WO2024005445A1

WO2024005445A1 - Method for depolymerization of polymer containing ester functional group by using mixture organic solvent

Info

Publication number: WO2024005445A1
Application number: PCT/KR2023/008649
Authority: WO
Inventors: 조정모
Original assignee: 한국화학연구원
Priority date: 2022-07-01
Filing date: 2023-06-22
Publication date: 2024-01-04
Also published as: KR20240003512A

Abstract

The present invention relates to a method for depolymerization of a polymer containing an ester functional group, wherein an aromatic compound having an alkoxy functional group and a compound having an alcohol functional group are mixed to be used as a solvent for reaction and an extractant for foreign material removal and an alkali hydroxide is applied as a reactant, thereby depolymerizing the polymer containing an ester functional group and obtaining high-purity monomers produced from the polymer.

Description

Depolymerization method for polymers containing ester functional groups using mixed organic solvents

The present invention relates to a method for depolymerization of a polymer containing an ester functional group. Specifically, an aromatic compound with an alkoxy functional group and a compound with an alcohol functional group are mixed and used as a solvent for reaction and an extractant for removing foreign substances, and an alkali hydroxide is used as a solvent for reaction and an extractant for removing foreign substances. It relates to a method of decomposing a polymer containing an ester functional group by applying as a reactant and obtaining the monomer produced therefrom with high purity.

Plastics are inexpensive and durable materials that can be used to produce a variety of products that find use in a wide range of applications. Accordingly, not only the production but also the consumption of plastic in daily life has increased dramatically over the past few decades, causing serious environmental problems ranging from the threat of environmental hormones that can be exposed and accumulated in the body to the destruction of the natural ecosystem. Moreover, more than 50% of these plastics are products with a short cycle of use, such as packaging, agricultural film, disposable beverage containers, etc., which are used as single-use disposable products or are discarded within one year of manufacture.

Most of the discarded plastic is randomly discharged into designated landfills and natural habitats around the world, where natural purification is difficult, and the severity of environmental problems is increasing day by day. Even biodegradable or biodegradable plastics can persist for decades, depending on local environmental factors such as levels of UV exposure, temperature, and the presence of degrading microorganisms.

To solve these problems, we aim to minimize the accumulation of plastics or reduce their environmental impact, from chemical decomposition of existing petroleum-based plastics to physical recycling and reprocessing of plastics, including the development of new plastic materials with short decomposition cycles in nature. Various research and efforts are being attempted for this purpose.

Among plastics discarded after consumption, polymers containing ester functional groups have the characteristic of being able to be returned to their original state before synthesis through a relatively simple chemical reaction path such as decomposition or exchange of the ester functional group, through chemical recycling based on depolymerization. It is attracting attention as a material that can be repeatedly reused. The most common examples of polymers containing ester functional groups are PET containers or polyester fibers for packaging. Polymers containing ester functional groups can generally be monomerized through chemical decomposition using a reaction solvent and catalyst for transesterification, and various chemical reaction pathways are known for this purpose. Some monomers produced through decomposition can theoretically have properties equivalent to the raw materials used in initial polymer synthesis. Depolymerization routes used industrially to recycle PET include glycolysis, methanolysis, hydrolysis using acid or base catalysts, and alkaline decomposition.

Glycolysis is a process of producing bis(2-hydroxyethyl) terephthalate (BHET) by adding an excessive amount of ethylene glycol (EG), one of the monomer raw materials. EG, which is part of the PET raw material, is used as a reactant, so there is a thermodynamic mixture with the reaction product. Because it has high chemical properties and the manufactured monomer product (BHET) is an intermediate product of polymer polymerization, it can be applied directly as a raw material for PET production by changing part of the raw material supply part of the existing facility. However, a metal catalyst and an excessive amount of EG are required to improve the decomposition rate of the polymer, and the final yield of the monomer is limited due to the relatively wide molecular weight distribution due to the reaction equilibrium between the monomer and the oligomer, and the EG as a solvent and the final product The high boiling point makes it difficult to purify the product through high-temperature distillation, and in the recrystallization process using water, the recrystallization rate of the monomer is slow, which may limit productivity and has a low product recovery rate. To increase the speed of the depolymerization reaction, acetic acid metal salt is used as a catalyst, and zinc acetate is a representative catalyst.

The methanolysis process is a reaction process that is widely applied in actual commercial processes, not only to global chemical companies but also to small and medium-sized plastic industries. It uses a variety of catalysts for transesterification reactions or uses high temperature and high pressure such as supercritical without a catalyst. Depolymerization can be carried out using only methanol. However, when high-temperature reaction conditions are required because methanol is used as a reaction solvent, high-pressure reactor design and leak-proof and explosion-proof equipment are required due to the generation of high methanol vapor pressure, and the energy consumption of unit processes for depolymerization reaction and purification may be excessive. You can. As transesterification catalysts, zinc acetate, magnesium acetate, cobalt acetate, lead dioxide, etc. are generally used, and dimethyl terephthalate (DMT) is obtained as the final monomer product. DMT, which can be manufactured from methanolysis, can be put into a reactor for PET synthesis in a molten state at 150℃, and a high temperature reaction process of 160~220℃ is performed by adding ethylene glycol to carry out transesterification reaction and condensation polymerization. PET can be manufactured through

PET polymerization using DMT as a raw material requires a separate process to produce BHET and generates a large amount of vapor methanol, so the process cost is high. PET production facilities based on DMT raw material were mainly used until the 1960s, before the development of a high-purity purification method for terephthalic acid (TPA). In modern times, the two-step synthesis method of initially synthesizing BHET by applying TPA and EG as raw materials and conducting a direct esterification reaction, and then proceeding with condensation polymerization by continuously removing moisture, is the most common manufacturing process for PET materials. occupies. Therefore, if high-purity TPA and EG can be economically produced from the depolymerization reaction of waste PET, there is an advantage in that the recycled monomers can be directly applied to PET production without changing equipment or operating conditions. The reaction pathways for producing TPA, a regenerated monomer, from depolymerization of waste PET include hydrolysis and alkaline decomposition.

In the case of hydrolysis, depolymerization proceeds under high temperature conditions in the presence of a high concentration of acid or base catalyst, and TPA is ultimately obtained as the depolymerization product. In the hydrolysis reaction using an acid catalyst, a very high concentration of sulfuric acid solution (87 wt%) is required to obtain high reactivity and yield, and it is known that it is difficult to secure economic feasibility due to corrosion of the reactor and generation of waste water, and hydrolysis using a base catalyst is known to be difficult. The decomposition reaction has a relatively slow reaction rate, so the purity of the product is low and catalyst recovery is difficult.

The alkaline decomposition reaction, in which alkali hydroxide is used at a high concentration or with a non-aqueous solvent, has the advantage of proceeding relatively quickly and producing high yields of TPA, but is uneconomical because excess alkali hydroxide is consumed as a reactant rather than a catalyst. It can be. In particular, since the product after depolymerization is obtained in the form of an alkali salt of terephthalate, acid treatment is necessary to obtain terephthalic acid. Since the alkali hydroxide used in excess to promote the reaction may remain, a large amount of acid and wastewater are required to neutralize it. There are disadvantages that arise.

As a prior art for the alkali decomposition reaction of PET, U.S. Patent Publication No. 10087130 (registered on October 2, 2018) relates to the production and recovery of TPA and EG, which are monomers obtained by depolymerizing PET using an excessive amount of alkali hydroxide. (i) non-polar solvent; and (ii) adding a mixture of alcohol and hydroxide to allow depolymerization of PET to proceed; It describes a method that can partially or completely depolymerize PET if sufficient time is applied even if no external heat is applied during the reaction. No. 10087130 can induce depolymerization of PET using a small amount of energy, but has the problem of using a non-polar solvent such as dichloromethane, which is harmful to the environment and the human body. In addition, when decomposing PET through an alkaline decomposition reaction, it is stated that in order to completely decompose into TPA and EG, which are depolymerization products, more than an equivalent amount of alkali hydroxide may be added or a long-time depolymerization reaction of up to 10 days may be required.

Korean Patent Publication No. 10-2223614 (announced on March 5, 2021) describes a method for depolymerization of a polymer containing an ester functional group, including (1) a straight-chain primary alcohol that does not contain halogen; (2) a polar aprotic solvent that does not contain halogen and contains at least one functional group from among ketone group, nitrile group, and furan group; and (3) a base compound containing a hydroxyl group; depolymerization is performed by contacting a polymer containing an ester functional group with a mixture containing the same, wherein the volume ratio of the primary alcohol and the polar aprotic solvent is as low as 1:1 to 1:20. It describes a method of alkaline decomposition reaction using positive alcohol as a cosolvent. In this technology, complete decomposition of PET may occur by using an excessive amount of alkali hydroxide in a ratio of about 4 to 14 moles relative to the number of unit moles of the repeating unit of the polymer containing an ester functional group, but carbonyl hydroxide in a polar aprotic solvent is used. As the aldol reaction and aldol condensation of the co-solvent containing the group progress, a portion of the co-solvent may be lost. In addition, foreign substances generated from the aldol reaction within the monomer generated by depolymerization remain, causing color changes in the product, and it is difficult to completely purify impurities through a simple purification process. In addition, due to the use of an excess amount of alkali hydroxide and a small amount of alcohol, unreacted alkali hydroxide may have limited solubility in the reaction mixture and may remain in the form of solids and be recovered as a filtration cake along with the monomer product during the filtration process. Therefore, reactants may be consumed unnecessarily and some waste water may be additionally generated.

In most other alkaline decomposition-based PET depolymerizations, a method of using an excess amount of alkali hydroxide is generally used to improve the conversion rate of PET and the yield of the monomer TPA. Most waste plastics are not made up of uniform materials or are discharged with a large amount of foreign substances, and are generally not completely removed through the classification and washing process. In particular, for foreign substances such as colored dyes or pigments, compounds designed to prevent loss under repeated external conditions such as sunlight, washing, and friction are generally used, and they are difficult to remove from products using simple physical separation and purification techniques. It's common.

