Method and apparatus for preparing monomer composition for synthesizing regenerated plastic, and monomer composition for synthesizing regenerated plastic, regenerated plastic, and molded article using same

Abstract

The present disclosure relates to a method for preparing a monomer composition for synthesizing recycled plastic, the method comprising the steps of: subjecting a polycarbonate-based resin to a depolymerization reaction in the presence of an alcohol; monitoring the Raman spectrum of the aromatic diol compound or alcohol resulting from the depolymerization reaction in a reactor in which the depolymerization reaction proceeds; and recovering the aromatic diol compound, and the present disclosure relates to an apparatus for preparing a monomer composition for synthesizing a reprocessed plastic, a monomer composition for synthesizing a reprocessed plastic, a reprocessed plastic, and a molded article using the same.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0109847 filed in the Korean Intellectual Property Office on August 22, 2023, the disclosure of which is incorporated herein by reference in its entirety.

[0003] The present disclosure relates to a method for preparing a monomer composition for synthesizing recycled plastics, a device for preparing a monomer composition for synthesizing recycled plastics, a monomer composition for synthesizing recycled plastics, a recycled plastic and a molded product using the recycled plastics, wherein a process of recovering an aromatic diol compound by chemical decomposition of a polycarbonate resin is monitored in real time to optimize reaction conditions and improve efficiency. Background Art

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

[0005] Although polycarbonate is widely used in various applications, environmental and health issues in waste disposal continue to rise.

[0006] Currently, a physical recycling method is performed, but in this case, a problem of accompanying quality deterioration occurs, and therefore, research on chemical recycling of polycarbonate is being conducted.

[0007] The chemical decomposition of polycarbonate refers to obtaining an aromatic diol compound (eg, bisphenol A (BPA)) as a monomer by decomposition of polycarbonate, and then the aromatic diol compound is used again in polymerization to obtain high-purity polycarbonate.

[0008] For such chemical decomposition, thermal decomposition, hydrolysis and alcohol decomposition are generally known. Among these, the most common method is alcohol decomposition using an alkali catalyst, but in the case of methanol decomposition, there is a problem of using methanol that is harmful to the human body, and in the case of ethanol, there is a problem that high temperature and high pressure conditions are required and the yield is not high.

[0009] Furthermore, although an alcohol decomposition method using an organic catalyst is known, it is economically disadvantageous.

[0010] On the other hand, as the reaction scale for decomposing polycarbonate increases to tens of liters, there arises a need to explore factors indicating depolymerization trends that differ from those at the laboratory level.

[0011] Typically, the conversion to the final product is analyzed by HPLC or NMR analysis, or samples are collected and analyzed during the course of the reaction.

[0012] However, as the scale of the reaction increases, the conversion rate of polycarbonate differs from that of the reaction carried out at the laboratory level, and the timing and extent of the production of side products also differ. Summary of the invention

[0013] Technical issues

[0014] An object of the present disclosure is to provide a method for preparing a monomer composition for synthesizing recycled plastics, or a device for preparing a monomer composition for synthesizing recycled plastics, wherein the process of recovering aromatic diol compounds by chemical decomposition of polycarbonate resins is monitored in real time to optimize reaction conditions and improve efficiency.

[0015] Another object of the present disclosure is to provide a monomer composition for synthesizing recycled plastic, recycled plastic, and a molded product using a method for preparing a monomer composition for synthesizing recycled plastic or an apparatus for preparing a monomer composition for synthesizing recycled plastic.

[0016] Technical Solution

[0017] In order to achieve the above-mentioned purpose, the present invention provides a method for preparing a monomer composition for synthesizing recycled plastics, which method comprises the following steps: subjecting a polycarbonate resin to a depolymerization reaction in the presence of an alcohol; monitoring the Raman spectrum of an aromatic diol compound or alcohol obtained from the depolymerization reaction in a reactor where the depolymerization reaction is carried out; and recovering the aromatic diol compound.

[0018] The present invention also provides a preparation device for a monomer composition for synthesizing recycled plastics, comprising: a reactor for subjecting a polycarbonate resin to a depolymerization reaction in the presence of an alcohol; an online analyzer inserted into the reactor to monitor the Raman spectrum of an aromatic diol compound or alcohol obtained from the depolymerization reaction; and a recovery unit for recovering the aromatic diol compound obtained from the depolymerization reaction.

[0019] The present invention further provides a monomer composition for synthesizing recycled plastics, comprising an aromatic diol compound obtained by the method for preparing the monomer composition for synthesizing recycled plastics or the device for preparing the monomer composition for synthesizing recycled plastics.

[0020] The present invention further provides a recycled plastic, comprising a reaction product of the monomer composition for synthesizing recycled plastic and a comonomer.

[0021] Further provided herein is a molded article comprising the recycled plastic.

[0022] Hereinafter, a method for preparing a monomer composition for synthesizing recycled plastic, a device for preparing a monomer composition for synthesizing recycled plastic, a monomer composition for synthesizing recycled plastic, a recycled plastic and a molded product using the recycled plastic according to a specific embodiment of the present disclosure will be described in more detail.

[0023] Unless explicitly stated herein, the technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the present invention.

[0024] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0025] As used herein, "pH" refers to hydrogen ion concentration (pH), which is a numerical value that indicates the acidity and basicity of a material. pH is determined by taking the reciprocal of the logarithmic dissociation concentration of hydrogen ions and is used as a measure of the strength of the acid and base of a material.

[0026] It should be understood that the terms "comprises", "includes", "has", etc. are used herein to illustrate the presence of described features, regions, integers, steps, actions, elements and / or components, but do not exclude the presence or addition of one or more other features, regions, integers, steps, actions, elements, components and / or groups.

[0027] In addition, the terms including ordinal numbers such as "first", "second", etc. are only used for the purpose of distinguishing one component from another component and are not limited by the ordinal numbers. For example, without departing from the scope of the present disclosure, the first component can be called the second component, or similarly, the second component can be called the first component.

[0028] 1. Preparation method of monomer composition for synthesizing recycled plastics

[0029] According to one embodiment of the present disclosure, a method for preparing a monomer composition for synthesizing recycled plastics can be provided, the method comprising the following steps: subjecting a polycarbonate resin to a depolymerization reaction in the presence of an alcohol; monitoring the Raman spectrum of an aromatic diol compound or the alcohol obtained from the depolymerization reaction in a reactor where the depolymerization reaction is carried out; and recovering the aromatic diol compound.

[0030] The present inventors have experimentally discovered that, similar to the method for preparing a monomer composition for recycled plastic synthesis according to one embodiment, in the process of recovering a polycarbonate resin by chemical decomposition, the Raman spectrum of an aromatic diol compound or alcohol obtained from a depolymerization reaction is monitored in a reactor where the depolymerization reaction is carried out, so that the depolymerization reaction can be terminated at an optimal time point, and therefore, a high-purity aromatic diol compound can be recovered with a high yield, and the present disclosure is completed.

[0031] Specifically, generally, since the conversion rate of the final product is analyzed by HPLC or NMR analysis, or a sample is collected and analyzed at an arbitrary time point during the reaction, there is a limitation that it is difficult to find the optimal reaction endpoint that ensures high purity and high yield of the aromatic diol compound (i.e., the material to be recovered).

[0032] Meanwhile, according to the present disclosure, in the process of recovering polycarbonate resin by chemical decomposition, the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction is obtained in real time during the depolymerization reaction by means of an analysis device installed in a reactor where the depolymerization reaction is carried out, and the approximate aromatic diol compound or alcohol can be determined by analyzing the spectrum, so that the optimal reaction endpoint can be found more accurately. In addition, by monitoring the possibility of the generation of reaction by-products in real time while minimizing the generation of such by-products, the effect of recovering the aromatic diol compound with high purity and high yield can be achieved.

[0033] Specifically, the method for preparing a monomer composition for synthesizing recycled plastics according to an embodiment may include a step of subjecting a polycarbonate-based resin to a depolymerization reaction in the presence of an alcohol.

