Method for preparing monomer for synthesizing recycled plastic, monomer for synthesizing recycled plastic using same, recycled plastic, and molded article

Abstract

The present invention relates to a method for preparing a monomer for synthesizing recycled plastic, a monomer for synthesizing recycled plastic using same, recycled plastic, and a molded article, the method comprising the steps of: recovering an aromatic diol compound obtained by a depolymerization reaction of a polycarbonate-based resin; melting the aromatic diol compound; crystallizing the melted aromatic diol compound; and obtaining the crystallized aromatic diol compound.

Description

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

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0151994 filed on October 31, 2024, and all contents disclosed in the document of said Korean patent application are incorporated herein as part of this specification.

[0003] The present invention relates to a method for producing a monomer for synthesizing recycled plastics capable of obtaining high-purity, high-yield aromatic diol compounds through recycling by chemical decomposition of polycarbonate-based resins, and to a monomer for synthesizing recycled plastics using the same, recycled plastics, and molded articles.

[0004] Polycarbonate is a thermoplastic polymer and a plastic with excellent characteristics, such as excellent transparency, flexibility, and relatively low manufacturing costs.

[0005] Although polycarbonate is widely used for various purposes, concerns regarding the environment and health during waste disposal have been continuously raised.

[0006] Currently, physical recycling methods are being used, but as this leads to quality degradation, research on the chemical recycling of polycarbonate is underway.

[0007] Chemical decomposition of polycarbonate refers to obtaining an aromatic diol compound (e.g., bisphenol A (BPA)) which is a monomer through the decomposition of polycarbonate, and then utilizing it again in polymerization to obtain high-purity polycarbonate.

[0008] Representative chemical decomposition methods include thermal decomposition, hydrolysis, and alcohol decomposition. Among these, the most common method is alcohol decomposition using base catalysts; however, methanol decomposition has the problem of using methanol, which is harmful to the human body, while ethanol decomposition requires high temperature and pressure conditions and suffers from low yields.

[0009] In addition, although alcohol decomposition methods using organic catalysts are known, they currently have disadvantages in terms of economics.

[0010] The present invention aims to provide a method for producing a monomer for recycled plastic synthesis that can obtain a high-purity, high-yield aromatic diol compound through recycling by chemical decomposition of a polycarbonate-based resin.

[0011] In addition, the present invention is intended to provide a monomer for synthesizing recycled plastic, a recycled plastic, and a molded article using the above-described method for manufacturing a monomer for synthesizing recycled plastic.

[0012] To solve the above problem, the present specification provides a method for producing a monomer for synthesizing recycled plastic, comprising the steps of: recovering an aromatic diol compound obtained by a depolymerization reaction of a polycarbonate-based resin; melting the aromatic diol compound; crystallizing the melted aromatic diol compound; and obtaining the crystallized aromatic diol compound.

[0013] In addition to this specification, a monomer for synthesizing recycled plastic is provided, comprising an aromatic diol compound obtained in the method for producing the monomer for synthesizing recycled plastic.

[0014] In addition to this specification, a recycled plastic is provided comprising a reaction product of the monomer for synthesizing the recycled plastic and the comonomer.

[0015] In addition to the above, a molded article comprising the recycled plastic is provided.

[0016] A method for manufacturing a monomer for synthesizing recycled plastic according to a specific embodiment of the invention, and a monomer for synthesizing recycled plastic, a recycled plastic, and a molded article using the same, will be described in more detail below.

[0017]

[0018] Unless explicitly stated otherwise in this specification, technical terms are used merely to refer to specific embodiments and are not intended to limit the invention.

[0019] The singular forms used in this specification include plural forms unless the phrases clearly indicate otherwise.

[0020] As used in this specification, 'pH' refers to hydrogen ion concentration (pH), a numerical value indicating the degree of acidity and alkalinity of a substance. It can be calculated by taking the reciprocal of the logarithm of the hydrogen ion dissociation concentration and is used as a measure of the acidity and base strength of a substance.

[0021] As used in this specification, the meaning of 'includes' specifies certain characteristics, regions, integers, steps, actions, elements, and / or components, and does not exclude the existence or addition of other specific characteristics, regions, integers, steps, actions, elements, components, and / or groups.

[0022] Also, in this specification, terms including ordinal numbers such as 'first' and 'second' are used for the purpose of distinguishing one component from another and are not limited by said ordinal numbers. For example, within the scope of the present invention, the first component may also be named the second component, and similarly, the second component may be named the first component.

[0023]

[0024] 1. Method for manufacturing monomers for synthesizing recycled plastics

[0025] According to another embodiment of the invention, a method for producing a monomer for synthesizing recycled plastic may be provided, comprising the steps of: recovering an aromatic diol compound obtained by a depolymerization reaction of a polycarbonate-based resin; melting the aromatic diol compound; crystallizing the melted aromatic diol compound; and obtaining the crystallized aromatic diol compound.

[0026] The inventors completed the invention by confirming through experiments that, as in the method for manufacturing monomers for recycled plastic synthesis of the above-described embodiment, an aromatic diol compound obtained during the process of recycling a polycarbonate-based resin by chemical decomposition can be purified through a melt crystallization process, thereby enabling the securing of an aromatic diol compound with high purity in a high yield while minimizing the impurity content, even though it was recovered through the recycling of a polycarbonate-based resin by chemical decomposition.

[0027] In particular, there is a problem where the yield decreases as the aromatic diol compound decomposes or the molten aromatic diol compound solidifies during the melting process of the aromatic diol compound. To solve this, the purity and yield of the aromatic diol compound can be improved by optimizing the melting and crystallization conditions of the aromatic diol compound.

[0028] Accordingly, as the content of impurities other than the aromatic diol compounds targeted for recovery is drastically reduced, it was confirmed through experiments that excellent physical properties can be achieved when synthesizing polycarbonate-based resins using this, and the invention was completed.

[0029] Specifically, the method for manufacturing a monomer for synthesizing recycled plastic of the above embodiment may include a step of recovering an aromatic diol compound obtained from the depolymerization reaction of a polycarbonate-based resin.

[0030] More specifically, the step of recovering an aromatic diol compound obtained from the depolymerization reaction of the polycarbonate-based resin may include: a step of depolymerizing the polycarbonate-based resin; a step of adding an acid to the depolymerization reaction product to neutralize it; a step of removing the water layer from the water layer and organic solvent layer formed in the neutralization step; and a step of distilling the organic solvent layer to recover the aromatic diol compound.

