Monomer composition for the synthesis of recycled plastic, process for its preparation and recycled plastic, shaped articles using the recycled plastic

Abstract

The present invention relates to a monomer composition for synthesizing a recycled plastic, comprising a high-purity aromatic diol compound recycled through recycling using chemical decomposition of a polycarbonate-based resin; a method of preparing the monomer composition; and a recycled plastic and a molded article using the same. In addition, the present invention relates to a monomer composition for synthesizing a recycled plastic, comprising a high-value-added by-product recycled through recycling using chemical decomposition of a polycarbonate-based resin; a method of preparing the monomer composition; and a recycled plastic and a molded article using the same.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of six Korean patent applications filed on September 13, 2021: 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, Korean Patent Application No. 10-2021-0128892, and Korean Patent Application No. 10-2021-0136153, all of which are incorporated herein by reference.

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

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

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

[0006] Despite the wide range of uses for polycarbonate, environmental and health problems associated with its disposal have been steadily increasing.

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

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

[0009] For this type of chemical decomposition, pyrolysis, hydrolysis, and alcoholysis are commonly known. Among them, the most commonly used method is alcoholysis 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 of requiring high temperature and high pressure conditions and having low yields.

[0010] Furthermore, although alcoholysis using organic catalysts is known, it is 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, which can ensure the recovery of high-purity aromatic diol compounds through recycling by 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, a recycled plastic, and a molded article using the monomer composition for synthesizing recycled plastics.

[0014] Technical solution

[0015] To achieve the above objectives, this document provides a monomer composition for synthesizing recycled plastics, comprising an aromatic diol compound, wherein the chromatic coordinate L* is greater than 95 and the chromatic coordinate a* is from -0.06 to 0.10, wherein the monomer composition for synthesizing recycled plastics is recovered from polycarbonate resins.

[0016] This document also provides a monomer composition for synthesizing recycled plastics, comprising two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, wherein the dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate are recovered from polycarbonate resins.

[0017] This article also provides a method for preparing monomer compositions for synthesizing recycled plastics, the method comprising the steps of: depolymerizing a polycarbonate resin in the presence of a solvent comprising methanol and ethanol; and separating a carbonate precursor from the depolymerization product.

[0018] This document also provides a recycled plastic comprising the reaction product of the monomer composition for synthesizing the recycled plastic and the comonomer.

[0019] This article also provides a molded article comprising the aforementioned recycled plastic.

[0020] Below, monomer compositions for synthesizing recycled plastics, methods for preparing them, and recycled plastics and molded articles using the recycled plastics will be described in more detail according to specific embodiments of the present invention.

[0021] Unless otherwise expressly stated herein, 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.

[0022] Unless the context clearly indicates otherwise, the singular forms “a,” “one,” and “the” used in this document are intended to include the plural forms.

[0023] It should be understood that the terms “comprising,” “including,” “having,” etc., used herein are used to specify the presence of the stated features, regions, integers, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, regions, integers, steps, actions, elements, components, and / or groups.

[0024] Furthermore, ordinal terms such as "first" and "second" are used only for the purpose of distinguishing one component from another and are not limited by ordinal numbers. 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.

[0025] 1. Monomer compositions for synthesizing recycled plastics

[0026] (1) First Composition

[0027] 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 chromatic coordinate L* is greater than 95 and the chromatic coordinate a* is from -0.06 to 0.10, wherein the monomer composition for synthesizing recycled plastics is recovered from a polycarbonate resin.

[0028] The inventors have discovered through experiments that, although a monomer composition for synthesizing recycled plastics in one embodiment utilizes the chemical decomposition of polycarbonate resins for recycling, the composition also meets the requirements of high purity and excellent chromaticity properties of newly synthesized aromatic diol compounds. Thus, excellent physical properties can be achieved in the synthesis of polycarbonate resins using it, and the present invention is thus completed.

[0029] Specifically, one embodiment includes a monomer composition for synthesizing recycled plastics (first composition), and another embodiment includes a monomer composition for synthesizing recycled plastics comprising two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate (second composition), wherein the dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate are recovered from polycarbonate resins and can be obtained simultaneously in a method for preparing the monomer composition for synthesizing recycled plastics, which will be described below.

[0030] That is, the present invention may have the following technical features: a first composition containing high-purity aromatic diol compounds is obtained by recycling the chemical decomposition of polycarbonate resins, and at the same time, a second composition containing two or more compounds selected from dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate as high-value-added by-products can also be obtained.

[0031] Specifically, one embodiment of the monomer composition for synthesizing recycled plastics is characterized in that it is recycled from polycarbonate resins. That is, this refers to recycling from polycarbonate resins to obtain the monomer composition for synthesizing recycled plastics of one embodiment, resulting in a monomer composition for synthesizing recycled plastics comprising aromatic diol compounds.

[0032] Polycarbonate resins are intended to include both homopolymers and copolymers comprising repeating polycarbonate units, and collectively refer to reaction products obtained by polymerization or copolymerization of monomers comprising aromatic diol compounds and carbonate precursors. Homopolymers can be synthesized when they comprise a single repeating carbonate unit obtained 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 when using two or more aromatic diol compounds and one carbonate precursor, or when using one or more other diols in addition to one aromatic diol compound and one carbonate precursor to comprise two or more carbonates. Depending on the molecular weight range, the homopolymers or copolymers can include all low molecular weight compounds, oligomers, and polymers.

