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

Abstract

The present invention relates to a monomer composition for synthesizing recycled plastics, which contains an aromatic diol compound, has a color coordinate b* of 0.1 to 1, and is produced in a yield of more than 75%. The monomer composition for synthesizing recycled plastics is recovered from a polycarbonate resin. The present invention also relates to a method for producing the monomer composition, and recycled plastics and molded articles using the monomer composition.

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0122001, filed September 13, 2021, Korean Patent Application No. 10-2021-0122002, filed September 13, 2021, Korean Patent Application No. 10-2021-0122003, filed September 13, 2021, Korean Patent Application No. 10-2021-0122004, filed September 29, 2021, Korean Patent Application No. 10-2021-0128892, filed September 29, 2021, and Korean Patent Application No. 10-2021-0136153, filed October 13, 2021, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a monomer composition for synthesizing recycled plastics, which 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. [Background technology]

[0003] Polycarbonate is a thermoplastic polymer, a plastic having excellent properties such as excellent transparency, flexibility and relatively low production costs.

[0004] Although polycarbonate is widely used for a variety of purposes, environmental and health concerns have been continually raised regarding its disposal.

[0005] Currently, physical recycling methods are being used, but since this involves problems associated with quality degradation, research is being conducted 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 the reality is that it has a drawback in terms of economics. 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 ensure a high yield of aromatic diol compounds having improved optical properties recovered by recycling polycarbonate resins through chemical decomposition.

[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 invention provides a monomer composition for synthesizing recycled plastics, which comprises an aromatic diol compound, has a color coordinate b* of 0.1 to 1, and has a yield of the aromatic diol compound represented by the following formula 1 of more than 75%, and is characterized in that the monomer composition for synthesizing recycled plastics is recovered from a polycarbonate resin.

[0012] [Formula 1] Yield(%)=W1 / W0 In the above formula 1, W0 is the mass of the aromatic diol compound obtained upon 100% decomposition, and W1 is the mass of the aromatic diol compound actually obtained.

[0013] The present invention also provides a method for producing a monomer composition for synthesizing recycled plastics, the method including the steps of depolymerizing a polycarbonate resin, adding an acid to the depolymerized reaction product so that the pH of the depolymerized reaction product is 2 to 8, removing impurities after the acid addition, and separating a carbonate precursor from the depolymerized reaction product.

[0014] The present invention also provides a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastics and a comonomer.

[0015] The present invention also provides a molded article comprising the recycled plastic.

[0016] Hereinafter, a monomer composition for synthesizing recycled plastics according to an embodiment 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.

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

[0020] As used herein, the meaning of "comprising" is to embody 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.

[0021] 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.

[0022] 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 b* of 0.1 to 1, and has a yield of the aromatic diol compound represented by the following formula 1 of more than 75%, and is recovered from a polycarbonate resin.

[0023] The present inventors have experimentally confirmed that the monomer composition for synthesizing recycled plastics according to the embodiment of the present invention can obtain aromatic diol compounds with a low color coordinate b* value equivalent to that of commercially available reagents or reagents used for polymerization of PC in high yields, even though the monomer composition is recovered by recycling through chemical decomposition of polycarbonate-based resins. Thus, the present invention has been completed.

[0024] Specifically, in the case of aromatic diol compounds recovered by recycling through the conventional chemical decomposition of polycarbonate resins, the color coordinate b* value is relatively high in the range of more than 1 and less than 4, and the hue is too yellow, resulting in poor color characteristics. On the other hand, the aromatic diol compounds recovered in the present invention can have a low color coordinate b* value of 0.1 to 1, or 0.1 to 0.5, or 0.2 to 0.5, or 0.21 to 0.43.

[0025] For commercially used polycarbonate, transparency and color specifications are important due to the characteristics of the applications in which it is used, but the color of polycarbonate depends on the color of the aromatic diol compound (e.g., bisphenol A (BPA)) that is the raw material. In the case of recycled BPA obtained by chemical decomposition of conventional polycarbonate, the color specifications of the recycled BPA are reduced due to unremoved by-products, which also affect the color of the polycarbonate polymerized using it. In particular, the color coordinate b* value of recycled BPA is important.

[0026] In addition, the content of impurities other than the aromatic diol compound, which is the main target of recovery, is extremely reduced, and it has been confirmed through experiments that excellent physical properties can be achieved when synthesizing polycarbonate resins using this, thereby completing the invention.