Waste plastics containing foreign substances often remain in products because the foreign substances are not easily removed even through depolymerization and purification processes. In order to improve the purity of the final product, a separate purification technology that causes energy consumption and product loss is required. It is essential, and it may be difficult to secure sound economic feasibility of an integrated process for producing regenerated monomers. Therefore, waste plastics containing a large amount of foreign substances, especially fibers with dyes or waste plastics with colored pigments applied, are materials that are difficult or impossible to recycle industrially, and cannot be disposed of through methods that discharge secondary pollutants such as incineration or landfill. Therefore, waste plastic is one of the biggest pollutants causing environmental problems.

[Prior art literature]

[Patent Document]

(Patent Document 1) U.S. Patent Publication No. 10087130 (registered on October 2, 2018)

(Patent Document 2) Korean Patent Publication No. 10-2223614 (announced on March 5, 2021)

The present invention seeks to provide an effective and economical depolymerization method that can improve the depolymerization performance of polymers containing ester functional groups and remove many organic and inorganic contaminants during the production of monomers.

In order to solve the above problems, the present invention provides (1) an aromatic compound having at least one alkoxy functional group and not having a proton donor functional group; (2) compounds with one or more alcohol functional groups; and (3) an alkali hydroxide. A method for depolymerizing a polymer containing an ester functional group is provided, characterized in that the mixture containing the above is brought into contact with a polymer containing an ester functional group to depolymerize the polymer.

In one embodiment of the present invention, the weight ratio of the aromatic compound having at least one alkoxy functional group without having a proton donor functional group and the compound having at least one alcohol functional group in the mixture may be 20:1 to 1:20.

In one embodiment of the present invention, the compound having the alcohol functional group is a straight-chain primary alcohol, and the aromatic compound having one or more alkoxy functional groups without the proton donor functional group is methoxybenzene, 1,2-dimethoxy Benzene, 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, 1-methoxy-2-methylbenzene, 1-methoxy-3-methylbenzene, 1-methoxy-4-methylbenzene, 1-methoxy-2-ethylbenzene, 1-methoxy-3-ethylbenzene, 1-methoxy-4-ethylbenzene, 1-methoxy-2-propylbenzene, 1-methoxy-3-propylbenzene, 1-methoxy-4-propylbenzene, ethoxybenzene, 1-ethoxy-2-methoxybenzene, 1-ethoxy- 3-methoxybenzene, 1,2-diethoxybenzene, 1,3-diethoxybenzene, 1,4-diethoxybenzene, 1,2,4-triethoxybenzene, 1,3,5-triethoxy Benzene, 1-ethoxy-2-methylbenzene, 1-ethoxy-3-methylbenzene, 1-ethoxy-4-methylbenzene, (1-methoxyethyl)benzene, (2-methoxyethyl)benzene, (2-methoxy)ethoxybenzene, 1-methoxy-2-(methoxymethoxy)benzene, 1-(diethoxymethyl)-4-methoxybenzene, propoxybenzene, 1,3-dimethyl-2 -One or more compounds selected from the group consisting of propoxybenzene, 1-methoxy-4-propoxybenzene, 1,3-dipropoxybenzene, phenoxyethanol, etc., and the alkali hydroxide is sodium hydroxide, potassium hydroxide, and calcium hydroxide. , lithium hydroxide, magnesium hydroxide, ammonium hydroxide, tetraalkyl ammonium hydroxide, and combinations thereof.

In one embodiment of the present invention, the temperature during depolymerization may be 10°C to 100°C.

In addition, a primary filtration step of separating solid and liquid from the reaction product after the depolymerization reaction can be additionally performed, and a secondary filtration step of separating and filtering the monomer product by adding water to the filter cake obtained through the primary filtration to dissolve the monomer product in water. may be further performed, and the water used in the secondary filtration process may contain alkali hydroxide in the same number of moles as the number of moles of monoalkyl terephthalate present in the monomer product or more.

In addition, in one embodiment of the present invention, in order to recover the monomers of the depolymerized polymer, the step of adding an acid to the aqueous solution containing the monomers to precipitate them as a salt may be further included.

In addition, the present invention may further include the step of separating the precipitate generated from the filtrate after adding the acid and then recovering high-purity terephthalic acid through a drying process.

Additionally, the present invention provides (1) an aromatic compound having at least one alkoxy functional group but not having a proton donor functional group; (2) compounds with one or more alcohol functional groups; and (3) an alkali hydroxide. It provides a composition for polymer depolymerization containing an ester functional group.

In the composition of the present invention, the weight ratio of the aromatic compound having at least one alkoxy functional group without having a proton donor functional group and the compound having at least one alcohol functional group may be 20:1 to 1:20.

The present invention provides a method for depolymerization of a polymer containing an ester functional group by adding an alkali hydroxide as a reactant without using high temperature and high pressure reaction conditions.

According to the present invention, by applying a reaction solvent mixed with an organic solvent, that is, a liquid mixture consisting of an alcohol and an aromatic compound with an alkoxy functional group, to the depolymerization of a polymer containing an ester functional group, the activation energy barrier of the reaction is lowered and the reaction rate is greatly increased. It is possible to completely decompose polymers containing ester functional groups and convert terephthalate monomers in high yield within 2 hours at low temperatures below the boiling point of the constituent solvent.

According to the present invention, the aromatic compound with an alkoxy functional group used can easily dissolve and separate materials designed to have a strong interaction with polymers, such as dyes or pigments, during the monomerization process of the polymer, thereby removing colored waste plastics that were previously difficult to recycle. Terephthalate monomer can be produced with high purity.

The aromatic compounds with an alkoxy functional group used in the present invention can be synthesized on a large scale naturally or artificially, and most of them are biodegradable in nature in a short cycle, so they can provide environmentally friendly operating conditions. In addition, in the depolymerization of polymers, eco-friendly materials with no or low hazard to the human body or the environment are used as solvents, and terephthalic acid, a raw material commonly used to reproduce the same material, can be directly manufactured through depolymerization of waste plastic, making it environmentally friendly. It is possible to provide an economical method of depolymerization of a polymer containing an ester functional group, a method of producing a regenerated monomer, and a method of designing a production process therefor.

The method for depolymerization of a polymer containing an ester functional group according to the present invention has a simple process, enables depolymerization at a relatively low temperature, and can obtain a high yield of monomer, providing a very effective and efficient chemical recycling method for waste plastic. . In addition, theoretically, it is possible to commercially produce recycled monomers that can be used indefinitely, contributing to the realization of a circular economy for plastics. Since depolymerization reaction, product purification, and repolymerization can be performed continuously together, it can be used in existing polymer polymerization facilities. It is possible to build an integrated chemical process that can produce recycled polymers on a large scale without separate reinvestment or facility changes.

Figure 1 shows the PET decomposition reaction path by the depolymerization reaction of the present invention.

Figure 2 shows the solvent and terephthalic acid product discharged after depolymerization of colored polyester polymer using an ethanol-anisole mixed solvent.

Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

Throughout the specification of the present application, when a part "includes" a certain component, this means that it may further include other components rather than excluding other components unless specifically stated to the contrary.

The method for depolymerizing a polymer containing an ester functional group of the present invention includes (1) an aromatic compound having at least one alkoxy functional group but not having a proton donor functional group; (2) compounds with one or more alcohol functional groups; and (3) depolymerizing the mixture containing the alkali hydroxide by contacting it with a polymer containing an ester functional group. In the above mixture, the aromatic compound having an alkoxy functional group of (1) has an alkoxy functional group but does not have a proton donor functional group. Examples of the proton donor functional group include functional groups that provide protons (H ⁺ ), such as hydroxy functional groups and carboxylic acid functional groups. The compound with the alcohol functional group in (2) also serves as a solvent to dissolve the alkali hydroxide in (3).

In addition, in the present invention, in the process of obtaining the converted monomer, the solvent used in the reaction and unreacted products (polymer and alkali hydroxide containing an ester functional group) can be recovered and reused by a simple physical separation method such as filtration, and depolymerization. The solvent with an alkoxy functional group used in can be effective as an extractant for removing foreign substances because it neutralizes the strong interaction that the terephthalate functional group has with foreign substances during the separation process. From this, high purity and high yield of terephthalic acid can be obtained as the final monomer.

The method of the present invention is useful for the depolymerization of polymers containing ester functional groups, wherein the polymers containing ester functional groups are mixed with other polymers, including but not limited to, for example, polyethylene, high-density polyethylene, low-density polyethylene, polypropylene, or combinations thereof. It may be in a form containing various types of organic and inorganic foreign substances.

In addition, polymers containing ester functional groups may be those produced by continuous condensation polymerization by dehydration using dicarboxylic acid and diol (dialcohol) as starting materials, or may have multiple ester bond structures at repeated or arbitrary positions. Here, the dicarboxylic acids include naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, succinic acid, and adipic acid. , sebacic acid, azelaic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, trimellitic acid, pyromellitic acid, and combinations thereof, and the dialcohol is trimethylene glycol, 1,2-propane. Diol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, decane methylene 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) ) It may be selected from the group consisting of propane and combinations thereof.

Examples of polymers containing the ester functional group include polyethylene terephthalate (PET), polyglycolide or polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), and polyhydroxyalkanoate (PHA). ), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polybutylene It may be selected from terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), Vectran, and combinations thereof.

Preferably, the polymer containing the ester functional group is polyethylene terephthalate, and in this case, the starting material for producing the polymer may be terephthalic acid or a salt thereof, and ethylene glycol.

The polymer containing an ester functional group used in the present invention may not be pure but may contain various impurities. Examples include, but are not limited to, polymers containing ester functional groups, bottle caps, adhesives, paper, residual liquid, dust, organic and inorganic materials for color (e.g. dyes or pigments), or combinations thereof. A mixture of can be used as a raw material for depolymerization.

In the method of depolymerizing a polymer containing an ester functional group according to the present invention, the mass of the polymer raw material initially added is the aromatic compound having at least one alkoxy functional group and at least one alcohol functional group without a proton donor functional group, which are added for depolymerization. It can be adjusted to a ratio of 1 to 100% of the mass of the mixed solvent in which the compound with Due to limitations, a problem may arise where the reaction speed is significantly lowered.

