Monomer composition for recycled plastic synthesis, method for producing the same, recycled plastic using the same, and molded article

Abstract

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

Description

Technical Field

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

[0002] The present invention relates to a monomer composition for recycled plastic synthesis, a method for manufacturing the same, a recycled plastic using the same, and a molded article, which can achieve excellent color quality despite being recovered by chemical decomposition and recycling of polycarbonate - based resins, and which has improved efficiency in the recovery process.

Background Art

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

[0004] Although polycarbonate is widely used in various applications, concerns about the environment and health during waste treatment have been continuously raised.

[0005] Currently, physical recycling methods are being carried out, but in this case, problems such as quality degradation have occurred, and research on chemical recycling of polycarbonate is underway.

[0006] Chemical decomposition of polycarbonate refers to obtaining an aromatic diol compound (for example, bisphenol A (BPA)), which is a monomer, by decomposing polycarbonate, and then re - using this for polymerization to obtain high - purity polycarbonate.

[0007] Typical chemical decompositions include thermal decomposition, hydrolysis, and alcoholysis. Among these, the most common method is alcoholysis using a base catalyst. However, in the case of methanolysis, there is a problem of using methanol, which is harmful to the human body. In the case of ethanolysis, high-temperature and high-pressure conditions are required, and the yield is not high.

[0008] In addition, an alcoholysis method using an organic catalyst is known, but currently, it has disadvantages in terms of economy.

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention provides a monomer composition for recycled plastic synthesis that can achieve excellent color quality and improve the efficiency of the recovery process, despite being recovered by chemical decomposition and reuse of a polycarbonate-based resin.

[0010] The present invention also provides a method for producing the monomer composition for recycled plastic synthesis, a recycled plastic using the monomer composition for recycled plastic synthesis, and a molded article.

Means for Solving the Problems

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

[0012] In this specification, there is also provided a method for producing a monomer composition for recycled plastic synthesis, including the steps of depolymerizing a polycarbonate resin; separating a carbonate precursor from the depolymerization reaction product; and purifying the depolymerization reaction product from which the carbonate precursor has been separated, wherein the step of purifying the depolymerization reaction product from which the carbonate precursor has been separated includes the steps of adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated; and adsorbing and purifying by adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated, and then removing the adsorbent.

[0013] In this specification, there is also provided recycled plastic including the reaction product of the monomer composition for recycled plastic synthesis and a comonomer.

[0014] In this specification, there is also provided a molded article including the recycled plastic.

[0015] Hereinafter, the monomer composition for recycled plastic synthesis, its production method, the recycled plastic using the same, and the molded article according to specific embodiments of the invention will be described in more detail.

[0016] In this specification, unless otherwise explicitly stated, technical terms are merely for referring to specific examples and are not intended to limit the present invention.

[0017] As used in this specification, the singular form also includes the plural form unless the context clearly indicates the contrary.

[0018] As used in this specification, "including" does not exclude the presence or addition of other specific characteristics, regions, integers, steps, operations, elements, components, and / or groups while specifying a particular characteristic, region, integer, step, operation, element, component, and / or group.

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

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

[0021] The inventors of the present invention have confirmed through experiments that, although the monomer composition for recycled plastic synthesis of the above-described embodiment is recovered by recycling through chemical decomposition of a polycarbonate-based resin, the main recovered aromatic diol compound can achieve excellent color quality, and excellent physical properties can be realized when synthesizing a polycarbonate-based resin using this, and thus completed the invention.

[0022] In particular, the monomer composition for recycled plastic synthesis of the above-described embodiment has the technical merit that it can reduce the amount of water used in the recrystallization process while reducing the amount of organic solvent used in the adsorption purification process among the manufacturing processes described later, and can achieve excellent color quality while enhancing the efficiency of the process.

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

[0024] Specifically, the monomer composition for recycling plastic synthesis according to the above-described embodiment is characterized by being recovered from a polycarbonate-based resin. That is, in order to obtain the monomer composition for recycling plastic synthesis according to the above-described embodiment, as a result of proceeding with the recovery from the polycarbonate-based resin, it means that a monomer composition for recycling plastic synthesis containing an aromatic diol compound is obtained together.

[0025] The polycarbonate-based resin includes all homopolymers or copolymers containing polycarbonate repeating units, and generally refers to reaction products obtained by a polymerization reaction or copolymerization reaction of monomers containing an aromatic diol compound and a carbonate precursor. When only one type of aromatic diol compound and one type of carbonate precursor are used to obtain a polycarbonate repeating unit, a homopolymer can be synthesized. Further, as the monomer, when one type of aromatic diol compound and two or more types of carbonate precursors are used, or 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 included by using one or more other diols in addition to one type of aromatic diol compound and one type of carbonate precursor, a copolymer can be synthesized. The homopolymer or copolymer can include all low molecular compounds, oligomers, and polymers depending on the molecular weight range.

