Monomer composition for synthetic recycled plastic, method of making the same, recycled plastic using the same, molded article, plasticizer composition

Abstract

The present invention relates to a monomer composition for synthetic recycled plastic, a method of making the monomer composition, and recycled plastic, molded articles, and plasticizer compositions using the monomer composition. The monomer composition has a high acid value upon recovery from (co)polymer synthesized from monomers comprising terephthalic acid.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims the benefit of Korean Patent Application Nos. 10-2021-0094470, 10-2021-0094471, 10-2021-0094472 and 10-2021-0094473, all filed on July 19, 2021, with the entire contents of which are incorporated herein by reference.

[0003] This invention relates to a monomer composition for synthesizing recycled plastics, which ensures high purity terephthalic acid and thus a high acid value when terephthalic acid is recovered through the depolymerization reaction of a (co)polymer synthesized from a monomer containing terephthalic acid. It also relates to a method for preparing the monomer composition, and recycled plastics, molding articles, and plasticizer compositions using the monomer composition. Background Technology

[0004] Polyethylene terephthalate (PET) is a thermoplastic (co)polymer with excellent properties such as excellent transparency and heat insulation. It is widely used in wire sheathing, daily necessities, toys, electrical insulators, radio and television casings, packaging materials, and more.

[0005] Despite the wide range of applications for polyethylene terephthalate (PET), environmental and health problems continue to arise during waste disposal. Currently, physical recycling methods are being implemented, but these methods often result in quality degradation. Therefore, research is underway into the chemical recycling of PET.

[0006] Terephthalic acid is a useful compound used as a raw material for various types of products. It is the main raw material for polyethylene terephthalate (PET), polyester fibers, and polyester films used for packaging and containers.

[0007] Polycondensing ethylene glycol with terephthalic acid to produce polyethylene terephthalate (PET) is a reversible reaction process, and PET can be depolymerized and recycled into monomers or oligomers.

[0008] Various methods have been proposed in the past for decomposing polyethylene terephthalate (PET) to recover monomers as raw materials. Monomers that can be used in polycondensation reactions to regenerate recycled plastics can be obtained through the alkaline decomposition of polyethylene terephthalate (PET) waste.

[0009] For example, the decomposition products of polyethylene terephthalate (PET) under alkaline conditions include ethylene glycol and salts of terephthalic acid, and the salts of terephthalic acid are further neutralized with a strong acid to prepare terephthalic acid.

[0010] However, terephthalic acid obtained by conventional methods typically contains 1% to 2% isophthalic acid as an impurity. Therefore, when it is reused as a raw material for the production of high-value-added plastics such as PBT / TPEE, there are limitations – problems such as deterioration of the physical properties of the (co)polymer (low melting point, low tensile strength, low stiffness, etc.) occur.

[0011] Therefore, in the process of decomposing (co)polymers synthesized from monomers containing terephthalic acid—including polyethylene terephthalate (PET)—and recovering the monomers as raw materials, there is a need to develop methods that can significantly reduce the content of isophthalic acid as an impurity. Summary of the Invention

[0012] Technical issues

[0013] One object of the present invention is to provide a monomer composition for synthesizing recycled plastics, wherein the monomer composition ensures high purity terephthalic acid and thus has a high acid value when terephthalic acid is recovered by depolymerization of a (co)polymer synthesized from a monomer containing terephthalic acid.

[0014] Another object of the present invention is to provide a method for preparing a monomer composition for synthesizing recycled plastics, and a recycled plastic, molding article and plasticizer composition using the monomer composition for synthesizing recycled plastics.

[0015] Technical solution

[0016] To achieve the above objectives, this document provides a monomer composition for synthesizing recycled plastics, comprising terephthalic acid, wherein the acid value, as determined by KS M ISO 2114, is ≥670 mg KOH / g, and wherein the monomer composition for synthesizing recycled plastics is recovered from a (co)polymer synthesized from monomers comprising terephthalic acid.

[0017] This document also provides a method for preparing monomer compositions for synthesizing recycled plastics, comprising the steps of: depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid and removing the diol component; washing the depolymerization product from which the diol component has been removed, wherein the washing step includes washing with a protic polar solvent at a temperature above 20°C and below 100°C; and washing with a washing solvent containing a non-protic polar solvent at a temperature above 20°C and below 110°C.

[0018] This article further provides a recycled plastic comprising a reaction product of a monomer composition for synthesizing recycled plastics and a comonomer.

[0019] This article further provides a molding article comprising the recycled plastic.

[0020] This article further provides a plasticizer composition comprising a reaction product of a monomer composition for synthesizing recycled plastics and an alcohol.

[0021] Below, monomer compositions for synthesizing recycled plastics, methods for preparing them, and recycled plastics, molding articles, and plasticizer compositions using them will be described in more detail according to specific embodiments of the present invention.

[0022] Unless otherwise expressly stated herein, the technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0023] Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” used in this document are intended to include the plural forms.

[0024] It should be understood that the terms “comprising,” “including,” “having,” etc., are used herein to specify the presence of the stated features, regions, integers, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, regions, integers, steps, actions, elements, components, and / or groups.

[0025] Furthermore, ordinal terms such as "first" and "second" are used only for the purpose of distinguishing one component from another and are not limited by ordinal numbers. For example, without departing from the scope of the invention, the first component may be referred to as the second component, or similarly, the second component may be referred to as the first component.

[0026] In this specification, (co)polymers include polymers and copolymers. A polymer is a homopolymer composed of a single repeating unit, and a copolymer is a composite polymer containing two or more types of repeating units.

[0027] 1. Monomer compositions for synthesizing recycled plastics

[0028] According to one embodiment of the invention, a monomer composition for synthesizing recycled plastics can be provided, comprising terephthalic acid, wherein the acid value as determined by KS M ISO 2114 is 670 mg KOH / g or higher, and wherein the monomer composition for synthesizing recycled plastics is recovered from a (co)polymer synthesized from monomers containing terephthalic acid.

[0029] The inventors have discovered through experimentation that, as in the monomer composition for synthesizing recycled plastics according to one embodiment described above, the purity of terephthalic acid can be increased to adequately raise the acid value to commercially available levels in the monomer composition for synthesizing recycled plastics recovered from (co)polymers synthesized from monomers containing terephthalic acid, thus completing the present invention.

[0030] Furthermore, the inventors have discovered through experiments that, although it is recovered from (co)polymers synthesized from monomers containing terephthalic acid, as in the monomer composition for synthesizing recycled plastics in one of the above embodiments, the proportion of isophthalic acid (which is another monomer and is not terephthalic acid, the main synthetic target material in this invention) is greatly reduced to less than 0.85 mol% based on the total monomer compounds contained in 100 mol% of the monomer composition for synthesizing recycled plastics. This allows for the achievement of excellent physical properties in the synthesis of polyethylene terephthalate or high-value-added plastics (PBT, TPEE), thus completing this invention.

[0031] In particular, terephthalic acid recovered from (co)polymers synthesized from monomers containing terephthalic acid by conventional methods typically contains 1% to 2% isophthalic acid as an impurity, whereas, according to the present invention, isophthalic acid can be almost completely removed by a secondary washing process, which is a feature of a method for preparing monomer compositions for synthesizing recycled plastics, the method of which will be described below.

[0032] Specifically, one embodiment of the monomer composition for synthesizing recycled plastics may contain terephthalic acid. The terephthalic acid is characterized by being recovered from a (co)polymer synthesized from monomers containing terephthalic acid, said (co)polymer being used to recover the monomer composition for synthesizing recycled plastics.

