Method for producing a monomer composition for synthesizing recycled plastics, and monomer composition for synthesizing recycled plastics, recycled plastics, and molded articles using the same

Abstract

The present invention relates to a method for producing a monomer composition for synthesizing recycled plastics, the method including the steps of depolymerizing a polycarbonate resin; adjusting the pH of the depolymerized reaction product, which has a pH of 13 or higher, to 8 to 12; adjusting the pH of the depolymerized reaction product, whose pH has been adjusted to 8 to 12, to less than 4; and collecting aromatic diol compound crystals formed by adding a crystallization solvent to the depolymerized reaction product, whose pH has been adjusted to less than 4.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0098843, filed on July 28, 2023, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for producing a monomer composition for synthesizing recycled plastics, which allows aromatic diol compounds recovered by chemical decomposition of polycarbonate resins to be recycled and have good yields and optical properties, and which improves the efficiency of the recycling process; and to a monomer composition for synthesizing recycled plastics, recycled plastics, and molded articles using the same. [Background technology]

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

[0004] Polycarbonate is widely used for a variety of purposes, but concerns about the environmental and health impacts of its disposal have been raised.

[0005] Currently, physical recycling methods are being used, but this has led to problems with quality degradation, and research is underway into chemical recycling of polycarbonate.

[0006] Chemical decomposition of polycarbonate refers to the process of decomposing polycarbonate to obtain a monomer, an aromatic diol compound (e.g., bisphenol A (BPA)), which is then used again in polymerization to obtain high-purity polycarbonate.

[0007] Typical examples of such chemical decomposition include pyrolysis, hydrolysis, and alcoholysis. Among these, alcoholysis using a base catalyst is the most common method. However, methanolysis has the drawback of using methanol, which is harmful to the human body, and ethanol requires high temperature and pressure conditions, resulting in a low yield.

[0008] In addition, an alcohol decomposition method using an organic catalyst is known, but currently, this method has economic disadvantages. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a method for producing a monomer composition for synthesizing recycled plastics, in which an aromatic diol compound recovered by chemical decomposition of a polycarbonate resin has good yield and optical properties, and the efficiency of the recycling process is improved.

[0010] The present invention also provides a monomer composition for synthesizing recycled plastics, recycled plastics, and molded articles produced using the method for producing the monomer composition for synthesizing recycled plastics. [Means for solving the problem]

[0011] In order to solve the above problems, the present specification provides a method for producing a monomer composition for synthesizing recycled plastics, including the steps of depolymerizing a polycarbonate resin; adjusting the pH of the depolymerized reaction product, which has a pH of 13 or higher, to 8 to 12; adjusting the pH of the depolymerized reaction product, whose pH has been adjusted to 8 to 12, to less than 4; and adding a crystallization solvent to the depolymerized reaction product, whose pH has been adjusted to less than 4, to form aromatic diol compound crystals, and recovering the resulting crystals.

[0012] The present specification also provides a monomer composition for synthesizing recycled plastics, which comprises an aromatic diol compound obtained by the method for producing a monomer composition for synthesizing recycled plastics.

[0013] Also provided herein is a recycled plastic comprising the reaction product of the monomer composition for synthesizing recycled plastic and a comonomer.

[0014] Also provided herein is a molded article comprising the recycled plastic.

[0015] Hereinafter, a method for producing a monomer composition for synthesizing recycled plastics according to a specific embodiment of the present invention, and a monomer composition for synthesizing recycled plastics, recycled plastics, and molded articles using the same will be described in more detail.

[0016] In this specification, unless expressly stated otherwise, terminology is for the purpose of referring to particular embodiments only and is not intended to limit the invention.

[0017] As used herein, the singular forms "a," "an," and "the" include the plural forms as well, unless the context clearly dictates to the contrary.

[0018] As used herein, "pH" refers to hydrogen ion concentration (pH), a numerical value that indicates the degree of acidity or alkalinity of a substance. It can be calculated by taking the reciprocal logarithm of the dissociated hydrogen ion concentration and is used as a measure of the acidity or base strength of a substance.

[0019] As used herein, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other certain properties, regions, integers, steps, operations, elements, components, and / or groups.

[0020] In this specification, terms including ordinal numbers such as "first" and "second" are used to distinguish one component from another, and are not limited by the ordinal numbers. For example, within the scope of the present invention, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component.

[0021] 1. Method for producing monomer composition for synthesizing recycled plastics According to one embodiment of the present invention, there is provided a method for producing a monomer composition for synthesizing recycled plastics, the method including: depolymerizing a polycarbonate-based resin; adjusting the pH of the depolymerized reaction product, which has a pH of 13 or higher, to 8 to 12; adjusting the pH of the depolymerized reaction product, whose pH has been adjusted to 8 to 12, to less than 4; and adding a crystallization solvent to the depolymerized reaction product, whose pH has been adjusted to less than 4, to recover aromatic diol compound crystals.

[0022] The present inventors have confirmed through experiments that in the process of recycling a polycarbonate-based resin by chemical decomposition, as in the method for producing a monomer composition for synthesizing recycled plastics according to one embodiment, the pH of the depolymerized polycarbonate-based resin can be adjusted stepwise over two stages, and the organic solvent can be separated and removed to a sufficient level in the neutralization step, and high-purity aromatic diol compound crystals can be recovered in high yield by immediate recrystallization without removing the organic solvent through a separate distillation process, thereby completing the invention.

[0023] In particular, in the conventional method, the pH is quickly lowered to a neutral or acidic level using a strong acid aqueous solution in the neutralization step, which leaves organic solvents such as ethanol and diethyl carbonate behind without sufficient separation and removal, necessitating a distillation step to remove such organic solvents. Also, due to the solubility between diethyl carbonate and ethanol, there is a limitation in that it is difficult to perform recrystallization of bisphenol A, an aromatic diol compound.