[0033] Furthermore, a monomer composition (first composition) for synthesizing recycled plastics according to one embodiment may comprise an aromatic diol compound. Specific examples of aromatic diol compounds 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 of the monomer composition (first composition) for synthesizing recycled plastics in one embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0034] The aromatic diol compound is characterized in that it is recovered from a polycarbonate resin used to recover monomer compositions for synthesizing recycled plastics. That is, this means that by recovering monomer compositions for synthesizing recycled plastics according to one embodiment from polycarbonate resin, an aromatic diol compound is also obtained. Therefore, the external addition of new aromatic diol compounds, other than recovering monomer compositions for synthesizing recycled plastics according to one embodiment, is not included in the scope of the aromatic diol compounds of this invention.

[0035] Specifically, "recovery from polycarbonate resins" refers to obtaining polycarbonate resins through a depolymerization reaction. The depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions, specifically under alkaline (basic) conditions. More specifically, as will be described below, the depolymerization reaction can preferably be carried out in the presence of a mixed solvent of ethanol and methanol.

[0036] Meanwhile, in one embodiment, the chromaticity coordinate b* value of the monomer composition for synthesizing recycled plastics can be less than 2, or greater than 0.1, or from 0.1 to 1.9, or from 1.49 to 1.80. Furthermore, in one embodiment, the chromaticity coordinate L* of the monomer composition for synthesizing recycled plastics can be greater than 95, or less than 100, or greater than 95 and less than 100, or from 95.8 to 100, or from 95.9 to 96.3. Additionally, in one embodiment, the chromaticity coordinate a* of the monomer composition for synthesizing recycled plastics can be from -0.06 to 0.10, or from -0.05 to 0.10, or from -0.04 to 0.09.

[0037] As used in this article, "color coordinates" refers to coordinates in the CIE Lab color space, which are color values ​​defined by CIE (Commonsion International de l'Eclairage). Any position in the CIE color space can be represented by three coordinate values, namely L*, a*, and b*.

[0038] Here, the L* value represents brightness; L* = 0 represents black, and L* = 100 represents white. Additionally, the a* value represents a color with a corresponding color coordinate biased towards either pure red or pure green, and the b* value represents a color with a corresponding color coordinate biased towards either pure yellow or pure blue.

[0039] 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, and a positive b* value indicates a color leaning towards pure yellow. When comparing b* = 50 and b* = 80, b* = 80 is closer to pure yellow than b* = 50.

[0040] When the color coordinate L* value of a monomer composition for synthesizing recycled plastics in one embodiment is excessively reduced to below 95, the color properties of the monomer composition for synthesizing recycled plastics in one embodiment deteriorate.

[0041] Meanwhile, when the chromatic coordinate a* value of the monomer composition for synthesizing recycled plastics in one embodiment increases excessively to greater than 0.10, the monomer composition for synthesizing recycled plastics in one embodiment exhibits an excessively red-biased color, resulting in poor color characteristics.

[0042] Furthermore, when the chromatic coordinate a* value of a monomer composition for synthesizing recycled plastics in one embodiment decreases excessively to less than -0.06, the monomer composition for synthesizing recycled plastics in one embodiment exhibits an excessively red-biased color, resulting in poor color characteristics.

[0043] There are no particular limitations on examples of methods for measuring the color coordinates L*, a*, b* values ​​of a monomer composition for synthesizing recycled plastics according to one embodiment, and various color characteristic measurement methods in the field of plastics can be applied without limitation.

[0044] 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.

[0045] Meanwhile, in one embodiment, the aromatic diol compound purity of the monomer composition for synthesizing recycled plastics can be greater than 99%, or less than 100%, or greater than 99% and less than 100%, or 99.1% to 100%, or 99.1% to 99.5%, or 99.1% to 99.4%.

[0046] There are no particular limitations on examples of methods for measuring the purity of aromatic diol compounds in monomer compositions for synthesizing recycled plastics according to one embodiment, and for example, 1H NMR, ICP-MS, HPLC, UPLC, etc., can be used without limitation. Various well-known methods, conditions, equipment, etc., for NMR, ICP-MS, HPLC, and UPLC can be applied without limitation.

[0047] An example of a method for measuring the purity of an aromatic diol compound in a monomer composition for synthesizing recycled plastics according to one embodiment is as follows. 1% by weight of the monomer composition for synthesizing recycled plastics according to one embodiment is dissolved in acetonitrile (ACN) solvent under normal pressure and at 20°C to 30°C, and then... The purity of bisphenol A (BPA) was analyzed by ultra-high performance liquid chromatography (UPLC) on a Waters HPLC system using a BEH C18 1.7 μm (2.1*50 mm column).

[0048] 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 greater than 99%, and other impurities are minimized, thereby enabling excellent physical properties when used to synthesize polycarbonate resins.

[0049] Simultaneously, 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 recover the monomer composition for synthesizing recycled plastics according to one embodiment.

[0050] That is, this refers to the recycling of monomer compositions from polycarbonate resins to obtain a monomer composition for synthesizing recycled plastics according to one embodiment, resulting in the acquisition of two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Therefore, the external addition of two or more compounds selected from new dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, in addition to the recycling of monomer compositions from polycarbonate resins to prepare a monomer composition for synthesizing recycled plastics according to one embodiment, is not included in the scope of the two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate described in this invention.

[0051] Specifically, "recovery from polycarbonate resins" refers to obtaining them through a depolymerization reaction of the polycarbonate resins. This depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions, particularly under alkaline (basic) conditions. Specifically, as will be described below, the depolymerization reaction can preferably be carried out in the presence of a mixed solvent of ethanol and methanol.

[0052] Since the primary target material for recycling in the monomer composition for synthesizing recycled plastics in one embodiment is an aromatic diol compound, two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate can be separated separately as byproducts.