[0027] In particular, a monomer composition for synthesizing recycled plastics (second composition) containing diethyl carbonate together with the monomer composition for synthesizing recycled plastics (first composition) of the one embodiment, the diethyl carbonate being recovered from a polycarbonate-based resin, is obtained simultaneously by a manufacturing method for a monomer composition for synthesizing recycled plastics described below.

[0028] In other words, the present invention has the technical advantage of being able to obtain a high-purity first composition containing an aromatic diol compound at a high purity by recycling a polycarbonate-based resin through chemical decomposition, while at the same time obtaining a second composition containing diethyl carbonate, which is a by-product with high added value.

[0029] 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 recovering from a polycarbonate-based resin in order 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.

[0030] 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 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. 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 and one type of 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.

[0031] 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 (bisphenol A), and bis(4-hydroxyphenyl)methane. Examples of the aromatic diol compound include 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 for synthesizing recycled plastics of the embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0032] The aromatic diol compound is characterized by being recovered from the polycarbonate-based resin used in recovering the monomer composition for synthesizing recycled plastics. That is, the aromatic diol compound is also obtained as a result of recovery from the polycarbonate-based resin to obtain the monomer composition for synthesizing recycled plastics of the embodiment. Therefore, when a new aromatic diol compound is added externally apart from 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 the aromatic diol compound of the present invention.

[0033] Specifically, the term "recovered from the polycarbonate-based resin" means that the polycarbonate-based resin is obtained by a depolymerization reaction. The depolymerization reaction may be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction may be carried out under basic (alkaline) conditions. In particular, the depolymerization reaction is preferably carried out in an ethanol solvent, as described below.

[0034] Meanwhile, the monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate b* value of 0.1 to 1, or 0.1 to 0.5, or 0.2 to 0.5, or 0.21 to 0.43. The monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate L* of 98 or more, or 100 or less, or 98 to 100, or 98.12 to 98.91. The monomer composition for synthesizing recycled plastics of the embodiment may have a color coordinate a* of 0 or less, or -0.2 or more, or -0.2 to 0, or -0.15 to -0.01.

[0035] In the present invention, the term "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 is expressed by three coordinate values: L*, a*, and b*.

[0036] 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.

[0037] 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.

[0038] When the color coordinate a* value of the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention is excessively increased to be greater than 0, or the color coordinate L* value of the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention is excessively decreased to be less than 98, the color characteristics of the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention become poor.

[0039] On the other hand, if the color coordinate b* value of the monomer composition for synthesizing recycled plastics of the embodiment is excessively increased to more than 1, the hue of the monomer composition for synthesizing recycled plastics of the embodiment becomes too yellow, resulting in poor color characteristics.

[0040] 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 −0.1, the hue of the monomer composition for synthesizing recycled plastics of the embodiment becomes too blue, resulting in poor color characteristics.

[0041] The method for measuring the color coordinates L*, a*, and b* 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 may be used without limitation.

[0042] However, as an example of a method for measuring the color coordinates L*, a*, and b* 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.

[0043] Meanwhile, in the monomer composition for synthesizing recycled plastics according to one embodiment, the purity of the aromatic diol compound may be 98% or more, or 100% or less, or 98% to 100%.

[0044] 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, devices, etc. of the NMR, ICP-MS, HPLC, and UPLC can be various conventionally known methods, conditions, devices, etc. without limitation.

[0045] 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 the embodiment, the monomer composition for synthesizing recycled plastics according to the embodiment was dissolved in acetonitrile (ACN) solvent at 1 wt % under normal pressure and 20 to 30° C., 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).

[0046] 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 98% or more, and other impurities are minimized, so that when polycarbonate-based resin is synthesized using this, excellent physical properties can be achieved.

[0047] Meanwhile, the monomer composition for synthesizing recycled plastics may further contain impurities other than the aromatic diol compound. The impurities refer to all substances other than the aromatic diol compound, which is the main target substance for recovery of the present invention, and the specific types thereof are not particularly limited, but may include, for example, sodium salts.

[0048] In particular, according to the method for producing a monomer composition for synthesizing recycled plastics described below, the pH of the depolymerization reaction product is adjusted to 2 to 8, so that aromatic diol compounds, which are the main target substances for recovery, can be present in the organic phase. As a result, water-soluble impurities can be separated into the aqueous layer and easily removed, and acidic organic impurities having stronger acidity than aromatic diol compounds can be further removed.

