Extracting agent and purification method of monomer of polymer containing ester functional group

Abstract

The present invention relates to an extractant and a method for purifying a monomer of a polymer containing an ester functional group, characterized in that a compound represented by chemical formula 1 is added as an additive. By applying the purification method of the present invention, it is possible to remove color-developing foreign matter from the monomer of the polymer and thereby produce a high-purity monomer.

Description

[0001] This application is a divisional application of the invention patent application "High-efficiency depolymerization method of polymers containing ester functional groups and purification method thereof" with application date of June 24, 2021 and application number 202180044094.0. Technical Field

[0002] The present invention relates to a method for performing low-temperature glycolysis on a polymer containing an ester functional group by adding an additive, a method for removing foreign matter that may be contained in a monomer from a depolymerization product of a colored polymer, a high-purity purification method for purifying a high-purity monomer using the method, and an environmentally friendly depolymerization method for the colored polymer.

[0003] Specifically, the present invention relates to an environmentally friendly depolymerization method capable of maintaining a high depolymerization yield under low temperature conditions by adding a specific additive to the glycolysis reaction of a colored polymer containing an ester functional group, a separation method capable of selectively separating colored foreign matter by means of liquid-liquid phase equilibrium by adjusting the thermodynamic conditions of the obtained reaction product, a high-purity purification method for high-value-added monomers using liquid-liquid extraction, and a depolymerization reaction of a colored polymer containing an ester functional group and a high-purity purification method for the monomer product, which can significantly reduce the content of harmful or organic and inorganic impurities that may cause quality degradation in a monomer product manufactured using a low-cost transesterification reaction catalyst that does not contain harmful metals. Background Art

[0004] Environmental pollution is becoming a growing problem as most discarded plastics are dumped into designated landfills or natural habitats where they are difficult to decompose naturally. Even plastics that are naturally or biodegradable may persist for decades depending on local environmental factors such as UV exposure levels, temperature, and the presence of decomposing microorganisms.

[0005] In order to solve the above problems, people are actively conducting various research activities that can minimize the accumulation of plastics or reduce environmental impact, starting from the chemical decomposition of existing petroleum-based plastics to the physical regeneration and reprocessing of plastics, including the development of new plastic materials with a shorter decomposition cycle in natural conditions.

[0006] Polymers containing ester functional groups can be converted to monomers through depolymerization, and various chemical reaction pathways have been developed. Theoretically, the monomers generated by decomposition can have the same properties as the raw materials used in the initial polymer synthesis. Depolymerization pathways used in the industrial field to recycle polyesters include hydrolysis, glycolysis, methanolysis, and ammonolysis. Various chemical depolymerization methods can also be used, such as composite processes that combine the advantages of different processes.

[0007] Next, the depolymerization manufacturing method of the polymer containing ester functional groups listed in the above content will be described in more detail. First, in the case of hydrolysis, decomposition can be carried out through various reaction paths in the presence of acid, alkali or metal salt catalysts. In the case of acid catalyst reaction, in order to achieve a higher reaction yield, a high concentration of sulfuric acid solution needs to be used, so there are problems such as poor economy in the design, operation and post-processing of the project. In the case of using alkali and metal salt catalysts, there are problems such as extremely slow decomposition reaction speed, low product purity and difficulty in recovering the catalyst, so its efficiency is low.

[0008] Methanol decomposition process is one of the most widely used processes in actual commercial projects in chemical companies and even in small and medium-sized plastic industries around the world. However, since methanol is used as a reaction solvent, harsh reaction conditions of high temperature and high pressure are required, which leads to an increase in the design cost of the device and the need to equip additional unit projects for recovering reactants and purifying products, which ultimately leads to high investment costs. In order to perform effective methanol decomposition, it is necessary to use an esterification catalyst alternately, and as a catalyst commonly used in the depolymerization reaction of polymers containing ester functional groups, substances containing metal cations such as zinc acetate, magnesium acetate, cobalt acetate and lead dioxide can be used as examples. However, this may cause the problem of residual metal components constituting the catalyst in the obtained depolymerization product, and depending on the use and purpose of the repolymerized material, in order to minimize the harmfulness to the human body or the impact on product quality, the type and amount of the catalyst must be reviewed under the premise of considering the efficiency and economy of the reaction and purification process.

[0009] Although hydrolysis and methanol decomposition processes are used in a variety of fields, the quality and yield of the products generated by these two reactions when decomposing polyester resins are relatively limited, and the decomposition reaction time is relatively long. In addition, as the main decomposition product, only one of terephthalic acid (TPA) or dimethyl terephthalate (DMT) can be produced, and other forms of terephthalate compounds will be handled as by-product impurities. Therefore, in order to resynthesize the produced products into high-quality polymer materials, it is necessary to equip them with purification processes that consume a lot of energy.

[0010] Glycolysis is a depolymerization reaction in which ethylene glycol is added as a reactant. The most common example of glycolysis is the process of producing bis(2-hydroxyethyl) terephthalate (BHET) by adding an excess of ethylene glycol (EG), one of the raw monomer materials. Since ethylene glycol, which is a part of the raw materials of polyethylene terephthalate (PET), is used as a reactant, it has the advantages of high thermodynamic miscibility with the reaction product, low equipment investment, and the ability to directly use the raw materials for production without performing separate chemical treatment. Glycolysis is usually performed under the reflux condition of the reactant ethylene glycol, and even when the polymer decomposition step is slow and the reaction is in equilibrium, the product is widely distributed, which may lead to problems such as limited reaction yield and even production yield of the product. In addition, a high-cost purification process must be performed to separate the final product, the monomer, from the reactant with high yield and high purity. As the reaction catalyst used, zinc acetate or lithium acetate is generally used, as described in Korean Patent Publication No. 2012-01228480 and Korean Registered Patent No. 1142328. The metal salt catalyst as described above may not be completely removed during the purification process, but remains in the product, that is, a very small amount of metal harmful to the human body may be contained in the regenerated monomer, resulting in the problem that the product produced by re-introducing the regenerated monomer is not suitable for use as a reprocessing raw material, especially for food materials, medical materials, and other daily necessities that require harmlessness. In addition, although glycolysis reacts at a relatively high temperature, the recovery and purification process of the product usually adopts a relatively low temperature recrystallization method, so there are also problems such as high energy consumption and reduced cost and efficiency in the heat source supply method of the production process.

[0011] It is estimated that if the depolymerization reaction rate can be increased under low temperature conditions and a less harmful environmentally friendly catalyst can be used during the glycolysis reaction as described above, not only efficient and economical operation can be achieved, but also a large amount of discharged polymers containing ester functional groups can be effectively used for the production of environmentally friendly raw materials without being restricted by product quality or use.

[0012] In addition, although the monomers generated by chemical decomposition such as the depolymerization can theoretically be manufactured to have the same properties as the raw materials input in the initial polymer synthesis or the purity that can be used for polymerizing the polymer, since the waste polymer materials discarded after use contain various forms of foreign matter, it will become the main cause of the quality decline of the final product.

[0013] In particular, color compounds such as dyes or pigments that are directly induced to penetrate into the polymer matrix are not only designed with materials for preventing discoloration, but also undergo a series of physical and chemical pre- and post-treatments and coloring processes to manufacture products. Therefore, it is difficult to remove them through a simple washing or cleaning process, and it is also difficult to chemically separate or isolate the compounds from the products of the depolymerization reaction, namely, low molecular weight compounds containing a terephthalic acid structure.

[0014] A pigment is a coloring matter that is dispersed in a solvent in the form of powder particles and has the characteristic of being insoluble in water or oil, while a dye is a very small particle size or molecular form that can be uniformly dissolved in most solvents. Pigments are usually introduced into polymer resins by painting or printing, while dyes are applicable to dyeing processes and are mostly used to dye fibers or leather. Dyes can be further classified into natural dyes obtained from plants, animals or minerals and artificial dyes synthesized artificial dyes. Artificial dyes can be exemplified by direct dyes, mordant dyes, vat dyes, chromogenic dyes, disperse dyes and reactive dyes, which are mainly used in polymer materials containing ester functional groups. They are classified according to chemical structure, and the most representative ones are azo and anthraquinone disperse dyes.

[0015] When obtaining high value-added monomers by purifying the depolymerization reaction products of polymers containing ester functional groups, the prior art for obtaining high-purity monomers with the pigment removed includes adsorption methods using adsorbents such as activated carbon, physical separation methods such as filtration or distillation, and chemical methods such as oxidation, reduction, hydrolysis, and electrolysis. However, even a trace amount of pigment compounds will develop color as long as they remain in the product, and the effect is usually very one-sided due to the coloring characteristics of forming a complex with the polymer monomer. In addition, the material and energy costs used in the separation process may be excessive, so it is usually difficult to ensure its economic efficiency.

[0016] As a related prior art, Japanese registered patent No. 4537288 discloses a method for producing dimethyl terephthalate and alkylene glycol from dye-dyed polyester fibers, including a dye extraction process, a solid-liquid separation process, a depolymerization reaction process, an ester exchange reaction process, and an effective component recovery process. In the patent, a process is disclosed in which xylene and alkylene glycol are used as an extraction solvent for extracting dyes from dye-dyed polyester fibers, and the dyes are extracted and removed at a temperature above the glass transition temperature of the polyester and below 220°C. After the dyes are extracted before depolymerization, alkylene glycol and a part of the depolymerization reaction liquid are added to the polyester fibers from which the dyes are extracted in the presence of a depolymerization catalyst to induce a depolymerization reaction, thereby obtaining a depolymerization solution containing bis-ω-hydroxyalkyl terephthalate (BHAT). However, the economic efficiency of extracting the dyes before depolymerization is poor and the extraction efficiency is low, so it is not advisable.

[0017] In addition, Korean registered patent No. 10-1142329 discloses a technology including the steps of contacting an oligomer solution obtained by depolymerizing polyester with an ion exchange resin to remove the catalyst in the oligomer solution, and passing the oligomer solution after the catalyst is removed through a decolorizing agent such as activated carbon, activated clay, and diatomaceous earth to adsorb the colored substances in the oligomer solution into the decolorizing agent and remove them. However, in the patent, the amount of decolorizing agent used may be too much and the regeneration of the adsorbent is relatively limited, so its economic efficiency is poor.

[0018] In order to solve the above problems, it is necessary to develop a material or process that can effectively remove color dyes or pigments from terephthalate derivatives generated when depolymerizing colored polymers containing ester functional groups or generated during the purification of products without consuming excessive energy. Summary of the invention

[0019] Technical issues In the present invention, when decomposing a polymer containing an ester functional group, the impurity content of the produced monomer can be adjusted to a very low state corresponding to the initial raw material before polymerization or in the existing petrochemical process. In addition, a method for producing high-quality recycled monomers based on glycolysis is provided, which can use waste polymers discarded after use as a raw material for depolymerization and can also reuse the produced monomers in the same process without performing additional pre-treatment processes, thereby contributing to the realization of a plastic circular economy.

[0020] In addition, a depolymerization method is provided which can carry out depolymerization under a very low temperature reaction condition compared with the conventional high temperature reaction condition, thereby significantly reducing energy consumption.

[0021] In addition, the present invention can adopt more environmentally friendly reaction materials, reaction pathways and systems compared with the original engineering, and simplify the purification process of the product depolymerized from the polymer containing ester functional groups, thereby providing a more economical and efficient monomer manufacturing method compared with other reaction technologies.

[0022] In addition, the present invention provides an extractant that selectively extracts and removes color-developing foreign substances present in a monomer of a polymer containing an ester functional group by being added to the monomer, and a purification method for purifying the monomer of a polymer containing an ester functional group using the extractant.

[0023] In addition, the present invention provides a method for purifying the product by performing purification in situ in the same process used in the depolymerization reaction or by adding one or more post-treatment processes in order to produce monomers of the polymer having the same quality as before polymerization from reactants generated in the depolymerization reaction or a monomer mixture generated in the purification process.

[0024] In addition, the present invention provides a method for producing a high-purity monomer or derivative compound of the polymer, which can adjust the purity of the product by continuously applying a repeated extraction process with a small amount of additives added.

[0025] Technical Solution In order to solve the above-mentioned problems, the present invention provides a method for depolymerizing a polymer containing an ester functional group, characterized in that: the polymer containing an ester functional group is decomposed by contacting a mixture containing (1) one or more polyols; (2) a transesterification reaction catalyst; and (3) a compound represented by the following chemical formula 1 with the polymer containing an ester functional group.

[0026]

Chemical formula 1

[0027] In one embodiment of the present invention, the transesterification catalyst may include at least one selected from metal salts of Group 1A, Group 2A, and Group 2B metals.

[0028] In one embodiment of the present invention, the counter-ion of the metal salt may be composed of an organic anion selected from carbonate, bicarbonate, alkoxide or acetate.