[0053] The monomer composition for synthesizing recycled plastics in another embodiment described above may correspond to separately separated by-product compositions.

[0054] One embodiment of the monomer composition for synthesizing recycled plastics can be used as a raw material for preparing various recycled plastics (e.g., polycarbonate (PC)) as described below.

[0055] One embodiment of the monomer composition (first composition) for synthesizing recycled plastics can be obtained by a method for preparing the monomer composition for synthesizing recycled plastics, which will be described below. That is, one embodiment of the monomer composition (first composition) for synthesizing recycled plastics is obtained by various filtration, purification, washing and drying processes to ensure only aromatic diol compounds of high purity as the main target material for recycling after the depolymerization of polycarbonate resins.

[0056] (2) Second Composition

[0057] Meanwhile, according to another embodiment of the present invention, a monomer composition for synthesizing recycled plastics can be provided, comprising two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, wherein the dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate are recovered from polycarbonate resins.

[0058] The inventors have discovered through experiments that a monomer composition (second composition) for synthesizing recycled plastics in another embodiment can be recovered through recycling by chemical decomposition of polycarbonate resins, thereby enabling the preparation of monomers with high added value, and thus completing the present invention.

[0059] Another embodiment of the monomer composition (second composition) for synthesizing recycled plastics may further comprise two or more or all three compounds selected from dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0060] That is, the monomer composition for synthesizing recycled plastics in another embodiment may further comprise: a mixture of two types of dimethyl carbonate and diethyl carbonate, a mixture of two types of dimethyl carbonate and methyl ethyl carbonate, a mixture of two types of diethyl carbonate and methyl ethyl carbonate, or a mixture of three types of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

[0061] The characteristic of two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate is that they are recovered from a polycarbonate resin used to recover the monomer composition for synthesizing recycled plastics according to another embodiment. That is, this refers to recovering from a polycarbonate resin to obtain the monomer composition for synthesizing recycled plastics according to another embodiment, resulting in the acquisition of two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Therefore, the external addition of two or more compounds selected from new dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, in addition to the recovery from a polycarbonate resin to prepare the monomer composition for synthesizing recycled plastics according to another embodiment, is not included in the scope of two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate according to another embodiment.

[0062] Specifically, "recovery from polycarbonate resins" refers to obtaining it through the depolymerization reaction of polycarbonate resins. This depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions; specifically, it can be carried out under alkaline (basic) conditions.

[0063] Another embodiment of the monomer composition for synthesizing recycled plastics may contain 1% to 30% or 3% to 25% dimethyl carbonate, 10% to 65% or 16% to 60% diethyl carbonate, and 30% to 60% or 37% to 57% methyl ethyl carbonate.

[0064] There are no particular limitations on the method for measuring the proportions of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, but one example is gas chromatography (GC) analysis. More specifically, standard samples of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are dissolved in EtOH solvent at the same concentration. The peak area values ​​measured by GC are set as reference values, and the proportion of the peak area values ​​of each carbonate byproduct (DEC, DMC, EMC) in the sample is obtained (peak area value of the sample / peak area value of the standard sample). When the sum of the proportions of the peak area values ​​of each carbonate byproduct (DEC, DMC, EMC) obtained by GC results is 100%, the relative proportions of each carbonate byproduct can be calculated.

[0065] As described above, another embodiment of the monomer composition for synthesizing recycled plastics contains an excess of high-value-added ethyl methyl carbonate, which can be used for recycling in various processes.

[0066] Another embodiment of the monomer composition for synthesizing recycled plastics can be used as a raw material for manufacturing various recycled plastics (e.g., polycarbonate (PC), polyurethane and epoxy resins) as described below.

[0067] Another embodiment of the monomer composition for synthesizing recycled plastics (the second composition) may also contain small amounts of other additives and solvents. There are no particular limitations on the specific types of said additives or solvents, and they can be applied to a wide variety of materials widely used in methods for recovering aromatic diol compounds through the depolymerization of polycarbonate resins, without limitation.

[0068] One embodiment of the monomer composition (second composition) for synthesizing recycled plastics can be obtained by a method for preparing the monomer composition for synthesizing recycled plastics, which will be described below. That is, another embodiment of the monomer composition (second composition) for synthesizing recycled plastics corresponds to the result obtained through various processes of filtration, purification, washing, and drying to ensure that only dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, as the main recycling target materials, are obtained in high purity after the depolymerization reaction of the polycarbonate resin.

[0069] 2. A method for preparing monomer compositions for synthesizing recycled plastics.

[0070] 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 in the presence of a solvent comprising methanol and ethanol; and separating a carbonate precursor from the depolymerization product.

[0071] Through experiments, the inventors confirmed that, similar to the method for preparing monomer compositions for synthesizing recycled plastics in another embodiment, in the depolymerization reaction of polycarbonate resins for recycling by chemical decomposition, alcoholysis is carried out by using both methanol and ethanol as reaction solvents. This not only ensures the high purity of aromatic diol compounds, which are the main target materials for the synthesis of this invention, but also ensures the availability of two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate as high-value-added byproducts, thus completing this invention.

[0072] In particular, when alcoholysis is performed using only methanol as in the past, or when alcoholysis is performed using only ethanol, it is difficult to ensure the production of ethyl methyl carbonate as a byproduct, and it is also difficult to ensure the production of dimethyl carbonate and diethyl carbonate as byproducts. However, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment of the present invention has the advantage that the aromatic diol compound as the main product has a purity equal to or higher than that of conventional aromatic diol compounds and excellent optical properties, and at the same time, it can ensure the production of two or more compounds selected from dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, especially ethyl methyl carbonate, with high added value in high yield.