[0033] That is, this means that by recycling (co)polymers synthesized from monomers containing terephthalic acid to obtain a monomer composition for synthesizing recycled plastics according to one embodiment, terephthalic acid is also obtained as a result. Therefore, the addition of new terephthalic acid from the outside is not included in the scope of the terephthalic acid of the present invention, except for the case of recycling from (co)polymers synthesized from monomers containing terephthalic acid to prepare a monomer composition for synthesizing recycled plastics according to one embodiment.

[0034] Specifically, "recovery from (co)polymers synthesized from monomers containing terephthalic acid" refers to its acquisition through a depolymerization reaction of the (co)polymer synthesized from monomers containing terephthalic acid. This depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions, particularly under alkaline (basic) conditions.

[0035] For example, when the depolymerization reaction is carried out under alkaline conditions, the polyethylene terephthalate mainly produces a terephthalate salt called Na2-TPA and ethylene glycol, and Na2-TPA is converted into TPA by secondary strong acid neutralization, thereby enabling the recovery of terephthalic acid.

[0036] That is, terephthalic acid recovered from a (co)polymer synthesized from monomers containing terephthalic acid may include the alkaline (base) decomposition product of the (co)polymer synthesized from monomers containing terephthalic acid, its acid neutralization product, or a mixture thereof. Specifically, the alkaline (base) decomposition product of the (co)polymer synthesized from monomers containing terephthalic acid may include Na2-TPA, and the acid neutralization product of the alkaline (base) decomposition product of the (co)polymer synthesized from monomers containing terephthalic acid may include terephthalic acid.

[0037] Based on the total monomer compounds contained in a 100 mol% monomer composition for synthesizing recycled plastics, the terephthalic acid may have a molar ratio of greater than 99.15 mol%, or more than 99.5 mol%, or more than 99.9 mol%, or more than 99.95 mol%, or more than 99.99 mol%, or greater than 99.15 mol% and less than 100 mol%, or more than 99.5 mol% and less than 100 mol%, or more than 99.9 mol% and less than 100 mol%, or more than 99.99 mol% and less than 100 mol%.

[0038] There are no particular limitations on the examples of methods used to measure the molar ratio of terephthalic acid, and, for example, methods can be used without limitation. 1 ¹H NMR, ICP-MS, HPLC, etc. For NMR, ICP-MS, and HPLC, various previously known methods, conditions, and equipment can be used without restriction.

[0039] In one example of a method for measuring the molar ratio of terephthalic acid, a monomer composition of at least 5 mg and less than 20 mg for synthesizing recycled plastics was collected as a sample under atmospheric pressure and at temperatures above 20°C and below 30°C. This sample was dissolved in 1 mL of DMSO-d6 solvent and subsequently analyzed by an Agilent DD1 500 MHz NMR instrument. 1 ¹H NMR spectra were analyzed, and the detection peaks of all materials, such as terephthalic acid (TPA) and isophthalic acid (IPA), were determined using analysis software (MestReC). The peaks were integrated, and the molar ratio (mol%) of terephthalic acid in 100 mol% of the total monomeric compounds in the analyzed sample was calculated based on the integrated value of the peak.

[0040] As described above, based on the total monomer compounds contained in the monomer composition for synthesizing recycled plastics at 100 mol%, the proportion of terephthalic acid, which is the main target material for synthesis in this invention, is greatly increased to greater than 99.15 mol%, and impurity monomers other than terephthalic acid (e.g., isophthalic acid) are reduced, thereby enabling the achievement of excellent physical properties in the synthesis of polyethylene terephthalate or high value-added plastics (PBT, TPEE).

[0041] Furthermore, based on the total monomer compounds contained in a monomer composition for synthesizing recycled plastics at 100 mol%, one embodiment of the monomer composition for synthesizing recycled plastics may further include isophthalic acid at a molar ratio of less than 0.85 mol%.

[0042] The isophthalic acid is characterized by being recovered from a (co)polymer synthesized from monomers containing terephthalic acid, said (co)polymer being used to recover monomer compositions for the synthesis of recycled plastics.

[0043] That is, this means that by recycling (co)polymers synthesized from monomers containing terephthalic acid to obtain a monomer composition for synthesizing recycled plastics according to one embodiment, isophthalic acid is also obtained. Therefore, the addition of new isophthalic acid from the outside is not included in the scope of the isophthalic acid of the present invention, except for the case of recycling (co)polymers synthesized from monomers containing terephthalic acid to prepare a monomer composition for synthesizing recycled plastics according to one embodiment.

[0044] Specifically, "recovery from (co)polymers synthesized from monomers containing terephthalic acid" refers to its acquisition through a depolymerization reaction of the (co)polymer synthesized from monomers containing terephthalic acid. This depolymerization reaction can be carried out under acidic, neutral, or alkaline conditions, particularly under alkaline (basic) conditions.

[0045] Based on the total monomer compounds contained in a 100 mol% monomer composition for synthesizing recycled plastics, the isophthalic acid may have a molar ratio of less than 0.85 mol%, or less than 0.5 mol%, or less than 0.1 mol%, or less than 0.05 mol%, or less than 0.01 mol%, or more than 0 mol% and less than 0.85 mol%, or more than 0 mol% and less than 0.5 mol%, or more than 0 mol% and less than 0.1 mol%, or more than 0 mol% and less than 0.05 mol%, or more than 0 mol% and less than 0.01 mol%.

[0046] There are no particular limitations on the examples of methods used to measure the molar ratio of isophthalic acid, and, for example, methods can be used without limitation. 1Analysis methods include ¹H NMR, ICP-MS, and HPLC. For NMR, ICP-MS, and HPLC, all previously known methods, conditions, and equipment can be applied without restriction.

[0047] In one example of a method for measuring the molar ratio of isophthalic acid, a monomer composition of at least 5 mg and less than 20 mg for synthesizing recycled plastics was collected as a sample under atmospheric pressure and at temperatures above 20°C and below 30°C. This sample was dissolved in 1 mL of DMSO-d6 solvent and subsequently analyzed by an Agilent DD1 500 MHz NMR instrument. 1 ¹H NMR spectra were analyzed, and the detection peaks of all materials, such as terephthalic acid (TPA) and isophthalic acid (IPA), were determined using analysis software (MestReC). The peaks were integrated, and the molar ratio (mol%) of isophthalic acid in 100 mol% of the total monomeric compounds in the analyzed sample was calculated based on the integrated value of the peak.

[0048] As described above, based on the total monomer compounds contained in a 100 mol% monomer composition for synthesizing recycled plastics, the proportion of isophthalic acid, an impurity monomer other than terephthalic acid, which is the main target material for synthesis in this invention, is greatly reduced to below 0.85 mol%, thereby enabling the achievement of excellent physical properties in the synthesis of polyethylene terephthalate or high value-added plastics (PBT, TPEE).

[0049] Furthermore, one embodiment of the monomer composition for synthesizing recycled plastics is characterized by recycling from a (co)polymer synthesized from monomers containing terephthalic acid. That is, this means recycling from a (co)polymer synthesized from monomers containing terephthalic acid to obtain a monomer composition for synthesizing recycled plastics according to one embodiment, resulting in a monomer composition for synthesizing recycled plastics containing both terephthalic acid and isophthalic acid.

[0050] In the context of (co)polymers synthesized from monomers containing terephthalic acid, the (co)polymer includes polymers and copolymers, and generally refers to the reaction products of (co)polymerization derived from monomers. Depending on the molecular weight range, the (co)polymer may include all low molecular weight compounds, oligomers, and polymers.

[0051] The (co)polymer synthesized from monomers containing terephthalic acid may include at least one (co)polymer selected from polyalkylene terephthalate, polyalkylene terephthalate copolymers, and thermoplastic polyester elastomers. That is, the (co)polymer synthesized from monomers containing terephthalic acid may include one type of polyalkylene terephthalate, one type of polyalkylene terephthalate copolymer, one type of thermoplastic polyester elastomer, or a mixture of two or more thereof.