[0026] Further, the monomer composition for recycling plastic synthesis according to the above 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 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 thereof. Preferably, the aromatic diol compound in the monomer composition for recycling plastic synthesis according to the above embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0027] The aromatic diol compound is characterized by being recovered from the polycarbonate resin used for the recovery of the monomer composition for recycling plastic synthesis. That is, in order to obtain the monomer composition for recycling plastic synthesis according to the above embodiment, as a result of proceeding with the recovery from the polycarbonate resin, it means that the aromatic diol compound is also obtained together. Therefore, when a new aromatic diol compound is added from the outside separately from the recovery from the polycarbonate resin in order to produce the monomer composition for recycling plastic synthesis according to the above embodiment, it is not included in the category of the aromatic diol compound of the present invention.

[0028] Specifically, being recovered from the polycarbonate resin means being obtained by the depolymerization reaction of the polycarbonate resin. The depolymerization reaction can be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction can be carried out under basic (alkaline) conditions. In particular, as will be described later, the depolymerization reaction preferably proceeds in an ethanol solvent.

[0029] On the other hand, the monomer composition for synthesizing recycled plastic of the above embodiment may have a b* value of the color coordinate of 1.8 or less, or 1.65 or less, or 0.1 or more, or 1.0 or more, or 0.1 to 1.8, or 1.0 to 1.8, or 0.1 to 1.65, or 1.0 to 1.65, or 1.6 to 1.7, or 1.6 to 1.65, or 1.65 to 1.7.

[0030] Also, the monomer composition for synthesizing recycled plastic of the above embodiment may have an L* value of the color coordinate of 95.5 or more, or 96 or more, or 100 or less, or 95.5 to 100, or 96 to 100, or 95.6 to 96.7, or 95.6 to 96, or 96 to 96.7.

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

[0032] In the present invention, the "color coordinate" means the coordinates in the CIE Lab color space, which is a color value defined by the CIE (Commission International de l’Eclairage), and any position in the CIE color space is represented by three coordinate values of L*, a*, and b*.

[0033] Here, the L* value indicates brightness. If L* = 0, it indicates black, and if L* = 100, it indicates white. Also, the a* value indicates whether the color having the color coordinates is biased towards pure red or pure green, and the b* value indicates whether the color having the color coordinates is biased towards pure yellow or pure blue.

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

[0035] If the b* value of the color coordinates of the monomer composition for recycled plastic synthesis in the above embodiment exceeds 1.8 and increases excessively, or if the L* value of the color coordinates is less than 95.5 and decreases excessively, or if the a* value of the color coordinates is outside the range of exceeding -0.2 or less than -0.7, the color characteristics of the monomer composition for recycled plastic synthesis in the above embodiment will deteriorate. The examples of the method for measuring the color coordinates L*, a*, and b* values of the monomer composition for recycled plastic synthesis in the above embodiment are not greatly limited, and various methods for measuring color characteristics in the plastic field can be applied without limitation.

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

[0037] On the one hand, the monomer composition for recycled plastic synthesis of the above-described embodiment may have an APHA Color value measured by ASTM D 1209 of 30 or less, or 29 or less, or 28 or less, or 25 or less, or 22 or less, or 0 or more, or 1 or more, or 0 to 30, or 0 to 29, or 0 to 28, or 0 to 25, or 0 to 22, or 1 to 30, or 1 to 29, or 1 to 28, or 1 to 25, or 1 to 22, or 22 to 28, or 22 to 25, or 25 to 28.

[0038] Examples of methods for measuring the APHA Color of the monomer composition for recycled plastic synthesis of the above-described embodiment are not greatly limited. For example, it can be measured by the ASTM D 1209 measurement method using a HunterLab UltraScan PRO Spectrophotometer device.

[0039] APHA Color is a value obtained from the color comparison between colorless water and a PtCo solution with a yellow color. The closer the value is to 0, the more colorless it is, and the closer it is to 500, the more yellow it shows. Therefore, by reducing the APHA Color of the monomer composition for recycled plastic synthesis of the above-described embodiment to 30 or less, it is possible to achieve transparent color physical properties during the synthesis of a polycarbonate-based resin using this composition.

[0040] On the other hand, if the APHA Color of the monomer composition for recycled plastic synthesis of the above-described embodiment excessively increases, such as exceeding 30, there is a limit that it becomes difficult to synthesize a colorless and transparent polycarbonate-based resin due to yellowing modification.

[0041] On the one hand, the monomer composition for recycled plastic synthesis of the above-described embodiment may further contain a hydrophilic reducing agent. The hydrophilic reducing agent is soluble in water and can be used as a bleaching agent that removes color by changing colored substances. The examples of the hydrophilic reducing agent are not greatly limited, and various conventionally known hydrophilic reducing bleaching agents can be applied without limitation. For example, sodium dithionite (SDT) can be mentioned.

[0042] On the other hand, diethyl carbonate is obtained as a by-product in the monomer composition for recycled plastic synthesis of the above-described embodiment. The diethyl carbonate is characterized by being recovered from the polycarbonate resin used for the recovery of the monomer composition for recycled plastic synthesis of the above-described embodiment.