[0034] Polycarbonate resin is intended to include homopolymers and copolymers comprising polycarbonate repeating units, and refers to the reaction product obtained by the polymerization reaction or copolymerization reaction of the monomer comprising aromatic diol compound and carbonate precursor. When polycarbonate resin comprises a carbonate repeating unit obtained by only using one type of aromatic diol compound and one type of carbonate compound, homopolymer can be synthesized. In addition, when using one type of aromatic diol compound and two or more types of carbonate compounds as monomers, or when using two or more types of aromatic diol compounds and one type of carbonate compounds, or when also using one or more types of other glycols to comprise two or more types of carbonates except one type of aromatic diol compound and one type of carbonate compounds, copolymer can be synthesized. According to molecular weight range, homopolymer or copolymer can include all low molecular weight compounds, oligomers and polymers.

[0035] Various forms and types of polycarbonate-based resins may be applied, such as new polycarbonate-based resins produced by synthesis, recycled polycarbonate-based resins produced by a recycling process, or polycarbonate-based resin wastes.

[0036] However, if necessary, before carrying out the depolymerization reaction of polycarbonate resin, a pretreatment step of polycarbonate resin can be carried out, so that the efficiency of the process of recovering aromatic diol compound and carbonate precursor can be improved. The example of pretreatment step can include washing, drying, grinding, ethylene glycol decomposition etc. There is no restriction on the specific method of each pretreatment step, and various methods widely used in the process of recovering aromatic diol compound and carbonate compound from polycarbonate resin can be applied without restriction.

[0037] In the process of the depolymerization reaction of the polycarbonate resin, the depolymerization reaction can be carried out under acidic, neutral or alkaline conditions, and specifically, the depolymerization reaction can be carried out under alkaline conditions. There is no particular limitation on the type of the alkali, and its examples include sodium hydroxide (NaOH) or potassium hydroxide (KOH). The alkali is an alkaline catalyst that acts as a catalyst and has economic advantages over organic catalysts that are mainly used under mild conditions. More specifically, in the process of the depolymerization reaction of the polycarbonate resin, the depolymerization reaction can be carried out in a pH range of greater than 8 and less than 12.

[0038] In the process of depolymerization of the polycarbonate resin, the depolymerization reaction can be carried out by reacting a base in an amount of 0.5 mol or less, or 0.4 mol or less, or 0.3 mol or less, or 0.1 mol or more, or 0.2 mol or more, or 0.1 mol to 0.5 mol, or 0.1 mol to 0.4 mol, or 0.1 mol to 0.3 mol, or 0.2 mol to 0.5 mol, or 0.2 mol to 0.4 mol, or 0.2 mol to 0.3 mol relative to 1 mol of the polycarbonate resin. When the polycarbonate resin is reacted with a base in an amount greater than 0.5 mol relative to 1 mol of the polycarbonate resin in the process of depolymerization of the polycarbonate resin, there is a limitation that impurities increase due to the influence of an increase in the amount of generated alkali metal salts, so the purity of the target recycled material decreases, and the economic efficiency of the catalytic reaction decreases.

[0039] In addition, the depolymerization reaction of the polycarbonate resin can be carried out in the presence of alcohol. The present invention can stably obtain bisphenol A as a high-purity monomer by decomposing the polycarbonate resin with alcohol, and has the advantage of further obtaining carbonate compounds with high added value such as dialkyl carbonate as reaction byproducts.

[0040] The number of hydroxyl groups in the alcohol is not particularly limited, but may include, for example, monohydric alcohol. Monohydric alcohol is a compound having one hydroxyl group in a molecule.

[0041] In addition, there is no particular limitation on the type of the monovalent organic functional group bonded to the hydroxyl group in the monohydric alcohol, but may include an organic functional group having 1 to 10 carbon atoms or 1 to 6 carbon atoms, such as an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or a combination of two or more thereof.

[0042] The alcohol may be a single compound of one type or a mixture of two or more types. Specific examples of the alcohol are not particularly limited, but examples thereof include ethanol, methanol, phenol, or a mixture thereof.

[0043] The content of alcohol may be 5 to 15 moles, or 8 to 13 moles relative to 1 mole of the polycarbonate resin. Since alcohol has good solubility in bisphenol A, alcohol within the above range should be substantially contained. When the content of alcohol is excessively reduced to less than 5 moles relative to 1 mole of the polycarbonate resin, it is difficult to fully perform alcohol decomposition of the polycarbonate resin. On the other hand, when the content of alcohol is excessively increased to more than 15 moles relative to 1 mole of the polycarbonate resin, the economy of the process may decrease due to excessive use of alcohol.

[0044] The solvent in which the depolymerization reaction of the polycarbonate-based resin is carried out may include at least one organic solvent selected from the group consisting of tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate.

[0045] The organic solvent may include tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof.

[0046] More preferably, dichloromethane may be used as the organic solvent. When dichloromethane is used as the organic solvent, there are advantages that solubility in polycarbonate may be improved and reactivity may be increased.

[0047] The content of the organic solvent may be 16 to 20 mol, or 16 to 18 mol, relative to 1 mol of the polycarbonate-based resin. In addition, the content of the organic solvent may be 1.5 to 2 mol relative to 1 mol of the alcohol. By mixing the polycarbonate-based resin, the alcohol, and the organic solvent within the above range, there is an advantage that the depolymerization reaction of the polymer can be performed at a desired level.

[0048] Meanwhile, the temperature at which the depolymerization reaction of the polycarbonate resin is performed is not particularly limited, but for example, the reaction may be performed at 20° C. to 100° C., or 50° C. to 70° C. In addition, the depolymerization reaction of the polycarbonate resin may be performed for 1 hour to 30 hours, or 4 hours to 6 hours.

[0049] Specifically, the conditions are mild process conditions relative to conventional pressurized / high temperature processes, and by stirring under the above conditions, the process can be performed in a mild process compared to pressurized / high temperature processes. Specifically, when stirring at 50° C. to 70° C. for 4 to 6 hours, there is an advantage in obtaining the most effective results in terms of reproducibility and stability.

[0050] That is, according to the present disclosure, since the type and mixing amount of the mixed solvent and the type and content of the alkali catalyst are adjusted without using an organic catalyst, there are the following advantages: a high-purity aromatic diol compound (e.g., bisphenol A) can be obtained under mild conditions without using a pressurized / high-temperature process, and diethyl carbonate can be obtained as a by-product by using ethanol.

[0051] Meanwhile, during the depolymerization reaction of the polycarbonate resin, an antioxidant may be added to the reaction solution. With the addition of the antioxidant, the aromatic diol compound recovered by regeneration through chemical decomposition of the polycarbonate resin may satisfy a low color coordinate b* value at a color level comparable to that of a commercially available agent or one used for PC polymerization.

[0052] The specific examples of antioxidants are not particularly limited, and various antioxidants widely used in the prior art can be applied without restriction. However, an example of antioxidants includes sodium thiosulfate, sodium sulfite, isoascorbic acid, butylated hydroxytoluene, butylated hydroxyanisole, alpha-tocopherol, tocopherol acetate, L-ascorbic acid and salts thereof, L-ascorbyl palmitate, L-ascorbyl stearate, tripentyl gallate, propyl gallate or disodium ethylenediaminetetraacetic acid (EDTA), sodium pyrophosphate, sodium metaphosphate or a mixture of two or more thereof.

[0053] There is no particular limitation on the specific amount of the antioxidant added, but as an example, the antioxidant can be added in the range of 0.1 wt % to 5 wt % or 0.1 wt % to 1 wt % based on the total weight of the reaction solution at a level that does not affect the physical properties of the monomer composition for synthesizing recycled plastics.

[0054] In addition, during the depolymerization reaction of the polycarbonate-based resin, the depolymerization may be performed under a nitrogen atmosphere.