[0031] First, in the step of depolymerizing the polycarbonate-based resin, the polycarbonate-based resin includes both homopolymers and copolymers containing polycarbonate repeating units, and collectively refers to reaction products obtained through the polymerization or copolymerization reaction of monomers including aromatic diol compounds and carbonate precursors. A homopolymer may be synthesized when containing one carbonate repeating unit obtained by using only one aromatic diol compound and one carbonate precursor. Additionally, a copolymer may be synthesized when containing two or more carbonates by using one aromatic diol compound and two or more carbonate precursors as monomers, using two or more aromatic diol compounds and one carbonate precursor, or using one or more other diols in addition to one aromatic diol compound and one carbonate precursor. The homopolymer or copolymer may include low molecular weight compounds, oligomers, and high molecular weights according to the molecular weight range.

[0032] The above polycarbonate resin can be applied regardless of various forms or types, such as new polycarbonate resin produced through synthesis, recycled polycarbonate resin produced through a recycling process, or polycarbonate resin waste.

[0033] When depolymerizing the above polycarbonate-based resin, the depolymerization reaction can be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction can proceed under basic (alkali) conditions. The type of base is not significantly limited, and examples include sodium hydroxide (NaOH) or potassium hydroxide (KOH). The base acts as a base catalyst and has the advantage of being economical compared to organic catalysts mainly used under mild conditions. More specifically, when depolymerizing the above polycarbonate-based resin, the depolymerization reaction can proceed within a pH range of greater than 8 and less than 12.

[0034] During the depolymerization reaction of the above polycarbonate-based resin, the reaction can be carried out by reacting a base in an amount of 0.5 moles or less, 0.4 moles or less, 0.3 moles or less, 0.1 moles or more, 0.2 moles or more, 0.1 to 0.5 moles, 0.1 to 0.4 moles, 0.1 to 0.3 moles, 0.2 to 0.5 moles, 0.2 to 0.4 moles, or 0.2 to 0.3 moles relative to 1 mole of the polycarbonate-based resin. However, if the base is reacted in an amount exceeding 0.5 moles relative to 1 mole of the polycarbonate-based resin during the depolymerization reaction of the above polycarbonate-based resin, there is a limitation in that impurities increase due to the increased amount of alkali salt generated, the purity of the target recovered material decreases, and the economic feasibility of the catalytic reaction decreases.

[0035] In addition, the depolymerization reaction of the above polycarbonate-based resin can be carried out under a solvent containing ethanol. The present invention has the advantage of being able to stably obtain high-purity monomer bisphenol A by decomposing a polycarbonate-based resin with a solvent containing ethanol, and additionally obtain high-value-added diethyl carbonate as a reaction byproduct.

[0036] The content of the above ethanol may be 5 to 15 moles or 8 to 13 moles relative to 1 mole of polycarbonate resin. Since the above ethanol has good solubility for bisphenol A, it is essential to include ethanol within the above range. If the content of the above ethanol is excessively reduced to less than 5 moles relative to 1 mole of polycarbonate resin, it is difficult for the alcohol decomposition of the polycarbonate resin to proceed sufficiently. On the other hand, if the content of the above ethanol is excessively increased to more than 15 moles relative to 1 mole of polycarbonate resin, the economic efficiency of the process may decrease due to excessive use of alcohol.

[0037] The solvent in which the depolymerization reaction of the above polycarbonate-based resin proceeds may further include one or more organic solvents selected from the group consisting of tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, and dipropyl carbonate, in addition to ethanol.

[0038] The above organic solvent may include tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more of these.

[0039] More preferably, methylene chloride can be used as the organic solvent. When methylene chloride is used as the organic solvent mixed with the ethanol, there is an advantage in that the solubility characteristics for polycarbonate are improved, thereby enhancing reactivity.

[0040] The content of the organic solvent may be 16 to 20 moles or 16 to 18 moles per 1 mole of polycarbonate-based resin. Additionally, the content of the organic solvent may be 1.5 to 2 moles per 1 mole of ethanol. Within the above range, mixing the polycarbonate-based resin, ethanol, and organic solvent has the advantage of allowing the depolymerization reaction of the polymer to proceed to the required level.

[0041] Meanwhile, the temperature at which the depolymerization reaction of the polycarbonate-based resin is carried out is not significantly limited, but, for example, it can be carried out at 20°C to 100°C or 50°C to 70°C. In addition, the time for which the depolymerization reaction of the polycarbonate-based resin is carried out can be 1 hour to 30 hours or 4 hours to 6 hours.

[0042] Specifically, the above conditions are mild process conditions compared to the existing pressurized / high-temperature process, and by performing stirring under these conditions, the process can be carried out in a mild process compared to the pressurized / high-temperature process, and in particular, there is an advantage of obtaining the most efficient results in terms of reproducibility and reliability when stirring for 4 to 6 hours at 50 ℃ to 70 ℃.

[0043] That is, the present invention has the advantage of being able to obtain high-purity aromatic diol compounds (e.g., bisphenol A) under mild conditions without using a pressurized / high-temperature process by controlling the type and amount of mixed solvent and the type and content of base catalyst without using an organic catalyst, and to obtain diethyl carbonate as a byproduct by using an ethanol solvent.

[0044] Meanwhile, during the depolymerization reaction of the above-mentioned polycarbonate-based resin, an antioxidant may be added to the reaction solution. By adding the antioxidant, the aromatic diol compound recovered through recycling by the chemical decomposition of the polycarbonate-based resin can satisfy a low color coordinate b* value at a color level equivalent to that of a reagent commercially sold or used for PC polymerization.

[0045] Specific examples of the above antioxidants are not significantly limited, and various antioxidants widely used in the field of the prior art can be applied without limitation. However, examples include sodium bisulfite, 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, or disodium ethylenediamine tetraacetate (EDTA), sodium pyrophosphate, sodium metaphosphate, or a mixture of two or more of these.

[0046] The specific amount of the above antioxidant added is not significantly limited, but for example, it can be added in a range of 0.1% to 5% by weight, or 0.1% to 2% by weight, or 0.5% to 2% by weight based on the total weight of the reaction solution, at a level that does not affect the physical properties of the monomer for synthesizing recycled plastic.

[0047] In addition, when the depolymerization reaction of the above polycarbonate-based resin is performed, the depolymerization reaction can be carried out under a nitrogen atmosphere.

[0048] Meanwhile, in the step of neutralizing the above depolymerization product by adding an acid, the acid may be a strong acid, for example, hydrochloric acid (HCl).

[0049] In the step of neutralizing the above depolymerization product by adding an acid, the salt of the aromatic diol compound contained in the depolymerization product can be converted into an aromatic diol compound. As the depolymerization reaction proceeds under basic conditions, the resulting aromatic diol compound exists in the form of a salt through reaction with the base and possesses hydrophilicity. Therefore, by adding an acid, the salt of the aromatic diol compound contained in the depolymerization product can be converted into an aromatic diol compound, thereby inducing it to possess hydrophobicity.

