Monomer composition for synthesizing recycled plastic, preparation method thereof, recycled plastic and molded product using the recycled plastic

Abstract

The present invention relates to a monomer composition for synthesizing recycled plastics, a method for preparing the monomer composition, recycled plastics, and molded products using the recycled plastics. The monomer composition contains an aromatic diol compound, wherein the color coordinate b* is 0.1 to 1, wherein the yield of the aromatic diol compound is greater than 75%, and wherein the monomer composition for synthesizing recycled plastics is recovered from a polycarbonate resin.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2021-0122001 filed on September 13, 2021, Korean Patent Application No. 10-2021-0122002 filed on September 13, 2021, Korean Patent Application No. 10-2021-0122003 filed on September 13, 2021, Korean Patent Application No. 10-2021-0122004 filed on September 13, 2021, 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, filed in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a monomer composition for synthesizing recycled plastics, a method for preparing the monomer composition, recycled plastics, and molded products using the recycled plastics. The monomer composition contains a high-purity aromatic diol compound recovered by recycling through chemical decomposition of a polycarbonate resin. Background Art

[0004] Polycarbonate is a thermoplastic polymer and is a plastic having excellent characteristics such as excellent transparency, ductility, and relatively low manufacturing cost.

[0005] Although polycarbonate is widely used for various purposes, environmental and health concerns continue to be raised during waste disposal.

[0006] Currently, physical recycling methods are being carried out, but in this case, there arises a problem of accompanying quality deterioration, and therefore, research on chemical recycling of polycarbonate is being conducted.

[0007] Chemical decomposition of polycarbonate refers to obtaining an aromatic diol compound (such as bisphenol A (BPA)) as a monomer by decomposing polycarbonate, which is then used again for polymerization to obtain high-purity polycarbonate.

[0008] Generally known chemical decomposition methods include thermal decomposition, hydrolysis, and alcoholysis. Among these, alcoholysis using an alkali catalyst is the most common method. However, methanolysis has the problem of using methanol, which is harmful to the human body, and ethanol requires high temperature and high pressure conditions, resulting in a low yield.

[0009] In addition, although an alcoholysis method using an organic catalyst is known, it is economically disadvantageous. Summary of the Invention

[0010] Technical issues

[0011] An object of the present invention is to provide a monomer composition for synthesizing recycled plastics, which can ensure a high yield of an aromatic diol compound having improved optical properties recovered by recycling using chemical decomposition of a polycarbonate-based resin.

[0012] Another object of the present invention is to provide a method for preparing the monomer composition for synthesizing recycled plastics, as well as a recycled plastic and a molded product using the monomer composition for synthesizing recycled plastics.

[0013] Technical Solution

[0014] To achieve the above object, the present invention provides a monomer composition for synthesizing recycled plastics, comprising an aromatic diol compound, wherein the color coordinate b* is 0.1 to 1, wherein the yield of the aromatic diol compound according to the following formula 1 is greater than 75%, and wherein the monomer composition for synthesizing recycled plastics is recovered from a polycarbonate resin:

[0015] [Formula 1]

[0016] Yield (%) = W1 / W0

[0017] In Formula 1, W0 is the mass of the aromatic diol compound obtained in the process of 100% decomposition, and W1 is the mass of the aromatic diol compound actually obtained.

[0018] The present invention also provides a method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: depolymerizing a polycarbonate resin; adding an acid to adjust the pH of the depolymerization reaction product to 2 to 8; removing impurities after adding the acid; and separating a carbonate precursor from the depolymerization reaction product.

[0019] The present invention also provides a recycled plastic comprising a reaction product of the monomer composition for synthesizing the recycled plastic and a comonomer.

[0020] The present invention also provides a molded product comprising the recycled plastic.

[0021] Hereinafter, a monomer composition for synthesizing recycled plastic, a method for preparing the monomer composition, and recycled plastic and a molded article using the recycled plastic according to a specific embodiment of the present invention will be described in more detail.

[0022] Unless otherwise specified 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 present invention.

[0023] As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0024] As used herein, "pH" refers to hydrogen ion concentration (pH), which is a numerical value that indicates the acidity and alkalinity of a material. The pH value can be determined by the reciprocal of the logarithmic dissociation concentration of hydrogen ions and is used as a measure of the strength of the acid and base of a material.

[0025] It should be understood that the terms "comprising", "including", "having", etc. used in this document are used to specify the presence of the described 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.

[0026] In addition, the terms including ordinal numbers such as "first", "second", etc. are only used to distinguish one component from another component and are not limited by the ordinal numbers. For example, without departing from the scope of the present invention, the first component can be referred to as the second component, or similarly, the second component can be referred to as the first component.

[0027] 1. Monomer composition for synthesizing recycled plastics

[0028] 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 color coordinate b* is 0.1 to 1, wherein the yield of the aromatic diol compound according to Formula 1 is greater than 75%, and wherein the monomer composition for synthesizing recycled plastics is recovered from a polycarbonate resin.

[0029] The present inventors have experimentally discovered that although a monomer composition for synthesizing recycled plastics according to one embodiment is recovered by recycling using chemical decomposition of a polycarbonate resin, an aromatic diol compound satisfying a low color coordinate b* value at a color level comparable to that of commercially available reagents or reagents used for PC polymerization can be obtained in high yield, thereby completing the present invention.

[0030] Specifically, in the case of the aromatic diol compound recovered by recycling using chemical decomposition of conventional polycarbonate-based resins, the color coordinate b* value is relatively high, within the range of greater than 1 and less than 4, and indicates that the color is excessively biased toward yellow, and thus, the color characteristics are deteriorated, whereas the aromatic diol compound recovered in the present invention ensures a low color coordinate b* value of 0.1 to 1, or 0.1 to 0.5, or 0.2 to 0.5, or 0.21 to 0.43.

[0031] In the case of commercially used polycarbonates, transparency and color specifications are important due to the nature of their applications. The color of polycarbonate depends on the color of the aromatic diol compound (such as bisphenol A (BPA)) used as a raw material. In the case of recycled BPA obtained by chemical decomposition of conventional polycarbonate, the color specifications of the recycled BPA are reduced due to the lack of removal of side reaction products, which also affects the color of the polycarbonate polymerized using it. In particular, the color coordinate b* value of the recycled BPA is very important.

[0032] Furthermore, the inventors have experimentally confirmed that the content of impurities other than the aromatic diol compound, which is the main recovery target, is significantly reduced, thereby enabling excellent physical properties to be achieved when using the same to synthesize a polycarbonate resin, thereby completing the present invention.

[0033] In particular, in the method for preparing a monomer composition for synthesizing recycled plastics described later, a monomer composition for synthesizing recycled plastics (first composition) of one embodiment and a monomer composition for synthesizing recycled plastics (second composition) containing diethyl carbonate can be obtained simultaneously, wherein the diethyl carbonate is recovered from a polycarbonate resin.