[0055] More specifically, the step of subjecting the polycarbonate resin to a depolymerization reaction may include: a first step of dissolving the polycarbonate resin in an organic solvent; and a second step of adding a catalyst solution containing an alcohol, an alkali, and an antioxidant. In the first step and the second step, the details of the alcohol, the organic solvent, the alkali, the antioxidant, and the polycarbonate resin are the same as described above.

[0056] Meanwhile, the preparation method of the monomer composition for synthesizing recycled plastics according to one embodiment may include the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is carried out. The Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction can be monitored in real time by the analytical equipment installed in the reactor where the depolymerization reaction is carried out during the depolymerization reaction, so that the optimal reaction end point can be found more accurately. In addition, since the generation of reaction byproducts can be minimized by monitoring the generation possibility of such byproducts in real time, the aromatic diol compound can be recovered with high purity and high yield.

[0057] In the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed, the Raman spectrum is data obtained by Raman analysis. For the specific details of the Raman analysis, various conventionally known analysis methods, analysis equipment and analysis conditions can be applied without limitation. However, as an example, a MarqMetrix All-in-one device can be used.

[0058] Specifically, the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is carried out can be performed by a Raman probe inserted into the reactor. More specifically, in one embodiment, an online probe (which is a Raman probe inserted into the reactor) can be used to analyze the real-time chemical component changes in the solid / liquid reaction solution in a non-destructive manner.

[0059] Therefore, the Raman spectrum of the aromatic diol compound (e.g., bisphenol A) or the alcohol (e.g., ethanol) involved in the reaction generated by the depolymerization reaction of the polycarbonate resin can be confirmed in real time by an online Raman probe, thereby indirectly predicting the real-time changes in the concentration and content of the aromatic diol compound (or alcohol). More specifically, the PLS (partial least squares) prediction model can be ensured by the correlation between the Raman spectral data and the concentration and content values ​​obtained by HPLC analysis.

[0060] The Raman measuring device can be manufactured to withstand the reaction pressure, and then inserted into the reactor where the depolymerization reaction is carried out to collect the reaction information in real time. One end of the Raman probe can be in contact with the reactants of the depolymerization reaction, and the other end can be connected to a computer so that the obtained Raman spectrum can be analyzed in real time. For the specific details of the Raman probe, any conventionally known content can be applied without limitation. However, as an example, a ball probe can be used.

[0061] In a specific example of monitoring the Raman spectrum, the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed may include the step of measuring the integrated ratio of the aromatic diol compound according to the following Mathematical Formula 1:

[0062] [Mathematical formula 1]

[0063] The integral ratio of the aromatic diol compound = {791.2 cm on the Raman spectrum -1 To 861.5cm -1 The integral value of the area / (663.4cm on the Raman spectrum -1 To 785.1cm -1 The integral value of the area + 234.8cm on the Raman spectrum -1 To 337.1cm -1 The integral value of the area)}

[0064] In mathematical formula 1, 791.2 cm -1 To 861.5cm -1 The region is the spectrum of aromatic diol compounds,

[0065] 663.4cm in Raman spectrum -1 To 785.1cm -1 and 234.8cm -1 To 337.1cm -1 The region is the spectrum of the reaction solvent.

[0066] In Mathematical Formula 1, since the dichloromethane component used as the depolymerization reaction solvent does not participate in the depolymerization reaction, the Raman band integral value of the reaction solvent is set as the standard value in the denominator, and then the Raman band integral value of the aromatic diol compound is taken as the numerator to calculate the relative integral value.

[0067] The integrated ratio of the aromatic diol compound according to Mathematical Formula 1 has a value between 0 and 0.15, starts from 0 to 0.06 at the start of the depolymerization reaction, rapidly increases to 0.1 or more or 0.1 to 0.11 within 30 minutes after the start of the reaction, and shows a tendency to converge to a value between 0.11 and 0.15, or between 0.11 and 0.13, or between 0.110 and 0.125, or between 0.115 and 0.125, or between 0.115 and 0.122, or between 0.12 and 0.122 after 30 minutes.

[0068] Based on the understanding of this trend, it is confirmed that when the integral ratio of the aromatic diol compound according to Mathematical Formula 1 is 0.115 to 0.125, or 0.115 to 0.122, or 0.12 to 0.122, the termination of the depolymerization reaction can achieve the recovery of high-purity and high-yield aromatic diol compounds while ensuring process efficiency. When the integral ratio of the aromatic diol compound according to Mathematical Formula 1 is reduced to less than 0.115, it is difficult to fully ensure the yield of the aromatic diol compound. On the other hand, when the integral ratio of the aromatic diol compound according to Mathematical Formula 1 is increased to more than 0.125, impurities other than the aromatic diol compound (for example, impurities from the aromatic diol compound) increase, which makes it difficult to fully ensure the purity of the aromatic diol compound, and there is a limitation that the reaction time is too long, resulting in a reduction in process efficiency.

[0069] Meanwhile, the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed may be repeated at time intervals of 5 minutes or less. Specifically, the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed may be repeated at time intervals of 5 minutes or less, or 4 minutes or less, or 3 minutes or less during the depolymerization reaction.

[0070] As the time interval for monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction becomes shorter, the optimal reaction endpoint can be found more accurately and the generation of reaction by-products can be minimized.

[0071] Furthermore, in another specific example of monitoring the Raman spectrum, the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed may include the step of measuring the integrated ratio of the alcohol according to the following Mathematical Formula 2:

[0072] [Mathematical formula 2]

[0073] The integral ratio of alcohol = {849.7 cm on Raman spectrum -1 To 910cm -1 The integral value of the area / (663.4cm on the Raman spectrum -1 To 785.1cm -1 The integral value of the area + 234.8cm on the Raman spectrum -1 To 337.1cm -1 The integral value of the area)}

[0074] In formula 2, 849.7 cm in the Raman spectrum -1 To 910cm -1 The region is the spectrum of alcohol, 663.4 cm in the Raman spectrum -1 To 785.1cm -1and 234.8cm -1 To 337.1cm -1 The region is the spectrum of the reaction solvent.

[0075] In Mathematical Formula 2, since the dichloromethane component used as the depolymerization reaction solvent does not participate in the depolymerization reaction, the Raman band integral value of the reaction solvent is set as the standard value in the denominator, and then the Raman band integral value of the alcohol is taken as the numerator to calculate the relative integral value.

[0076] The integrated ratio of alcohol according to Mathematical Formula 2 has a value between 0 and 1.1, which starts from 0.15 or more, or 0.15 to 1.1, at the start of the depolymerization reaction, then rapidly decreases to 0.11 or less, or 0.1 to 0.11 within 30 minutes after the start of the reaction, and then tends to converge to a value between 0.09 and 0.1, or between 0.095 and 0.1 after 30 minutes.

[0077] Based on the understanding of this trend, it is confirmed that when the integral ratio of the alcohol according to Mathematical Formula 2 is 0.09 to 0.1, or 0.095 to 0.1, terminating the depolymerization reaction can achieve recovery of high-purity and high-yield aromatic diol compounds while ensuring process efficiency. When the integral ratio of the alcohol according to Mathematical Formula 2 increases to more than 0.1, it is difficult to fully ensure the yield of the aromatic diol compound. On the other hand, when the integral ratio of the alcohol according to Mathematical Formula 2 decreases to less than 0.09, impurities other than the aromatic diol compound (for example, impurities from the aromatic diol compound) increase, which makes it difficult to fully ensure the purity of the aromatic diol compound, and there is a limitation that the reaction time is too long, resulting in a reduction in process efficiency.

[0078] In addition, the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed can be repeated at time intervals of 5 minutes or less. Specifically, the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed can be repeated at time intervals of 5 minutes or less, or 4 minutes or less, or 3 minutes or less during the depolymerization reaction. As the time interval for monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction is shorter, the optimal reaction endpoint can be found more accurately, and the generation of reaction by-products can be minimized.

[0079] Meanwhile, the step of monitoring the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed may further include the step of monitoring the Raman spectrum of impurities from the aromatic diol compound generated by the depolymerization reaction.

