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

Abstract

The present invention relates to a monomer composition for synthesizing recycled plastics, which contains a high-purity aromatic diol compound recovered by recycling polycarbonate resins through chemical decomposition, a method for producing the same, and recycled plastics and molded articles made from the same.

Description

[Technical field]

[0001] [Cross-reference to related applications] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0122001 dated September 13, 2021, Korean Patent Application No. 10-2021-0122002 dated September 13, 2021, Korean Patent Application No. 10-2021-0122003 dated September 13, 2021, Korean Patent Application No. 10-2021-0122004 dated September 29, 2021, Korean Patent Application No. 10-2021-0128892 dated September 29, 2021, and Korean Patent Application No. 10-2021-0136153 dated October 13, 2021, and all contents disclosed in the documents of these Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a monomer composition for synthesizing recycled plastics, which contains a high-purity aromatic diol compound recovered by recycling polycarbonate resins through chemical decomposition, a method for producing the same, and recycled plastics and molded articles each using the same.

[0003] The present invention also relates to a monomer composition for synthesizing recycled plastics, which contains high-value-added by-products recovered by recycling polycarbonate resins through chemical decomposition, a method for producing the same, and recycled plastics and molded articles using the same. [Background technology]

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

[0005] Although polycarbonate is widely used for a variety of purposes, environmental and health concerns have been continually raised regarding its disposal.

[0006] Currently, physical recycling methods are used, but these have caused problems with quality degradation, and research is underway into chemical recycling of polycarbonate.

[0007] 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.

[0008] 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.

[0009] In addition, although an alcohol decomposition method using an organic catalyst is known, it has a drawback in terms of economics. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention provides a monomer composition for synthesizing recycled plastics, which can ensure a high-purity aromatic diol compound recovered by recycling polycarbonate resins through chemical decomposition.

[0011] The present invention also provides a method for producing the monomer composition for synthesizing recycled plastics, and recycled plastics and molded articles using the monomer composition for synthesizing recycled plastics. [Means for solving the problem]

[0012] 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 L* of 94 or more, and a color coordinate b* of 0 to 4.2, and is recovered from a polycarbonate resin.

[0013] The present specification also provides a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate-based resin; introducing a first adsorbent into the depolymerized reaction product to purify the depolymerized reaction product by adsorption, and then removing the first adsorbent; separating a carbonate precursor from the depolymerized reaction product; and purifying the depolymerized reaction product from which the carbonate precursor has been separated, the step of purifying the depolymerized reaction product from which the carbonate precursor has been separated comprising introducing a second adsorbent into the depolymerized reaction product from which the carbonate precursor has been separated to purify the depolymerized reaction product by adsorption, and then removing the second adsorbent.

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

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

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

[0017] Unless otherwise expressly stated herein, the terminology used is for the purpose of referring to particular embodiments only and is not intended to be limiting of the invention.

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

[0019] As used herein, "comprising" means embodying certain properties, regions, integers, steps, operations, elements, components and / or components, and does not exclude the presence or addition of other certain properties, regions, integers, steps, operations, elements, components and / or groups.

[0020] 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.

[0021] 1. Monomer composition for synthesizing recycled plastics According to one embodiment of the present invention, there is provided a monomer composition for synthesizing recycled plastics, which comprises an aromatic diol compound, has a color coordinate L* of 94 or more, and a color coordinate b* of 0 to 4.2, and is recovered from a polycarbonate resin.

[0022] 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 content of impurities other than the aromatic diol compound, which is the main target of recovery, is extremely reduced, and that by using this to synthesize polycarbonate-based resins, excellent physical properties can be achieved, thereby completing the invention.

[0023] In particular, a monomer composition for synthesizing recycled plastics (second composition) containing diethyl carbonate and recovered from polycarbonate-based resins together with the monomer composition for synthesizing recycled plastics (first composition) of the one embodiment can be obtained simultaneously by a method for producing a monomer composition for synthesizing recycled plastics described below.

[0024] In other words, the present invention has the technical advantage of being able to obtain a first composition containing an aromatic diol compound with high purity by recycling a polycarbonate-based resin through chemical decomposition, while also being able to obtain a second composition containing diethyl carbonate, which is a by-product with high added value.

[0025] 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 performing 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.