[0073] Specifically, a method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include depolymerizing a polycarbonate resin in the presence of a solvent containing methanol and ethanol.

[0074] Polycarbonate resins are intended to include both homopolymers and copolymers comprising repeating polycarbonate units, and collectively refer to reaction products obtained by polymerization or copolymerization of monomers comprising aromatic diol compounds and carbonate precursors. Homopolymers can be synthesized when they comprise a single repeating carbonate unit obtained 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 when using two or more aromatic diol compounds and one carbonate precursor, or when using one or more other diols in addition to one aromatic diol compound and one carbonate precursor to comprise two or more carbonates. Depending on the molecular weight range, the homopolymers or copolymers can include all low molecular weight compounds, oligomers, and polymers.

[0075] The polycarbonate resin can be used in any form and type, such as new polycarbonate resin prepared by synthesis, recycled polycarbonate resin prepared by regeneration methods, or polycarbonate resin waste.

[0076] 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, diol decomposition, etc. There are no restrictions on the specific methods for each pretreatment process, and various methods widely used in processes for recovering aromatic diols and carbonate precursors from polycarbonate resins can be applied without limitation.

[0077] In the depolymerization reaction of polycarbonate resins, the reaction can be carried out under acidic, neutral, or alkaline conditions; in particular, it can be carried out under alkaline (basic) conditions. There are no particular limitations on the type of base, examples of which include sodium hydroxide (NaOH) or potassium hydroxide (KOH). This base acts as a base catalyst and has economic advantages compared to organic catalysts, which are primarily used under mild conditions.

[0078] In the depolymerization reaction of polycarbonate resins, the reaction can be carried out by reacting an alkali in amounts of less than 0.5 mol, less than 0.4 mol, less than 0.3 mol, less than 0.1 mol, less than 0.2 mol, or 0.1 to 0.5 mol, or 0.1 to 0.4 mol, or 0.1 to 0.3 mol, or 0.2 to 0.5 mol, or 0.2 to 0.4 mol, or 0.2 to 0.3 mol relative to 1 mol of polycarbonate resin. When the 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, a limitation exists: due to the increased amount of alkali metal salts produced, impurities increase, thus reducing the purity of the target recycled material and decreasing the economic efficiency of the catalytic reaction.

[0079] Furthermore, the depolymerization reaction of polycarbonate resins can be carried out in the presence of solvents containing methanol and ethanol. This invention, by decomposing polycarbonate resins with a solvent containing methanol and ethanol, can stably obtain high-purity bisphenol A monomer, and has the advantage of further obtaining two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate as reaction byproducts, which have high added value.

[0080] Specifically, the ethanol content relative to 1 mole of methanol can be 1 to 15 moles, or 1.1 to 15 moles, 1.2 to 15 moles, or 1.1 to 10 moles, or 1.2 to 10 moles. When ethanol is used in excessively small amounts relative to 1 mole of methanol, such as less than 1 mole, or less than 1.1 moles, or less than 1.2 moles, there is a problem of excessively increasing the content of methanol, which is harmful to human health. Furthermore, when ethanol is used in excessive amounts, such as more than 15 moles relative to 1 mole of methanol, there is a limitation that, due to the reduced methanol content, it is difficult to adequately ensure the production of dimethyl carbonate and ethyl methyl carbonate as byproducts.

[0081] The content of methanol and ethanol relative to 1 mole of polycarbonate resin can be 5 to 15 moles, 8 to 13 moles, or 10 to 12 moles. The methanol and ethanol content refers to the sum of the methanol and ethanol contents. Furthermore, since methanol and ethanol have good solubility in bisphenol A, they should essentially be included within the above range. When the methanol and ethanol content is excessively reduced to less than 5 moles relative to 1 mole of polycarbonate resin, it is difficult to achieve sufficient alcoholysis of the polycarbonate resin. On the other hand, when the methanol and ethanol content is excessively increased to more than 15 moles relative to 1 mole of polycarbonate resin, the economics of the process will decrease due to the excessive use of alcohol.

[0082] In addition to methanol and ethanol, the solvent in which polycarbonate resins undergo depolymerization may also include at least one organic solvent selected from tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0083] 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.

[0084] More preferably, dichloromethane can be used as the organic solvent. When dichloromethane is used as an organic solvent and mixed with methanol and ethanol, it has the advantage of improving solubility in polycarbonate and increasing reactivity.

[0085] 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 the total amount of 1 mole of methanol and ethanol can be from 1.5 to 2 moles. By mixing the polycarbonate resin, methanol, ethanol, and organic solvent within the above ranges, it is advantageous that the depolymerization reaction of the polymer can proceed at the desired level.

[0086] Meanwhile, there is no particular limitation on the temperature at which the depolymerization reaction of polycarbonate resins can take place, 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 4 hours to 6 hours.

[0087] Specifically, these conditions are mild compared to conventional pressurized / high-temperature processes, and by stirring under these conditions, the process can be carried out in a milder environment compared to pressurized / high-temperature processes. In particular, the advantage of stirring at 50°C to 70°C for 4 to 6 hours is that the most effective results are obtained in terms of reproducibility and acceptability.

[0088] 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 using pressure / high temperature processes, and diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate can be obtained as byproducts by using methanol and ethanol solvents.

[0089] More specifically, the step of depolymerizing polycarbonate resin in the presence of a solvent containing methanol and ethanol may include: adding an alkali to a mixed solvent of methanol and ethanol with an organic solvent to prepare a catalyst solution; and adding the polycarbonate resin to the catalyst solution and stirring the mixture. In the first step, the detailed descriptions of methanol, ethanol, organic solvent, alkali, and polycarbonate resin are the same as described above.