[0052] Polyalkylene terephthalate copolymers refer to copolymers obtained by further reacting an additional comonomer based on alkylene glycol with terephthalic acid, which is a monomer used to synthesize polyalkylene terephthalate.

[0053] (Co)polymers synthesized from monomers containing terephthalic acid may contain the reaction product of terephthalic acid and a comonomer. That is, monomers containing terephthalic acid may further contain a comonomer and terephthalic acid.

[0054] There are no particular limitations on examples of comonomers capable of reacting with terephthalic acid, and specific examples may include aliphatic diols, polyalkylene oxides, fatty acids, fatty acid derivatives, or combinations thereof.

[0055] As an aliphatic diol, for example, a diol with a number-average molecular weight (Mn) of 300 g / mol or less can be used, namely, at least one selected from ethylene glycol, propylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol (1,4-BG), 1,5-pentanediol, 1,6-hexanediol, and 1,4-cyclohexenedimethanol (1,4-CHDM). As a specific example, 1,4-butanediol, ethylene glycol, 1,4-cyclohexenedimethanol, or mixtures thereof can be used.

[0056] The polyoxyalkylene oxide is a unit constituting a soft segment and may include aliphatic polyethers as constituent components. As an example, at least one selected from polyethylene glycol, polypropylene glycol, poly(tetramethylene ether) glycol (PTMEG), polyhexamethylene glycol, copolymers of ethylene oxide and propylene oxide, ethylene oxide addition polymers of polypropylene oxide glycol, and copolymers of ethylene oxide and tetrahydrofuran can be used. As a specific example, PTMEG can be used. In particular, PTMEG with a number-average molecular weight (Mn) of 600 g / mol to 3,000 g / mol, 1,000 g / mol to 2,500 g / mol, or 1,500 g / mol to 2,200 g / mol can be used.

[0057] The fatty acid can be, for example, at least one type of aliphatic carboxylic acid compound other than terephthalic acid; as a specific example, adipic acid can be used. The fatty acid derivative is a compound derived from the aforementioned fatty acid; as an example, at least one selected from fatty acid esters, fatty acyl chlorides, fatty acid anhydrides, and fatty acid amides can be used, and as a specific example, adipate esters can be used.

[0058] In a more specific example, when 1,4-butanediol, as an aliphatic diol, is used as a comonomer capable of reacting with terephthalic acid, polybutylene terephthalate (PBT), as a type of polyalkylene terephthalate, can be obtained by the polymerization reaction of terephthalic acid with 1,4-butanediol.

[0059] Furthermore, when ethylene glycol, as an aliphatic diol, is used as a comonomer capable of reacting with terephthalic acid, polyethylene terephthalate (PET), a type of polyalkylene terephthalate, can be obtained through the polymerization reaction of terephthalic acid and ethylene glycol.

[0060] Furthermore, when 1,4-butanediol, as an aliphatic diol, is used together with PTMEG, as a polyepoxide, as a comonomer capable of reacting with terephthalic acid, thermoplastic polyester elastomers (TPEEs) can be obtained through the polymerization reaction of terephthalic acid, 1,4-butanediol, and PTMEG.

[0061] Furthermore, when 1,4-butanediol, as an aliphatic diol, is used together with adipic acid, as a fatty acid, as a comonomer capable of reacting with terephthalic acid, polybutylene terephthalate (PBAT), as a type of polyalkylene terephthalate copolymer, can be obtained through the polymerization reaction of terephthalic acid, 1,4-butanediol, and adipic acid.

[0062] Furthermore, when ethylene glycol, as an aliphatic diol, is used together with 1,4-cyclohexanediethanol as a comonomer capable of reacting with terephthalic acid, a glycol-modified PET resin (glycol-modified polyethylene terephthalate, PETG) as a type of polyalkylene terephthalate copolymer can be obtained through the polymerization reaction of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol.

[0063] As a specific example, polyalkylene terephthalate may include at least one (co)polymer selected from polybutylene terephthalate, polyethylene terephthalate, polycyclohexyl dimethyl terephthalate, polyethylene naphthalate, polybutylene naphthalate and polypropylene terephthalate.

[0064] In addition, as a specific example, polyalkylene terephthalate copolymers may include at least one (co)polymer selected from polybutylene terephthalate (PBAT) and glycol-modified PET resin (glycol-modified polyethylene terephthalate, PETG).

[0065] Meanwhile, measured by KS M ISO 2114, the acid value of the monomer composition used to synthesize recycled plastics can be above 670 mg KOH / g, or above 671 mg KOH / g, or above 672 mg KOH / g, or above 673 mg KOH / g, or above 674 mg KOH / g, or below 680 mg KOH / g, or between 670 mg KOH / g and 680 mg KOH / g, or between 671 mg KOH / g and 680 mg KOH / g, or between 672 mg KOH / g and 680 mg KOH / g, or between 673 mg KOH / g and 680 mg KOH / g, or between 674 mg KOH / g and 680 mg KOH / g.

[0066] The acid value corresponds to the mass (in milligrams) of potassium hydroxide required to neutralize 1 gram of regenerated terephthalic acid monomer composition under the conditions specified in KS M ISO 2114.

[0067] The acid value of the monomer composition used to synthesize recycled plastics is increased to above 670 mg KOH / g in order to reduce VOC impurities other than terephthalic acid (e.g., formic acid, glycolic acid, 4-CBA, etc.), thereby achieving excellent physical properties when synthesizing polyethylene terephthalate or high value-added plastics (PBT, TPEE).

[0068] When the acid value of the monomer composition used to synthesize recycled plastics decreases to less than 670 mg KOH / g, the physical properties of the recovered terephthalic acid and the (co)polymer synthesized therefrom may be degraded due to excessive VOC impurities (such as formic acid, glycolic acid, 4-CBA, etc.) remaining in the terephthalic acid.

[0069] One embodiment of the monomer composition for synthesizing recycled plastics may further include certain small amounts of other additives and solvents, the specific types of which are not particularly limited, and various materials widely used in the terephthalic acid recycling step, which is carried out by depolymerization of (co)polymers synthesized from monomers containing terephthalic acid, may be used without limitation.

[0070] One embodiment of the monomer composition for synthesizing recycled plastics can be obtained by a method for preparing a monomer composition for synthesizing recycled plastics, which will be described below. Specifically, one embodiment of the monomer composition for synthesizing recycled plastics corresponds to a product obtained after depolymerization of a (co)polymer synthesized from monomers containing terephthalic acid through various filtration, purification, washing, and drying steps to ensure high purity of terephthalic acid, which is the primary synthetic target material in this invention.

[0071] One embodiment of the monomer composition for synthesizing recycled plastics can be used as a raw material for preparing monomers used to synthesize various recycled plastics (e.g., polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene adipate (PBAT), glycol-modified PET resin (glycol-modified polyethylene terephthalate, PETG), thermoplastic polyester elastomer (TPEE)), which will be described below, or can be used as a raw material for other additives (e.g., dioctyl terephthalate plasticizer) used in the processing of plastics (e.g., polyvinyl chloride (PVC)).

[0072] 2. A method for preparing monomer compositions for synthesizing recycled plastics.

[0073] According to another embodiment of the present invention, a method for preparing a monomer composition for synthesizing recycled plastics can be provided, comprising the steps of: depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid and removing the diol component; and washing the depolymerization product from which the diol component has been removed, wherein the washing step includes washing with a protic polar solvent at a temperature above 20°C and below 100°C; and washing with a washing solvent containing a non-protic polar solvent at a temperature above 20°C and below 110°C.

