Monomer compositions for synthesizing recycled plastics, methods for their preparation, and recycled plastics and molded articles using the same.

Abstract

This invention relates to a monomer composition for synthesizing recycled plastics, a method for preparing the same, and recycled plastics and molded articles using the monomer composition, the monomer composition comprising high-purity aromatic diol compounds recovered through chemical decomposition of polycarbonate resins.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2021-0122001, Korean Patent Application No. 10-2021-0122002, Korean Patent Application No. 10-2021-0122003, Korean Patent Application No. 10-2021-0122004, Korean Patent Application No. 10-2021-0128892, filed on September 29, 2021, and Korean Patent Application No. 10-2021-0136153, filed on October 13, 2021, all of which are incorporated herein by reference.

[0003] This invention relates to a monomer composition for synthesizing recycled plastics, a method for preparing the same, and recycled plastics and molded articles using the monomer composition, the monomer composition comprising high-purity aromatic diol compounds recovered through chemical decomposition of polycarbonate resins.

[0004] Furthermore, the present invention relates to a monomer composition for synthesizing recycled plastics, a method for preparing the same, and recycled plastics and molded articles using the monomer composition, the monomer composition comprising high-value-added byproducts recovered through chemical decomposition of polycarbonate resins. Background Technology

[0005] Polycarbonate is a thermoplastic polymer and a plastic with excellent properties such as good transparency, ductility and relatively low manufacturing cost.

[0006] Despite the wide range of uses for polycarbonate, environmental and health issues related to waste disposal have been continuously raised.

[0007] Currently, physical recycling methods are being used, but this leads to quality degradation. Therefore, research on the chemical recycling of polycarbonate is underway.

[0008] Chemical decomposition of polycarbonate refers to the process of breaking down polycarbonate to obtain aromatic diol compounds (such as bisphenol A (BPA)) as monomers, which are then reused in polymerization to obtain high-purity polycarbonate.

[0009] For this type of chemical decomposition, thermal decomposition, hydrolysis, and alcohol decomposition are commonly known. Among these, the most common method is alcohol decomposition using an alkaline catalyst. However, in the case of methanol decomposition, there is the problem of using methanol, which is harmful to human health. In the case of ethanol, there are problems such as the need for high temperature and high pressure conditions and low yield.

[0010] Furthermore, although alcohol decomposition methods using organic catalysts are known, they are economically disadvantageous. Summary of the Invention

[0011] Technical issues

[0012] One object of the present invention is to provide a monomer composition for synthesizing recycled plastics, said monomer composition being able to ensure the recovery of high-purity aromatic diol compounds through regeneration by utilizing the chemical decomposition of polycarbonate resins.

[0013] Another object of the present invention is to provide a method for preparing the monomer composition for synthesizing recycled plastics, and a recycled plastic and a molded article using the monomer composition for synthesizing recycled plastics.

[0014] Technical solution

[0015] To achieve the above objectives, a monomer composition for synthesizing recycled plastics is provided herein, comprising an aromatic diol compound, wherein the impurity ratio according to Formula 1 below is less than 1.2%, wherein the yield of the aromatic diol compound according to Formula 2 below is greater than 65%, and wherein the monomer composition for synthesizing recycled plastics is obtained from the recycling of polycarbonate resins.

[0016] [Formula 1]

[0017] Impurity ratio = {(Total peak area in liquid chromatography - Bisphenol A peak area in liquid chromatography) / Total peak area in liquid chromatography} × 100

[0018] [Formula 2]

[0019] Yield (%) = W1 / W0

[0020] In Formula 2, W0 is the mass of the aromatic diol compound obtained during the 100% decomposition of polycarbonate resin, and W1 is the actual mass of the aromatic diol compound obtained.

[0021] Also provided is a method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the steps of: depolymerizing a polycarbonate resin; adding an alkali such that the pH of the depolymerization product is above 12; adding water after adding the alkali to separate the carbonate precursor from the depolymerization product; and adding an acid such that the pH of the depolymerization product from which the carbonate precursor has been separated is below 4.

[0022] Also provided is a recycled plastic comprising the monomer composition for synthesizing recycled plastic and the reaction product of the comonomer.

[0023] A molded article comprising the recycled plastic is also provided herein.

[0024] Below, a monomer composition for synthesizing recycled plastics according to a specific embodiment of the present invention, a method for preparing the same, and recycled plastics and molded articles using the monomer composition will be described in more detail.

[0025] Unless otherwise expressly stated in this specification, the technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] The singular forms “a,” “an,” and “this” used herein are intended to include the plural forms unless the context clearly specifies otherwise.

[0027] The “pH” used here refers to the hydrogen ion concentration (pH), which is a numerical value representing the acidity and alkalinity of a substance. pH can be determined by taking the reciprocal of the logarithmic dissociation concentration of hydrogen ions and is used as a measure of the strength of a substance as an acid or base.

[0028] It should be understood that the terms “comprising,” “including,” “having,” etc., in this specification are used to describe the presence of the described features, regions, integers, steps, functions, elements, and / or components, but do not exclude the presence or addition of one or more other features, regions, integers, steps, functions, elements, components, and / or groups.

[0029] Furthermore, terms including ordinal numbers such as "first" and "second" are used only for the purpose of distinguishing one component from another and are not limited by the ordinal number. For example, without departing from the scope of the invention, the first component may be referred to as the second component, or similarly, the second component may be referred to as the first component.

[0030] 1. Monomer compositions for synthesizing recycled plastics

[0031] According to one embodiment of the present invention, a monomer composition for synthesizing recycled plastics can be provided, comprising an aromatic diol compound, wherein the impurity ratio according to Formula 1 below is less than 1.2%, wherein the yield of the aromatic diol compound according to Formula 2 below is greater than 65%, and wherein the monomer composition for synthesizing recycled plastics is obtained from the recycling of polycarbonate resins.

[0032] [Formula 1]

[0033] Impurity ratio = {(Total peak area in liquid chromatography - Bisphenol A peak area in liquid chromatography) / Total peak area in liquid chromatography} × 100

[0034] [Formula 2]

[0035] Yield (%) = W1 / W0

[0036] In Formula 2, W0 is the mass of the aromatic diol compound obtained during the 100% decomposition of polycarbonate resin, and W1 is the actual mass of the aromatic diol compound obtained.

[0037] The inventors have discovered through experiments that, although the monomer composition for synthesizing recycled plastics in one embodiment is recycled by utilizing the chemical decomposition of polycarbonate resins, the aromatic diol compounds, which are the main targets for recycling, are ensured to have high purity and high yield. Thus, when the monomer composition is used to synthesize polycarbonate resins, excellent physical properties can be achieved, thereby completing the present invention.