[0029] In one embodiment of the present invention, the polyol may be one or more selected from ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-octanediol, 1,9-nonanediol, neopentyl glycol, 1,4-cyclohexanediol, isosorbide and 1,4-cyclohexanedimethanol.

[0030] In one embodiment of the present invention, the polymer containing an ester functional group may be one or more selected from the group consisting of polyethylene terephthalate (PET), polytrimethylene terephthalate (PPT), polyglycolide or polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN) and Vectran.

[0031] In one embodiment of the present invention, the compound represented by Chemical Formula 1 may be selected from methoxybenzene, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, 1,3,5-trimethoxybenzene, 1,2,3,4-tetramethoxybenzene, 1,2,3,5-tetramethoxybenzene, 1,2,4,5-tetramethoxybenzene, 2-methoxyphenol, 1,3-dimethoxy-2-hydroxybenzene, 4-hydroxy-3,5-dimethoxybenzoic acid, 3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enal, 4-hydroxy-3,5-dimethoxybenzaldehyde, 4-hydroxy-3,5-dimethoxyacetophenone, 3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enoic acid, 4-enyl-2,6-dimethoxyphenol , 4-hydroxy-3-methoxybenzaldehyde, 3-hydroxy-4-methoxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, 2-hydroxy-4-methoxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 1-methoxy-4-[(E)-prop-1-enyl]benzene, 1-bromo-4-methoxybenzene, 2-tert-butyl-4-methoxyphenol, ethoxybenzene, 1,3,5-trichlorobenzaldehyde One or more selected from the group consisting of -2-methoxybenzene, 1,3,5-tribromo-2-methoxybenzene, 4-(prop-2-en-1-yl)phenol, 1-methoxy-4(prop-2-en-1-yl)benzene, 5-(prop-2-en-1-yl)-2H-1,3-benzodioxole, 4-methoxy-2-[(E)-prop-1-yl]phenol and 2-methoxy-4-(prop-1-en-yl)phenol.

[0032] In addition, the present invention provides a composition as a composition for depolymerizing a polymer containing an ester functional group, comprising: (A) one or more polyols; (B) a transesterification reaction catalyst; and (C) the compound represented by Chemical Formula 1.

[0033] The catalyst for the transesterification reaction may be one or more selected from an organic compound catalyst containing no metal or a metal salt of Group 1A, Group 2A, and Group 2B.

[0034] The composition comprises a polyol in an amount of 1 to 50 moles per mole of a repeating monomer of a polymer to be depolymerized, a transesterification catalyst in an amount of 0.001 to 1 mole per mole of a repeating monomer of a polymer to be depolymerized, and a compound represented by Chemical Formula 1 in an amount of 0.001 to 50 moles per mole of a repeating monomer of a polymer to be depolymerized.

[0035] Furthermore, the present invention provides a method for purifying a diol addition monomer obtained by applying the depolymerization method of the present invention.

[0036] The purification method comprises: (1) a step of separating the compound represented by Chemical Formula 1 from the depolymerization reaction product by gas-liquid separation or liquid-liquid extraction; (2) a solid matter separation step of separating a solid matter including a polymer containing unreacted ester functional groups after the step (1); and (3) a recovery step of recrystallizing and recovering a diol addition monomer after the solid matter is separated in the step (2).

[0037] In one embodiment of the present invention, the purification method can separate the solid matter containing unreacted ester functional groups by physical filtration, and the step of separating the oligomers can be first performed before recrystallizing the diol addition monomer in step (3).

[0038] In addition, the present invention provides an extractant for removing color-forming foreign substances from a monomer of a polymer resin containing an ester functional group, as an extractant for removing color-forming foreign substances from a monomer of a polymer resin containing an ester functional group, characterized in that it contains the compound represented by Chemical Formula 1.

[0039] In one embodiment of the present invention, it is characterized in that: the monomer of the polymer resin containing an ester functional group is obtained by a depolymerization reaction of the polymer resin containing an ester functional group.

[0040] In addition, the present invention provides a purification method for removing color-forming foreign matter from a monomer of a polymer containing an ester functional group and generating a high-purity monomer. As a purification method for removing foreign matter from a monomer of a polymer resin containing an ester functional group and generating a high-purity monomer, the method comprises: 1) adding the compound represented by Chemical Formula 1 to the monomer of the polymer containing an ester functional group containing color-forming foreign matter and mixing them; 2) inducing liquid-liquid phase separation by allowing the mixed solution in the step 1 to stand; and, 3) separating the liquid-liquid layer of the phase separation into an organic solution layer of an upper phase and an aqueous solution layer of a lower phase and discharging them.

[0041] In another embodiment of the purification method of the present invention, it is characterized in that: in the step 1), in addition to the compound represented by chemical formula 1, a hydrophilic solution or water that will not mix with the compound represented by chemical formula 1 is added to the monomer containing the color-forming foreign matter.

[0042] In another embodiment of the purification method of the present invention, it is characterized in that the monomer is a reaction product obtained by depolymerizing a polymer containing an ester functional group, or a product of partially purifying a mixture after the depolymerization reaction.

[0043] In addition, in the purification method applicable to the present invention, the step of further extracting the colored foreign matter by adding the compound represented by Chemical Formula 1 to the separated aqueous solution layer can be repeated more than once; it can also include: adding a hydrophilic solution or water that will not mix with the compound represented by Chemical Formula 1 to the separated organic solution layer and mixing them, and then performing the phase separation step again.

[0044] The purification method applicable to the present invention may further include a step of recovering monomers of the polymer resin containing an ester functional group from the separated aqueous solution phase by recrystallization.

[0045] In addition, the present invention provides a purification method for removing colored foreign matter from a monomer obtained by depolymerizing a colored polymer containing an ester functional group and producing a high-purity monomer, comprising: (a) a step of adding the compound of Chemical Formula 1 to the colored polymer containing an ester functional group; (b) a step of depolymerizing the polymer containing an ester functional group; (c) a step of adding a hydrophilic solution or water that does not mix with the compound represented by Chemical Formula 1 to the depolymerization reaction product obtained by the depolymerization reaction and mixing the mixture; (d) a step of inducing liquid-liquid phase separation by allowing the mixed solution in step (c) to stand; and (e) a step of separating the liquid-liquid layer of the phase separation into an organic solution layer of an upper phase and an aqueous solution layer of a lower phase and discharging the liquid-liquid layer.

[0046] Furthermore, in yet another embodiment of the present invention, it is characterized in that the organic solvent is recovered from the organic solution layer separated and discharged in step (e) by distillation and reused.

[0047] Technical Effects By the depolymerization method of the polymer containing ester functional groups of the present invention, the raw material material before manufacturing or for re-synthesizing the polymer, i.e., diol addition monomer (e.g., bis(2-hydroxyalkyl)terephthalate), can be produced from the polymer containing ester functional groups with high yield and high purity, and the polymer discharged after use, i.e., polyethylene terephthalate (PET) or waste polyester fiber can also be effectively used as a raw material to produce high-purity recycled monomers such as bis(2-hydroxyethyl)terephthalate (BHET) on a large scale.

[0048] Through the present invention, more relaxed reaction conditions than the original reaction conditions and a reaction system composed of environmentally friendly materials can be used to produce glycolysis-based depolymerization monomers, thereby ensuring both the reactivity for decomposition of polymers containing ester functional groups and the selectivity for target monomers. Moreover, most of the materials containing the post-reaction catalyst can be effectively applied to thermodynamic phase separation methods such as liquid-liquid extraction or gas-liquid separation, thereby making it easy to recover and greatly reducing the impurity content in the decomposition products.

[0049] Furthermore, compared with the glycolysis process reported in the prior art, the present invention can obtain a diol addition monomer with a high yield and high purity even at a relatively low temperature and atmospheric pressure.

[0050] Furthermore, a wide variety of catalyst types can be selected in the technology applicable to the present invention, and catalysts that are less toxic and less expensive than commercial catalysts used in the past (e.g., zinc acetate) can be used, thereby producing not only products that are harmless to the human body, but also environmentally friendly and economical products.

[0051] The monomers depolymerized by applying the technology of the present invention can be recycled as raw materials for plastic or resin products without any restrictions on quality or use, thereby realizing a perfect chemical recycling technology.

[0052] Furthermore, the monomer of the polymer containing an ester functional group can be purified to a high purity by the extractant and purification method of the present invention.

[0053] Furthermore, the monomer of the polymer is obtained by depolymerizing a colored polymer containing an ester functional group, so that the depolymerized monomer or addition monomer (e.g., bis(hydroxyethyl) terephthalate (BHET)) of the same quality as before manufacturing the polymer can be produced in high yield and high purity.

[0054] In addition, because the extractant does not participate in the depolymerization reaction, it can be directly used without separation in the monomer purification process after the depolymerization reaction, and can be put into use in the steps before or after the depolymerization reaction, so its engineering efficiency and operation convenience are high.

[0055] In addition, the extractant can be used to adjust the non-covalent mutual attraction such as the hydrogen bond forming ability between foreign matter and additives, the π-stacking between aromatic rings of different types of compounds, etc., so as to reduce the affinity with the depolymerized low-molecular compound, and the freed pigment compound is distributed in the organic phase at a high concentration, while the product, i.e., the terephthalate compound, is distributed in a high concentration in the hydrophilic lower phase, so that the product can be purified at a high concentration by physical phase separation, and after the depolymerization reaction, the reaction process itself can be converted into a purification process or realized in a series process by continuous flow, thereby simplifying the project structure and reducing energy consumption.

[0056] The present invention can be applied to more relaxed operating conditions than the existing separation process and minimize energy loss, and can apply compounds composed of environmentally friendly materials in each process. In addition, the extractant and part or all of the compounds used in the reaction can be recovered and reused through a separate separation process, thereby realizing an environmentally friendly and economical purification process.

[0057] In addition, the extractant and purification method of the present invention do not require complex engineering units, and the purity of the depolymerization product is improved by applying a simple repeated phase separation method, so that it can be applied to high-purity and high-yield purification technology through various forms or methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a hydrogen nuclear magnetic resonance (HNMR) of bis(hydroxyethyl) terephthalate (BHET) obtained by depolymerization of polyethylene terephthalate (PET) according to a comparative example of the present invention. 1 H-NMR) spectroscopy.

[0059] Figure 2 This is a hydrogen nuclear magnetic resonance (HNMR) of a sample obtained by performing a multiple water washing process on bis(hydroxyethyl) terephthalate (BHET) obtained by depolymerization of polyethylene terephthalate (PET) according to a comparative example of the present invention. 1 H-NMR) spectroscopy.

[0060] Figure 3 The hydrogen nuclear magnetic resonance (HNMR) of bis(hydroxyethyl) terephthalate (BHET) obtained by depolymerization of polyethylene terephthalate (PET) according to one embodiment of the present invention is shown in FIG. 1 H-NMR) spectroscopy.

[0061] Figure 4 This is a schematic diagram illustrating a liquid-liquid phase equilibrium diagram (Tx) of a two-component compound consisting of anisole and a hydrophilic solvent (water or ethylene glycol), which is one type of extractant suitable for the present invention.

[0062] Figure 5 The hydrogen nuclear magnetic resonance (HNMR) of organic pigments extracted from the depolymerization and product purification process of colored waste polyethylene terephthalate (PET) polymer and the purified depolymerization monomer products according to some comparative examples and embodiments of the present invention is as follows: 1 H-NMR) spectroscopy.

[0063] Figure 6 The hydrogen nuclear magnetic resonance (HNMR) of the organic dye extracted from the depolymerization and product purification process of the colored polyester fiber and the purified depolymerization monomer product is applicable to some embodiments of the present invention. 1 H-NMR) spectroscopy. DETAILED DESCRIPTION

[0064] Unless otherwise defined, the meaning of all technical and scientific terms used in this specification is the same as that commonly understood by a skilled professional in the technical field to which the present invention belongs. Generally speaking, the nomenclature used in this specification is a general nomenclature well-known in the technical field.

[0065] Throughout the present specification, when a certain part is described as “including / comprising” a certain constituent element, unless otherwise clearly described to the contrary, it does not mean that other constituent elements are excluded but that other constituent elements may be included.

[0066] The present invention provides a method for depolymerizing a polymer containing an ester functional group, characterized in that: the polymer containing an ester functional group is depolymerized by contacting a mixture containing (A) one or more polyols; (B) a transesterification reaction catalyst; and (C) a compound represented by the following chemical formula 1 with the polymer containing an ester functional group.

[0067] In addition, the present invention provides a composition for depolymerizing a polymer containing an ester functional group, characterized in that: as a composition for depolymerizing a polymer containing an ester functional group, it contains: (A) one or more polyols; (B) a transesterification reaction catalyst; and (C) a compound represented by the following Chemical Formula 1.