In the method for depolymerizing a polymer containing an ester functional group according to the present invention, the mixed solvent includes (1) an aromatic compound having at least one alkoxy functional group but not having a proton donor functional group, and (2) at least one alcohol functional group. It is a mixture of compounds with an alcohol functional group. Some of the compounds with an alcohol functional group can participate in the alcoholesis reaction, but most serve as a reaction medium for the alkaline decomposition reaction, and compounds with an alkoxy functional group directly participate as a reactant in the depolymerization reaction. However, it is used as a co-solvent to facilitate nucleophilic attack on the ester bond of alkali hydroxide or other types of anions derived therefrom, and can exhibit the property of improving the depolymerization reaction rate.

The compound having an alkoxy functional group but not having a proton donor functional group has at least one aromatic ring, and at least one of the hydrogens bonded to the carbon of the hydrocarbon constituting the aromatic ring is bonded to the alkoxy functional group or the carbon connected thereto. It is an organic compound that does not contain functional groups that can provide protons, such as hydroxyl functional groups and carboxylic acid functional groups, in the compound structure, specifically methoxybenzene, 1,2-dimethoxybenzene, and 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, 1-methoxy-2-methylbenzene, 1-methoxy-3-methylbenzene , 1-methoxy-4-methylbenzene, 1-methoxy-2-ethylbenzene, 1-methoxy-3-ethylbenzene, 1-methoxy-4-ethylbenzene, 1-methoxy-2-propylbenzene , 1-methoxy-3-propylbenzene, 1-methoxy-4-propylbenzene, ethoxybenzene, 1-ethoxy-2-methoxybenzene, 1-ethoxy-3-methoxybenzene, 1,2 -diethoxybenzene, 1,3-diethoxybenzene, 1,4-diethoxybenzene, 1,2,4-triethoxybenzene, 1,3,5-triethoxybenzene, 1-ethoxy-2- Methylbenzene, 1-ethoxy-3-methylbenzene, 1-ethoxy-4-methylbenzene, (1-methoxyethyl)benzene, (2-methoxyethyl)benzene, (2-methoxy)ethoxybenzene , 1-methoxy-2-(methoxymethoxy)benzene, 1-(diethoxymethyl)-4-methoxybenzene, propoxybenzene, 1,3-dimethyl-2-propoxybenzene, 1-methoxy One or more compounds selected from the group consisting of -4-propoxybenzene, 1,3-dipropoxybenzene, phenoxyethanol, etc. may be used.

The compound having the alcohol functional group may be a straight-chain primary alcohol, and an alcohol that can have high solubility in alkali hydroxide, such as methanol or ethanol, may be more preferable, but a straight-chain primary alcohol with 3 or more carbon atoms may be used. For example, one or more alcohols selected from propanol, butanol, etc. may be used.

The reaction solvent for performing depolymerization in the present invention is a mixed solvent containing both at least one selected from aromatic compounds having at least one alkoxy functional group and not having the proton donor functional group and at least one selected from compounds having the alcohol functional group. The use of is one of the characteristics of the invention.

In the mixed solvent, the weight ratio of the aromatic compound and the alcohol compound having an alkoxy functional group is 1:20 to 20:1, preferably 2:1 to 1:2.

The alkali hydroxide added to perform depolymerization in the present invention may be selected from the group consisting of alkali metal hydroxide, alkaline earth metal hydroxide, ammonium hydroxide, and combinations thereof. For example, it may be selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, magnesium hydroxide, ammonium hydroxide, tetraalkyl ammonium hydroxide, and combinations thereof. Preferably, the alkaline hydroxide may be sodium hydroxide, potassium hydroxide, or a combination thereof.

The alkaline hydroxide can be used in an amount of 0.1 to 100 times, preferably 2 to 50 times, the number of moles of repeating units of the polymer containing an ester functional group.

The depolymerization of the polymer containing the ester functional group may be carried out in a temperature range of 10°C to 100°C, preferably 30°C to 65°C, and alkali hydroxide participates as part of the reactant, causing the polymer to rapidly decompose into monomers. Depolymerization may proceed along the decomposition reaction path.

The depolymerization of the polymer containing the ester functional group may be carried out in an insulated reactor due to the heat of mixing, heat of dissolution, etc. generated in the process of preparing the mixed solution for the depolymerization reaction without inputting an additional heat source. Additionally, in some embodiments according to the present invention, depolymerization may be performed while supplying an external heat source.

In addition, in the polymer depolymerization method of the present invention, since depolymerization proceeds below the boiling point of the applied alcohol, positive pressure may not be generated, but when some low-boiling alcohol solvents are used, the reaction occurs under a low absolute pressure of 1.0 to 1.5 atm. can be performed.

In the method of depolymerizing a polymer containing an ester functional group according to the present invention, the time of the depolymerization reaction may vary depending on the amount and form of the applied polymer, but when the composition and conditions of the reactants are applied to perform rapid depolymerization, Within 2 hours of the initial reaction time, dominant polymer decomposition occurs due to a very fast depolymerization reaction rate, and after 4 hours of reaction, almost all of the initial polymer mass can be decomposed into monomer form. In controlling the time of the depolymerization reaction according to the present invention, depolymerization may be performed from 0.5 to 12 hours after the start of the reaction to ensure sufficient polymer decomposition, but to ensure economic efficiency and productivity, depolymerization may be performed within the range of 0.5 to 4 hours. It may be desirable to perform.

In the method of depolymerizing a polymer containing an ester functional group according to the present invention, a primary filtration step of separating solid and liquid from the reaction product may be additionally performed after completion of the depolymerization reaction. Among the reaction products, those that exist in the solid phase may be unreacted polymers and alkali salts of terephthalate produced by depolymerization, while those that exist in the liquid phase may include aromatic compounds that do not have a proton donor functional group but have one or more alkoxy functional groups and one or more alcohol functional groups. It may be a reaction solvent in which a compound having a mixture is mixed with each other, an unreacted alkali hydroxide dissolved in the reaction solvent, and a color-distributed foreign substance mainly distributed by an aromatic compound having an alkoxy functional group in the reaction solvent.

In the first filtration step, all or part of the colored hydrophobic organic contaminants contained in the polymer before decomposition are discharged together with the filtrate due to their high affinity with aromatic compounds with alkoxy functional groups in the reaction solvent recovered in the filtrate. The residual amount of the hydrophobic organic contaminants in the cake is greatly reduced.

The solution containing colored organic foreign substances separated from the filtrate can be re-introduced into the depolymerization reaction by adding a purification process such as distillation or evaporation to separate the purified reaction solvent, and removing the foreign substances through adsorption, etc. It can be reintroduced as a raw material for a new reaction to perform depolymerization by replenishing the unreacted alkali hydroxide and reaction solvent consumed or lost during the depolymerization reaction without removing foreign substances.

In the primary filtration process, the filtration cake separated into the solid phase is composed of a mixture of alkali terephthalate, monoalkyl terephthalate alkali salt, and unreacted polymers prepared from depolymerization, so the terephthalic acid salt must be recovered from the filtration cake. .

Since the intermediates for producing the monomer, alkali terephthalate and alkali monoalkyl terephthalate, are soluble in water, they can be filtered in situ by adding water to the primary filtered filter cake, or dissolved using a separately prepared filter outside. The terephthalic acid salt can be recovered through secondary filtration in which the alkali salt of terephthalate and the alkali monoalkyl terephthalate are separated from the solid filter cake by passing through a filter. Since what is separated into the filtration cake in the secondary filtration process is unreacted polymer material, it can be reintroduced as a new reaction raw material in the depolymerization process.

If monoalkyl terephthalate is included in the product prepared by the depolymerization reaction, it is present in the filtrate during the secondary filtration process. The alkyl of the monoalkyl terephthalate can be substituted with an alkali salt to finally produce an alkali salt of terephthalic acid. To this end, the step of converting the monoalkyl terephthalate alkali salt into the terephthalic acid alkali salt by adding a mole number of alkali hydroxide equal to the number of moles of monoalkyl terephthalate to the water used in the secondary filtration process or the filtrate after filtration may be further included. .

At this time, the amount of alkali hydroxide used can be more than the number of moles of monoalkyl terephthalate alkali salt, but it is preferable to add 1.0 to 1.2 times the equivalent amount, and the decomposition reaction of monoalkyl terephthalate alkali salt proceeds quickly and irreversibly. Therefore, in order to reduce material waste, it is most desirable to add 1.0 times the equivalent amount.

In the process of converting the monoalkyl terephthalate alkali salt to terephthalic acid alkali salt, the aqueous solution to which alkali hydroxide is added is mixed well for 5 to 30 minutes at a temperature above room temperature to convert all monomer products generated from polymer depolymerization into terephthalic acid alkali salt. Let it be done.

The product obtained as a filtrate in the filtration process is an aqueous solution mainly composed of components that are easily soluble in water (alcohol, alkali salt of terephthalate, etc.), and may contain some colored organic foreign substances. In order to further separate the organic impurities from the filtrate, an aromatic compound having an alkoxy functional group may be added to the filtrate to induce distribution of the organic impurities into the organic phase having the alkoxy functional group, thereby separating the colored organic impurities once more. . At this time, if an aromatic compound having an alkoxy functional group is added to the filtrate, a thermodynamically unstable phase may be created. In order to smoothly redistribute the foreign substances, stirring for a short period of time within 30 minutes and then leaving it to stand can induce separation into an organic phase and an aqueous solution phase. Since the organic foreign substances are concentrated in the separated organic phase, the organic foreign substances can be further separated.

The present invention may further include the step of adding acid to an aqueous solution containing the alkali salt product of terephthalic acid obtained in the process of separating the depolymerization reaction product to convert it into terephthalic acid and precipitate it, followed by physical separation. The purity of terephthalic acid can be further improved through separation (e.g., filtration) of terephthalic acid from the prepared aqueous solution, followed by washing and drying.