[0038] In particular, together with a monomer composition for synthesizing recycled plastics (first composition) of one embodiment, a monomer composition for synthesizing recycled plastics (second composition) containing diethyl carbonate (wherein the diethyl carbonate is recycled from a polycarbonate resin) can be obtained simultaneously in a method for preparing a monomer composition for synthesizing recycled plastics (the method will be described later).

[0039] In other words, the present invention may have the following technical features: a first composition containing aromatic diol compounds is obtained with high purity by regenerating polycarbonate resin through chemical decomposition, and at the same time, a second composition containing diethyl carbonate (i.e., a byproduct with high added value) can also be obtained.

[0040] Specifically, one embodiment of the monomer composition for synthesizing recycled plastics is characterized in that it is obtained from the recycling of polycarbonate resins. That is, this means that the monomer composition for synthesizing recycled plastics of one embodiment is obtained by recycling polycarbonate resins, and as a result, a monomer composition for synthesizing recycled plastics comprising aromatic diol compounds is also obtained.

[0041] Polycarbonate resins refer to both homopolymers and copolymers containing repeating polycarbonate units, and are collectively referred to as reaction products obtained through polymerization or copolymerization of monomers containing aromatic diol compounds and carbonate precursors. Homopolymers can be synthesized when they contain only one repeating carbonate unit obtained by using only one aromatic diol compound and one carbonate precursor. Furthermore, copolymers can be synthesized when using one aromatic diol compound and two or more carbonate precursors as monomers, or using two or more aromatic diol compounds and one carbonate precursor, or using one or more other diols in addition to one aromatic diol compound and one carbonate precursor to contain two or more carbonates. Depending on the molecular weight range, homopolymers or copolymers can include all low molecular weight compounds, oligomers, and polymers.

[0042] Furthermore, a monomer composition (first composition) for synthesizing recycled plastics according to one embodiment may comprise an aromatic diol compound. Specific examples of said 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 mixtures of two or more thereof. Preferably, the aromatic diol compound in the monomer composition (first composition) for synthesizing recycled plastics according to one embodiment can be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0043] The aromatic diol compound is characterized in that it is obtained from the recycling of polycarbonate resins used to recycle monomer compositions for the synthesis of recycled plastics. That is, this means that the polycarbonate resin is recycled to obtain a monomer composition for the synthesis of recycled plastics according to one embodiment, and as a result, an aromatic diol compound is also obtained. Therefore, the addition of new aromatic diol compounds from external sources, other than the preparation of a monomer composition for the synthesis of recycled plastics according to one embodiment from the recycling of polycarbonate resin, is not included in the scope of the aromatic diol compounds of this invention.

[0044] Specifically, "obtained from recycled polycarbonate resins" means obtained through a depolymerization reaction of the polycarbonate resins. The depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions, particularly under alkaline (basic) conditions. In particular, the depolymerization reaction can preferably be carried out in the presence of an ethanol solvent, as will be described later.

[0045] Meanwhile, the color coordinate b* value of the monomer composition for synthesizing recycled plastics in one embodiment can be 0 to 4.2, or 1 to 4, or 1 to 3, or 1.5 to 2.5, or 1.5 to 2.4, or 1.57 to 2.24. Furthermore, the color coordinate L* of the monomer composition for synthesizing recycled plastics in one embodiment can be 94 or more, 95 or more, or 100 or less, or 94 to 100, or 94 to 98, or 95 to 100, or 95 to 98, or 95.9 to 97.1. Furthermore, the color coordinate a* of the monomer composition for synthesizing recycled plastics in one embodiment can be 0.5 or less, or 0.3 or less, or 0 or more, or 0.01 or more, or 0 to 0.5, or 0 to 0.3, or 0.01 to 0.5, or 0.01 to 0.3, or 0.01 to 0.25.

[0046] As used in this specification, "color coordinates" refers to coordinates in the CIE laboratory color space, which are color values ​​defined by the CIE (International Commission on Illumination). Any position in the CIE color space can be represented by three coordinate values: L*, a*, and b*.

[0047] Here, the L* value represents brightness; when L* = 0, it represents black, and when L* = 100, it represents white. Furthermore, the a* value represents a color with corresponding color coordinates tending towards either pure red or pure green, and the b* value represents a color with corresponding color coordinates tending towards either pure yellow or pure blue.

[0048] Specifically, the a* value ranges from -a to +a. The maximum a* value (a*max) represents pure red, and the minimum a* value (a*min) represents pure green. Similarly, the b* value ranges from -b to +b. The maximum b* value (b*max) represents pure yellow, and the minimum b* value (b*min) represents pure blue. For example, a negative b* value indicates a color leaning towards pure blue, while a positive b* value indicates a color leaning towards pure yellow. When comparing b* = 50 with b* = 80, b* = 80 is closer to pure yellow than b* = 50.

[0049] When the chromaticity coordinate a* value of a monomer composition for synthesizing recycled plastics in one embodiment increases excessively to greater than 0.5, or the chromaticity coordinate L* value decreases excessively to less than 94, the monomer composition for synthesizing recycled plastics in one embodiment deteriorates in terms of color properties.

[0050] Meanwhile, when the color coordinate b* value of the monomer composition for synthesizing recycled plastics in one embodiment increases excessively to greater than 4.2, the monomer composition for synthesizing recycled plastics in that embodiment indicates an excessive tendency towards a yellow color, resulting in poor color characteristics.

[0051] Furthermore, when the color coordinate b* value of a monomer composition for synthesizing recycled plastics in one embodiment is excessively reduced to less than 0, the monomer composition for synthesizing recycled plastics in that embodiment exhibits an excessive tendency towards a blue color, resulting in poor color characteristics.

[0052] Examples of methods for measuring the color coordinates L*, a*, b* values ​​of a monomer composition for synthesizing recycled plastics in one embodiment are not particularly limited, and various color characteristic measurement methods in the field of plastics can be applied without limitation.

[0053] However, as an example, the color coordinates L*, a*, and b* values ​​of a monomer composition for synthesizing recycled plastics in one embodiment can be measured in reflectance mode using a HunterLab UltraScan PRO spectrophotometer.

[0054] Meanwhile, in one embodiment, the purity of the aromatic diol compound in the monomer composition for synthesizing recycled plastics can be more than 99%, or less than 100%, or 99% to 100%, or 99% to 99.9%, or 99% to 99.8% or 99% to 99.7%.

[0055] Examples of methods for measuring the purity of aromatic diol compounds in monomer compositions for synthesizing recycled plastics according to one embodiment are not particularly limited; for example, methods may be used... 1 Analysis methods such as ¹H NMR, ICP-MS, HPLC, and UPLC are not restricted. Regarding specific methods, conditions, and equipment for NMR, ICP-MS, HPLC, and UPLC, all well-known methods can be applied without limitation.