[0068] The present invention uses the above-mentioned one or more polyols as raw materials for the glycolysis reaction, and as the reaction catalyst, an existing catalyst such as zinc acetate can be used, and a salt composed of a Group 1A, Group 2A or Group 2B metal cation and a counter-ion (counter-ion) composed of an organic anion such as carbonate, bicarbonate, alkoxide or acetate can be used as a catalyst, and a non-metallic organic compound catalyst composed of an organic substance that does not contain a metal can also be used.

[0069] In addition, the present invention can significantly reduce the activation energy of the depolymerization reaction for converting the polymer raw material containing ester functional groups into diol addition monomers by adding the compound represented by the following chemical formula 1 as an additive, and as mentioned above, not only the 2B group but also low-cost catalysts containing various forms of metals such as 1A or 2A group or organic catalysts that can be decomposed at high temperatures can be selected as reaction materials, thereby ensuring the economy of material reuse and recycling and easily controlling impurities. Therefore, the present invention is characterized in that it can not only maintain a high depolymerization reactivity at low temperatures, but also improve the purity, yield and reaction selectivity of the depolymerized monomer.

[0070]

Chemical formula 1

[0071] In the chemical formula 1, the substituent R1 is selected from hydrogen, hydroxyl, aldehyde, carboxyl, C1-C6 alkyl, C4-C6 cycloalkyl and C6-C 12 wherein n is an integer from 0 to 5, and when n is 2 or more, R1 are the same or different, and the substituent R2 is C1-C 10 wherein m is an integer from 1 to 6, and when m is 2 or more, -O-R2 are the same or different.

[0072] The depolymerization method of the present invention can be effectively applied to the depolymerization of a polymer containing an ester functional group, wherein the polymer containing an ester functional group can be in the form of waste plastics alone or in a mixture, for example, polyethylene, high-density polyethylene, low-density polyethylene, polypropylene or a combination thereof mixed with the polymer containing an ester functional group. The other polymers exemplarily listed in the above content that are mixed with the polymer containing an ester functional group are only exemplary content and are not limited to the substances listed.

[0073] In addition, the polymer containing an ester functional group can be a polymer formed by condensation polymerization of a dicarboxylic acid and a diol, wherein the dicarboxylic acid is selected from the group consisting of terephthalic acid, naphthalene dicarboxylic acid, diphthalic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, sebacic acid, cyclohexane dicarboxylic acid, trimellitic acid, pyromellitic acid, and combinations thereof, and the diol is selected from the group consisting of ethylene glycol, trimethylene glycol, 1,2-propanediol, The invention can be selected from the group consisting of glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, decamethylene glycol, dodecamethylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, di(tetramethylene) glycol, tri(tetramethylene) glycol, polytetramethylene glycol, pentaerythritol, 2,2-bis(4-β-hydroxyethoxyphenyl)propane and combinations thereof.

[0074] As an example, the polymer comprising an ester functional group can be selected from polyethylene terephthalate (PET), polytrimethylene terephthalate (PPT), polyglycolide or polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), Vectran, and combinations thereof.

[0075] One of the most common examples of the polymer containing ester functional groups is polyethylene terephthalate, where the starting materials used to make the polymer are terephthalic acid or its derivative monomers and ethylene glycol.

[0076] The polymer containing ester functional groups used in the present invention may be in an impure state, that is, may contain various impurities. For example, in addition to the polymer containing ester functional groups, it may also contain bottle caps, adhesives, paper, residual liquid, dust, or a combination thereof, but is not limited thereto, and a mixture of various residues may be used as a raw material for depolymerization.

[0077] In the depolymerization method of the polymer containing an ester functional group to which the present invention is applied, the polymer containing an ester functional group may contain about 0.1% to about 70% by mass of the reaction raw materials. When the initial input amount is less than 0.1% by mass, it may be difficult to ensure its economic efficiency, and when the initial input amount is more than 70% by mass, the reaction rate may be significantly reduced due to mass transfer limitation.

[0078] The polyol used for the glycolytic depolymerization of the polymer containing an ester functional group is a compound having at least two alcohol functional groups, especially a compound having two or more hydroxyl groups such as a linear secondary alcohol, but is not limited thereto.

[0079] The polyol may be used in a ratio ranging from 1 to 50 moles per mole of the repeating monomer of the polymer.

[0080] Examples of polyols having at least two alcohol functional groups to which the present invention is applicable include one or more selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-octanediol, 1,9-nonanediol, neopentyl glycol, 1,4-cyclohexanediol, isosorbide and 1,4-cyclohexanedimethanol.

[0081] As an example of a catalyst for the transesterification reaction of the present invention, a catalyst in the form of an organic substance that does not contain a metal can be used. As a non-limiting example of the catalyst in the form of an organic substance, it can be selected from linear amines (e.g., ethylenediamine, diethylenetriamine, tris(2-aminoethyl)amine and tetraethylenepentamine), amides (e.g., acetamide), guanidines (e.g., triazabicyclodecene), imidazoles (e.g., 2-ethyl-4-methylimidazole), ureas (e.g., urea, 1,1-dimethylurea and 1,3-dimethylurea), aromatic amines (e.g., benzyl dimethylamine) and cycloalkylamines (e.g., cyclohexylmethylamine and dimethylcyclohexylamine) One or more, it is preferable that the compound constituting the catalyst itself does not directly participate in the reaction.

[0082] As another example of a catalyst suitable for the present invention, a salt composed of a Group 1A, Group 2A or Group 2B metal cation and a counter-ion selected from an anion such as carbonate, bicarbonate, alkoxide or acetate may be used as a catalyst.

[0083] The Group 1A ions used as the catalyst may be lithium (Li + ), sodium (Na + ) and potassium (K + ), the Group 2A metal may be magnesium (Mg 2+ ) and calcium (Ca 2+ ), the Group 2B metal may be zinc (Zn 2+ ), etc., but is not limited to these.

[0084] The catalyst may be used in an amount ranging from 0.001 to 1 mole ratio per mole of the repeating monomer of the polymer, preferably from 0.01 to 0.1 mole ratio per mole of the repeating monomer.

[0085] The compound represented by Chemical Formula 1 is used as an additive during the depolymerization reaction in order to improve the depolymerization reactivity of the polymer containing the ester functional group and to improve the selectivity of the useful product. As an example, the substituent R2 can be C1 to C 10 The alkyl group may preferably be a C1-C6 alkyl group, and more preferably be a C1-C3 alkyl group.

[0086] In one embodiment of the present invention, the compound represented by Chemical Formula 1 contained in the additive may be methoxybenzene, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, 1,3,5-trimethoxybenzene, 1,2,3,4-tetramethoxybenzene, 1,2,3,5-tetramethoxybenzene, 1,2,4,5-tetramethoxybenzene Oxybenzene, 2-methoxyphenol, 1,3-dimethoxy-2-hydroxybenzene, 4-hydroxy-3,5-dimethoxybenzoic acid, 3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enal, 4-hydroxy-3,5-dimethoxybenzaldehyde, 4-hydroxy-3,5-dimethoxyacetophenone, 3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enoic acid, 4-vinyl-2,6-dimethoxyphenol, 4 -Hydroxy-3-methoxybenzaldehyde, 3-hydroxy-4-methoxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde, 2-hydroxy-4-methoxybenzaldehyde, 3,4-dihydroxybenzaldehyde, 1-methoxy-4-[(E)-prop-1-enyl]benzene, 1-bromo-4-methoxybenzene, 2-tert-butyl-4-methoxyphenol, ethoxybenzene, 1,3,5-trichloro-2-methoxybenzene , 1,3,5-tribromo-2-methoxybenzene, 4-(prop-2-en-1-yl)phenol, 1-methoxy-4(prop-2-en-1-yl)benzene, 5-(prop-2-en-1-yl)-2H-1,3-benzodioxole, 4-methoxy-2-[(E)-prop-1-yl]phenol and 2-methoxy-4-(prop-1-en-yl)phenol, etc., selected from the group consisting of natural or synthetic compounds.

[0087] The additive may be used in an amount ranging from 0.001 to 50 mole ratios per mole of the repeating monomer of the polymer, preferably in an amount ranging from 0.1 to 10 mole ratios per mole of the repeating monomer.

[0088] The method for depolymerizing a polymer according to the present invention provides a quick method for depolymerizing a polymer containing an ester functional group at a temperature in the range of 100° C. to 200° C., preferably in the range of 130° C. to 160° C. As a result, the method for depolymerizing a polymer containing an ester functional group provided in the present application can react even at low temperatures compared to the conventional method, thereby saving energy, and the catalyst and additives used can be recovered and reused through a separate recovery process, thereby having excellent economic efficiency.

[0089] Furthermore, the method for depolymerizing a polymer of the present invention may be performed under atmospheric pressure, but may also be performed under pressurized conditions depending on the formation of the vapor pressure of the added additives or reactants.

[0090] In the method described in the present application, the depolymerization reaction time may vary depending on the amount of polymer used, and can be performed according to a reaction time of 0.5 to 12 hours. In order to minimize the yield of by-products, a reaction time of 0.5 to 4 hours is preferably selected.

[0091] After the reaction, a process of separating and removing unreacted polymer substances by filtering them out from the reaction mixture may be additionally performed.

[0092] The depolymerization of the polymer containing ester functional groups applicable to the present invention is carried out by using polyols, and thus can be equivalent to a glycolytic depolymerization reaction.

[0093] The method for purifying the diol addition monomer obtained by applying the depolymerization method of the present invention may include (1) a step of separating the compound represented by Chemical Formula 1 as an additive from the depolymerization reaction product by gas-liquid separation or liquid-liquid extraction; (2) a solid matter separation step of separating a solid matter including a polymer containing unreacted ester functional groups after the step (1); and (3) a recovery step of recrystallizing and recovering the diol addition monomer after the solid matter is separated in the step (2).

[0094] The gas-liquid separation of the additive can be performed independently of the reaction or continuously after the reaction is completed. For example, the vaporized additive can be condensed and refluxed into the reactor using a pre-installed condenser to maintain low temperature, and the temperature can be increased or maintained after the reaction is completed, wherein the condensed and refluxed additive is separated by changing the flow path of the additive to the outside of the reactor instead of the inside.

[0095] Liquid-liquid extraction is a method of adding water and separating in order to recover and purify the target product. When water is added, a clear phase separation boundary can be formed, so that most of the additives can be physically separated by separating only the organic layer under low temperature conditions. As for additives that may remain in the aqueous solution after separation, they will have very limited solubility when the water content is increased or the temperature is lowered, so most of them can be separated and recovered. Most of the products can be recovered by crystallization, and as for the very small amount of additives that may remain in the purified target product, they can be simply and thoroughly removed by heating and drying at 50 to 150°C, preferably by heating and drying under a vacuum state.

[0096] The gas-liquid phase separation for recovering the additives according to the method described in the present application includes a method in which the temperature of the reactor is raised to a temperature above the reaction temperature after the reaction in order to vaporize or volatilize part or all of the additives, thereby distilling and separating the additives to the outside. When separating the additives by liquid-liquid extraction, it is most economical to use water, and hydrophilic substances that can induce thermodynamically unstable phases with the additives, such as glycols or diols used as reactants, can also be used.

[0097] The solid matter containing the polymer containing unreacted ester functional groups can be removed before or after the end of the reaction by various physical methods such as precipitation, filtration, coagulation, suspension and extrusion after the depolymerization reaction, and can be re-added during the depolymerization. In the removal method using filtration, a filter having fine pores smaller than the particle size of the unreacted polymer can be used, and in order to increase the flow rate of the filtrate, pressurization or decompression can be performed in parallel.

[0098] The method for recovering the diol addition monomer by the recrystallization process is preferably performed after removing the unreacted products in the reaction process, and can be performed after additionally performing the step of separating the oligomers by filtration at a temperature above room temperature, for example, in the range of 60°C to 120°C, preferably in the range of 90°C to 110°C, using water of the corresponding temperature or a solvent required for crystallization of the target product. The filtrate can be maintained at a low temperature and recovered as a product through the recrystallization process, and in order to adjust the impurity concentration in the product, the physical separation and recrystallization process can be repeatedly performed. Before the recrystallization of the diol addition monomer in the step (3), a step of separating the oligomers can be first performed.

[0099] In the process of constructing a reaction system according to the depolymerization method of the present invention, when a non-metallic catalyst or a metal salt composed of a Group 1A or Group 2A metal cation and a counter-ion (counter-ion) composed of an organic anion such as carbonate, bicarbonate, alkoxide or acetate is used as a catalyst, the harmfulness of the metal components that may remain in the purified monomer product is low and the removal rate in the purification process is high, so the impurity concentration can be easily managed.