[0043] That is, in order to obtain the monomer composition for recycled plastic synthesis of the above-described embodiment, as a result of proceeding with the recovery from the polycarbonate resin, it means that diethyl carbonate is also obtained together. Therefore, when adding a new diethyl carbonate from the outside separately from the recovery from the polycarbonate resin in order to produce the monomer composition for recycled plastic synthesis of the above-described embodiment, it is not included in the scope of the diethyl carbonate of the above-described embodiment.

[0044] Specifically, being recovered from the polycarbonate resin means being obtained by the depolymerization reaction of the polycarbonate resin. The depolymerization reaction is carried out under acidic, neutral, or basic conditions. In particular, the depolymerization reaction can be carried out under basic (alkaline) conditions. In particular, as will be described later, the depolymerization reaction preferably proceeds in an ethanol solvent.

[0045] Since the main recovery target substance in the monomer composition for recycled plastic synthesis of the above-described embodiment is an aromatic diol compound, the diethyl carbonate can be separately separated and recovered from the monomer composition for recycled plastic synthesis of the above-described embodiment as a by-product.

[0046] The monomer composition for recycled plastic synthesis of the above-described embodiment can be used as a raw material for manufacturing various recycled plastics (for example, polycarbonate (PC)) described later.

[0047] The monomer composition for recycled plastic synthesis of the above-described embodiment can further contain a small amount of other additives and solvents. The types of specific additives and solvents are not greatly limited, and various substances widely used in the process of recovering aromatic diol compounds by depolymerization of polycarbonate resins can be applied without limitation.

[0048] The monomer composition for recycled plastic synthesis of the above-described embodiment may be obtained by the manufacturing method of the monomer composition for recycled plastic synthesis described later. That is, the monomer composition for recycled plastic synthesis of the above-described embodiment corresponds to the result obtained through various filtration, purification, washing, and drying steps in order to ensure only the aromatic diol compound, which is the main recovery target substance, with high purity after the depolymerization reaction of the polycarbonate resin.

[0049] 2. Manufacturing Method of Monomer Composition for Recycled Plastic Synthesis According to another embodiment of the invention, there is provided a method for manufacturing a monomer composition for recycled plastic synthesis, including the steps of subjecting a polycarbonate resin to a depolymerization reaction; separating a carbonate precursor from the depolymerization reaction product; and purifying the depolymerization reaction product from which the carbonate precursor has been separated, wherein the step of purifying the depolymerization reaction product from which the carbonate precursor has been separated includes the steps of adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated; and adsorbing and purifying by adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated, and then removing the adsorbent.

[0050] The inventors have confirmed through experiments that, like the method for producing the monomer composition for recycled plastic synthesis of the other embodiments, in the process of recycling the polycarbonate resin by chemical decomposition, by including a step of adding a hydrophilic reducing agent and a step of adsorption purification using an adsorbent, it is possible to reduce the amount of the organic solvent used in the adsorption purification step, improve the efficiency of the process, and achieve excellent color quality, thereby completing the invention.

[0051] Specifically, the method for producing the monomer composition for recycled plastic synthesis of the other embodiments may further include a pretreatment step of the polycarbonate resin before the step of depolymerizing the polycarbonate resin.

[0052] The polycarbonate resin means all homopolymers or copolymers containing polycarbonate repeating units, and generally refers to reaction products obtained by polymerization or copolymerization of monomers containing an aromatic diol compound and a carbonate precursor. When only one type of aromatic diol compound and one type of carbonate precursor are used to obtain a carbonate repeating unit, a homopolymer can be synthesized. Also, as the monomer, when using one type of aromatic diol compound and two or more types of carbonate precursors, or two or more types of aromatic diol compounds and one type of carbonate precursor, or using one or more other diols in addition to one type of aromatic diol compound and one type of carbonate precursor such that two or more types of carbonates are included, a copolymer can be synthesized. The homopolymer or copolymer can include all low molecular weight compounds, oligomers, and polymers depending on the molecular weight range.

[0053] The polycarbonate resin is applicable regardless of various forms and types, such as newly produced polycarbonate resin by synthesis, recycled polycarbonate resin produced by a recycling process, or waste of polycarbonate resin.

[0054] The efficiency of the step of pretreating the polycarbonate resin to recover the aromatic diol compound and the carbonate precursor from the polycarbonate resin can be increased. Examples of the pretreatment step include filtration, washing, drying, pulverization, glycolysis, etc. The specific methods of each pretreatment step are not limited, and various methods widely used in the step of recovering the aromatic diol compound and the carbonate precursor by depolymerization of the polycarbonate resin can be applied without limitation.

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

[0056] On the other hand, the method for producing the monomer composition for recycling plastic synthesis of the other embodiment can include a step of subjecting the polycarbonate resin to a depolymerization reaction.