[0049] Specifically, the monomer composition for synthesizing recycled plastics may have a weight ratio of sodium salt impurities of less than 10 μg per 1 g of the monomer composition for synthesizing recycled plastics, as measured using ion chromatography.

[0050] The method for measuring the weight ratio of sodium salt impurities in the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and for example, ion chromatography (IC) analysis can be used. Specific methods, conditions, devices, etc. of the IC can be applied to various contents known in the art without any restrictions.

[0051] In this way, in the monomer composition for synthesizing recycled plastics of the embodiment, the weight ratio of sodium salt impurities other than the aromatic diol compound, which is the main target substance for recovery, is extremely reduced to less than 10 μg per 1 g of the monomer composition for synthesizing recycled plastics, and when this is used to synthesize polycarbonate-based resins, excellent physical properties can be achieved.

[0052] Meanwhile, the monomer composition for synthesizing recycled plastics of the embodiment may have a yield of aromatic diol compound of more than 75%, or 76% or more, or 77% or more, or 100% or less, or more than 75% and 100% or less, or 77% to 100%, or 78% to 100%. The fact that the yield of aromatic diol compound is high, more than 75%, is considered to be due to the manufacturing method of the monomer composition for synthesizing recycled plastics described later.

[0053] The method for measuring the yield of the aromatic diol compound in the monomer composition for synthesizing recycled plastics according to the embodiment is not particularly limited, and can be calculated, for example, by the following formula 1.

[0054] [Formula 1] Yield(%)=W1 / W0 In the above formula 1, W0 is the mass of the aromatic diol compound obtained upon 100% decomposition, and W1 is the mass of the aromatic diol compound actually obtained.

[0055] The mass of the aromatic diol compound in the above formula 1 can be measured by various commonly known mass measuring methods without limitation, for example, by using a balance.

[0056] In this way, the yield of aromatic diol compounds, which are the main target substances for recovery, in the monomer composition for synthesizing recycled plastics according to one embodiment of the present invention is significantly increased to more than 75%, thereby improving the efficiency of the recycling process for polycarbonate-based resins.

[0057] 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.

[0058] That is, 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 externally in addition to the 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.

[0059] 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 in particular, under basic (alkaline) conditions. In particular, the depolymerization is preferably carried out in an ethanol solvent, as described below.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 2. Manufacturing method of monomer composition for synthesizing recycled plastics According to another embodiment of the present invention, there is provided a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate resin; adding an acid so that the pH of the depolymerized reaction product is 2 to 8; removing impurities after the addition of the acid; and separating a carbonate precursor from the depolymerized reaction product.

[0065] The present inventors have confirmed through experiments that, in the process of recycling polycarbonate-based resins by chemical decomposition as in the method for producing a monomer composition for synthesizing recycled plastics according to the other embodiment, the pH of the depolymerized polycarbonate-based resin is adjusted, and aromatic diol compounds having a low color coordinate b* value equivalent to that of commercially available reagents or reagents used for polymerization of PC can be obtained in high yields even though the polycarbonate-based resins are recycled by chemical decomposition. Thus, the present invention has been completed.

[0066] In particular, the pH of the depolymerization reaction product is adjusted to 2 to 8, so that the aromatic diol compound, which is the main target substance for recovery, can be present in the organic phase, and thus water-soluble impurities can be separated into the aqueous layer and easily removed, and acidic organic impurities having stronger acidity than the aromatic diol compound can be further removed.

[0067] Therefore, the present invention was completed by confirming through experiments that the content of impurities other than the aromatic diol compound, which is the main target of recovery, is extremely reduced, and that excellent physical properties can be achieved when synthesizing polycarbonate resins using this.

[0068] 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.

[0069] 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 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. 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 and one type of 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.

[0070] 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.

[0071] 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.

[0072] The depolymerization reaction of the polycarbonate-based 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) or 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. More specifically, the depolymerization reaction of the polycarbonate-based resin is carried out in a pH range of more than 8 and less than 12.

[0073] 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, per mol of the polycarbonate-based resin. If the depolymerization reaction of the polycarbonate-based resin is carried out with a base in an amount of more than 0.5 mol, impurities increase due to the effect of an increase in the amount of alkali 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.

[0074] The depolymerization reaction of the polycarbonate resin can be carried out in a solvent containing ethanol. The present invention has an 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 diethyl carbonate, which has high added value, can be further obtained as a reaction by-product.