[0100] In addition, the present invention provides an extractant, characterized in that: as an extractant for removing color-forming foreign substances such as pigments or dyes from monomers of a polymer containing an ester functional group, the extractant comprises the compound represented by Chemical Formula 1. The compound represented by Chemical Formula 1 can connect at least one or more alkyl groups to an aromatic ring through a connecting group, and the connecting group has at least one or more oxygen.

[0101] Examples of the compound represented by Chemical Formula 1 as the extractant are the same as those exemplified in the compound represented by Chemical Formula 1 included in the additive for removing foreign matter, and thus duplicate description is omitted to avoid confusion.

[0102] Furthermore, in one embodiment of the present invention, the monomer of the polymer containing an ester functional group may be obtained by a depolymerization reaction of the polymer containing an ester functional group. In particular, the polymer containing an ester functional group may be a colored polymer. The compound represented by Chemical Formula 1 does not directly participate in the depolymerization of the polymer containing an ester functional group as a reactant when put into the depolymerization reaction, but has the characteristic of maintaining the performance related to the depolymerization reactivity and product selectivity even under low temperature reaction conditions, so that it can be used in a form of being mixed with the polymer before the depolymerization reaction and then depolymerized.

[0103] The extractant applicable to the present invention can be effectively used as an extractant for removing color pigments and foreign matters such as dyes from monomers of polymers containing ester functional groups, wherein the polymers containing ester functional groups can be in the form of waste plastics alone or in a mixture, for example, polyethylene, high-density polyethylene, low-density polyethylene, polypropylene or a combination thereof mixed with the polymers containing ester functional groups. The other polymers exemplarily listed in the above content to be mixed with the polymers containing ester functional groups are only exemplary content and are not limited to the substances listed.

[0104] Furthermore, the present invention provides a purification method for removing foreign substances from a monomer of a polymer containing an ester functional group and producing a high-purity monomer.

[0105] The purification method is characterized in that it includes: 1) adding the compound represented by Chemical Formula 1 to a monomer of a polymer containing an ester functional group and containing a color-forming foreign substance and mixing the mixture; 2) inducing liquid-liquid phase separation by allowing the mixed solution in step 1 to stand; and 3) separating the liquid-liquid layer of the phase separation into an organic solution layer of an upper phase and an aqueous solution layer of a lower phase.

[0106] The step 1) is a step of adding an extractant for extracting foreign matters from the monomer of the polymer containing an ester functional group and mixing the extractant so that more foreign matters are distributed to the extractant.

[0107] Regarding the extraction partition temperature in the step 1), although the extraction process can be performed after inducing phase separation without adding a hydrophilic solvent at a general depolymerization reaction temperature of the polymer containing an ester functional group or in a low temperature region lower than the reaction temperature, it is also possible to form a more clear phase separation boundary by adding an excess of water having very limited solubility in the substance represented by Chemical Formula 1, and to induce an extreme asymmetric partition of the depolymerization product and foreign matter, thereby recovering the monomer with high purity.

[0108] The compound represented by chemical formula 1 is a substance that also has a relatively high affinity for color-forming organic substances such as dyes or pigments. Therefore, in the step 1), color-forming foreign substances such as dyes or pigments will move to the organic phase mostly composed of the compound represented by chemical formula 1, while other hydrophobic compounds and monomer products will mostly transfer to the hydrophilic phase.

[0109] The temperature range of the extraction and distribution in step 1) may be 25 to 150°C.

[0110] It is most economical to use water in the removal of foreign matter such as dyes or pigments and the purification of monomers by liquid-liquid extraction applicable to the present invention, but a hydrophilic substance that can induce a thermodynamically unstable phase with the additive may also be used, and the process may be performed in the presence of the polyol used without adding a separate solvent.

[0111] The step 2) is a step of causing asymmetric distribution of foreign matter etc. by mixing the mixed liquid and then causing liquid-liquid phase separation of the mixed liquid.

[0112] The induction of the liquid-liquid phase separation can be performed continuously or intermittently using well-known means such as a pouring scrubber, and can use components and temperatures that can phase separate because their thermodynamic miscibility is sufficiently low. Since the components and temperatures that can phase separate can be easily calculated by a general technician, detailed descriptions thereof will be omitted.

[0113] As an example, in Figure 4 In the embodiment of the present invention, the reaction conditions for depolymerization and the purification conditions for extraction are schematically illustrated on the liquid-liquid phase equilibrium curves at different temperatures determined by titration to distinguish the thermodynamic state of a two-component compound composed of anisole, one of the extractants applicable to the present invention, and a hydrophilic solvent (water or ethylene glycol). The x-axis represents the molar fraction of the component of the organic extractant, anisole, and the y-axis represents the reaction or purification temperature. By referring to the Figure 1 From the diagram in Figure 1, appropriate compositions and temperatures for phase separation can be selected.

[0114] The step 3) is a step of separating and discharging the organic phase (organic solution layer) and the aqueous phase (aqueous solution layer) from the phase-separated mixture. The separation can be carried out by common means, and the organic phase and the aqueous phase after separation can be further improved by separate post-treatment to improve the recovery rate of the target product.

[0115] Another embodiment of the purification method of the present invention may further include: adding a hydrophilic solvent such as water to the organic solution layer (or organic phase) mostly composed of the compound represented by Chemical Formula 1 separated for the first time in step 3) to redistribute the small amount of monomers remaining in the organic phase, thereby performing back extraction and thereby recovering the monomer product.

[0116] In addition, in order to recover the additive represented by Chemical Formula 1 from the organic phase separated and discharged by the liquid-liquid extraction to which the present invention is applied, a method such as distillation using gas-liquid separation may be included to separate the dye and the pigment.

[0117] The monomer product concentrated in the separated and discharged aqueous solution layer can be mostly recovered by crystallization, while the extremely small amount of additives that may remain in the purified target product can be simply and thoroughly removed by heating and drying at 50 to 150°C, preferably by heating and drying under a vacuum state.

[0118] In the monomer purification process of the polymer containing an ester functional group to which the present invention is applied, a process of separating and removing a part of foreign matter by physical filtration may be performed in addition or in parallel.

[0119] In one embodiment of the present invention, the monomer of the polymer containing an ester functional group in the step 1) may be a depolymerization reaction mixture obtained by depolymerizing the polymer containing an ester functional group or a derivative compound obtained thereby, and the depolymerization reaction mixture may be in a state without being purified after the reaction or in a state after being partially purified.

[0120] As described above, in the case where the monomer of the polymer containing an ester functional group in the step 1) of the present invention is a depolymerization reaction mixture obtained by depolymerizing the polymer containing an ester functional group or a derivative compound obtained thereby, the operation of adding the extractant can be performed in the previous step or the next step of the depolymerization reaction process.

[0121] Polymers containing ester functional groups can be decomposed into low molecular weight compounds such as monomers, dimers or oligomers through depolymerization reactions. Available depolymerization reaction pathways may include hydrolysis, glycolysis, methanolysis and ammonialysis, and composite engineering of their combination may also be used.

[0122] Specifically, the method for removing colored foreign matter in the depolymerization reaction mixture by adding the extractant to the step before the depolymerization reaction process and purifying the monomer obtained by depolymerizing the colored polymer containing an ester functional group to a high purity may include: (a) adding the compound of Chemical Formula 1 to the colored polymer containing an ester functional group; (b) depolymerizing the polymer containing an ester functional group; (c) adding water or a hydrophilic solution that does not mix with the compound represented by Chemical Formula 1 to the depolymerization reaction mixture obtained by the depolymerization reaction and mixing the mixture; (d) inducing liquid-liquid phase separation by allowing the mixed solution in step (c) to stand; and (e) separating the liquid-liquid layer of the phase separation into an organic solution layer of the upper phase and an aqueous solution layer of the lower phase and discharging the separated liquid-liquid layer.

[0123] The depolymerization monomer purification process of the colored polymer containing an ester functional group to which the present invention is applied may be performed in addition to or in parallel with a process of separating and removing unreacted polymer substances or a portion of foreign matter by physical filtration from the depolymerization reaction mixture.

[0124] The depolymerization of the polymer containing an ester functional group to which the present invention is applied can be carried out by adding alcohol, water or hydroxide in the presence or absence of a catalyst to thereby perform a transesterification reaction.

[0125] Next, the detailed information of the process of the present invention will be described through examples, comparative examples and test examples. It should be noted that these descriptions are only representative examples related to the present invention, and the scope of application of the present invention is not limited thereby.

[0126] 1. Depolymerization method of polymers containing ester functional groups

Raw materials 1 to 4

[0127] [Test Example 1: Depolymerization reaction step (when no additive is added before the reaction)] About 10 g of the polymer raw material prepared according to raw material 1 was quantitatively used as a reaction raw material. 38.75 g of ethylene glycol (12 moles per mole of polymer repeating monomer) as a diol polar solvent was placed in a three-necked flask and a reflux cooler was installed at atmospheric pressure. Then, heating and stirring were performed using a heating magnetic stirrer. When the temperature reached 177°C, 10 g of the polymer raw material was added and stirred while continuing to heat. When the reaction mixture reached 197°C or reflux temperature, a catalyst reaction was started by adding 0.04 moles of a catalyst per mole of polymer repeating monomer. Then, the reaction temperature was stably maintained within the range of ±0.5°C while stirring was continued for 2 hours, and the reaction was performed using a condenser with one end exposed to atmospheric pressure. The unreacted products in the reaction product were separated and quantified by filtration, and the concentrations of the decomposed monomers, dimers, by-products, namely mono(hydroxyethyl) terephthalate (MHET), and oligomers were quantified using a high performance liquid chromatography (HPLC, reverse phase C18 column (250 mm, 5 microns), UV detector (λ=254 nm)) calibrated with standard samples. When performing the HPLC analysis, a mixed solution of methanol: water with a volume ratio of 70:30 was used as the mobile phase at a stable flow rate of 0.7 mL / min.

[0128] [Test Example 2: Depolymerization reaction step (additives added before reaction)] Before starting the depolymerization reaction, 4 moles of additives were added to each mole of the repeating monomer of the polymer raw material together with 38.75 g of ethylene glycol (12 moles per mole of the repeating monomer of the polymer) as a diol polar solvent in a three-neck flask and a reflux cooler was installed under atmospheric pressure. Then, heating and stirring were performed using a heating magnetic stirrer. When the temperature reached 20°C lower than the final reaction temperature, 10 g of the polymer raw material was added and stirring was continued while the temperature was raised. When the reaction mixture reached the reaction temperature, the catalyst reaction was started by adding 0.04 moles of catalyst per mole of the repeating monomer of the polymer. The reaction and analysis were carried out in the same manner as in Example 1, except that the additives were added and the reaction temperature was maintained at a low temperature of less than 153°C.

[0129] [Test Example 3: Product Purification Steps] After mixing the reaction product and 400 mL of distilled water in a 500 mL round-bottom flask, stirring was continued for about 1 hour at a temperature between 90 and 95°C. After the reaction, the oligomers in the mixture were removed by a vacuum pump through a filter paper (Whatman, pore diameter: 3 microns) placed in the filter. The filtrate obtained for the first time was re-filtered using the same filter to separate and remove the recrystallized oligomers and solid matter. The filtrate obtained was crystallized by storing it in a low-temperature tank maintained at below 4°C for more than 16 hours, and then the precipitate was recovered by a vacuum filter, and then dried in an oven maintained at about 80°C for 6 hours, and the white powder obtained was finally quantified as a diol addition product.

[0130] In order to confirm the residual content of metals in the purified product, about 0.1 g of the purified product was dissolved in HNO3 for acid treatment and then measured using inductively coupled plasma-atomic emission spectrometry (ICP-AES, model: Thermo Fisher Scientific iCAP 6500Duo) and inductively coupled plasma-mass spectrometry (ICP-MS, model: Thermo Fisher Scientific XSeries).

[0131] To characterize the purified product, approximately 0.1 g of the purified product was diluted into dimethyl sulfoxide-d 6 (DMSO- d 6) solvent and prepared a sample with a monomer concentration of 6.25% and analyzed by hydrogen nuclear magnetic resonance ( 1 Hnuclear magnetic resonance, 1 H-NMR, model: Bruker AVANCE ‖ + 500 MHz) to obtain nuclear magnetic resonance (NMR) spectra.

[0132] [Test Example 4: Additional purification step] The white powder obtained by Test Example 3 was placed in a 250 mL round-bottom flask filled with 100 mL of distilled water and stirred while maintaining a temperature in the range of 90 to 95°C. After stirring for about 1 hour, it was moved to a low-temperature tank maintained at below 4°C, and then recrystallized by leaving it for more than 16 hours. The precipitate obtained by additional washing was recovered using the same filter as in Test Example 3. The obtained precipitate was dried in an oven maintained at about 80°C for 6 hours to obtain a white powder equivalent to a diol addition monomer. For the powder product obtained by additional purification, inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and hydrogen nuclear magnetic resonance ( 1 H-NMR) analysis.

