatic diol compounds of the present invention.

[0028] Specifically, the term "recovered from the polycarbonate-based resin" means that the polycarbonate-based resin is obtained by depolymerization of the polycarbonate-based resin. The depolymerization can be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions. In particular, the depolymerization is preferably carried out in an ethanol solvent, as described below.

[0029] Meanwhile, the monomer composition for synthesizing recycled plastics according to one embodiment may have a color coordinate b* value of 1.8 or less, or 1.65 or less, or 0.1 or more, or 1.0 or more, or 0.1 to 1.8, or 1.0 to 1.8, or 0.1 to 1.65, or 1.0 to 1.65, or 1.6 to 1.7, or 1.6 to 1.65, or 1.65 to 1.7.

[0030] In addition, the monomer composition for synthesizing recycled plastics according to the embodiment may have a color coordinate L* of 95.5 or more, or 96 or more, or 100 or less, or 95.5 to 100, or 96 to 100, or 95.6 to 96.7, or 95.6 to 96, or 96 to 96.7.

[0031] Furthermore, the monomer composition for synthesizing recycled plastics according to the embodiment may have a color coordinate a* of -0.7 to -0.2, or -0.6 to -0.2, or -0.5 to -0.2, or -0.4 to -0.2, or -0.7 to -0.3, or -0.6 to -0.3, or -0.5 to -0.3, or -0.4 to -0.3, or -0.7 to -0.5, or -0.6 to -0.5.

[0032] In the present invention, "color coordinates" refers to coordinates in the CIE Lab color space, which are color values ​​defined by the CIE (Commission International de l'Eclairage), and any position in the CIE color space is expressed by three coordinate values: L*, a*, and b*.

[0033] Here, the L* value indicates brightness, with L* = 0 indicating black and L* = 100 indicating white. Additionally, the a* value indicates whether the color having the color coordinates is biased toward pure red or pure green, and the b* value indicates whether the color having the color coordinates is biased toward pure yellow or pure blue.

[0034] Specifically, the a* value ranges from -a to +a. The maximum value of a* (a*max) indicates pure red, and the minimum value of a* (a*min) indicates pure green. The b* value ranges from -b to +b. The maximum value of b* (b*max) indicates pure yellow, and the minimum value of b* (b*min) indicates pure blue. For example, if the b* value is a negative number, it means that the color is biased toward pure blue, and if it is a positive number, it means that the color is biased toward pure yellow. When comparing b*=50 and b*=80, it means that b*=80 is closer to pure yellow than b*=50.

[0035] If the color coordinate b* value of the monomer composition for synthesizing recycled plastics of the embodiment is excessively increased to more than 1.8, if the color coordinate L* value is excessively decreased to less than 95.5, or if the color coordinate a* value is deviated to more than -0.2 or less than -0.7, the color characteristics of the monomer composition for synthesizing recycled plastics of the embodiment are poor. Examples of methods for measuring the color coordinates L*, a*, and b* values ​​of the monomer composition for synthesizing recycled plastics of the embodiment are not greatly limited, and various methods for measuring color characteristics in the plastics field can be applied without limitation.

[0036] However, as an example of a method for measuring the color coordinates L*, a*, and b* values ​​of the monomer composition for synthesizing recycled plastics according to the embodiment, the values ​​can be measured in reflection mode using a HunterLab UltraScan PRO Spectrophotometer device.

[0037] Meanwhile, the monomer composition for synthesizing recycled plastics according to one embodiment may have an APHA Color value measured by ASTM D 1209 of 30 or less, or 29 or less, or 28 or less, or 25 or less, or 22 or less, or 0 or more, or 1 or more, or 0 to 30, or 0 to 29, or 0 to 28, or 0 to 25, or 0 to 22, or 1 to 30, or 1 to 29, or 1 to 28, or 1 to 25, or 1 to 22, or 22 to 28, or 22 to 25, or 25 to 28.

[0038] The method for measuring the APHA Color of the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited. For example, the APHA Color can be measured by the ASTM D 1209 measurement method using a HunterLab UltraScan PRO Spectrophotometer.

[0039] APHA Color is a value obtained by comparing the color of colorless water with a yellow PtCo solution, and the closer the value is to 0, the more colorless the color is, and the closer the value is to 500, the more yellow the color is. Therefore, since the APHA Color of the monomer composition for synthesizing recycled plastics according to one embodiment is reduced to 30 or less, transparent color properties can be achieved when synthesizing polycarbonate-based resin using the same.

[0040] On the other hand, if the APHA Color of the monomer composition for synthesizing recycled plastics according to the embodiment is excessively increased, such as exceeding 30, there is a limitation in that it becomes difficult to synthesize a colorless and transparent polycarbonate-based resin due to yellowing.

[0041] Meanwhile, the monomer composition for synthesizing recycled plastics according to the embodiment may further include a hydrophilic reducing agent. The hydrophilic reducing agent is soluble in water and can be used as a bleaching agent that changes colored materials to remove color. Examples of the hydrophilic reducing agent are not particularly limited, and various conventionally known hydrophilic reducing bleaching agents can be used without limitation, one example of which is sodium dithionite (SDT).

[0042] Meanwhile, in the monomer composition for synthesizing recycled plastics according to the embodiment, diethyl carbonate is obtained as a by-product. The diethyl carbonate is recovered from the polycarbonate-based resin used in recovering the monomer composition for synthesizing recycled plastics according to the embodiment.