[0026] The polycarbonate-based resin includes both homopolymers and copolymers containing polycarbonate repeating units, and is a general term for reaction products obtained by polymerization or copolymerization of monomers including aromatic diol compounds and carbonate precursors. When one type of carbonate repeating unit is contained, obtained by using only one type of aromatic diol compound and one type of carbonate precursor, a homopolymer can be synthesized. In addition, when one type of aromatic diol compound and two or more types of carbonate precursors are used as the monomers, or when two or more types of aromatic diol compounds and one type of carbonate precursor are used, or when two or more types of carbonates are contained by using one type of aromatic diol compound, one type of carbonate precursor, and 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.

[0027] In addition, the monomer composition for synthesizing recycled plastics (first composition) of the embodiment may contain 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 (bisphenol A), and bis(4-hydroxyphenyl)cyclohexane (bisphenol B). Bisphenol 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 (first composition) for synthesizing recycled plastics of the embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0028] 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. That is, the aromatic diol compound is also obtained as a result of recovery using a polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when a new aromatic diol compound is added externally apart from recovery using a 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.

[0029] 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 may be carried out under acidic, neutral, or basic conditions, and may be carried out under basic (alkaline) conditions. In particular, the depolymerization is preferably carried out in an ethanol solvent, as described below.

[0030] Meanwhile, the monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate b* value of 0 to 4.2, or 1.0 to 4.2, or 2 to 4.2, or 2.1 to 4.2. The monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate L* of 94 or more, or 100 or less, or 94 to 100, or 94 to 97. The monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate a* of 0.5 or less, or -0.1 or more, or -0.1 to 0.5, or -0.05 to 0.5.

[0031] In the present invention, "color coordinates" refers to coordinates in the CIE Lab color space, which is a hue value defined by the CIE (Commission International de l'Eclairage), and any position in the CIE color space can be expressed by three coordinate values: L*, a*, and b*.

[0032] Here, the L* value indicates brightness, with L* = 0 indicating black and L* = 100 indicating white. In addition, the a* value indicates whether the color having the corresponding color coordinates is biased toward pure red or pure green, and the b* value indicates whether the color having the corresponding color coordinates is biased toward pure yellow or pure blue.

[0033] 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, a negative b* value indicates a hue biased toward pure blue, and a positive b* value indicates a hue biased toward pure yellow. Comparing b*=50 and b*=80, this means that b*=80 is closer to pure yellow than b*=50.

[0034] If the color coordinate b* value of the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention is excessively increased to more than 4.2 or the color coordinate L* value is excessively decreased to less than 94, the color characteristics of the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention will be poor.

[0035] Specifically, when the color coordinate b* value of the monomer composition for synthesizing recycled plastics according to one embodiment is excessively increased to exceed 4.2, the hue of the monomer composition for synthesizing recycled plastics according to one embodiment is excessively biased toward yellow, resulting in poor color characteristics.

[0036] In addition, if the color coordinate b* value of the monomer composition for synthesizing recycled plastics of the embodiment is excessively decreased to less than 0, the hue of the monomer composition for synthesizing recycled plastics of the embodiment is excessively blue-biased, resulting in poor color characteristics.

[0037] The method for measuring the color coordinates L*, a*, b* values ​​of the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and various methods for measuring color characteristics in the plastics field can be used without limitation.

[0038] However, as an example of a method for measuring the color coordinates L*, a*, b* values ​​of the monomer composition for synthesizing recycled plastics according to the embodiment, the color coordinates can be measured in reflection mode using a HunterLab UltraScan PRO Spectrophotometer.

[0039] Meanwhile, in the monomer composition for synthesizing recycled plastics of the embodiment, the purity of the aromatic diol compound may be 99% or more, or 100% or less, or 99% to 100%, or 99% to 99.9%, or 99% to 99.8%, or 99% to 99.7%.

[0040] The method for measuring the purity of the aromatic diol compound in the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and may be, for example, 1 H NMR, ICP-MS analysis, HPLC analysis, UPLC analysis, etc. can be used without limitation. Specific methods, conditions, equipment, etc. of the NMR, ICP-MS, HPLC, and UPLC can be various conventional methods without limitation.

[0041] As an example of a method for measuring the purity of the aromatic diol compound of the monomer composition for synthesizing recycled plastics according to one embodiment, the monomer composition for synthesizing recycled plastics according to one embodiment was dissolved in an acetonitrile (ACN) solvent at 1 wt % under normal pressure and 20 to 30° C. conditions, and the purity of bisphenol A (BPA) was analyzed using UPLC (ultra performance liquid chromatography) with a Waters HPLC system using an ACQUITY UPLC (registered trademark) BEH C18 1.7 μm (2.1*50 mm column).