[0133]

Calculation formula

[0134] Depolymerization conversion rate of polymer during depolymerization (%) = (Initial amount of polymer input - unreacted polymer amount) / (Initial amount of polymer input) × 100 The yield of monomers obtained during depolymerization (%) = (The number of moles of bis(hydroxyethyl) terephthalate (BHET) obtained) / (The number of moles of terephthalate monomer in the polymer structure fed) × 100 The yield of dimers obtained during depolymerization (%) = (Number of moles of dimer obtained) / (Number of moles of terephthalate monomer in the polymer structure fed) × 100 Yield (%) of by-product (monohydroxyethyl terephthalate (MHET)) obtained during depolymerization = (The number of moles of monohydroxyethyl terephthalate (MHET) obtained) / (The number of moles of terephthalate monomer in the polymer structure fed) × 100 1.1 Comparison of depolymerization reaction characteristics using metal salts as catalysts

Table 1

[0135] Table 1 is the result of evaluating the performance of the glycolysis reaction of a polymer raw material containing an ester functional group under the most commonly used reaction conditions in order to compare and illustrate the effects of the embodiments of the present invention. For this purpose, an excess of ethylene glycol (12 moles per mole of polymer repeating monomer) was used and the glycolysis reaction was carried out under ethylene glycol reflux conditions (197°C) at atmospheric pressure. The most commonly used zinc acetate catalyst was added and the depolymerization reaction was carried out in the same manner as in Experimental Example 1 as described above, and its depolymerization performance on polyethylene terephthalate was used as Comparative Example 1. In addition, the depolymerization reaction was carried out by selecting the same number of moles of alkali metal acetate as a catalyst that can be combined according to an example of the present invention instead of zinc acetate and adding the same number of moles of the catalyst added in Comparative Example 1 as Comparative Examples 2 and 3.

[0136] As reported in various patents and non-patent prior literature, when zinc acetate was used as a catalyst (Comparative Example 1), all polymers were decomposed in only two hours, and the yield of bis(hydroxyethyl)terephthalate (BHET) was as high as 90%. In contrast, in the depolymerization of polyethylene terephthalate performed under the same reaction conditions using acetate having an alkali metal cation such as potassium or sodium as a catalyst, high reactivity was also observed, but at the same time, low selectivity was observed for the monomer, bis(hydroxyethyl)terephthalate (BHET). The relatively low yield of bis(hydroxyethyl)terephthalate (BHET) may affect productivity and also lead to various economic and environmental problems such as the need for purification work to separate low-value by-products and the need to treat the by-products.

[0137] 1.2 Glycolysis of polyethylene terephthalate (PET) under low temperature conditions In the case where the glycolysis reaction pathway is selected to depolymerize the polymer containing ester functional groups, as described in the depolymerization reaction conditions of Comparative Examples 1 to 3, the reaction is generally performed at a high temperature of the boiling point (197°C) or higher of ethylene glycol added as an additional reactant for the transesterification reaction. Even when an excess of catalyst is used or a very dilute concentration of the polymer raw material is applied to the reaction, if the reaction temperature is lowered, the reactivity becomes very low or the rate of the side reaction increases relatively because sufficient activation energy required for the depolymerization reaction cannot be obtained, and the desired product cannot be obtained. In addition, for manufacturing processes that require higher reaction temperatures, the applicable methods of dyes or utilities for supplying reaction heat sources are inevitably limited, and excessive costs may be required in terms of equipment investment and operation of the process. Therefore, the design of a low-temperature glycolysis depolymerization reaction that can achieve high reactivity and high yield can provide an effective and decisive means for ensuring the economy of the corresponding process.

[0138] Most of the previous literature on the depolymerization of polymers containing ester functional groups according to the glycolysis reaction pathway proposes reaction conditions at a temperature equivalent to the boiling point of ethylene glycol (197°C) or higher, and it is difficult to reduce the reaction activation energy even when a catalyst consisting of a single or specific component or a composite material mixed with the catalyst is simply added. In particular, there are no substantial examples reported on reaction systems that can significantly reduce the reaction temperature while maintaining equivalent performance.

[0139] As a means for overcoming the above-mentioned problems, the present invention proposes to provide a novel reaction pathway that can significantly reduce the activation energy of the catalyst reaction by using a compound having at least one oxygen in the bonding functional group between the aromatic ring and the alkyl group as an additive, thereby depolymerizing the polymer containing an ester functional group in a low temperature region that is 40°C or more lower than the general glycolysis reaction temperature. Thus, a method for realizing a low-temperature glycolysis reaction that can use a metal salt composed of an organic compound or a cation of a Group 1A or Group 2A metal that is less harmful to the human body as a catalyst that is difficult to maintain performance or difficult to recover due to the possibility of decomposition at high temperatures is proposed.

[0140] In order to specifically illustrate the effect of the low-temperature glycolysis reaction applicable to the present invention, the results of the glycolysis reaction carried out at low temperature (153°C) according to the same component composition as the comparative example are shown in Table 2. In order to illustrate the characteristics of the low-temperature glycolysis reaction applicable to the present invention, the reaction results of each catalyst system are divided into comparative examples and examples and described based on the presence or absence of additives under the premise that all conditions are the same.

[0141] In Comparative Examples 4 to 6, except for adding polymer raw materials, reaction catalysts and ethylene glycol and maintaining the reaction temperature at 153°C, glycolysis depolymerization was performed and evaluated in the same manner as in the previous comparative examples. In Comparative Example 4, glycolysis was performed using zinc acetate as a catalyst, while in Comparative Examples 5 and 6, glycolysis was performed using potassium acetate and sodium acetate as catalysts. In Example 1, zinc acetate was used as a catalyst and anisole, a compound equivalent to the chemical formula 1, was added as an additive, and depolymerization was performed in accordance with the method of Experimental Example 2. In Examples 2 and 3, potassium acetate or sodium acetate was used as a catalyst, respectively, and the others were tested in the same manner as in Example 1.

[0142] The anisole used as an additive can not only be extracted from natural substances, but also can be synthesized in large quantities through industrial methods and used as a raw material or precursor for making spices or perfumes. Compared with other aromatic compounds, its harmfulness is very low.

[0143] The raw material derived from polyethylene terephthalate (PET) bottles used in the above-mentioned comparative examples and examples has an amorphous structure, and because a raw material with a thickness of less than 0.3 mm and a large unit area is put into the reaction, it can be located at a higher effective contact area with additives, catalysts, reactants, etc. from the initial step of depolymerization. In contrast, depolymerization raw materials with different polymerization degrees, shapes, and geometric forms such as material thickness may affect changes in mass transfer and reaction rates, and may also have a significant impact on the yield and performance of the target depolymerization product finally obtained. In Examples 4 to 6, bottles of polyethylene terephthalate (PET) materials composed of multiple layers in waste plastics that may be discarded in daily life, polyethylene terephthalate (PET) colored label paper, and polyester fibers are crushed into 1 cm 2 The following waste resins in an area were quantitatively used as polymer raw materials and then subjected to depolymerization reaction respectively, and the depolymerization was carried out under the same reaction conditions as in Example 3 using raw material 1.

[0144]

Table 2

[0145] As shown in Table 1, although most of polyethylene terephthalate (PET) was decomposed in Comparative Example 1 using zinc acetate as a catalyst and applying a high temperature of 197°C, the results shown in Comparative Example 4 in Table 2, in which depolymerization was performed at a low temperature (153°C) with the same reaction mixture composition, showed an extremely low reactivity of less than 10% conversion rate. In addition, a relatively high ratio of by-products was shown compared to the target product.

[0146] In Comparative Examples 5 and 6, a metal salt containing an alkali metal cation was used in place of zinc acetate in a similar manner, specifically potassium acetate and sodium acetate were used as catalysts for the reaction. Compared with Comparative Example 4, although the conversion rate was slightly improved, the reactivity was not significantly improved. At the same time, the amount of by-products generated was greatly increased, and a higher selectivity for bis(hydroxyethyl) terephthalate (BHET) was observed compared with the case of using zinc acetate (Comparative Examples 1 and 4).

[0147] The reaction result of Example 1 is the result of performing low-temperature (153°C) glycolysis using zinc acetate by adding only anisole to the reactant composition of Comparative Example 4. By comparing the depolymerization results of Comparative Example 4 and Example 1, it can be found that when the additive applicable to the present invention is added, a very significant effect can be brought about on the change of depolymerization performance. Although the reaction temperature of Example 1 is a low-temperature reaction of more than 40°C, an 82.5% yield of bis(hydroxyethyl) terephthalate (BHET) can be achieved within 2 hours, and when the depolymerization reaction time is continued for more than 3 hours, an 85% to 90% yield of bis(hydroxyethyl) terephthalate (BHET) can be achieved.

[0148] When the catalyst was changed to an alkali metal acetic acid catalyst, a more significant effect was observed. For example, the results of the glycolysis reaction carried out at low temperature (153°C) using potassium acetate and sodium acetate as catalysts and in the presence of additives (Examples 2 and 3) can be compared with the cases of high temperature reactions (Comparative Examples 2 and 3) and low temperature glycolysis reactions without additives (Comparative Examples 5 and 6). Regarding Example 2 (or Example 3) in which anisole was added to the reactant composition of Comparative Example 5 (or Comparative Example 6) and low temperature glycolysis was performed, the same high depolymerization reactivity as that of Example 1 in which depolymerization was performed in the presence of additives and zinc acetate was used as a catalyst was observed. By adding anisole to the reaction system using an alkali metal as a catalyst and performing depolymerization, a high reactivity was observed in which all the raw material polyethylene terephthalate (PET) was completely decomposed within 2 hours, even when the reaction temperature was maintained at a low temperature of 153°C, and it was also found that the selectivity of bis(hydroxyethyl) terephthalate (BHET) was greatly improved. For other modified catalysts that are effective in high-temperature glycolysis reactions at 197°C, such as catalysts in other salt forms containing alkali metals or catalysts in non-metallic organic forms such as guanidine, the addition of anisole can also significantly improve their reactivity in low-temperature glycolysis reactions below 153°C, and selectivity improvements can be observed in some catalyst systems. The low-temperature depolymerization performance under different catalyst types will be described in more detail in Section 1.7.

[0149] In addition, by comparing the depolymerization reaction results of Examples 4 to 6 using polymer raw materials of different characteristics under the same conditions, it was found that in Example 6, in which polyester fiber, which is expected to be relatively less subject to mass transfer limitation during depolymerization due to its low intrinsic viscosity (IV~0.65), was used as a raw material, a higher yield of bis(hydroxyethyl) terephthalate (BHET) was obtained compared with other cases in which polyethylene terephthalate (PET) was used as a raw material (IV=0.74). In Example 4, in which a multi-layered polyethylene terephthalate (PET) sheet was used as a raw material, a slightly lower yield of bis(hydroxyethyl) terephthalate (BHET) of 82.5% was observed when the reaction was performed for only 2 hours.

[0150] In addition, in Example 5, in which colored polyethylene terephthalate (PET) in a film form, which is expected to be relatively less affected by mass transfer, was used as a raw material, a relatively low yield of less than 80% was observed, although a relatively high initial reactivity was observed. In the above case, no improvement in yield was observed even after long-term exposure to the reaction conditions, and it can be inferred that the poor yield of bis(hydroxyethyl) terephthalate (BHET) may be the result of impurities such as pigments having a certain adverse effect on the depolymerization performance.

[0151] 1.3 Temperature range of low temperature depolymerization reaction The following specific examples are used to illustrate the effective range of low-temperature reaction or depolymerization reaction while maintaining the effective reactant composition in the previous low-temperature glycolysis reaction. Therefore, the following examples include specific embodiments of changing the temperature and observing the depolymerization performance while maintaining other reaction conditions other than the temperature unchanged in order to determine the qualitative and quantitative reaction characteristics of the depolymerization reaction.

[0152]

Table 3

[0153] Table 3 shows the results of glycolytic depolymerization and evaluation performed in the same manner as in Example 3 except that the reaction temperature was maintained at 130 to 150°C. 0.04 mol of sodium acetate (NaOAc) was used as a catalyst per mol of polymer repeating monomer, and 4 mol and 12 mol of anisole and ethylene glycol were used, respectively. The experiment was repeated for a total reaction time of 3 hours or 6 hours, and the resulting reactants were prepared into samples using the same method, and then the conversion rates and yields were compared after quantitative analysis by high performance liquid chromatography (HPLC).

[0154] According to an example of the reactant composition applicable to the present invention, the result of adding anisole and subjecting polyethylene terephthalate (PET) raw material to low-temperature glycolysis showed obvious and effective reaction characteristics above 130°C, and a very significant effect of a conversion rate close to 100% was observed when exposed to the reaction for a long time (6 hours) above 145°C.