[0043] In other words, diethyl carbonate is also obtained as a result of recovery from polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when new diethyl carbonate is added from outside in addition to recovery from polycarbonate-based resin to produce the monomer composition for synthesizing recycled plastics of the embodiment, it is not included in the category of diethyl carbonate of the embodiment.

[0044] Specifically, the term "recovered from the polycarbonate-based resin" means that the polycarbonate-based resin is obtained by depolymerization of the polycarbonate-based resin. The depolymerization can be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions. In particular, the depolymerization is preferably carried out in an ethanol solvent, as described below.

[0045] Since the main target material for recovery in the monomer composition for synthesizing recycled plastics of the embodiment is an aromatic diol compound, the diethyl carbonate can be separated and recovered as a by-product from the monomer composition for synthesizing recycled plastics of the embodiment.

[0046] The monomer composition for synthesizing recycled plastics according to one embodiment can be used as a raw material for producing various recycled plastics (e.g., polycarbonate (PC)) as described below.

[0047] The monomer composition for synthesizing recycled plastics according to one embodiment may further include a small amount of other additives and solvents. The specific types of additives and solvents are not particularly limited, and various substances that are widely used in the process of recovering aromatic diol compounds by depolymerization of polycarbonate-based resins may be used without limitation.

[0048] The monomer composition for synthesizing recycled plastics according to the embodiment may be obtained by a method for producing a monomer composition for synthesizing recycled plastics, which will be described later. That is, the monomer composition for synthesizing recycled plastics according to the embodiment corresponds to a resultant product obtained through various filtration, purification, washing, and drying processes in order to obtain only aromatic diol compounds, which are the main target substances for recovery, in high purity after the depolymerization reaction of polycarbonate-based resin.

[0049] 2. Manufacturing method of monomer composition for synthesis of recycled plastics According to another embodiment of the present invention, there is provided a method for producing a monomer composition for synthesizing recycled plastics, comprising: depolymerizing a polycarbonate-based resin; separating a carbonate precursor from the depolymerized reaction product; and purifying the depolymerized reaction product from which the carbonate precursor has been separated, the purifying step including: introducing a hydrophilic reducing agent into the depolymerized reaction product from which the carbonate precursor has been separated; and introducing an adsorbent into the depolymerized reaction product from which the carbonate precursor has been separated to perform adsorption purification, and then removing the adsorbent.

[0050] The present inventors have confirmed through experiments that, as in the method for producing a monomer composition for synthesizing recycled plastics according to the other embodiment, by including a hydrophilic reducing agent injection process and an adsorption purification process using an adsorbent in the process of recycling a polycarbonate-based resin by chemical decomposition, the amount of organic solvent used in the adsorption purification process can be reduced, thereby improving process efficiency and achieving excellent color quality, and thus completed the invention.

[0051] Specifically, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a step of pretreating the polycarbonate-based resin prior to the step of depolymerizing the polycarbonate-based resin.

[0052] The polycarbonate resin includes all homopolymers or copolymers containing polycarbonate repeating units, and is a general term for reaction products obtained by polymerization or copolymerization of monomers containing aromatic diol compounds and carbonate precursors. When it contains one type of carbonate repeating unit obtained by using only one aromatic diol compound and one carbonate precursor, a homopolymer can be synthesized. When it contains two or more carbonates by using one aromatic diol compound and two or more carbonate precursors, two or more aromatic diol compounds and one carbonate precursor, or one aromatic diol compound and one carbonate precursor as well as one or more other diols, a copolymer can be synthesized. The homopolymer or copolymer can include all low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0053] The polycarbonate-based resin may be a new polycarbonate-based resin produced by synthesis, a recycled polycarbonate-based resin produced by a recycling process, or a waste polycarbonate-based resin, regardless of its various forms and types.

[0054] The efficiency of the process of recovering aromatic diol compounds and carbonate precursors from polycarbonate resins can be improved by carrying out the pretreatment process of the polycarbonate resin. Examples of the pretreatment process include filtration, washing, drying, pulverization, and glycol decomposition. The specific method of each pretreatment process is not limited, and various methods widely used in the process of recovering aromatic diol compounds and carbonate precursors by depolymerization of polycarbonate resins can be applied without limitation.

[0055] However, an example of the pretreatment step is a method of dissolving the polycarbonate resin in an organic solvent and then filtering the solution, the organic solvent including tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more of these.

[0056] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of depolymerizing a polycarbonate-based resin.

[0057] The depolymerization reaction of the polycarbonate resin may be carried out under acidic, neutral, or basic conditions, and may be carried out under basic (alkaline) conditions. The type of base is not particularly limited, and examples include sodium hydroxide (NaOH) and potassium hydroxide (KOH). The base is a base catalyst that acts as a catalyst, and has the advantage of being more economical than organic catalysts that are mainly used under mild conditions.

[0058] The depolymerization reaction of the polycarbonate-based resin can be carried out by reacting the base with a content 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-based resin. If the base is reacted with more than 0.5 mol relative to 1 mol of the polycarbonate-based resin, impurities increase due to the effect of an increase in the amount of alkaline salt generated, which reduces the purity of the target recovered material and reduces the economic efficiency of the catalytic reaction.