[0075] The ethanol amount is 5 to 15 moles per mole of polycarbonate resin, 10 moles to 15 moles, Or, it may be 8 moles to 13 moles. Since the ethanol has good solubility in bisphenol A, the ethanol must be contained within the above range. amount When the amount of ethanol is excessively reduced to less than 5 moles per mole of the polycarbonate resin, the alcoholysis of the polycarbonate resin is difficult to proceed sufficiently. amount If the amount of alcohol is excessively increased to more than 15 moles per mole of polycarbonate resin, the economic efficiency of the process decreases due to excessive use of alcohol.

[0076] The solvent in which the depolymerization reaction of the polycarbonate-based resin is carried out may further include, in addition to ethanol, one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0077] 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.

[0078] 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 is improved.

[0079] The content of the organic solvent may be 16 to 20 moles, or 16 to 18 moles, per mole of the polycarbonate resin. The content of the organic solvent may be 1.5 to 2 moles per mole of ethanol. By mixing the polycarbonate resin, ethanol and the organic solvent within the above ranges, it is advantageous that a required level of depolymerization reaction of the polymer can be carried out.

[0080] The temperature for carrying out the depolymerization reaction of the polycarbonate-based resin is not particularly limited, and may be, for example, 20° C. to 100° C., or 50° C. to 70° C. The time for carrying out the depolymerization reaction of the polycarbonate-based resin is 1 hour to 30 hours, or 4 hours to 6 hours.

[0081] Specifically, the above conditions are milder process conditions than the conventional pressurized / high temperature process, and stirring under the above conditions allows the process to be carried out under milder conditions than the conventional 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.

[0082] That is, the present invention has an 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 because an ethanol solvent is used.

[0083] Meanwhile, during the depolymerization reaction of the polycarbonate-based resin, an antioxidant can be added to the reaction solution, and by adding the antioxidant, the aromatic diol compound recovered by recycling through chemical decomposition of the polycarbonate-based resin can satisfy a low color coordinate b* value of a color level equivalent to that of a reagent commercially sold or used for polymerization of PC.

[0084] Specific examples of the antioxidant are not particularly limited, and various antioxidants known in the art can be used without limitation, however, examples include sodium hyposulfite, sodium sulfite, erythorbic acid, dibutylhydroxytoluene, butylhydroxyanisole, α-tocopherol, tocopherol acetate, L-ascorbic acid and its salts, L-ascorbic acid palmitate, L-ascorbic acid stearate, triamyl gallate, propyl gallate, disodium ethylenediaminetetraacetate (EDTA), sodium pyrophosphate, sodium metaphosphate, or a mixture of two or more of these.

[0085] The specific amount of the antioxidant to be added is also not particularly limited. For example, the antioxidant may be added in a range of 0.1 wt % to 5 wt %, or 0.1 wt % to 1 wt %, based on the total weight of the reaction solution, at a level that does not affect the physical properties of the monomer composition for synthesizing recycled plastics.

[0086] In addition, during the depolymerization reaction of the polycarbonate-based resin, the depolymerization reaction may be carried out under a nitrogen atmosphere.

[0087] 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, a base, and an antioxidant. The ethanol, organic solvent, base, antioxidant, and polycarbonate-based resin in the first and second steps are as described above.

[0088] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8. The acid may be a strong acid, for example, hydrochloric acid (HCI).

[0089] In the step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8, the salt of the aromatic diol compound contained in the depolymerization reaction product is converted to an aromatic diol compound. The depolymerization reaction is carried out under basic conditions, and the aromatic diol compound produced exists in the form of a salt by reaction with the base and has hydrophilicity. Therefore, by adding an acid, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted to an aromatic diol compound and induced to have hydrophobicity.

[0090] Therefore, in the step of removing impurities by adding water after the addition of the acid, which will be described later, a water layer containing impurities and an organic solvent layer containing the aromatic diol compound and the carbonate precursor can be formed. The aromatic diol compound and the carbonate precursor are hydrophobic, so they are contained in the organic solvent layer between water and the organic solvent, and various water-soluble impurities are contained in the water layer. Therefore, even a simple process of changing the pH can easily separate the aromatic diol compound, which is the main product, from the by-products.

[0091] Meanwhile, in the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment, the step of adding water may be further included in the step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8. Thus, in the impurity removal step described below, a layer separated into an aqueous layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate precursor may be formed.

[0092] The order of the step of adding acid and the step of adding water is not particularly limited, and water may be added after the addition of acid, or water may be added after the addition of acid, or both water and acid may be added simultaneously.