[0155] In addition, in Example 11, in which the depolymerization was performed at 150°C, it was completely decomposed within 3 hours due to its high reactivity, but a relatively low selectivity to the monomer product (bis(hydroxyethyl) terephthalate (BHET)) was observed when it was exposed to the reaction conditions for a long time. This is because when the target product that has been generated is continuously exposed to high temperature conditions, the yield of mono(hydroxyethyl) terephthalate (MHET) gradually increases due to the side reaction pathway, namely the hydrolysis of bis(hydroxyethyl) terephthalate (BHET). Therefore, in order to ensure that the quality of the polymer is completely decomposed and prevent the increase in the rate of side reactions, the reaction time is also optimized while optimizing the temperature, so as to improve the final yield of the target product.

[0156] 1.4 Performance evaluation of depolymerization reaction at different additive inputs The following specific examples are used to illustrate the effective range of the additive effect while maintaining the effective reactant composition and reaction conditions in the previous low-temperature glycolysis reaction. The following examples include specific examples of changing the amount of additive added while maintaining the reaction conditions unchanged and observing the depolymerization performance in order to determine the characteristics of the depolymerization reaction.

[0157] Table 4 shows the distribution change results of the products obtained after 2 hours of low-temperature (153°C) depolymerization of polyethylene terephthalate (PET) without adding additives (Comparative Examples 5 and 6) and when the amount of additives added to the reaction was changed (Examples 12 and 13). That is, the test was repeated while changing the amount of anisole added as an additive within the range of 0 g to 39.4 g (7 moles per mole of polymer repeating monomers), and the glycolytic depolymerization was performed and evaluated in the same manner as in Example 2 or Example 3 except for the amount of additives.

[0158]

Table 4

[0159]

[0160] A metal salt containing an alkali metal cation was used as a catalyst. In Comparative Examples 5 and 6, in which no additive corresponding to Chemical Formula 1 of the present invention was added, low glycolysis reaction performance was observed. However, the results of Examples 12 and 13, in which only a small amount of additive (anisole) was added, showed that while the reactivity increased, the selectivity of bis(hydroxyethyl) terephthalate (BHET) generated by the glycolysis reaction of polyethylene terephthalate (PET) was also greatly improved. In particular, when the amount of additive added was increased to more than 3 molar ratios compared to the applicable polymer raw material, most of the polymer could be decomposed in only two hours of reaction, and the selectivity of the target product could be maintained at a fairly high value.

[0161] In addition, when the temperature of the additive used is reduced to below 100°C, it can be phase-separated from the excess ethylene glycol used as a reactant, and even when an excess of water is added to purify the target product, only a very limited concentration of the additive will remain in the aqueous solution in which the target product is dissolved, so it can be easily recovered. Therefore, although the additive can be easily separated by liquid-liquid extraction, from the perspective of efficiency, a gas-liquid separation method in which the reaction temperature is raised to the boiling point of the additive at the end of the reaction and then a part or all of the condensed additive is separated into an external flow by a condenser may be more advantageous. Although the additive applicable to the present invention is a compound that does not directly participate in the reaction, it has characteristics similar to those of a catalyst because of its significant effect in reducing the activation energy of the reaction. However, it cannot directly improve the reactivity in the presence of a metal salt or other catalyst, and therefore actually exhibits characteristics similar to those of a co-catalyst.

[0162] 1.5 Performance evaluation of depolymerization reaction at different catalyst amounts The following specific examples are used to illustrate the effect of adjusting the amount of catalyst added while maintaining the effective reactant composition and reaction conditions in the previous low-temperature glycolysis reaction. The following examples include specific examples of changing the amount of catalyst added while maintaining the reaction conditions unchanged (reaction temperature: 153°C, reaction time: 2 hours, additive: anisole) and observing the depolymerization performance in order to determine the characteristics of the depolymerization reaction.

[0163]

Table 5

[0164] Table 5 shows the results of glycolytic depolymerization and evaluation performed in the same manner as in Example 2 and Example 3, except that the amount of catalyst (metal salt containing alkali metal cations) added was changed from 0 g to 1.0 g (0.20 mol per mol of polymer repeating monomer) and the test was repeated. The results are recorded as Example 14 and Example 15, respectively.

[0165] When the amount of catalyst added was less than 0.01 molar ratio compared to the repeating monomer of the polymer raw material, a significant decrease in reactivity was observed, but at the same time, a higher selectivity for the target product, bis(hydroxyethyl) terephthalate (BHET), was observed. It can be inferred that this is because the increase in the amount of catalyst added has a greater impact on the increase in the rate of side reactions. When the amount of catalyst added exceeded 0.01 molar ratio compared to the repeating monomer of the polymer raw material, most of the added polyethylene terephthalate (PET) was decomposed due to the higher reactivity, and it was completely decomposed when it exceeded 0.03. When the catalyst was used in a ratio of more than 0.03 but less than 0.10 mol to achieve complete decomposition, it was observed that different amounts of catalyst caused slight changes in the selectivity or yield of the target product (bis(hydroxyethyl) terephthalate (BHET)), but when an excessive amount of catalyst was used, the amount of byproducts generated increased, and it was confirmed that the yield of bis(hydroxyethyl) terephthalate (BHET) decreased. The results of observing the depolymerization reaction characteristics at different catalyst input amounts showed that the reaction performance can be maintained and adjusted in a wide range according to the catalyst input amount. It can be inferred that even if a part of the catalyst is reused after the reaction, the catalyst concentration cannot be accurately adjusted, and it is sufficient to replenish a part of the catalyst that is expected to disappear, thereby ensuring flexibility during the operation of the project.

[0166] 1.6 Performance evaluation of depolymerization reaction with different additive types The following specific examples are used to illustrate the reaction effects when a part or all of the additives applicable to the present invention are modified while maintaining the effective reactant composition and reaction conditions in the previous low-temperature glycolysis reaction. In order to determine the characteristics of the depolymerization reaction, the specific examples include observing the depolymerization performance when the number of functional groups bonded or the modified form of the additive is changed while maintaining the reaction conditions (reaction temperature 153°C, reaction time 2 hours, catalyst: KOAc) and using a compound containing oxygen in the functional group bonded between the aromatic ring and the alkyl group.

[0167]

Table 6

[0168] Table 6 is used to understand the effect of low-temperature depolymerization when depolymerization is performed using other forms of additives instead of anisole used as an additive in the previous example. Glycolytic depolymerization was performed and evaluated in the same manner as in Example 2 except that 4 moles of other forms of additives were used instead of anisole per mole of the polymer repeating monomer.

[0169] By comparing the results of Comparative Example 5 in which polyethylene terephthalate (PET) glycolysis was performed without adding an additive, and Examples 2, 16 to 20 in which a compound containing at least one oxygen in the bonding functional group between an aromatic ring and an alkyl group was added, it can be confirmed that, although there are certain performance differences, the effect of adding the additive applicable to the present invention is very significant. In the depolymerization performance results of Examples 16 to 18, which are examples of modified additives, it is observed that the reactivity and selectivity of the target product decrease when m in the chemical formula 1 increases to 2 or more. Examples 19 and 20 are examples related to the depolymerization of modified additives in which the carbon number of the alkyl group bonded by oxygen is not one or other forms of functional groups that can be additionally bonded to non-alkyl functional groups are added. Through the depolymerization results of Examples 18 and 19, it is observed that there are certain deviations in reactivity and the yield of bis(hydroxyethyl) terephthalate (BHET), but the effect of the present invention can also be clearly observed. Comparative Example 7 is the result of evaluating the depolymerization performance of methoxycyclohexane (a saturated cycloalkane compound with the same carbon number as the additive to which the present invention is applied, in which at least one alkyl group is connected via a linking group, the linking group having at least one oxygen, but the central functional group is not an aromatic ring) which has a similar structure to the additive to which the present invention is applied, but the central functional group of the compound is in another form. Compared with the case of Comparative Example 5 in which no additive is added, relatively lower reactivity and selectivity for bis(hydroxyethyl) terephthalate (BHET) are observed.

[0170] In a specific embodiment of the present invention, the additives added are evaluated on the same molar basis, but when the form of the binding functional group changes, the interaction with the raw materials and the additives may also change. Therefore, the performance deficiencies can be compensated by adjusting the form or amount of the additives added to the reactants.

[0171] 1.7 Performance evaluation of low-temperature depolymerization using different catalysts The following specific examples are used to illustrate the reaction effects when a part or all of the catalyst types applicable to the present invention are modified and used while maintaining the effective reactant composition and reaction conditions (reaction temperature 153°C, reaction time 2 hours) in the previous low-temperature glycolysis reaction. In order to determine the characteristics of the depolymerization reaction, a metal salt containing an alkali metal or alkaline earth metal cation is used as a catalyst while maintaining the reaction conditions unchanged, and the counter ion is changed to other forms such as carbonic acid, bicarbonate, and alkoxide, or a metal-free organic compound catalyst is used to observe the change in depolymerization performance.

[0172]

Table 7

[0173] Table 7 shows the results of comparative evaluation of the low temperature (153°C) depolymerization performance when various forms of the catalysts described are applied. The additives applicable to the present invention were added, but the amount of all compounds added was limited compared to the polymer, and the evaluation was performed in the reaction rate limited region (kinetic limited regime) so that the performance difference between the different catalysts was more significant. Glycolytic depolymerization was performed and evaluated in the same manner as in Example 1, except that 0.02 moles of catalyst were added per mole of polymer repeating monomers, and about 32.30 g (10 moles per mole of polymer repeating monomers) and about 16.88 g (3 moles per mole of polymer repeating monomers) were used. Although it is not included in the results and Table 7 lists the use of one of the various modified catalysts or organic compounds with different forms of counterions as catalysts, the independent performance of the catalyst was first observed by performing low temperature (153°C) depolymerization without adding the additives applicable to the present invention. First, it can be predicted from the results described in the previous specific comparison that even when the catalyst is changed, as shown in the performance results of Comparative Examples 4 to 6 in which the reaction is performed without adding an additive, lower reactivity and very limited yield of bis(hydroxyethyl) terephthalate (BHET) are observed.

[0174] In Examples 21 and 22, where the cation is a metal salt catalyst composed of a group 1A metal and the anion is a carbonate ion, high reactivity and high monomer yield were observed, similar to the case where the anion was a catalyst composed of an acetate ion. In contrast, in Examples 23 and 25, where the same mole of bicarbonate was used as an anion, relatively low reactivity was observed. In the case of a glycolysis reaction performed under the same conditions using a metal carbonate catalyst composed of a group 2A metal cation as a substitute (Example 25), higher reactivity and higher monomer yield were observed compared to the previous alkali metal salt catalyst using bicarbonate as an anion. In addition, when the same conditions were applied and the same mole of a metal-free organic compound catalyst, i.e., triazabicyclodecene, was used as a catalyst (Example 27), a very ideal glycolysis reaction was observed with a reaction conversion rate of 99.0% or more and a bis(hydroxyethyl)terephthalate (BHET) yield of 81.8% or more.

[0175] As shown in the previous depolymerization reaction results using various modified forms of transesterification catalysts, by adding the additive applicable to the present invention (the compound represented by Chemical Formula 1), the glycolytic reactivity of the polymer containing an ester functional group can be greatly improved, and bis(hydroxyethyl) terephthalate (BHET) can be obtained at a high yield below the boiling point of ethylene glycol.

[0176] 1.8 Purification and analysis of diol addition monomers generated after depolymerization The following specific examples are used to understand the physical and chemical characteristics of the bis(hydroxyethyl)terephthalate (BHET) product, including purity, obtained by a purification process after depolymerization of a polymer containing ester functional groups according to the method of the present invention. The process may include a separation method for recovering additives. As described in the previous specific examples, by adding additives, a high-performance glycolysis reaction can be performed in a low-temperature region below 153°C, so that a catalyst system that is difficult to use in a high-temperature region above 197°C can be introduced, which can bring many advantages to the purification process. As an example, the range of catalyst reactions that perform best in low-temperature regions can be expanded to alkali metal salts, and organic compounds that may decompose at high temperatures can be used as catalysts without loss, thereby promoting purification or material recovery. In addition, there is no need to use catalysts containing harmful metals such as zinc, lead and other heavy metals that are mainly used in existing commercial projects, so raw materials for high-quality environmentally friendly materials can be produced, or it is expected to be a recycling technology for creating a complete waste plastic recycling economy.

[0177] The following examples include specific examples conducted to evaluate the yield and purity of the diol addition monomer obtained by performing a purification process on the reaction products obtained by a high temperature (197°C) depolymerization reaction without additives and using a zinc acetate catalyst and a low temperature (153°C) depolymerization reaction with anisole added and using an acetate of a Group 1A metal as a catalyst, while maintaining the mass ratio of the compounds proposed in the present invention.