[0059] In addition, the depolymerization reaction of the polycarbonate resin is carried out in a solvent containing ethanol. The present invention has the advantage that the polycarbonate resin is decomposed in a solvent containing ethanol to stably obtain bisphenol A, which is a monomer with high purity, and diethyl carbonate, which has high added value, can be additionally obtained as a reaction by-product.

[0060] The content of the ethanol may be 5 to 15 mol, or 8 to 13 mol, relative to 1 mol of the polycarbonate-based resin. Since the ethanol has good solubility in bisphenol A, the ethanol content must be within the above range. If the content of the ethanol is excessively reduced to less than 5 mol relative to 1 mol of the polycarbonate-based resin, the alcoholysis of the polycarbonate-based resin is difficult to be sufficiently carried out. On the other hand, if the content of the ethanol is excessively increased to more than 15 mol relative to 1 mol of the polycarbonate-based resin, the economic efficiency of the process may be reduced due to the excessive use of alcohol.

[0061] The solvent in which the depolymerization reaction of the polycarbonate-based resin is carried out may further include at least one organic solvent selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate, in addition to ethanol.

[0062] The organic solvent may include tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0063] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent to be mixed with ethanol, there is an advantage that the dissolving property for polycarbonate is improved, and the reactivity can be improved.

[0064] The content of the organic solvent may be 16 to 20 moles, or 16 to 18 moles, relative to 1 mole of the polycarbonate resin. The content of the organic solvent may be 1.5 to 2 moles, relative to 1 mole of ethanol. By mixing the polycarbonate resin, ethanol and the organic solvent within the above ranges, there is an advantage that a required level of depolymerization reaction of the polymer is carried out.

[0065] Meanwhile, the temperature at which the depolymerization reaction of the polycarbonate-based resin proceeds is not particularly limited, but may be, for example, at 20° C. to 100° C., or 50° C. to 70° C. The time for which the depolymerization reaction of the polycarbonate-based resin proceeds may be 1 hour to 30 hours, or 4 hours to 6 hours.

[0066] Specifically, the above conditions are milder process conditions than the existing pressurized / high temperature process, and by performing stirring under the above conditions, the process can be performed in a milder process than the pressurized / high temperature process. In particular, stirring at 50°C to 70°C for 4 to 6 hours has the advantage of being able to obtain the most efficient results in terms of reproducibility and stability.

[0067] In other words, the present invention has the advantage that a high-purity aromatic diol compound (e.g., bisphenol A) can be obtained under mild conditions without using an organic catalyst and without using a pressurized / high-temperature process by adjusting the type and amount of the mixed solvent and the type and content of the base catalyst, and that diethyl carbonate can be obtained as a by-product by using an ethanol solvent.

[0068] More specifically, the step of depolymerizing the polycarbonate-based resin may include a first step of dissolving the carbonate-based resin in an organic solvent, and a second step of adding and stirring a catalyst solution containing ethanol and a base. The ethanol, organic solvent, base, and polycarbonate-based resin in the first and second steps are as described above.

[0069] In addition, the step of depolymerizing the polycarbonate-based resin may include the step of adding an antioxidant to a reactant containing the polycarbonate-based resin, whereby an aromatic diol compound obtained during the depolymerization of the polycarbonate-based resin is easily oxidized under basic conditions, and therefore an antioxidant may be added to the reaction solution.

[0070] The antioxidant may include one or more compounds selected from the group consisting of sodium dithionite (Na2S2O4, SDT), sodium metabisulfite (Na2S2O5), and sodium sulfite (Na2SO3). That is, the antioxidant may include one type of sodium dithionite (Na2S2O4, SDT), one type of sodium metabisulfite (Na2S2O5), one type of sodium sulfite (Na2SO3), or a mixture of two or more of these.

[0071] The amount of the antioxidant to be added is not particularly limited, but is, for example, 0.05% by weight to 4% by weight based on the weight of the polycarbonate resin. Within this range, there is an antioxidant effect, it is advantageous in terms of cost, and the decomposition reaction rate does not decrease.

[0072] The adsorbent may include one or more activated carbons selected from the group consisting of plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste material activated carbon.

[0073] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a step of neutralizing the depolymerization reaction product with an acid before the step of separating a carbonate precursor from the depolymerization reaction product.

[0074] For example, the alkaline decomposition product of the polycarbonate resin contains an aromatic diol compound or a salt thereof, and since the main target material of the present invention is the aromatic diol compound, the salt of the aromatic diol compound obtained by the alkaline decomposition can be converted to the aromatic diol compound by an additional neutralization process with an acid. That is, when the depolymerization reaction of the polycarbonate resin is alkaline decomposition, it can go through a neutralization reaction step with an acid.

[0075] The acid used in the neutralization reaction may be a strong acid, such as hydrochloric acid (HCl). The neutralization reaction using the strong acid can satisfy the pH of 4 or less, or less than 2, at the end of the neutralization reaction. The temperature during the neutralization reaction can be adjusted to 25°C or more and 100°C or less.

[0076] In addition, if necessary, after the neutralization step of the depolymerization reaction product with an acid, a process of removing remaining impurities by filtration or adsorption can be additionally performed. Specifically, the aqueous layer and the organic layer can be separated, and the organic layer can be filtered by vacuum filtration to recover a liquid containing the aromatic diol compound.