[0024] In contrast, in the present invention, a multi-stage neutralization process is carried out in which the pH is first lowered to 8-12 once and then sequentially lowered to less than 4. By adding an acidic aqueous solution during the pH lowering process to 8-12 and then removing the separated aqueous layer, water-soluble impurities such as salts can be easily removed, improving the color characteristics of the monomer composition for synthesizing recycled plastics. Furthermore, the solubility of ethanol in water is increased, allowing for the effective removal of ethanol remaining in the organic layer without a distillation step. Furthermore, the process of separating the aqueous and organic solvent layers in multiple stages also allows for sufficient recrystallization and precipitation of bisphenol A, an aromatic diol compound, even with a small amount of recrystallization solvent.

[0025] Specifically, the method for preparing a monomer composition for synthesizing recycled plastics according to one embodiment may include a step of depolymerizing a polycarbonate-based resin.

[0026] The term "polycarbonate-based resin" refers to any homopolymer or copolymer containing a polycarbonate repeating unit, collectively referring to a reaction product obtained by the polymerization or copolymerization of a monomer containing an aromatic diol compound and a carbonate precursor. A homopolymer can be synthesized by using only one aromatic diol compound and one carbonate precursor to obtain a single carbonate repeating unit. Alternatively, a copolymer can be synthesized by using one aromatic diol compound and two or more carbonate precursors, two or more aromatic diol compounds and one carbonate precursor, or one aromatic diol compound and one carbonate precursor plus one or more other diols to obtain two or more carbonates. The homopolymer or copolymer can include low molecular weight compounds, oligomers, and polymers within a range of molecular weights.

[0027] The polycarbonate-based resin may be applied regardless of various forms and types, such as a new polycarbonate-based resin produced by synthesis, a recycled polycarbonate-based resin produced by a recycling process, or a polycarbonate-based resin waste.

[0028] However, if necessary, a pretreatment process for the polycarbonate resin may be performed before the depolymerization reaction of the polycarbonate resin to increase the efficiency of the process for recovering the aromatic diol compound and the carbonate precursor from the polycarbonate resin. Examples of the pretreatment process include washing, drying, pulverization, and glycol decomposition. The specific method for each pretreatment process is not limited, and various methods widely used in the process for recovering the aromatic diol compound and the carbonate precursor by depolymerization of the polycarbonate resin may be applied without limitation.

[0029] The depolymerization reaction of the polycarbonate-based resin may be carried out under acidic, neutral, or basic conditions, and particularly under basic (alkaline) conditions. The type of base is not particularly limited, and examples include sodium hydroxide (NaOH) and potassium hydroxide (KOH). The base is a basic catalyst that acts as a catalyst and has the advantage of being more economical than organic catalysts that are mainly used under mild conditions. More specifically, the depolymerization reaction of the polycarbonate-based resin may be carried out at a pH of 13 or higher, or in the range of 13 to 14.

[0030] The depolymerization of the polycarbonate resin can be carried out by reacting the base in an amount of 0.5 moles or less, or 0.4 moles or less, or 0.3 moles or less, or 0.1 moles or more, or 0.2 moles or more, or 0.1 to 0.5 moles, or 0.1 to 0.4 moles, or 0.1 to 0.3 moles, or 0.2 to 0.5 moles, or 0.2 to 0.4 moles, or 0.2 to 0.3 moles, per mole of the polycarbonate resin. If the base is reacted in an amount exceeding 0.5 moles per mole of the polycarbonate resin, the increased amount of alkali salt generated increases impurities, reducing the purity of the target recovered material and reducing the economic viability of the catalytic reaction.

[0031] The depolymerization reaction of the polycarbonate resin may be carried out in a solvent containing ethanol. The present invention has the advantage that by decomposing the polycarbonate resin in a solvent containing ethanol, the highly pure monomer bisphenol A can be stably obtained, and further, high-value-added diethyl carbonate can be additionally obtained as a reaction by-product.

[0032] The ethanol content may be 1 to 5 mol, 1 to 4 mol, or 1 to 3.75 mol per 1 mol of polycarbonate-based resin. Because ethanol has good solubility in bisphenol A, the ethanol content must be within the above range. If the ethanol content is too low (less than 1 mol per 1 mol of polycarbonate-based resin), the alcoholysis of the polycarbonate-based resin may be insufficient. On the other hand, if the ethanol content is too high per 1 mol of polycarbonate-based resin, the ethanol may be difficult to remove sufficiently in the neutralization step described below, and the additional distillation step may reduce the economic efficiency of the process.

[0033] The solvent in which the depolymerization reaction of the polycarbonate-based resin is carried out may further include, in addition to ethanol, one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0034] The organic solvent may include tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0035] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent to be mixed with ethanol, there is an advantage that the dissolving property for polycarbonate is improved, thereby improving reactivity.

[0036] The content of the organic solvent may be 10 to 20 moles or 10 to 15 moles per mole of the polycarbonate resin. The content of the organic solvent may be 2.2 to 5 moles per mole of ethanol. By mixing the polycarbonate resin, ethanol, and organic solvent within the above ranges, a desired level of depolymerization reaction of the polymer can be achieved.

[0037] Meanwhile, the temperature at which the depolymerization reaction of the polycarbonate resin proceeds is not particularly limited, but may be, for example, 20° C. to 100° C. or 70° C. to 90° C. The time for which the depolymerization reaction of the polycarbonate resin proceeds may be 1 hour to 30 hours.

[0038] Specifically, the above conditions are milder process conditions than the existing pressurized / high temperature process, and by performing stirring under these conditions, the process can be carried out in a milder manner than the pressurized / high temperature process.

[0039] In other words, the present invention has the advantage that a high-purity aromatic diol compound (e.g., bisphenol A) can be obtained under mild conditions without using an organic catalyst, by adjusting the type and amount of the mixed solvent and the type and content of the base catalyst, and without using a pressurized / high-temperature process, and that diethyl carbonate can be obtained as a by-product because an ethanol solvent is used.