[0090] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a neutralization reaction step of neutralizing the depolymerization product with acid before the step of separating the carbonate precursor from the depolymerization product.

[0091] For example, the alkaline decomposition products of polycarbonate resins include aromatic diol compounds or their salts, but the primary target material for recovery in this invention is aromatic diol compounds. Therefore, in the case of salts of aromatic diol compounds obtained by alkaline decomposition, they can be converted into aromatic diol compounds through an additional acid neutralization process. That is, when the depolymerization reaction of polycarbonate resins is alkaline decomposition, it can undergo a neutralization reaction step with acid.

[0092] The acid used in the neutralization reaction can be a strong acid, such as hydrochloric acid (HCl). Because the neutralization reaction is carried out by a strong acid, the pH can be less than 6, or below 4 or 2 when the neutralization reaction is complete. The temperature during the neutralization reaction can be adjusted to be above 25°C and below 100°C.

[0093] Furthermore, if necessary, after the neutralization reaction step with acid on the depolymerization products, a step can be performed to remove residual impurities by filtration or absorption. 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 aromatic diol compounds.

[0094] Meanwhile, a method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include the step of separating a carbonate precursor from the depolymerization reaction product. The separated carbonate precursor corresponds to a second composition according to one embodiment. Therefore, the separated carbonate precursor may contain two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0095] For example, the depolymerization products of polycarbonate resins contain aromatic diol compounds or their salts and carbonate precursors. The contents relating to aromatic diol compounds and carbonate precursors include all of the contents described in one of the above embodiments.

[0096] The step of separating the carbonate precursor from the depolymerization product may include a vacuum distillation step of the depolymerization product. There are no particular limitations on the examples of vacuum distillation conditions, but in one specific example, the depolymerization product of the polycarbonate resin is pressurized at a pressure of 200 to 300 mbar and a temperature of 20°C to 30°C, and then depressurized at a pressure of 10 to 50 mbar and a temperature of 20°C to 30°C for cryogenic distillation.

[0097] The isolated carbonate precursors can be recycled without a separate purification process, or, if necessary, recycled through separation and purification, 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 regarding specific purification equipment and methods.

[0098] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may further include a step of purifying the depolymerization reaction product from which the carbonate precursor has been separated. This yields an aromatic diol compound as the main recycled material, corresponding to the first composition according to one embodiment.

[0099] Specifically, the purification steps of the depolymerization reaction products from which the carbonate precursor has been separated may include washing the depolymerization reaction products from which the carbonate precursor has been separated. Furthermore, the purification steps of the depolymerization reaction products from which the carbonate precursor has been separated may include adsorption purification steps. Additionally, the purification steps of the depolymerization reaction products from which the carbonate precursor has been separated may include recrystallization steps.

[0100] There are no particular restrictions on the order of the washing, adsorption purification, and recrystallization steps, and they are not particular about the order in which they are performed; 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. There are no restrictions on the specific washing and adsorption equipment and methods used, and various well-known purification techniques can be applied.

[0101] Specifically, in the washing step of the depolymerization product from which the carbonate precursor has been separated, the depolymerization product may contain aromatic diol compounds. However, since various impurities remain during the recovery process of the aromatic diol compounds, washing can be performed to thoroughly remove these impurities and ensure high purity of the aromatic diol compounds.

[0102] 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. The 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.

[0103] In the washing step, a solvent washing step can be performed first at a temperature above 10°C and below 30°C, and then a solvent washing step can be performed subsequently 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, and then a solvent washing step can be performed subsequently at a temperature above 10°C and below 30°C.

[0104] More preferably, in the washing step, a solvent washing step can be performed first at a temperature of 10°C to 30°C, and then a solvent washing step can be performed subsequently at a temperature of 40°C to 80°C. This minimizes reactor corrosion caused by strong acid after the neutralization step.

[0105] 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.

[0106] In addition, if necessary, a step of washing with solvent at a temperature of 10°C or higher and 30°C or lower may be performed; and after washing with solvent at a temperature of 40°C or higher and 80°C or lower, a step of removing residual solvent by filtration may also be performed.

[0107] 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.

[0108] 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 solvent 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.

[0109] 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.

[0110] 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 increases excessively to more than 50°C, harsh conditions are created in order to maintain extreme temperature conditions, which reduces process efficiency.

[0111] 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 a mixture of two or more thereof may be used.

[0112] Based on the 1 mole of polycarbonate resin used in the depolymerization reaction, the solvent used in the washing step can be used in a weight ratio of 1 to 30 moles or 2 to 25 moles.

[0113] 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, the organic solvent can be used in amounts of 1 to 10 moles or 1 to 5 moles based on 1 mole of polycarbonate resin.

[0114] 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, the solvent can be used in an amount of 20 to 30 moles or 20 to 25 moles based on 1 mole of polycarbonate resin.

[0115] Simultaneously, in the adsorption purification step of the depolymerization reaction product from which the carbonate precursor has been separated, the adsorbent can be contacted with the depolymerization reaction product. Examples of adsorbents that can be used include activated carbon, charcoal, diatomaceous earth, or mixtures thereof. That is, the adsorption purification step of the depolymerization reaction product from which the carbonate precursor has been separated may include: adding an adsorbent to the depolymerization reaction product from which the carbonate precursor has been separated for adsorption purification, and then removing the adsorbent.