[0077] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include separating a carbonate precursor from the depolymerization reaction product. Thus, the separated carbonate precursor may include diethyl carbonate.

[0078] For example, the depolymerization reaction product of the polycarbonate resin includes an aromatic diol compound or a salt thereof, and a carbonate precursor. The content related to the aromatic diol compound and the carbonate precursor includes all of the content described above in the one embodiment.

[0079] The step of separating the carbonate precursor from the depolymerization reaction product may include a step of distilling the depolymerization reaction product under reduced pressure. Although the examples of the reduced pressure distillation conditions are not particularly limited, in a specific example, the polycarbonate-based resin may be distilled by reducing the pressure of the depolymerization reaction product under conditions of a pressure of 200 mbar to 300 mbar and a temperature of 20°C to 30°C, then reducing the pressure under conditions of a pressure of 50 mbar to 150 mbar and a temperature of 25°C to 35°C, and then reducing the pressure under conditions of a pressure of 10 mbar to 50 mbar and a temperature of 35°C to 45°C. Methylene chloride (MC) may be removed by distillation under conditions of a pressure of 200 mbar to 300 mbar and a temperature of 20°C to 30°C. Also, ethanol (EtOH) may be removed by distillation under conditions of a pressure of 50 mbar to 150 mbar and a temperature of 25°C to 35°C. Then, under reduced pressure conditions of 10 mbar to 50 mbar and a temperature of 35°C to 45°C, the carbonate precursor can be separated and recovered.

[0080] The separated carbonate precursor can be reused without a separate separation and purification process, or can be reused after, if necessary, separation and purification such as conventional extraction, adsorption, drying, etc. Specific purification conditions are not particularly limited, and various existing known purification techniques can be applied without limitation to specific purification devices and methods.

[0081] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to the other embodiment may include a purification step of the depolymerization reaction product from which the carbonate precursor is separated, thereby obtaining an aromatic diol compound, which is a main recovered material, and corresponds to the monomer composition for synthesizing recycled plastics according to the one embodiment.

[0082] Specifically, the step of purifying the depolymerization reaction product from which the carbonate precursor is separated may include the steps of: introducing a hydrophilic reducing agent into the depolymerization reaction product from which the carbonate precursor is separated; and introducing an adsorbent into the depolymerization reaction product from which the carbonate precursor is separated to perform adsorption purification, and then removing the adsorbent.

[0083] The order of the hydrophilic reducing agent introduction step and the adsorption purification step in the purification step is not particularly limited and may be performed in any order, but for example, the purification steps may be performed in the order of the hydrophilic reducing agent introduction step and the adsorption purification step. The hydrophilic reducing agent introduction step and the adsorption purification step may each be repeated at least once. Regarding the specific reducing agent introduction and adsorption device and method, various existing known purification techniques may be applied without any restrictions.

[0084] Meanwhile, before the step of adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor is separated, the method may further include a step of washing the depolymerization reaction product from which the carbonate precursor is separated.

[0085] Specifically, in the step of washing the depolymerization reaction product from which the carbonate precursor is separated, the depolymerization reaction product from which the carbonate precursor is separated may contain an aromatic diol compound. However, since various impurities remain during the recovery process for obtaining the aromatic diol compound, washing may be performed to sufficiently remove the impurities to obtain a high-purity aromatic diol compound.

[0086] Specifically, the washing step may include washing with a solvent at a temperature of 10° C. to 30° C., or 20° C. to 30° C.; and washing with a solvent at a temperature of 40° C. to 80° C., or 40° C. to 60° C., or 45° C. to 55° C. The temperature condition refers to the temperature inside a washing vessel where washing with a solvent is performed, and various heating devices can be used without limitation to maintain a high temperature that is higher than room temperature.

[0087] The washing step may be performed by first performing the step of washing with a solvent at a temperature of 10° C. to 30° C., and then performing the step of washing with a solvent at a temperature of 40° C. to 80° C. Alternatively, the step of washing with a solvent at a temperature of 40° C. to 80° C. may be performed first, and then performing the step of washing with a solvent at a temperature of 10° C. to 30° C.

[0088] More preferably, the washing step may be performed by first washing with a solvent at a temperature of 10° C. to 30° C., and then washing with a solvent at a temperature of 40° C. to 80° C. This can minimize corrosion of the reactor due to strong acid after the neutralization step.

[0089] The step of washing with a solvent at a temperature of 10° C. to 30° C. and the step of washing with a solvent at a temperature of 40° C. to 80° C. can each be repeated at least once.

[0090] In addition, if necessary, after the step of washing with a solvent at a temperature of 10°C to 30°C and the step of washing with a solvent at a temperature of 40°C to 80°C, a step of removing the remaining solvent by filtration can be additionally performed.

[0091] More specifically, the difference between the temperature in the step of washing with a solvent at a temperature of 40°C to 80°C and the temperature in the step of washing with a solvent at a temperature of 10°C to 30°C may be 20°C to 50°C.

[0092] The difference between the temperature in the step of washing with a solvent at a temperature of 40°C to 80°C and the temperature in the step of washing with a solvent at a temperature of 10°C to 30°C means a value obtained by subtracting the temperature in the step of washing with a solvent at a temperature of 10°C to 30°C from the temperature in the step of washing with a solvent at a temperature of 40°C to 80°C.