[0080] Impurities from the aromatic diol compound are byproducts generated when the depolymerization reaction is excessively performed, and there is a problem of reducing the purity of bisphenol A, which is the aromatic diol compound to be recovered. Therefore, the Raman spectrum of the impurities from the aromatic diol compound generated by the depolymerization reaction is monitored in real time to monitor the generation of reaction byproducts in real time and minimize the byproducts, thereby being able to recover the aromatic diol compound with high purity and high yield.

[0081] The impurities derived from the aromatic diol compound refer to all substances other than the aromatic diol compound which is the main substance to be recovered in the present disclosure, and there is no particular limitation on the specific type thereof, but an example thereof may be p-tert-butylphenol.

[0082] Specifically, the step of monitoring the Raman spectrum of impurities from the aromatic diol compound generated by the depolymerization reaction may include the step of measuring an integrated ratio of impurities from the aromatic diol compound according to the following Mathematical Formula 3:

[0083] [Mathematical formula 3]

[0084] The integrated ratio of impurities from aromatic diol compounds = {800 cm-1 on Raman spectrum -1 Up to 850cm -1 The integral value of the area / (663.4cm on the Raman spectrum -1 To 785.1cm -1 The integral value of the area + 234.8cm on the Raman spectrum -1 To 337.1cm -1 The integral value of the area)}

[0085] In formula 3, 800 cm -1 Up to 850cm -1 This region is the spectrum of impurities from aromatic diol compounds, with 663.4 cm in the Raman spectrum. -1 To 785.1cm -1 and 234.8cm -1 To 337.1cm -1 The region is the spectrum of the reaction solvent.

[0086] In Mathematical Formula 3, since the dichloromethane component used as the depolymerization reaction solvent does not participate in the depolymerization reaction, the Raman band integral value of the reaction solvent is set as the standard value in the denominator, and then the Raman band integral value of the impurity from the aromatic diol compound is used as the numerator to calculate the relative integral value.

[0087] When the integral ratio of impurities derived from the aromatic diol compound exceeds 0.12 according to Mathematical Formula 3, terminating the depolymerization reaction can achieve recovery of the aromatic diol compound with high purity and high yield while ensuring process efficiency. When the integral ratio of impurities derived from the aromatic diol compound according to Mathematical Formula 3 increases to more than 0.12, impurities other than the aromatic diol compound (for example, impurities derived from the aromatic diol compound) increase, which makes it difficult to fully ensure the purity of the aromatic diol compound, and there is a limitation that the reaction time is too long, resulting in a decrease in process efficiency.

[0088] At the same time, the preparation method of the monomer composition for synthesizing recycled plastics may include the step of recovering the aromatic diol compound obtained from the depolymerization reaction. Specific examples of the aromatic diol compound include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), 2,2-bis(4-hydroxyphenyl) 1,1-bis(4-hydroxyphenyl)-1-phenylethane, or a mixture of two or more thereof. Preferably, the aromatic diol compound of the monomer composition for synthesizing recycled plastics of one embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0089] Specifically, the step of recovering the aromatic diol compound obtained from the depolymerization reaction may further include the step of adding an acid so that the pH of the depolymerization reaction product becomes 2 to 8. A strong acid may be used as the acid, and examples thereof include hydrochloric acid (HCl).

[0090] In the step of adding an acid so that the pH of the depolymerization reaction product becomes 2 to 8, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted into the aromatic diol compound. Since the depolymerization reaction is carried out under alkaline conditions, the resulting aromatic diol compound exists in the form of a salt when reacting with the base, and thus has hydrophilicity. Therefore, by adding an acid, the salt of the aromatic diol compound contained in the depolymerization reaction product can be converted into the aromatic diol compound, thereby making it hydrophobic.

[0091] Therefore, in the step of adding water to remove impurities after adding acid to be described later, a layer can be formed that is divided into a water layer containing impurities and an organic solvent layer containing aromatic diol compounds and carbonate precursors. Because aromatic diol compounds and carbonate precursors have hydrophobicity, they can be contained in the organic solvent layer among water and organic solvents, and various water-soluble impurities can be contained in the water layer. Therefore, the main product, i.e. aromatic diol compounds and impurities, can be easily separated by only the simple step of changing pH.

[0092] Meanwhile, the step of adding an acid so that the pH of the depolymerized product is 2 to 8 may further include the step of adding water. Therefore, in the step of removing impurities to be described later, a layer separated into a water layer containing impurities and an organic solvent layer containing an aromatic diol compound and a carbonate precursor may be formed.

[0093] The order of the step of adding the acid and the step of adding the water is not particularly limited, and the water may be added after the acid is added, the acid may be added after the water is added, or the water and the acid may be added simultaneously.

[0094] Meanwhile, the step of recovering the aromatic diol compound obtained from the depolymerization reaction may include a step of removing impurities after adding an acid. Therefore, the impurity is a material having hydrophilicity, and examples thereof may include salt compounds, ion compounds, acid compounds, and the like.

[0095] As described above, after the step of adding an acid so that the pH of the depolymerization reaction product is 2 to 8, as the step of removing impurities from the depolymerization reaction product after the addition of the acid proceeds, the depolymerization reaction product forms a layer separated into an aqueous layer containing impurities and an organic solvent layer containing the aromatic diol compound and the carbonate precursor, and thus the aqueous layer containing impurities can be separated and removed.

[0096] In the step of removing impurities from the depolymerization reaction product after adding the acid, the aqueous layer may be separated from the organic layer to remove impurities contained in the aqueous layer. There is no particular limitation on the specific separation conditions for separating the aqueous layer from the organic layer. For the specific separation device and method, various known purification techniques may be applied without limitation. However, as an example, a drain device may be used.

[0097] Meanwhile, the step of recovering the aromatic diol compound obtained from the depolymerization reaction may include the step of separating the carbonate precursor from the depolymerization reaction product. Therefore, the separated carbonate precursor may include diethyl carbonate.

[0098] The step of separating the carbonate precursor from the depolymerization reaction product may include a reduced pressure distillation step of the depolymerization product. Examples of reduced pressure distillation conditions are not particularly limited, but in a specific example, the product of the depolymerization reaction of the polycarbonate resin is pressurized at a pressure of 200 to 300 mbar and a temperature of 20° C. to 30° C., and then reduced pressure at a pressure of 10 to 50 mbar and a temperature of 20° C. to 30° C. and subjected to low temperature distillation.

[0099] The separated carbonate precursor can be recycled without independent purification process, or can be recycled by separation and purification such as conventional extraction, adsorption and drying when necessary. There is no particular restriction on specific purification conditions. For specific purification device and method, various known purification techniques can be applied without restriction.

[0100] Meanwhile, after the step of separating the carbonate precursor from the depolymerization reaction product, the step of recovering the aromatic diol compound obtained from the depolymerization reaction may further include a step of purifying the depolymerization reaction product from which the carbonate precursor has been separated.

[0101] Specifically, the step of purifying the depolymerization reaction product of the separated carbonate precursor may include the step of washing the depolymerization reaction product of the separated carbonate precursor. In addition, the step of purifying the depolymerization reaction product of the separated carbonate precursor may include the step of adsorption purification of the depolymerization reaction product of the separated carbonate precursor. In addition, the step of purifying the depolymerization reaction product of the separated carbonate precursor may include the step of recrystallizing the depolymerization reaction product of the separated carbonate precursor.

[0102] There is no particular limitation on the order of the washing step, the adsorption purification step or the recrystallization step, and it does not matter whether they are performed in any order, but for example, they may be performed in the order of the washing step, the adsorption purification step and the recrystallization step. The washing step, the adsorption purification step and the recrystallization step may be repeated at least once or more times. For specific washing, adsorption and recrystallization equipment and methods, various well-known purification techniques may be applied without limitation.

[0103] Specifically, in the washing step of the depolymerization reaction product from which the carbonate precursor has been separated, the depolymerization reaction product from which the carbonate precursor has been separated may contain an aromatic diol compound. However, since various impurities remain during the recovery process for obtaining the aromatic diol compound, washing may be performed to fully remove these impurities and ensure a high-purity aromatic diol compound.