[0074] Through experiments, the inventors have demonstrated that, similar to other embodiments of the method for preparing monomer compositions for synthesizing recycled plastics, in the process of recovering terephthalic acid from (co)polymers synthesized from monomers containing terephthalic acid, the proportion of isophthalic acid, a monomer other than terephthalic acid and the main target material for synthesis in this invention, is greatly reduced by applying a multi-stage washing process with two or more stages separated by temperature ranges. This enables the achievement of excellent physical properties in the synthesis of polyethylene terephthalate or high-value-added plastics (PBT, TPEE), thus completing this invention.

[0075] In particular, terephthalic acid recovered from (co)polymers synthesized from monomers containing terephthalic acid by conventional methods typically contains 1% to 2% isophthalic acid as an impurity, whereas, according to the present invention, isophthalic acid can be almost completely removed by a secondary washing process, which is a feature of a method for preparing monomer compositions for synthesizing recycled plastics, the method of which will be described below.

[0076] This is because the solubility of terephthalic acid increases during the washing step with an aprotic polar solvent at a temperature above 20°C and below 110°C, thus maximizing the dissolution and removal of impurities such as isophthalic acid and sodium (Na) between the crystals or crystals.

[0077] Specifically, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may include the steps of depolymerizing a (co)polymer synthesized from a monomer containing terephthalic acid and removing the diol component.

[0078] (Co)polymers synthesized from monomers containing terephthalic acid can be applied regardless of various forms and types, such as (co)polymers synthesized from monomers containing new terephthalic acid obtained through synthesis, (co)polymers synthesized from monomers containing recycled terephthalic acid obtained through a regeneration step, or (co)polymer wastes synthesized from monomers containing terephthalic acid.

[0079] However, if necessary, a pretreatment step of the (co)polymer synthesized from monomers containing terephthalic acid can be performed before the depolymerization reaction of the (co)polymer, thereby improving the efficiency of the step of recovering terephthalic acid from the (co)polymer. Examples of pretreatment steps may include washing, drying, grinding, glycol decomposition, etc. There are no limitations on the specific method of each pretreatment process, and various methods widely used in the terephthalic acid recovery step through the depolymerization of the (co)polymer synthesized from monomers containing terephthalic acid can be applied without limitation.

[0080] In the depolymerization reaction of (co)polymers synthesized from monomers containing terephthalic acid, the depolymerization reaction can be carried out under acidic, neutral, or basic conditions, particularly under basic (alkaline) conditions. More specifically, the depolymerization reaction of (co)polymers synthesized from monomers containing terephthalic acid can be carried out in the presence of water, alkylene glycols, or alcohol solvents. Specific examples of alkylene glycol solvents include ethylene glycol, and specific examples of alcohol solvents include ethanol.

[0081] Furthermore, the depolymerization of (co)polymers synthesized from monomers containing terephthalic acid can be carried out under alkaline conditions. There are no particular limitations on the type of alkali, examples of which include sodium hydroxide (NaOH).

[0082] The depolymerization of a (co)polymer synthesized from a monomer containing terephthalic acid can be carried out by reacting with a base in amounts of 2.3 moles or less, or 1 mole or more and 2.3 moles or less, or 1.5 moles or more and 2.3 moles or less, relative to 1 mole of a (co)polymer synthesized from a monomer containing terephthalic acid.

[0083] In the depolymerization reaction of (co)polymers synthesized from monomers containing terephthalic acid, when the base reacts in an amount exceeding 2.3 moles relative to 1 mole of (co)polymer synthesized from monomers containing terephthalic acid, the amount of isophthalic acid and sodium (Na), which are impurities other than terephthalic acid (which is the main target material), increases due to the decrease in the solubility of isophthalate salts and the increase in the amount of alkaline salts generated, making it difficult to remove them sufficiently even by the washing steps described below.

[0084] Furthermore, there is no particular limitation on the temperature for the depolymerization reaction of the (co)polymer synthesized from monomers containing terephthalic acid; however, for example, the reaction can be carried out at a temperature above 25°C and below 200°C, or above 130°C and below 180°C. Additionally, the time required for the depolymerization reaction of the (co)polymer synthesized from monomers containing terephthalic acid can be above 0 minutes and below 3 hours.

[0085] Simultaneously, after depolymerizing the (co)polymer synthesized from monomers containing terephthalic acid, the diol component can be removed. For example, the alkaline decomposition products of this polyethylene terephthalate (PET) include ethylene glycol and terephthalate.

[0086] Since the primary target material for recovery in this invention is terephthalic acid, other byproducts can be removed by filtration. The filtered byproducts can be recovered without separation and purification during the depolymerization reaction of the (co)polymer synthesized from monomers containing terephthalic acid, or, if necessary, can be recovered by separation and purification using conventional distillation, extraction, and adsorption methods.

[0087] Furthermore, since the main target material for recycling in this invention is terephthalic acid, in the case of terephthalic acid, it can be converted into terephthalic acid through a neutralization process using an additional strong acid as described below.

[0088] As a specific example, the depolymerization product of a (co)polymer synthesized from monomers containing terephthalic acid is cooled to below 50°C, and then ethylene glycol is removed by vacuum filtration to obtain terephthalate.

[0089] Meanwhile, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may include the step of washing the depolymerization product from which the diol component has been removed.

[0090] As described above, in the depolymerization product from which the glycol components have been removed, ethylene glycol is removed, and terephthalic acid obtained by neutralizing terephthalate may be included. However, since various impurities remain in the recovery step to obtain terephthalic acid, washing can be performed to adequately remove these impurities to ensure high-purity terephthalic acid.

[0091] Specifically, the washing steps may include washing with a proton-polar solvent at temperatures above 20°C and below 100°C, or above 20°C and below 50°C, or above 20°C and below 40°C, or above 20°C and below 30°C; and washing with a washing solvent containing a non-proton-polar solvent at temperatures above 20°C and below 110°C, or above 50°C and below 110°C, or above 70°C and below 110°C, or above 80°C and below 110°C. These temperature conditions refer to the temperature inside the washing container where solvent washing is performed. Various heating devices can be used without limitation to maintain a high temperature outside of room temperature.

[0092] In this washing step, the step of washing with a proton-polar solvent at a temperature of 20°C to 100°C can be performed first, followed by the step of washing with a washing solvent containing a non-proton-polar solvent at a temperature of 20°C to 110°C. Alternatively, the step of washing with a washing solvent containing a non-proton-polar solvent at a temperature of 20°C to 110°C can be performed first, followed by the step of washing with a proton-polar solvent at a temperature of 20°C to 100°C.

[0093] More preferably, in this washing step, the step of washing with a proton-polar solvent at a temperature of 20°C or higher and 100°C can be performed first, and the step of washing with a washing solvent containing a non-proton-polar solvent at a temperature of 20°C or higher and 110°C can be performed subsequently. This can minimize the corrosion of the reactor by the strong acid after the neutralization step.

[0094] The steps of washing with a proton-polar solvent at a temperature above 20°C and below 100°C, and washing with a washing solvent containing a non-proton-polar solvent at a temperature above 20°C and below 110°C, may be repeated at least once or more.

[0095] Furthermore, if necessary, after performing the steps of washing with a proton-polar solvent at a temperature above 20°C and below 100°C, and washing with a washing solvent containing a non-proton-polar solvent at a temperature above 20°C and below 110°C, a further step of removing residual solvent by filtration may be performed.

[0096] The proton polar solvent may include water or alcohol. Preferably, water can be used as the proton polar solvent. When an organic solvent such as ethanol is used instead of water, the salt (NaCl) cannot be effectively removed, which leads to an increase in the amount of residual sodium (Na) in the composition.

[0097] Proton polar solvents have acidic protons, meaning they are polar solvents, typically those with hydroxyl or amino groups.