[0093] If the temperature difference between the step of washing with a solvent at a temperature of 40°C to 80°C and the step of washing with a solvent at a temperature of 10°C to 30°C is too low, such as less than 20°C, it is difficult to sufficiently remove impurities.

[0094] If the temperature difference between the step of washing with a solvent at a temperature of 40°C to 80°C and the step of washing with a solvent at a temperature of 10°C to 30°C is excessively increased to exceed 50°C, harsh conditions are formed in order to maintain the extreme temperature conditions, and the efficiency of the process may decrease.

[0095] The solvent used in the washing step may include one of water, alcohol, and organic solvents, such as tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more of these.

[0096] The solvent used in the washing step may be used in a weight ratio of 1 to 30 parts by weight, or 1 to 10 parts by weight, based on 1 part by weight of the polycarbonate-based resin used in the depolymerization reaction.

[0097] 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. As the organic solvent, methylene chloride can be preferably used. In this case, the organic solvent can be used in an amount of 1 part by weight to 10 parts by weight per part by weight of the polycarbonate resin.

[0098] The solvent used in the step of washing with a solvent at a temperature of 40° C. to 80° C. may be water. By using water, residual salt-type impurities can be effectively removed. In this case, the solvent can be used in an amount of 1 part by weight to 10 parts by weight per part by weight of the polycarbonate resin.

[0099] Meanwhile, the method may further include a re-dissolving step of adding a mixture of an organic solvent and an aqueous solvent to the depolymerization reaction product from which the carbonate precursor has been separated, prior to the step of adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated. By adding a mixture of an organic solvent and an aqueous solvent to the depolymerization reaction product from which the carbonate precursor has been separated, the aromatic diol compound crystals contained in the depolymerization reaction product from which the carbonate precursor has been separated can be re-dissolved in the mixture of an organic solvent and an aqueous solvent. An example of the organic solvent is ethanol, and an example of the aqueous solvent is water.

[0100] The order of the washing step and the re-dissolving step is not particularly limited and may be performed in any order, but for example, the purification step may be performed in the order of the washing step, the re-dissolving step, and the like. The washing step and the re-dissolving step may each be repeated at least once. Regarding specific washing and dissolving apparatuses and methods, various existing known purification techniques may be applied without any restrictions.

[0101] Specifically, the mixture of the organic solvent and the aqueous solvent may contain 15 wt% to 50 wt% of the organic solvent and 50 wt% to 85 wt% of the aqueous solvent based on the weight of the entire mixture. If the aqueous solvent is reduced to less than 50 wt% based on the weight of the entire mixture, the organic solvent is relatively excessively contained, which increases the process cost due to the use and recovery of the organic solvent, thereby reducing the process efficiency. On the other hand, if the aqueous solvent is increased to more than 85 wt% based on the weight of the entire mixture, the solubility of the carbonate precursor in the aromatic diol compound crystals contained in the separated depolymerization reaction product decreases, which makes it difficult to sufficiently redissolve the carbonate precursor.

[0102] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor is separated.

[0103] The hydrophilic reducing agent is soluble in water and can be used as a bleaching agent that removes color by changing colored substances, and thus, by adding the hydrophilic reducing agent, the colorless property of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor is separated can be enhanced.

[0104] The hydrophilic reducing agent is not particularly limited, and various conventionally known hydrophilic reducing bleaching agents can be used without limitation. One example is sodium dithionite (SDT).

[0105] In addition, based on the weight of the depolymerization reaction product from which the carbonate precursor is separated, the amount of the hydrophilic reducing agent added may be 0.1 wt% to 7 wt%, or 0.1 wt% to 6 wt%, or 0.1 wt% to 5 wt%, or 1 wt% to 7 wt%, or 1 wt% to 6 wt%, or 1 wt% to 5 wt%, or 3 wt% to 7 wt%, or 3 wt% to 6 wt%, or 3 wt% to 5 wt%, or 0.1 wt% to 3 wt%, or 1 wt% to 3 wt%.

[0106] The depolymerization reaction product from which the carbonate precursor is separated may contain an aromatic diol compound, that is, based on the weight of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor is separated, the amount of the hydrophilic reducing agent added may be 0.1 wt% to 7 wt%, or 0.1 wt% to 6 wt%, or 0.1 wt% to 5 wt%, or 1 wt% to 7 wt%, or 1 wt% to 6 wt%, or 1 wt% to 5 wt%, or 3 wt% to 7 wt%, or 3 wt% to 6 wt%, or 3 wt% to 5 wt%, or 0.1 wt% to 3 wt%, or 1 wt% to 3 wt%.

[0107] If the amount of the hydrophilic reducing agent is excessively increased, the hydrophilic reducing agent may not be fully dissolved or may have side reactions, making it difficult to fully achieve the effect of improving color characteristics.On the other hand, if the amount of the hydrophilic reducing agent is excessively decreased, it is difficult to fully achieve the effect of improving color characteristics by the hydrophilic reducing agent.

[0108] Meanwhile, in the step of adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated to perform adsorption purification and then removing the adsorbent, the adsorbent may be contacted with the depolymerization reaction product.

[0109] Examples of the adsorbent include activated carbon, charcoal, celite, or a mixture thereof. The activated carbon is a black carbon material having fine pores produced by subjecting a raw material to a carbonization process at about 500°C and an activated carbon process at about 900°C. Examples are not particularly limited, and various activated carbons such as plant-based, coal-based, petroleum-based, and waste-based activated carbons can be used without limitation depending on the type of raw material.