[0093] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include removing impurities after the addition of the acid. Thus, the impurities may be hydrophilic substances, such as salt compounds, ion compounds, and acid compounds.

[0094] As described above, by performing the step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8 and then removing impurities from the depolymerization reaction product after the addition of the acid, the depolymerization reaction product forms layers separated into an aqueous layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate precursor, and the aqueous layer containing impurities can be separated and removed.

[0095] In the step of removing impurities from the depolymerization reaction product after the addition of the acid, the aqueous layer may be separated from the organic layer, and the impurities contained in the aqueous layer may be removed. Specific conditions for separating the aqueous layer from the organic layer are not particularly limited, and various known purification techniques may be applied to specific separation devices and methods without limitation. However, for example, a drain device may be used.

[0096] 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.

[0097] 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 conditions of the vacuum distillation are 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.

[0098] The separated carbonate precursor may be recycled without a separate separation and purification process, or may be recycled after, as necessary, conventional separation and purification such as extraction, adsorption, drying, etc. Specific purification conditions are not particularly limited, and various known purification techniques may be applied to specific purification devices and methods without limitation.

[0099] In addition, the method for producing a monomer composition for synthesizing recycled plastics according to another embodiment may further include, after the step of separating a carbonate precursor from the depolymerization reaction product, a step of purifying the depolymerization reaction product from which the carbonate precursor has been separated.

[0100] Specifically, the purification step of the depolymerization reaction product from which the carbonate precursor is separated may include a washing step of the depolymerization reaction product from which the carbonate precursor is separated. Also, the purification step of the depolymerization reaction product from which the carbonate precursor is separated may include an adsorption purification step of the depolymerization reaction product from which the carbonate precursor is separated. Also, the purification step of the depolymerization reaction product from which the carbonate precursor is separated may include a recrystallization step of the depolymerization reaction product from which the carbonate precursor is separated.

[0101] The order of the washing step, the adsorption purification step, and the recrystallization step is not particularly limited and may be any order, but for example, the washing step, the adsorption purification step, and the recrystallization step may be performed in that order. The washing step, the adsorption purification step, and the recrystallization step may each be repeated at least once. Specific apparatuses and methods for washing, adsorption, and recrystallization may be applied to various known purification techniques without any restrictions.

[0102] 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 of obtaining the aromatic diol compound, washing may be performed to sufficiently remove the impurities to obtain a high-purity aromatic diol compound.

[0103] Specifically, the cleaning step may include a step of cleaning with a solvent at a temperature of 10° C. to 30° C., or 20° C. to 30° C., and a step of cleaning 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 cleaning vessel where cleaning 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.

[0104] 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. Alternatively, the washing step may be performed by first washing with a solvent at a temperature of 40° C. to 80° C. and then washing with a solvent at a temperature of 10° C. to 30° C.

[0105] 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 due to strong acid after the neutralization step.

[0106] 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. may each be repeated at least once.

[0107] 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 further performed.

[0108] 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.

[0109] 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.

[0110] If 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. is too low, such as less than 20° C., it is difficult to sufficiently remove impurities.

[0111] If the difference in temperature 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 more than 50° C., harsh conditions are formed in order to maintain the extreme temperature conditions, and the efficiency of the process is reduced.

[0112] 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.

[0113] 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 mole of the polycarbonate-based resin used in the depolymerization reaction.

[0114] 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. As the organic solvent, methylene chloride may be preferably used. 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.

[0115] 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.

[0116] In addition, the step of adsorbing and purifying the depolymerization reaction product from which the carbonate precursor is separated may include a step of introducing an adsorbent into the depolymerization reaction product from which the carbonate precursor is separated, adsorbing and purifying the product, and then removing the adsorbent. In the step of introducing an adsorbent into the depolymerization reaction product from which the carbonate precursor is separated, adsorbing and purifying the product, and then removing the adsorbent, the adsorbent may be contacted with the depolymerization reaction product.

[0117] Examples of the adsorbent include activated carbon, charcoal, 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.

[0118] More specifically, examples of plant-based activated carbon include coconut shell activated carbon, wood activated carbon, and sawdust activated carbon. Examples of coal-based activated carbon include lignite activated carbon, bituminous 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.

[0119] The adsorbent may include one or more activated carbons selected from the group consisting of plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon, i.e., the adsorbent may include plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, waste-based activated carbon, or a mixture of two or more of these.