[0098] In the step of washing with a proton-polar solvent at a temperature above 20°C and below 100°C, the proton-polar solvent may be used in amounts of 5 parts by weight or more and 30 parts by weight, or 10 parts by weight or more and 30 parts by weight, or 15 parts by weight or more and 25 parts by weight, based on 1 part by weight of the (co)polymer synthesized from a monomer containing terephthalic acid.

[0099] Meanwhile, the washing solvent may include one of an aprotic polar solvent or a mixture of an aprotic polar solvent and a protic polar solvent. That is, the washing solvent may include an aprotic polar solvent, and the washing solvent may include a mixture of an aprotic polar solvent and a protic polar solvent.

[0100] The aprotic polar solvent may include tetrahydrofuran or acetonitrile. The protic polar solvent may include water or alcohol. An aprotic polar solvent is a polar solvent that does not have an acidic proton, typically a solvent without hydroxyl or amino groups. These solvents can be proton acceptors but do not act as proton donors in hydrogen bonding.

[0101] A mixture of aprotic polar solvent and protic polar solvent is a solution in which aprotic polar solvent and protic polar solvent are mixed, wherein the weight ratio of aprotic polar solvent can be more than 60% by weight and less than 90% by weight, and the weight ratio of protic polar solvent can be more than 10% by weight and less than 40% by weight.

[0102] As described above, in a mixture of aprotic polar solvent and protic polar solvent, when an excess of aprotic polar solvent is contained, impurities that cannot be removed in water (which is a protic polar solvent) are dissolved and removed by the aprotic polar solvent, thereby improving the purity of terephthalic acid and minimizing the amount of terephthalic acid lost along with impurities during washing with protic polar solvent, thereby improving the yield of terephthalic acid.

[0103] Conversely, in mixtures of aprotic and protic polar solvents, the yield of terephthalic acid may decrease when an excess of protic polar solvent is present, and the purity of terephthalic acid may also decrease due to increased impurities.

[0104] In the step of washing with a washing solvent containing an aprotic polar solvent at a temperature of 20°C or higher and 110°C or lower, the washing solvent may be used in an amount of 5 parts by weight or more and 30 parts by weight or more and 10 parts by weight or more and 30 parts by weight or more and 15 parts by weight or more and 25 parts by weight, based on 1 part by weight of the (co)polymer synthesized from a monomer containing terephthalic acid.

[0105] The washing step with a washing solvent containing a nonprotic polar solvent can be carried out at a temperature above 20°C and below 110°C, or above 50°C and below 110°C, or above 70°C and below 110°C, or above 80°C and below 110°C.

[0106] When the temperature of the washing step using a washing solvent containing aprotic polar solvent is excessively increased to above 110°C, harsh conditions are created to maintain extreme temperature conditions, and process efficiency may decrease due to increased dangers in terms of pressure or explosion risks.

[0107] The temperature difference between the step of washing with a washing solvent containing a non-proton polar solvent at a temperature above 20°C and below 110°C and the step of washing with a proton polar solvent at a temperature above 20°C and below 100°C can be above 30°C and below 100°C, or above 40°C and below 90°C, or above 50°C and below 80°C.

[0108] The difference between the temperature of the step of washing with a washing solvent containing a non-proton polar solvent at a temperature above 20°C and below 110°C and the temperature of the step of washing with a proton polar solvent at a temperature above 20°C and below 100°C is the value obtained by subtracting the temperature of the step of washing with a washing solvent containing a non-proton polar solvent from the temperature of the step of washing with a washing solvent containing a non-proton polar solvent at a temperature above 20°C and below 110°C.

[0109] When the temperature difference between the step of washing with a washing solvent containing a non-protic polar solvent at a temperature above 20°C and below 110°C and the step of washing with a protic polar solvent at a temperature above 20°C and below 100°C is excessively reduced to less than 30°C, it is difficult to sufficiently remove isophthalic acid and sodium (Na), which are impurities other than terephthalic acid, the main target material.

[0110] When the temperature difference between the step of washing with a washing solvent containing a nonprotic polar solvent at a temperature above 20°C and below 110°C and the step of washing with a protic polar solvent at a temperature above 20°C and below 100°C is excessively increased to greater than 100°C, harsh conditions are created to maintain extreme temperature conditions, and process efficiency may decrease due to increased dangers in terms of pressure or explosion risks.

[0111] Meanwhile, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may further include a step of neutralizing the depolymerization product from which the diol component has been removed with an acid before the step of washing the depolymerization product from which the diol component has been removed.

[0112] For example, the alkaline decomposition products of polyethylene terephthalate (PET) include ethylene glycol and terephthalate. However, since the primary target material for recycling in this invention is terephthalic acid, in the case of obtaining terephthalate through alkaline decomposition, it can be converted back to terephthalic acid through a further neutralization step using a strong acid. That is, when the depolymerization reaction of the (co)polymer synthesized from monomers containing terephthalic acid is an alkaline decomposition, it can be neutralized using an acid.

[0113] The acid used in the neutralization reaction can be a strong acid, examples of which include hydrochloric acid (HCl). Because the neutralization reaction is carried out by a strong acid, the pH can be below 4 or below 2 when the neutralization reaction is complete. The temperature during the neutralization reaction can be adjusted to be above 25°C and below 100°C.

[0114] Furthermore, if necessary, after the neutralization reaction step of neutralizing the depolymerization product from which the diol component has been removed with acid, a further step of removing residual impurities by filtration can be performed.

[0115] In addition, after the step of subjecting the (co)polymer synthesized from monomers containing terephthalic acid to a depolymerization reaction and removing the diol component, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may further include the step of purifying the depolymerization product from which the diol component has been removed.

[0116] Residual impurities can be removed through this purification process, and there are no particular restrictions on the specific purification conditions. Various previously known purification techniques can be applied without limitation to the specific purification apparatus and method.

[0117] In one specific example, the purification step of the depolymerization product from which the diol component has been removed may include the steps of dissolving and filtering the depolymerization product from which the diol component has been removed; and the adsorption step by an adsorbent.

[0118] In the step of dissolving and filtering the depolymerization product from which the glycol components have been removed, water can be used as the solvent for dissolving the depolymerization product from which the glycol components have been removed, and the dissolution temperature can be above 25°C and below 100°C. This removes residual (co)polymers synthesized from monomers containing terephthalic acid, which did not react in the depolymerization reaction.

[0119] Activated carbon, charcoal, diatomaceous earth, or mixtures thereof can be used as adsorbents in the adsorption step via an adsorbent.

[0120] In the purification steps of the depolymerization product from which the diol component has been removed, extraction, washing, precipitation, recrystallization, drying, and other steps may be applied without limitation if necessary.

[0121] Furthermore, as described above, in the case where the depolymerization reaction is alkaline decomposition, if a purification step of the depolymerization product from which the glycol component has been removed is performed, after the purification step of the depolymerization product from which the glycol component has been removed, a step of neutralizing the depolymerization product from which the glycol component has been removed with acid can be performed, followed by washing the depolymerization product from which the glycol component has been removed.

[0122] In addition to the step of washing the depolymerization product from which the diol component has been removed, another embodiment of the method for preparing a monomer composition for synthesizing recycled plastics may further include a drying step. Residual solvent can be removed by drying, and there are no particular limitations on the specific drying conditions; however, for example, the drying can be carried out at a temperature above 100°C and below 150°C. Various known drying techniques can be applied without limitation to the specific drying apparatus and method used in the drying process.

[0123] 3. Recycled plastics

[0124] According to another embodiment of the invention, a recycled plastic comprising the reaction product of a monomer composition for synthesizing recycled plastics according to one embodiment and a comonomer can be provided. Details of the monomer composition for synthesizing recycled plastics include all that has been described above in one embodiment.