[0057] During the depolymerization reaction of the polycarbonate resin, the depolymerization reaction is carried out under acidic, neutral, or basic conditions. In particular, the depolymerization reaction can be carried out under basic (alkaline) conditions. The type of the base is not greatly limited. As an example, sodium hydroxide (NaOH) or potassium hydroxide (KOH) can be mentioned. The base is a base catalyst that acts as a catalyst and has the advantage of being more economical than organic catalysts mainly used under mild conditions.

[0058] During the depolymerization reaction of the polycarbonate resin, the reaction can be carried out by reacting a base in an amount of 0.5 mol or less, or 0.4 mol or less, or 0.3 mol or less, or 0.1 mol or more, or 0.2 mol or more, or 0.1 mol to 0.5 mol, or 0.1 mol to 0.4 mol, or 0.1 mol to 0.3 mol, or 0.2 mol to 0.5 mol, or 0.2 mol to 0.4 mol, or 0.2 mol to 0.3 mol, per 1 mol of the polycarbonate resin. When the base is reacted in an amount exceeding 0.5 mol per 1 mol of the polycarbonate resin during the depolymerization reaction of the polycarbonate resin, there is a limit that impurities increase due to an increase in the amount of alkali salt generated, the purity of the target recovered substance decreases, and the economic efficiency of the catalytic reaction decreases.

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

[0060] The content of the ethanol may be 5 mol to 15 mol, or 8 mol to 13 mol, per 1 mol of the polycarbonate resin. Since ethanol has good solubility in bisphenol A, ethanol within the above range must be essentially contained. If the content of the ethanol is excessively reduced to less than 5 mol per 1 mol of the polycarbonate resin, it is difficult to sufficiently carry out the alcohol decomposition of the polycarbonate resin. On the contrary, if the content of the ethanol is excessively increased to more than 15 mol per 1 mol of the polycarbonate resin, the economic efficiency of the process may decrease due to excessive use of alcohol.

[0061] The solvent in which the depolymerization reaction of the polycarbonate resin is carried out can further contain 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 in addition to ethanol.

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

[0063] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent to be mixed with the ethanol, there is an advantage that the dissolution characteristics with respect to the polycarbonate are improved and the reactivity can be enhanced.

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

[0065] On the other hand, the temperature at which the depolymerization reaction of the polycarbonate resin proceeds is not greatly limited. For example, it can proceed at 20°C to 100°C, or 50°C to 70°C. Also, the time for the depolymerization reaction of the polycarbonate resin to proceed can be 1 hour to 30 hours, or 4 hours to 6 hours.

[0066] Specifically, the conditions are mild process conditions compared to the existing pressurization / high-temperature process. By performing stirring under these conditions, the process can be carried out under milder conditions than the pressurization / high-temperature process. In particular, when stirring at 50°C to 70°C for 4 to 6 hours, there is an advantage that the most efficient results can be obtained in terms of reproducibility and stability.

[0067] That is, the present invention can obtain a high-purity aromatic diol compound (for example, bisphenol A) under mild conditions without using a pressurization / high-temperature process by adjusting the types and mixing amounts of the mixed solvents and the types and contents of the base catalysts. Since an ethanol solvent is used, there is an advantage that diethyl carbonate can be obtained as a by-product.

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

[0069] Also, the step of depolymerizing the polycarbonate resin can include a step of adding an antioxidant to the reactant containing the polycarbonate resin. Thus, since the aromatic diol compound obtained during the depolymerization reaction of the polycarbonate resin is easily oxidized under basic conditions, an antioxidant can be added to the reaction solution.

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

[0071] The addition amount of the antioxidant is not greatly limited. For example, it is added in an amount of 0.05% to 4% by weight based on the weight of the polycarbonate resin. Within this range, there is an antioxidant effect, it is cost-effective, and the decomposition reaction rate does not decrease.

[0072] The adsorbent can 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.

[0073] On the other hand, the method for producing the monomer composition for recycling plastic synthesis according to the other embodiment can further include a step of neutralizing the depolymerization reaction product with an acid before separating the carbonate precursor from the depolymerization reaction product.

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

[0075] The acid used during the neutralization reaction can be a strong acid, for example, hydrochloric acid (HCl). Through the neutralization reaction with the strong acid, at the end of the neutralization reaction, the pH can satisfy being 4 or less, or less than 2. The temperature during the neutralization reaction can be adjusted to be 25°C or higher and 100°C or lower.

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

[0077] On the other hand, the method for producing the monomer composition for recycling plastic synthesis of the other embodiment can include a step of separating a carbonate precursor from the depolymerization reaction product. Therefore, the separated carbonate precursor can contain diethyl carbonate.