[0104] Specifically, the washing step may include a step of washing 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 in the washing container where the solvent washing is performed. In order to maintain a high temperature deviating from the room temperature, various heating devices may be applied without limitation.

[0105] The solvent used in the washing step may include one of water, alcohol and an organic solvent. As the organic solvent, tetrahydrofuran, toluene, dichloromethane, chloroform, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixture of two or more thereof may be used.

[0106] The solvent used in the washing step may be used in a weight ratio of 1 part by weight to 30 parts by weight, or 1 part by weight to 10 parts by weight, based on 1 part by weight of the polycarbonate-based resin used in the depolymerization reaction.

[0107] More specifically, the solvent in the step of washing with a solvent at a temperature of 10° C. to 30° C. may be an organic solvent. Preferably, dichloromethane may be used as the organic solvent. At this time, the organic solvent may be used in an amount of 1 part by weight to 10 parts by weight based on 1 part by weight of the polycarbonate resin.

[0108] In addition, the step of subjecting the depolymerization reaction product of the separated carbonate precursor to adsorption purification may include the steps of adding an adsorbent to the depolymerization reaction product of the separated carbonate precursor for adsorption purification and then removing the adsorbent. In the step of adding an adsorbent to the depolymerization reaction product of the separated carbonate precursor for adsorption purification and then removing the adsorbent, the adsorbent may be brought into contact with the depolymerization reaction product.

[0109] Examples of adsorbents that can be used include activated carbon, charcoal, or a mixture thereof. Activated carbon is a black carbon material having micropores produced by subjecting a raw material to a carbonization process at about 500° C. and an activated carbon process at about 900° C. Examples of activated carbon are not particularly limited, but for example, various activated carbons such as plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon can be applied without limitation depending on the type of raw material.

[0110] In a more specific example, the plant-based activated carbon may include coconut activated carbon, wood activated carbon and sawdust activated carbon. In addition, the coal-based activated carbon may include lignite activated carbon, bituminous coal activated carbon and anthracite activated carbon. In addition, the petroleum-based activated carbon may include petroleum coke activated carbon and oil charcoal activated carbon. In addition, the waste-based activated carbon may include synthetic resin activated carbon and pulp activated carbon.

[0111] The adsorbent may include at least one activated carbon selected from the group consisting of plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, and waste-based activated carbon. That is, the adsorbent may include plant-based activated carbon, coal-based activated carbon, petroleum-based activated carbon, waste-based activated carbon, or a mixture of two or more thereof.

[0112] More specifically, the adsorbent may include at least one activated carbon selected from the group consisting of coconut activated carbon, lignite activated carbon, anthracite activated carbon, and bituminous coal activated carbon. That is, the adsorbent may include coconut activated carbon, lignite activated carbon, anthracite activated carbon, bituminous coal activated carbon, or a mixture of two or more thereof.

[0113] There is no particular limitation on the adsorption purification conditions by the adsorbent, and various known adsorption purification conditions can be used without limitation. However, in one example, the adsorbent may be added in an amount of 40% to 60% by weight relative to the polycarbonate resin, the adsorption time may be 1 to 5 hours, and the adsorption method may be stirring adsorption or an adsorption tower for laboratory use.

[0114] If necessary, described method can further be included in the step of adding sorbent to carry out adsorption purification and then removing sorbent in the depolymerization reaction product of separated carbonate precursor, and in the depolymerization reaction product of separated carbonate precursor, add solvent.The example of solvent comprises ethanol, and relative to 1 mole of polycarbonate resin, ethanol can add with 1 mole to 20 mole or 10 mole to 20 mole or 15 mole to 20 mole ratio.By in the depolymerization reaction product of separated carbonate precursor, add solvent step, the aromatic diol compound crystal contained in the depolymerization reaction product of separated carbonate precursor can be dissolved in the solvent again.

[0115] Meanwhile, in the recrystallization step of the depolymerization reaction product of the separated carbonate precursor, a high-purity aromatic diol compound can be ensured by sufficiently removing various impurities contained in the depolymerization product of the separated carbonate precursor.

[0116] Specifically, the recrystallization step may include a step of adding water to the depolymerization reaction product of the separated carbonate precursor for recrystallization. By adding water to the depolymerization reaction product of the separated carbonate precursor for recrystallization, the solubility of the aromatic diol compound or its salt contained in the depolymerization reaction product increases, so that the crystals or impurities interposed between the crystals can be dissolved to the greatest extent with the solvent, and further, since the dissolved aromatic diol compound has a poor solubility relative to the impurities, when the temperature is subsequently lowered, the aromatic diol compound can be easily precipitated into aromatic diol compound crystals by the difference in solubility.

[0117] More specifically, in the step of adding water to carry out recrystallization in the depolymerization reaction product of separated carbonate precursor, relative to 1 mole of polycarbonate resin, can use 200 moles to 400 moles or 250 moles to 350 moles of water.When using water with too little amount, the temperature of the aromatic diol compound included in the depolymerization reaction product of separated carbonate precursor for dissolving becomes too high, thereby reduces process efficiency, and is not easy to remove impurity by recrystallization.On the other hand, when using water with excessive amount, the solubility of the aromatic diol compound included in the depolymerization reaction product of separated carbonate precursor becomes too high, therefore, the yield of the aromatic diol compound reclaimed after the recrystallization reduces, and owing to using a large amount of solvents, process efficiency may reduce.

[0118] If necessary, after the step of recrystallizing the depolymerization reaction product from which the carbonate precursor has been separated is performed, a step of removing residual impurities by filtration or adsorption may be further performed.

[0119] In addition, if necessary, after the recrystallization step, the method may further include a drying step. The residual solvent may be removed by drying, and there is no particular limitation on the specific drying conditions, but for example, the drying may be performed at a temperature of 10° C. to 100° C., or 10° C. to 50° C. For the specific drying equipment and method used in the drying, various known drying techniques may be applied without limitation.

[0120] 2. Preparation device for monomer composition for synthesizing recycled plastics

[0121] According to another embodiment of the present invention, there may be provided a device for preparing a monomer composition for synthesizing recycled plastics, comprising: a reactor for subjecting a polycarbonate resin to a depolymerization reaction in the presence of an alcohol; an online analyzer inserted into the reactor to monitor the Raman spectrum of an aromatic diol compound or alcohol obtained from the depolymerization reaction; and a recovery unit for recovering the aromatic diol compound obtained from the depolymerization reaction.

[0122] The details of depolymerizing the polycarbonate resin in the presence of alcohol include all the contents described in the above embodiment. The specific shape, material and size of the reactor are not particularly limited, and various reactors widely used in conventional polymer depolymerization reactions can be applied without limitation.

[0123] The details of the Raman spectrum inserted into the reactor to monitor the aromatic diol compound or alcohol obtained from the depolymerization reaction include all those described in the above one embodiment.

[0124] The online analyzer may include a Raman probe. The Raman probe may be manufactured to withstand the reaction pressure and then inserted into the reactor where the depolymerization reaction is carried out to collect reaction information in real time. One end of the Raman probe may be in contact with the reactant of the depolymerization reaction, and the other end may be connected to a computer so that the obtained Raman spectrum may be analyzed in real time. Specifically, the values ​​of mathematical formulas 1, 2, and 3 in the embodiment may be analyzed by a computer.

[0125] The online analyzer may include a detection unit in contact with the reactants in the reactor. In addition, the preparation device may further include a computer for analyzing the Raman spectrum measured by the online analyzer. One end of the online analyzer may be in contact with the reactants in the reactor, and the other end may be connected to the computer to analyze the spectrum obtained in real time.

[0126] The details of recovering the aromatic diol compound obtained from the depolymerization reaction in the recovery unit include all the contents described in the above embodiments. There is no particular limitation on the specific shape, material and size of the recovery unit, and various recovery equipment that has been widely used in conventional polycarbonate depolymerization reactions can be applied without limitation. However, for example, a distillation device, a washing device, a filtering device, a recrystallization device, etc. can be used in the recovery unit.