[0050] Accordingly, after proceeding with the step of neutralizing the depolymerization reaction product by adding acid, a layer can be formed that is separated into a water layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate precursor. Since the aromatic diol compound and the carbonate precursor are hydrophobic, they can be contained in the organic solvent layer among water and organic solvent, and various water-soluble impurities can be contained in the water layer. Accordingly, the main product, the aromatic diol compound, and the impurities can be easily separated with only a simple process of changing the pH.

[0051] Meanwhile, the step of neutralizing the depolymerization reaction product by adding acid may further include a step of adding water. Through this, in the impurity removal step described later, a layer can be formed that is separated into a water layer containing impurities and an organic solvent layer containing aromatic diol compounds and carbonate precursors.

[0052] The order of the acid addition process and the water addition process is not strictly limited; adding water after acid, adding acid after water, or adding water and acid simultaneously are all possible.

[0053] Meanwhile, in the step of removing the water layer from the water layer and organic solvent layer formed in the above neutralization step, the water layer containing impurities can be separated and removed from the layer divided into the water layer containing impurities and the organic solvent layer containing aromatic diol compounds and carbonate precursors. The impurities are hydrophilic substances and may include, for example, salt compounds, ionic compounds, acid compounds, etc.

[0054] The specific separation conditions for removing the water layer from the organic solvent layer are not significantly limited, and various existing known purification technologies can be applied without restriction regarding the specific separation equipment and methods. However, for example, a drain device may be used.

[0055] Meanwhile, in the step of recovering the aromatic diol compound by distilling the organic solvent layer, a carbonate precursor can be separated from the depolymerization reaction product. The separated carbonate precursor may include diethyl carbonate.

[0056] The separated carbonate precursor described above can be recycled without a separate separation and purification process, or, if necessary, recycled through separation and purification such as extraction, adsorption, or drying. Specific purification conditions are not significantly limited, and various previously known purification technologies can be applied without restriction regarding specific purification equipment and methods.

[0057] More specifically, the step of recovering the aromatic diol compound by distilling the organic solvent layer may include a multi-stage vacuum distillation step in which the organic solvent layer is vacuum distilled in three or more stages. In this way, in the step of recovering the aromatic diol compound by distilling the organic solvent layer, high purity can be secured by effectively removing impurities other than the aromatic diol compound through multi-stage vacuum distillation divided into three or more stages, such as the first, second, and third stages.

[0058] Although specific examples of the above multi-stage vacuum distillation step are not significantly limited, for example, a first vacuum distillation step in which the organic solvent layer is vacuum distilled at a pressure of 0.12 MPa to 0.45 MPa and a temperature of 48 ℃ to 160 ℃ from a pressure of 0.45 MPa or more and a temperature of 160 ℃ or more; and a second vacuum distillation step in which the residual solution of the first vacuum distillation step is pressurized to a pressure of 0.45 MPa or more and a temperature of 125 ℃ or more, and then vacuum distilled at a pressure of 0.009 MPa to 0.45 MPa and a temperature of 42 ℃ to 160 ℃. and may include a third vacuum distillation step in which the residual solution of the second vacuum distillation step is vacuum distilled at a pressure of 0.0005 MPa or more and a temperature of 155 ℃ or more, and then vacuum distilled at a pressure of 0.0003 MPa to 0.0005 MPa and a temperature of 42 ℃ to 87 ℃.

[0059] In the first vacuum distillation step, the organic solvent layer can be vacuum distilled at a pressure of 0.12 MPa to 0.45 MPa and a temperature of 48 ℃ to 160 ℃, rather than at a pressure of 0.45 MPa or higher and a temperature of 160 ℃ or higher. Through this, most of the organic solvent, ethanol, and water contained in the organic solvent layer can be separated and removed through vacuum distillation. Although the examples of the vacuum distillation conditions are not significantly limited, as a specific example, the organic solvent layer can be introduced into a distillation column at a pressure of 0.45 MPa and a temperature of 160 ℃, and then distilled under reduced pressure at a pressure of 0.12 MPa and a temperature of 48 to 160 ℃.

[0060] In the second distillation step, the residual solution from the first vacuum distillation step can be pressurized to a pressure of 0.45 MPa or higher and a temperature of 125 ℃ or higher, and then vacuum distilled at a pressure of 0.009 MPa and a temperature of 42 ℃ to 160 ℃. Through this, the organic solvent, mainly DEC, contained in the residual solution of the first distillation step can be separated and removed through vacuum distillation. Although the examples of the vacuum distillation conditions are not significantly limited, as a specific example, the residual solution from the first distillation step can be pressurized to a pressure of 0.45 MPa and a temperature of 125 ℃, and then distilled by reducing the pressure to a pressure of 0.009 to 0.45 MPa and a temperature of 42 to 160 ℃.

[0061] In the third distillation step, the residual solution from the second vacuum distillation step may be subjected to vacuum distillation at a pressure of 0.0005 MPa or higher and a temperature of 155 ℃ or higher, followed by vacuum distillation at a pressure of 0.0003 MPa to 0.0005 MPa and a temperature of 42 ℃ to 87 ℃. Through this, organic solvents and phenolic compounds contained in the residual solution of the second distillation step can be separated and removed through vacuum distillation. Although the examples of the vacuum distillation conditions are not significantly limited, as a specific example, the residual solution from the second distillation step may be subjected to vacuum distillation at a pressure of 0.0005 MPa and a temperature of 155 ℃, followed by vacuum distillation at a pressure of 0.0003 MPa and a temperature of 42 to 162 ℃.

[0062] Meanwhile, prior to the step of recovering the aromatic diol compound obtained from the depolymerization reaction of the polycarbonate-based resin, a pretreatment step of passing the polycarbonate-based resin through a filter with a pore diameter of 0.1 μm or less may be further included. Through the pretreatment step, various impurities can be filtered out and removed by the filter.

[0063] The above polycarbonate-based resin can be passed through a filter in a solution state dissolved in an organic solvent, and the organic solvent may include tetrahydrofuran, toluene, methylene chloride, chloroform, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more of these.

[0064] The above pretreatment step is operated under temperature conditions where the solvent does not volatilize, and fine impurities of 0.3 μm or less can be removed using a filter with a pore diameter of 0.3 μm or less. The type of filter can be applied without restriction, such as a filter aid type or a cartridge type.