[0120] More specifically, the adsorbent may include one or more activated carbons selected from the group consisting of coconut shell activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous activated carbon, i.e., the adsorbent may include coconut shell activated carbon, lignite activated carbon, anthracite activated carbon, bituminous activated carbon, or a mixture of two or more thereof.

[0121] The adsorption purification conditions using the 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 is 40% by weight to 60% by weight relative to the polycarbonate resin, the adsorption time is 1 hour to 5 hours, and the adsorption method is stirring adsorption or a lab adsorption tower.

[0122] If necessary, the method may further include a step of adding a solvent to the depolymerization reaction product from which the carbonate precursor has been separated, before the step of adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated and removing the 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 has been separated, the crystals of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor has been separated are redissolved in the solvent.

[0123] Meanwhile, 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.

[0124] Specifically, the recrystallization step may include a step of adding water to the depolymerization reaction product from which the carbonate precursor is separated to perform recrystallization. By performing the step of adding water to the depolymerization reaction product from which the carbonate precursor is 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 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 is easily precipitated as crystals due to the difference in solubility.

[0125] More specifically, in the step of adding water to the depolymerization reaction 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 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 an excessive amount of water is used, 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 a reduced process efficiency due to the use of a large amount of solvent.

[0126] If necessary, after the depolymerization reaction product from which the carbonate precursor has been separated is recrystallized, a process of removing remaining impurities by filtration or adsorption may be further performed.

[0127] If necessary, a drying step may be further included after the recrystallization step. The residual solvent can be removed by the drying, and the specific drying conditions are not particularly limited, but the drying can be performed 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 known drying techniques can be applied without any restrictions.

[0128] 3. Recycled plastics According to yet 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.

[0129] The content relating to the monomer composition for synthesizing recycled plastics in the one embodiment includes all of the content described above in the embodiment.

[0130] 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.

[0131] 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 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 is 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 and one type of carbonate precursor as well as one or more other diols, a copolymer is synthesized. The homopolymer or copolymer may include all low molecular weight compounds, oligomers, and polymers according to the molecular weight range.

[0132] More specifically, in the recycled plastics including 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.

[0133] 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 methods for producing polycarbonate can be applied without any restrictions.

[0134] 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 composition containing a monomer composition for synthesizing recycled plastics and 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 allows easy molecular weight control.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] In addition, the polymerization can be carried out in the presence of a molecular weight regulator in order 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, relative to 100 parts by weight of the aromatic diol compound, and a desired molecular weight can be obtained within the above range.

[0139] 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 further used.

[0140] 4. Molded products According to yet another embodiment of the present invention, there is provided a molded product including the recycled plastic of the other embodiment. The content related to the recycled plastic includes all of the content described above in the other embodiment.

[0141] 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.

[0142] The molded article is not particularly limited, and may be applied to various molded articles using plastics without any restrictions, such as automobile parts, electric and electronic products, communication products, daily necessities, building materials, optical parts, exterior materials, etc.

[0143] In addition to the recycled plastic of the other embodiment, the molded article may further contain, as necessary, one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact modifiers, fluorescent brighteners, ultraviolet absorbers, pigments, and dyes.

[0144] 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 into an injection molding machine. Effect of the Invention

[0145] According to the present invention, it is possible to provide a monomer composition for synthesizing recycled plastics, which can ensure an aromatic diol compound having improved optical properties in high yield, a method for producing the same, and recycled plastics and molded articles each using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0146] The present invention will be described in detail below with reference to examples. However, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0147] <Examples and Comparative Examples: Production of Recycled Bisphenol A Monomer Composition> Example 1 (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of methylene chloride (MC), and then added to a 3L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH). Sodium hydrosulfite was added as an antioxidant at 0.7% by weight based on the total solution, the atmosphere in the system was replaced with nitrogen, and the PC depolymerization reaction was carried out by stirring at 60°C for 6 hours in an inert state.

[0148] (2. Adjustment of pH) After the product of the depolymerization reaction was cooled to 30° C. or less, the pH of the bisphenol A was adjusted to 8 by adding 10% hydrochloric acid (HCl) and water to the product.

[0149] (3. Layer Separation) After that, in a state where an aqueous layer and a methylene chloride (MC) layer were formed, the organic layer located at the bottom was recovered using a drain device at the bottom of the reactor, and the aqueous layer located at the top was discharged and discarded.

[0150] (4. Distillation) The recovered methylene chloride (MC) layer was then subjected to low-temperature distillation at 250 mbar, 20-30°C and reduced pressure at 30 mbar, 30°C, to separate and recover the by-product diethyl carbonate (DEC).