[0110] More specifically, examples of plant-based activated carbon include coconut activated carbon, wood activated carbon, and sawdust activated carbon. Examples of coal-based activated carbon include lignite activated carbon, smokeless coal activated carbon, and anthracite activated carbon. Examples of petroleum-based activated carbon include petroleum coke activated carbon and oil carbon activated carbon. Examples of waste activated carbon include synthetic resin activated carbon and pulp activated carbon.

[0111] The adsorbent may include one or more types of 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 second 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 of these.

[0112] More specifically, the adsorbent may include one or more activated carbons selected from the group consisting of coconut activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous activated carbon, i.e., the adsorbent may include coconut activated carbon, lignite activated carbon, anthracite activated carbon, bituminous activated carbon, or a mixture of two or more thereof.

[0113] In this way, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment of the present invention not only ensures high purity of aromatic diol compounds, which are the main synthesis target substances in the present invention, but also significantly reduces the content of impurities other than aromatic diol compounds, by applying an adsorption purification process using an adsorbent during the depolymerization reaction in which polycarbonate-based resins are reused by chemical decomposition.

[0114] The adsorption purification conditions using the adsorbent are not particularly limited, and various conventionally known adsorption purification conditions can be used without limitation. However, for example, the amount of the adsorbent added may be 40% by weight to 60% by weight relative to the polycarbonate resin, the adsorption time may be 0.1 hours to 5 hours, and the adsorption method may be stirring adsorption or a lab adsorption tower.

[0115] Meanwhile, the method may further include the steps of: introducing an adsorbent into the depolymerization reaction product from which the carbonate precursor is separated to perform adsorption purification; removing the adsorbent; and then recrystallizing the depolymerization reaction product from which the carbonate precursor is separated.

[0116] In the recrystallization step of the depolymerization reaction product from which the carbonate precursor is separated, various impurities contained in the depolymerization reaction product from which the carbonate precursor is separated can be sufficiently removed to obtain a high purity aromatic diol compound.

[0117] Specifically, the recrystallization step may include a step of adding a recrystallization solvent to the depolymerization reaction product from which the carbonate precursor has been separated to perform recrystallization. By adding a recrystallization solvent to the depolymerization reaction product from which the carbonate precursor has been separated to perform recrystallization, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product is increased, so that the impurities sandwiched between the crystals or between the crystals can be dissolved in the solvent to the maximum extent, and since the dissolved aromatic diol compound has poor solubility compared to the impurities, when the temperature is subsequently lowered, the aromatic diol compound can be easily precipitated as crystals due to the difference in solubility. The recrystallization solvent may be water.

[0118] More specifically, the recrystallization step of the depolymerization reaction product from which the carbonate precursor is separated may include adding 5 to 25 parts by weight of a recrystallization solvent to 1 part by weight of the aromatic diol compound contained in the depolymerization reaction product. If the recrystallization solvent is used too little, the temperature for dissolving the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor is separated becomes too high, resulting in poor process efficiency and making it difficult to remove impurities by recrystallization. On the other hand, if the recrystallization solvent is used too much, the solubility of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor is separated becomes too high, resulting in a reduced yield of the aromatic diol compound recovered after recrystallization, and the use of a large amount of solvent may reduce process efficiency.

[0119] If necessary, after the recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated, a step of removing remaining impurities by filtration or adsorption may be additionally performed.

[0120] In addition, if necessary, a drying step may be included after the recrystallization step. The residual solvent can be removed by the drying, and the specific drying conditions are not particularly limited, but the drying can be carried out at a temperature of, for example, 10° C. to 100° C., or 10° C. to 50° C. Regarding the specific drying device and method used in the drying, various existing known drying techniques can be applied without any restrictions.

[0121] 3. Recycled plastic According to yet another embodiment of the invention, there is provided a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic of the above embodiment and a comonomer.

[0122] The content of the monomer composition for synthesizing recycled plastics in the one embodiment includes all of the contents described above in the one embodiment and other embodiments.

[0123] The examples of the recycled plastics are not limited to those mentioned above, and various plastics synthesized using aromatic diol compounds such as bisphenol A as monomers can be used without limitation. A more specific example of the recycled plastics is polycarbonate resin.

[0124] The polycarbonate resin includes all homopolymers or copolymers containing polycarbonate repeating units, and is a general term for reaction products obtained by polymerization or copolymerization of monomers containing aromatic diol compounds and carbonate precursors. When it contains one type of carbonate repeating unit obtained by using only one aromatic diol compound and one carbonate precursor, a homopolymer can be synthesized. When it contains two or more carbonates by using one aromatic diol compound and two or more carbonate precursors, two or more aromatic diol compounds and one carbonate precursor, or one aromatic diol compound and one carbonate precursor as well as one or more other diols, a copolymer can be synthesized. The homopolymer or copolymer can include all low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0125] More specifically, in the recycled plastics containing the reaction product of the monomer composition for synthesizing recycled plastics and the comonomer of the embodiment, a carbonate precursor can be used as the comonomer. Specific examples of the carbonate precursor include phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl)carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis(diphenyl)carbonate, and bishaloformates.

[0126] The examples of the reaction process of the monomer composition for synthesis and the comonomer are not particularly limited, and various previously known methods for producing polycarbonates can be applied without any restrictions.