[0065] Meanwhile, the method for manufacturing a monomer for synthesizing recycled plastic according to one embodiment above may include the step of melting the aromatic diol compound; and the step of crystallizing the melted aromatic diol compound.

[0066] The product obtained through the step of recovering the aromatic diol compound obtained from the depolymerization reaction of the aforementioned polycarbonate resin is mostly bisphenol A, and there are small amounts of impurities such as aromatic diol compounds or bisphenol dimers. The melt crystallization purification method is a purification method that utilizes the difference in solubility according to temperature between the above impurities dissolved in the molten bisphenol A.

[0067] Specifically, the step of melting the aromatic diol compound may involve heating the aromatic diol compound at a temperature of 190°C or lower, or between 180°C and 190°C. Although specific examples of the heating time are not significantly limited, for example, heating may be performed for 9 hours or less, or for 6 to 8 hours.

[0068] Since aromatic diol compounds tend to decompose at temperatures above 160°C, they can be melted by heating them temporarily to a temperature above 160°C for a very short period of time. Therefore, if the aromatic diol compounds are heated at a temperature above 190°C for an excessively long time, a problem may arise in which the yield decreases due to the decomposition of the aromatic diol compounds.

[0069] Meanwhile, prior to the step of crystallizing the molten aromatic diol compound, the method may further include a step of melting and purifying the molten aromatic diol compound at a temperature of 130°C to 180°C for 2 to 6 hours, or 2 to 3 hours. By further melting and purifying the molten aromatic diol compound prior to the step of crystallizing the molten aromatic diol compound, impurities other than the aromatic diol compound can be effectively removed to ensure high purity.

[0070] More specifically, the melting and purifying step may include: cooling the molten aromatic diol compound to form aromatic diol compound crystals; recovering purified aromatic diol compound crystals obtained by partially melting the aromatic diol compound crystals; and melting the purified aromatic diol compound crystals.

[0071] The step of cooling the molten aromatic diol compound to form an aromatic diol compound crystal may involve cooling the molten aromatic diol compound to a temperature of less than 158°C. Since bisphenol A, a specific example of the aromatic diol compound, has a melting point of 158°C, cooling to a temperature of less than 158°C can cause the aromatic diol compound, which was in a liquid state, to undergo a phase transition to a solid.

[0072] The step of recovering purified aromatic diol compound crystals obtained by partially melting the above aromatic diol compound crystals may involve partially melting the aromatic diol compound crystals by increasing their temperature to have intermediate solid and liquid characteristics. The purified aromatic diol crystals recovered here can achieve higher purity as impurities are further purified.

[0073] Meanwhile, the purified aromatic diol compound crystals are transported in a molten state to ensure smooth movement within the equipment.

[0074] As described above, since aromatic diol compounds tend to decompose at temperatures above 160°C, it is desirable to heat them temporarily to a temperature above 160°C for a very short period of time for partial melting or melting of the aromatic diol compounds. If the aromatic diol compounds are heated at a temperature above 160°C for an excessively long time, a problem may arise in which the yield decreases due to the decomposition of the aromatic diol compounds.

[0075] Meanwhile, the melt purification step described above can be repeated 2 to 5 times, or 3 to 4 times. One cycle of the melt purification step proceeds in the order of cooling, sweating, and melting, and the ratio of impurities removed in each cycle varies depending on the type of impurity. The starting temperature and cooling temperature of each cycle differ slightly, and it is essential to control the total cycle time to 2 to 3 hours or less to prevent the deterioration of Bisphenol A quality to the maximum extent. As each cycle passes, the purity of Bisphenol A increases, and other impurities, such as aromatic diol compounds, are drained and discharged to the bottom of the crystallizer. To improve yield, the discharged drain is reused along with the feed from the previous cycle, or a portion of the Bisphenol A within the drain is recovered through a static-type crystallizer.

[0076] Although specific methods and equipment for carrying out the above-mentioned melt purification step are not limited, for example, purification can be carried out through single-stage fractional melt crystallization or multi-stage fractional melt crystallization in a thin-film fluid-flow dynamic crystallizer. In the present invention, results were obtained by utilizing the technology of Sulzer, which possesses excellent technical capabilities in the field of melt crystallization processes.

[0077] Compositions in molten form are typically subjected to multi-stage fractional melt crystallization. The temperature is gradually lowered until it is approximately below the melting point of the target substance [in the case of Bisphenol-A, MP 156.7°C]. In some cases, the composition must be heated above the melting point of the target substance and then lowered below the freezing point. Clearly, this particular process is advantageous for separating impurities from the target component of the composition. Ideally, the target component crystallizes on the surface of the container holding the molten composition. The theory of fractional melt crystallization is to preferably crystallize the target component from the melt, while leaving undesired impurities in their liquid state or capturing them to a limited extent within the crystalline medium. In multi-stage fractional melt crystallization, the purity of the target crystalline component is enhanced as it passes through the crystallization phase, the partial melting phase, and the total melting phase in successive stages. A preferred apparatus for performing fractional melt crystallization is a Sulzer melt crystallization apparatus, specifically, a thin-film fluid-flow dynamic crystallizer.

[0078] Meanwhile, the step of crystallizing the molten aromatic diol compound may involve cooling the molten aromatic diol compound to a temperature of less than 158°C. Since bisphenol A, a specific example of the aromatic diol compound, has a melting point of 158°C, cooling to a temperature of less than 158°C can cause the aromatic diol compound, which was in a liquid state, to undergo a phase transition to a solid.

[0079] Meanwhile, the method for manufacturing a monomer for synthesizing recycled plastic according to the above embodiment may include the step of obtaining the crystallized aromatic diol compound.

[0080] In the step of obtaining the crystallized aromatic diol compound, if necessary, a process to remove residual impurities from the crystallized aromatic diol compound through filtration or adsorption may be carried out.

[0081] In the step of obtaining the crystallized aromatic diol compound, a drying step may be performed as necessary. The residual solvent can be removed through the drying, and although the specific drying conditions are not significantly limited, drying may be performed at a temperature of, for example, 10°C to 100°C or 10°C to 50°C. Regarding the specific drying equipment and method used during the drying, various existing known drying technologies may be applied without limitation.

[0082] Specific examples of the above aromatic diol compounds include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (Bisphenol Z), 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, and 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane. Examples include 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 of these. Preferably, the aromatic diol compound of the monomer for synthesizing recycled plastic in the above embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0083] The purity of the crystallized aromatic diol compound may be 99.94% or more, or 99.95% or more, or 100% or less, or 99.99% or less, or 99.94% to 100%, or 99.95% to 100%, or 99.94% to 99.99%, or 99.95% to 99.99%. Examples of methods for measuring the purity of the aromatic diol compound are not significantly limited, and for example, 1 1H NMR, ICP-MS analysis, HPLC analysis, UPLC analysis, etc., can be used without limitation. Specific methods, conditions, equipment, etc. of the above NMR, ICP-MS, HPLC, and UPLC can be applied without limitation to various previously known contents.