[0042] In this way, in the monomer composition for synthesizing recycled plastics according to one embodiment, the purity of the aromatic diol compound, which is the main target material for recovery, is significantly increased to 99% or more, and other impurities are minimized, so that when polycarbonate-based resin is synthesized using this, excellent physical properties can be achieved.

[0043] Meanwhile, the monomer composition for synthesizing recycled plastics may further contain impurities other than aromatic diol compounds. The impurities refer to all substances other than aromatic diol compounds, which are the main target substances for recovery in the present invention, and the specific types thereof are not particularly limited, but may include, for example, p-tert-butylphenol.

[0044] In addition, the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention is the below described The impurity ratio according to the formula may be 1.2% or less, or 1.1% or less, or 1% or less, or 0.1% or more, or 0.2% or more, or 0.3% or more, or 0.1% to 1.2%, or 0.1% to 1.1%, or 0.1% to 1%, or 0.2% to 1.2%, or 0.2% to 1.1%, or 0.2% to 1%, or 0.3% to 1.2%, or 0.3% to 1.1%, or 0.3% to 1%. [Formula] Impurity ratio = {(total peak area on liquid chromatography - bisphenol A peak area on liquid chromatography) / total peak area on liquid chromatography} x 100

[0045] The method for measuring the impurity ratio of the aromatic diol compound in the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and may be, for example, LC analysis. The specific method, conditions, equipment, etc. of the LC may be various contents known in the art without any limitations.

[0046] In this way, in the monomer composition for synthesizing recycled plastics according to one embodiment, the ratio of impurities other than the aromatic diol compound, which is the main target material for recovery, is extremely reduced to 1.2% or less, and when this is used to synthesize polycarbonate-based resin, excellent physical properties can be achieved.

[0047] Meanwhile, the monomer composition for synthesizing recycled plastics according to the embodiment may have diethyl carbonate as a by-product. The diethyl carbonate is recovered from a polycarbonate-based resin used in recovering the monomer composition for synthesizing recycled plastics according to the embodiment.

[0048] That is, diethyl carbonate is also obtained as a result of recovery using polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when new diethyl carbonate is added externally in addition to recovery using 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.

[0049] 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.

[0050] 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 separately as a by-product from the monomer composition for synthesizing recycled plastics of the embodiment.

[0051] 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.

[0052] 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.

[0053] The monomer composition for synthesizing recycled plastics according to one embodiment may be obtained by a method for producing a monomer composition for synthesizing recycled plastics, which will be described later. That is, the monomer composition for synthesizing recycled plastics according to one embodiment corresponds to a resultant product obtained through various filtration, purification, washing, and drying processes in order to obtain only aromatic diol compounds, which are the main target substances for recovery, in high purity after the depolymerization reaction of polycarbonate-based resin.

[0054] 2. Manufacturing method of monomer composition for synthesizing recycled plastics According to another embodiment of the present invention, there may be provided a method for producing a monomer composition for synthesizing recycled plastics, comprising: depolymerizing a polycarbonate-based resin; introducing a first adsorbent into the depolymerized reaction product to purify the depolymerized reaction product by adsorption, and then removing the first adsorbent; separating a carbonate precursor from the depolymerized reaction product; and purifying the depolymerized reaction product from which the carbonate precursor has been separated; wherein the purifying step of the depolymerized reaction product from which the carbonate precursor has been separated comprises introducing a second adsorbent into the depolymerized reaction product from which the carbonate precursor has been separated to purify the depolymerized reaction product by adsorption, and then removing the second adsorbent.

[0055] The present inventors have confirmed through experiments that, in the process of recycling polycarbonate-based resins by chemical decomposition, both a first adsorption purification process using a first adsorbent and a second adsorption purification process using a second adsorbent can be applied, as in the manufacturing method of a monomer composition for synthesizing recycled plastics according to the other embodiment, to ensure high purity of aromatic diol compounds, which are the main synthesis target substances in the present invention, as well as significantly reduce the content of impurities other than aromatic diol compounds, and thus completed the invention.

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

[0057] The polycarbonate resin includes both homopolymers and 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 one type of carbonate repeating unit is contained, obtained by using only one type of aromatic diol compound and one type of carbonate precursor, a homopolymer can be synthesized. When one type of aromatic diol compound and two or more types of carbonate precursors are used as the monomers, or when two or more types of aromatic diol compounds and one type of carbonate precursor are used, or when two or more types of carbonates are contained by using one type of aromatic diol compound, one type of carbonate precursor, and one or more other diols, a copolymer can be synthesized. The homopolymer or copolymer can include low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0058] The polycarbonate-based resin may be applied regardless of various forms and types, such as a new polycarbonate-based resin produced by synthesis, a recycled polycarbonate-based resin produced by a recycling process, or a polycarbonate-based resin waste.