[0040] Meanwhile, an antioxidant can be added to the reaction solution during the depolymerization of the polycarbonate-based resin. By adding the antioxidant, the aromatic diol compound recovered by recycling the polycarbonate-based resin through chemical decomposition can satisfy a low color coordinate b* value at a color level equivalent to that of commercially available reagents or reagents used for PC polymerization.

[0041] Specific examples of the antioxidant are not particularly limited, and various antioxidants that have been widely used in conventional technical fields can be used without limitation, including, for example, sodium hyposulfite, sodium sulfite, erythorbic acid, dibutylhydroxytoluene, butylhydroxyanisole, α-tocopherol, tocopherol acetate, L-ascorbic acid and its salts, L-ascorbic acid palmitate, L-ascorbic acid stearate, triamyl gallate, propyl gallate, disodium ethylenediaminetetraacetate (EDTA), sodium pyrophosphate, sodium metaphosphate, or a mixture of two or more thereof.

[0042] The specific amount of the antioxidant to be added is not particularly limited, but for example, it may be added in a range of 0.1 wt % to 5 wt % or 0.1 wt % to 1 wt % based on the weight of the total reaction solution, at a level that does not affect the physical properties of the monomer composition for synthesizing recycled plastics.

[0043] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to one embodiment may include adjusting the pH of the depolymerization reaction product, which has a pH of 13 or more, or 13-14, to 8-12, or 8-11, or 8-10, or 8-9.

[0044] Specifically, the step of adjusting the pH of the depolymerization reaction product to 8 to 12 may include adding an acidic aqueous solution to adjust the pH of the depolymerization reaction product to 8 to 12. By adjusting the pH of the depolymerization reaction product to 8 to 12, water-soluble salt impurities can be effectively removed, thereby improving color properties. In addition, the solubility of unreacted ethanol remaining in the depolymerization reaction product in water can be increased, thereby minimizing the amount of residual ethanol.

[0045] Specifically, a layer separated into an organic solvent layer and an aqueous layer may be formed in the step of adding an acidic aqueous solution so that the pH of the depolymerization reaction product is 8 to 12. More specifically, the layer separated into an aqueous layer containing impurities and an organic solvent layer containing an aromatic diol compound may be formed.

[0046] The aromatic diol compound is hydrophobic and may be contained in the organic solvent layer, and various water-soluble impurities may be contained in the aqueous layer. The impurities are hydrophilic substances, such as salt compounds, ionic compounds, or acid compounds. The aqueous layer containing the impurities may further contain unreacted ethanol.

[0047] The acidic aqueous solution is a mixture of acid and water, and the acid may be a strong acid, such as hydrochloric acid (HCl). The depolymerization reaction is carried out under strong basic conditions of pH 13 or higher, so that the resulting aromatic diol compound exists in the form of a salt through a reaction with the base and is hydrophilic. However, by adding an acidic aqueous solution, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted to the aromatic diol compound, thereby making it hydrophobic.

[0048] Meanwhile, the method may further include a step of removing the aqueous layer from the organic solvent layer and the aqueous layer after adjusting the pH of the depolymerization reaction product from 13 or more to 8 to 12. Since various water-soluble impurities are separated into the aqueous layer from the aqueous layer separated into the organic solvent layer and the aqueous layer by the addition of the acidic aqueous solution, the impurities can be easily removed from the aromatic diol compound, which is the main product, by the simple process of removing the aqueous layer.

[0049] The specific conditions for removing the aqueous layer from the organic layer are not particularly limited, and various known purification techniques may be applied without limitation to the specific removal device and method, for example, a drain device may be used.

[0050] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to one embodiment may include adjusting the pH of the depolymerization reaction product, the pH of which has been adjusted to 8 to 12, to less than 4, or 1 to 3, or 1 to 2.

[0051] Specifically, the step of adjusting the pH of the depolymerization reaction product, the pH of which has been adjusted to 8 to 12, to less than 4 may include adding an acidic aqueous solution to the depolymerization reaction product so that the pH of the depolymerization reaction product becomes less than 4. By adding an acidic aqueous solution to the depolymerization reaction product so that the pH of the depolymerization reaction product becomes less than 4, the salt of the aromatic diol compound remaining in the depolymerization reaction product, the pH of which has been adjusted to 8 to 12, is converted into the aromatic diol compound, thereby increasing the yield of the aromatic diol compound.

[0052] Specifically, a layer separated into an organic solvent layer and an aqueous layer may be formed in the step of adding an acidic aqueous solution so that the pH of the depolymerization reaction product is less than 4. More specifically, the layer separated into an aqueous layer containing impurities and an organic solvent layer containing an aromatic diol compound may be formed.

[0053] The aromatic diol compound may be contained in the organic solvent layer because of its hydrophobicity, and various water-soluble impurities may be contained in the aqueous layer. The impurities may be hydrophilic substances, such as salt compounds, ionic compounds, and acid compounds.

[0054] The acidic aqueous solution is a solution in which an acid and water are mixed, and the acid may be a strong acid, for example, hydrochloric acid (HCl). By adding the acidic aqueous solution to the depolymerization reaction product whose pH has been adjusted to 8 to 12, the salt of the aromatic diol compound remaining in the depolymerization reaction product can be converted to the aromatic diol compound, thereby deriving hydrophobicity.

[0055] Meanwhile, the method may further include a step of removing the aqueous layer from the organic solvent layer and the aqueous layer after adjusting the pH of the depolymerization reaction product, the pH of which has been adjusted to 8 to 12, to less than 4. Since various water-soluble impurities are separated into the aqueous layer from the organic solvent layer by the addition of the acidic aqueous solution, the impurities can be easily removed from the aromatic diol compound, which is the main product, by the simple process of removing the aqueous layer.

[0056] The specific conditions for removing the aqueous layer from the organic layer are not particularly limited, and various known purification techniques can be applied without limitation to the specific removal device and method, for example, a drain device can be used.