[0125] There are no particular limitations on the examples corresponding to recycled plastics, and various plastics synthesized using terephthalic acid as a monomer can be applied without limitation. More specific examples can be (co)polymers synthesized from monomers containing terephthalic acid.

[0126] In a (co)polymer synthesized from monomers containing terephthalic acid, the (co)polymer includes polymers or copolymers, and generally refers to the reaction product obtained via the (co)polymerization of monomers. Depending on the molecular weight range, the (co)polymer may include all low molecular weight compounds, oligomers, and polymers.

[0127] The (co)polymer synthesized from monomers containing terephthalic acid may include at least one (co)polymer selected from polyalkylene terephthalate, polyalkylene terephthalate copolymers, and thermoplastic polyester elastomers. That is, the (co)polymer synthesized from monomers containing terephthalic acid may include one type of polyalkylene terephthalate, one type of polyalkylene terephthalate copolymer, one type of thermoplastic polyester elastomer, or a mixture of two or more thereof.

[0128] Polyalkylene terephthalate copolymers refer to copolymers obtained by further reacting additional comonomers based on alkylene glycols with terephthalic acid, a monomer used to synthesize polyalkylene terephthalates.

[0129] There are no particular limitations on examples of comonomers capable of reacting with high-purity terephthalic acid contained in a monomer composition for synthesizing recycled plastics according to one embodiment, and specific examples include aliphatic diols, polyepoxides, fatty acids, fatty acid derivatives, or combinations thereof.

[0130] As an aliphatic diol, for example, a diol with a number-average molecular weight (Mn) of less than 300 g / mol can be used, namely at least one selected from ethylene glycol, propylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol (1,4-BG), 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediethanol (1,4-CHDM). As a specific example, 1,4-butanediol, ethylene glycol, 1,4-cyclohexanediethanol or mixtures thereof can be used.

[0131] Polyoxyalkylene oxides are the units constituting the soft segments and may include aliphatic polyethers as constituent components. As an example, at least one selected from polyethylene glycol, polypropylene glycol, poly(tetramethylene ether) glycol (PTMEG), polyhexamethylene glycol, copolymers of ethylene oxide and propylene oxide, ethylene oxide addition polymers of polypropylene oxide glycol, and copolymers of ethylene oxide and tetrahydrofuran can be used. As a specific example, PTMEG can be used. In particular, PTMEG with a number-average molecular weight (Mn) of 600 g / mol to 3,000 g / mol, 1,000 g / mol to 2,500 g / mol, or 1,500 g / mol to 2,200 g / mol can be used.

[0132] The fatty acid can be, for example, at least one type of aliphatic carboxylic acid compound other than terephthalic acid; as a specific example, adipic acid can be used. The fatty acid derivative is a compound derived from the aforementioned fatty acid; as an example, at least one selected from fatty acid esters, fatty acyl chlorides, fatty acid anhydrides, and fatty acid amides can be used, and as a specific example, adipate esters can be used.

[0133] In a more specific example, when 1,4-butanediol, as an aliphatic diol, is used as a comonomer capable of reacting with terephthalic acid, polybutylene terephthalate (PBT), as a type of polyalkylene terephthalate, can be obtained by the polymerization reaction of terephthalic acid with 1,4-butanediol.

[0134] Furthermore, when ethylene glycol, as an aliphatic diol, is used as a comonomer capable of reacting with high-purity terephthalic acid contained in a monomer composition for synthesizing recycled plastics according to one embodiment, polyethylene terephthalate (PET), as a type of polyalkylene terephthalate, can be obtained through the polymerization reaction of terephthalic acid and ethylene glycol.

[0135] Furthermore, when 1,4-butanediol, as an aliphatic diol, is used together with PTMEG, as a polyepoxide, as a comonomer capable of reacting with high-purity terephthalic acid contained in a monomer composition for synthesizing recycled plastics according to one embodiment, a thermoplastic polyester elastomer (TPEE) can be obtained through the polymerization reaction of terephthalic acid, 1,4-butanediol, and PTMEG.

[0136] Furthermore, when 1,4-butanediol, as an aliphatic diol, is used together with adipic acid, as a fatty acid, as a comonomer capable of reacting with high-purity terephthalic acid contained in a monomer composition for synthesizing recycled plastics according to one embodiment, polybutylene terephthalate (PBAT), as a type of polyalkylene terephthalate copolymer, can be obtained by polymerization of terephthalic acid, 1,4-butanediol, and adipic acid.

[0137] Furthermore, when ethylene glycol, as an aliphatic diol, is used together with 1,4-cyclohexanediol as a comonomer capable of reacting with high-purity terephthalic acid contained in a monomer composition for synthesizing recycled plastics according to one embodiment, a glycol-modified PET resin (glycol-modified polyethylene terephthalate, PETG) as a type of polyalkylene terephthalate copolymer can be obtained by polymerization of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediol.

[0138] As a specific example, polyalkylene terephthalate may include at least one (co)polymer selected from polybutylene terephthalate, polyethylene terephthalate, polycyclohexyl dimethyl terephthalate, polyethylene naphthalate, polybutylene naphthalate and polypropylene terephthalate.

[0139] Furthermore, as a specific example, polyalkylene terephthalate copolymers may include at least one (co)polymer selected from polybutylene terephthalate (PBAT) and glycol-modified PET resin (glycol-modified polyethylene terephthalate, PETG).

[0140] There are no particular limitations on the examples of reaction methods between the monomer composition used to synthesize recycled plastics and the comonomer, and various known methods can be applied without limitation. However, specific examples of the reaction between the monomer composition used to synthesize recycled plastics and the comonomer may include melt polycondensation and solid-state polymerization.

[0141] As a more concrete example, in the preparation of thermoplastic polyester elastomers (TPEE) from recycled plastics, an esterification reaction of aromatic dicarboxylic acids, aliphatic diols, and polyepoxides is carried out at temperatures above 180°C and below 250°C for 30 minutes to 210 minutes to produce BHBT (bis(4-hydroxy)butyl terephthalate) oligomers. Subsequently, the TBT catalyst is reloaded, and a melt polycondensation reaction can be carried out at temperatures above 200°C and below 270°C for 20 minutes to 240 minutes, while the pressure is gradually reduced from 760 Torr to 0.3 Torr. After the melt polycondensation reaction is complete, it can be discharged into the reactor under nitrogen pressure to granulate the strands into pellets.

[0142] Subsequently, the granules can be solid-phase polymerized in a solid-phase polymerization reactor or a rotatable vacuum dryer for a temperature range of 140°C to 200°C for more than 10 hours and less than 24 hours under an inert gas flow (such as nitrogen under high vacuum).

[0143] In addition, in the production of polyalkylene terephthalate from recycled plastics, aromatic dicarboxylic acids and aliphatic diols with a number average molecular weight (Mn) of less than 300 g / mol can be melt-polymerized and subsequently solid-phase polymerized.

[0144] For polyalkylene terephthalate resin, low molecular weight granules obtained by melt polymerization are placed in a solid-phase polymerization reactor and reacted under the high vacuum and inert conditions given in the solid-phase polymerization of thermoplastic polyester elastomers (TPEE) as described above, thereby obtaining a high molecular weight resin.

[0145] Because the reaction of the monomer composition used to synthesize recycled plastics with the comonomer is not particularly limited in terms of the specific methods for preparing polybutylene terephthalate, polyethylene terephthalate, polycyclohexyl dimethyl terephthalate, polyethylene naphthalate, polybutylene naphthalate, polypropylene terephthalate, or polybutylene adipate, various methods well-known in the field of existing recycled plastics synthesis can be applied without limitation.