[0151] (5. Purification step - Filtration) After removing diethyl carbonate (DEC), the residue was washed with methylene chloride (MC) in an amount twice the mass of PC used at 20-30°C and vacuum filtered. The filtrate was washed with water in an amount twice the mass of PC used at 50°C for the second time.

[0152] (6-1. Additional purification step-redissolution step) Then, bisphenol A was redissolved in 16.6 mol of ethanol.

[0153] (6-2. Additional purification step-adsorption step) Then, lignite activated carbon was added as an adsorbent in a ratio of 50% by weight to the waste polycarbonate, and the mixture was purified by adsorption for 3 hours, and then filtered to remove the lignite activated carbon.

[0154] (6-3. Additional purification step-recrystallization step) Then, 300 mol of water was added to recrystallize bisphenol A, and the resulting slurry was vacuum filtered at 20 to 30° C. to recover bisphenol A (BPA) crystals.

[0155] (7. Drying step) After that, the mixture was dried in a convection oven at 40° C. to produce a recycled bisphenol A monomer composition from which recycled bisphenol A (BPA) was recovered.

[0156] Example 2 A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the pH was adjusted to 7 instead of 8 in (2. Adjustment of pH).

[0157] Example 3 A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the pH was adjusted to 5 instead of 8 in (2. Adjustment of pH).

[0158] Example 4 A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the pH was adjusted to 2 instead of 8 in (2. Adjustment of pH).

[0159] Comparative Example 1 A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that (2. pH adjustment) and (3. phase separation) in Example 1 were not carried out.

[0160] Comparative Example 2 A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that in (2. Adjustment of pH) of Example 1, 10% hydrochloric acid (HCl) was not added, and only water was added to adjust the pH to more than 10.

[0161] <Experimental Example> The recycled bisphenol A monomer compositions obtained in the above Examples and Comparative Examples were measured for physical properties by the following methods. The results are shown in Table 1.

[0162] 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, 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).

[0163] 2. Color coordinates (L*, a*, b*) The recycled bisphenol A monomer composition was analyzed using a HunterLab UltraScan PRO Spectrophotometer instrument in reflectance mode.

[0164] 3. Yield When the polycarbonate used in the reaction was 100% decomposed, the weight of the produced BPA was measured, and the weight of the obtained BPA was measured to calculate the BPA yield according to the following formula 1. [Formula 1] Yield(%)=W1 / W0 In the above formula 1, W0 is the mass of BPA obtained at 100% decomposition, and W1 is the mass of BPA actually obtained. Specifically, when about 100g of polycarbonate is decomposed, the mass of BPA theoretically obtained at 100% decomposition is 89g. If the mass of BPA actually obtained is 80g, the yield is 80 / 89*100=90%.

[0165] 4. Impurity content of sodium salt 1 ml of the recycled bisphenol A monomer composition was collected as a sample and analyzed by ion chromatography (IC) under the following conditions to measure the weight ratio (unit: μg / g) of sodium salt impurities contained therein based on 1 g of the sample.

[0166] <Ion chromatography (IC) conditions> a) Column: HP-1 (L: 30 m, ID: 0.32 mm, film: 1.05 m) b) Injection volume: 1 μl c) Inlet Temp.: 260 °C, Pressure: 6.92 psi, Total flow: 64.2 ml / min, Split flow: 60 ml / min, split ratio: 50:1 d) Column flow: 1.2 ml / min e) Oven temp.: 70 °C / 3 min - 10 °C / min - 280 °C / 41 min (Total 65 min) f) Detector Temp.: 280 °C, H2: 35 ml / min, Air: 300 ml / min, He: 20 ml / min

[0167]

Table 1

[0168] As shown in Table 1 above, the recycled bisphenol A monomer compositions obtained in Examples 1 to 4 exhibited high purities of 99.29% to 99.92%. In addition, the recycled bisphenol A monomer compositions obtained in Examples 1 to 4 exhibited color coordinates L* of 98.12 to 98.91, a* of -0.15 to -0.01, and b* of 0.21 to 0.43, and exhibited excellent optical properties. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 to 4 were measured to have high BPA yields of 79.1% to 83%. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 to 4 were measured to have low impurity contents of less than 10 μg / g. On the other hand, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 had purities of 96.82% to 97.14%, which were lower than those of the Examples. In addition, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 showed poor optical properties compared to the Examples, with color coordinates L* of 97.12 to 97.82, a* of 0.06 to 0.31, and b* of 1.16 to 1.62. Furthermore, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 showed a BPA yield of 65.1% to 69.1%, which was lower than that of the Examples.