[0127] However, as an example of the method for producing the polycarbonate, a method for producing the polycarbonate may be used that includes a step of polymerizing a monomer composition for synthesizing recycled plastics and a composition containing a comonomer. In this case, the polymerization may be performed by interfacial polymerization, which allows the polymerization reaction at normal pressure and low temperature, and makes it easy to control the molecular weight.

[0128] The polymerization temperature may be 0° C. to 40° C., and the reaction time may be 10 minutes to 5 hours. The pH during the reaction may be maintained at 9 or more or 11 or more.

[0129] The solvent that can be used in the polymerization is not particularly limited as long as it is a solvent that is used in the polymerization of polycarbonates in the art. For example, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0130] The polymerization can be carried out in the presence of an acid binder, and as the acid binder, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an amine compound such as pyridine can be used.

[0131] Furthermore, during the polymerization, the polymerization can be carried out in the presence of a molecular weight regulator in order to regulate the molecular weight of the polycarbonate. As the molecular weight regulator, an alkylphenol having 1 to 20 carbon atoms can be used, and specific examples thereof include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol, or triacontylphenol. The molecular weight regulator can be added before, during, or after the initiation of polymerization. The molecular weight regulator can be used in an amount of 0.01 to 10 parts by weight, or 0.1 to 6 parts by weight, based on 100 parts by weight of the aromatic diol compound, and a desired molecular weight can be obtained within the range.

[0132] In addition, in order to accelerate the polymerization reaction, a reaction accelerator such as a tertiary amine compound, a quaternary ammonium compound, or a quaternary phosphonium compound, such as triethylamine, tetra-n-butylammonium bromide, or tetra-n-butylphosphonium bromide, may be additionally used.

[0133] 4. Molded products According to yet another embodiment of the present invention, there is provided a molded product comprising the recycled plastic of the other embodiment. The content relating to the recycled plastic includes all of the content described above in the other embodiment.

[0134] The molded product may be obtained by subjecting the recycled plastic to various known plastic molding methods without limitation, and examples of the molding methods include injection molding, foam injection molding, blow molding, and extrusion molding.

[0135] The examples of the molded products are not particularly limited, and the molded products can be applied to various molded products using plastics without any restrictions. Examples of the molded products include automobile parts, electric and electronic products, communication products, daily necessities, building materials, optical parts, exterior materials, etc.

[0136] The molded article may further contain, in addition to the recycled plastic of the other embodiment, one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact modifiers, fluorescent brighteners, ultraviolet absorbers, pigments, and dyes, as necessary.

[0137] As an example of a method for manufacturing the molded product, the method may include thoroughly mixing the recycled plastic of the other embodiment and an additive using a mixer, extruding the mixture in an extruder to prepare pellets, drying the pellets, and then injecting the pellets in an injection molding machine. Effect of the Invention

[0138] According to the present invention, there are provided a monomer composition for synthesizing recycled plastics, which can achieve excellent color quality despite being recovered by recycling polycarbonate-based resins through chemical decomposition and improve the efficiency of the recovery process, a method for producing the same, and recycled plastics and molded articles using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0139] The present invention will be described in more detail with reference to the following examples, however, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0140] <Examples, Comparative Examples, and Reference Examples: Production of Recycled Bisphenol A Monomer Composition> Example 1 (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of methylene chloride (MC), and then added to a 3L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH). 2.5 g (1% by weight based on the weight of PC) of sodium dithionite (Na2S2O4, SDT) was added, and the mixture was stirred at 60°C for 6 hours to carry out the PC depolymerization reaction.

[0141] (2. Neutralization Step) The product of the depolymerization reaction was cooled to below 30°C and neutralized at 20 to 30°C using 0.25 mol of 10% hydrochloric acid (HCl).

[0142] (3. Distillation step) Then, methylene chloride (MC) was distilled off at 250 mbar and 20°C, ethanol (EtOH) was distilled off at 80 mbar and 30°C, and the by-product diethyl carbonate (DEC) was recovered by vacuum distillation at 30 mbar and 40°C.

[0143] (4. Washing step) After removing diethyl carbonate (DEC), the residue was washed with methylene chloride (MC) in an amount equal to 1 part by weight of the PC used at 20-30°C and vacuum filtered. The filtrate was washed with water in an amount equal to 1 part by weight of the PC used at 50°C for the second time.

[0144] (5. Redissolving step) 6 g of the washed bisphenol A was redissolved in 15 g of ethanol and 15 g of water at room temperature.

[0145] (6. Reducing agent addition step) Then, 0.06 g (1% by weight based on the weight of bisphenol A) of sodium dithionite (Na2S2O4, SDT) was added to the solution and dissolved.

[0146] (7. Adsorption step) Then, 3 g of lignite activated carbon was added to the solution as an adsorbent and stirred for 10 minutes. After that, the activated carbon was primarily removed using a sieve filter (75 μm), and the remaining activated carbon was secondary removed using a syringe filter (0.45 μm).

[0147] (8. Recrystallization step) After that, the mixture was stirred and 75 g of water was gradually added to recrystallize bisphenol A, and then a solid was obtained by filtration.

[0148] (9. Drying step) Then, the mixture was dried in a vacuum oven at 30 to 50° C. to prepare a recycled bisphenol A monomer composition.