[0084] As an example of a method for measuring the purity of the above aromatic diol compound, the monomer for synthesizing recycled plastic of the above embodiment was dissolved in a methanol (MeOH) solvent at 1 w% under conditions of atmospheric pressure and 20 to 30 ℃, and then the purity of bisphenol A (BPA) was analyzed using UPLC (ultra performance liquid chromatography) in a Waters HPLC system using an ACQUITY UPLC®BEH C18 1.7 μm (2.1*50 mm column).

[0085] As such, in the method for manufacturing monomers for synthesizing recycled plastics according to the above embodiment, the purity of the aromatic diol compound, which is the main target material for recovery, is increased to 99.9% or higher, and other impurities are minimized, thereby enabling the realization of excellent physical properties when synthesizing polycarbonate-based resins using this.

[0086] That is, the monomer for synthesizing recycled plastic may further include impurities other than aromatic diol compounds. The impurities refer to all substances excluding aromatic diol compounds, which are the main recovery target substances of the present invention, and their specific types are not significantly limited. However, examples include phenol, 4-tert-butylphenol (PTBP), or p-isopropenylphenol (IPP).

[0087] Meanwhile, the yield of the crystallized aromatic diol compound may be 88% or more, or 90% or more, or 100% or less, or 88% to 100%, or 90% to 100%. Examples of methods for measuring the yield of the crystallized aromatic diol compound are not significantly limited, and, for example, can be calculated using Formula 1 below.

[0088] [Equation 1]

[0089] Yield (%) = (W1 / W0)x100

[0090] In the above Equation 1, W0 is the mass of the aromatic diol compound obtained upon 100% decomposition, and W1 is the actual mass of the aromatic diol compound obtained. In the above Equation 1, the mass of the aromatic diol compound can be measured using any generally known mass measurement method without limitation, for example, a balance can be used.

[0091] In this way, in the method for manufacturing monomers for synthesizing recycled plastics according to the above embodiment, the yield of the aromatic diol compound, which is the main target material for recovery, is increased to 90% or more, thereby improving the efficiency of the recycling process for polycarbonate-based resins.

[0092] Meanwhile, in the monomer for synthesizing recycled plastic of the above embodiment, diethyl carbonate may be obtained as a byproduct. The diethyl carbonate is characterized by being recovered from a polycarbonate-based resin used in the method for manufacturing the monomer for synthesizing recycled plastic of the above embodiment.

[0093] That is, it means that as a result of proceeding with recovery from a polycarbonate-based resin to obtain a monomer for synthesizing recycled plastic according to the above embodiment, diethyl carbonate is also obtained. Therefore, cases in which a novel diethyl carbonate is added from an external source separately from the recovery from the polycarbonate-based resin used in the method for manufacturing a monomer for synthesizing recycled plastic according to the above embodiment are not included in the category of diethyl carbonate.

[0094] Specifically, the term "recovered from the polycarbonate-based resin" means that it was obtained through the depolymerization reaction of the polycarbonate-based resin. The depolymerization reaction can be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction can be carried out under basic (alkali) conditions. In particular, as described below, it is preferable that the depolymerization reaction be carried out in an ethanol solvent.

[0095] Since the main target substance for recovery in the monomer for synthesizing recycled plastic of the above embodiment is an aromatic diol compound, the diethyl carbonate can be separated and recovered as a byproduct in the method for manufacturing the monomer for synthesizing recycled plastic of the above embodiment.

[0096]

[0097] 2. Monomers for the synthesis of recycled plastics

[0098] According to another embodiment of the invention, a monomer for synthesizing recycled plastic comprising an aromatic diol compound obtained in the method for manufacturing a monomer for synthesizing recycled plastic of the first embodiment may be provided.

[0099] That is, the monomer for synthesizing recycled plastic of the other embodiment above may be obtained by the method for manufacturing the monomer for synthesizing recycled plastic of the first embodiment above. The details regarding the method for manufacturing the monomer for synthesizing recycled plastic of the first embodiment above include all the details described above in the first embodiment.

[0100] Specific examples of the above aromatic diol compounds include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (Bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (Bisphenol Z), 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, and 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane. Examples include 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 of these. Preferably, the aromatic diol compound of the monomer for synthesizing recycled plastic in the above embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0101] The above aromatic diol compound is characterized by being obtained in the method for preparing a monomer for recycling plastic synthesis of the above embodiment. That is, the above aromatic diol compound is characterized by being recovered from a polycarbonate-based resin used for recovering the monomer for recycling plastic synthesis. Accordingly, cases in which a novel aromatic diol compound is added externally, separate from recovery from the polycarbonate-based resin, to prepare the monomer for recycling plastic synthesis of the above other embodiment are not included in the scope of the aromatic diol compound of the present invention.

[0102] Specifically, the term "recovered from the polycarbonate-based resin" means that it was obtained through the depolymerization reaction of the polycarbonate-based resin. The depolymerization reaction can be carried out under acidic, neutral, or basic conditions, and in particular, the depolymerization reaction can be carried out under basic (alkali) conditions. In particular, as described below, it is preferable that the depolymerization reaction be carried out in an ethanol solvent.

[0103] The monomer for synthesizing recycled plastic of the above other embodiment can be used as a raw material for manufacturing various recycled plastics (e.g., polycarbonate (PC)) described below.

[0104] The monomer for synthesizing recycled plastic of the above other embodiment may further include some small amounts of other additives and solvents, and the specific types of additives or solvents are not significantly limited, and various materials widely used in the process of recovering aromatic diol compounds by depolymerization of polycarbonate resins can be applied without limitation.

[0105]

[0106] 3. Recycled plastic

[0107] According to another embodiment of the invention, a recycled plastic comprising a reaction product of a monomer for synthesizing recycled plastic and a comonomer of the other embodiment may be provided.

[0108] The details regarding the monomer for synthesizing recycled plastic in the other embodiment above include all the details described above in the other embodiment.

[0109] Examples corresponding to the above recycled plastics are not significantly limited, and various plastics synthesized using aromatic diol compounds such as bisphenol A and carbonate precursors such as dimethyl carbonate, diethyl carbonate, or ethylmethyl carbonate as monomers can be applied without limitation, and more specific examples include polycarbonate resins.