[0116] Activated carbon is a microporous black carbon material prepared by carbonizing raw materials at approximately 500°C and then activating them at approximately 900°C. There are no particular limitations on its examples; however, depending on the type of raw material, various types of activated carbon, such as plant-based, coal-based, petroleum-based, and waste-based activated carbon, can be used without limitation. More specifically, 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-carbon activated carbon. Furthermore, waste-based activated carbon can include synthetic resin activated carbon and pulp activated carbon.

[0117] There are no particular limitations on the adsorption and purification conditions of the first adsorbent, and various known adsorption and purification conditions can be used without restriction. However, as an 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 a laboratory adsorption tower.

[0118] If necessary, the method may further include adding a solvent to the depolymerization product from which the carbonate precursor has been separated, prior to the adsorption purification step from which the depolymerization product from which the carbonate precursor has been separated. Examples of the solvent include ethanol, and ethanol may be added in a ratio of 1 to 20 moles, 10 to 20 moles, or 15 to 20 moles relative to 1 mole of polycarbonate resin. By adding the solvent to the depolymerization product from which the carbonate precursor has been separated, the aromatic diol compound crystals contained in the depolymerization product from which the carbonate precursor has been separated can be redissolved in the solvent.

[0119] Meanwhile, in the recrystallization step from which the depolymerization product from which the carbonate precursor has been separated, high-purity aromatic diol compounds can be ensured by thoroughly removing various impurities contained in the depolymerization product from which the carbonate precursor has been separated.

[0120] Specifically, the recrystallization step may include adding water to the depolymerization product from which the carbonate precursor has been separated to carry out recrystallization. By adding water to the depolymerization product from which the carbonate precursor has been separated to carry out recrystallization, the solubility of the aromatic diol compound or its salt contained in the depolymerization product is increased, thereby maximally dissolving the crystals or impurities intercalated between the crystals with the solvent. Furthermore, since the dissolved aromatic diol compound has poor solubility relative to the impurities, it can easily precipitate as aromatic diol compound crystals due to the difference in solubility when the temperature is subsequently lowered.

[0121] More specifically, in the step of adding water to the depolymerization product from which the carbonate precursor has been separated 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 from which the carbonate precursor has been separated becomes too high, which degrades process efficiency and makes 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 from which the carbonate precursor has been separated becomes too high, thereby reducing the yield of the aromatic diols recovered after recrystallization, and reducing process efficiency due to the use of a large amount of solvent.

[0122] If necessary, after the recrystallization step from which the depolymerization product from which the carbonate precursor has been separated, a step of removing residual impurities by filtration or adsorption can also be performed.

[0123] Furthermore, if necessary, the method may 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 known drying techniques can be applied without limitation regarding the specific drying equipment and methods used in the drying process.

[0124] 3. Recycled plastics

[0125] According to another embodiment of the present invention, a recycled plastic comprising a reaction product of a monomer composition (first composition) for synthesizing recycled plastics according to one embodiment and a comonomer can be provided. Alternatively, a recycled plastic comprising a reaction product of a monomer composition (second composition) for synthesizing recycled plastics according to another embodiment and a comonomer can be provided.

[0126] The detailed descriptions of a monomer composition (first composition) for synthesizing recycled plastics in one embodiment and a monomer composition (second composition) for synthesizing recycled plastics in another embodiment include all the contents described above in one embodiment and the other embodiment.

[0127] There are no particular limitations on examples of recycled plastics, and they may include polycarbonate resins, polyurethane resins, epoxy resins, etc. Specifically, for recycled plastics comprising the reaction product of a monomer composition (first composition) for synthesizing recycled plastics according to one embodiment and a comonomer, various plastics synthesized from aromatic diol compounds such as bisphenol A as monomers can be used without limitation, and a more specific example may be polycarbonate resins.

[0128] Furthermore, specifically, for recycled plastics comprising the reaction product of a monomer composition (second composition) for synthesizing recycled plastics according to another embodiment and a comonomer, various plastics synthesized from carbonate precursors such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate as monomers can be used without limitation, and a more specific example can be polycarbonate resins, or polyurethane resins, or epoxy resins.

[0129] Specifically, the term "polycarbonate resin" is intended to include both homopolymers and copolymers comprising repeating polycarbonate units, and collectively refers to reaction products obtained by polymerization or copolymerization of monomers comprising aromatic diol compounds and carbonate precursors. Homopolymers can be synthesized when they comprise a single repeating carbonate unit obtained 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 when using two or more aromatic diol compounds and one carbonate precursor, or when using one or more other diols in addition to one aromatic diol compound and one carbonate precursor to comprise two or more carbonates. Depending on the molecular weight range, the homopolymers or copolymers can include all low molecular weight compounds, oligomers, and polymers.

[0130] More specifically, in a recycled plastic comprising a monomer composition (first composition) for synthesizing recycled plastics according to one embodiment and a reaction product of a comonomer, a carbonate precursor can be used as a comonomer. Specific examples of carbonate precursors include: phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, xylene carbonate, bis(chlorophenyl) carbonate, m-toluene carbonate, dinaphthalene carbonate, bis(biphenyl) carbonate, or dihalocarbamates. A monomer composition (second composition) for synthesizing recycled plastics according to another embodiment, comprising two or more compounds selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate as carbonate precursors, can be used.

[0131] Furthermore, in the recycled plastic comprising the reaction product of a monomer composition (second composition) for synthesizing recycled plastics according to another embodiment and a comonomer, the comonomer may include an aromatic diol compound.

[0132] Specific examples of the aromatic diol compounds 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, mixtures of two or more thereof, etc. A monomer composition (first composition) comprising an aromatic diol compound as an aromatic diol compound, according to one embodiment, for the synthesis of recycled plastics, may be used.