[0059] However, if necessary, a pretreatment process of the polycarbonate resin may be performed before the depolymerization reaction of the polycarbonate resin to increase the efficiency of the process of recovering the aromatic diol compound and the carbonate precursor from the polycarbonate resin. Examples of the pretreatment process include washing, drying, pulverization, and glycol decomposition, and the specific method of each pretreatment process is not limited, and various methods widely used in the process of recovering the aromatic diol compound and the carbonate precursor by depolymerization of the polycarbonate resin may be applied without limitation.

[0060] The depolymerization reaction of the polycarbonate resin may be carried out under acidic, neutral, or basic conditions, and in particular under basic (alkali) 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.

[0061] 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 influence of the increase in the amount of alkaline salt generated, the purity of the target recovered material decreases, and there is a limit to the decrease in the economic efficiency of the catalytic reaction.

[0062] In addition, the depolymerization reaction of the polycarbonate resin can be carried out in a solvent containing ethanol. The present invention has the advantage that the polycarbonate resin can be decomposed in a solvent containing ethanol to stably obtain bisphenol A, which is a high-purity monomer, and that diethyl carbonate, which has high added value, can be additionally obtained as a reaction by-product.

[0063] The content of the ethanol is 5 to 15 moles per mole of the polycarbonate resin. ,MaThe amount of ethanol may be 8 to 13 mol. Since the ethanol has good solubility in bisphenol A, the amount of ethanol within the above range must be included as an essential component. If the amount of ethanol is excessively reduced to less than 5 mol per mol of polycarbonate-based resin, it is difficult to sufficiently alcoholize the polycarbonate-based resin. On the other hand, if the amount of ethanol is excessively increased to more than 15 mol per mol of polycarbonate-based resin, the economic efficiency of the process may decrease due to excessive use of alcohol.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] The content of the organic solvent may be 16 to 20 moles, or 16 to 18 moles, per mole of the polycarbonate resin. Also, the content of the organic solvent may be 1.5 to 2 moles per mole of ethanol. By mixing the polycarbonate resin, ethanol and the organic solvent within the above range, it is advantageous that a required level of depolymerization reaction of the polymer can be carried out.

[0068] Meanwhile, the temperature at which the depolymerization reaction of the polycarbonate-based resin is carried out is not particularly limited, and may be, for example, 20° C. to 100° C., or 50° C. to 70° C. The time for which the depolymerization reaction of the polycarbonate-based resin is carried out is 1 hour to 30 hours, or 4 hours to 6 hours.

[0069] 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, there is an advantage that the most efficient results can be obtained in terms of reproducibility and stability during stirring at 50°C to 70°C for 4 to 6 hours.

[0070] In other words, the present invention has the advantage that a high purity aromatic diol compound (e.g., bisphenol A) can be obtained under mild conditions without using an organic catalyst by adjusting the type and amount of the mixed solvent and the type and content of the base catalyst, and without using a pressurized / high temperature process, and that diethyl carbonate can be obtained as a by-product because an ethanol solvent is used.

[0071] 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 details of the ethanol, organic solvent, base, and polycarbonate-based resin in the first and second steps are the same as those described above.

[0072] 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 a step of introducing a first adsorbent into the depolymerization reaction product to perform adsorption purification and then removing the first adsorbent.

[0073] 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 for recovery in the present invention is an 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 step with an acid. That is, when the depolymerization reaction of the polycarbonate resin is an alkaline decomposition, a neutralization step with an acid can be performed.

[0074] 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 a 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.

[0075] 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.

[0076] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may include the step of introducing a first adsorbent into the depolymerization reaction product to perform adsorption purification, and then removing the first adsorbent. In the step of introducing a first adsorbent into the depolymerization reaction product to perform adsorption purification, and then removing the first adsorbent, the adsorbent may be contacted with the depolymerization reaction product.

[0077] Examples of the first 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 of the activated carbon 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.

[0078] 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, bituminous 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.

[0079] The first 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, i.e., the first 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.

[0080] More specifically, the first 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 first adsorbent may include coconut activated carbon, lignite activated carbon, anthracite activated carbon, bituminous activated carbon, or a mixture of two or more thereof.