The acid added to convert terephthalic acid salt to terephthalic acid can be an organic acid or an inorganic acid. However, inorganic acids that ionize well in aqueous solution and can easily provide protons (H ⁺ ), such as hydrochloric acid (HCl) and nitric acid (HNO ₃ ) , it may be preferable to use one or more selected from phosphoric acid (H ₃ PO ₄ ) and sulfuric acid (H ₂ SO ₄ ).

In addition, even if the monomer product does not use a method such as filtration, other types of physical separation methods such as centrifugation may be applied to separate the relatively high-density solid product from the reaction mixture.

All or part of the final monomer produced according to the method for depolymerizing a polymer containing an ester functional group of the present invention has been purified to a level that can be reintroduced as a raw material for repolymerization.

At this time, the monomer obtained from the depolymerization of the polymer containing the ester functional group of the present invention can be used as a polymerization raw material for polymer synthesis, and the monomer may contain less than about 1% of impurities (w/w), Impurities may be heterogeneous organic substances such as isophthalic acid, phthalic acid, 4-methylbenzoic acid, and 4-formylbenzoic acid, or may include one or more of metal contaminants that are by-produced from the catalyst or manufacturing process.

In addition, the present invention provides a method for producing a final monomer product with improved purity by further removing foreign substances having the above color.

Dyes and pigments, which are colored foreign substances contained in polymers containing colored ester functional groups, are often materials designed to have a strong interaction with the terephthalate functional group, and are complexed with the terephthalate functional group during the purification and recovery process. Because it forms a shape and moves material like a single structure, it can be difficult to remove using general purification methods alone. In other words, the interaction (π-π interaction or hydrogen bonding force) of the compound having an alkoxy functional group with foreign substances of the same color as dyes or pigments partially weakens the binding force between foreign substances and terephthalate. It is effective, but in order to more effectively and irreversibly separate foreign substances into products, an adsorbent with a strong binding force to the foreign substances may be useful.

Therefore, the present invention provides a method for producing a monomer product through depolymerization of a colored polymer through depolymerization of a colored polymer compound containing an ester functional group, which further includes the step of treating colored foreign substances using the adsorbent. .

Since the irreversible separation of foreign substances using the adsorbent can be most effectively applied when the terephthalate functional group is dissociated in the aqueous solution in ionic form, it is better to apply the adsorbent to the aqueous filtrate before converting the terephthalate metal salt to terephthalic acid by adding acid. This may be most appropriate.

The adsorbent may include carbon-based adsorbents such as activated carbon, fly ash, ion exchange resin, natural clay, bentonite clay, zeolite, kaolinite, chitosan, metal-organic framework (MOF), etc. Preferably, activated carbon can be used.

The present invention also provides (1) aromatic compounds having at least one alkoxy functional group but not having a proton donor functional group; (2) compounds with one or more alcohol functional groups; and (3) a composition for depolymerization of a polymer containing an ester functional group containing an alkali hydroxide.

Since each component of the depolymerization composition is the same as described above, repeated description will be omitted.

Hereinafter, details of the present invention process will be described through examples, comparative examples, and experimental examples. This is a representative example related to the present invention, and this alone does not limit the scope of application of the present invention.

원료 1 (에스테르 작용기를 포함하고 있는 투명 폐PET 플레이크)Raw material 1 (transparent waste PET flakes containing ester functional groups)

As a waste polymer material containing an ester functional group, flake chips manufactured by washing and cutting discarded transparent polyethylene terephthalate (PET) bottles were supplied from Saerom ENG, a recycling product manufacturer, and were processed with excessive amounts of ethanol and water. Washed and dried, only flake chips with an area of 1 square centimeter or less were prepared as raw material 1.

원료 2 (에스테르 작용기를 포함하고 있는 유색 폐PET 플레이크)Raw material 2 (colored waste PET flakes containing ester functional groups)

As a waste polymer material containing an ester functional group, flake chips manufactured by washing and cutting discarded polyethylene terephthalate (PET) bottles (including colored ones) were supplied by the Korea Plastics Single Materials Association. After washing and drying with excess ethanol and water, only flake chips with an area of 1 square centimeter or less were prepared as raw material 2. Among all plastic chip raw materials, the mass ratio of colored ones was about 56.8%, and the mass ratio of transparent ones was about 43.2%.

원료 3 (에스테르 작용기를 포함하고 있는 유색 복합소재 고분자)Raw material 3 (colored composite polymer containing ester functional group)

Waste polymer material in the form of hair, which was discharged as scraps after manufacturing the material, was supplied from Joohyun Chemical and used as a raw material for the colored composite material for depolymerization. A polymer material containing an ester functional group in the form of a black filament mixed by weight of approximately 63.8% polyethylene terephthalate (PET), approximately 35.4% polybutylene terephthalate (PBT), and carbon black (0.8%) as a coloring material. It was cut so that each strand did not exceed 2 centimeters in length, and was prepared as raw material 3.

원료 4 (에스테르 작용기를 포함하고 있는 유색 복합소재 고분자)Raw Material 4 (Colored composite polymer containing ester functional group)

It is a waste polymer material in the form of hair discharged as scraps, and is black in color with about 26.1% polyethylene terephthalate (PET), 73.1% polybutylene terephthalate (PBT), and carbon black (0.8%) mixed by weight ratio. A polymer material containing a filament-shaped ester functional group was cut so that each strand did not exceed 2 centimeters in length to prepare raw material 4.

비교예 1Comparative Example 1 :

(a) Depolymerization of polymers containing ester functional groups

Approximately 15.0 g of raw material 1 (transparent PET flake chip) was used as a raw material for depolymerization, and absolute ethanol was used as a reaction solvent. After adding and dissolving 12.49 g of sodium hydroxide (NaOH) (4 times the number of moles of repeating units in the PET raw material) to 120 g of ethanol, a thermocouple for temperature measurement and a Teflon septum for collecting liquid samples are installed at the side entrance, respectively, of the bushing type. It is placed in a 500 mL three-necked flask with a Teflon seal connected to the center inlet so that a stirring bar connected through an adapter and equipped with an impeller that can be rotated by an external overhead stirrer passes through the center, and then maintained at a constant temperature by a PID temperature controller. The mixture was stirred at a speed of 300 rpm until the temperature inside the reactor reached 60°C. When the temperature inside the reactor was stabilized, about 15.0 g of the prepared polymer raw material was added and the reaction was started.

(b) Quantitative analysis of depolymerization reaction products

10 mg of liquid sample was taken at intervals of 30 minutes or 1 hour, diluted using THF and a mobile phase solution (methanol and water mixed at a volume ratio of 70:30), and chromatographed using high-performance liquid chromatography (High The concentration of each product was quantified using Performance Liquid Chromatography; HPLC, Younglin YL 3000 with C18 column (250×4.5mm) and UV detector (λ=254nm). During HPLC analysis, a mixed solution of methanol:water with a volume ratio of 70:30 was used as the mobile phase, and the total flow rate was maintained at 0.7 ml/min.

The conversion rate of PET obtained from the depolymerization reaction and the yield of intermediate monomers, sodium mono-ethyl terephthalate (Na-MET) and sodium terephthalate (Na ₂ -TPA), were calculated using the following generalized formula.

PET conversion rate = (M _o - M)/M _o (Equation 1)

MAT alkaline salt yield = (N _MAT / N _o ) × 100% (Equation 2)

TPA alkaline salt yield = (N _TPA / N _o ) × 100% (Equation 3)

In the above formula, M _o is the mass of the initially input polymer, M is the mass of the unreacted polymer, N _o is the number of moles of the repeating unit of the initially input raw material polymer (PET), and N _MAT and N _TPA are the produced monoalkyl terephthalate It is the number of moles of phthalate alkali salt (e.g. Na-MET) and terephthalic acid alkali salt (e.g. Na ₂ -TPA).

(c) Separation and purification of monomer products

When the desired reaction time was reached, the reactant was immediately transferred to a vacuum filter and primary filtration was performed. When filtration was completed, the flask container containing the filtrate was replaced with an empty container, and then secondary filtration was started. In the second filtration, 200 ml of distilled water was added to recover unreacted PET as a solid (filtration cake). Unreacted PET was placed in an evaporation dish, moved to a vacuum dryer maintained at 80°C, dried for 24 hours, and then quantified. The obtained secondary filtrate was stirred for 30 minutes, then an equivalent amount of hydrochloric acid aqueous solution was added to the filtrate to convert all monomers into terephthalic acid. Stored at 4°C or lower for 12 hours, the precipitated crystals were washed and filtered, and transferred to an evaporation dish. It was placed in a vacuum dryer maintained at 80°C and dried for 24 hours to obtain about 12.30 g of a white product.

(d) Characterization of monomer products

The obtained product was confirmed through ¹ H-NMR, EI-MS, etc. and was consistent with the chemical structure of terephthalic acid, and the purity of the product was determined through calibrated HPLC. Some of the obtained products were manufactured as solid samples and their unique colors were observed using a spectrophotometer (manufacturer: Konica Minolta, model name: CM-3600A). After taking approximately 200 mg of the finally obtained terephthalic acid, a circular disk with a diameter of 13 mm was manufactured using a pellet manufacturing mold (Pike Evacuable KBr Die Kit) and a hydraulic press (Hydraulic Press, Pike CrushIR) (applied pressure: 10 tons). . The color space coordinate values (L* a* b*) of the manufactured disk sample were measured using a spectrophotometer. The values expressed as L* a* b* are coordinate values of the color space standardized by the International Commission on Illumination (CIE), and L* is expressed as 0 (black) to 100 (white) representing lightness. It is a numerical value, and a* and b* are numerical values expressed along the complementary color axes of green (-128)/red (127) and blue (-128)/yellow (127), respectively.

비교예 2Comparative Example 2 :

Depolymerization reaction, quantitative analysis of depolymerization products, and purification and characterization of monomer products were performed using the same methods and procedures as in Comparative Example 1, except that 180 g of ethanol was used as a solvent in the reaction. Through the monomer manufacturing process, approximately 12.39 g of terephthalic acid was finally obtained.