[0057] On the other hand, the pH difference value according to the following mathematical formula 1 may be 4 to 9, or 5 to 8, or 6 to 7.

[0058] [Formula 1] pH difference value=(pH of the depolymerization reaction product adjusted to a pH of 8 to 12)−(pH of the depolymerization reaction product adjusted to a pH of less than 4).

[0059] When the pH difference value according to the above mathematical formula 1 satisfies 4 or more, or 4 to 10, or 5 to 8, or 6 to 7, the effect of removing salt impurities and residual ethanol by adjusting the pH to 8 to 12 and the effect of improving the yield of the aromatic diol compound by adjusting the pH to less than 4 can be further maximized.

[0060] Furthermore, the pH difference value according to the following mathematical formula 2 may be 4 to 11, or 4 to 10, or 4 to 9, or 4 to 8, or 4 to 7, or 5 to 6.

[0061] [Formula 2] pH difference value=(pH of the depolymerization reaction product)−(pH of the depolymerization reaction product having the pH adjusted to 8 to 12).

[0062] When the pH difference value according to the above formula 2 satisfies 1 to 6, or 2 to 6, or 3 to 6, or 4 to 6, or 5 to 6, the effect of removing salt impurities and residual ethanol by adjusting the pH to 8 to 12 can be further maximized.

[0063] Specifically, the residual ethanol ratio contained in the depolymerization reaction product, the pH of which is adjusted to less than 4 according to the following Equation 3, may be less than 1%, or 0.1% to 0.9%, or 0.1% to 0.8%, or 0.1% to 0.7%, or 0.1% to 0.6%, or 0.1% to 0.5%.

[0064] [Formula 3] Residual ethanol ratio (%) = {( 1 H NMR ethanol peak area) / ( 1 H NMR ethanol peak area +1 H NMR peak area of ​​aromatic diol compound) × 100.

[0065] Specifically, in the above formula 3, 1 The ethanol peak in H NMR is at 3.63 ppm (quartet, 2H), 1 The peak of the aromatic diol compound (bisphenol A (BPA)) in H NMR is the peak at 6.67 ppm (4H).

[0066] As a result of the reduction in the amount of residual ethanol, the ethanol is sufficiently removed, and the aromatic diol compound can be precipitated with high purity and high yield without a separate distillation process, thereby improving the economic efficiency of the process.

[0067] On the other hand, when the residual amount of ethanol contained in the depolymerization reaction product adjusted to a pH of less than 4 according to Equation 3 increases to 1% or more, a distillation process for removing ethanol is required to precipitate the aromatic diol compound. Even if a large amount of crystallization solvent is added, the yield of the aromatic diol compound obtained by precipitation decreases, resulting in poor process efficiency.

[0068] Meanwhile, the method for producing a monomer composition for synthesizing recycled plastics according to one embodiment may include recovering the aromatic diol compound crystals formed by adding a crystallization solvent to the depolymerization reaction product, the pH of which has been adjusted to less than 4. By precipitating the aromatic diol compound using the crystallization solvent in this manner, the aromatic diol compound, which is the main synthesis target material in the present invention, can be obtained in high purity and high yield.

[0069] The step of recovering the aromatic diol compound crystals formed by adding a crystallization solvent to the depolymerization reaction product, the pH of which has been adjusted to less than 4, may include the step of adding 100 mol or less, or 50 mol to 100 mol, or 50 mol to 90 mol, or 50 mol to 80 mol, or 50 mol to 70 mol of water relative to 1 mol of the polycarbonate resin to the depolymerization reaction product, the pH of which has been adjusted to less than 4, to precipitate the aromatic diol compound crystals.

[0070] If the amount of water added during the precipitation of the aromatic diol compound is too small, the aromatic diol compound may not be sufficiently extracted, resulting in a reduced yield. On the other hand, if the amount of water added during the precipitation of the aromatic diol compound is too large, excessive water is required, which may reduce the efficiency of the extraction process.

[0071] Meanwhile, the method for preparing a monomer composition for synthesizing recycled plastics according to one embodiment may further include purifying the aromatic diol compound after collecting the aromatic diol compound crystals formed by adding a crystallization solvent to the depolymerization reaction product having a pH adjusted to less than 4.

[0072] Specifically, the purification step of the aromatic diol compound may include a washing step of the aromatic diol compound, and may also include a dissolution step and an adsorption purification step of the aromatic diol compound.

[0073] The order of the washing step and the adsorption purification step is not particularly limited and may be any order. For example, the washing step may be followed by the adsorption purification step. The washing step and the adsorption purification step may each be repeated at least once. Specific washing and adsorption apparatuses and methods may be applied without limitation to a variety of known purification techniques.

[0074] In the washing step of the aromatic diol compound, various impurities remain during the recovery process of obtaining the aromatic diol compound, and washing can be carried out to sufficiently remove these impurities to obtain a high-purity aromatic diol compound.

[0075] Specifically, the cleaning step may include cleaning with a solvent at a temperature of 10° C. to 30° C. or 20° C. to 30° C. The temperature condition refers to the temperature inside a cleaning vessel where cleaning with a solvent is performed, and various heating devices can be used without limitation to maintain a high temperature above room temperature.

[0076] The solvent used in the washing step may include one of water, alcohol, and organic solvents, such as tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0077] The solvent used in the washing step may be used in a weight ratio of 1 to 30 parts by weight, or 1 to 10 parts by weight, based on 1 part by weight of the polycarbonate-based resin used in the depolymerization reaction.

[0078] More specifically, the solvent used in the step of washing with a solvent at a temperature of 10° C. to 30° C. may be an organic solvent. Preferably, methylene chloride can be used as the organic solvent.

[0079] Meanwhile, the dissolving step and the adsorption purification step of the aromatic diol compound may include a dissolving step of the aromatic diol compound and a adsorption purification step of the aromatic diol compound.