[0146] The physical properties of recycled plastics can be varied depending on the weight ratio of the monomer composition to the comonomer in one embodiment for synthesizing recycled plastics, and there is no particular limitation on the weight ratio of the monomer composition to the comonomer in one embodiment for synthesizing recycled plastics. In one example, based on thermoplastic polyester elastomer (TPEE), it can be synthesized at a weight ratio of TPA / (TPA+PTMG) = 61.5.

[0147] 4. Molded products

[0148] According to another embodiment of the invention, a molded article comprising the recycled plastic of the other embodiment can be provided. Details of the recycled plastic include all those described above in other embodiments.

[0149] This molded article can be obtained by applying the recycled plastic without limitation to various known plastic molding methods. Examples of molding methods include injection molding, foam injection molding, blow molding, or extrusion molding.

[0150] There are no particular limitations on the examples of molded articles, and they can be applied without restriction to a wide variety of molded articles using plastics. Examples of molded articles include automotive, electrical and electronic products, communication products, and everyday consumer goods.

[0151] 5. Plasticizer composition

[0152] According to another embodiment of the invention, a plasticizer composition comprising the reaction product of a monomer composition for synthesizing recycled plastics according to one embodiment and an alcohol can be provided. Details of the monomer composition for synthesizing recycled plastics include all that has been described above in one embodiment.

[0153] Plasticizers are typically obtained by appropriately adding resins such as polyvinyl chloride (PVC) and various additives such as fillers, stabilizers, pigments, and antifogging agents to provide a variety of processing physical properties. They are used as materials for a variety of products, such as wires, pipes, flooring, wallpaper, sheets, artificial leather, tarpaulins, tapes, and food packaging materials, through processing methods such as extrusion molding, injection molding, and calendering.

[0154] Typically, for plasticizers, alcohols react with polycarboxylic acids such as phthalic acid and adipic acid to form the corresponding esters. Furthermore, considering domestic and international regulations on phthalate plasticizers that are harmful to human health, research is ongoing on plasticizer compositions that can replace phthalate plasticizers (such as terephthalates, trimellites, and other polymeric plasticizers).

[0155] The reaction product of a monomer composition for synthesizing recycled plastics and an alcohol in one embodiment may include terephthalic acid esters. Specifically, terephthalic acid esters can be obtained by a direct esterification reaction between terephthalic acid contained in the monomer composition for synthesizing recycled plastics in one embodiment and an alcohol.

[0156] The direct esterification reaction may include the following steps: adding terephthalic acid to an alcohol, followed by adding a catalyst and reacting the mixture under a nitrogen atmosphere; removing unreacted alcohol and neutralizing unreacted acid; and dehydrating the product by vacuum distillation and filtering.

[0157] There are no particular limitations on examples of terephthalic acid ester compounds, but examples include dioctyl terephthalate (DOTP), diisononyl terephthalate (DINTP), diisodecyl terephthalate (DIDTP), or di(2-propylheptyl) terephthalate (DPHTP).

[0158] The terephthalic acid ester compounds can be prepared by direct esterification, in which an alcohol selected from octanol, isononol, isodecanol and 2-propylheptanol reacts with terephthalic acid.

[0159] This plasticizer composition can be used in the manufacture of wires, flooring materials, automotive interior materials, films, sheets, wallpapers, or pipes.

[0160] Beneficial effects

[0161] According to the present invention, a monomer composition for synthesizing recycled plastics is provided, which ensures high purity of terephthalic acid and thereby has a high acid value when terephthalic acid is recovered through the depolymerization reaction of a (co)polymer synthesized from a monomer containing terephthalic acid. A method for preparing the monomer composition is also provided, as well as recycled plastics, molding articles and plasticizer compositions using the monomer composition. Detailed Implementation Plan

[0162] The present invention will be explained in detail below with reference to the following embodiments. However, these embodiments are for illustrative purposes only, and the scope of the invention is not limited thereto.

[0163] <Example>

[0164] Example 1

[0165] (1) Preparation of recycled terephthalic acid monomer composition

[0166] 300 g (1.56 mol) of polyethylene terephthalate (PET) bottle scrap, 1647 g (26.53 mol) of ethylene glycol (EG), and 128 g (3.2 mol) of sodium hydroxide (NaOH) were placed in a 3 L SUS reactor, and then stirred at 180 °C for 2 hours in a closed system to carry out the PET depolymerization reaction. The product of the depolymerization reaction was cooled to below 50 °C, and then vacuum filtered to obtain sodium terephthalate (Na2-TPA).

[0167] The filtrate containing sodium terephthalate (Na2-TPA) was completely dissolved in 3000 g of water, and then vacuum filtered again to remove unreacted PET. Subsequently, 15 g of charcoal and 30 g of diatomaceous earth were added to the filtrate, and the mixture was stirred for 1 hour to purify it by adsorption, followed by filtration to remove the charcoal.

[0168] Subsequently, the product was neutralized with 500–550 mL of 6M HCl at 20–30°C, and the slurry was vacuum filtered again to lower the pH to below 2 to obtain terephthalic acid (TPA).

[0169] To remove the NaCl generated during the neutralization step, the solution was washed once with 6000 g of water (20 times the mass of the PET used) at 20°C–30°C, followed by vacuum filtration. The filtrate was then washed a second time for 1 hour at 80°C with 6000 g of tetrahydrofuran (THF) (20 times the mass of the PET used).

[0170] After performing a first and second water washing step, the mixture was dried in a convection oven at 100°C for 12 hours to recover regenerated terephthalic acid (TPA), thereby preparing a regenerated terephthalic acid monomer composition.

[0171] (2) Preparation of recycled plastics

[0172] 200 g of the regenerated terephthalic acid monomer composition obtained in Example 1 (1), 200 g of 1,4-butanediol, and 125 g of poly(tetramethylene) glycol (PTMEG) with a number average molecular weight of 1,000 to 2,000 g / mol were placed in an ester exchange reactor, and then 0.1 wt% of TBT catalyst was added. The mixture was reacted for 120 to 180 minutes while maintaining a temperature of 200°C to 240°C, and the reaction was terminated when the reaction rate (a value obtained by converting the amount of water as the effluent to the reaction rate) was above 90% to obtain oligomers.

[0173] Subsequently, the prepared oligomers were transferred to a polycondensation reactor, to which 0.1 wt% TBT catalyst, 0.14–0.15 wt% hindered phenolic antioxidant, and 0.15–0.2 wt% aromatic amine antioxidant or sulfur stabilizer were added. While maintaining a temperature of 230–250°C, the pressure was reduced from 760 Torr to 0.3 Torr over 30 minutes to carry out melt polycondensation, followed by melt polycondensation under a high vacuum below 0.3 Torr until the torque applied to the stirrer reached the desired torque. After the reaction was complete, the product was vented under nitrogen pressure, spun into strands, cooled, and subsequently granulated to prepare thermoplastic polyester elastomer (TPEE) resin.

[0174] Example 2

[0175] The recycled terephthalic acid monomer composition and recycled plastic were prepared in the same manner as in Example 1, except that, as shown in Table 1 below, in Example 1(1), a secondary wash was performed at a temperature of 100°C using a mixture of 4800 g of THF and 1200 g of water.

[0176] Example 3

[0177] The recycled terephthalic acid monomer composition and recycled plastic were prepared in the same manner as in Example 1, except that, as shown in Table 1 below, in Example 1(1), a second washing was performed using acetonitrile at a temperature of 100°C.

[0178] Example 4

[0179] The recycled terephthalic acid monomer composition and recycled plastic were prepared in the same manner as in Example 1, except that, as shown in Table 1 below, in Example 1 (1), a secondary wash was performed using a mixed solution of 4800 g of acetonitrile and 1200 g of water at a temperature of 100°C.