[0034] That is, the present invention can have the following technical features: a first composition containing an aromatic diol compound is obtained with high purity by recycling through chemical decomposition of a polycarbonate resin, and at the same time, a second composition containing diethyl carbonate as a by-product with high added value can also be obtained.

[0035] Specifically, the monomer composition for synthesizing recycled plastics according to one embodiment is characterized in that it is recovered from a polycarbonate resin. Specifically, the monomer composition for synthesizing recycled plastics according to one embodiment is recovered from the polycarbonate resin, and as a result, a monomer composition for synthesizing recycled plastics containing an aromatic diol compound is also obtained.

[0036] Polycarbonate resin is intended to comprise homopolymer and the multipolymer that comprise polycarbonate repeating unit, and is collectively referred to as the reaction product that obtains by the polyreaction or copolymerization reaction of the monomer that comprises aromatic diol compound and carbonate precursor.When it comprises a kind of carbonate repeating unit that obtains by only using a kind of aromatic diol compound and a kind of carbonate precursor, can synthesize homopolymer.In addition, when using a kind of aromatic diol compound and two or more kinds of carbonate precursor as monomer, or when using two or more kinds of aromatic diol compound and a kind of carbonate precursor, or when also using one or more other glycols to comprise two or more kinds of carbonate except a kind of aromatic diol compound and a kind of carbonate precursor, can synthesize multipolymer.According to molecular weight range, described homopolymer or described multipolymer can comprise all low-molecular compounds, oligomer and polymkeric substance.

[0037] In addition, the monomer composition for synthesizing recycled plastics of one embodiment may contain an aromatic diol compound. Specific examples of the aromatic diol compound include: bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), 2,2-bis(4-hydroxyphenyl)butane, Bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 2,2-bis(4-hydroxy-3-bromophenyl)propane, 2,2-bis(4-hydroxy-3-chlorophenyl)propane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, or a mixture of two or more thereof. Preferably, the aromatic diol compound of the monomer composition for synthesizing recycled plastics according to one embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0038] The aromatic diol compound is characterized by being recovered from a polycarbonate resin used to recover a monomer composition for synthesizing recycled plastics. Specifically, the aromatic diol compound is recovered from the polycarbonate resin to obtain the monomer composition for synthesizing recycled plastics according to one embodiment, and as a result, the aromatic diol compound is also obtained. Therefore, in addition to recovering the aromatic diol compound from the polycarbonate resin to prepare the monomer composition for synthesizing recycled plastics according to one embodiment, the aromatic diol compound is not included in the scope of the aromatic diol compound of the present invention.

[0039] Specifically, "recovered from a polycarbonate resin" means obtained by depolymerization of the polycarbonate resin. The depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions. Specifically, the depolymerization reaction can be carried out under alkaline (basic) conditions. Specifically, as described below, the depolymerization reaction can preferably be carried out in the presence of an ethanol solvent.

[0040] At the same time, the color coordinate b* value of the monomer composition for synthesizing recycled plastics of one embodiment can be 0.1 to 1, or 0.1 to 0.5, or 0.2 to 0.5, or 0.21 to 0.43. In addition, the color coordinate L* of the monomer composition for synthesizing recycled plastics of one embodiment can be 98 or more, or 100 or less, or 98 to 100, or 98.12 to 98.91. In addition, the color coordinate a* of the monomer composition for synthesizing recycled plastics of one embodiment can be 0 or less, or -0.2 or more, or -0.2 to 0, or -0.15 to -0.01.

[0041] As used herein, “color coordinates” refer to coordinates in the CIE Lab color space, which are color values ​​defined by CIE (Commission International de l'Eclairage), and any position in the CIE color space can be represented by three coordinate values, namely L*, a*, and b*.

[0042] Here, the L* value indicates brightness, with L* = 0 representing black and L* = 100 representing white. Furthermore, the a* value indicates a color with corresponding color coordinates leaning toward pure red or pure green, and the b* value indicates a color with corresponding color coordinates leaning toward pure yellow or pure blue.

[0043] 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. Furthermore, 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 that tends toward pure blue, while a positive b* value indicates a color that tends toward pure yellow. When comparing b*=50 and b*=80, b*=80 is closer to pure yellow than b*=50.

[0044] When the color coordinate a* value of the monomer composition for synthesizing recycled plastic of one embodiment excessively increases to be greater than 0, or the color coordinate L* value excessively decreases to be less than 98, the color characteristics of the monomer composition for synthesizing recycled plastic of one embodiment deteriorate.

[0045] Meanwhile, when the color coordinate b* value of the monomer composition for synthesizing recycled plastic of one embodiment excessively increases to be greater than 1, the monomer composition for synthesizing recycled plastic of one embodiment exhibits a color that is excessively biased toward yellow, and thus, color characteristics are deteriorated.

[0046] Furthermore, when the color coordinate b* value of the monomer composition for synthesizing recycled plastic of one embodiment is excessively reduced to less than 0.1, the monomer composition for synthesizing recycled plastic of one embodiment exhibits a color excessively biased toward blue, and thus, color characteristics are deteriorated.

[0047] Examples of a method for measuring the color coordinates L*, a*, and b* values ​​of the monomer composition for synthesizing recycled plastics of one embodiment are not particularly limited, and various color property measurement methods in the field of plastics may be applied without limitation.

[0048] However, as an example, the color coordinates L*, a*, and b* values ​​of the monomer composition for synthesizing recycled plastics according to one embodiment can be measured using a HunterLab UltraScan PRO spectrophotometer in reflectance mode.

[0049] Meanwhile, the purity of the aromatic diol compound of the monomer composition for synthesizing recycled plastics according to one embodiment may be 98% or more, or 100% or less, or 98% to 100%.

[0050] There is no particular limitation on examples of a method for measuring the purity of the aromatic diol compound of the monomer composition for synthesizing recycled plastics according to one embodiment, and for example, the purity of the aromatic diol compound can be measured using 1 H NMR, ICP-MS analysis, HPLC analysis, UPLC analysis, etc. are not limited. As for the specific methods, conditions, apparatuses, etc. of NMR, ICP-MS, HPLC, and UPLC, various known methods can be applied without limitation.

[0051] An example of a method for measuring the purity of the aromatic diol compound of the monomer composition for synthesizing recycled plastics according to one embodiment is as follows. Under normal pressure and 20° C. to 30° C., 1% by weight of the monomer composition for synthesizing recycled plastics according to one embodiment is dissolved in acetonitrile (ACN) solvent, and then the purity is measured using ACQUITY The purity of bisphenol A (BPA) was analyzed by ultra-performance liquid chromatography (UPLC) on a Waters HPLC system using a C18 1.7 μm column (2.1*50 mm).

[0052] As described above, in the monomer composition for synthesizing recycled plastics of one embodiment, the purity of the aromatic diol compound as the main recycling target material is significantly improved to more than 98%, and other impurities are minimized, thereby, when using it to synthesize polycarbonate resins, excellent physical properties can be obtained.