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

[0079] In the step of separating the carbonate precursor from the depolymerization reaction product, a vacuum distillation step of the depolymerization reaction product can be included. Examples of the vacuum distillation conditions are not greatly limited, but to give a specific example, the polycarbonate resin is depressurized at a pressure of 200 mbar to 300 mbar and a temperature of 20 °C to 30 °C for the product of the depolymerization reaction, and then at a pressure of 50 mbar to 150 mbar and a temperature of 25 °C to 35 °C, and then at a pressure of 10 mbar to 50 mbar and a temperature of 35 °C to 45 °C for distillation. Methylene chloride (MC) can be removed by distillation under the condition of depressurization at a pressure of 200 mbar to 300 mbar and a temperature of 20 °C to 30 °C. Also, ethanol (EtOH) can be removed by distillation under the condition of depressurization at a pressure of 50 mbar to 150 mbar and a temperature of 25 °C to 35 °C. And the carbonate precursor can be separated and recovered under the condition of depressurization at a pressure of 10 mbar to 50 mbar and a temperature of 35 °C to 45 °C.

[0080] The separated carbonate precursor can be reused without another separation and purification process, or can be reused after separation and purification such as ordinary extraction, adsorption, drying, etc. as needed. Specific purification conditions are not greatly limited, and for specific purification apparatuses and methods, various existing known purification techniques can be applied without limitation.

[0081] On the other hand, the method for producing the monomer composition for recycled plastic synthesis of the other embodiment can include a purification step of the depolymerization reaction product from which the carbonate precursor has been separated. Thereby, an aromatic diol compound, which is the main recovered substance, can be obtained, and this corresponds to the monomer composition for recycled plastic synthesis in the above-mentioned one embodiment.

[0082] Specifically, the purification step of the depolymerization reaction product from which the carbonate precursor has been separated can include the step of adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated; and the step of adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated for adsorption purification and then removing the adsorbent.

[0083] In the purification step, the order of the hydrophilic reducing agent addition step and the adsorption purification step is not particularly limited, and they may proceed in any order. For example, after the hydrophilic reducing agent addition step, the purification step can proceed in the order of the adsorption purification step. The hydrophilic reducing agent addition step and the adsorption purification step can each be repeated at least once or more. Regarding specific apparatuses and methods for reducing agent addition and adsorption, various existing known purification techniques can be applied without limitation.

[0084] On the other hand, before the step of adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated, a washing step of the depolymerization reaction product from which the carbonate precursor has been separated can be further included.

[0085] Specifically, in the washing step of the depolymerization reaction product from which the carbonate precursor has been separated, the depolymerization reaction product from which the carbonate precursor has been separated can contain an aromatic diol compound. However, since various impurities remain during the recovery process of obtaining the aromatic diol compound, washing can be carried out to sufficiently remove them and ensure a high-purity aromatic diol compound.

[0086] Specifically, the washing step can include a step of washing with a solvent at a temperature of 10°C to 30°C, or 20°C to 30°C; and a step of 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 conditions refer to the temperature inside the washing container where washing with the solvent is performed, and various heating devices can be applied without limitation to maintain a high temperature outside normal temperature.

[0087] The washing step can first perform the step of washing with a solvent at a temperature of 10°C to 30°C and then perform the step of washing with a solvent at a temperature of 40°C to 80°C. Also, the step of washing with a solvent at a temperature of 40°C to 80°C can be performed first, and then the step of washing with a solvent at a temperature of 10°C to 30°C can be performed.

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

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

[0090] Also, if necessary, after performing 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, an additional step of removing the remaining solvent by filtration can be passed through.

[0091] More specifically, the difference value 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.

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

[0093] If the difference value 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 less than 20°C and decreases excessively, it is difficult to sufficiently remove impurities.

[0094] If the difference value 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 exceeds 50°C and increases excessively, harsh conditions may be formed to maintain extreme temperature conditions, and the efficiency of the process may decrease.

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

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

[0097] More specifically, the solvent in the step of washing with a solvent at a temperature of 10°C to 30°C may be an organic solvent. As the organic solvent, preferably, methylene chloride can be used. And at this time, the organic solvent can be used in an amount of 1 part by weight or more and 10 parts by weight or less per 1 part by weight of the polycarbonate resin.

[0098] Also, the solvent in the step of washing with a solvent at a temperature of 40°C to 80°C may be water. By using the water, impurities in the form of salts remaining can be effectively removed. And at this time, the solvent can be used in an amount of 1 part by weight or more and 10 parts by weight or less per 1 part by weight of the polycarbonate resin.

[0099] On the other hand, before the step of adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated, a redissolution step of adding a mixture of an organic solvent and an aqueous solvent to the depolymerization reaction product from which the carbonate precursor has been separated can be further included. By the step of adding a mixture of an organic solvent and an aqueous solvent to the depolymerization reaction product from which the carbonate precursor has been separated, the aromatic diol compound crystals contained in the depolymerization reaction product from which the carbonate precursor has been separated can be redissolved in the mixture of the organic solvent and the aqueous solvent. Examples of the organic solvent include ethanol, and examples of the aqueous solvent include water.