[0180] Example 5

[0181] (1) Preparation of recycled terephthalic acid monomer composition

[0182] The recycled terephthalic acid monomer composition was prepared in the same manner as in Example 1 (1).

[0183] (2) Preparation of recycled plastics

[0184] 300 g of the regenerated terephthalic acid monomer composition obtained in Example 1 (1) and 300 g of 1,4-butanediol were placed in an esterification reactor, and 0.1 wt% of TBT catalyst was added thereto. The mixture was reacted for 120 to 180 minutes while maintaining a temperature of 200°C to 240°C, and the reaction was terminated when the reaction rate (when the amount of water as the effluent is converted to the reaction rate) was above 90% to obtain oligomers.

[0185] The prepared oligomers were then transferred to a polycondensation reactor, where, while maintaining a temperature of 230–260°C, the pressure was reduced from 760 Torr to 0.3 Torr over 30 minutes for melt polycondensation. The melt polycondensation reaction was then carried out under a high vacuum below 0.3 Torr until the torque applied to the stirrer reached the desired level. After the reaction was complete, the mixture was vented under nitrogen pressure, formed into strands, cooled, and subsequently granulated to prepare polybutylene terephthalate (PBT) resin.

[0186] <Comparative Example>

[0187] Comparative Example 1

[0188] The recycled terephthalic acid monomer composition and recycled plastic were prepared in the same manner as in Example 1, except that, as shown in Table 1 below, in Example 1(1), a second washing with water was performed at a temperature of 25°C.

[0189] <Reference Example>

[0190] Reference Example 1

[0191] The recycled terephthalic acid monomer composition and recycled plastic were prepared in the same manner as in Example 1, except that, as shown in Table 1 below, in Example 1(1), the depolymerization solvent was replaced with water and a second washing was performed at a temperature of 25°C.

[0192] See Example 2

[0193] The recycled terephthalic acid monomer composition and recycled plastic were prepared in the same manner as in Example 1, except that, as shown in Table 1 below, in Example 1(1), the depolymerization solvent was replaced with water and a second wash was performed using acetonitrile at a temperature of 25°C.

[0194] See Example 3

[0195] The recycled terephthalic acid monomer composition and recycled plastic were prepared in the same manner as in Example 1, except that, as shown in Table 1 below, in Example 1(1), the depolymerization solvent was replaced with water and a second wash was performed with acetone at a temperature of 25°C.

[0196] See Example 4

[0197] The recycled terephthalic acid monomer composition and recycled plastic were prepared in the same manner as in Example 1, except that, as shown in Table 1 below, in Example 1(1), the depolymerization solvent was replaced with water and a second wash was performed with water at a temperature of 25°C.

[0198] <Experimental Examples>

[0199] The physical properties of the regenerated terephthalic acid monomer compositions obtained in the Examples, Comparative Examples and Reference Examples were measured using the following methods, and the results are shown in Table 1 below.

[0200] 1. Content of terephthalic acid (TPA) and isophthalic acid (IPA)

[0201] 5–20 mg of regenerated terephthalic acid monomer composition was collected as a sample under normal pressure and 20–30 °C, dissolved in 1 mL of DMSO-d6 solvent, and then analyzed by an Agilent DD1 500 MHz NMR instrument. 1 ¹H NMR spectra. Peaks for all detected materials, such as terephthalic acid (TPA) and isophthalic acid (IPA), were determined and integrated using analysis software (MestReC). Based on the peak integral values, the molar ratio (mol%) of terephthalic acid and isophthalic acid in 100 mol% of all monomeric compounds analyzed in the sample was calculated.

[0202] 2. Acid value

[0203] The acid value of the recycled terephthalic acid monomer compositions obtained in the examples and comparative examples was measured according to KS M ISO 2114. This acid value corresponds to the mass (in milligrams) of potassium hydroxide required to neutralize 1 gram of the recycled terephthalic acid monomer composition under the conditions specified in KS M ISO 2114.

[0204] [Table 1]

[0205] Measurement results of the test examples

[0206]

[0207]

[0208] As shown in Table 1, the regenerated terephthalic acid monomer compositions obtained in Examples 1 to 4 contained terephthalic acid in an amount of 100 mol%, thereby completely removing isophthalic acid as an impurity and exhibiting high terephthalic acid purification efficiency. On the other hand, it can be confirmed that the regenerated terephthalic acid monomer composition obtained in Comparative Example 1 contained isophthalic acid as an impurity in an amount of 1.6 mol%, which is an excessive amount compared to the examples, thereby significantly reducing the terephthalic acid purification efficiency.

[0209] Furthermore, it can be confirmed that the monomers contained in the regenerated terephthalic acid monomer composition obtained in the reference example contain isophthalic acid as an impurity in an amount of 1.1 mol% to 2.3 mol%, which is an excessive amount compared to the examples, thereby greatly reducing the terephthalic acid purification efficiency.

[0210] Furthermore, it can be confirmed that the acid value of the recycled terephthalic acid monomer composition obtained in the examples is 674 mg KOH / g, which is improved to the commercially available level. On the other hand, it can be confirmed that the acid value of the recycled terephthalic acid monomer composition obtained in Comparative Example 1 is 660 mg KOH / g, which is lower than the acid value of the examples.

[0211] Furthermore, it can be confirmed that the acid value of the regenerated terephthalic acid monomer composition obtained in the reference example is 658 mg KOH / g to 663 mg KOH / g, which is lower than the acid value of the example.

Claims

1. A method for preparing a monomer composition for synthesizing recycled plastics, comprising the following steps: The (co)polymer synthesized from monomers containing terephthalic acid is depolymerized and the diol component is removed. and The depolymerization products from which the diol component has been removed are washed away. The washing steps include: The step of washing with a proton-polar solvent at a temperature above 20°C and below 40°C; and The step of washing with a washing solvent containing a non-protic polar solvent at a temperature above 70°C and below 110°C. In this process, the depolymerization of the (co)polymer synthesized from monomers containing terephthalic acid is carried out by reacting with less than 2.3 moles of a base, relative to 1 mole of the (co)polymer synthesized from monomers containing terephthalic acid. Prior to the step of washing the depolymerization products from which the diol component has been removed, The method further includes neutralizing the depolymerization product from which the diol component has been removed with an acid. The aprotic polar solvent includes tetrahydrofuran or acetonitrile. In the step of washing with a washing solvent containing an aprotic polar solvent at a temperature of 70°C or higher and 110°C or lower, the amount of the washing solvent is 15 parts by weight or more and 25 parts by weight or less, based on 1 part by weight of the (co)polymer synthesized from a monomer containing terephthalic acid.

2. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The proton polar solvent comprises water or alcohol.

3. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The washing solvent comprises one of an aprotic polar solvent or a mixture of an aprotic polar solvent and a protic polar solvent.

4. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: In the washing step using a proton-polar solvent at a temperature above 20°C and below 40°C, Based on 1 part by weight of the (co)polymer synthesized from monomers containing terephthalic acid, the amount of the proton polar solvent is 5 parts by weight or more and 30 parts by weight or less.

5. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: After the step of washing with a proton-polar solvent at a temperature above 20°C and below 40°C, the washing step is followed by washing with a washing solvent containing a non-proton-polar solvent at a temperature above 70°C and below 110°C.

6. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The temperature difference between the step of washing with a proton-polar solvent at a temperature above 20°C and below 40°C and the step of washing with a washing solvent containing a non-proton-polar solvent at a temperature above 70°C and below 110°C is 30°C or more and 100°C or less.

7. The method for preparing a monomer composition for synthesizing recycled plastics according to claim 1, wherein: The depolymerization reaction of (co)polymers synthesized from monomers containing terephthalic acid is carried out in the presence of alkylene glycol solvents.

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