[0056] An example of a method for measuring the purity of aromatic diol compounds in a monomer composition for synthesizing recycled plastics according to one embodiment is as follows. 1 wt% of the monomer composition for synthesizing recycled plastics according to one embodiment is dissolved in acetonitrile (ACN) solvent under ambient pressure and at 20°C to 30°C, and then the solution is analyzed using an ACQUITY HPLC system on a Waters HPLC system. The purity of bisphenol A (BPA) was analyzed by ultra-high performance liquid chromatography (UPLC) using a BEH C18 1.7μm (2.1*50mm column).

[0057] As described above, in one embodiment of the monomer composition for synthesizing recycled plastics, the purity of the aromatic diol compound, which is the main target material for recycling, is significantly increased to over 99%, and other impurities are minimized, thereby enabling the synthesis of polycarbonate resins using the monomer composition to obtain excellent physical properties.

[0058] Furthermore, the monomer composition for synthesizing recycled plastics may further contain impurities other than aromatic diol compounds. Impurities refer to all substances other than the aromatic diol compounds, the primary target material for recycling in this invention, and their specific types are not particularly limited; however, for example, they may include p-tert-butylphenol.

[0059] Furthermore, the impurity ratio of the monomer composition used for synthesizing recycled plastics according to Formula 1 may be less than 1.2%, or less than 0.9%, or less than 0.8%, or less than 0.7%, or less than 0.5%, or more than 0.1%, or 0.1% to 1.2%, or 0.1% to 0.9%, or 0.1% to 0.8%, or 0.1% to 0.7%, or 0.1% to 0.5%.

[0060] Examples of methods for measuring the impurity ratio of a monomer composition for synthesizing recycled plastics in one embodiment are not particularly limited; for example, LC analysis can be used. Various well-known methods, conditions, equipment, etc., regarding LC can be applied without limitation.

[0061] As described above, in one embodiment of the monomer composition for synthesizing recycled plastics, the impurity ratio, other than the main target recycled substance aromatic diol compounds, is greatly reduced to below 1.2%, thereby enabling excellent physical properties when the monomer composition is used to synthesize polycarbonate resins.

[0062] Meanwhile, in one embodiment, the yield of the aromatic diol compound in the monomer composition for synthesizing recycled plastics can be greater than 65%, or greater than 67%, or greater than 68%, or less than 100%, or greater than 65% and less than 100%, or 67% to 100%, or 68% to 100%. The increased yield of the aromatic diol compound to greater than 65% is considered to be attributable to the method for preparing the monomer composition for synthesizing recycled plastics, which will be described later.

[0063] Examples of methods for measuring the yield of aromatic diol compounds in a monomer composition for synthesizing recycled plastics according to one embodiment are not particularly limited; for example, the yield can be calculated by Formula 2 below.

[0064] [Formula 2]

[0065] Yield (%) = W1 / W0

[0066] In Formula 2, W0 is the mass of the aromatic diol compound obtained during the 100% decomposition of polycarbonate resin, and W1 is the actual mass of the aromatic diol compound obtained.

[0067] For the measurement of the mass of the aromatic diol compound in Formula 2, various well-known mass measurement methods can be used without restriction; for example, a balance can be used.

[0068] As described above, in one embodiment of the monomer composition for synthesizing recycled plastics, the yield of aromatic diol compounds, which are the main target substances for recycling, is greatly increased to more than 65%, thereby improving the efficiency of the recycling process for polycarbonate resins.

[0069] Meanwhile, in one embodiment of the monomer composition for synthesizing recycled plastics, diethyl carbonate can be obtained as a byproduct. This diethyl carbonate is characterized in that it is recovered from a polycarbonate resin used to recycle the monomer composition for synthesizing recycled plastics according to one embodiment.

[0070] In other words, this means that a monomer composition for synthesizing recycled plastics according to one embodiment is obtained by recycling polycarbonate resins, and diethyl carbonate is also obtained as a result. Therefore, the external addition of new diethyl carbonate, except for the preparation of a monomer composition for synthesizing recycled plastics according to one embodiment by recycling polycarbonate resins, is not included in the scope of diethyl carbonate of the present invention.

[0071] Specifically, "obtained from recycled polycarbonate resins" means obtained through the depolymerization reaction of polycarbonate resins. This depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions, particularly under alkaline (basic) conditions. In particular, the depolymerization reaction can preferably be carried out in the presence of an ethanol solvent, as will be described later.

[0072] Since the primary target substance for recycling in a monomer composition for synthesizing recycled plastics according to one embodiment is an aromatic diol compound, diethyl carbonate can be separately separated and recycled as a byproduct from the monomer composition for synthesizing recycled plastics according to one embodiment.

[0073] The monomer composition for synthesizing recycled plastics in one embodiment can be used as a raw material for preparing a variety of recycled plastics (e.g., polycarbonate (PC)), which will be described later.

[0074] The monomer composition for synthesizing recycled plastics according to one embodiment may also contain small amounts of other additives and solvents. There are no particular limitations on the specific types of additives or solvents, and a wide variety of materials widely used in processes for recovering aromatic diol compounds through the depolymerization of polycarbonate resins can be used without restriction.

[0075] The monomer composition for synthesizing recycled plastics according to one embodiment can be obtained by a method for preparing a monomer composition for synthesizing recycled plastics (the method will be described later). That is, the monomer composition for synthesizing recycled plastics according to one embodiment corresponds to the result of multiple processes of filtration, purification, washing and drying to ensure only high purity of the main target recycled substance, aromatic diol compounds, after the depolymerization reaction of polycarbonate resins.

[0076] 2. A method for preparing monomer compositions for synthesizing recycled plastics.

[0077] According to another embodiment of the present invention, a method for preparing a monomer composition for synthesizing recycled plastics can be provided, the method comprising the steps of: depolymerizing a polycarbonate resin; adding an alkali such that the pH of the depolymerization product is above 12; adding water after adding the alkali to separate the carbonate precursor from the depolymerization product; and adding an acid such that the pH of the depolymerization product from which the carbonate precursor has been separated is below 4.

[0078] Through experiments, the inventors have demonstrated that, similar to the method for preparing monomer compositions for synthesizing recycled plastics in other embodiments, the pH of the depolymerized polycarbonate resin is gradually adjusted during the chemical decomposition and recycling of polycarbonate resins. This ensures that the aromatic diol compound, the main target material for synthesis in this invention, has high purity and high yield within a rapid process time, thus completing this invention.

[0079] In particular, distillation has been used in the past to remove carbonate monomers from depolymerized polycarbonate resins, but the advantage of the present invention is that, by gradually adjusting the pH instead of distillation, aromatic diol compounds can be obtained in high yields at a faster process time than the distillation process.

[0080] Specifically, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may include the step of depolymerizing a polycarbonate resin.