[0127] There is no particular limitation on the specific example of the preparation device for the monomer composition for synthesizing recycled plastics according to another embodiment of the present invention, but as an example, refer to Figure 3 , which may include a reactor 1 for subjecting a polycarbonate-based resin to a depolymerization reaction in the presence of an alcohol; an online analyzer 2 inserted into the reactor to monitor the Raman spectrum of an aromatic diol compound or alcohol obtained from the depolymerization reaction; and a recovery unit 5 for recovering the aromatic diol compound obtained from the depolymerization reaction. More specifically, the online analyzer may include a detection unit 3 in contact with the reactants in the reactor. In addition, the preparation apparatus may further include a computer 4 for analyzing the Raman spectrum measured by the online analyzer.

[0128] 3. Monomer composition for synthesizing recycled plastics

[0129] According to another embodiment of the present invention, a monomer composition for synthesizing recycled plastics can be provided, comprising an aromatic diol compound obtained by a method for preparing a monomer composition for synthesizing recycled plastics according to one embodiment, or a device for preparing a monomer composition for synthesizing recycled plastics according to another embodiment.

[0130] That is, the monomer composition for recycled plastic synthesis of other embodiments can be obtained by the preparation method of the monomer composition for recycled plastic synthesis of one embodiment. The details of the preparation method of the monomer composition for recycled plastic synthesis of one embodiment include all the contents described in the above one embodiment.

[0131] In addition, the monomer composition for synthesizing recycled plastics of other embodiments can be obtained by the preparation device for synthesizing the monomer composition for recycled plastics of other embodiments. The details of the preparation device for synthesizing the monomer composition for recycled plastics of other embodiments include all the contents described in the above one embodiment.

[0132] Specific examples of the aromatic diol compound include bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfone, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)ketone, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane (bisphenol A), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)cyclohexane (bisphenol Z), 2,2-bis(4-hydroxyphenyl)butane, 1,1-bis(4-hydroxyphenyl)-1-phenylethane, or a mixture of two or more thereof. Preferably, the aromatic diol compound of the monomer composition for synthesizing recycled plastics of one embodiment may be 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).

[0133] The aromatic diol compound is characterized in that it is obtained from the method for preparing a monomer composition for synthesizing recycled plastics according to one embodiment, or obtained from the apparatus for preparing a monomer composition for synthesizing recycled plastics according to other embodiments. That is, the aromatic diol compound is characterized in that it is recovered from a polycarbonate resin used in the recovery of a monomer composition for synthesizing recycled plastics. Therefore, except for recovery from a polycarbonate resin to prepare a monomer composition for synthesizing recycled plastics according to other embodiments, the scope of the aromatic diol compound disclosed in the present invention does not include the case where a new aromatic diol compound is added from the outside.

[0134] Specifically, "recovered from a polycarbonate resin" means obtained by depolymerization of a polycarbonate resin. The depolymerization reaction can be carried out under acidic, neutral or alkaline conditions, and specifically, the depolymerization reaction can be carried out under alkaline conditions. Specifically, the depolymerization reaction can be preferably carried out in the presence of an ethanol solvent, as will be described later.

[0135] 4. Recycled plastic

[0136] According to another embodiment of the present invention, a recycled plastic comprising a reaction product of the monomer composition for synthesizing recycled plastic according to other embodiments and a comonomer may be provided.

[0137] The details of the monomer composition for synthesizing recycled plastics of other embodiments include all the contents described in the other embodiments above.

[0138] There is no particular limitation on examples corresponding to recycled plastics, and various plastics synthesized from aromatic diol compounds such as bisphenol A and carbonate precursors such as dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate as monomers can be applied without limitation, and a more specific example may be a polycarbonate resin.

[0139] Polycarbonate resin is intended to include homopolymers and copolymers comprising polycarbonate repeating units, and is collectively referred to as the reaction product obtained by the polymerization reaction or copolymerization reaction of the monomer comprising aromatic diol compound and carbonate precursor. When polycarbonate resin comprises a type of carbonate repeating unit obtained by only using an aromatic diol compound and a type of carbonate compound, homopolymer can be synthesized. In addition, when using an aromatic diol compound and two or more types of carbonate compounds as monomers, or when using two or more types of aromatic diol compounds and a type of carbonate compounds, or when using one or more types of other diols to include two or more carbonates except an aromatic diol compound and a type of carbonate compounds, copolymer can be synthesized. According to molecular weight range, homopolymer or copolymer can include all low molecular weight compounds, oligomers and polymers.

[0140] More specifically, in the recycled plastics comprising the reaction product of the monomer composition for synthesizing recycled plastics according to one embodiment and a comonomer, a carbonate precursor can be used as a comonomer. Specific examples of carbonate compounds include phosgene, triphosgene, diphosgene, bromophosgene, dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, diphenyl carbonate, ditolyl carbonate, bis(chlorophenyl) carbonate, m-tolyl carbonate, dinaphthyl carbonate, bis(diphenyl) carbonate or dihaloformate.

[0141] There is no particular limitation on the example of the reaction process for synthesizing the polycarbonate-based resin from the monomer composition for synthesizing recycled plastic and the comonomer, and various known methods for preparing polycarbonate can be applied without limitation.

[0142] However, in one example of the method for preparing polycarbonate, a method for preparing polycarbonate comprising the step of polymerizing a composition comprising a monomer composition for synthesizing recycled plastic and a comonomer can be used. In this case, polymerization can be performed by interfacial polymerization, and during the interfacial polymerization, the polymerization reaction can be performed at normal pressure and low temperature, and the molecular weight is easily controlled.

[0143] The polymerization temperature may be 0° C. to 40° C., and the reaction time may be 10 minutes to 5 hours. In addition, during the reaction, the pH may be maintained at 9 or above or 11 or above.

[0144] There is no particular limitation on the solvent that can be used for the polymerization as long as it is a solvent used for the polymerization of polycarbonate in the art, and as examples, halogenated hydrocarbons such as methylene chloride and chlorobenzene can be used.

[0145] Furthermore, the polymerization may be carried out in the presence of an acid binder. As the acid binder, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide, or an amine compound such as pyridine may be used.

[0146] In addition, in order to regulate the molecular weight of polycarbonate in the process of polymerization, polymerization can be carried out in the presence of a molecular weight regulator. Alkylphenols with carbon atoms of 1 to 20 can be used as molecular weight regulators, and its specific examples include p-tert-butylphenol, p-cumylphenol, decylphenol, dodecylphenol, tetradecylphenol, hexadecylphenol, octadecylphenol, eicosylphenol, docosylphenol or triacontylphenol. Molecular weight regulators can be added before polymerization initiation, during polymerization initiation or after polymerization initiation. Based on the aromatic diol compound of 100 weight parts, the consumption of molecular weight regulator can be 0.01 weight part to 10 weight parts or 0.1 weight part to 6 weight parts, and the molecular weight desired can be obtained within this range.

[0147] Furthermore, in order to promote the polymerization reaction, a reaction accelerator such as a tertiary amine compound, a quaternary ammonium compound or a quaternary phosphonium compound including triethylamine, tetra-n-butylammonium bromide or tetra-n-butylphosphonium bromide may be further used.

[0148] 5. Molded products

[0149] According to another embodiment of the present invention, a molded product comprising the recycled plastic according to another embodiment may be provided. The details of the recycled plastic include all the contents described above in another embodiment.

[0150] The molded product can be obtained by applying the recycled plastic to various known plastic molding methods without limitation. As examples of the molding method, injection molding, foam injection molding, blow molding or extrusion molding can be mentioned.

[0151] There is no particular limitation on examples of molded products, and it can be applied to various molded products using plastics without limitation. Examples of molded products include automobiles, electric and electronic products, communication products, daily necessities, building materials, optical components, exterior materials, and the like.