[0110] The above polycarbonate-based resin includes both homopolymers and copolymers containing polycarbonate repeating units, and collectively refers to reaction products obtained through the polymerization or copolymerization reaction of monomers including aromatic diol compounds and carbonate precursors. A homopolymer can be synthesized when containing one carbonate repeating unit obtained by using only one aromatic diol compound and one carbonate precursor. Additionally, a copolymer can be synthesized when containing two or more carbonates by using one aromatic diol compound and two or more carbonate precursors as monomers, using two or more aromatic diol compounds and one carbonate precursor, or using one or more other diols in addition to one aromatic diol compound and one carbonate precursor. The above homopolymer or copolymer may include low molecular weight compounds, oligomers, and high molecular weights according to the molecular weight range.

[0111] More specifically, in a recycled plastic comprising the reaction product of the monomer and comonomer for the synthesis of the recycled plastic, a carbonate precursor may be used as the comonomer. Specific examples of the carbonate precursor include phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditoryl carbonate, bis(chlorophenyl) carbonate, m-cresyl carbonate, dinaphthyl carbonate, bis(diphenyl) carbonate, or bishaloformate.

[0112] Examples of reaction processes for the monomers and comonomers used to synthesize the above-mentioned polycarbonate-based resin are not significantly limited, and various previously known methods for manufacturing polycarbonate can be applied without restriction.

[0113] However, as an example of the above-mentioned method for manufacturing polycarbonate, a method for manufacturing polycarbonate may be used that includes the step of polymerizing a composition comprising a monomer for synthesizing recycled plastic and a comonomer. In this case, the polymerization may be performed as interfacial polymerization, and during interfacial polymerization, the polymerization reaction is possible at atmospheric pressure and low temperature, and molecular weight control is easy.

[0114] The polymerization temperature may be 0 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 higher or 11 or higher.

[0115] The solvent that can be used for the above polymerization is not particularly limited as long as it is a solvent used in the industry for the polymerization of polycarbonates, and for example, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0116] In addition, the polymerization can be carried out in the presence of an acid binder, and an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an amine compound such as pyridine, can be used as the acid binder.

[0117] In addition, to control the molecular weight of the polycarbonate during the above polymerization, polymerization may be carried out in the presence of a molecular weight regulator. An alkylphenol having 1 to 20 carbon atoms may be used as the molecular weight regulator, and specific examples thereof include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol, or triacontylphenol. The molecular weight regulator may be added before, during, or after the start of polymerization. The molecular weight regulator may 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 a desired molecular weight can be obtained within this range.

[0118] In addition, to promote the polymerization reaction, reaction promoters such as tertiary amine compounds, quaternary ammonium compounds, and quaternary phosphonium compounds, such as triethylamine, tetra-n-butylammonium bromide, tetra-n-butylphosphonium bromide, etc., may be additionally used.

[0119]

[0120] 4. Molded product

[0121] According to another embodiment of the invention, a molded article comprising recycled plastic of the other embodiment may be provided. The details regarding the recycled plastic include all details described above in the other embodiment.

[0122] The above-mentioned molded article may be obtained by applying various known plastic molding methods to the above-mentioned recycled plastic without limitation, and examples of the above-mentioned molding methods include injection molding, foam injection molding, blow molding, or extrusion molding.

[0123] Examples of the above-mentioned molded articles are not significantly limited and can be applied without restriction to various molded articles using plastic. Examples of the above-mentioned molded articles include automotive parts, electrical and electronic products, communication products, household goods, building materials, optical components, exterior materials, etc.

[0124] In addition to the recycled plastic of the other embodiment above, the molded article may additionally include one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact modifiers, fluorescent whitening agents, ultraviolet absorbers, pigments, and dyes, as needed.

[0125] As an example of a method for manufacturing the above-mentioned molded product, the method may include the step of thoroughly mixing the recycled plastic and additive of the above-mentioned other embodiment using a mixer, then extruding them into pellets using an extruder, drying the pellets, and then injecting them using an injection molding machine.

[0126] According to the present invention, a method for producing a monomer for synthesizing recycled plastics capable of obtaining a high-purity, high-yield aromatic diol compound through recycling by chemical decomposition of a polycarbonate-based resin, and a monomer for synthesizing recycled plastics, a recycled plastic, and a molded article using the same may be provided.

[0127] The invention is described in more detail in the following examples. However, the following examples are merely illustrative of the invention, and the scope of the invention is not limited by the following examples.

[0128]

[0129] <Examples, Comparative Examples, and Reference Examples: Preparation of Recycled Bisphenol A Monomers>

[0130] Example 1

[0131] (1. Pretreatment step) A solution in which waste polycarbonate (PC) was dissolved in methylene chloride (MC) (containing 18.73 wt% waste polycarbonate (PC), 78.27 wt% methylene chloride (MC), and 3 wt% other impurities) was recovered as a filter filtrate with a pore diameter of 3.0 μm or less. At this time, the filter filtrate contained 18.76 wt% waste polycarbonate (PC), 78.30 wt% methylene chloride (MC), and 2.94 wt% other impurities.

[0132] (2. Decomposition Step) The above filtrate was introduced into a 3L high-pressure reactor, ethanol (EtOH), sodium hydroxide (NaOH), and sodium hydrosulfite were introduced, and the atmosphere in the system was replaced with nitrogen to inert the PC depolymerization reaction by stirring at 60°C for 6 hours. At this time, the ingredients were introduced to satisfy a molar ratio of 17 mol of methylene chloride (MC), 11 mol of ethanol (EtOH), and 0.25 mol of sodium hydroxide (NaOH) per 1 mol of waste polycarbonate (PC), and sodium hydrosulfite was introduced at 1% by weight relative to the total reaction solution.

[0133] (3. Neutralization) The product of the above depolymerization reaction was cooled to 30°C or lower, and then 10% hydrochloric acid (HCl) and water were added to neutralize it to a pH of 7. At this time, the neutralized solution contained 10.33 wt% bisphenol A, 49.53 wt% methylene chloride (MC), 19.30 wt% ethanol (EtOH), 13.03 wt% water, 5.48 wt% diethyl carbonate (DEC), and 2.33 wt% other impurities.

[0134] (4. Layer Separation) After the water layer and the methylene chloride (MC) layer were formed, the methylene chloride (MC) layer located at the bottom was recovered using a drain device at the bottom of the reactor, and the water layer located at the top was disposed of through a separate solvent recovery process. At this time, the methylene chloride (MC) layer contained 11.99 wt% bisphenol A, 56.76 wt% methylene chloride (MC), 18.70 wt% ethanol (EtOH), 4.61 wt% water, 6.26 wt% diethyl carbonate (DEC), 0.12 wt% phenol, 0.37 wt% 4-tert-butylphenol (PTBP), 0.16 wt% p-isopropenylphenol (IPP), and 1.03 wt% other impurities.