[0100] The order of the washing step and the redissolution step is not particularly limited, and they may proceed in any order. For example, after the washing step, the purification step can proceed in the order of the redissolution step. The washing step and the redissolution step can each be repeated at least once or more. Regarding specific washing and dissolution apparatuses and methods, various existing known purification techniques can be applied without limitation.

[0101] Specifically, the mixture of the organic solvent and the aqueous solvent can contain 15% to 50% by weight of the organic solvent and 50% to 85% by weight of the aqueous solvent based on the weight of the entire mixture. If the aqueous solvent decreases to less than 50% by weight based on the weight of the entire mixture, the organic solvent is relatively excessively contained, resulting in an increase in the process cost due to the use and recovery of the organic solvent and a decrease in the efficiency of the process. On the contrary, if the aqueous solvent increases to more than 85% by weight based on the weight of the entire mixture, the solubility in the depolymerization reaction product from which the carbonate precursor has been separated and containing aromatic diol compound crystals decreases, and redissolution is difficult to perform sufficiently.

[0102] On the other hand, the method for producing the monomer composition for recycled plastic synthesis of the other embodiment can include the step of adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated.

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

[0104] The examples of the hydrophilic reducing agent are not greatly limited, and various conventionally known hydrophilic reducing bleaching agents can be applied without limitation. For example, sodium dithionite (SDT) can be mentioned.

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

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

[0107] If the input amount of the hydrophilic reducing agent increases too much, the hydrophilic reducing agent may not dissolve sufficiently, or the improvement effect on color characteristics may not be fully realized due to side reactions. On the contrary, if the input amount of the hydrophilic reducing agent decreases excessively to a small amount, the improvement effect on color characteristics by the hydrophilic reducing agent may not be fully realized.

[0108] On the other hand, after adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated for adsorption purification and then removing the adsorbent, the adsorbent can be brought into contact with the depolymerization reaction product.

[0109] As examples of the adsorbent, activated carbon, charcoal, celite, or a mixture thereof can be used. The activated carbon is a black carbon material having micropores produced through a carbonization process of the raw material at about 500°C and an activation process at about 900°C. Although the examples are not greatly limited, for example, depending on the type of raw material, various activated carbons such as plant-based, coal-based, petroleum-based, and waste material activated carbons can be applied without limitation.

[0110] To give a more specific example, as plant-based activated carbons, coconut shell activated carbon, wood activated carbon, and sawdust activated carbon can be mentioned. Also, as coal-based activated carbons, lignite activated carbon, bituminous coal activated carbon, and anthracite activated carbon can be mentioned. Also, as petroleum-based activated carbons, petroleum coke activated carbon and oil carbon activated carbon can be mentioned. Also, as waste material activated carbons, synthetic resin activated carbon and pulp activated carbon can be mentioned.

[0111] The adsorbent can include one or more activated carbons selected from the group consisting of plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste material activated carbon. That is, the second adsorbent can include plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, waste material activated carbon, or a mixture of two or more of these.

[0112] More specifically, the adsorbent can include one or more activated carbons selected from the group consisting of coconut shell activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous coal activated carbon. That is, the adsorbent can include coconut shell activated carbon, lignite activated carbon, anthracite activated carbon, bituminous coal activated carbon, or a mixture of two or more of these.

[0113] Thus, in the method for producing the monomer composition for recycling plastic synthesis according to the other embodiments, during the depolymerization reaction of recycling the polycarbonate-based resin by chemical decomposition, by applying the adsorption purification step using an adsorbent, in the present invention, not only can the aromatic diol compound, which is the main synthetic target substance, be ensured with high purity, but also the content of impurities other than the aromatic diol compound can be significantly reduced.

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

[0115] On the other hand, after adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated and performing adsorption purification, and after the step of removing the adsorbent, a recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated can be further included.

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

[0117] Specifically, the recrystallization step can include a step of adding a recrystallization solvent to the depolymerization reaction product from which the carbonate precursor has been separated and performing recrystallization. By the step of adding a recrystallization solvent to the depolymerization reaction product from which the carbonate precursor has been separated and performing recrystallization, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product increases, and crystals or impurities sandwiched between the crystals can be maximally dissolved in the solvent. Since the dissolved aromatic diol compound has a worse solubility than the impurities, when the temperature is subsequently lowered, the aromatic diol compound can be easily precipitated as crystals due to the difference in solubility. Water can be used as the recrystallization solvent.

[0118] More specifically, the recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated may include a step of adding 5 to 25 parts by weight of a recrystallization solvent with respect to 1 part by weight of the aromatic diol compound contained in the depolymerization reaction product. If the recrystallization solvent is used in an excessively small amount, the temperature for dissolving the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor has been separated becomes excessively high, resulting in poor process efficiency and difficulty in removing impurities by recrystallization. On the contrary, if the recrystallization solvent is used in an excessively large amount, the solubility of the aromatic diol compound contained in the depolymerization reaction product from which the carbonate precursor has been separated becomes excessively high, resulting in a decrease in the yield of the aromatic diol compound recovered after recrystallization and a possible decrease in process efficiency due to the use of a large amount of solvent.