[0081] The conditions for adsorption purification using the first adsorbent are not particularly limited, and various conventionally known adsorption purification conditions can be used without limitation. However, as an example, the amount of adsorbent added can be 40% by weight to 60% by weight relative to the polycarbonate resin, the adsorption time can be 1 hour to 5 hours, and the adsorption method can be stirring adsorption or a lab adsorption tower.

[0082] 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.

[0083] 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 above embodiment.

[0084] The step of separating the carbonate precursor from the depolymerization reaction product may include a step of vacuum distillation of the depolymerization reaction product. Although the example of the vacuum distillation condition is not particularly limited, in a specific example, the polycarbonate-based resin may be subjected to low-temperature distillation by pressurizing the depolymerization reaction product under conditions of a pressure of 200 mbar to 300 mbar and a temperature of 20°C to 30°C, and then reducing the pressure under conditions of a pressure of 10 mbar to 50 mbar and a temperature of 20°C to 30°C.

[0085] The separated carbonate precursor can be recycled without a separate separation and purification process, or can be recycled after, as necessary, conventional separation and purification such as extraction, adsorption, drying, etc. Specific purification conditions are not particularly limited, and specific purification equipment and methods can be applied without limitation to various purification techniques that have been publicly known in the art.

[0086] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to the second 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 first embodiment.

[0087] Specifically, the step of purifying the depolymerization reaction product from which the carbonate precursor is separated may include the step of introducing a second adsorbent into the depolymerization reaction product from which the carbonate precursor is separated, performing adsorption purification, and then removing the second adsorbent. In the step of introducing a second adsorbent into the depolymerization reaction product from which the carbonate precursor is separated, performing adsorption purification, and then removing the second adsorbent, the adsorbent may be contacted with the depolymerization reaction product.

[0088] Examples of the second 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.

[0089] 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, bituminous 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.

[0090] The second 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, i.e., 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.

[0091] More specifically, the second 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 second adsorbent may include coconut activated carbon, lignite activated carbon, anthracite activated carbon, bituminous activated carbon, or a mixture of two or more of these.

[0092] In this manner, 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 both a first adsorption purification process using a first adsorbent and a second adsorption purification process using a second adsorbent during the depolymerization reaction for recycling polycarbonate-based resins by chemical decomposition.

[0093] The first and second adsorbents may be the same or different from each other, and each may independently comprise 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. More specifically, the first and second adsorbents may be the same or different from each other, and each may independently comprise one or more activated carbons selected from the group consisting of coconut activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous activated carbon.

[0094] The weight ratio of the first adsorbent and the second adsorbent added is not particularly limited, but as an example, the amount of the first adsorbent added may be 1 part by weight to 1000 parts by weight per 100 parts by weight of the second adsorbent added.

[0095] The conditions for adsorption purification using the second adsorbent are not particularly limited, and various conventionally known adsorption purification conditions can be used without limitation. However, as an example, the amount of adsorbent added can be 40% by weight to 60% by weight relative to the polycarbonate resin, the adsorption time can be 1 hour to 5 hours, and the adsorption method can be stirring adsorption or a lab adsorption tower.

[0096] If necessary, the method may further include a step of adding a solvent to the depolymerization reaction product from which the carbonate precursor is separated before the step of adding a second adsorbent to the depolymerization reaction product from which the carbonate precursor is separated and then removing the second adsorbent. An example of the solvent is ethanol, and the ethanol may be added in a ratio of 1 mol to 20 mol, 10 mol to 20 mol, or 15 mol to 20 mol, per mol of the polycarbonate resin. By adding a solvent to the depolymerization reaction product from which the carbonate precursor is separated, the aromatic diol compound crystals contained in the depolymerization reaction product from which the carbonate precursor is separated may be redissolved in the solvent.

[0097] In addition, the purification step may further include a step of recrystallizing the depolymerization reaction product from which the carbonate precursor is separated, after the step of introducing a second adsorbent into the depolymerization reaction product from which the carbonate precursor is separated to perform adsorption purification and then removing the second adsorbent.

[0098] 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.

[0099] Specifically, the recrystallization step may include a step of adding water to the depolymerization reaction product from which the carbonate precursor has been separated to perform recrystallization. By performing the process of adding water 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 impurities present in the crystals or between the crystals can be dissolved in the solvent as much as possible, and since the dissolved aromatic diol compound has poor solubility compared to the impurities, it can be easily precipitated as aromatic diol compound crystals due to the difference in solubility when the temperature is subsequently lowered.