[0133] There are no particular limitations on the examples of reaction processes between monomer compositions for synthesizing recycled plastics and comonomers used to synthesize polycarbonate resins, and various well-known polycarbonate preparation methods can be applied without limitation.

[0134] 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, 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 can be easily controlled.

[0135] 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 process can be maintained above 9 or 11.

[0136] 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 polycarbonates, and as an example, halogenated hydrocarbons such as dichloromethane and chlorobenzene can be used.

[0137] 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.

[0138] Furthermore, to adjust the molecular weight of polycarbonate during polymerization, 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, and specific examples 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 the aromatic glycol compound, the amount of molecular weight regulator can be from 0.01 parts by weight to 10 parts by weight or from 0.1 parts by weight to 6 parts by weight, and the desired molecular weight can be obtained within this range.

[0139] 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 promote the polymerization reaction.

[0140] 4. Molded products

[0141] According to yet another embodiment of the invention, a molded article of recycled plastic comprising another embodiment can be provided. The detailed description of recycled plastic includes all that has been described above in the other embodiment.

[0142] The molded article can be obtained by applying the recycled plastic to various known plastic molding methods without limitation. Examples of molding methods include injection molding, foam injection molding, blow molding, or extrusion molding.

[0143] 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. Examples of molded articles include: automobiles, electrical and electronic products, communication products, daily necessities, building materials, optical components, exterior materials, etc.

[0144] In addition to the recycled plastic of another embodiment, the molded article may also include, if desired, one or more additives selected from antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact enhancers, fluorescent whitening agents, ultraviolet absorbers, pigments and dyes.

[0145] An example of the method for manufacturing the molded article may include the following steps: thoroughly mixing the recycled plastic of another embodiment with additives using a mixer, extruding the mixture into pellets using an extruder, drying the pellets, and then injecting them using an injection molding machine.

[0146] Beneficial effects

[0147] According to the present invention, a monomer composition for synthesizing recycled plastics can be provided, comprising a high-purity aromatic diol compound recovered through recycling by chemical decomposition of polycarbonate resins; a method for preparing said monomer composition; and recycled plastics and molded articles using the recycled plastics. Furthermore, a monomer composition for synthesizing recycled plastics can be provided, comprising a high-value-added byproduct recovered through recycling by chemical decomposition of polycarbonate resins; a method for preparing said monomer composition; recycled plastics and molded articles using the recycled plastics. Detailed Implementation Plan

[0148] The present invention will be described 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.

[0149] <Example: Preparation of a Regenerated Bisphenol A Monomer Composition>

[0150] Example 1

[0151] (1. Decomposition Step) 28 mol of a mixed solvent of ethanol / methanol / dichloromethane (ethanol:methanol:dichloromethane molar ratio = 10:1:17) and 0.25 mol of sodium hydroxide were added to a 250 mL three-necked flask and stirred. Then, 1 mol of waste polycarbonate (PC) was added and the mixture was stirred at 60 °C for 6 hours to depolymerize the PC. The depolymerization product was cooled to room temperature to obtain a mixture of bisphenol A.

[0152] (2. Neutralization stage) The mixture containing bisphenol A is neutralized with 0.25 moles of 1N hydrochloric acid (HCl) at 20°C to 30°C, the aqueous layer and the organic layer are separated, and the organic layer is filtered by vacuum filtration to obtain a liquid containing bisphenol A.

[0153] (3-1. Purification-Distillation Step) After that, 23 moles of water were added to the organic layer which was lowered to less than pH 6, and the byproducts diethyl carbonate (DEC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), as well as the previously used dichloromethane, methanol, ethanol and water, were recovered by low-temperature distillation from 250 mbar and 20°C to 30°C and 30°C.

[0154] (3-2. Purification-Washing Steps) When distilled for a period of time through the above process, bisphenol A precipitates and forms a slurry. The solid is vacuum filtered and recovered, then washed for the first time at 20°C to 30°C with 3 mol of dichloromethane (MC), vacuum filtered and recovered, and then washed for the second time at 50°C with 23 mol of water.

[0155] (4-1. Additional purification step - redissolution step) Add 16.6 mol of ethanol to the washed material and redissolve it.

[0156] (4-2. Additional purification step - adsorption step) After that, lignite activated carbon is added at a ratio of 50% by weight relative to the waste polycarbonate, and purified by adsorption for 3 hours, and then filtered to remove the lignite activated carbon.

[0157] (4-3. Additional purification step - recrystallization step) After that, 260 moles of water are slowly added to recrystallize bisphenol A, and then the resulting slurry is vacuum filtered at 20°C to 30°C to recover bisphenol A (BPA) crystals.

[0158] (5. Drying step) After that, it is dried in a vacuum convection oven at 40°C to prepare a regenerated bisphenol A monomer composition in which regenerated bisphenol A (BPA) is recovered.

[0159] Example 2

[0160] Except that, in Example 1, the molar ratio of ethanol:methanol:dichloromethane was changed to 9:2:17 as shown in Table 1 below, the regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1.

[0161] Example 3

[0162] Except that, in Example 1, the molar ratio of ethanol:methanol:dichloromethane was changed to 8:3:17 as shown in Table 1 below, the regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1.

[0163] Example 4

[0164] Except that, in Example 1, the molar ratio of ethanol:methanol:dichloromethane was changed to 7:4:17 as shown in Table 1 below, the regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1.