[0053] Meanwhile, in addition to the aromatic diol compound, the monomer composition for synthesizing recycled plastics may also contain impurities. The impurities refer to all substances other than the aromatic diol compound as the main recycling target material of the present invention, and there is no particular limitation on their specific types, but examples thereof include sodium salts.

[0054] In particular, according to the method for preparing the monomer composition for synthesizing recycled plastics to be described later, the pH of the depolymerization reaction product is adjusted to 2 to 8, so that the aromatic diol compound as the main material to be recovered can be present in the organic phase, thereby, water-soluble impurities can be separated into the water layer and easily removed, and acidic organic impurities having stronger acidity than the aromatic diol compound can be further removed.

[0055] Specifically, in the monomer composition for synthesizing recycled plastics, a weight ratio of sodium salt impurities measured using ion chromatography may be less than 10 μg relative to 1 g of the monomer composition for synthesizing recycled plastics.

[0056] The example of the method for measuring the weight ratio of the sodium salt impurity in the monomer composition for synthesizing recycled plastics according to one embodiment is not particularly limited, and, for example, ion chromatography (IC) analysis can be used. As for the specific method, conditions, and apparatus of IC, various known contents can be applied without particular limitation.

[0057] As described above, in the monomer composition for synthesizing recycled plastics of one embodiment, the weight ratio of sodium salt impurities other than the aromatic diol compound as the main recycling target material is significantly reduced to less than 10 μg relative to 1 g of the monomer composition for synthesizing recycled plastics, thereby achieving excellent physical properties when synthesizing a polycarbonate resin.

[0058] At the same time, the yield of the aromatic diol compound in the monomer composition for synthesizing recycled plastics according to one embodiment can be greater than 75%, or greater than 76%, or greater than 77%, or less than 100%, or greater than 75% and less than 100%, or between 77% and 100%, or between 78% and 100%. It is believed that the increase in the yield of the aromatic diol compound to greater than 75% is due to the method for preparing the monomer composition for synthesizing recycled plastics, which will be described later.

[0059] An example of a method for measuring the yield of the aromatic diol compound of the monomer composition for synthesizing recycled plastics according to one embodiment is not particularly limited, and for example, the yield can be calculated by the following Formula 1.

[0060] [Formula 1]

[0061] Yield (%) = W1 / W0

[0062] In Formula 1, W0 is the mass of the aromatic diol compound obtained by 100% decomposition, and W1 is the mass of the aromatic diol compound actually obtained.

[0063] For measurement of the mass of the aromatic diol compound in Formula 1, various well-known mass measurement methods can be used without particular limitation, and for example, a balance can be used.

[0064] As described above, in the monomer composition for synthesizing recycled plastics of one embodiment, the proportion of impurities other than the aromatic diol compound as the main recycling target material is greatly increased to more than 75%, thereby improving the efficiency of the recycling process of polycarbonate resins.

[0065] At the same time, in the monomer composition for synthesizing recycled plastics of one embodiment, diethyl carbonate can be obtained as a by-product. The diethyl carbonate is characterized in that it is recovered from the polycarbonate resin used to recover the monomer composition for synthesizing recycled plastics of one embodiment.

[0066] Specifically, this refers to the recovery of diethyl carbonate from a polycarbonate resin to obtain a monomer composition for synthesizing recycled plastics according to one embodiment, resulting in the simultaneous production of diethyl carbonate. Therefore, the addition of new diethyl carbonate from the outside, other than the recovery of diethyl carbonate from a polycarbonate resin to prepare a monomer composition for synthesizing recycled plastics according to one embodiment, is not included in the scope of diethyl carbonate of the present invention.

[0067] Specifically, "recovered from a polycarbonate resin" means obtained by depolymerization of the polycarbonate resin. The depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions. In particular, the depolymerization reaction can be carried out under alkaline (basic) conditions. In particular, as will be described later, the depolymerization reaction can preferably be carried out in the presence of an ethanol solvent.

[0068] Since the main recovery target material in the monomer composition for synthesizing recycled plastics of one embodiment is the aromatic diol compound, diethyl carbonate as a by-product can be separately separated and recovered from the monomer composition for synthesizing recycled plastics of one embodiment.

[0069] The monomer composition for synthesizing recycled plastics according to one embodiment may be used as a raw material for preparing various recycled plastics (eg, polycarbonate (PC)) to be described later.

[0070] The monomer composition for synthesizing recycled plastics according to one embodiment may further include small amounts of other additives and solvents. The specific types of additives or solvents are not particularly limited, and various materials widely used in methods for recovering aromatic diol compounds by depolymerization of polycarbonate resins can be applied without limitation.

[0071] The monomer composition for synthesizing recycled plastics according to one embodiment can be obtained by a method for preparing the monomer composition for synthesizing recycled plastics, which will be described later. Specifically, the monomer composition for synthesizing recycled plastics according to one embodiment corresponds to the product obtained by filtering, purifying, washing, and drying after the depolymerization reaction of a polycarbonate resin to ensure only the highly pure aromatic diol compound, which is the main target material for recovery.

[0072] 2. Method for preparing monomer composition for synthesizing recycled plastics

[0073] 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 acid so that the pH of the depolymerization reaction product is 2 to 8; removing impurities after adding the acid; and separating a carbonate precursor from the depolymerization reaction product.

[0074] The present inventors have experimentally confirmed that, similar to the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment, although the pH of the depolymerized polycarbonate resin is adjusted during the recycling of the polycarbonate resin by chemical decomposition, and the polycarbonate resin is recycled by chemical decomposition, an aromatic diol compound satisfying a low color coordinate b* value at a color level comparable to that of commercially available reagents or reagents used for PC polymerization can be obtained in high yield, thereby completing the present invention.

[0075] In particular, the pH of the depolymerization reaction product is adjusted to 2 to 8 so that the aromatic diol compound, which is the main material to be recovered, can be present in the organic phase, whereby water-soluble impurities can be separated into the aqueous layer and easily removed, and acidic organic impurities having stronger acidity than the aromatic diol compound can be further removed.

[0076] Therefore, the present inventors have experimentally confirmed that, as the content of impurities other than the aromatic diol compound that is the main recovery target is significantly reduced, excellent physical properties can be achieved when using it to synthesize a polycarbonate resin, and have completed the present invention.

[0077] Specifically, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may include a step of depolymerizing a polycarbonate-based resin.

[0078] Polycarbonate resin is intended to comprise homopolymer and the multipolymer that comprise polycarbonate repeating unit, and refers to the reaction product that obtains by the polyreaction or copolymerization reaction of the monomer that comprises aromatic diol compound and carbonate precursor.When it comprises a kind of carbonate repeating unit that obtains by only using a kind of aromatic diol compound and a kind of carbonate precursor, can synthesize homopolymer.In addition, when using a kind of aromatic diol compound and two or more kinds of carbonate precursor as monomer, or when using two or more kinds of aromatic diol compound and a kind of carbonate precursor, or when using one or more other glycols to comprise two or more kinds of carbonate except a kind of aromatic diol compound and a kind of carbonate precursor, can synthesize multipolymer.According to molecular weight range, described homopolymer or described multipolymer can comprise all low-molecular compounds, oligomer and polymkeric substance.