[0100] More specifically, in the step of adding water to the depolymerization product from which the carbonate precursor is separated to recrystallize, 200 to 400 mols or 250 to 350 mols of water can be used per mol of polycarbonate-based resin. If the amount of water used is too small, the temperature for dissolving the aromatic diol compound contained in the depolymerization 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 an excessive amount of water is used, the solubility of the aromatic diol compound contained in the depolymerization 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 process efficiency may be reduced due to the use of a large amount of solvent.

[0101] 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.

[0102] 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 performed at a temperature of, for example, 10° C. to 100° C., or 10° C. to 50° C. Regarding the specific drying equipment and method used in the drying, various drying techniques known in the art can be applied without any restrictions.

[0103] Meanwhile, the purification step may further include a step of washing the depolymerization reaction product from which the carbonate precursor has been separated. The order of the washing steps 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 washing step, the adsorption purification step, and the recrystallization step. Each of the washing step, the adsorption purification step, and the recrystallization step may be repeated at least once. Specific equipment and methods for washing, adsorption, and recrystallization may be applied without limitation to various purification techniques that have been known in the art.

[0104] Specifically, in a 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 a recovery process for obtaining an aromatic diol compound, washing may be performed to sufficiently remove the impurities to obtain a high-purity aromatic diol compound.

[0105] 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 mechanisms may be applied without limitation to maintain a high temperature that is higher than room temperature.

[0106] The washing step may be performed by first washing with a solvent at a temperature of 10° C. to 30° C., followed by washing with a solvent at a temperature of 40° C. to 80° C. Alternatively, the washing with a solvent at a temperature of 40° C. to 80° C. may be performed by first washing with a solvent at a temperature of 10° C. to 30° C., followed by washing with a solvent at a temperature of 10° C. to 30° C.

[0107] 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., thereby minimizing corrosion of the reactor by strong acid after the neutralization step.

[0108] The steps of washing with a solvent at a temperature of 10° C. to 30° C. and 40° C. to 80° C. may each be repeated at least once.

[0109] 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 may be additionally performed.

[0110] More specifically, the difference between the temperature of the step of washing with a solvent at a temperature of 40°C to 80°C and the temperature of the step of washing with a solvent at a temperature of 10°C to 30°C may be 20°C to 50°C.

[0111] 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.

[0112] If the difference between the temperature of the step of washing with a solvent at a temperature of 40° C. to 80° C. and the temperature of the step of washing with a solvent at a temperature of 10° C. to 30° C. is excessively reduced to less than 20° C., it is difficult to sufficiently remove impurities.

[0113] If the difference between the temperature of the step of washing with a solvent at a temperature of 40° C. to 80° C. and the temperature of the step of washing with a solvent at a temperature of 10° C. to 30° C. is excessively increased beyond 50° C., severe conditions may be created in order to maintain the extreme temperature conditions, and the efficiency of the process may be reduced.

[0114] 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.

[0115] 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 resin used in the depolymerization reaction.

[0116] More specifically, the solvent used in the step of washing with a solvent at a temperature of 10° C. to 30° C. may be an organic solvent. The organic solvent may preferably be methylene chloride. In this case, the organic solvent may be used in an amount of 1 part by weight to 10 parts by weight per part by weight of the polycarbonate resin.

[0117] The solvent used in the step of washing with a solvent at a temperature of 40° C. to 80° C. may be water. When water is used, residual salt-type impurities can be effectively removed. In this case, the solvent may be used in an amount of 1 part by weight to 10 parts by weight per 1 part by weight of the polycarbonate resin.

[0118] 3. Recycled plastics According to another embodiment of the present invention, a recycled plastic may be provided, comprising a reaction product of the monomer composition for synthesizing recycled plastics of the above embodiment and a comonomer.

[0119] The content related to the monomer composition for synthesizing recycled plastics of the one embodiment includes all of the contents described above in the one embodiment and other embodiments.

[0120] Examples of the recycled plastics are not particularly limited, and various plastics synthesized using an aromatic diol compound such as bisphenol A and a carbonate precursor such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate as a monomer can be used without limitation. A more specific example is a polycarbonate resin.

[0121] The polycarbonate-based resin includes both homopolymers and copolymers containing polycarbonate repeating units, and is a general term for reaction products obtained by polymerization or copolymerization of monomers including aromatic diol compounds and carbonate precursors. When one type of carbonate repeating unit is contained, obtained by using only one type of aromatic diol compound and one type of carbonate precursor, a homopolymer can be synthesized. In addition, when one type of aromatic diol compound and two or more types of carbonate precursors are used as the monomers, or when two or more types of aromatic diol compounds and one type of carbonate precursor are used, or when two or more types of carbonates are contained by using one type of aromatic diol compound, one type of carbonate precursor, and one or more other diols, a copolymer can be synthesized. The homopolymer or copolymer can include low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0122] More specifically, in the recycled plastics comprising the reaction product of the monomer composition for synthesizing recycled plastics of the embodiment and a comonomer, 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, or bishaloformates.