[0149] (Example 2, Comparative Examples 1-2, Reference Examples 1-2) The recycled bisphenol A monomer compositions of Example 2, Comparative Examples 1-2, and Reference Examples 1-2 were prepared in the same manner as in Example 1, except that the process conditions were changed as shown in Table 1 below.

[0150] [Table 1]

[0151] <Experimental Example> The properties of the recycled bisphenol A monomer compositions obtained in the above Examples, Comparative Examples and Reference Examples were measured by the following methods. The results are shown in Table 2.

[0152] 1. APHA Color The recycled bisphenol A monomer composition was measured using a HunterLab UltraScan PRO Spectrophotometer instrument according to the ASTM D 1209 measurement method.

[0153] 2. Color coordinates (L*, a*, b*) The recycled bisphenol A monomer composition was measured using a HunterLab UltraScan PRO Spectrophotometer instrument in reflectance mode.

[0154] [Table 2]

[0155] As shown in Table 2, the recycled bisphenol A monomer compositions obtained in Examples 1 and 2 exhibited excellent optical properties, with color coordinates L* of 95.6 to 96.7, a* of -0.6 to -0.3, b* of 1.6 to 1.7, and APHA Color values ​​of 22 to 28. In contrast, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 to 3 exhibited color coordinates L* of 94.8 to 96.1, a* of 0 to 1.5, b* of 2.0 to 5.0, and APHA Color values ​​of 34 to 100, showing poor optical properties compared to the Examples.

[0156] Meanwhile, the recycled bisphenol A monomer composition obtained in Reference Example 1 exhibited optical properties similar to those of the Examples. However, in order to achieve this, as shown in Table 1, an excess of water (180 g) had to be used in the recrystallization step, resulting in reduced process efficiency.

[0157] In addition, the recycled bisphenol A monomer composition obtained in Reference Example 2 had a color coordinate b* of 3.0 and an APHA Color value of 44, and thus exhibited poor optical properties compared to the Examples.

Claims

1. Contains an aromatic diol compound, The color coordinate b* is 1.8 or less, APHA Color value as measured by ASTM D 1209 is 30 or less; A monomer composition for use in synthesizing recycled plastics, which is recovered from polycarbonate resin.

2. The monomer composition for synthesizing recycled plastics according to claim 1, wherein the monomer composition for synthesizing recycled plastics has a color coordinate L* of 95.5 or more.

3. The monomer composition for synthesizing recycled plastics according to claim 1, wherein the monomer composition for synthesizing recycled plastics has a color coordinate a* of -0.7 to -0.

2.

4. The monomer composition for synthesizing recycled plastics according to claim 1 , wherein the aromatic diol compound comprises bisphenol A.

5. The monomer composition for synthesizing recycled plastics according to claim 1, wherein the aromatic diol compound is recovered from a polycarbonate resin.

6. The monomer composition for synthesizing recycled plastics according to claim 1 , further comprising a hydrophilic reducing agent.

7. A step of depolymerizing the polycarbonate-based resin; separating a carbonate precursor from the depolymerization reaction product; and purifying the depolymerization reaction product from which the carbonate precursor has been separated; The purification step of the depolymerization reaction product from which the carbonate precursor has been separated includes: adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated; and and removing the adsorbent from the depolymerization reaction product from which the carbonate precursor has been separated.

8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the hydrophilic reducing agent is sodium dithionite.

9. 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the amount of the hydrophilic reducing agent added is 0.1% by weight to 7% by weight based on the weight of the depolymerization reaction product from which the carbonate precursor is separated.

10. before adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated, The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, further comprising a redissolving step of adding a mixture of an organic solvent and an aqueous solvent to the depolymerization reaction product from which the carbonate precursor has been separated.

11. The mixture is The method for producing a monomer composition for synthesizing recycled plastics according to claim 10, comprising 15% to 50% by weight of an organic solvent and 50% to 85% by weight of an aqueous solvent, based on the weight of the entire mixture.

12. The step of depolymerizing the polycarbonate-based resin includes:

8. The method of claim 7, further comprising adding an antioxidant to the reactants containing the polycarbonate resin.

13. The method for producing a monomer composition for synthesizing recycled plastics according to claim 12, wherein the antioxidant comprises one or more compounds selected from the group consisting of sodium dithionite, sodium metabisulfite, and sodium sulfite.

14. before adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated, The method further comprises a step of washing the depolymerization reaction product from which the carbonate precursor has been separated, The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, wherein the washing step includes washing with a solvent at a temperature of 10°C to 30°C; and washing with a solvent at a temperature of 40°C to 80°C.

15. The depolymerization reaction of the polycarbonate resin is 8. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, characterized in that the reaction proceeds in a solvent containing ethanol.

16. separating a carbonate precursor from the depolymerization reaction product, The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, further comprising a step of vacuum distillation of the depolymerization reaction product.

17. The depolymerization reaction product from which the carbonate precursor has been separated is purified by adding an adsorbent, and then removing the adsorbent. The method for producing a monomer composition for synthesizing recycled plastics according to claim 7, further comprising: a recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated.

18. The recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated includes:

18. The method for producing a monomer composition for synthesizing recycled plastics according to claim 17, further comprising adding 5 to 25 parts by weight of a recrystallization solvent based on 1 part by weight of an aromatic diol compound contained in the depolymerization reaction product.

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

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

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