[0079] The polycarbonate-based resin may be applied regardless of various forms and types, such as a new polycarbonate-based resin prepared by synthesis, a recycled polycarbonate-based resin prepared by a recycling process, or polycarbonate-based resin waste.

[0080] However, as needed, a pretreatment step of the polycarbonate resin can be performed before the depolymerization reaction of the polycarbonate resin, thereby improving the efficiency of the process for recovering the aromatic diol compound and the carbonate precursor from the polycarbonate resin. Examples of the pretreatment process may include washing, drying, grinding, ethylene glycol decomposition, etc. There is no limitation on the specific method of each pretreatment process, and various methods widely used in the process for recovering the aromatic diol compound and the carbonate precursor from the polycarbonate resin can be applied without limitation.

[0081] In the process of the depolymerization reaction of the polycarbonate resin, the depolymerization reaction can be carried out under acid, neutral or alkaline conditions, specifically, the depolymerization reaction can be carried out under alkaline (basic) conditions. There is no particular limitation on the type of alkali, examples of which include sodium hydroxide (NaOH) or potassium hydroxide (KOH). The alkali is an alkaline catalyst that acts as a catalyst and has economic advantages over the organic catalysts mainly used under mild conditions. More specifically, in the process of the depolymerization reaction of the polycarbonate resin, the depolymerization reaction can be carried out in a pH range of greater than 8 and less than 12.

[0082] During the depolymerization reaction of the polycarbonate resin, the depolymerization reaction can be carried out by reacting the base in an amount of 0.5 mol or less, or 0.4 mol or less, or 0.3 mol or less, or 0.1 mol or more, or 0.2 mol or more, or 0.1 mol to 0.5 mol, or 0.1 mol to 0.4 mol, or 0.1 mol to 0.3 mol, or 0.2 mol to 0.5 mol, or 0.2 mol to 0.4 mol, or 0.2 mol to 0.3 mol relative to 1 mol of the polycarbonate resin. When the polycarbonate resin is reacted with the base in an amount greater than 0.5 mol relative to 1 mol of the polycarbonate resin during the depolymerization process of the polycarbonate resin, there is a limitation in that the amount of alkali metal salt generated increases, thereby increasing impurities, thereby reducing the purity of the target recycled material and reducing the economic benefits of the catalytic reaction.

[0083] Furthermore, the depolymerization reaction of the polycarbonate resin can be carried out in the presence of a solvent containing ethanol. By using a solvent containing ethanol to decompose the polycarbonate resin, the present invention can stably obtain high-purity monomeric bisphenol A and further has the advantage of obtaining high-value-added diethyl carbonate as a reaction byproduct.

[0084] The content of ethanol can be 5 to 15 mol, or 8 to 13 mol, relative to 1 mol of the polycarbonate resin. Since ethanol has good solubility in bisphenol A, ethanol within the above range should be substantially contained. If the ethanol content is excessively reduced to less than 5 mol relative to 1 mol of the polycarbonate resin, sufficient alcohol decomposition of the polycarbonate resin becomes difficult. On the other hand, if the ethanol content is excessively increased to greater than 15 mol relative to 1 mol of the polycarbonate resin, the economic efficiency of the process may be reduced due to excessive use of alcohol.

[0085] The solvent in which the polycarbonate resin is depolymerized may further include, in addition to ethanol, at least one organic solvent selected from tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0086] 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.

[0087] More preferably, dichloromethane can be used as the organic solvent. When dichloromethane is used as the organic solvent mixed with ethanol, there are advantages in that the solubility of polycarbonate can be improved and the reactivity can be increased.

[0088] The content of the organic solvent may be 16 to 20 mol, or 16 to 18 mol, per mol of the polycarbonate resin. Furthermore, the content of the organic solvent may be 1.5 to 2 mol per mol of ethanol. Mixing the polycarbonate resin, ethanol, and organic solvent within these ranges advantageously allows the depolymerization reaction of the polymer to proceed at a desired level.

[0089] Meanwhile, the temperature at which the depolymerization reaction of the polycarbonate resin is performed is not particularly limited, but for example, the reaction may be performed at a temperature of 20° C. to 100° C. or 50° C. to 70° C. In addition, the depolymerization of the polycarbonate resin may be performed for 1 to 30 hours or 4 to 6 hours.

[0090] Specifically, the conditions are mild process conditions compared to conventional pressurized / high-temperature processes, and by stirring under the above conditions, the process can be performed in a mild process compared to pressurized / high-temperature processes. In particular, stirring at 50°C to 70°C for 4 to 6 hours has the advantage of obtaining the most effective results in terms of reproducibility and acceptability.

[0091] That is, according to the present invention, by adjusting the type and mixing amount of the mixed solvent and the type and content of the base catalyst without using an organic catalyst, there are advantages in that a high-purity aromatic diol compound (e.g., bisphenol A) can be obtained under mild conditions without using a pressure / high-temperature process, and diethyl carbonate can be obtained as a by-product by using an ethanol solvent.

[0092] Meanwhile, an antioxidant may be added to the reaction solution during the depolymerization reaction of the polycarbonate resin. When the antioxidant is added, the aromatic diol compound recovered by chemical decomposition of the polycarbonate resin and recycled can achieve a low color coordinate b* value at a color level comparable to that of commercially available reagents or reagents used for PC polymerization.

[0093] The specific examples of antioxidants are not particularly limited, and various antioxidants widely used in the prior art can be applied without restriction. However, an example thereof includes: sodium thiosulfate, sodium sulfite, isoascorbic acid, butylated hydroxytoluene, butylated hydroxyanisole, alpha-tocopherol, tocopheryl acetate, L-ascorbic acid and salts thereof, L-ascorbyl palmitate, L-ascorbyl stearate, tripentyl gallate, propyl gallate or disodium ethylenediaminetetraacetic acid (EDTA), sodium pyrophosphate, sodium metaphosphate or a mixture of two or more thereof.

[0094] The specific amount of the antioxidant added is not particularly limited, but as an example, the antioxidant can be added in the range of 0.1 wt % to 5 wt % or 0.1 wt % to 1 wt % based on the total weight of the reaction solution at a level that does not affect the physical properties of the monomer composition for synthesizing recycled plastics.

[0095] In addition, during the depolymerization reaction of the polycarbonate resin, the depolymerization may be performed under a nitrogen atmosphere.

[0096] More specifically, the step of depolymerizing the polycarbonate resin may include: first, dissolving the polycarbonate resin in an organic solvent; and second, adding a catalyst solution containing ethanol, a base, and an antioxidant and stirring. In the first and second steps, the contents of ethanol, the organic solvent, the base, the antioxidant, and the polycarbonate resin are the same as described above.

[0097] Meanwhile, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may further include a step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8. A strong acid may be used as the acid, and examples thereof include hydrochloric acid (HCl).