[0080] The step of dissolving the aromatic diol compound may include adding a solvent to the aromatic diol compound. An example of the solvent is ethanol, and the ethanol may be added in a ratio of 1 to 20 moles, 1 to 10 moles, or 5 to 10 moles per mole of the polycarbonate resin. By adding the solvent to the aromatic diol compound, the aromatic diol compound crystals can be redissolved in the solvent.

[0081] The step of adsorbing and purifying the aromatic diol compound may include a step of adding an adsorbent to the aromatic diol compound, adsorbing and purifying the aromatic diol compound, and then removing the adsorbent. In the step of adding an adsorbent to the aromatic diol compound, adsorbing and purifying the aromatic diol compound, and then removing the adsorbent, the aromatic diol compound may be contacted with the adsorbent.

[0082] Examples of the adsorbent include activated carbon, charcoal, or a mixture thereof. Activated carbon is a black carbon material with micropores produced by subjecting raw materials to a carbonization process at about 500°C and an activated carbon process at about 900°C. Examples of the activated carbon include, but are not limited to, various activated carbons, such as plant-based, coal-based, petroleum-based, and waste-based activated carbons, depending on the type of raw material.

[0083] More specific examples of plant-based activated carbon include coconut activated carbon, wood activated carbon, and sawdust activated carbon. Furthermore, coal-based activated carbon includes lignite activated carbon, bituminous activated carbon, and anthracite activated carbon. Furthermore, petroleum-based activated carbon includes petroleum coke activated carbon and oil carbon activated carbon. Furthermore, waste-based activated carbon includes synthetic resin activated carbon and pulp activated carbon.

[0084] The adsorbent may include one or more activated carbons selected from the group consisting of plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon, i.e., the adsorbent may include plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, waste-based activated carbon, or a mixture of two or more thereof.

[0085] More specifically, the adsorbent may include one or more activated carbons selected from the group consisting of palm activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous activated carbon, i.e., palm activated carbon, lignite activated carbon, anthracite activated carbon, bituminous activated carbon, or a mixture of two or more thereof.

[0086] The adsorption purification conditions using the adsorbent are not particularly limited, and various conventionally known adsorption purification conditions can be used without limitation. However, for example, the amount of adsorbent added may be 10% by weight to 50% by weight relative to the polycarbonate resin, the adsorption time may be 1 hour to 5 hours, and the adsorption method may be stirring adsorption or a laboratory adsorption tower.

[0087] Meanwhile, after the dissolving step and the adsorption purification step of the aromatic diol compound, a recrystallization step of the aromatic diol compound may be further included, in which various impurities contained in the aromatic diol compound are sufficiently removed to obtain a high-purity aromatic diol compound.

[0088] Specifically, the recrystallization step can include adding water to the solution containing the aromatic diol compound to recrystallize it. By adding water to the solution containing the aromatic diol compound to recrystallize it, the solubility of the aromatic diol compound or its salt contained in the solution containing the aromatic diol compound can be increased, allowing impurities present in the crystals or between the crystals to be dissolved in the solvent to the maximum extent. Since the dissolved aromatic diol compound has poorer solubility than the impurities, it can easily precipitate into aromatic diol compound crystals when the temperature is subsequently lowered due to the difference in solubility.

[0089] More specifically, in the step of adding water to the solution containing the dissolved aromatic diol compound to recrystallize it, 20 to 40 moles or 25 to 35 moles of water can be used per mole of polycarbonate resin. If too little water is used, the temperature required to dissolve the aromatic diol compound in the solution containing the dissolved aromatic diol compound becomes too high, resulting in poor process efficiency and making it difficult to remove impurities through recrystallization. On the other hand, if too much water is used, the solubility of the aromatic diol compound in the solution containing the dissolved aromatic diol compound becomes too high, resulting in a reduced yield of the aromatic diol compound recovered after recrystallization, and the use of a large amount of solvent can reduce process efficiency.

[0090] If necessary, after the recrystallization of the aromatic diol compound, a process for removing remaining impurities by filtration or adsorption may be additionally carried out.

[0091] Furthermore, if necessary, a drying step may be further included after the recrystallization step. The residual solvent can be removed by the drying, and the specific drying conditions are not particularly limited, but the drying can be performed at a temperature of, for example, 10°C to 100°C, or 10°C to 50°C. Regarding the specific drying apparatus and method used in the drying, various known drying techniques can be applied without any restrictions.

[0092] 2. Monomer composition for synthesizing recycled plastics According to another embodiment of the present invention, there is provided a monomer composition for synthesizing recycled plastics, comprising an aromatic diol compound obtained by the method for producing a monomer composition for synthesizing recycled plastics according to the above embodiment.

[0093] The monomer composition for synthesizing recycled plastics according to the other embodiment may be obtained by the method for producing a monomer composition for synthesizing recycled plastics according to the first embodiment. The method for producing a monomer composition for synthesizing recycled plastics according to the other embodiment includes all of the above-described aspects of the first embodiment.

[0094] That is, the monomer composition for synthesizing recycled plastics according to the other embodiment corresponds to a resultant product obtained through various filtration, purification, washing, and drying processes in order to obtain only the aromatic diol compound, which is the main target substance for recovery, in high purity after the depolymerization reaction of the polycarbonate-based resin.

[0095] 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, and 1,1-bis(4-hydroxyphenyl)cyclohexane (bis(4-hydroxyphenyl)). Examples of the aromatic diol compound include bisphenol Z, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane, 2,2-bis(4-hydroxy-3-bromophenyl)propane, 2,2-bis(4-hydroxy-3-chlorophenyl)propane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, and mixtures of two or more thereof. Preferably, the aromatic diol compound in the monomer composition for recycled plastic synthesis of the embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0096] The aromatic diol compound is obtained by the method for producing a monomer composition for synthesizing recycled plastics according to the first embodiment. That is, the aromatic diol compound is recovered from the polycarbonate resin used to recover the monomer composition for synthesizing recycled plastics. Therefore, when a new aromatic diol compound is added externally, separately from the one recovered from the polycarbonate resin, to produce the monomer composition for synthesizing recycled plastics according to the second embodiment, the aromatic diol compound does not fall within the scope of the aromatic diol compound of the present invention.