[0178] Table 8 shows the results of adding a certain amount of polymer raw material, reaction catalyst and ethylene glycol used in the depolymerization reaction at a mass ratio of 1:0.1:4 (when adding additives, the additive is used in an amount twice the mass of the polymer raw material) and performing depolymerization according to the method of Example 1 or Example 2. In Comparative Example 8 in which no catalyst is added and zinc acetate is used as a catalyst, the depolymerization is performed at a high temperature (197°C), while in Examples 28 and 29 in which anisole is added and potassium acetate and sodium acetate are used as catalysts, the depolymerization is performed at a low temperature (153°C), and then the depolymerization product is obtained according to the same purification process as in Experimental Example 3. The depolymerization product was obtained by inductively coupled plasma (ICP) and hydrogen nuclear magnetic resonance (HNMR). 1 For Comparative Example 8, the product was washed according to the process in Experimental Example 4, and the improvement of the quality of the product (Comparative Example 9) was confirmed.

[0179]

Table 8

[0180] The residual metal amounts of Comparative Example 8 and Examples 28 to 29 given in Table 8 are the results of analyzing the residual metal content in bis(hydroxyethyl) terephthalate (BHET) obtained by obtaining the product according to the glycolysis reaction pathway of polyethylene terephthalate (PET) and subjecting it to the first recrystallization by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) with a detection limit of more than 1 ppm.

[0181] A certain amount of residual metal was detected in bis(hydroxyethyl)terephthalate (BHET) after the reaction with zinc acetate and the purification process. Although zinc used as a catalyst is classified as an inorganic substance important to the human body, it is also classified as a harmful metal that may cause digestive system disorders when excessive or continuous intake is taken by the human body through the use of products such as beverage containers. Since the zinc remaining in plastic is discharged into the nature as waste and accumulated in animals and plants and then reabsorbed by the human body through an indirect route, it may induce various side effects. Therefore, low-temperature depolymerization reaction technology based on harmless metal catalysts that can replace it not only has excellent product commerciality, but is also relatively beneficial in reducing environmental pollution.

[0182] Therefore, an alkali metal salt was used as a catalyst, and the same mass of the catalyst as the zinc acetate used in Comparative Example 8 was added (in terms of the molar number of the metal, a larger amount was used than in Comparative Example 8) and the reaction and purification were performed. Referring to the results of Example 28 (or Example 29), no metal residue was detected in the final product manufactured using the alkali metal salt catalyst. The metal ions constituting the catalyst are also essential dielectrics in the human body and have the advantage of being less harmful than zinc. The reason why the metal residue in the products manufactured according to Examples 28 and 29 is low is that the components constituting the catalyst have a very high degree of ionization in the aqueous solution compared to zinc acetate during the purification process, so they are easily dissociated, and the amount of metal remaining in the bis(hydroxyethyl) terephthalate (BHET) product recovered in a solid state or not eluted into the aqueous solution phase during the recrystallization and physical filtration process is very thin.

[0183] By hydrogen nuclear magnetic resonance ( 1 The qualitative characteristics of the purified diol addition monomer were observed by H-NMR. The specific spectra measured are as follows: Figures 1 to 3 shown.

[0184] The hydrogen nuclear magnetic resonance (H NMR) of the monomers obtained by purification according to the method of Comparative Example 8 based on high temperature glycolysis 1 The results of H-NMR are shown below.

[0185] 1 H-NMR (500 MHz, DMSO- d 6) δ (ppm): 8.12 ( s , 4H), 4.99 ( br s , 2H),4.33 ( t , 4H), 3.73 ( t , 4H) Referring to a number of prior literatures related to the nuclear magnetic resonance (NMR) spectrum of bis(hydroxyethyl) terephthalate (BHET) monomer obtained by glycolysis of polyethylene terephthalate (PET) using ethylene glycol, it was found that a characteristic peak due to hydrogen in the terminal group, i.e., the hydroxyl group, was observed at around 4.95 ppm, which was divided into a triplet due to hydrogen in the adjacent vinyl group, and a characteristic peak due to hydrogen (attached) bound to the carbon adjacent to the hydroxyl group was observed at around 3.73 ppm. Figures 2 to 3 In c ) is a peak of a quartet morphology. However, the hydrogen nuclear magnetic resonance (HNMR) of the bis(hydroxyethyl)terephthalate (BHET) monomer obtained by simple purification by the method in Comparative Example 8 is 1 In the H-NMR spectrum, a broad single peak was observed at around 4.99 ppm, and a triplet line was observed at around 3.27 ppm. It can be inferred that this is due to interference caused by the zinc acetate catalyst, which is an impurity remaining in bis(hydroxyethyl) terephthalate (BHET) as shown in Table 8.

[0186] In Comparative Example 9, an additional purification method was performed to reduce the amount of metal residues in the diol addition monomer obtained by Comparative Example 8. When performing additional purification according to the method of Experimental Example 4, distilled water maintained at a certain temperature was added to the white powder product finally obtained by Comparative Example 8 and stirred for about 1 hour. After completion, the additional washed precipitate was recovered and dried using the same filter as in Comparative Example 8. The additional purification process was repeated according to the method shown in Experimental Example 4, and after obtaining the bis(hydroxyethyl)terephthalate (BHET) monomer in which no metal could be detected within the detection limit of inductively coupled plasma (ICP), the hydrogen nuclear magnetic resonance (HNMR) was re-measured. 1 The characteristic peaks of the H NMR spectrum are shown below.

[0187] 1 H-NMR (500 MHz, DMSO- d 6) δ (ppm): 8.12 ( s , 4H), 4.97 ( t , 2H), 4.33( t , 4H), 3.73 ( q , 4H) In the monomer based on high temperature glycolysis purified by the method in Comparative Example 8, a broad single peak was observed at around 4.99 ppm, a triplet line was observed at around 4.97 ppm, and a quartet line other than a triplet peak was observed at around 3.73 ppm.

[0188] Next, after glycolysis was performed according to the method in Example 28 (using potassium acetate) and the product was purified, the bis(hydroxyethyl)terephthalate (BHET) monomer recovered without performing an additional purification process was analyzed by hydrogen nuclear magnetic resonance (H NMR) in the same manner as in Comparative Example 8. 1 H-NMR) structural analysis was performed and the characteristic peaks observed are shown below.

[0189] 1 H-NMR (500 MHz, DMSO- d 6) δ (ppm): 8.12 ( s , 4H), 4.95 ( t , 2H), 4.33( t , 4H), 3.73 ( q , 4H) Almost the same H NMR ( 1 H-NMR) spectroscopy.

[0190] Through the comparative examples and embodiments, it can be confirmed that, similar to the difference in structural characteristics between monomers containing lead metal residues and high-purity monomers, the bis(hydroxyethyl) terephthalate (BHET) obtained by using the catalyst system prepared according to the present invention only requires a simple purification process to obtain a high-purity product, so purification can be carried out efficiently, and it is also more advantageous in terms of productivity and economy.

[0191] 2. An extractant for removing color-developing foreign substances from a monomer of a polymer containing an ester functional group and a method for removing color-developing foreign substances from a monomer of a polymer containing an ester functional group Method for purifying monomers of extracting agent [Raw materials 5 and 6] From the waste plastic containers discarded after use, only the colored label paper whose component polymer is polyethylene terephthalate (PET) is recovered and separated according to the main component color, and then cut into raw materials 5 with a single-sided size of less than 0.5 cm. Next, the polyester fiber dyed with disperse dyes is cut into 1 cm 2 The following fiber raw material is raw material 6.

[0192] Test Example 5: Liquid-Liquid Extraction Step After the reaction was completed, about 200 g of distilled water at 95 to 100° C. was added to the filtrate obtained by filtration. Next, the mixture was moved to a container maintained at 75° C. and stirred for 1 hour, and after stopping the stirring, when phase separation occurred, the lower aqueous solution layer was extracted and placed at room temperature to lower its temperature.

[0193] Test Example 6: Liquid-Liquid Stripping Step After adding about 200 g of distilled water at 95 to 100° C. to the organic solution layer separated by the same liquid-liquid extraction step as in Experimental Example 5, move it to a container maintained at 75° C. and stir it for 1 hour. After stopping the stirring, when phase separation occurs, extract the lower aqueous solution layer and place it at room temperature to lower its temperature.

[0194] Test Example 7: Depolymerization Productization Step After the reaction mixture solution containing the monomers or the aqueous solution phase extracted in Test Example 5 or Test Example 6 was placed in a storage maintained at 4°C for 12 hours, a large amount of water in the crystallized solid phase was removed by physical filtration to extract the solid component. Then, it was moved to a vacuum dryer maintained at 60°C and vacuum dried for more than 12 hours to obtain a depolymerized product.

[0195] Test Example 8: Organic solvent and pigment recovery steps The upper phase (organic layer) remaining after separation of the aqueous solution layer in Test Example 5 or Test Example 6 was condensed into a liquid phase after anisole was separated into a vapor phase using a single distiller, and the residual components containing a large amount of pigments could obtain a viscous semi-solid phase product. The obtained products were quantified using a high-precision scale with an accuracy of ±0.1 mg.

[0196] 2.1 Production of high purity monomers from waste polyethylene terephthalate (PET) film containing pigments In Comparative Examples 10 and 11, a colored polyethylene terephthalate (PET) film containing a pigment (raw material 5 classified as yellow and green) was used as a polymer raw material, wherein depolymerization was performed using the reaction conditions and compound components of Comparative Examples 1 and 2 described in Table 1, and for the resulting products, after removing oligomers in the reactants by the filtration method in Experimental Example 3, respectively, a monomer product was obtained by the process in Experimental Example 7.

[0197] In Example 30, depolymerization was carried out using raw material 5 according to the same reactant components and reaction conditions as in Example 2, and the aqueous solution phase was extracted after liquid-liquid extraction according to the method in Experimental Example 5, and the monomer product was obtained through the process in Experimental Example 7, while in Example 31, anisole (22.5 g) was added to the aqueous solution layer obtained in Example 30, and the liquid-liquid extraction step in Experimental Example 5 was repeated once, and then the monomer product was obtained through the process in Experimental Example 7.

[0198] In Example 32, after adding about 22.5 g of anisole and about 200 g of distilled water at 95 to 100° C. to the depolymerization product obtained by Comparative Example 10, liquid-liquid extraction was performed according to the method in Experimental Example 5, and then the aqueous solution phase was extracted and the monomer product was obtained by the method in Experimental Example 7.

[0199] In Example 33, the organic layer separated in the liquid-liquid extraction process of Example 31 was used to perform the liquid-liquid stripping step in Experimental Example 6, and then the aqueous solution phase was extracted, and the monomer product was obtained by the method in Experimental Example 7.

[0200] The structural characteristics of the purified monomers were confirmed using a nuclear magnetic resonance spectrometer (Bruker Avance II 500 MHz), and the residual amount of colored organic foreign matter in the depolymerization product was estimated based on the measured sample mass value and the relative area ratio of the characteristic peak. In the measurement process, 20 mg of the purified monomers and 10 mg of the organic foreign matter were diluted to 0.7 ml of dimethyl sulfoxide- d 6 (DMSO- d 6) Samples in solvent.

[0201] exist Figure 5 The figure shows the H NMR (100 Å) of a monomer such as bis(2-hydroxyethyl)terephthalate (BHET) which can be obtained by glycolysis reaction using a polymer containing an ester functional group as a raw material and the concentrated pigment recovered from a polyethylene terephthalate (PET) film on the right (produced according to Test Example 8). 1 H-NMR) spectrum. The depolymerized product produced by the process of Example 31 to Example 33 is equivalent to a bis(hydroxyethyl)terephthalate (BHET) monomer purified to a high purity of more than 99.9%, and the H-NMR ( 1 H NMR) spectra, we observed results similar to the benchmark values ​​of characteristic peaks reported in most previous literature.

[0202] 1 H-NMR (500 MHz, DMSO- d 6) δ (ppm): 8.13 ( s , 4H), 4.96 ( t , 2H), 4.32( t , 4H), 3.72 ( q , 4H) Similar to the report, the characteristic peak due to the hydrogen contained in the terminal group, the hydroxyl group, was observed at around 4.96ppm, which was divided into a triplet due to the interaction of the hydrogen in the adjacent hydroxyl group, and the hydrogen directly bonded to the functional group adjacent to the hydroxyl group (equivalent to Figure 5 3 and 4) in the chemical formula of bis(hydroxyethyl) terephthalate (BHET) shown in FIG. 1 are peaks of a characteristic quartet form.