[0098] During the step of adding an acid to adjust the pH of the depolymerization reaction product to 2 to 8, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted into an aromatic diol compound. When the depolymerization reaction is carried out under alkaline conditions, the resulting aromatic diol compound exists as a salt upon reaction with the base and therefore has hydrophilicity. Therefore, by adding an acid, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted into an aromatic diol compound, thereby inducing hydrophobicity.

[0099] Therefore, after adding acid, in the step of adding water to remove impurities, a layer can be formed that is divided into a water layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate precursor, which will be described later. Since the aromatic diol compound and the carbonate precursor have hydrophobicity, they can be contained in the organic solvent layer in water and the organic solvent, and various water-soluble impurities can be contained in the water layer. Therefore, the aromatic diol compound and impurities as the main product can be easily separated by a simple step of changing pH.

[0100] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to another embodiment may further include: adding water in the step of adding an acid so that the pH of the depolymerized product is 2 to 8. Thus, in the step of removing impurities described later, a layer can be formed which is divided into a water layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate precursor.

[0101] The order of the step of adding the acid and the step of adding the water is not particularly limited, and the water may be added after the acid is added, the acid may be added after the water is added, or the water and the acid may be added simultaneously.

[0102] Meanwhile, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may include a step of removing impurities after adding acid. Therefore, the impurities are hydrophilic materials, examples of which may include salt compounds, ionic compounds, acid compounds, etc.

[0103] As described above, after the step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8, as the step of removing impurities from the depolymerization reaction product after the addition of the acid proceeds, the depolymerization reaction product forms a layer separated into an aqueous layer containing impurities and an organic solvent layer containing the aromatic diol compound and the carbonate precursor, so that the aqueous layer containing impurities can be separated and removed.

[0104] In the step of removing impurities from the depolymerization reaction product after adding the acid, the aqueous layer and the organic layer may be separated to remove impurities contained in the aqueous layer. The specific separation conditions for separating the aqueous layer from the organic layer are not particularly limited. As for the specific separation device and method, various known purification techniques can be applied without limitation. However, as an example, a drainage device may be used.

[0105] Meanwhile, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may include a step of separating a carbonate precursor from the depolymerization reaction product. Therefore, the separated carbonate precursor may contain diethyl carbonate.

[0106] In the step of separating the carbonate precursor from the depolymerization reaction product, a reduced pressure distillation step of the depolymerization product may be included. Examples of reduced pressure distillation conditions are not particularly limited, but in a specific example, the product of the depolymerization reaction of the polycarbonate resin is pressurized at a pressure of 200 to 300 mbar and a temperature of 20° C. to 30° C., then reduced in pressure at a pressure of 10 to 50 mbar and a temperature of 20° C. to 30° C., and subjected to low-temperature distillation.

[0107] The isolated carbonate precursor can be recycled under the situation of not having independent purification process, or, as required, can be recycled by separation and purification such as conventional extraction, adsorption and drying.Concrete purification conditions are not particularly restricted.For concrete purification plant and method, various known purification techniques can be applied without restriction.

[0108] Meanwhile, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may include: after the step of separating the carbonate precursor from the depolymerization reaction product, a step of purifying the depolymerization reaction product from which the carbonate precursor is separated.

[0109] Specifically, the purification step of the depolymerization reaction product of the carbonate precursor may include a step of washing the depolymerization reaction product of the carbonate precursor. In addition, the purification step of the depolymerization reaction product of the carbonate precursor may include an adsorption purification step of the depolymerization reaction product of the carbonate precursor. In addition, the purification step of the depolymerization reaction product of the carbonate precursor may include a recrystallization step of the depolymerization reaction product of the carbonate precursor.

[0110] The order of the washing step, the adsorption purification step, and the recrystallization step is not particularly limited, and they can be performed in any order. However, for example, the washing step, the adsorption purification step, and the recrystallization step can be performed in this order. The washing step, the adsorption purification step, and the recrystallization step can each be repeated at least once or multiple times. As for the specific washing, adsorption, and recrystallization apparatus and methods, various known purification techniques can be applied without limitation.

[0111] Specifically, in the step of washing the depolymerization reaction product from which the carbonate precursor is separated, the depolymerization reaction product from which the carbonate precursor is separated may contain an aromatic diol compound. However, since various impurities remain during the recovery process of obtaining the aromatic diol compound, washing may be performed to fully remove these impurities and ensure a high-purity aromatic diol compound.

[0112] Specifically, the washing step may include: washing with a solvent at a temperature of 10°C to 30°C, or 20°C to 30°C; and washing with a solvent at a temperature of 40°C to 80°C, or 40°C to 60°C, or 45°C to 55°C. The temperature conditions refer to the temperature within the washing container where the washing with the solvent is performed. To maintain a high temperature that deviates from room temperature, various heating devices can be used without limitation.

[0113] In the washing step, a step of washing with a solvent at a temperature of 10° C. to 30° C. may be performed first, and then a step of washing with a solvent at a temperature of 40° C. to 80° C. may be performed. Alternatively, a step of washing with a solvent at a temperature of 40° C. to 80° C. may be performed first, and then a step of washing with a solvent at a temperature of 10° C. to 30° C. may be performed.

[0114] More preferably, in the washing step, a step of washing with a solvent at a temperature of 10° C. to 30° C. may be performed first, and then a step of washing with a solvent at a temperature of 40° C. to 80° C. may be performed. Thus, corrosion of the reactor due to the strong acid after the neutralization step can be minimized.

[0115] The step of washing with a solvent at a temperature of 10° C. or higher and 30° C. or lower; and the step of washing with a solvent at a temperature of 40° C. or higher and 80° C. or lower may be repeated at least once or more, respectively.

[0116] Furthermore, if necessary, after the steps of washing with a solvent at a temperature of 10° C. to 30° C. and washing with a solvent at a temperature of 40° C. to 80° C., a step of removing the residual solvent by filtration may be performed.

[0117] More specifically, the difference between the temperature of the step of washing with a solvent at a temperature of 40°C to 80°C and the temperature of the step of washing with a solvent at a temperature of 10°C to 30°C may be 20°C to 50°C.

[0118] The difference between the temperature of the step of washing with a solvent at a temperature of 40°C to 80°C and below and the temperature of the step of washing with a solvent at a temperature of 10°C to 30°C is a value obtained by subtracting the temperature of the step of washing with a solvent at a temperature of 10°C to 30°C from the temperature of the step of washing with a solvent at a temperature of 40°C to 80°C.

[0119] When the difference between the temperature of the step of washing with a solvent at a temperature of 40°C to 80°C and the temperature of the step of washing with a solvent at a temperature of 10°C to 30°C is excessively reduced to less than 20°C, it is difficult to sufficiently remove impurities.

[0120] When the difference between the temperature of the step of washing with a solvent at a temperature of 40°C to 80°C and the temperature of the step of washing with a solvent at a temperature of 10°C to 30°C excessively increases to more than 50°C, harsh conditions are formed in order to maintain extreme temperature conditions, which may reduce process efficiency.