[0081] Polycarbonate resins refer to both homopolymers and copolymers containing repeating polycarbonate units, and are collectively referred to as reaction products obtained through polymerization or copolymerization of monomers containing aromatic diol compounds and carbonate precursors. Homopolymers can be synthesized when they contain only one repeating carbonate unit obtained by using only one aromatic diol compound and one carbonate precursor. Furthermore, copolymers can be synthesized when using one aromatic diol compound and two or more carbonate precursors as monomers, or using two or more aromatic diol compounds and one carbonate precursor, or using one or more other diols in addition to one aromatic diol compound and one carbonate precursor to contain two or more carbonates. Depending on the molecular weight range, homopolymers or copolymers can include all low molecular weight compounds, oligomers, and polymers.

[0082] Polycarbonate resins can be applied regardless of their form and type, such as new polycarbonate resins produced through synthesis, recycled polycarbonate resins produced through recycling processes, or polycarbonate resin waste.

[0083] However, if necessary, a pretreatment step of the polycarbonate resin can be performed before the depolymerization reaction, thereby improving the efficiency of the process for recovering aromatic diols and carbonate precursors from polycarbonate resins. Examples of pretreatment processes can include washing, drying, grinding, and glycol decomposition, etc. The specific method of each pretreatment process is not limited, and many methods widely used in the process of recovering aromatic diols and carbonate precursors from polycarbonate resins can be applied without limitation.

[0084] In the depolymerization of polycarbonate resins, the depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions, particularly under alkaline (basic) conditions. The type of alkali is not particularly limited; examples include sodium hydroxide (NaOH) or potassium hydroxide (KOH). The alkali is a basic catalyst, which offers an economic advantage compared to organic catalysts primarily used under mild conditions. More specifically, in the depolymerization of polycarbonate resins, the depolymerization reaction can be carried out within a pH range greater than 8 and less than 12.

[0085] In the depolymerization reaction of polycarbonate resins, the reaction can be carried out by reacting with an alkali in an amount of less than 0.5 mol, less than 0.4 mol, less than 0.3 mol, more than 0.1 mol, more than 0.2 mol, between 0.1 mol and 0.5 mol, between 0.1 mol and 0.4 mol, between 0.1 mol and 0.3 mol, between 0.2 mol and 0.5 mol, between 0.2 mol and 0.4 mol, or between 0.2 mol and 0.3 mol relative to 1 mol of polycarbonate resin. When polycarbonate resin reacts with an alkali in an amount greater than 0.5 mol (relative to 1 mol of polycarbonate resin) during the depolymerization process, the increase in impurities is limited due to the increased amount of basic salts generated, thus reducing the purity of the target recovered material and decreasing the economic efficiency of the catalytic reaction.

[0086] Furthermore, the depolymerization reaction of polycarbonate resins can be carried out in the presence of a solvent containing ethanol. This invention can stably obtain high-purity bisphenol A monomer by decomposing polycarbonate resins with a solvent containing ethanol, and it has the advantage of further yielding high-value-added diethyl carbonate as a reaction byproduct.

[0087] The ethanol content relative to 1 mole of polycarbonate resin can be 5 to 15 moles, or 8 to 13 moles. Since ethanol has good solubility in bisphenol A, it should essentially be contained within the above range. When the ethanol content is excessively reduced to less than 5 moles relative to 1 mole of polycarbonate resin, it becomes difficult to sufficiently decompose the polycarbonate resin into alcohol. On the other hand, when the ethanol content is excessively increased to more than 15 moles relative to 1 mole of polycarbonate resin, the economics of the process decrease due to the excessive use of alcohol.

[0088] In addition to ethanol, the solvents used for the depolymerization reaction of polycarbonate resins may further include at least one organic solvent selected from tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0089] The organic solvent may include tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0090] More preferably, dichloromethane can be used as the organic solvent. When dichloromethane is used as an organic solvent to mix with ethanol, it has the advantage of improving the solubility in polycarbonate and increasing reactivity.

[0091] The content of the organic solvent relative to 1 mole of polycarbonate resin can be from 16 to 20 moles, or from 16 to 18 moles. Furthermore, the content of the organic solvent relative to 1 mole of ethanol can be from 1.5 to 2 moles. By mixing the polycarbonate resin, ethanol, and organic solvent within the above ranges, there is the advantage that the depolymerization reaction of the polymer can proceed at the desired level.

[0092] Meanwhile, there is no particular limitation on the temperature for the depolymerization reaction of polycarbonate resins, but for example, the reaction can be carried out at temperatures ranging from 20°C to 100°C, or from 50°C to 70°C. Furthermore, the depolymerization of polycarbonate resins can be carried out for 1 hour to 30 hours, or from 4 hours to 6 hours.

[0093] Specifically, the conditions described are milder than conventional pressurized / high-temperature processes, and by stirring under these conditions, the process can be carried out at a gentler pace compared to pressurized / high-temperature processes. In particular, stirring at 50°C to 70°C for 4 to 6 hours yields the advantage of most effective results in terms of reproducibility and acceptability.

[0094] That is, according to the present invention, by adjusting the type and amount of the mixed solvent and the type and content of the base catalyst without using an organic catalyst, it is advantageous that high-purity aromatic diol compounds (e.g., bisphenol A) can be obtained under mild conditions without the use of a pressurized / high-temperature process, and diethyl carbonate can be obtained as a byproduct by using an ethanol solvent.

[0095] More specifically, the steps for depolymerizing polycarbonate resins may include: first, dissolving the polycarbonate resin in an organic solvent; and second, adding a catalyst solution containing ethanol and an alkali and stirring. In both steps, the contents of ethanol, organic solvent, alkali, and polycarbonate resin are the same as described above.

[0096] Meanwhile, another embodiment of the method for preparing monomer compositions for synthesizing recycled plastics may further include the step of adding an alkali to make the pH of the depolymerization reaction product above 12, or between 12 and 14. The alkali may be a strong alkali, examples of which include sodium hydroxide (NaOH).

[0097] In the step of adding alkali to make the pH of the depolymerization product above 12, the aromatic diol compounds contained in the depolymerization product can be converted into salts of aromatic diol compounds.

[0098] In the step of adding water after adding alkali to separate the carbonate precursor from the depolymerization product, the depolymerization product can form a layer consisting of an aqueous layer containing a salt of an aromatic diol compound and an organic solvent layer containing diethyl carbonate. Since the salt of the aromatic diol compound is hydrophilic, it can be contained in the aqueous layer in both water and organic solvent, and since diethyl carbonate is hydrophobic, it can be contained in the organic solvent layer in both water and organic solvent. Therefore, the aromatic diol compound, as the main product, and diethyl carbonate, as a byproduct, can be easily separated by a simple process of changing the pH.