[0119] Optionally, after the recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated, a step of removing residual impurities by filtration or adsorption can be additionally carried out.

[0120] Also, optionally, after the recrystallization step, a drying step can be further included. Residual solvents can be removed by the drying. Specific drying conditions are not greatly limited. For example, drying can be carried out at a temperature of 10°C to 100°C, or 10°C to 50°C. Regarding the specific drying apparatus and method used during the drying, various existing known drying techniques can be applied without limitation.

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

[0122] The content regarding the monomer composition for synthesizing the recycled plastic of the above embodiment includes all of the above-described content in the above embodiment and other embodiments respectively.

[0123] Examples corresponding to the recycled plastic are not greatly limited, and various plastics synthesized using aromatic diol compounds such as bisphenol A as monomers can be applied without limitation. More specific examples include polycarbonate resins.

[0124] The polycarbonate resin means all homopolymers or copolymers containing polycarbonate repeating units, and generally refers to reaction products obtained by polymerization or copolymerization of monomers containing aromatic diol compounds and carbonate precursors. When only one type of aromatic diol compound and one type of carbonate precursor are used to obtain a carbonate repeating unit, a homopolymer can be synthesized. Also, as the monomer, when using one type of aromatic diol compound and two or more types of carbonate precursors, or two or more types of aromatic diol compounds and one type of carbonate precursor, or using one or more other diols in addition to one type of aromatic diol compound and one type of carbonate precursor to contain two or more types of carbonates, a copolymer can be synthesized. The homopolymer or copolymer can include all low molecular weight compounds, oligomers, and polymers depending on the molecular weight range.

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

[0126] Examples of the reaction process of the monomer composition for synthesis and the comonomer are not greatly limited, and various known polycarbonate manufacturing methods can be applied without limitation.

[0127] However, as an example of the method for producing the polycarbonate, a method for producing a polycarbonate including a step of polymerizing a composition containing a monomer composition for synthesizing recycled plastic and a comonomer can be used. At this time, the polymerization can be carried out by interfacial polymerization. During interfacial polymerization, the polymerization reaction is possible at normal pressure and low temperature, and the molecular weight can be easily adjusted.

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

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

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

[0131] Furthermore, during the polymerization, for adjusting the molecular weight of the polycarbonate, polymerization can be carried out in the presence of a molecular weight regulator. As the molecular weight regulator, an alkylphenol having 1 to 20 carbon atoms can be used. Specific examples thereof include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol, or triacontylphenol. The molecular weight regulator can be added before, during, or after the 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.

[0132] In addition, for the promotion of the polymerization reaction, reaction accelerators such as tertiary amine compounds such as triethylamine, tetra-n-butylammonium bromide, tetra-n-butylphosphonium bromide, quaternary ammonium compounds, and quaternary phosphonium compounds can be additionally used.

[0133] 4. Molded article According to still another embodiment of the invention, a molded article containing the recycled plastic of the other embodiment is provided. The content regarding the recycled plastic includes all the content described above in the other embodiment.

[0134] The molded article may be obtained by applying the recycled plastic to various known plastic molding methods without limitation. Examples of the molding method include injection molding, foam injection molding, blow molding, or extrusion molding.

[0135] The examples of the molded article are not greatly limited and can be applied without limitation to various molded articles using plastic. Examples of the molded article include automotive parts, electrical and electronic products, communication products, daily necessities, building materials, optical parts, exterior materials, and the like.

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

[0137] As an example of the method for manufacturing the molded article, after thoroughly mixing the recycled plastic of the other embodiment and the additives using a mixer, extrusion molding is performed with an extruder to produce pellets, and after drying the pellets, an injection molding machine can be used for injection.

Advantages of the Invention

[0138] According to the present invention, despite being recovered by the reuse of polycarbonate-based resins through chemical decomposition, a monomer composition for synthesizing recycled plastics that can achieve excellent color quality and has improved efficiency in the recovery process, a method for manufacturing the same, recycled plastics using the same, and molded articles are provided.

Mode for Carrying Out the Invention

[0139] The invention will be described in more detail with the following examples. However, the following examples are merely illustrative of the invention, and the content of the invention is not limited by the following examples.

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

[0141] (2. Neutralization Step) After cooling the product of the depolymerization reaction to 30 °C or lower, it was neutralized at 20 - 30 °C using 0.25 mol of 10% hydrochloric acid (HCl).

[0142] (3. Distillation Step) Thereafter, methylene chloride (MC) was removed by distillation at 250 mbar and 20 °C, ethanol (EtOH) was removed by distillation at 80 mbar and 30 °C, and then diethyl carbonate (DEC), a by-product, was recovered by vacuum distillation at 30 mbar and 40 °C.

[0143] (4. Washing Step) Subsequently, the residue from which diethyl carbonate (DEC) had been removed was washed once at 20 - 30 °C with methylene chloride (MC) in an amount 1 times the mass ratio of PC used, and then vacuum filtered. The filtrate was washed a second time at 50 °C with water in an amount 1 times the mass ratio of PC used.