[0121] The solvent used in the washing step may include one of water, alcohol and an organic solvent. As the 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.

[0122] The weight ratio of the solvent used in the washing step may be 1 part by weight or more and 30 parts by weight or less, or 1 part by weight or more and 10 parts by weight or less, based on 1 part by weight of the polycarbonate-based resin used in the depolymerization reaction.

[0123] More specifically, the solvent in the step of washing with a solvent at a temperature of 10°C to 30°C can be an organic solvent. Preferably, dichloromethane can be used as the organic solvent. In this case, the amount of the organic solvent used can be 1 part by weight to 10 parts by weight based on 1 part by weight of the polycarbonate resin.

[0124] In addition, the solvent in the step of washing with a solvent at a temperature of 40°C to 80°C can be water. When water is used, impurities in the form of residual salts can be effectively removed. In this case, the amount of the solvent used can be 1 part by weight to 10 parts by weight based on 1 part by weight of the polycarbonate resin.

[0125] Furthermore, the step of adsorption purification of the depolymerization reaction product from which the carbonate precursor is separated may include the steps of adding an adsorbent to the depolymerization reaction product from which the carbonate precursor is separated for adsorption purification and then removing the adsorbent. In the steps of adding an adsorbent to the depolymerization reaction product from which the carbonate precursor is separated for adsorption purification and then removing the adsorbent, the adsorbent may be in contact with the depolymerization reaction product.

[0126] Examples of adsorbents that can be used include activated carbon, charcoal, or mixtures thereof. Activated carbon is a black carbon material having micropores produced by subjecting a raw material to a carbonization process at about 500° C. and an activated carbon process at about 900° C., and examples thereof are not particularly limited. However, for example, various activated carbons such as plant-based, coal-based, petroleum-based, and waste-based activated carbons can be applied without limitation depending on the type of raw material.

[0127] In a more specific example, the plant-based activated carbon may include coconut shell activated carbon, wood activated carbon, and sawdust activated carbon. Furthermore, the coal-based activated carbon may include lignite activated carbon, bituminous coal activated carbon, and anthracite activated carbon. Furthermore, the petroleum-based activated carbon may include petroleum coke activated carbon and oil charcoal activated carbon. Furthermore, the waste-based activated carbon may include synthetic resin activated carbon and paper pulp activated carbon.

[0128] 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. Specifically, the adsorbent may include plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, waste-based activated carbon, or a mixture of two or more thereof.

[0129] 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 adsorbent may include coconut shell activated carbon, lignite activated carbon, anthracite activated carbon, bituminous coal activated carbon, or a mixture of two or more thereof.

[0130] There are no particular limitations on the adsorption purification conditions of the adsorbent, and various known adsorption purification conditions can be used without limitation. However, in one embodiment, the adsorbent can be added in an amount of 40% to 60% by weight relative to the polycarbonate resin, the adsorption time can be 1 to 5 hours, and the adsorption method can be stirred adsorption or a laboratory adsorption tower.

[0131] As required, said method can also comprise the steps: adding sorbent to carry out adsorption purification in the depolymerization reaction product of therefrom separated carbonate precursor, then before the step of removing sorbent, adding solvent in the depolymerization reaction product of therefrom separated carbonate precursor.The example of solvent comprises ethanol, and relative to 1 mole of polycarbonate resin, ethanol can add with 1 mole to 20 moles or 10 moles to 20 moles or 15 moles to 20 moles ratio.By in the depolymerization reaction product of therefrom separated carbonate precursor, adding the step of solvent, the aromatic diol compound crystal that comprises in the depolymerization reaction product of therefrom separated carbonate precursor can be made to be dissolved in the solvent again.

[0132] At the same time, in the recrystallization step of the depolymerization reaction product from which the carbonate precursor is separated, a high-purity aromatic diol compound can be ensured by sufficiently removing various impurities contained in the depolymerization product from which the carbonate precursor is separated.

[0133] Specifically, the recrystallization step may include adding water to the depolymerization reaction product from which the carbonate precursor is separated to perform recrystallization. By adding water to the depolymerization reaction product from which the carbonate precursor is separated to perform recrystallization, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product is increased, so that crystals or impurities between crystals can be dissolved by the solvent to the greatest extent possible. Furthermore, since the dissolved aromatic diol compound has a poor solubility relative to the impurities, when the temperature is subsequently lowered, it can be easily precipitated as aromatic diol compound crystals due to the difference in solubility.

[0134] More specifically, in the step of adding water to carry out recrystallization in the depolymerization reaction product of therefrom separated carbonate precursor, with respect to 1 mole of polycarbonate resin, can use 200 moles to 400 moles, or 250 moles to 350 moles of water.When the consumption of water was too few, the temperature that was used to dissolve the aromatic diol compound that comprised in the depolymerization reaction product of therefrom separated carbonate precursor became too high, thus, process efficiency deteriorated, and was difficult to remove impurity by recrystallization.On the other hand, when the consumption of water was too large, the solubility of the aromatic diol compound that comprised in the depolymerization reaction product of therefrom separated carbonate precursor became too high, therefore, the yield of the aromatic diol compound that reclaims after the recrystallization reduced, and owing to using a large amount of solvents, process efficiency reduced.

[0135] If necessary, after the recrystallization step of the depolymerization reaction product from which the carbonate precursor is separated, a step of removing residual impurities by filtration or adsorption may be performed.

[0136] Furthermore, the method may further include a drying step after the recrystallization step, as needed. The remaining solvent may be removed by drying, and specific drying conditions are not particularly limited, but for example, drying may be performed at a temperature of 10° C. to 100° C. or 10° C. to 50° C. As for the specific drying apparatus and method used in the drying, various known drying techniques may be applied without limitation.

[0137] 3. Recycled plastic

[0138] According to another embodiment of the present invention, a recycled plastic may be provided, comprising a reaction product of the monomer composition for synthesizing recycled plastic according to one embodiment and a comonomer.

[0139] The details of the monomer composition for synthesizing recycled plastics of one embodiment include all the contents described above in one embodiment and another embodiment.

[0140] There is no particular limitation on the examples corresponding to the recycled plastics, and various plastics synthesized from aromatic diol compounds such as bisphenol A as monomers and carbonate precursors such as dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate can be applied without limitation, and a more specific example can be polycarbonate resins.

[0141] Described polycarbonate resin is intended to comprise homopolymer and the multipolymer that comprise polycarbonate repeating unit, and refers to the reaction product that obtains by the polyreaction or copolymerization reaction of the monomer that comprises aromatic diol compound and carbonate precursor.When it comprises a kind of carbonate repeating unit that obtains by only using a kind of aromatic diol compound and a kind of carbonate precursor, can synthesize homopolymer.In addition, when using a kind of aromatic diol compound and two or more kinds of carbonate precursor as monomer, or when using two or more kinds of aromatic diol compound and a kind of carbonate precursor, or when using one or more other glycols to comprise two or more kinds of carbonate except a kind of aromatic diol compound and a kind of carbonate precursor, can synthesize multipolymer.According to molecular weight range, described homopolymer or described multipolymer can comprise all low-molecular compounds, oligomer and polymkeric substance.