[0099] Meanwhile, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may include the step of adding water after the addition of an alkali to separate a carbonate precursor from the depolymerization product. Therefore, the separated carbonate precursor may include diethyl carbonate.

[0100] As described above, since the step of adding alkali to make the pH of the depolymerization product above 12 is followed by the step of adding water to separate the carbonate precursor from the depolymerization product, the depolymerization product is formed into an aqueous layer containing a salt of an aromatic diol compound and an organic solvent layer containing diethyl carbonate, thereby the layer separated by the organic solvent layer containing diethyl carbonate can be separated.

[0101] In the step of adding water after the addition of alkali to separate the carbonate precursor from the depolymerization product, the organic layer is separated from the aqueous layer, allowing the carbonate precursor to be recovered from the separated organic layer. There are no particular limitations on the specific separation conditions used to separate the organic and aqueous layers, and various well-known purification techniques can be applied without restriction to the specific separation apparatus and method. However, in one instance, a separatory funnel may be used.

[0102] The separated carbonate precursors can be reused without separate separation and purification processes, or, if desired, can be reused through separation and purification methods such as conventional extraction, adsorption, and drying. There are no particular limitations on specific purification conditions. Various well-known purification techniques can be applied without restriction to specific purification apparatus and methods.

[0103] The method may also include the step of adding an acid to bring the pH of the depolymerization product separated from the carbonate precursor to below 4, below 2, between 1 and 4, or between 1 and 2. This yields an aromatic diol compound as the main recycled material, corresponding to a monomer composition for synthesizing recycled plastics according to one embodiment.

[0104] As described above, because after the step of adding alkali to make the pH of the depolymerization product 12 or higher, the step of adding water after adding alkali to separate the carbonate precursor from the depolymerization product is performed. Therefore, the depolymerization product can form a layer consisting of an aqueous layer containing a salt of an aromatic diol compound and an organic solvent layer containing diethyl carbonate. Furthermore, since the organic layer and the aqueous layer are separate, after the step of separating the carbonate precursor from the depolymerization product, the aqueous layer containing the salt of the aromatic diol compound remains in the depolymerization product.

[0105] Since the primary target substance for recovery in this invention is aromatic diol compounds, the salts of aromatic diols contained in the aqueous layer can be converted into aromatic diol compounds through an additional acid neutralization step. Specifically, in the step of adding acid to bring the pH of the depolymerization reaction product from which the carbonate precursor has been separated to below 4, the salts of aromatic diol compounds contained in the depolymerization reaction product can be converted into aromatic diol compounds.

[0106] The acid may be a strong acid, examples of which include hydrochloric acid (HCl).

[0107] Meanwhile, in another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics, after the step of adding acid to bring the pH of the depolymerization product separated from the carbonate precursor to below 4, a further step of purifying the depolymerization product separated from the carbonate precursor may be included.

[0108] Specifically, the purification steps for the depolymerization products isolated from the carbonate precursor may include washing the isolated depolymerization products. Furthermore, the purification steps for the depolymerization products isolated from the carbonate precursor may include adsorption purification steps. Additionally, the purification steps for the depolymerization products isolated from the carbonate precursor may include recrystallization steps.

[0109] There are no particular restrictions on the order of the washing, adsorption purification, or recrystallization steps, and it is irrelevant whether they are performed in any order; however, for example, they can be performed in the order of washing, adsorption purification, and recrystallization. The washing, adsorption purification, and recrystallization steps can be repeated at least once or more. Various well-known purification techniques can be applied without limitation to specific washing, adsorption, and recrystallization apparatus and methods.

[0110] Specifically, in the washing step of the depolymerization product separated from the carbonate precursor, the separated depolymerization product may contain aromatic diol compounds. However, since various impurities exist during the recovery process of aromatic diol compounds, washing can be performed to thoroughly remove these impurities and ensure high purity of the aromatic diol compounds.

[0111] Specifically, the washing steps may include: washing with solvent at a temperature above 10°C and below 30°C, or above 20°C and below 30°C; and washing with solvent at a temperature above 40°C and below 80°C, or above 40°C and below 60°C, or above 45°C and below 55°C. Temperature conditions refer to the temperature inside the washing container where solvent washing is performed. Various heating devices can be used without limitation to maintain a high temperature deviating from room temperature.

[0112] In the washing step, a solvent washing step can be performed first at a temperature above 10°C and below 30°C, followed by a solvent washing step at a temperature above 40°C and below 80°C. Alternatively, a solvent washing step can be performed first at a temperature above 40°C and below 80°C, followed by a solvent washing step at a temperature above 10°C and below 30°C.

[0113] More preferably, in the washing step, a solvent washing step can be performed first at a temperature above 10°C and below 30°C, followed by a solvent washing step at a temperature above 40°C and below 80°C. Therefore, corrosion of the reactor due to strong acid after the neutralization step can be minimized.

[0114] The steps of washing with solvent at a temperature above 10°C and below 30°C, and the steps of washing with solvent at a temperature above 40°C and below 80°C, may be repeated at least once or more.

[0115] Furthermore, if necessary, after performing the steps of washing with solvent at a temperature above 10°C and below 30°C, and washing with solvent at a temperature above 40°C and below 80°C, a further step of removing residual solvent by filtration can be performed.

[0116] More specifically, the temperature difference between the solvent washing step at a temperature above 40°C and below 80°C and the solvent washing step at a temperature above 10°C and below 30°C can be above 20°C and below 50°C.

[0117] The difference between the temperature of the solvent washing step at a temperature above 40°C and below 80°C and the temperature of the solution washing step at a temperature above 10°C and below 30°C is the value obtained by subtracting the temperature of the solvent washing step at a temperature above 10°C and below 30°C from the temperature of the solvent washing step at a temperature above 40°C and below 80°C.

[0118] When the temperature difference between the solvent washing step at a temperature above 40°C and below 80°C and the solvent washing step at a temperature above 10°C and below 30°C decreases excessively to less than 20°C, it becomes difficult to remove impurities sufficiently.

[0119] When the temperature difference between the solvent washing step at temperatures above 40°C and below 80°C and the solvent washing step at temperatures above 10°C and below 30°C increases excessively to more than 50°C, harsh conditions are created to maintain extreme temperature conditions, which reduces the efficiency of the process.

[0120] The solvent used in the washing step may include one of water, alcohol, and organic solvents. As an organic solvent, tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or mixtures of two or more thereof may be used.

[0121] The solvent used in the washing step may be used in a weight ratio of more than 1 part by weight and less than 30 parts by weight, or more than 1 part by weight and less than 10 parts by weight, based on 1 part by weight of the polycarbonate resin used in the depolymerization reaction.