실시예 1:Example 1:

PET depolymerization reaction and quantitative analysis of the product were performed using the same method and procedure as in Comparative Example 1, except that instead of using only ethanol as the solvent used in the reaction, a mixture of 90 g of ethanol and 30 g of anisole was used.

After completing the depolymerization reaction, a trace amount of Na-MET, a reaction intermediate, was detected in the product, and the same mole number of Na-MET detected in the process of '(c) separation and purification of monomer product' (in this example, repetition of the initial polymer A solution of sodium hydroxide (41 mg in this example) corresponding to the production of 0.013 moles of Na-MET relative to the number of moles of monomers dissolved in 100 ml of distilled water was added to the filtration cake, and then an additional 100 ml of distilled water was added to perform secondary filtration. After stirring the prepared filtrate for 30 minutes, an equivalent amount of aqueous hydrochloric acid was added to the filtrate to convert all monomers into terephthalic acid. The prepared filtrate was recrystallized, washed, and dried using the same method as in Comparative Example 1 to obtain about 12.37 g of a white product. Afterwards, the product was analyzed according to the same method and procedure as in Comparative Example 1.

실시예 2:Example 2:

Depolymerization reaction, quantitative analysis of the depolymerization product, and purification and characterization of the monomer product were performed using the same methods and procedures as in Example 1, except that 90 g of ethanol and 90 g of anisole were used as a solvent for the reaction. Through the monomer manufacturing process, approximately 12.39 g of terephthalic acid was finally obtained.

실시예 3:Example 3:

Depolymerization reaction, quantitative analysis of depolymerization products, and purification and characterization of monomer products were performed using the same methods and procedures as in Example 1, except that 90 g of ethanol and 180 g of anisole were used as solvents added to the reaction. Through the monomer preparation process, approximately 12.56 g of terephthalic acid was finally obtained.

비교예 3Comparative Example 3 :

Quantitative analysis of the depolymerization reaction and depolymerization product was performed using the same method and procedure as in Comparative Example 1, except that only 120 g of anisole was used as the solvent added to the reaction. PET was hardly decomposed, and when the reaction product was purified, little terephthalic acid could be obtained.

실시예 4:Example 4:

The depolymerization reaction, quantitative analysis of the depolymerization product, and purification and characterization of the monomer product were performed using the same methods and procedures as in Example 1, except that 90 g of methanol and 90 g of anisole, rather than ethanol, were used as a solvent in the reaction. It was carried out. Through the monomer preparation process, approximately 12.48 g of terephthalic acid was finally obtained.

비교예 4:Comparative Example 4:

Quantitative analysis of the depolymerization reaction and depolymerization products was performed using the same method and procedure as in Example 1, except that sodium hydroxide was not added to the reaction. PET was hardly decomposed, and when the reaction product was purified, little terephthalic acid could be obtained.

실시예 5:Example 5:

Depolymerization reaction, quantitative analysis of the depolymerization product, and quantitative analysis of the depolymerization product were performed using the same method and procedure as in Example 1, except that the amount of sodium hydroxide (NaOH) added to the reaction was 1.56 g so that the mole ratio was 0.5 compared to the number of moles of the repeating unit of the polymer. Purification and characterization of the monomer product were performed. Through the monomer manufacturing process, approximately 5.18 g of terephthalic acid was finally obtained.

실시예 6:Example 6:

Depolymerization reaction, quantitative analysis of the depolymerization product, and quantitative analysis of the depolymerization product were performed using the same method and procedure as in Example 1, except that the amount of sodium hydroxide (NaOH) added to the reaction was 3.12 g so that the molar ratio of 1.0 to the number of moles of the repeating unit of the polymer was added. Purification and characterization of the monomer product were performed. Through the monomer manufacturing process, approximately 9.96 g of terephthalic acid was finally obtained.

실시예 7:Example 7:

Depolymerization reaction and depolymerization product were carried out in the same manner and procedure as in Example 1, except that 6.24 g of sodium hydroxide (NaOH) added to the reaction was added to achieve a molar ratio (equivalent) of 2.0 compared to the number of moles of repeating units of the polymer. Quantitative analysis, purification and characterization of monomer products were performed. Through the monomer preparation process, approximately 12.44 g of terephthalic acid was finally obtained.

실시예 8:Example 8:

Excluding that 37.5 g of ethanol and 30 g of anisole were mixed as solvents added to the reaction, and that the amount of sodium hydroxide (NaOH) added to the reaction was 6.24 g so that the molar ratio (equivalent) was 2.0 compared to the number of moles of repeating units of the polymer. Then, the depolymerization reaction, quantitative analysis of the depolymerization product, and purification and characterization of the monomer product were performed using the same method and procedure as in Example 1. Through the monomer preparation process, approximately 12.64 g of terephthalic acid was finally obtained.

실시예 9:Example 9:

A mixture of 37.5 g of ethanol and 30 g of anisole was used as the solvent used in the reaction, and potassium hydroxide (KOH) was used instead of sodium hydroxide (NaOH) as the alkali hydroxide added to the reaction, with a molar ratio of 2.0 compared to the number of moles of repeating units of the polymer ( Depolymerization reaction, quantitative analysis of the depolymerization product, and purification and characterization of the monomer product were performed using the same method and procedure as in Example 1, except that 8.74 g was added to obtain the equivalent weight. Through the monomer manufacturing process, approximately 12.70 g of terephthalic acid was finally obtained.

실시예 10:Example 10:

Depolymerization reaction, quantitative analysis of depolymerization products, and purification and characterization of monomer products were performed using the same methods and procedures as in Example 2, except that the temperature of the depolymerization reaction was maintained at 30°C. The reaction proceeded for a total of more than 6 hours, and approximately 10.32 g of terephthalic acid was finally obtained through the monomer preparation process.

실시예 11:Example 11:

Depolymerization reaction, quantitative analysis of depolymerization product, purification and characterization of monomer product using the same methods and procedures as in Example 2, except that the temperature of the depolymerization reaction was maintained at a temperature close to the boiling point of ethanol (78°C) and carried out under reflux. Analysis was conducted. Through the monomer preparation process, approximately 12.22 g of terephthalic acid was finally obtained.

실시예 12:Example 12:

Depolymerization reaction, quantitative analysis of the depolymerization product, and quantitative analysis of the depolymerization product using the same method and procedure as in Example 2, except that 90 g of ethanol and 90 g of 1,2-dimethoxybenzene (DMB), rather than anisole, were used as a solvent for the reaction. Purification and characterization of the monomer product were performed. Through the monomer preparation process, approximately 12.34 g of terephthalic acid was finally obtained.

실시예 13:Example 13:

Depolymerization reaction, quantitative analysis of depolymerization products, and monomer products were performed using the same methods and procedures as in Example 2, except that 90 g of ethanol and 90 g of phenetole (Phenetole or ethoxy benzene), not anisole, were used as a solvent for the reaction. Purification and characterization were performed. Through the monomer preparation process, approximately 12.07 g of terephthalic acid was finally obtained.

비교예 5:Comparative Example 5:

Depolymerization reaction, quantitative analysis of the depolymerization product, and quantitative analysis of the depolymerization product using the same method and procedure as in Example 2, except that 90 g of ethanol and 90 g of guaiacol (or 2-methoxyphenol), not anisole, were used as a solvent for the reaction. Purification and characterization of the monomer product were performed. Through the monomer manufacturing process, approximately 0.49 g of trace solids including terephthalic acid were finally obtained.

비교예 6:Comparative Example 6:

Depolymerization reaction, quantitative analysis of depolymerization product, and quantitative analysis of depolymerization product using the same method and procedure as Comparative Example 2, except that about 15.0 g of raw material 2 (colored waste PET flake chip) was used as the raw material for depolymerization instead of raw material 1 (transparent PET flake chip). Purification and characterization of the monomer product were performed. Through the monomer manufacturing process, approximately 10.96 g of dark-colored terephthalic acid was finally obtained.

실시예 14:Example 14:

Depolymerization reaction and quantitative analysis of the product were performed using the same method and procedure as in Example 2, except that about 15.0 g of raw material 2 (colored waste PET flake chip) was used as the raw material for depolymerization instead of raw material 1 (transparent PET flake chip). did.

After completing the depolymerization reaction, an additional 10 g of anisole was added to the filtrate prepared by performing secondary filtration in the '(c) Separation and purification of monomer product' process and stirred for 30 minutes, and then anisole and colored foreign substances were concentrated. The organic layer was removed, and an equivalent amount of aqueous hydrochloric acid was added to the aqueous solution to convert all monomers into terephthalic acid. The prepared filtrate was recrystallized, washed, and dried in the same manner as in Comparative Example 1 to obtain about 12.14 g of a nearly white product. Afterwards, the product was analyzed according to the same method and procedure as in Comparative Example 1.

비교예 7:Comparative Example 7:

Depolymerization reaction, quantitative analysis of depolymerization product, and monomer were performed using the same method and procedure as Comparative Example 2, except that about 15.0 g of raw material 3 (colored composite polymer) was used as the raw material for depolymerization instead of raw material 1 (transparent PET flake chip). Purification and characterization of the product were performed. Through the monomer manufacturing process, approximately 11.91 g of dark-colored terephthalic acid was finally obtained.

실시예 15:Example 15:

Depolymerization reaction and quantitative analysis of the product were performed using the same method and procedure as in Example 2, except that about 15.0 g of raw material 3 (colored composite polymer) was used as the raw material for depolymerization instead of raw material 1 (transparent PET flake chip). .

After completing the depolymerization reaction, an additional 10 g of anisole was added to the filtrate prepared by performing secondary filtration in the '(c) Separation and purification of monomer product' process and stirred for 30 minutes, and then anisole and colored foreign substances were concentrated. The organic layer was removed, and an equivalent amount of aqueous hydrochloric acid was added to the aqueous solution to convert all monomers into terephthalic acid. The prepared filtrate was recrystallized, washed, and dried in the same manner as in Comparative Example 1 to obtain about 12.04 g of a nearly white product. Afterwards, the product was analyzed according to the same method and procedure as in Comparative Example 1.