[0135] (5-1. Distillation - First vacuum distillation) Afterwards, the recovered methylene chloride (MC) layer was introduced into the first distillation section of the distillation column at a pressure of 0.45 MPa and a temperature of 160 ℃, and the pressure was reduced to 0.12 MPa and the temperature was reduced to 48~160 ℃ to distill and remove the methylene chloride (MC), ethanol (EtOH), and water from the methylene chloride (MC) layer, and the residual solution was transferred to the second distillation section.

[0136] (5-2. Distillation - Second vacuum distillation) Afterwards, in the second distillation section of the distillation column, the residual solution was pressurized to a pressure of 0.45 MPa and a temperature of 125 ℃, then reduced to a pressure of 0.009 MPa and a temperature of 42 to 160 ℃ to distill and remove diethyl carbonate (DEC) from the residual solution, and the residual solution was transferred to the third distillation section.

[0137] (5-3. Distillation - Third vacuum distillation) Afterwards, in the third distillation section of the distillation column, the residual solution was reduced to a pressure of 0.0005 MPa and a temperature of 155 ℃, and then reduced to a pressure of 0.0003 MPa and a temperature of 42–162 ℃ to distill and remove diethyl carbonate (DEC) and phenolic impurities from the residual solution, thereby obtaining a bisphenol A solution.

[0138] At this time, the bisphenol A solution contained 90.04 wt% bisphenol A, 0.52 wt% diethyl carbonate (DEC), 0.02 wt% phenol, 1.35 wt% 4-tert-butylphenol (4-tert-Butylphenol, PTBP), 0.59 wt% p-isopropenylphenol (p-isopropenylphenol, IPP), and 7.48 wt% other impurities.

[0139] (6. Melt Crystallization) 3,200 g of the above bisphenol A solution was subjected to a fractional melt crystallization process in a drop membrane dynamic crystallizer (manufactured by Suzler) to obtain recycled bisphenol A monomer. At this time, the recycled bisphenol A monomer obtained in Example 1 contained 99.95 wt% bisphenol A and 0.05 wt% bisphenol A dimer.

[0140] Specifically, the fractional melting crystallization process described above proceeds in the following process sequence.

[0141] 1) The above bisphenol A solution was heated at 185°C for 6 to 8 hours to melt it.

[0142] 2) For the molten bisphenol A obtained in 1), a purification cycle consisting of “cooling - sweating - melting” was performed three times. At this time, the purification cycle, which was performed three times in total, was carried out at a temperature of 130–180°C for 2–3 hours. Specifically, the purification cycle includes a process of melting the purified bisphenol A crystals obtained by partially melting the bisphenol A crystals obtained by cooling the molten bisphenol A and then sweating the bisphenol A crystals.

[0143] 3) After recovering the molten bisphenol A obtained in 2), the crystallized recycled bisphenol A monomer was obtained by cooling it at less than 157°C in a nitrogen atmosphere.

[0144]

[0145] Example 2

[0146] Recycled bisphenol A monomer was prepared in the same manner as in Example 1, except that the number of purification cycles in (6. melt crystallization) of Example 1 was changed from 3 to 4.

[0147]

[0148] Comparative Example 1

[0149] (1. Decomposition step) 1 mol of pretreated waste polycarbonate (PC) was dissolved in 17 mol of methylene chloride (MC), then added to a 3L high-pressure reactor along with 11 mol of ethanol (EtOH) and 0.25 mol of sodium hydroxide (NaOH). Sodium hydrosulfite was added as an antioxidant at 0.7 wt% relative to the total solution, and the atmosphere in the system was replaced with nitrogen to maintain an inert state. The PC depolymerization reaction was carried out by stirring at 60°C for 6 hours.

[0150] (2. pH adjustment) The product of the above depolymerization reaction was cooled to 30°C or lower, and then 10% hydrochloric acid (HCl) and water were added to the bisphenol A product to adjust the pH to 7.

[0151] (3. Layer Separation) After the water layer and methylene chloride (MC) layer were formed, the organic solvent layer located at the bottom was recovered using a drain device at the bottom of the reactor, and the water layer located at the top was discharged and discarded.

[0152] (4. Distillation) Afterwards, the recovered methylene chloride (MC) layer was separated and recovered by low-temperature distillation at reduced pressure from 250 mbar and 20 to 30 ℃ to 30 mbar and 30 ℃.

[0153] (5. Purification step - Filtration) Afterwards, the residue from which diethyl carbonate (DEC) had been removed was washed first at 20 to 30 ℃ using methylene chloride (MC) in an amount equal to twice the mass of PC used, and vacuum filtered. The filtrate was washed secondarily at 50 ℃ using water in an amount equal to twice the mass of PC used.

[0154] After (6-1. Additional purification step - redissolution step), bisphenol A was added to 16.6 mol of ethanol and redissolved.

[0155] (6-2. Additional purification step - adsorption step) Afterwards, lignite activated carbon was added as an adsorbent at a ratio of 50% by weight relative to the waste polycarbonate, purified through adsorption for 3 hours, and then the lignite activated carbon was removed through filtration.

[0156] (6-3. Additional purification step - crystallization step) Afterwards, 300 mol of water was added and bisphenol A was crystallized, and then bisphenol A (BPA) crystals were recovered from the obtained slurry through vacuum filtration at 20 to 30 ℃.

[0157] (7. Drying step) Afterwards, recycled bisphenol A monomers were prepared by vacuum drying in a 40 ℃ convection oven to recover recycled bisphenol A (BPA).

[0158]

[0159] Reference Example 1

[0160] A recycled bisphenol A monomer was prepared in the same manner as in Example 1, except that the (5. distillation) described below was performed instead of (5-1. distillation - 1st vacuum distillation), (5-2. distillation - 2nd vacuum distillation), and (5-3. distillation - 3rd vacuum distillation) of Example 1.

[0161] (5. Distillation) A bisphenol A solution was obtained by performing low-temperature distillation on the recovered methylene chloride (MC) layer at 250 mbar and 20 to 30 ℃, reducing the pressure to 30 mbar and 30 ℃.

[0162]

[0163] <Experimental Example>

[0164] For the recycled bisphenol A monomers obtained in the above examples, comparative examples, and reference examples, physical properties were measured by the following method, and the results are shown in Table 1.