[0142] More specifically, in the recycled plastic comprising the reaction product of the monomer composition for synthesizing recycled plastic according to one embodiment and a comonomer, a carbonate precursor can be used as a comonomer. Specific examples of the carbonate precursor include: phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate, m-tolyl carbonate, dinaphthyl carbonate, bis(biphenyl) carbonate, or dihaloformate.

[0143] Examples of the reaction process of the monomer composition for synthesizing recycled plastics and the comonomer for synthesizing the polycarbonate-based resin are not particularly limited, and various known methods for preparing polycarbonate may be applied without limitation.

[0144] However, in one example of a polycarbonate production method, a polycarbonate production method including polymerizing a monomer composition for synthesizing recycled plastic and a comonomer may be used. In this case, the polymerization may be performed by interfacial polymerization, and during the interfacial polymerization, the polymerization reaction may be performed at normal pressure and low temperature, and the molecular weight may be easily controlled.

[0145] The polymerization temperature may be 0° C. to 40° C., and the reaction time may be 10 minutes to 5 hours. In addition, the pH during the reaction may be maintained at 9 or 11 or higher.

[0146] The solvent that can be used for the polymerization is not particularly limited as long as it is a solvent used for polymerization of polycarbonate in the art, and as an example, halogenated hydrocarbons such as dichloromethane and chlorobenzene can be used.

[0147] Furthermore, the polymerization may be carried out in the presence of an acid binder. As the acid binder, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an amine compound such as pyridine can be used.

[0148] In addition, in order to control the molecular weight of polycarbonate in the polymerization process, polymerization can be carried out in the presence of a molecular weight regulator. Alkylphenols with 1 to 20 carbon atoms can be used as molecular weight regulators, and their specific examples include: p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol or triacontylphenol. The molecular weight regulator can be added before polymerization initiation, during polymerization initiation or after polymerization initiation. Based on 100 weight parts of aromatic diol compounds, the consumption of the molecular weight regulator can be 0.01 weight part to 10 weight parts or 0.1 weight part to 6 weight parts, and within this range, desired molecular weight can be obtained.

[0149] In addition, in order to promote the polymerization reaction, a reaction accelerator such as a tertiary amine compound, a quaternary ammonium compound or a quaternary phosphonium compound, including triethylamine, tetra-n-butylammonium bromide or tetra-n-butylphosphonium bromide, may also be used.

[0150] 4. Molded products

[0151] According to another embodiment of the present invention, a molded article comprising the recycled plastic of another embodiment may be provided. The details of the recycled plastic include all the contents described in the above another embodiment.

[0152] The molded article can be obtained by applying the recycled plastic to various known plastic molding methods without limitation. As examples of molding methods, injection molding, foam injection molding, blow molding, or extrusion molding can be mentioned.

[0153] Examples of molded articles are not particularly limited, and can be applied to various molded articles using plastics without limitation. Examples of the molded articles include automobiles, electrical and electronic products, communication products, daily necessities, building materials, optical parts, exterior materials, and the like.

[0154] If necessary, in addition to the recycled plastic of another embodiment, the molded article may further include one or more additives selected from antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact enhancers, fluorescent brighteners, ultraviolet absorbers, pigments and dyes.

[0155] One example of a method for producing the molded article may include the steps of fully mixing the recycled plastic of another embodiment with an additive using a mixer, extruding the mixture with an extruder to produce pellets, drying the pellets, and then injecting them with an injection molding machine.

[0156] Beneficial effects

[0157] According to the present invention, a monomer composition for synthesizing recycled plastics, a method for preparing the monomer composition, and a molded product using the recycled plastics and the recycled plastics can be provided. The monomer composition can ensure a high yield of an aromatic diol compound with improved optical properties recovered by recycling through chemical decomposition of a polycarbonate resin. DETAILED DESCRIPTION

[0158] Hereinafter, the present invention will be described in detail with reference to the following examples. However, these examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.

[0159] <Examples and Comparative Examples: Preparation of Regenerated Bisphenol A Monomer Composition>

[0160] Example 1

[0161] (1. Decomposition Step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of dichloromethane (MC), and then added to a 3 L high-pressure reactor together with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH). 0.7 wt % of sodium dithionite was added as an antioxidant relative to the entire solution. The atmosphere inside the system was replaced with nitrogen, and the mixture was stirred in an inactive state at 60° C. for 6 hours to perform a PC depolymerization reaction.

[0162] (2. pH Adjustment) The depolymerization reaction product was cooled to below 30° C., and then bisphenol A was adjusted to a pH of 8 by adding 10% hydrochloric acid (HCl) and water to the product.

[0163] (3. Layer Separation) After that, in a state where a water layer and a dichloromethane (MC) layer were formed, the organic layer at the bottom was recovered using a drain device located at the bottom end of the reactor, and the water layer at the top was discharged and then discarded.

[0164] (4. Distillation) Thereafter, the recovered methylene chloride (MC) layer was subjected to low-temperature distillation at a reduced pressure of 250 mbar and 20 to 30° C. to 30 mbar and 30° C., thereby separating and recovering diethyl carbonate (DEC) as a by-product.

[0165] (5. Purification Step - Filtration) After that, the residue from which diethyl carbonate (DEC) was removed was washed once with dichloromethane (MC) twice the weight of PC at 20°C to 30°C and vacuum filtered. The filtrate was washed twice with water twice the weight of PC at 50°C.

[0166] (6-1. Additional Purification Step - Redissolution Step) Thereafter, bisphenol A was added to 16.6 mol of ethanol and re-dissolved.

[0167] (6-2. Additional Purification Step - Adsorption Step) Thereafter, lignite activated carbon was added as an adsorbent in a ratio of 50 wt % relative to the waste polycarbonate, and then purified by adsorption for 3 hours, and then the lignite activated carbon was removed by filtration.

[0168] (6-3. Additional Purification Step - Recrystallization Step) Thereafter, 300 mol of water was added to recrystallize bisphenol A, and the resulting slurry was vacuum filtered at 20° C. to 30° C. to recover bisphenol A (BPA) crystals.

[0169] (7. Drying Step) Thereafter, the mixture was dried in a convection oven at 40° C. under vacuum to prepare a recycled bisphenol A monomer composition in which recycled bisphenol A (BPA) was recovered.

[0170] Example 2

[0171] A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the pH was adjusted to 7 instead of 8 in (2. pH adjustment) of Example 1.

[0172] Example 3

[0173] A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the pH was adjusted to 5 instead of 8 in (2. pH adjustment) of Example 1.

[0174] Example 4

[0175] A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the pH was adjusted to 2 instead of 8 in (2. pH adjustment) of Example 1.