비교예 8:Comparative Example 8:

Depolymerization reaction, quantitative analysis of depolymerization product, and monomer were performed using the same method and procedure as Comparative Example 2, except that about 15.0 g of raw material 4 (colored composite polymer) was used as the raw material for depolymerization instead of raw material 1 (transparent PET flake chip). Purification and characterization of the product were performed. Through the monomer manufacturing process, approximately 10.86 g of dark-colored terephthalic acid was finally obtained.

실시예 16:Example 16:

Depolymerization reaction and quantitative analysis of the product were performed using the same method and procedure as in Example 2, except that about 15.0 g of raw material 4 (colored composite polymer) was used as the raw material for depolymerization instead of raw material 1 (transparent PET flake chip). .

After completing the depolymerization reaction, an additional 10 g of anisole was added to the filtrate prepared by performing secondary filtration in the '(c) Separation and purification of monomer product' process and stirred for 30 minutes, and then anisole and colored foreign substances were concentrated. The organic layer was removed, and an equivalent amount of aqueous hydrochloric acid was added to the aqueous solution to convert all monomers into terephthalic acid. The prepared filtrate was recrystallized, washed, and dried in the same manner as Comparative Example 1 to obtain about 11.04 g of a nearly white product. Afterwards, the product was analyzed according to the same method and procedure as in Comparative Example 1.

실시예 17:Example 17:

Quantitative analysis of the depolymerization reaction and product was performed using the same method and procedure as in Example 14, and 10 g of anisole was added to the filtrate prepared through secondary filtration in the process of '(c) Separation and purification of monomer product'. After adding and stirring for 30 minutes, the organic layer containing concentrated anisole and colored foreign substances was removed, and the resulting aqueous solution was passed through an activated carbon layer. An equivalent amount of aqueous hydrochloric acid was added to the aqueous solution that passed through the activated carbon layer to convert all monomers into terephthalic acid. The prepared filtrate was recrystallized, washed, and dried in the same manner as in Comparative Example 1 to obtain about 12.06 g of a nearly pure white product. Afterwards, the product was analyzed according to the same method and procedure as in Comparative Example 1.

실시예 18:Example 18:

Quantitative analysis of the depolymerization reaction and product was performed using the same method and procedure as in Example 15, and 10 g of anisole was added to the filtrate prepared through secondary filtration in the process of '(c) Separation and purification of monomer product'. After adding and stirring for 30 minutes, the organic layer containing concentrated anisole and colored foreign substances was removed, and the resulting aqueous solution was passed through an activated carbon layer. An equivalent amount of aqueous hydrochloric acid was added to the aqueous solution that passed through the activated carbon layer to convert all monomers into terephthalic acid. The prepared filtrate was recrystallized, washed, and dried in the same manner as in Comparative Example 1 to obtain about 12.00 g of a nearly pure white product. Afterwards, the product was analyzed according to the same method and procedure as in Comparative Example 1.

실시예 19:Example 19:

Quantitative analysis of the depolymerization reaction and product was performed using the same method and procedure as in Example 16, and 10 g of anisole was added to the filtrate prepared through secondary filtration in the process of '(c) Separation and purification of monomer product'. After adding and stirring for 30 minutes, the organic layer containing concentrated anisole and colored foreign substances was removed, and the resulting aqueous solution was passed through an activated carbon layer. An equivalent amount of aqueous hydrochloric acid was added to the aqueous solution that passed through the activated carbon layer to convert all monomers into terephthalic acid. The prepared filtrate was recrystallized, washed, and dried in the same manner as in Comparative Example 1 to obtain about 10.98 g of a nearly pure white product. Afterwards, the product was analyzed according to the same method and procedure as in Comparative Example 1.

Previous patent literature (Korean Patent No. 10-0983349) provides examples of alkaline decomposition reactions using various alcohols with different carbon numbers as a single reaction solvent. Alkaline hydroxides generally have low solubility in organic solvents, but when a large amount of alcohol is used as a reaction solvent as in prior literature, there is an advantage in that excess alkali hydroxides used for polymer decomposition can be uniformly dissolved. . However, when only alcohol is applied as a reaction solvent, the depolymerization of a polymer containing an ester functional group has limited reactivity, and in order to speed up the decomposition rate of the polymer or improve the conversion rate, there is a problem in that the reaction temperature must be maintained above the boiling point of the applied alcohol. There may be. Accordingly, the internal pressure of the reactor may be maintained higher than atmospheric pressure while depolymerization is performed, and it may be necessary to design a reaction facility that requires pressure resistance and airtightness.

In another prior patent document (Korean Patent No. 10-2223614), a polar aprotic solvent containing a ketone group, a nitrile group, or a furan group in a linear primary alcohol was used as a method to improve the reaction rate or perform depolymerization at low temperature. An alkaline depolymerization method through a mixed reaction solvent composition with additional addition is published. The polar aprotic solvent described in the relevant prior literature serves as a cosolvent to improve the decomposition rate through relaxation of the ester functional group and promotion of transesterification reaction due to interaction with the polymer substrate. However, when reaction heat is generated or heat is applied from the outside in the presence of a cosolvent having a ketone group in the relevant prior literature and an excess amount of alkali hydroxide is added as a reactant, colored organic matter is formed by an aldol condensation reaction of polar aprotic solvent molecules. Foreign substances may be generated, which may have a negative effect on the purity and quality of the terephthalic acid that is ultimately produced, and cause the problem of consumption of the polar aprotic solvent. In addition, in order to obtain the monomer product produced by depolymerization, that is, terephthalic acid, with high purity, an additional purification process requiring high energy may be required, and product loss may occur during the high purification process, which may adversely affect the final yield of the product. there is.

Meanwhile, existing prior literature provides examples for improving the performance of depolymerization reaction of polymers containing ester functional groups or the yield of monomer products, but most of them do not describe methods or examples for improving product quality. am. On the other hand, in the field of waste polymer recycling where related technologies are applied, it is more common to supply raw materials containing organic and inorganic contaminants, and impurities remaining in the manufactured monomer (terephthalic acid) have a significant impact on the quality of the resynthesized material. Because of this, several stages of purification processes requiring high energy may be required.

In the present invention, an aromatic compound with an alkoxy functional group and a compound with an alcohol functional group are mixed to form a solvent for the reaction, through a reaction and purification process that is completely different from the previously known method of producing terephthalic acid through alkaline decomposition of PET. The performance of the depolymerization reaction can be improved while simultaneously improving the quality of the final monomer product.

Table 1 shows a comparative observation of the characteristics of the alkaline decomposition reaction of PET (reaction temperature: 60°C) according to the composition of the reaction solvent. In the analysis of all depolymerization products performed in the present invention, incompletely decomposed compounds such as dimers or oligomers were not observed in the product distribution. In addition, it is less decomposed and ethylene glycol remains in the terephthalate structure, or the ethylene glycol released from the transesterification reaction is recombined to form an ester bond with the alkylene functional group, such as mono(hydroxyethylene)methyl terephthalate (HEMT) or bis. Monomers such as (hydroxyethylene)terephthalate (BHET) were not observed under any of the conditions of the present invention. Therefore, the depolymerization of PET using alkaline hydroxide and alcohol as reaction solvents can be expected to proceed according to the two reaction paths shown in FIG. 1.

As the depolymerization of the polymer containing the ester functional group progressed, the alkaline decomposition reaction (reaction path A in Figure 1) progressed, and the alkali salt form of terephthalic acid, the final monomer, was predominantly produced from the beginning of the reaction. In some examples of reactions, when alcohol was used as a reaction solvent, a partial alcoholesis reaction (reaction path B in Figure 1) in which an alkali hydroxide acted as a catalyst proceeded, and monoalkyl terephthalate alkali salt was observed as a reaction intermediate.

In the prior literature (Korean Patent No. 10-0983349), an excess of alkali hydroxide and primary alcohol are added to the reactant to decompose the polymer containing an ester functional group through an alkaline decomposition reaction path, and depolymerization is performed to obtain terephthalic acid as a product. Posting the method. Similar to the preceding literature, in Comparative Example 1, the sodium hydroxide added as a reactant was added in an excess amount of 4 times compared to the number of moles of repeating units of the polymer containing an ester bond group, and a large amount of alcohol equivalent to 8 times the weight of the polymer was added. This was added as a reaction solvent. At the beginning of the reaction, the alkaline decomposition reaction of PET proceeded rapidly, and the conversion rate exceeded about 84% within 2 hours of the reaction. However, as some of the alkali hydroxides were involved in the reaction and the concentration decreased, the speed of the reaction gradually slowed down, and the reaction took 6 hours. Even after passage of time, complete decomposition did not proceed.

In Comparative Example 2, in which the amount of alcohol added was 1.5 times greater than that of Comparative Example 1, relatively rapid decomposition of the polymer was observed even though the concentration was diluted by adding the same mole number of alkali hydroxide to the reaction. Within 2 hours of reaction, alkali decomposition reaction and partial alcoholesis reaction proceeded simultaneously, and after 4 hours of reaction, all products that could be generated from depolymerization of polymer were converted to alkali salt products of terephthalic acid, which are produced when alkaline decomposition continues. It has been done.

From the results of Comparative Example 1 and Comparative Example 2, it can be seen that the depolymerization reaction rate of a polymer containing an ester functional group can be improved by increasing the amount of alcohol solvent added. However, in order to increase the speed of the depolymerization reaction, an excessively large amount of alcohol must be added compared to the input polymer raw materials. This increases the volume of the reactor compared to the throughput and requires more heat to maintain the reaction temperature, resulting in high investment costs in process equipment. and may require high operating costs.

Anisole is a type of cosolvent added to demonstrate the effect of the present invention, and has the simplest structure among aromatic compounds to which an alkoxy functional group is bonded. In Example 1, a depolymerization reaction was performed after replacing part of the weight of the alcohol used in Comparative Example 1 with anisole. As a result of applying the co-solvent according to the present invention, most of the polymer at the beginning of the reaction was decomposed, and the conversion rate reached 98.4% after 2 hours of reaction time, and almost all of the PET was decomposed after 4 hours of reaction. In Comparative Example 1, which was performed by adding only ethanol, much higher reactivity was observed by replacing only 1/3 of the constituent ethanol with anisole, and the yield of monomers prepared from depolymerization was also observed to be very high.