[0122] More specifically, the solvent used in the solvent washing step at a temperature above 10°C and below 30°C can be an organic solvent. Preferably, dichloromethane can be used as the organic solvent. In this case, based on 1 part by weight of polycarbonate resin, the amount of organic solvent can be more than 1 part by weight and less than 10 parts by weight.

[0123] Furthermore, the solvent used in the solvent washing step at a temperature above 40°C and below 80°C can be water. When water is used, impurities in the form of residual salts can be effectively removed. In this case, based on 1 part by weight of polycarbonate resin, the amount of solvent used can be more than 1 part by weight and less than 10 parts by weight.

[0124] Furthermore, the adsorption purification step of the depolymerization reaction product separated from the carbonate precursor may include adding an adsorbent to the depolymerization reaction product separated from the carbonate precursor for adsorption purification, and then removing the adsorbent. In the step of adding an adsorbent to the depolymerization reaction product separated from the carbonate precursor for adsorption purification and then removing the adsorbent, the adsorbent may be brought into contact with the depolymerization reaction product.

[0125] Examples of adsorbents that can be used include activated carbon, charcoal, or mixtures thereof. Activated carbon is a microporous carbon black material prepared by carbonizing the raw material at about 500°C and activating it at about 900°C. Examples of activated carbon are not particularly limited, but, for example, depending on the type of raw material, various types of activated carbon, such as plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon, can be used without limitation.

[0126] In more specific examples, plant-based activated carbon can include coconut shell activated carbon, wood activated carbon, and sawdust activated carbon. Furthermore, coal-based activated carbon can include lignite activated carbon, bituminous coal activated carbon, and anthracite activated carbon. Additionally, petroleum-based activated carbon can include petroleum coke activated carbon and oil coke activated carbon. Furthermore, waste-based activated carbon can include synthetic resin activated carbon and pulp activated carbon.

[0127] The adsorbent may include at least one activated carbon selected from plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon. That is, the adsorbent may include plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon, or a mixture of two or more of them.

[0128] More specifically, the adsorbent may include at least one activated carbon selected from coconut shell activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous coal activated carbon. That is, the first adsorbent may include coconut shell activated carbon, lignite activated carbon, anthracite activated carbon, bituminous coal activated carbon, or a mixture of two or more of them.

[0129] There are no particular restrictions on the adsorption and purification conditions of the adsorbent, and various well-known adsorption and purification conditions can be applied without limitation. However, in one example, the amount of adsorbent added can be 40% to 60% by weight relative to the polycarbonate resin, the adsorption time can be 1 hour to 5 hours, and the adsorption method can be stirred adsorption or an adsorption tower used in the laboratory.

[0130] If desired, the method may further include adding a solvent to the depolymerization product separated from the carbonate precursor, prior to the steps of adding an adsorbent to the depolymerization product separated from the carbonate precursor for adsorption purification and then removing the adsorbent. Examples of such solvents include ethanol, and ethanol may be added in proportions of 1 to 20 moles, 10 to 20 moles, or 15 to 20 moles relative to 1 mole of polycarbonate resin. By adding a solvent to the depolymerization product separated from the carbonate precursor, aromatic diol crystals contained in the depolymerization product separated from the carbonate precursor can be redissolved in the solvent.

[0131] Meanwhile, in the recrystallization step of the depolymerization product separated from the carbonate precursor, high-purity aromatic diol compounds can be ensured by thoroughly removing various impurities contained in the depolymerization product separated from the carbonate precursor.

[0132] Specifically, the recrystallization step may include adding water to the depolymerization product of the carbonate precursor to carry out recrystallization. By adding water to the depolymerization product of the carbonate precursor to carry out recrystallization, the solubility of the aromatic diol compound or its salt contained in the depolymerization product increases. Therefore, the crystals or impurities in between can be dissolved to the maximum extent by the solvent. In addition, since the dissolved aromatic diol compound has poor solubility relative to the impurities, it can easily precipitate into aromatic diol compound crystals due to the difference in solubility when the temperature is subsequently lowered.

[0133] More specifically, in the step of adding water to the depolymerization product separated from the carbonate precursor for recrystallization, 200 to 400 moles or 250 to 350 moles of water can be used relative to 1 mole of polycarbonate resin. When too little water is used, the temperature required to dissolve the aromatic diols contained in the depolymerization product separated from the carbonate precursor becomes too high, thus reducing process efficiency and making it difficult to remove impurities by recrystallization. On the other hand, when too much water is used, the solubility of the aromatic diols contained in the depolymerization product separated from the carbonate precursor becomes too high, thus reducing the yield of the aromatic diols recovered after recrystallization, and reducing process efficiency due to the use of a large amount of solvent.

[0134] If necessary, after the recrystallization step of the depolymerization reaction products separated from the carbonate precursor, a further step of removing residual impurities by filtration or adsorption can be performed.

[0135] Furthermore, if necessary, the method may further include a drying step after the recrystallization step. Residual solvent can be removed by drying, and there are no particular limitations on the specific drying conditions; however, for example, drying may be carried out at temperatures ranging from 10°C to 100°C, or from 10°C to 50°C. Various well-known drying techniques can be applied without limitation for the specific drying apparatus and method used in the drying process.

[0136] 3. Recycled plastics

[0137] According to yet another embodiment of the present invention, a recycled plastic can be provided comprising the monomer composition for synthesizing the recycled plastic of the first embodiment and the reaction product of the comonomer.

[0138] Details of the monomer composition for synthesizing recycled plastics according to one embodiment include all that is described above in one embodiment and another embodiment.

[0139] Examples corresponding to recycled plastics are not particularly limited. A variety of plastics synthesized from aromatic diol compounds such as bisphenol A and carbonate precursors such as dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate as monomers can be used without limitation, and more specific examples can be polycarbonate resins.

[0140] Polycarbonate resins refer to both homopolymers and copolymers containing repeating polycarbonate units, and are collectively referred to as reaction products obtained through polymerization or copolymerization of monomers containing aromatic diol compounds and carbonate precursors. Homopolymers can be synthesized when they contain only one repeating carbonate unit obtained by using only one aromatic diol compound and one carbonate precursor. Furthermore, copolymers can be synthesized when using one aromatic diol compound and two or more carbonate precursors as monomers, or using two or more aromatic diol compounds and one carbonate precursor, or using one or more other diols in addition to one aromatic diol compound and one carbonate precursor to contain two or more carbonates. Depending on the molecular weight range, homopolymers or copolymers can include all low molecular weight compounds, oligomers, and polymers.

[0141] More specifically, in a recycled plastic comprising a monomer composition for synthesizing recycled plastics and a reaction product of a comonomer in one embodiment, a carbonate precursor may be used as the comonomer. Specific examples of carbonate precursors include phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, dimethyl carbonate, di(chlorophenyl) carbonate, m-cresyl carbonate, dinaphthalene carbonate, bis(diphenyl) carbonate, or bishaloformate.