[0097] Specifically, the term "recovered from a polycarbonate-based resin" means that the polycarbonate-based resin is obtained by depolymerization of the polycarbonate-based resin. The depolymerization may be carried out under acidic, neutral, or basic conditions, and is particularly allowed to proceed under basic (alkaline) conditions. In particular, the depolymerization is preferably carried out in an ethanol solvent, as described below.

[0098] 3. Recycled plastic According to yet another embodiment of the present invention, there is provided a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic according to the other embodiment and a comonomer.

[0099] The content relating to the monomer composition for synthesizing recycled plastics of the other embodiment includes all of the content described above in the other embodiment.

[0100] Examples of the recycled plastics are not particularly limited, and various plastics synthesized using an aromatic diol compound such as bisphenol A and a carbonate precursor such as dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate as a monomer can be used without limitation. A more specific example is a polycarbonate resin.

[0101] The term "polycarbonate-based resin" refers to any homopolymer or copolymer containing a polycarbonate repeating unit, and is a general term for reaction products obtained by the polymerization or copolymerization of monomers containing an aromatic diol compound and a carbonate precursor. A homopolymer can be synthesized by using only one type of carbonate repeating unit obtained using only one aromatic diol compound and one carbonate precursor. Alternatively, a copolymer can be synthesized by using one aromatic diol compound and two or more carbonate precursors, two or more aromatic diol compounds and one carbonate precursor, or one aromatic diol compound and one carbonate precursor plus one or more other diols to produce two or more carbonates. The homopolymer or copolymer can include low molecular weight compounds, oligomers, and polymers within a range of molecular weights.

[0102] More specifically, in the recycled plastics containing the reaction product of the monomer composition for recycled plastic synthesis and a comonomer according to the embodiment, the comonomer may be a carbonate precursor, such as phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl)carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis(diphenyl)carbonate, or bishaloformates.

[0103] The reaction process of the monomer composition and comonomer for synthesizing recycled plastics to synthesize the polycarbonate-based resin is not particularly limited, and various conventionally known polycarbonate manufacturing methods can be applied without limitation.

[0104] However, as an example of the method for producing polycarbonate, a method for producing polycarbonate can be used that includes polymerizing a composition containing a monomer composition for synthesizing recycled plastics and a comonomer. In this case, the polymerization can be performed by interfacial polymerization, which can be performed at atmospheric pressure and low temperature, and allows for easy molecular weight control.

[0105] The polymerization temperature may be 0° C. to 40° C., and the reaction time may be 10 minutes to 5 hours. The pH during the reaction may be maintained at 9 or higher or 11 or higher.

[0106] The solvent that can be used in the polymerization is not particularly limited as long as it is a solvent that is used in the polymerization of polycarbonates in the art. For example, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0107] The polymerization can be carried out in the presence of an acid binder, and examples of the acid binder include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amine compounds such as pyridine.

[0108] Furthermore, the polymerization can be carried out in the presence of a molecular weight regulator to control the molecular weight of the polycarbonate. The molecular weight regulator can be an alkylphenol having 1 to 20 carbon atoms, and 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, during, or after the initiation of polymerization. The molecular weight regulator can be used in an amount of 0.01 to 10 parts by weight, or 0.1 to 6 parts by weight, per 100 parts by weight of the aromatic diol compound, and the desired molecular weight can be obtained within this range.

[0109] In addition, to accelerate the polymerization reaction, a reaction accelerator such as a tertiary amine compound, a quaternary ammonium compound, or a quaternary phosphonium compound, such as triethylamine, tetra-n-butylammonium bromide, or tetra-n-butylphosphonium bromide, may be additionally used.

[0110] 4. Molded products According to yet another embodiment of the present invention, there is provided a molded product including the recycled plastic of the other embodiment. The content relating to the recycled plastic includes all of the content described above in the other embodiment.

[0111] The molded product may be obtained by applying the recycled plastic to various known plastic molding methods without limitation, and examples of the molding methods include injection molding, foam injection molding, blow molding, and extrusion molding.

[0112] The molded products are not particularly limited and may be applied to various molded products using plastics without limitation, such as automobile parts, electrical and electronic products, communication products, daily necessities, building materials, optical parts, exterior materials, etc.

[0113] In addition to the recycled plastic of the other embodiment, the molded article may further contain, as necessary, one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact modifiers, fluorescent brighteners, ultraviolet absorbers, pigments, and dyes.

[0114] An example of a method for manufacturing the molded product may include thoroughly mixing the recycled plastic of the other embodiment and an additive using a mixer, extruding the mixture in an extruder to form pellets, drying the pellets, and then injecting the pellets into an injection molding machine. [Effects of the Invention]

[0115] According to the present invention, there are provided a method for producing a monomer composition for synthesizing recycled plastics, in which an aromatic diol compound recovered by recycling polycarbonate-based resins through chemical decomposition has good yield and optical properties, and the efficiency of the recycling process is improved, as well as a monomer composition for synthesizing recycled plastics, recycled plastics, and molded articles using the same. DETAILED DESCRIPTION OF THE INVENTION

[0116] The present invention will be described in more detail in the following examples, but the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0117] <Examples and Comparative Examples: Production of Recycled Bisphenol A Monomer Composition> Example 1 (1. Decomposition step) 14 mol of methylene chloride (MC), 6 mol of ethanol (EtOH), and 0.25 mol of sodium hydroxide (NaOH) were added to a 3 L high-pressure reactor and stirred. Then, 1.2 mol of waste polycarbonate (PC) was added and stirred at 80°C to allow the PC depolymerization reaction to proceed.