[0123] The reaction process of the monomer composition and the comonomer for synthesizing recycled plastics to synthesize the polycarbonate-based resin is not particularly limited, and various conventionally known polycarbonate production methods can be applied without limitation.

[0124] However, as an example of the method for producing polycarbonate, a method for producing polycarbonate including a step of polymerizing a composition containing a monomer composition for synthesizing recycled plastics and a comonomer can be used. At this time, the polymerization can be performed by interfacial polymerization, which can be performed at normal pressure and low temperature, and can easily control the molecular weight.

[0125] 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.

[0126] The solvent that can be used in the polymerization is not particularly limited as long as it is a solvent used in the polymerization of polycarbonates in the art. For example, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0127] 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.

[0128] In addition, the polymerization can be carried out in the presence of a molecular weight regulator to regulate the molecular weight of the polycarbonate during the polymerization. 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 the start of polymerization, during the start of polymerization, or after the start 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 this range.

[0129] 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.

[0130] 4. Molded products According to yet another embodiment of the present invention, a molded product including the recycled plastic of the other embodiment may be provided. The content related to the recycled plastic includes all of the content described above in the other embodiment.

[0131] 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.

[0132] The examples of the molded products are not particularly limited, and the molded products may 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.

[0133] In addition to the recycled plastic of the other embodiments, the molded article may further contain 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.

[0134] As an example of a method for producing 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 produce pellets, drying the pellets, and then injecting the pellets into an injection molding machine. Effect of the Invention

[0135] According to the present invention, it is possible to provide a monomer composition for synthesizing recycled plastics, which contains a high-purity aromatic diol compound recovered by recycling through chemical decomposition of polycarbonate-based resins, a method for producing the same, and recycled plastics and molded articles using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0136] The present invention will be described in more detail in the following examples, but the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0137] <Examples and Comparative Examples: Production of Recycled Bisphenol A Monomer Composition> Example 1 (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of methylene chloride (MC), and then added to a 3L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH), and stirred at 60°C for 6 hours to carry out the PC depolymerization reaction.

[0138] (2. Neutralization Step) The depolymerization product was cooled to below 30°C, and then the product containing bisphenol A was neutralized at 20 to 30°C using 0.25 mol of 10% hydrochloric acid (HCl).

[0139] (3-1. Purification-adsorption step) After that, lignite activated carbon was added as the first adsorbent to the product with a pH lower than 2 in a ratio of 50% by weight relative to the waste polycarbonate, and the product was purified by adsorption for 3 hours, and then filtered using Celite to remove the lignite activated carbon.

[0140] (3-2. Purification-distillation step) Thereafter, the by-product diethyl carbonate (DEC) was recovered by low-temperature distillation by reducing the pressure from 250 mbar and 20-30°C to 30 mbar and 30°C.

[0141] (3-3. Purification-Washing Step) After that, the residue from which diethyl carbonate (DEC) was removed was washed with methylene chloride (MC) in an amount equal to one part by weight of PC used at 20-30°C and vacuum filtered. The filtrate was washed with water in an amount equal to three parts by weight of PC used at 50°C for the second time.

[0142] (4-1. Further purification step-redissolution step) The washed material was redissolved in 16.6 mol of ethanol.

[0143] (4-2. Additional purification step-adsorption step) Then, lignite activated carbon was added as a second adsorbent in a ratio of 50% by weight to the waste polycarbonate, and the mixture was purified by adsorption for 3 hours, and the lignite activated carbon was removed by filtration.

[0144] (4-3. Additional purification step-recrystallization step) Then, 300 mol of water was added to recrystallize bisphenol A, and the resulting slurry was subjected to vacuum filtration at 20 to 30° C. to recover bisphenol A (BPA) crystals.

[0145] (5. Drying step) Then, the mixture was vacuum dried in a 40° C. convection oven to produce a recycled bisphenol A monomer composition from which recycled bisphenol A (BPA) was recovered.

[0146] (Examples 2-6, Comparative Examples 1-4) As shown in Table 1 below, recycled bisphenol A monomer compositions were prepared in the same manner as in Example 1, except that the types of the first and second adsorbents and whether or not they were used were changed in Example 1.