[0165] Example 5

[0166] Except that, in Example 1, the molar ratio of ethanol:methanol:dichloromethane was changed to 6:5:17 as shown in Table 1 below, the regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1.

[0167] <Comparative Example: Preparation of Regenerated Bisphenol A Monomer Composition>

[0168] Comparative Example 1

[0169] Except that, in Example 1, the molar ratio of ethanol:methanol:dichloromethane was changed to 0:11:17 as shown in Table 1 below, the regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1.

[0170] Comparative Example 2

[0171] Except that, in Example 1, the molar ratio of ethanol:methanol:dichloromethane was changed to 11:0:17 as shown in Table 1 below, the regenerated bisphenol A monomer composition was prepared in the same manner as in Example 1.

[0172] <Experimental Example>

[0173] 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.

[0174] 1. Purity

[0175] Under normal pressure and at 20°C to 30°C, 1% by weight of the regenerated bisphenol A monomer composition was dissolved in acetonitrile (ACN) solvent, and then ACQUITY was used. 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) system with a Waters HPLC system.

[0176] 2. Color coordinates (L*, a*, and b*)

[0177] The color coordinates of the regenerated bisphenol A monomer composition were analyzed in reflectance mode using a HunterLab UltraScan PRO spectrophotometer.

[0178] 3. Content of impurities (DMC, DEC, EMC)

[0179] Take 1 ml of a solution of a mixture of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) byproducts separated in the distillation step, containing MC, MeOH, EtOH, and water, as a sample and perform gas chromatography (GC) analysis under the following conditions.

[0180] <Gas Chromatography (GC) Conditions>

[0181] ① Column: HP-1 (L: 30m, ID: 0.32mm, membrane: 1.05m)

[0182] ② Injection volume: 1 μl

[0183] ③Entrance

[0184] Temperature: 260℃, Pressure: 6.92psi, Total Flow Rate: 64.2ml / min

[0185] Split rate: 60 ml / min, split ratio: 50:1

[0186] ④ Column flow rate: 1.2 ml / min

[0187] ⑤ Oven temperature: 70℃ / 3min - 10℃ / min - 280℃ / 41min (total 65min)

[0188] ⑥ Detector

[0189] Temperature: 280℃, H2: 35ml / min, Air: 300ml / min, He: 20ml / min

[0190] ⑦GC Model: Agilent 7890

[0191] Then, standard samples of diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were dissolved in EtOH solvent at the same concentration. The peak area measured by GC was set as the reference value, and the ratio of the peak area values ​​of each carbonate byproduct (diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC)) in the sample (peak area value of the sample / peak area value of the standard sample) was obtained.

[0192] When the sum of the peak area values ​​of each carbonate byproduct (diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC)) obtained by GC results is set to 100%, the relative proportions of each carbonate byproduct are calculated and shown in Table 1 below.

[0193] [Table 1]

[0194] Measurement results of Experiment Example 1

[0195]

[0196] As shown in Table 1, the regenerated bisphenol A monomer compositions obtained in Examples 1 to 5 exhibited a high purity of 99.1% to 99.4%. Furthermore, the regenerated bisphenol A monomer compositions obtained in Examples 1 to 5 exhibited chromaticity coordinates L* of 95.9 to 96.3, a* of -0.04 to 0.09, and b* of 1.49 to 1.80, demonstrating excellent optical properties. In addition, in the regenerated bisphenol A monomer compositions obtained in Examples 1 to 5, all three carbonates—diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC)—were obtained as byproducts. On the other hand, the purity of the regenerated bisphenol A monomer composition obtained in Comparative Example 2 was 99.0%, which was lower than that of the examples. Furthermore, the regenerated bisphenol A monomer composition obtained in Comparative Example 1 exhibited a color coordinate L* of 95.77, a* of -0.08, and b* of 1.51, while the regenerated bisphenol A monomer composition obtained in Comparative Example 2 exhibited a color coordinate a* of 0.11, showing inferior optical performance compared to the examples. Moreover, in the regenerated bisphenol A monomer composition obtained in Comparative Example 1, only dimethyl carbonate (DMC) was obtained as a byproduct, and in the regenerated bisphenol A monomer composition obtained in Comparative Example 2, only diethyl carbonate (DEC) was obtained as a byproduct.

Claims

1. A method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: Polycarbonate resins are depolymerized in the presence of solvents containing methanol and ethanol. and Separation of carbonate precursors from depolymerization reaction products The content of methanol and ethanol is 10 to 15 moles relative to 1 mole of the polycarbonate resin. In addition to methanol and ethanol, the solvent also includes at least one organic solvent selected from tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate. The content of the organic solvent is 1.5 to 2 moles relative to the total amount of 1 mole of methanol and ethanol.

2. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: Ethanol is contained in amounts ranging from 1 to 15 moles relative to 1 mole of methanol.

3. 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.

4. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The content of the organic solvent is 16 to 20 moles relative to 1 mole of the polycarbonate resin.

5. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The step of depolymerizing the polycarbonate resin in the presence of a solvent containing methanol and ethanol includes... A base is added to a mixed solvent of methanol, ethanol, and an organic solvent to prepare a catalyst solution; and The carbonate resin is added to the catalyst solution and the mixture is stirred.

6. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The step of separating the carbonate precursor from the depolymerization reaction products includes: The depolymerization reaction product is subjected to a vacuum distillation step.

7. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising: Purification of the depolymerization product from which the carbonate precursor has been isolated.

8. The method for preparing monomer compositions for synthesizing recycled plastics according to claim 1, The method further includes: Prior to the step of separating the carbonate precursor from the depolymerization product, the depolymerization product undergoes a neutralization reaction with an acid.

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