[0118] (2-1. First pH Adjustment Step) The depolymerization reaction product (pH 14) containing bisphenol A was cooled to below 30°C, and then a 10% HCl aqueous solution was added to the depolymerization reaction product to adjust the pH to 8, and the aqueous layer was removed.

[0119] (2-2. Second pH Adjustment Step) The depolymerization reaction product adjusted to pH 8 was adjusted to pH 2 by adding 10% aqueous hydrochloric acid (HCl) solution, and the aqueous layer was removed.

[0120] (3. Precipitation Step) Approximately 1500 g (approximately 83 mol) of water was added to the depolymerization reaction product obtained in the pH adjustment step, and the mixture was stirred to precipitate bisphenol A (BPA) crystals, which were then recovered by vacuum filtration.

[0121] (4. Purification step - filtration) After that, bisphenol A was washed with 300 g of methylene chloride (MC) at 20 to 30°C and filtered under vacuum.

[0122] (5-1. Additional Purification Step-Redissolution Step) Then, bisphenol A was redissolved in 500 g of ethanol.

[0123] (5-2. Additional Purification Step-Adsorption Step) Then, lignite activated carbon was added as an adsorbent in a ratio of 30% by weight to the waste polycarbonate, and the mixture was purified through an adsorption tower, and the lignite activated carbon was removed by filtration.

[0124] (5-3. Additional Purification Step-Recrystallization Step) Then, 750 g of water was added to recrystallize bisphenol A, and the resulting slurry was vacuum filtered at 20-30°C to recover bisphenol A (BPA) crystals.

[0125] (6. Drying step) After that, the mixture was vacuum dried in a convection oven at 40°C to prepare a recycled bisphenol A monomer composition from which recycled bisphenol A (BPA) was recovered.

[0126] Example 2 A recycled bisphenol A monomer composition was prepared in the same manner as in Example 1, except that the pH was adjusted to 9 instead of 8 in (2-1. First pH Adjustment Step) of Example 1.

[0127] (Comparative Example 1) (1. Decomposition step) 14 mol of methylene chloride (MC), 6 mol of ethanol (EtOH), and 0.25 mol of sodium hydroxide (NaOH) were added to a 3 L high-pressure reactor and stirred. Then, 1.2 mol of waste polycarbonate (PC) was added and stirred at 80°C to allow the PC depolymerization reaction to proceed.

[0128] (2. pH Adjustment Step) The depolymerization reaction product (pH 14) containing bisphenol A was cooled to below 30°C, and then a 10% aqueous solution of hydrochloric acid (HCl) was added to the depolymerization reaction product to adjust the pH to 2, and the aqueous layer was removed.

[0129] (3. Precipitation Step) Approximately 8,000 g of water (approximately 444 mol) was added to the depolymerization reaction product obtained in the pH adjustment step, and the mixture was stirred to precipitate bisphenol A (BPA) crystals, which were then recovered by vacuum filtration.

[0130] (4. Purification step - filtration) After that, bisphenol A was washed with 300 g of methylene chloride (MC) at 20 to 30°C and filtered under vacuum.

[0131] (5-1. Additional Purification Step-Redissolution Step) Then, bisphenol A was redissolved in 500 g of ethanol.

[0132] (5-2. Additional Purification Step-Adsorption Step) Then, lignite activated carbon was added as an adsorbent in a ratio of 30% by weight to the waste polycarbonate, and the mixture was purified through an adsorption tower, and the lignite activated carbon was removed by filtration.

[0133] (5-3. Additional Purification Step-Recrystallization Step) Then, 750 g of water was added to recrystallize bisphenol A, and the resulting slurry was vacuum filtered at 20-30°C to recover bisphenol A (BPA) crystals.

[0134] (6. Drying step) After that, the mixture was vacuum dried in a convection oven at 40°C to prepare a recycled bisphenol A monomer composition from which recycled bisphenol A (BPA) was recovered.

[0135] (Comparative Example 2) A recycled bisphenol A monomer composition was prepared in the same manner as in Comparative Example 1, except that the pH was adjusted to 8 instead of 2 in (2. pH adjustment step) of Comparative Example 1.

[0136] <Experimental Example> The physical properties were measured by the following methods, and the results are shown in Table 1.

[0137] 1. Purity The recycled bisphenol A monomer composition was dissolved in acetonitrile (ACN) solvent at 1 wt% under atmospheric pressure and 20-30°C, and the purity of bisphenol A (BPA) was analyzed using an ACQUITY UPLC® RBEH C18 1.7 μm (2.1 x 50 mm column) and a Waters HPLC system by ultra performance liquid chromatography (UPLC).

[0138] 2. Color coordinates (L*, a*, b*) The recycled bisphenol A monomer composition was analyzed using a HunterLab UltraScan PRO Spectrophotometer instrument in reflectance mode.

[0139] 3. Yield The weight of BPA produced when the polycarbonate used in the reaction was 100% decomposed was measured, and the weight of the resulting BPA was measured to calculate the BPA yield according to the following Equation A.

[0140] [Formula A] Yield (%) = (W1 / W0) x 100 (%) In the formula A, W0 is the mass of BPA obtained at 100% decomposition, and W1 is the mass of BPA 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 mass of BPA actually obtained is 80 g, the yield is 80 / 89 × 100 = 90%.

[0141] 4. Residual ethanol ratio The depolymerization reaction product obtained in the pH adjustment step of (3. Precipitation step) was diluted with methanol-d4 to a concentration of 10 mg / ml to prepare a sample. 1An NMR spectrum detected by a 1 H NMR device was obtained, and the area ratio of the ethanol peak to the peak of bisphenol A (BPA) was measured and used as the residual ethanol ratio.

[0142] Specifically, the peak for ethanol was 3.63 ppm (quartet, 2H) and the peak for bisphenol A (BPA) was 6.67 ppm (4H), and the residual ethanol content was calculated using the following formula B.