[0152] In addition to the recycled plastic according to other embodiments, the molded article may further include one or more additives selected from the group consisting of antioxidants, plasticizers, antistatic agents, nucleating agents, flame retardants, lubricants, impact enhancers, optical brighteners, ultraviolet absorbers, pigments and dyes, if necessary.

[0153] An example of a method for producing a molded article may include the steps of well mixing the recycled plastic according to another embodiment with an additive using a mixer, extrusion-molding the mixture with an extruder to produce pellets, drying the pellets, and then injecting the pellets with an injection molding machine.

[0154] Beneficial Effects

[0155] According to the present disclosure, a method for preparing a monomer composition for synthesizing recycled plastics, a device for preparing a monomer composition for synthesizing recycled plastics, a monomer composition for synthesizing recycled plastics, recycled plastics and a molded product using the recycled plastics can be provided, wherein the process of recovering aromatic diol compounds by chemical decomposition of polycarbonate resins is monitored in real time to optimize reaction conditions and improve efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0156] Figure 1 Raman spectra obtained in Examples are shown.

[0157] Figure 2 The integrated ratio of the aromatic diol compound obtained in Example 1 and the integrated ratio of the alcohol are shown.

[0158] Figure 3 A schematic diagram showing a preparation apparatus for a monomer composition for synthesizing recycled plastics. DETAILED DESCRIPTION

[0159] Hereinafter, the present disclosure will be explained in detail with reference to the following examples. However, these examples are for illustrative purposes only, and the scope of the present disclosure is not limited thereto.

[0160] <Examples and Comparative Examples: Preparation of Regenerated Bisphenol A Monomer Composition>

[0161] Example 1

[0162] (1. Decomposition step) 1 mol of waste polycarbonate (PC) was added to the reactor 1 and dissolved using dichloromethane (MC), and then impurities were filtered out. Then, 11 mol of ethanol (EtOH), 0.2 mol of sodium hydroxide (NaOH) and an antioxidant were added thereto, and stirred at 60°C to perform a PC depolymerization reaction.

[0163] During the PC depolymerization reaction, the online analyzer 2, i.e., the Raman probe, was inserted into the reactor 1 and arranged so that the detection unit 3 would not be disturbed by the viscosity of the polycarbonate (PC) during the stirring process. The Raman spectrum was measured at fixed time intervals (about 3 minutes) for a total of 6 hours after the start of the reaction, and a computer 4 program was used for real-time analysis, and the reaction was terminated at the optimal reaction point (BPA / MC Raman integral ratio = 0.12).

[0164] (2. pH Adjustment) The product of the depolymerization reaction was cooled to below 30°C and then adjusted to pH 8 by adding 10% hydrochloric acid (HCl) and water.

[0165] (3. Layer Separation) After that, in a state where a water layer and a methylene chloride (MC) layer are formed, the organic layer located on the lower side is recovered using a discharge device located at the lower end of the reactor, and the water layer located on the upper side is discharged and then discarded.

[0166] (4. Distillation) After that, the recovered methylene chloride (MC) layer is moved to the recovery unit 5, and the by-product diethyl carbonate (DEC) is separated and recovered by reducing the pressure from 250 mbar at 20-30°C to 30 mbar at 30°C by low-temperature distillation.

[0167] (5. Purification step - filtration) After that, the residue from which diethyl carbonate (DEC) was removed was washed with dichloromethane (MC) twice the weight of the PC used at 20-30°C and vacuum filtered.

[0168] (6-1. Additional Purification Step - Redissolution Step) Thereafter, bisphenol A was added to 16.6 mol of ethanol and re-dissolved.

[0169] (6-2. Additional Purification Step - Adsorption Step) Thereafter, lignite activated carbon was added as an adsorbent at a ratio of 30 wt % relative to the waste polycarbonate, purified by an adsorption tower for 3 hours, and then filtered to remove the lignite activated carbon.

[0170] (6-3. Additional Purification Step - Recrystallization Step) After that, water is added to recrystallize bisphenol A, and the resulting slurry is vacuum filtered at 20-30° C. to recover bisphenol A (BPA) crystals.

[0171] (7. Drying Step) Thereafter, the product was vacuum dried in a convection oven at 40° C. to prepare a recovered bisphenol A monomer composition from which bisphenol A (BPA) had been recovered.

[0172] Example 2

[0173] A recovered bisphenol A monomer composition was prepared in the same manner as in Example 1, except that (1. decomposition step) of Example 1 was changed as follows.

[0174] (1. Decomposition step) 1 mol of waste polycarbonate (PC) was added to the reactor 1, and dissolved using dichloromethane (MC), and then impurities were filtered out. Then, 11 mol of ethanol (EtOH), 0.2 mol of sodium hydroxide (NaOH) and an antioxidant were added thereto, and stirred at 80°C to perform a PC depolymerization reaction.

[0175] During the PC depolymerization reaction, the online analyzer 2, i.e., the Raman probe, is inserted into the reactor 1 and is arranged so that the detection unit 3 is not disturbed by the viscosity of the polycarbonate (PC) during the stirring process. The Raman spectrum is measured at fixed time intervals (about 3 minutes) for a total of 6 hours after the start of the reaction, and a computer 4 is used for real-time analysis, and the reaction is terminated at the optimal reaction point (BPA / MC Raman integral ratio = 0.12).

[0176] <Experimental example>

[0177] The physical properties were measured by the following methods and the results are shown in Tables 1 and 2 and Figure 1 and Figure 2 shown.

[0178] 1. Raman spectroscopy analysis results

[0179] (1) Integral ratio of aromatic diol compounds

[0180] In (1. Decomposition step) of the embodiment, the integral ratio of bisphenol A (BPA) as an aromatic diol compound was obtained at fixed time intervals (about 3 minutes) within a total of 6 hours after the start of the PC depolymerization reaction by an online Raman analyzer. The integral ratios of Example 1 are shown in Tables 1 and Figure 2 The integral ratio of Example 2 is shown in Table 2. Specifically, the integral ratio of the aromatic diol compound (BPA) can be calculated according to the following mathematical formula 1: -1 To 861.5cm -1 ) divided by the integral value of the MC band (663.4cm -1 To 785.1cm -1 and 234.8cm -1 To 337.1cm -1 ) is calculated by the integral value:

[0181] [Mathematical formula 1]

[0182] The integral ratio of the aromatic diol compound = {791.2 cm on the Raman spectrum -1 To 861.5cm -1 The integral value of the area / (663.4cm on the Raman spectrum -1 To 785.1cm -1 The integral value of the area + 234.8cm on the Raman spectrum -1 To 337.1cm -1 The integral value of the area)}

[0183] In mathematical formula 1, 791.2 cm -1 To 861.5cm -1 The region is the spectrum of bisphenol A (BPA), 663.4 cm in the Raman spectrum -1 To 785.1cm -1 and 234.8cm -1 To 337.1cm -1 The region is the spectrum of dichloromethane (MC).

[0184] Raman analysis was performed using a MarqMetrix all-in-one device and a spherical probe. The spectra were measured in real time in the reactor under the conditions of an excitation laser (785 nm, 400 Mw) and baseline correction was performed linearly in the region of each component of MC and BPA.

[0185] (2) Integral ratio of alcohol

[0186] In (1. Decomposition step) of the embodiment, the integral ratio of ethanol (EtOH) as alcohol was obtained at fixed time intervals (about 3 minutes) within a total of 6 hours after the start of the PC depolymerization reaction by an online Raman analyzer. The integral ratios of Example 1 are shown in Tables 1 and Figure 2 The integral ratio of Example 2 is shown in Table 2. Specifically, the integral ratio of alcohol (EtOH) can be obtained according to the following mathematical formula 2: -1 To 910cm -1 ) divided by the integral value of the MC band (663.4cm -1 To 785.1cm -1 and 234.8cm -1 To 337.1cm -1 ) is calculated by the integral value:

[0187] [Mathematical formula 2]

[0188] The integral ratio of alcohol = {849.7 cm on Raman spectrum -1 To 910cm-1 The integral value of the area / (663.4cm on the Raman spectrum -1 To 785.1cm -1 The integral value of the area + 234.8cm on the Raman spectrum -1 To 337.1cm -1 The integral value of the area)}

[0189] In formula 2, 849.7 cm in the Raman spectrum -1 To 910cm -1 The region is the spectrum of ethanol (EtOH), 663.4 cm in the Raman spectrum -1 To 785.1cm -1 and 234.8cm -1 To 337.1cm -1 The region is the spectrum of dichloromethane (MC).