[0147] <Experimental Example> The properties of the recycled bisphenol A monomer compositions or by-products obtained in the above Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1.

[0148] 1. Purity The recycled bisphenol A monomer composition was dissolved in acetonitrile (ACN) solvent at 1 w% under normal pressure and 20 to 30°C conditions, and the purity of bisphenol A (BPA) was analyzed using UPLC (ultra performance liquid chromatography) on a Waters HPLC system using an ACQUITY UPLC (registered trademark) BEH C18 1.7 μm (2.1 * 50 mm column).

[0149] 2.Color coordinates (L*,a*,b*) The recycled bisphenol A monomer composition was analyzed using a HunterLab UltraScan PRO Spectrophotometer in reflectance mode.

[0150] 3.Impurity ratio 1 ml of the recycled bisphenol A monomer composition was collected as a sample and subjected to liquid chromatography (LC) analysis under the following conditions, and the impurity ratio was calculated using the following formula: As a result of the measurement using liquid chromatography, all substances except bisphenol A were considered to be impurities.

[0151] <Liquid chromatography (LC) conditions> (1)Column:HP-1(L:30m, ID:0.32mm,film:1.05m) (2) Injection volume: 1 μl (3) Inlet Temp.:260℃, Pressure:6.92psi, Total flow:64.2ml / min, Split flow:60ml / min, spill ratio:50:1 (4) Column flow: 1.2 ml / min (5)Oven temp.:70℃ / 3min-10℃ / min-280℃ / 41min (Total 65min) (6)Detector Temp.:280℃, H2:35ml / min, Air:300ml / min, He:20ml / min (7)GC Model: Agilent 7890

[0152] [Formula] Impurity ratio={(total peak area on liquid chromatography−bisphenol A peak area on liquid chromatography) / total peak area on liquid chromatography}×100.

[0153] [Table 1]

[0154] As shown in Table 1, the recycled bisphenol A monomer compositions obtained in Examples 1 to 6 exhibited high purity of 99.0% to 99.7%. In addition, the recycled bisphenol A monomer compositions obtained in Examples 1 to 6 exhibited excellent optical properties, with color coordinates L* of 94.5 to 96.3, a* of -0.01 to 0.44, and b* of 2.12 to 4.12. In addition, the recycled bisphenol A monomer compositions obtained in Examples 1 to 6 were measured to have low impurity ratios of 0.3% to 1%. In contrast, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 to 4 exhibited purities of 98.2% to 98.4%, which were lower than those of the Examples. In addition, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 to 4 exhibited color coordinates L* of 92.3 to 93.2, a* of 0.89 to 1.24, and b* of 4.32 to 5.67, which were lower than those of the Examples. Furthermore, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 to 4 had impurity ratios of 1.3% to 1.8%, which were higher than those of the Examples.

Claims

1. A step of depolymerizing the polycarbonate-based resin; adding a first adsorbent to the depolymerization reaction product to purify the product by adsorption, and then removing the first adsorbent; separating a carbonate precursor from the depolymerization reaction product; and purifying the depolymerization reaction product from which the carbonate precursor has been separated; The step of purifying the depolymerization reaction product from which the carbonate precursor is separated includes the steps of: introducing a second adsorbent into the depolymerization reaction product from which the carbonate precursor is separated, adsorbing and purifying the product, and then removing the second adsorbent.

2. 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the first adsorbent and the second adsorbent are the same or different from each other, and each independently comprises 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.

3. 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the amount of the first adsorbent added is 1 to 1000 parts by weight per 100 parts by weight of the second adsorbent added.

4. The depolymerization reaction of the polycarbonate resin is 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, which is carried out in a solvent containing ethanol.

5. The method for producing a monomer composition for synthesizing recycled plastics according to claim 4, wherein the amount of ethanol is 5 to 15 moles per mole of the polycarbonate resin.

6. The depolymerization reaction of the polycarbonate resin is 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the reaction is carried out by reacting the polycarbonate resin with a base in an amount of 0.5 mol or less per mol of the polycarbonate resin.

7. separating a carbonate precursor from the depolymerization reaction product, The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising a step of vacuum distillation of the depolymerization reaction product.

8. In the purification step, a second adsorbent is added to the depolymerization reaction product from which the carbonate precursor has been separated, and the second adsorbent is then removed. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising: a recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated.

9. before the step of adding a first adsorbent to the depolymerization reaction product for adsorption purification and then removing the first adsorbent, 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising a step of neutralizing the depolymerization reaction product with an acid.

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