Claims

1. A monomer for synthesizing recycled plastics recovered from polycarbonate-based resins, the monomer for synthesizing recycled plastics being an aromatic diol compound, the color coordinate b* is between 0.1 and 1; The yield of the aromatic diol compound represented by the following formula 1 is more than 75%, The monomer for synthesizing recycled plastics is characterized in that diethyl carbonate is obtained as a by-product, and the diethyl carbonate is recovered from polycarbonate-based resin. [Formula 1] Yield (%) = (W 1 / W 0 ) x 100 In the above formula 1, W 0 is the mass of the aromatic diol compound obtained when the polycarbonate resin is decomposed 100%, and W 1 is the mass of the aromatic diol compound actually obtained.

2. The monomer for synthesizing recycled plastics according to claim 1, wherein the monomer for synthesizing recycled plastics has a color coordinate L* of 98 or more.

3. The monomer for synthesizing recycled plastics according to claim 1 , wherein the color coordinate a* of the monomer for synthesizing recycled plastics is 0 or less.

4. The monomer for synthesizing recycled plastics according to claim 1, wherein the purity of the aromatic diol compound is 98% or more.

5. The monomer for synthesizing recycled plastics according to claim 1, wherein the weight ratio of sodium salt impurities measured using ion chromatography is less than 10 μg / g per 1 g of the monomer for synthesizing recycled plastics.

6. A method for producing a monomer for synthesizing recycled plastics according to any one of claims 1 to 5, comprising the steps of: A step of depolymerizing a polycarbonate-based resin; adding an acid to the depolymerization reaction product so that the pH of the depolymerization reaction product is 2 to 8; removing impurities after the addition of the acid; and separating a carbonate precursor from the depolymerization reaction product.

7. adding an acid to the depolymerization reaction product so that the pH of the depolymerization reaction product is 2 to 8; 7. The method for producing a monomer for synthesizing recycled plastics according to claim 6, wherein the salt of the aromatic diol compound contained in the depolymerization reaction product is converted into an aromatic diol compound.

8. removing impurities after the addition of the acid, 7. The method for producing a monomer for synthesizing recycled plastics according to claim 6, wherein an aqueous layer containing impurities is separated from an organic solvent layer containing the aromatic diol compound and the carbonate precursor.

9. The depolymerization reaction of the polycarbonate resin is The method for producing a monomer for synthesizing recycled plastics according to claim 6, characterized in that the reaction is carried out in a solvent containing ethanol.

10. The method for producing a monomer for synthesizing recycled plastics according to claim 9, wherein the amount of ethanol is 10 to 15 moles per mole of polycarbonate resin.

11. The depolymerization reaction of the polycarbonate resin is 7. The method for producing a monomer for synthesizing recycled plastics according to claim 6, 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.

12. During the depolymerization reaction of the polycarbonate-based resin, 7. The method for producing a monomer for synthesizing recycled plastics according to claim 6, further comprising adding an antioxidant to the reaction solution.

13. separating a carbonate precursor from the depolymerization reaction product, The method for producing a monomer for synthesizing recycled plastics according to claim 6, further comprising a step of vacuum distillation of the depolymerization reaction product.

14. After the step of separating the carbonate precursor from the depolymerization reaction product, The method for producing a monomer for synthesizing recycled plastics according to claim 6, further comprising a purification step of the depolymerization reaction product from which the carbonate precursor has been separated.

15. The purification step of the depolymerization reaction product from which the carbonate precursor has been separated includes: The method for producing a monomer for synthesizing recycled plastics according to claim 14, further comprising a step of washing the depolymerization reaction product from which the carbonate precursor has been separated.

16. The purification step of the depolymerization reaction product from which the carbonate precursor has been separated includes: The method for producing a monomer for synthesizing recycled plastics according to claim 14, further comprising a step of recrystallizing the depolymerized reaction product from which the carbonate precursor has been separated.

17. The purification step of the depolymerization reaction product from which the carbonate precursor has been separated includes: The method for producing a monomer for synthesizing recycled plastics according to claim 14, further comprising an adsorption purification step of the depolymerization reaction product from which the carbonate precursor has been separated.

18. A recycled plastic comprising a reaction product of the monomer and comonomer for synthesizing recycled plastic according to any one of claims 1 to 5.

19. A molded article comprising the recycled plastic according to claim 18.

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