Examples 2 to 3 are the results of increasing the amount of anisole added. When the amount of anisole added exceeded the weight of ethanol, complete decomposition of PET could be induced quickly from the beginning of the reaction, and a terephthalic acid yield close to the ideal value could be obtained.

Comparative Example 3 is the result of a depolymerization experiment conducted to determine whether the alkaline decomposition reaction of PET proceeds when anisole is used alone without using alcohol. Alkaline hydroxide (here, sodium hydroxide) added as a reactant has a very low solubility in organic solvents such as anisole, and when alcohol is not added, it remains in a solid state in the reaction mixture, which may prevent uniform contact with the applied polymer. You can. Referring to the results of Comparative Example 3, almost no reactivity for depolymerization of the polymer containing an ester functional group was observed from the beginning of the reaction. Even though it was exposed to the same reaction conditions as the previous examples and left for a long time (more than 4 hours), only a very small amount of monomer product was detected in the reaction mixture.

Example 4 maintained the same reactant composition as Example 2, but used methanol as the type of alcohol added. At the beginning of the reaction, a high concentration of monomethyl terephthalate sodium salt (Na-MMT), a reaction intermediate product, was observed due to the fast reaction rate of methanolysis, but when exposed to depolymerization reaction conditions for more than 2 hours, almost all of PET was removed. was decomposed and converted into alkali terephthalic acid salt, the final product of the alkaline decomposition reaction.

Table 2 shows the results of PET depolymerization reaction (reaction temperature: 60°C) according to the initial concentration of alkali hydroxide. Changes in product production were observed after exposure to depolymerization reaction conditions for 2 hours in a ratio of 0.0 to 4.0 moles of sodium hydroxide (NaOH) relative to the number of moles of repeating units of the polymer.

In the case of Comparative Example 4, in which no alkali hydroxide was added, there was no base reactant for alkali decomposition as well as a material that exerts a catalytic function for alcoholesis, so almost no decomposition of PET occurred, as expected. The number of moles (equivalence ratio) that must be added to cause complete alkaline decomposition through depolymerization of the polymer corresponds to 2.0 moles compared to the number of moles of the repeating unit, and Example 5 (0.5 mole of NaOH) and Example 6 (NaOH) were added in amounts less than that. In the case of 1.0 mol), after 2 hours of depolymerization reaction, sodium monoethyl terephthalate (Na-MET), which is a reaction intermediate in the product, was observed at a much higher concentration than sodium terephthalate (Na ₂ -TPA). This explains that the polymer decomposition reaction due to partial alcohollysis (reaction path A in Figure 1) progressed more dominantly in the early stages of depolymerization.

In Example 7, in which sodium hydroxide was added in an amount equivalent to the alkaline decomposition reaction for producing terephthalic acid, PET depolymerization by alkali decomposition reaction and partial alcohollysis reaction proceeded simultaneously (reaction paths A and B in FIG. 1), reaction 2 In the distribution of the products produced after time, Na-MET and Na ₂ -TPA were observed in similar mole numbers.

Meanwhile, in Example 1, in which an excess amount of sodium hydroxide was added from the beginning of the reaction, alkali decomposition proceeded very quickly from the beginning of the reaction, and a high concentration of Na ₂ -TPA was produced directly from the depolymerization reaction.

Table 3 shows the results of the depolymerization reaction (reaction temperature: 60°C) when only the type of alkali hydroxide was changed and other reaction conditions were kept the same. In these examples, an amount of mixed solvent close to the minimum that allows all PET flakes used as raw materials to be completely submerged in the reaction solution was added to PET, 2.5 times the amount of alcohol compared to the amount of polymer added, and a compound with an alkoxy bond (anisole). ) is twice the weight applied. In addition, the amount of added metal hydroxide compared to the number of moles of repeating units of the polymer containing an ester functional group was adjusted to the equivalent amount required for producing terephthalic acid by alkaline decomposition.

In the case of Example 9 in which potassium was used as the cation of the alkali hydroxide, the reaction rate of alcoholesis and the overall reaction rate of depolymerization in which PET was decomposed were observed to be somewhat higher than in Example 8 in which sodium was used, but in both cases Almost all of the PET was decomposed within 2 hours after the start of the depolymerization reaction, and alkali terephthalic acid was produced in high yield.

Table 4 shows the characteristics of PET depolymerization when depolymerization was performed using reactants of the same composition and the reaction temperature was changed.

Referring to the results of Example 10, in which depolymerization was performed under relatively mild reaction conditions (30°C), the PET conversion rate due to depolymerization was observed to be less than 84% even though the reaction took 6 hours. Meanwhile, in the product distribution observed through quantitative analysis, the yield of sodium terephthalate salt was 67.6%, and the yield of monoethyl terephthalate sodium salt (Na-MET), which can be produced through the reaction path of partial alcoholesis, was also 16.4%. It was found that it was obtained with a relatively small yield.

In Examples 2 and 11, where the reaction temperature was maintained at 60°C and close to the boiling point of alcohol, PET was completely or mostly decomposed despite exposure to a short reaction time of less than 2 hours, resulting in very high reactivity. It can be seen that depolymerization has progressed. In both cases, dominant depolymerization proceeded according to the alkaline decomposition reaction path, and as a result, a high concentration of alkali salt of terephthalic acid was obtained as a product.

Table 5 shows the results of depolymerization (reaction temperature: 60°C) of a polymer containing an ester functional group applied by changing the type of cosolvent. As in Example 12, when 1,2-DMB, in which two methoxy groups were substituted for the hydrogen bonded to the aromatic carbon, was applied as a reaction solvent along with alcohol, it exhibited very high depolymerization performance, and under the same conditions, anisole was used as a cosolvent. Similar to the case of Example 2 where , PET was rapidly depolymerized by the dominant alkali decomposition reaction from the beginning of the reaction.

In Example 13, in which phenetol was used as a cosolvent, high reactivity was observed from the beginning of the reaction, and the reaction system constructed from the analysis results of the prepared reactants was observed to provide high selectivity for alkali terephthalic acid. Even when a compound in which another alkoxy functional group having two or more carbon atoms is bonded to an aromatic ring is applied as a co-solvent for the alkaline decomposition reaction, the depolymerization is much higher than those in which depolymerization was performed using only alcohol (Comparative Example 1 or Comparative Example 2). A level of response performance was observed.

On the other hand, as in Comparative Example 5, when guaiacol, which additionally has a proton donor functional group in addition to the alkoxy functional group, was used as a cosolvent, completely different results were obtained. Aromatic compounds such as guaiacol, which have both an alkoxy functional group and a hydroxy functional group, may undergo an acid-base reaction when they come into contact with an alkali hydroxide. In fact, when sodium hydroxide was added in the process of preparing the mixed solvent of Comparative Example 5, white precipitate occurred very quickly. The precipitate formed at this time was Guaiacol sodium, which resulted in the sodium hydroxide added for alkaline decomposition being consumed even before the depolymerization reaction. PET was added to the obtained mixed solution and the progress of the reaction was observed, but the depolymerization reaction due to alkaline decomposition hardly proceeded. These results clearly explain that aromatic compounds containing a proton donor functional group that can react with alkali hydroxide, even if they contain an alkoxy functional group, are difficult to utilize as a co-solvent for the alkaline decomposition reaction of a polymer with an ester functional group.

Table 6 shows the performance of alkaline decomposition reaction (reaction temperature: 60°C) performed on colored waste PET and waste polyester raw materials discharged after consumption according to an example of the prior patent document (KR 10-0983349) and the depolymerization method of the present invention. is compared.

Comparative Example 6 is the result of depolymerization of raw materials prepared by crushing colored PET bottles using only alcohol. Compared to Comparative Example 2, where the same depolymerization reaction conditions were applied but depolymerization was performed using colorless PET raw materials, the conversion rate and yield of the reaction at the beginning of the reaction were almost similar, but when exposed to the reaction for a long time, the conversion rate and the alkali salt of terephthalic acid decreased. Much lower yields were observed. This is because foreign substances discharged outside the polymer matrix as depolymerization progresses, especially colored pigments or organic colorants, generally consume the alkali hydroxide through various reaction pathways when they come into direct contact with the alkali hydroxide. At the beginning of the reaction, foreign substances were not exposed and did not have a significant effect. However, as the decomposition of the polymer progresses, the foreign substances released show that they have a direct and substantial effect on the depolymerization reactivity.

Example 14 is the result of depolymerization by adding anisole, an organic cosolvent, according to the present invention. Unlike the results of Comparative Example 6, in which only alcohol was applied without adding a cosolvent, polymer decomposition progressed rapidly. From the beginning of the reaction, the conversion rate and yield of alkali terephthalic acid were maintained above 90%, and after 4 hours of reaction, most of the PET was decomposed and a very high yield of alkali terephthalic acid was detected. As in Example 14, when a compound having an alkoxy functional group but not having a proton donor functional group, which is a co-solvent according to the present invention, is added, since the compound with the alkoxy functional group is hydrophobic, the solvent mixture for the reaction becomes hydrophobic, so that sodium hydroxide The rate of consumption by impurities is greatly reduced. In addition, most of the colored foreign substances did not remain in the solid content of the product during the filtration process, but were discharged along with the mixed solvent consisting of alcohol and anisole. Accordingly, despite applying the same purification and acid treatment process as in Comparative Example 6, high depolymerization performance was maintained when depolymerization was performed according to Example 14, and the manufactured product was a high-quality terephthalic acid that was relatively white. . It was easy to see with the naked eye that the manufactured terephthalic acid product did not have a large amount of residual colored foreign substances.