[0203] Nuclear magnetic resonance (NMR) spectra of pigmented organic foreign matter extracted from colored polyethylene terephthalate (PET) film ( Figure 5 The upper spectrum in the figure is very complex, and it can be seen that in the process of purifying the polymer depolymerization product, if only the general physical filtration method is applied, although some organic matter can be removed, it is difficult to remove the colored organic mixture. In particular, although only a trace amount of organic compounds characterized by chemical shift values ​​of 0.94 and 4.69 ppm are contained, it has a color characteristic similar to that of the starting material, that is, the colored polyethylene terephthalate (PET) film, and by applying the extraction method of the present invention, the polymer depolymerization monomer product (bis(hydroxyethyl) terephthalate (BHET)) can be purified to a high purity.

[0204] The foreign matter content was calculated by comparing the mass values ​​of the samples (organic foreign matter and purified bis(hydroxyethyl) terephthalate (BHET)) used in the nuclear magnetic resonance (NMR) spectrum with the integrated values ​​of the characteristic peaks. The estimated foreign matter content based on the respective chemical shift values ​​is given in Table 9.

[0205]

Table 9

[0206] Regarding the yield of the depolymerized product, the total molar number of repeating units in the polymer fed as the initial raw material was set as 100, and the molar ratio (%) to the amount of the depolymerized product obtained by quantifying the amount of the product by high performance liquid chromatography (HPLC) was calculated. In Table 9, the amount of the depolymerized monomer product recovered according to Comparative Example 10, Comparative Example 11, and Examples 30 to 33 using the waste polyethylene terephthalate (PET) film that was colored due to the inclusion of a pigment as a raw material is listed as the molar number (%) value of bis (hydroxyethyl) terephthalate (BHET). When the extraction process was repeated more than two times, a very low foreign matter content was observed, but the yield of the final product decreased with the increase in the mass of the monomer lost during the purification process of the product.

[0207] 2.2 Production of high purity monomers from polyester fibers containing dyes Unlike pigments that are dispersed in a solvent and then colored in the form of particles or powders, dyes used in a state dissolved in a solvent are mainly used for dyeing fiber materials, leather, etc. In particular, in order to color polymer fibers containing ester functional groups, such as fiber materials such as polyester, dyes in the form of organic compounds containing at least one aromatic ring are generally used for coloring.

[0208] As the dye, in order to prevent the phenomenon of discoloration from the polymer fiber, a substance having a very high affinity with the terephthalate functional group constituting the fiber is used as a pigment, and it is required to have the characteristics of being physically and chemically uniformly dispersed on the fiber. Therefore, even in the case of depolymerization, it may be difficult to separate and purify a high-purity product because it has a high interaction with the monomer or low-molecular compound generated by the depolymerization. Therefore, although there is a certain degree of miscibility with the product, that is, the monomer or low-molecular compound, by supplying a large amount of a solvent having a strong affinity with the organic dye and adding an excessive amount of a hydrophilic solvent thereto, it is possible to induce asymmetric solute (dye) distribution and thereby recover a high-purity product.

[0209] In Comparative Example 12, a monomer product was obtained in the same manner as in Comparative Example 11 except that raw material 6 (dark blue waste polyester fiber) was used. In Example 34, a monomer product was obtained in the same manner as in Example 31 except that raw material 6 was used.

[0210] In Example 35, the organic layer separated in the repeated liquid-liquid extraction process of Example 34 is used as a raw material to perform the liquid-liquid stripping step in Experimental Example 6, and then the aqueous solution phase is extracted, and the monomer product is obtained by the method in Experimental Example 7.

[0211] In Example 36, the aqueous solution phase was extracted after the liquid-liquid extraction process performed in Example 34 was repeated 4 times, and the monomer product was obtained by the method in Experimental Example 7.

[0212] exist Figure 6 The nuclear magnetic resonance (NMR) spectra of bis(hydroxyethyl) terephthalate (BHET) monomer obtained by reaction after depolymerization using colored polyester fiber as a raw material and the fuel recovered and concentrated by Test Example 8 are shown in FIG.

[0213] In the hydrogen nuclear magnetic resonance ( 1 In the H-NMR spectrum, the main peak was clearly observed in the inherent chemical shift value showing the structural characteristics of the bis(hydroxyethyl)terephthalate (BHET) monomer, similar to the spectra obtained by the previous Examples 30 to 33 using raw materials containing pigments. However, when the number of extractions is limited or the product is recovered by back extraction, although the overall yield of the depolymerization product can be improved, the purity of the bis(hydroxyethyl)terephthalate (BHET) monomer is limited to a level of less than 99%, indicating that foreign matter cannot be effectively removed due to the inherent color of the dye. The results of observing the monomer product manufactured according to the specific test example of the present invention show that even in the case of a trace amount of organic dye less than 1% by mass, it can be easily distinguished by the naked eye because the product contains pigment foreign matter.

[0214] In order to recover bis(hydroxyethyl) terephthalate (BHET) of the same quality as the high-purity monomer product obtained by purifying the reactants obtained by depolymerizing the pigment-containing waste polyethylene terephthalate (PET) raw materials as previously exemplified (Examples 11 to 33), it is necessary to perform the same repeated extraction process as the purification process in Example 36.

[0215] Table 10 is a specific example of a process for obtaining a high-purity monomer from a depolymerization reaction mixture obtained using a colored polyester raw material. It can be seen that by performing an extraction and purification process (Test Example 5) after adding the compound represented by Chemical Formula 1, the colored organic disperse dye can be effectively removed. Although the product obtained in the case of repeating the extraction and purification process more than 2 times (Example 34) and performing back extraction using the organic phase generated in the 2nd extraction process (Example 35) has a purity of more than 99.5%, due to a trace amount of residual dye, a powder product with a light red color is finally obtained. In the case of repeating the extraction and purification process more than 4 times, although the final product yield is as low as about 51%, the residual amount of dye detected reaches a level of less than 0.1%, and a high-purity white bis(hydroxyethyl) terephthalate (BHET) product can be obtained.

[0216]

Table 10

[0217] In the above content, specific parts of the present invention are described in detail, but people with general knowledge of the industry should understand that the specific technology is only a preferred embodiment, and the scope of the present invention is not limited thereto. Therefore, the substantive scope of the present invention should be defined by the attached claims and their equivalents.

[0218] Industry availability The present invention relates to a method for depolymerizing a polymer containing an ester functional group which may or may not contain a pigment or a dye, a composition for performing the depolymerization, and a purification method for selectively separating foreign matter from the monomers of the polymer, which can be effectively applied to technical fields such as the manufacture, recovery and reuse of polymers containing ester functional groups, and therefore has industrial applicability.

Claims

1. An extractant for removing chromogenic foreign matter from a monomer of a polymer containing an ester functional group, characterized in that: The extractant comprises a compound represented by the following chemical formula 1: 【Chemical formula 1】 In the chemical formula 1, R1 is selected from hydrogen, hydroxyl, aldehyde, carboxyl, C1-C6 alkyl, C4-C6 cycloalkyl and C6-C 12 One of the aromatic groups selected from The n is an integer from 0 to 5, and when the n is 2 or more, R1 are the same or different. R2 is C1-C 10 The alkyl group The m is an integer from 1 to 6, and when the m is 2 or more, -O-R2 are the same or different.

2. The extractant for removing color-forming foreign matter from a monomer of a polymer containing an ester functional group according to claim 1, characterized in that: The compound represented by Chemical Formula 1 is selected from methoxybenzene, 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, 1,2,3-trimethoxybenzene, 1,2,4-trimethoxybenzene, 1,3,5-trimethoxybenzene, 1,2,3,4-tetramethoxybenzene, 1,2,3,5-tetramethoxybenzene, 1,2,4,5-tetramethoxybenzene, 2-methoxyphenol, 1,3-dimethoxy-2-hydroxybenzene, 4-hydroxy-3,5-dimethoxybenzoic acid, 3-(4-hydroxy-3,5-dimethoxyphenyl)prop-2-enal, 4-hydroxy-3,5-dimethoxybenzaldehyde, 4-hydroxy-3,5-dimethoxyacetophenone, 3-(4-hydroxy-3 One or more selected from the group consisting of 1,3,5-trichloro-2-methoxybenzene, 1,3,5-tribromo-2-methoxybenzene, 1-methoxy-4-[(E)-prop-1-enyl]benzene, 2-tert-butyl-4-methoxyphenol, 1-methoxy-4-[(E)-prop-1-enyl]benzene, 1-bromo-4-methoxybenzene, 2-tert-butyl-4-methoxyphenol, ethoxybenzene, 1,3,5-trichloro-2-methoxybenzene, 1,3,5-tribromo-2-methoxybenzene, 1-methoxy-4-[(E)-prop-1-enyl]benzene, and 2-methoxy-4-[(E)-prop-1-enyl]benzene.

3. The extractant for removing color-forming foreign matter from a monomer of a polymer containing an ester functional group according to claim 1, characterized in that: The monomer of the polymer containing an ester functional group is obtained by depolymerization reaction of the polymer containing an ester functional group.

4. A purification method for removing color-forming foreign matter from a monomer of a polymer containing an ester functional group and producing a high-purity monomer, characterized in that: include: 1) adding a compound represented by the following chemical formula 1 to a monomer of a polymer containing an ester functional group and containing a color-forming foreign substance and mixing the mixture; 2) a step of inducing liquid-liquid phase separation by allowing the mixed solution in step 1) to stand; as well as, 3) The step of separating the phase-separated liquid-liquid layer into an upper organic solution layer and a lower aqueous solution layer and discharging the layers: 【Chemical formula 1】 In the chemical formula 1, R1 is selected from hydrogen, hydroxyl, aldehyde, carboxyl, C1-C6 alkyl, C4-C6 cycloalkyl and C6-C 12 One of the aromatic groups selected from The n is an integer from 0 to 5, and when the n is 2 or more, R1 are the same or different. R2 is C1-C 10 The alkyl group The m is an integer from 1 to 6, and when the m is 2 or more, -O-R2 are the same or different.

5. The purification method for removing color-developing foreign matter from a monomer of a polymer containing an ester functional group and generating a high-purity monomer according to claim 4, characterized in that: In the step 1), in addition to the compound represented by Chemical Formula 1, a hydrophilic solution or water that does not mix with the compound represented by Chemical Formula 1 is added to the monomer containing the color-forming foreign matter.

6. The purification method for removing color-developing foreign matter from a monomer of a polymer containing an ester functional group and generating a high-purity monomer according to claim 4, characterized in that: The monomer is a mixture after depolymerization obtained by depolymerizing a polymer including an ester functional group, or a product of partially purifying the mixture after depolymerization.

7. The purification method for removing color-developing foreign matter from a monomer of a polymer containing an ester functional group and generating a high-purity monomer according to claim 4, characterized in that: The step of further extracting the colored foreign matter by adding the compound represented by Chemical Formula 1 to the separated aqueous solution layer is repeated one or more times.

8. The purification method for removing color-forming foreign matter from a monomer of a polymer containing an ester functional group and generating a high-purity monomer according to claim 4, characterized in that: Also includes: A hydrophilic solution or water that does not mix with the compound represented by Chemical Formula 1 is added to the separated organic solution layer and mixed, and then the phase separation step is performed again.

9. The purification method for removing color-developing foreign matter from a monomer of a polymer containing an ester functional group and generating a high-purity monomer according to claim 4, characterized in that: Also includes: A step of recovering monomers of a polymer containing an ester functional group from the separated aqueous solution phase by recrystallization.

10. A purification method for removing colored foreign matter from a monomer obtained by depolymerizing a colored polymer containing an ester functional group and producing a high-purity monomer, characterized in that: include: (a) adding a compound of the following Chemical Formula 1 to a colored polymer containing an ester functional group; (b) a step of depolymerizing the polymer comprising ester functional groups; (c) adding a hydrophilic solution or water that does not mix with the compound represented by Chemical Formula 1 to the depolymerization reaction mixture obtained by the depolymerization reaction and mixing the mixture; (d) a step of inducing liquid-liquid phase separation by allowing the mixed solution in step (c) to stand; as well as, (e) separating the phase-separated liquid-liquid layer into an upper organic solution layer and a lower aqueous solution layer and discharging the layers: 【Chemical formula 1】 In the chemical formula 1, R1 is selected from hydrogen, hydroxyl, aldehyde, carboxyl, C1-C6 alkyl, C4-C6 cycloalkyl and C6-C 12 One of the aromatic groups selected from The n is an integer from 0 to 5, and when the n is 2 or more, R1 are the same or different. R2 is C1-C 10 The alkyl group The m is an integer from 1 to 6, and when the m is 2 or more, -O-R2 are the same or different.

11. The purification method for removing colored foreign matter from a monomer obtained by depolymerizing a colored polymer containing an ester functional group and generating a high-purity monomer according to claim 10, characterized in that: The organic solvent is recovered from the organic solution layer separated and discharged in the step (e) by distillation and reused.

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