[0190] Raman analysis was performed using a MarqMetrix all-in-one instrument and a spherical probe. The spectra were measured in real time in the reactor under the conditions of an excitation laser (785 nm, 400 Mw) and baseline correction was performed linearly in the region of each component of EtOH and BPA.

[0191] 2. BPA Purity

[0192] In (1. Decomposition step) of the embodiment, the depolymerization reaction was carried out at fixed time intervals (about 3 minutes) for a total of 6 hours after the start of the PC depolymerization reaction, and the weight of bisphenol A (BPA) generated from the reaction was confirmed by HPLC measurement. The weight of BPA generated when the polycarbonate used in the reaction was 100% decomposed was measured, and the yield of BPA was calculated according to the following equation 4.

[0193] [Equation 4]

[0194] Yield (%) = (W1 / W0) * 100

[0195] In equation 4, W0 is the mass of BPA obtained when 100% is decomposed, and W1 is the mass of BPA actually obtained. Specifically, when about 100g of polycarbonate is decomposed, the mass of BPA obtained when 100% is theoretically decomposed is 89g. If the mass of BPA actually obtained is 80g, the yield is (80 / 89)*100=90%.

[0196] [Table 1]

[0197] Experimental Example Measurement Results of Example 1

[0198] Measurement results (min) Mathematical formula 1 Mathematical formula 2 BPA yield (%) 3 0.05 0.18 9.8 6 0.082 0.179 16.8 16 0.101 0.17 30.9 25 0.105 0.11 55.8 36 0.106 0.105 66.2 55 0.111 0.10 78.3 70 0.112 0.098 82.1 80 0.113 0.097 83.6 120 0.12 0.095 90.1

[0199] [Table 2]

[0200] Experimental results of Example 2

[0201] Measurement results (min) Mathematical formula 1 BPA yield (%) 3 0.06 9.3 6 0.09 17.1 16 0.105 31.1 25 0.11 65.4 60 0.115 88.1 70 0.116 89.9 80 0.118 90.1 90 0.12 90.2 100 0.122 92.1

Claims

1. A method for preparing a monomer composition for synthesizing recycled plastics, the method comprising the following steps: Depolymerizing a polycarbonate resin in the presence of an alcohol; monitoring a Raman spectrum of the aromatic diol compound or the alcohol obtained from the depolymerization reaction in a reactor where the depolymerization reaction is performed; as well as The aromatic diol compound is recovered.

2. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: monitoring the Raman spectrum of the aromatic diol compound or the alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed, This is done by a Raman spectroscopy measurement device inserted into the reactor.

3. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: monitoring the Raman spectrum of the aromatic diol compound or the alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed, The method comprises measuring the integrated ratio of the aromatic diol compound according to the following mathematical formula 1: [Mathematical formula 1] Integration ratio of aromatic diol compound = {integral value of 791.2 cm-1 to 861.5 cm-1 region on Raman spectrum / (integral value of 663.4 cm-1 to 785.1 cm-1 region on Raman spectrum + integrated value of 234.8 cm-1 to 337.1 cm-1 region on Raman spectrum)} In Mathematical Formula 1, the region from 791.2 cm-1 to 861.5 cm-1 on the Raman spectrum is the spectrum of the aromatic diol compound. The regions from 663.4 cm-1 to 785.1 cm-1 and from 234.8 cm-1 to 337.1 cm-1 on the Raman spectrum are the spectra of the reaction solvent.

4. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 3, wherein: When the integration ratio of the aromatic diol compound according to Mathematical Formula 1 is 0.115 to 0.125, the depolymerization reaction is terminated.

5. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: monitoring the Raman spectrum of the aromatic diol compound or the alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed, It includes measuring the integrated ratio of alcohol according to the following mathematical formula 2: [Mathematical formula 2] The integral ratio of alcohol = {integral value of the region from 849.7 cm-1 to 910 cm-1 on the Raman spectrum / (integral value of the region from 663.4 cm-1 to 785.1 cm-1 on the Raman spectrum + integral value of the region from 234.8 cm-1 to 337.1 cm-1 on the Raman spectrum)} In Mathematical Formula 2, the region from 849.7 cm-1 to 910 cm-1 on the Raman spectrum is the spectrum of the alcohol. The regions from 663.4 cm-1 to 785.1 cm-1 and from 234.8 cm-1 to 337.1 cm-1 on the Raman spectrum are the spectra of the reaction solvent.

6. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 5, wherein: When the integrated ratio of the alcohol according to Mathematical Formula 2 is 0.09 to 0.1, the depolymerization reaction is terminated.

7. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The aromatic diol compound is bisphenol A.

8. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The alcohol is ethanol.

9. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: monitoring the Raman spectrum of the aromatic diol compound or the alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed, Further comprising monitoring a Raman spectrum of impurities of the aromatic diol compound generated from the depolymerization reaction.

10. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 9, wherein: the monitoring of the Raman spectrum of impurities of the aromatic diol compound produced from the depolymerization reaction, It includes measuring the integrated ratio of impurities from the aromatic diol compound according to the following mathematical formula 3: [Mathematical formula 3] The integrated ratio of impurities from the aromatic diol compound = {800 cm-1 to 850 cm-1 on the Raman spectrum 1 The integral value of the area / (the integral value of the area from 663.4cm-1 to 785.1cm-1 on the Raman spectrum + the integral value of the area from 234.8cm-1 to 337.1cm-1 on the Raman spectrum)} In Mathematical Formula 3, the region from 800 cm-1 to 850 cm-1 on the Raman spectrum is a spectrum of impurities derived from the aromatic diol compound. The regions from 663.4 cm-1 to 785.1 cm-1 and from 234.8 cm-1 to 337.1 cm-1 on the Raman spectrum are the spectra of the reaction solvent.

11. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 10, wherein: When the integrated ratio of impurities derived from the aromatic diol compound calculated according to Mathematical Formula 3 is greater than 0.12, the depolymerization reaction is terminated.

12. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: monitoring the Raman spectrum of the aromatic diol compound or the alcohol obtained from the depolymerization reaction in the reactor where the depolymerization reaction is performed, Repeat at intervals of 5 minutes or less.

13. A preparation device for a monomer composition for synthesizing recycled plastics, comprising: A reactor for carrying out a depolymerization reaction of the polycarbonate resin in the presence of an alcohol; an online analyzer inserted into the reactor to monitor the Raman spectrum of the aromatic diol compound or alcohol obtained from the depolymerization reaction; as well as A recovery unit recovers the aromatic diol compound obtained from the depolymerization reaction.

14. The device for preparing a monomer composition for synthesizing recycled plastics according to claim 13, wherein: The online analyzer includes a Raman spectroscopy measurement device.

15. The device for preparing a monomer composition for synthesizing recycled plastics according to claim 13, The method further includes a computer for analyzing the Raman spectrum measured by the online analyzer.

16. The device for preparing a monomer composition for synthesizing recycled plastics according to claim 13, wherein: The online analyzer includes a detection unit in contact with reactants in the reactor.

17. A monomer composition for synthesizing recycled plastics, comprising an aromatic diol compound obtained by the method for preparing a monomer composition for synthesizing recycled plastics according to claim 1 or the apparatus for preparing a monomer composition for synthesizing recycled plastics according to claim 13.

18. A recycled plastic, comprising a reaction product of the monomer composition for synthesizing recycled plastic according to claim 17 and a comonomer.

19. A molded product comprising the recycled plastic according to claim 18.

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