In Comparative Example 7 and Example 15, depolymerization was performed using colored waste plastic as a raw material, which is a composite of multiple polymers (composition ratio: PET 63.8%, PBT 35.4%) containing ester functional groups with different chemical structures and shapes. , the reaction performance was compared for two cases with different solvent compositions. Similar to the performance comparison of Comparative Example 6 and Example 14, the speed in Example 15 in which depolymerization was performed after adding a co-solvent (anisole) was faster than in Comparative Example 7 in which depolymerization was performed by simply adding alcohol. An alkaline decomposition reaction was observed, and the yield of the terephthalic acid product obtained after the reaction was also observed to be high. In addition, in Example 15, most of the colored foreign substances (organic additives for dyeing, including carbon black) introduced into the initial polymer were discharged/removed by the co-solvent, and a brighter colored terephthalic acid product was obtained than that of Comparative Example 7. .

In Comparative Example 8 and Example 16, a polymer in the form of a composite was used as in Comparative Example 7 and Example 15, but depolymerization was performed using waste polymer raw materials with different compositions (composition ratio: PET 26.1%, PBT 73.1%). am. As in the two cases where performance was compared by applying different raw materials, the depolymerization reaction in which depolymerization was performed after adding a cosolvent (anisole) compared to the case where depolymerization was performed using only alcohol as a reaction solvent (Comparative Example 8) In Example 16), a faster rate of alkali decomposition reaction was observed, and the yield of terephthalic acid product obtained after the reaction was also observed to be high.

Table 7 lists each color space coordinate value (L* a* b*) measured using a spectrophotometer to observe the quality of terephthalic acid products manufactured by various methods. Reagent-grade commercial terephthalic acid (Sigma-Aldric, product number: 185361) and the final product obtained through purification and commercialization after depolymerization of colored polymers were manufactured into circular disks and used as samples in a spectrophotometer to observe color characteristics. .

The brightness value (L*) of the terephthalic acid products obtained from the process of Comparative Examples 6 to 8, in which the colored polymers of Raw Materials 2 to 4 were depolymerized using only alcohol as a reaction solvent, was observed in the range of 87 to 89. , This is a result that well explains the fact that it has a much darker color compared to commercial terephthalic acid, which has a brightness value (L*) of 96.16. Terephthalic acid products prepared from the alkaline decomposition reaction of colored polymers (Examples 14 to 16) performed by replacing part of the alcohol solvent with the cosolvent (anisole) according to the present invention were similar to those of the previous comparative examples conducted using only alcohol. The color was lighter than before, and the brightness value (L*) measured using a spectrophotometer was over 90.

The production flow and form of the reaction solvent and final monomer product (prepared as a disk sample) discharged during the depolymerization reaction of the colored polymer containing an ester functional group and the purification process of the product performed according to the embodiments of the present invention are shown in Figure 2. It was.

During the primary filtration process to separate the terephthalic acid product from the reaction product after depolymerization, a large amount of colored foreign substances were observed to be discharged together with the solvent applied to the reaction (Figure 2(b)). Therefore, it can be seen that simply applying a co-solvent instead of alcohol is effective in removing residual foreign substances in the final product (Figure 2(c)). Foreign substances contained in the solvent discharged during this process generally have a higher boiling point than the solvent used, so they can be purified by simple methods such as distillation or evaporation, and the solvent purified in this way can be reintroduced into a new depolymerization process. there is.

As shown in Table 7, the color characteristics measured by optical methods for the terephthalic acid prepared in Examples 14 to 16 were still observed to have low brightness and a large absolute value of saturation compared to those for commercial terephthalic acid. It has been done. The method of forming a reaction solvent by mixing a co-solvent with alcohol according to the present invention is effective in removing impurities in a product, but is not a means of completely removing impurities.

To improve this, residual impurities in the reactant were removed using an adsorbent, but the existing purification method was changed and applied. In the existing purification process, the filter cake (solid material) obtained through primary filtration to separate the reaction solvent from the product produced after the depolymerization reaction contains most of the terephthalate alkali salt that can be converted into the final product, which is converted into unreacted polymer or raw material. In order to separate the terephthalate alkaline salt from the high molecular materials (e.g. PE or PP) that have flowed into the product, the alkali salt of terephthalate is dissolved using water or an aqueous solution, then recovered as a filtrate, and acid is added to the filtrate to precipitate the final product, terephthalic acid. can be used

In Examples 17 to 19, the polymer having an ester functional group was depolymerized according to Examples 14 to 16, and the polymer was further passed through an adsorbent layer before conversion to terephthalic acid by adding acid during the purification process. It shows the color characteristics of the manufactured product. Here, activated carbon was used as an example of the adsorbent. The measured brightness value (L*) of terephthalic acid recorded a very high value of over 97.6, and the coordinate values (a* and b*) indicating the relative positions of 'red to green' and 'yellow to blue' were also very close to neutral. The values are shown (Figure 2(d)). This extreme effect of purifying foreign substances is a result that cannot be achieved by simply applying an adsorbent alone. Even though most of the co-solvent is physically separated/removed during the filtration process of the depolymerization reaction according to the present invention, a trace amount of the co-solvent with an alkoxy functional group present dissolved in the aqueous filtrate may weaken the interaction between organic foreign substances and terephthalate alkali salt. , this can be interpreted as a result of inducing more effective and irreversible adsorption of foreign substances.

As the specific parts of the present invention have been described in detail above, it will be clear to those skilled in the art that these specific techniques are merely preferred embodiments and do not limit the scope of the present invention. will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims

(1) Aromatic compounds having at least one alkoxy functional group but not having a proton donor functional group;

(2) compounds with one or more alcohol functional groups; and

(3) A method for depolymerizing a polymer containing an ester functional group, characterized in that a mixture containing an alkali hydroxide is brought into contact with a polymer containing an ester functional group to depolymerize the polymer.
According to paragraph 1,

Depolymerization of a polymer containing an ester functional group, characterized in that the weight ratio of the aromatic compound having at least one alkoxy functional group and the compound having at least one alcohol functional group without a proton donor functional group in the mixture is 20:1 to 1:20. method.
According to paragraph 1,

A method for depolymerization of a polymer containing an ester functional group, wherein the compound having the alcohol functional group is a straight-chain primary alcohol.
According to paragraph 1,

Aromatic compounds having one or more alkoxy functional groups without having a proton donor functional group include 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-tetrame Toxybenzene, 1,2,4,5-tetramethoxybenzene, 1-methoxy-2-methylbenzene, 1-methoxy-3-methylbenzene, 1-methoxy-4-methylbenzene, 1-methoxy -2-ethylbenzene, 1-methoxy-3-ethylbenzene, 1-methoxy-4-ethylbenzene, 1-methoxy-2-propylbenzene, 1-methoxy-3-propylbenzene, 1-methoxy -4-propylbenzene, ethoxybenzene, 1-ethoxy-2-methoxybenzene, 1-ethoxy-3-methoxybenzene, 1,2-diethoxybenzene, 1,3-diethoxybenzene, 1, 4-diethoxybenzene, 1,2,4-triethoxybenzene, 1,3,5-triethoxybenzene, 1-ethoxy-2-methylbenzene, 1-ethoxy-3-methylbenzene, 1- Ethoxy-4-methylbenzene, (1-methoxyethyl)benzene, (2-methoxyethyl)benzene, (2-methoxy)ethoxybenzene, 1-methoxy-2-(methoxymethoxy)benzene , 1-(diethoxymethyl)-4-methoxybenzene, propoxybenzene, 1,3-dimethyl-2-propoxybenzene, 1-methoxy-4-propoxybenzene, 1,3-dipropoxybenzene A method for depolymerization of a polymer containing an ester functional group, characterized in that it is one or more compounds selected from the group consisting of phenoxyethanol, etc.
According to paragraph 1,

The alkali hydroxide is selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, magnesium hydroxide, ammonium hydroxide, tetraalkyl ammonium hydroxide, and combinations thereof. A method for depolymerization of a polymer containing an ester functional group.
According to paragraph 1,

A method for depolymerizing a polymer containing an ester functional group, characterized in that the temperature during depolymerization is 10°C to 100°C.
According to paragraph 1,

A method for depolymerization of a polymer containing an ester functional group, characterized in that a primary filtration step of performing solid-liquid separation from the reaction product after the depolymerization reaction is additionally performed.
In clause 7,

A method for depolymerization of a polymer containing an ester functional group, characterized in that a secondary filtration step is further performed in which water is added to the filtration cake obtained through the primary filtration to dissolve the monomer product in water and then separate and filtered.
According to clause 8,

A method for depolymerization of a polymer containing an ester functional group, characterized in that the water used in the filtration process further contains alkali hydroxide in a mole number equal to or greater than the mole number of monoalkyl terephthalate present in the monomer product.
According to clause 8,

A method for depolymerization of a polymer containing an ester functional group, characterized in that an aromatic compound having an alkoxy functional group is added to the filtrate obtained in the secondary filtration step to further separate colored organic impurities.
According to clause 8,

A method for depolymerization of a polymer containing an ester functional group, characterized in that it further includes the step of contacting an aqueous solution containing colored organic foreign substances with an adsorbent to adsorb and remove the colored foreign substances.
According to clause 8,

A method for depolymerizing a polymer containing an ester functional group, further comprising adding an acid to an aqueous solution containing the monomer to precipitate it as a salt in order to recover the monomer of the depolymerized polymer.
According to clause 12,

A method for depolymerization of a polymer containing an ester functional group, characterized in that it further comprises the step of separating the precipitate generated from the filtrate after adding acid and then recovering high purity terephthalic acid through a drying process.
A composition for depolymerizing a polymer containing an ester functional group,

(1) Aromatic compounds having at least one alkoxy functional group but not having a proton donor functional group;

(2) compounds with one or more alcohol functional groups; and

(3) A composition for polymer depolymerization containing an ester functional group, characterized in that it contains an alkali hydroxide.
According to clause 14,

A composition for polymer depolymerization containing an ester functional group, characterized in that the weight ratio of the aromatic compound having at least one alkoxy functional group and the compound having at least one alcohol functional group without having a proton donor functional group is 20:1 to 1:20.