[0165]

[0166] 1. Purity

[0167] Recycled bisphenol A monomer was dissolved in methanol (MeOH) solvent at 1 w% under atmospheric pressure and 20 to 30 ℃ conditions, and then the purity of bisphenol A (BPA) was analyzed using UPLC (ultra performance liquid chromatography) in a Waters HPLC system using ACQUITY UPLC®BEH C18 1.7 µm (2.1*50 mm column).

[0168]

[0169] 2. Yield

[0170] The weight of BPA produced when the polycarbonate used in the reaction was 100% decomposed was measured, and the weight of the obtained BPA was measured to calculate the yield of BPA as shown in Equation 1 below.

[0171] [Equation 1]

[0172] Yield (%) = (W1 / W0)x100

[0173] In Equation 1 above, W0 is the mass of BPA obtained at 100% decomposition, and W1 is the actual mass of BPA 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%.

[0174]

[0175] Experimental Example Measurement Results Classification Purity (%) BPA Yield (%) Example 1 99.9594 Example 2 99.9890 Comparative Example 1 99.9282.2 Reference Example 1 99.8893.5

[0176] As shown in Table 1 above, the recycled bisphenol A monomers obtained in Examples 1 and 2 exhibited a very high purity of 99.95% to 99.98%. In addition, the recycled bisphenol A monomers obtained in Examples 1 and 2 showed a high BPA yield of 90% to 94%. On the other hand, the recycled bisphenol A monomer obtained in Comparative Example 1 had a purity of 99.92%, which was lower than that of the examples. Furthermore, the recycled bisphenol A monomer obtained in Comparative Example 1 showed a BPA yield of 82.2%, which was lower than that of the examples.

Claims

1. A step of recovering an aromatic diol compound obtained from the depolymerization reaction of a polycarbonate-based resin; A step of melting the above aromatic diol compound; A step of crystallizing the above-mentioned molten aromatic diol compound; and A step of obtaining the crystallized aromatic diol compound; comprising Method for manufacturing monomers for synthesizing recycled plastics.

2. In Paragraph 1, The step of crystallizing the above-mentioned molten aromatic diol compound is, Cooling the above-mentioned molten aromatic diol compound to a temperature of less than 158°C, Method for manufacturing monomers for synthesizing recycled plastics.

3. In Paragraph 1, Prior to the step of crystallizing the above-mentioned molten aromatic diol compound, The method further comprises the step of melting and purifying the above-mentioned molten aromatic diol compound at a temperature of 130 ℃ to 180 ℃ for 2 to 6 hours. Method for manufacturing monomers for synthesizing recycled plastics.

4. In Paragraph 3, The above melting and purifying step is, A step of cooling the above-mentioned molten aromatic diol compound to form aromatic diol compound crystals; A step of recovering purified aromatic diol compound crystals obtained by partially melting the above aromatic diol compound crystals; and A step comprising melting the crystals of the purified aromatic diol compound; Method for manufacturing monomers for synthesizing recycled plastics.

5. In Paragraph 3, The above melting and purifying step is, A method for manufacturing a monomer for synthesizing recycled plastic, which is repeated 2 to 5 times.

6. In Paragraph 3, The above melting and purifying step is, A method for producing a monomer for synthesizing recycled plastics, wherein purification is carried out by one-stage fractional melt crystallization or multi-stage fractional melt crystallization in a thin-film fluid-flow dynamic crystallizer.

7. In Paragraph 1, The crystallized aromatic diol compound having a purity of 99.94% or higher, Method for manufacturing monomers for synthesizing recycled plastics.

8. In Paragraph 1, The yield of the crystallized aromatic diol compound above is 88% or higher, Method for manufacturing monomers for synthesizing recycled plastics.

9. In Paragraph 1, The step of recovering the aromatic diol compound obtained from the depolymerization reaction of the above-mentioned polycarbonate resin is: A step of depolymerizing a polycarbonate-based resin; A step of neutralizing the above depolymerization product by adding acid; A step of removing the water layer from the water layer and organic solvent layer formed in the above neutralization step; and A step of recovering an aromatic diol compound by distilling the above organic solvent layer; comprising Method for manufacturing monomers for synthesizing recycled plastics.

10. In Paragraph 9, The step of recovering an aromatic diol compound by distilling the above organic solvent layer is, A method for producing a monomer for synthesizing recycled plastic, comprising a multi-stage vacuum distillation step of vacuum distilling the organic solvent layer in three or more stages.

11. In Paragraph 10, The above multi-stage vacuum distillation step is, A first vacuum distillation step of vacuum distilling the above organic solvent layer at a pressure of 0.12 MPa to 0.45 MPa and a temperature of 48 ℃ to 160 ℃ from a pressure of 0.45 MPa or more and a temperature of 160 ℃ or more; A second vacuum distillation step in which the residual solution of the first vacuum distillation step is pressurized to a pressure of 0.45 MPa or more and a temperature of 125 ℃ or more, and then vacuum distilled at a pressure of 0.009 MPa to 0.45 MPa and a temperature of 42 ℃ to 160 ℃; and A third vacuum distillation step comprising: reducing the residual solution of the second vacuum distillation step to a pressure of 0.0005 MPa or more and a temperature of 155 ℃ or more, and then vacuum distilling it at a pressure of 0.0003 MPa to 0.0005 MPa and a temperature of 42 ℃ to 87 ℃; Method for manufacturing monomers for synthesizing recycled plastics.

12. In Paragraph 1, The depolymerization reaction of the above polycarbonate-based resin is, Characterized by proceeding under a solvent containing ethanol, Method for manufacturing monomers for synthesizing recycled plastics.

13. In Paragraph 12, The content of the above ethanol is 10 to 15 moles per 1 mole of polycarbonate resin, Method for manufacturing monomers for synthesizing recycled plastics.

14. In Paragraph 1, The depolymerization reaction of the above polycarbonate-based resin is, Characterized by proceeding with a reaction of a base at a content of 0.5 moles or less per 1 mole of polycarbonate resin, Method for manufacturing monomers for synthesizing recycled plastics.

15. In Paragraph 1, Prior to the step of recovering the aromatic diol compound obtained from the depolymerization reaction of the above polycarbonate-based resin, A method further comprising a pretreatment step of passing a polycarbonate-based resin through a filter having a pore diameter of 0.3 μm or less, Method for manufacturing monomers for synthesizing recycled plastics.

16. A monomer for synthesizing recycled plastic, comprising an aromatic diol compound obtained in the method for manufacturing a monomer for synthesizing recycled plastic according to claim 1.

17. Recycled plastic comprising the reaction product of the monomer and comonomer for the synthesis of recycled plastic of paragraph 16.

18. A molded article comprising recycled plastic of paragraph 17.