[0143] [Formula B] Residual ethanol ratio (%) = {( 1 H NMR ethanol peak area) / ( 1 H NMR ethanol peak area + 1 H NMR BPA peak area) × 100.

[0144] [Table 1]

[0145] As shown in Table 1, the recycled bisphenol A monomer compositions obtained in Examples 1 and 2 exhibited high purities of 99.4% to 99.5%. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 and 2 exhibited excellent optical properties, with color coordinates L* of 97.6 to 98.03, a* of -0.12 to 0.06, and b* of 0.59 to 0.75. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 and 2 exhibited high BPA yields of 98.6% to 98.8%. Furthermore, the recycled bisphenol A monomer compositions obtained in Examples 1 and 2 exhibited low residual ethanol contents of 0.5% to 0.7%.

[0146] In contrast, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 had a purity of 97.2% to 98.9%, which was lower than that of Examples. Furthermore, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 exhibited color coordinates L* of 95.67 to 97.4, a* of 0.06 to 0.16, and b* of 1.47 to 1.72, showing poor optical properties compared to Examples.

[0147] In particular, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 had a precipitated BPA yield of 18.2% to 21.1%, which was significantly lower than that of the Examples, despite the addition of a much larger amount of water than that of the Examples. Also, the recycled bisphenol A monomer compositions obtained in Comparative Examples 1 and 2 had a residual ethanol content of 1.6% to 2.2%, which was higher than that of the Examples.

Claims

1. A step of depolymerizing the polycarbonate-based resin; adjusting the pH of the depolymerization reaction product, which has a pH of 13 or more, to 8 to 12; adjusting the pH of the depolymerization reaction product adjusted to a pH of 8 to 12 to less than 4; and and recovering the formed aromatic diol compound crystals by adding a crystallization solvent to the depolymerization reaction product whose pH has been adjusted to less than 4.

2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the pH difference value according to the following formula 1 is 4 to 11: [Formula 1] pH difference value=(pH of the depolymerization reaction product having the pH adjusted to 8 to 12)−(pH of the depolymerization reaction product having the pH adjusted to less than 4).

3. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the pH difference value according to the following formula 2 is 1 to 6: [Formula 2] pH difference value=(pH of the depolymerization reaction product)−(pH of the depolymerization reaction product after adjusting the pH to 8 to 12).

4. The step of adjusting the pH of the depolymerization reaction product to 8 to 12 comprises:

2. The method of claim 1, further comprising adding an acidic aqueous solution to the depolymerized reaction product so that the pH of the depolymerized reaction product is 8 to 12.

5. After adjusting the pH of the depolymerization reaction product from 13 or more to 8 to 12, 2. The method of claim 1, further comprising removing the aqueous layer from the organic solvent layer and the aqueous layer.

6. The step of adjusting the pH of the depolymerization reaction product adjusted to a pH of 8 to 12 to less than 4 comprises:

2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising adding an acidic aqueous solution to the depolymerized reaction product whose pH has been adjusted to 8 to 12 so that the pH of the depolymerized reaction product is less than 4.

7. After adjusting the pH of the depolymerization reaction product adjusted to pH 8 to 12 to less than 4, 2. The method of claim 1, further comprising removing the aqueous layer from the organic solvent layer and the aqueous layer.

8. 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the depolymerization reaction product, the pH of which is adjusted to less than 4 according to the following Equation 3, has a residual ethanol ratio of less than 1%: [Formula 3] Residual ethanol ratio (%) = {( 1 H NMR ethanol peak area) / ( 1 H NMR ethanol peak area + 1 H NMR peak area of ​​aromatic diol compound) × 100.

9. The depolymerization reaction of the polycarbonate resin is 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the reaction proceeds in a solvent containing ethanol.

10. The method for producing a monomer composition for synthesizing recycled plastics according to claim 9, wherein the content of the ethanol is 1 mol to 5 mol of the polycarbonate resin.

11. 10. The method for producing a monomer composition for synthesizing recycled plastics according to claim 9, wherein the content of the ethanol is 1 mol to 4 mol of the polycarbonate resin.

12. The depolymerization reaction of the polycarbonate resin is 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, wherein the base is reacted in an amount of 0.5 mol or less relative to 1 mol of the polycarbonate resin.

13. The step of recovering the aromatic diol compound crystals formed by adding a crystallization solvent to the depolymerization reaction product adjusted to a pH of less than 4 includes:

2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising adding 100 moles or less of water relative to 1 mole of the polycarbonate resin to the depolymerization reaction product having a pH adjusted to less than 4, thereby precipitating aromatic diol compound crystals.

14. After the step of adding a crystallization solvent to the depolymerization reaction product adjusted to a pH of less than 4 to form aromatic diol compound crystals and recovering the crystals, 2. The method for producing a monomer composition for synthesizing recycled plastics according to claim 1, further comprising a step of purifying the aromatic diol compound.

15. The step of purifying the aromatic diol compound includes: The method for producing a monomer composition for synthesizing recycled plastics according to claim 14, further comprising a step of washing the aromatic diol compound.

16. The step of purifying the aromatic diol compound includes: The method for producing a monomer composition for synthesizing recycled plastics according to claim 14, comprising a dissolving step of the aromatic diol compound and an adsorption purification step.

17. After the dissolution step and the adsorption purification step of the aromatic diol compound, The method for producing a monomer composition for synthesizing recycled plastics according to claim 16, further comprising a step of recrystallizing the aromatic diol compound.

18. A monomer composition for use in synthesizing recycled plastics, comprising an aromatic diol compound obtained by the method for producing a monomer composition for use in synthesizing recycled plastics according to claim 1.

19. A recycled plastic comprising the reaction product of the recycled plastic synthesis monomer composition of claim 18 and a comonomer.

20. A molded article comprising the recycled plastic of claim 19.

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