[0176] Comparative Example 1

[0177] A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that (2. pH adjustment) and (3. layer separation) of Example 1 were not performed.

[0178] Comparative Example 2

[0179] A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that in (2. pH adjustment) of Example 1, 10% hydrochloric acid (HCl) was not added, only water was added, and the pH was adjusted to more than 10.

[0180] <Test Example>

[0181] The physical properties of the recycled bisphenol A monomer compositions obtained in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 1 below.

[0182] 1. Purity

[0183] 1 wt% of the regenerated bisphenol A monomer composition was dissolved in acetonitrile (ACN) solvent at normal pressure and 20°C to 30°C, and then, ACQUITY The purity of bisphenol A (BPA) was analyzed by ultra-performance liquid chromatography (UPLC) on a Waters HPLC system using a BEH C18 1.7 μm column (2.1*50 mm).

[0184] 2. Color coordinates (L*, a*, and b*)

[0185] The color coordinates of the recycled bisphenol A monomer composition were analyzed using a HunterLab UltraScan PRO spectrophotometer in reflectance mode.

[0186] 3. Yield

[0187] The weight of BPA generated when the polycarbonate used in the reaction was 100% decomposed was measured, and the weight of the obtained BPA was measured, and the yield of BPA was calculated according to the following Formula 1.

[0188] [Formula 1]

[0189] Yield (%) = W1 / W0

[0190] In Formula 1, W0 is the mass of the aromatic diol compound obtained if 100% decomposition is achieved, and W1 is the mass of the aromatic diol compound actually obtained. Specifically, when approximately 100 g of polycarbonate is decomposed, the theoretical mass of BPA obtained at 100% decomposition is 89 g. If the actual mass of BPA obtained is 80 g, the yield is 80 / 89 × 100 = 90%.

[0191] 4. Content of sodium salt impurities

[0192] 1 ml of the regenerated bisphenol A monomer composition was collected as a sample and subjected to ion chromatography (IC) analysis under the following conditions: Based on 1 g of the sample, the weight ratio (unit: μg / g) of the sodium salt impurity contained therein was measured.

[0193] <Ion Chromatography (IC) Conditions>

[0194] ① Column: HP-1 (L: 30m, ID: 0.32mm, membrane: 1.05m)

[0195] ②Injection volume: 1 μl

[0196] ③Entrance

[0197] Temperature: 260°C, pressure: 6.92 psi, total flow rate: 64.2 ml / min,

[0198] Split flow: 60ml / min, split ratio: 50:1

[0199] ④ Column flow rate: 1.2 ml / min

[0200] ⑤ Oven temperature: 70℃ / 3min-10℃ / min-280℃ / 41min (total 65min)

[0201] ⑥Detector

[0202] Temperature: 280°C, H2: 35ml / min, Air: 300ml / min, He: 20ml / min

[0203] [Table 1]

[0204] Test case measurement results

[0205]

[0206] As shown in Table 1, the recycled bisphenol A monomer compositions obtained in Examples 1 to 4 exhibited high purities of 99.29% to 99.92%. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 to 4 exhibited color coordinates L* of 98.12 to 98.91, a* of -0.15 to -0.01, and b* of 0.21 to 0.43, exhibiting excellent optical properties. Furthermore, the BPA yields measured for the recycled bisphenol A monomer compositions obtained in Examples 1 to 4 ranged from 79.1% to 83%. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 to 4 were measured to have low impurity contents of less than 10 μg / g. On the other hand, the purities of the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 ranged from 96.82% to 97.14%, which were lower than those in the Examples. Furthermore, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 exhibited color coordinates L* of 97.12 to 97.82, a* of 0.06 to 0.31, and b* of 1.16 to 1.62, exhibiting inferior optical properties compared to the Examples. Furthermore, the BPA yields of the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 were 65.1% to 69.1%, which were measured to be lower than those of the Examples.

Claims

1. A method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: Depolymerize polycarbonate resins; adding an acid so that the pH of the depolymerization reaction product is 2 to 8; Impurities are removed after adding acid; and separating a carbonate precursor from the depolymerization reaction product, wherein the polycarbonate resin is depolymerized in the presence of a solvent containing ethanol, The content of the ethanol is 10 mol to 15 mol relative to 1 mol of the polycarbonate resin; Wherein, in the step of removing impurities after adding acid, The water layer containing the impurities and the organic solvent layer containing the aromatic diol compound and the carbonate precursor are separated; Wherein, in the step of separating the carbonate precursor from the depolymerization reaction product, the method includes a step of vacuum distillation of the depolymerization reaction product; wherein, after the step of separating the carbonate precursor from the depolymerization reaction product, the method further comprises a step of purifying the depolymerization reaction product from which the carbonate precursor is separated; The purification step of the depolymerization reaction product from which the carbonate precursor is separated includes a washing step, a recrystallization step, and an adsorption purification step.

2. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: In the step of adding acid to make the pH of the depolymerization reaction product be 2 to 8, The salt of the aromatic diol compound contained in the depolymerization reaction product is converted into an aromatic diol compound.

3. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The polycarbonate-based resin is depolymerized by reacting with a base in an amount of 0.5 mol or less relative to 1 mol of the polycarbonate-based resin.

4. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: In the step of depolymerizing the polycarbonate-based resin, an antioxidant is added to the reaction solution.

5. A monomer composition for synthesizing recycled plastics prepared by the method according to claim 1, The monomer composition comprises an aromatic diol compound, in, The color coordinate b* is 0.1 to 1, wherein the yield of the aromatic diol compound according to the following formula 1 is greater than 75%, and Wherein, the monomer composition for synthesizing recycled plastics is recovered from polycarbonate resin: [Formula 1] Yield (%) = W1 / W0 In Formula 1, W0 is the mass of the aromatic diol compound obtained in a 100% decomposition process, and W1 is the mass of the aromatic diol compound actually obtained.

6. The monomer composition for synthesizing recycled plastics according to claim 5, wherein: The color coordinate L* of the monomer composition for synthesizing recycled plastics is greater than 98.

7. The monomer composition for synthesizing recycled plastics according to claim 5, wherein: The color coordinate a* of the monomer composition for synthesizing recycled plastics is less than 0.

8. The monomer composition for synthesizing recycled plastics according to claim 5, wherein: The monomer composition for synthesizing recycled plastics also has an aromatic diol compound purity of more than 98%.

9. The monomer composition for synthesizing recycled plastics according to claim 5, wherein: The weight ratio of the sodium salt impurity in the monomer composition for synthesizing recycled plastics measured by ion chromatography is less than 10 μg relative to 1 g of the monomer composition for synthesizing recycled plastics.

10. The monomer composition for synthesizing recycled plastics according to claim 5, wherein: The monomer composition for synthesizing recycled plastics contains diethyl carbonate as a by-product, and the diethyl carbonate is recovered from the polycarbonate-based resin.

11. A recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic according to claim 5 and a comonomer.

12. A molded product comprising the recycled plastic according to claim 11.

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