[0142] Examples of reaction processes for monomer compositions and comonomers used to synthesize polycarbonate resins for the synthesis of recycled plastics are not particularly limited, and various well-known methods for the preparation of polycarbonates can be applied without restriction.

[0143] However, in one example of a polycarbonate preparation method, a method comprising the step of polymerizing a composition containing a monomeric composition for synthesizing recycled plastics and a comonomer can be used. In this case, the polymerization can be carried out via interfacial polymerization, and during interfacial polymerization, the polymerization reaction can be conducted at atmospheric pressure and low temperature, and the molecular weight is easily controlled.

[0144] The polymerization temperature can range from 0°C to 40°C, and the reaction time can range from 10 minutes to 5 hours. In addition, the pH during the reaction can be maintained above 9 or 11.

[0145] There are no particular limitations on the solvents that can be used for polymerization, as long as they are solvents used in the art for the polymerization of polycarbonate, and as an example, halogenated hydrocarbons such as dichloromethane and chlorobenzene can be used.

[0146] Furthermore, the polymerization can be carried out in the presence of an acid binder. Alkali metal hydroxides such as sodium hydroxide or potassium hydroxide, or amine compounds such as pyridine, can be used as acid binders.

[0147] Furthermore, to control the molecular weight of polycarbonate during polymerization, the polymerization can be carried out in the presence of a molecular weight regulator. Alkylphenols having 1 to 20 carbon atoms can be used as molecular weight regulators, specific examples of which include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, dodecylphenol, or triacontylphenol. The molecular weight regulator can be added before, during, or after polymerization initiation. Based on 100 parts by weight of an aromatic glycol compound, the molecular weight regulator can be used in amounts of 0.01 to 10 parts by weight, or 0.1 to 6 parts by weight, and the desired molecular weight can be obtained within this range.

[0148] In addition, reaction promoters, such as tertiary amine compounds, quaternary ammonium compounds, or quaternary phosphonium compounds, including triethylamine, tetra-n-butylammonium bromide, or tetra-n-butylphosphonium bromide, can be used to further promote the polymerization reaction.

[0149] 4. Molded products

[0150] According to another embodiment of the invention, a molded article comprising the recycled plastic of another embodiment can be provided. Details of the recycled plastic include all those described above in the other embodiment.

[0151] Molded articles can be obtained by applying recycled plastics to a variety of known plastic molding methods without limitation. Examples of molding methods include injection molding, foam injection molding, blow molding, or extrusion.

[0152] There are no particular limitations on the examples of molded articles, and the application can be made to a wide variety of molded articles using plastics without restriction. Examples of molded articles include automotive, electrical and electronic products, communication products, daily necessities, building materials, optical components, and exterior materials.

[0153] If desired, in addition to recycled plastics from another embodiment, the molded article may also contain one or more additives selected from antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact enhancers, optical brighteners, ultraviolet absorbers, pigments, and dyes.

[0154] Examples of methods for manufacturing molded articles may include the following steps: mixing recycled plastic and additives according to another embodiment well using a mixer, extruding the mixture using an extruder to produce granules, drying the granules, and then injection molding the granules using an injection molding machine.

[0155] Beneficial effects

[0156] According to the present invention, a monomer composition for synthesizing recycled plastics, a method for preparing the monomer composition, and recycled plastics and molded articles using the monomer composition are provided, the monomer composition comprising a high-purity and high-yield aromatic diol compound recovered by chemical decomposition of polycarbonate resins. Detailed Implementation

[0157] The invention will be explained in detail below with reference to the following embodiments. However, these embodiments are for illustrative purposes only, and the scope of the invention is not limited thereto.

[0158] <Examples and Comparative Examples: Preparation of Regenerated Bisphenol A Monomer Compositions>

[0159] Example 1

[0160] (1. Decomposition Step) Dissolve 1 mol of pretreated waste polycarbonate (PC) in 17 mol of dichloromethane (MC), and then add it together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH) into a 3L high-pressure reactor. Stir the mixture at 60°C for 6 hours to carry out the PC depolymerization reaction.

[0161] (2. Alkalization step) Cool the product of the depolymerization reaction to below 30°C, and then alkalize the product containing bisphenol A with 2 mol of 40% sodium hydroxide (NaOH) until its pH reaches 14.

[0162] (3. Layer Separation Step) After this, water is added to form an aqueous layer and a dichloromethane (MC) layer. The lower dichloromethane (MC) layer is removed using a separatory funnel, and the upper aqueous layer is recovered.

[0163] (4. Acidification Step) The recovered water layer is acidified by adding 10% HCl and water until its pH reaches 1 to 2. Bisphenol A is then recovered by filtration through vacuum filtration.

[0164] (5-1. Additional purification steps - redissolution step) Add bisphenol A to 16.6 mol of ethanol and redissolve.

[0165] (5-2. Additional purification steps - adsorption steps) After that, lignite activated carbon as an adsorbent is added at a ratio of 50 wt.% relative to the waste polycarbonate, and purification is carried out by adsorption for 3 hours, followed by filtration to remove the lignite activated carbon.

[0166] (5-3. Additional purification steps - recrystallization step) Add 300 mol of water to recrystallize bisphenol A, and then vacuum filter the resulting slurry at 20-30°C to recover bisphenol A (BPA) crystals.

[0167] (6. Drying step) After that, it is vacuum dried in a convection oven at 40°C to prepare a regenerated bisphenol A monomer composition in which the regenerated bisphenol A (BPA) is recovered.

[0168] Example 2

[0169] Except for the addition of the following (washing step) between (4. acidification step) and (5-1. additional purification step - redissolution step) in Example 1, the regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1.

[0170] (Washing Steps) Wash once with dichloromethane (MC) at 20-30°C using one times the mass of PC used, then filter under vacuum. Wash the filtrate a second time at 50°C using three times the mass of PC used.

[0171] Example 3

[0172] The regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the (5-2. Additional purification step - adsorption step) in Example 1 was omitted.

[0173] Comparative Example 1

[0174] The regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the following (distillation step) was performed instead of (3. layer separation step) and (4. acidification step) in Example 1.

[0175] (Distillation step) After that, the product, which has been reduced to pH 2, is subjected to low-temperature distillation, with the pressure reduced from 250 mbar and 20-30°C to 30 mbar and 30°C.

[0176] <Experimental Examples>

[0177] The physical properties of the regenerated bisphenol A monomer compositions or byproducts obtained in the examples and comparative examples were measured using the following methods, and the results are shown in Table 1 below.