[0144] (5. Redissolution Step) To 6 g of the washed bisphenol A, 15 g of ethanol and 15 g of water were added and redissolved at room temperature.

[0145] (6. Reducing Agent Addition Step) Subsequently, 0.06 g of sodium dithionite (Na2S2O4, SDT) (1 wt% of the weight ratio of bisphenol A) was added to the solution and dissolved.

[0146] (7. Adsorption Step) Subsequently, 3 g of lignite activated carbon was added to the solution as an adsorbent and stirred for 10 minutes. Then, the activated carbon was removed once using a sieve filter (75 μm), and the residual activated carbon was removed a second time using a syringe filter (0.45 μm).

[0147] (8. Recrystallization Step) Subsequently, it was stirred, and 75 g of water was gradually added to recrystallize bisphenol A, and then a solid was obtained by filtration.

[0148] (9. Drying Step) Subsequently, it was dried in a vacuum oven at 30 - 50 °C to produce a reusable bisphenol A monomer composition.

[0149] (Example 2, Comparative Examples 1 - 2, Reference Examples 1 - 2) Except for changing to the process conditions described in Table 1 below, reusable bisphenol A monomer compositions of Example 2, Comparative Examples 1 - 2, and Reference Examples 1 - 2 were produced in the same manner as in Example 1.

[0150]

Table 1

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

[0152] 1. APHA Color For the recycled bisphenol A monomer composition, it was measured by the ASTM D 1209 measurement method using a HunterLab UltraScan PRO Spectrophotometer device.

[0153] 2. Color coordinates (L*, a*, b*) For the recycled bisphenol A monomer composition, it was measured in reflection mode using a HunterLab UltraScan PRO Spectrophotometer device.

[0154] [Table 2]

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

[0156] On the other hand, the recycled bisphenol A monomer composition obtained in Reference Example 1 showed optical physical properties similar to those of the Examples. However, in order to achieve this, as shown in Table 1 above, there was a problem of reduced process efficiency in that 180 g of excessive water had to be used in the recrystallization stage.

[0157] In addition, the recycled bisphenol A monomer composition obtained in Reference Example 2 showed a b* chromaticity coordinate of 3.0, and the APHA Color value was also measured to be 44, indicating poor optical properties compared to the examples.

Claims

1. comprising an aromatic diol compound, wherein the color coordinate b* is 1.8 or less, the APHA Color value measured by ASTM D 1209 is 30 or less, and being recovered from a polycarbonate resin, a monomer composition for recycled plastic synthesis.

2. The monomer composition for recycled plastic synthesis according to claim 1, wherein the color coordinate L* of the monomer composition for recycled plastic synthesis is 95.5 or more.

3. The monomer composition for recycled plastic synthesis according to claim 1, wherein the color coordinate a* of the monomer composition for recycled plastic synthesis is -0.7 to -0.

2.

4. The monomer composition for recycled plastic synthesis according to claim 1, wherein the aromatic diol compound contains bisphenol A.

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

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

7. depolymerizing a polycarbonate resin; separating a carbonate precursor from the depolymerization reaction product; and purifying the depolymerization reaction product from which the carbonate precursor has been separated, wherein the step of purifying the depolymerization reaction product from which the carbonate precursor has been separated comprises adding a hydrophilic reducing agent to the depolymerization reaction product from which the carbonate precursor has been separated; and adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated, subjecting it to adsorption purification, and then removing the adsorbent, a method for producing a monomer composition for recycled plastic synthesis.

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

9. Based on the weight of the depolymerization reaction product from which the carbonate precursor has been separated, the amount of the hydrophilic reducing agent added is 0.1% by weight to 7% by weight, the method for producing a monomer composition for recycled plastic synthesis according to claim 7.

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

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

12. The step of subjecting the polycarbonate resin to a depolymerization reaction is The method for producing a monomer composition for recycled plastic synthesis according to claim 7, comprising the step of adding an antioxidant to the reactant containing the polycarbonate resin.

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

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

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

16. In the step of separating the carbonate precursor from the depolymerization reaction product, The method for producing a monomer composition for recycled plastic synthesis according to claim 7, comprising a step of vacuum distilling the depolymerization reaction product.

17. After adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated, subjecting it to adsorption purification, and then removing the adsorbent, The method for producing a monomer composition for recycled plastic synthesis according to claim 7, further comprising a recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated;

18. The recrystallization step of the depolymerization reaction product from which the carbonate precursor has been separated is The method for producing a monomer composition for recycled plastic synthesis according to claim 17, comprising the step of adding 5 to 25 parts by weight of a recrystallization solvent to 1 part by weight of the aromatic diol compound contained in the depolymerization reaction product.

19. Recycled plastic comprising the reaction product of the monomer composition for recycled plastic synthesis and the comonomer according to any one of claims 1 to 6.

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

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