[0178] 1. Purity

[0179] Under normal pressure and at 20 to 30°C, 1 wt% of the regenerated bisphenol A monomer composition was dissolved in acetonitrile (ACN) solvent, and then analyzed using the ACQUITY HPLC system on a Waters HPLC system. The purity of bisphenol A (BPA) was analyzed by ultra-high performance liquid chromatography (UPLC) using a BEH C18 1.7 μm (2.1*50 mm column).

[0180] 2. Color coordinates (L*, a*, and b*)

[0181] The color coordinates of the regenerated bisphenol A monomer composition were analyzed in reflectance mode using a HunterLab UltraScan PRO spectrophotometer.

[0182] 3. Yield

[0183] The weight of BPA produced when the polycarbonate used in the reaction is 100% decomposed, and the weight of the obtained BPA are measured, and the yield of BPA is calculated according to Formula 2 below.

[0184] [Formula 2]

[0185] Yield (%) = W1 / W0

[0186] In Formula 2, W0 is the mass of the aromatic diol compound obtained during 100% decomposition, and W1 is the actual mass of the aromatic diol compound obtained. Specifically, when approximately 100g of polycarbonate is decomposed, theoretically, the mass of BPA obtained during 100% decomposition is 89g. If the actual mass of BPA obtained is 80g, the yield is 80 / 89*100 = 90%.

[0187] 4. Impurity ratio

[0188] Collect 1 ml of the regenerated bisphenol A monomer composition as a sample, perform ion chromatography (IC) analysis under the following conditions, and determine the impurity ratio according to Formula 1 below. As a result of the liquid chromatography measurement, all substances other than bisphenol A are considered impurities.

[0189] <Liquid Chromatography (LC) Conditions>

[0190] ①Chromatographic column: HP-1 (L: 30m, ID: 0.32mm, membrane: 1.05m)

[0191] ② Injection volume: 1 μl

[0192] ③Entrance

[0193] Temperature: 260℃, Pressure: 6.92psi, Total Flow Rate: 64.2ml / min

[0194] Split rate: 60 ml / min, split ratio: 50:1

[0195] ④ Column flow rate: 1.2 ml / min

[0196] ⑤ Oven temperature: 70℃ / 3min - 10℃ / min - 280℃ / 41min (total 65min)

[0197] ⑥ Detector

[0198] Temperature: 280℃, H2: 35ml / min, Air: 300ml / min, He: 20ml / min

[0199] ⑦GC Model: Agilent 7890

[0200] [Formula 1]

[0201] Impurity ratio = {(Total peak area in liquid chromatography - Bisphenol A peak area in liquid chromatography) / Total peak area in liquid chromatography} × 100

[0202] [Table 1]

[0203] Measurement results of Experiment Example 1

[0204] category purity(%) L* a* b* Yield (%) Impurities (%) Example 1 99.3 96.4 0.12 1.82 72 0.7 Example 2 99.7 97.1 0.01 1.57 68 0.3 Example 3 99.1 95.9 0.25 2.24 73 0.9 Comparative Example 1 99.1 96.0 0.34 2.49 65 0.9

[0205] As shown in Table 1, the regenerated bisphenol A monomer compositions obtained in Examples 1 to 3 exhibited a high purity of 99.1% to 99.7%. Furthermore, the regenerated bisphenol A monomer compositions obtained in Examples 1 to 3 showed excellent optical properties with L* coordinates of 95.9 to 97.1, a* of 0.01 to 0.25, and b* of 1.57 to 2.24. Additionally, the regenerated bisphenol A monomer compositions obtained in Examples 1 to 3 were measured to have a high BPA yield of 68% to 73%. Furthermore, the regenerated bisphenol A monomer compositions obtained in Examples 1 to 3 were measured to have a low impurity ratio of 0.3% to 0.9%. On the other hand, compared to the examples, the regenerated bisphenol A monomer composition obtained in Comparative Example 1 showed excellent optical properties with L* coordinates of 96.0, a* of 0.34, and b* of 2.49. Furthermore, the BPA yield of the regenerated bisphenol A monomer composition obtained in Comparative Example 1 was measured to be 65%, lower than that of the examples.

Claims

1. A method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: This causes polycarbonate resins to depolymerize; Adding alkali makes the pH of the depolymerization reaction products above 12; Water is added after the addition of alkali to separate the carbonate precursor from the depolymerization product; and The addition of acid lowers the pH of the depolymerization products separated from the carbonate precursor to below 2. In the step of adding water after adding alkali to separate the carbonate precursor from the depolymerization product, The aqueous layer containing the salt of aromatic diol compounds and the organic solvent layer containing diethyl carbonate were separated. The monomer composition used to synthesize recycled plastics contains aromatic diol compounds. The monomer composition used for synthesizing recycled plastics has an impurity ratio of 0.3% to 0.9% according to Formula 1 below. The yield of aromatic diol compounds according to Formula 2 below is greater than 68% to 73%. Wherein, the chromaticity coordinate L* of the monomer composition used for synthesizing recycled plastics is 95.9 to 97.1, the chromaticity coordinate a* is 0.01 to 0.25, the chromaticity coordinate b* is 1.57 to 2.24, and The monomer composition used to synthesize recycled plastics is obtained from the recycling of polycarbonate resins. [Formula 1] Impurity ratio = {(Total peak area in liquid chromatography - Bisphenol A peak area in liquid chromatography) / Total peak area in liquid chromatography} × 100 [Formula 2] Yield (%) = (W1 / W0) × 100 In Formula 2, W0 is the mass of the aromatic diol compound obtained during the 100% decomposition of polycarbonate resin, and W1 is the actual mass of the aromatic diol compound obtained.

2. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: In the step of adding alkali to make the pH of the depolymerization product above 12, The aromatic diol compounds contained in the depolymerization reaction products are converted into salts of aromatic diol compounds.

3. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: In the step of adding acid to bring the pH of the depolymerization products separated from the carbonate precursor to below 2, The salts of aromatic diol compounds contained in the depolymerization reaction products are converted into aromatic diol compounds.

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

5. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 4, wherein: The ethanol content is 10 to 15 moles relative to 1 mole of polycarbonate resin.

6. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The depolymerization reaction of the polycarbonate resin is carried out by reacting less than 0.5 moles of alkali with 1 mole of polycarbonate resin.

7. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: After the step of adding acid to bring the pH of the depolymerization products separated from the carbonate precursor to below 2, The method further includes: The purification step of the depolymerization reaction product isolated from the carbonate precursor.

8. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, wherein: The purification steps for the depolymerization products isolated from the carbonate precursor include: The recrystallization step of the depolymerization reaction products separated from the carbonate precursor.

9. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, wherein: The purification steps for the depolymerization products isolated from the carbonate precursor include: Adsorption purification step for depolymerization products separated from carbonate precursors.

10. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 7, wherein: The purification steps for the depolymerization products isolated from the carbonate precursor include: A washing step for the depolymerization products separated from carbonate precursors.