KR20240033640A - Preparation method of terephthalic acid and terephthalic acid prepared therefrom - Google Patents

Abstract

The present invention relates to an environmentally friendly method of producing terephthalic acid using waste polyester. Specifically, according to one embodiment of the present invention, the method for producing terephthalic acid includes (1) alcoholizing waste polyester with an alcohol having 4 or more carbon atoms to prepare a liquid composition containing the compound represented by Formula 1; steps; and (2) hydrolyzing the liquid composition, thereby making it possible to produce terephthalic acid in an environmentally friendly manner, improve processability, and reduce process costs.

Description

Method for producing terephthalic acid and terephthalic acid produced thereby {PREPARATION METHOD OF TEREPHTHALIC ACID AND TEREPHTHALIC ACID PREPARED THEREFROM}

The present invention relates to an environmentally friendly method of producing terephthalic acid using waste polyester and recycled terephthalic acid produced therefrom.

Because polyester has excellent mechanical strength, heat resistance, transparency, and gas barrier properties, it is widely used in materials such as beverage filling containers, packaging films, audio and video films, and industrial materials such as medical fibers and tire cords. there is. In particular, polyester sheets and plates have good transparency and excellent mechanical strength, and are widely used as materials for cases, boxes, partitions, shelves, panels, packaging, building materials, and interior and exterior materials.

As the amount of plastic waste made of polyester is generated every year worldwide at an unmanageable level, interest in recycling waste polyester or a recovery process using waste polyester is increasing. Additionally, countries around the world have recently been preparing regulations and measures for recycling waste plastic resources, including waste polyester. For example, regulations such as requiring a certain percentage of recycled resin to be used in packaging materials used in various fields are being discussed.

In particular, polyethylene terephthalate (PET) is widely used to manufacture a wide range of products such as films, fibers, bottles, and containers due to its excellent properties such as heat resistance, processability, transparency, and non-toxicity, but most of it is landfilled after use. Since it is being disposed of or incinerated, research on recycling or regeneration processes using it is continuing.

For example, Korean Patent Publication No. 1997-0042469 discloses a technology for producing terephthalic acid by hydrolyzing waste polyethylene terephthalate with an aqueous alkaline solution to create a slurry of alkali metal and earth metal salts of terephthalic acid and neutralizing it with acid. As a result of the decomposition reaction, terephthalic acid salts, not terephthalic acid, are produced, so a neutralization step by adding acid is necessary to convert it to terephthalic acid. The by-products produced as a result of this result in the generation of environmental pollutants or a large amount of acid treatment waste fluid. There is a problem that arises.

Korean Patent Publication No. 1997-0042469

Therefore, the present invention seeks to provide an environmentally friendly method of producing terephthalic acid by alcoholizing and hydrolyzing waste polyester using a specific alcohol, and regenerated terephthalic acid produced therefrom.

A method for producing terephthalic acid according to an embodiment of the present invention includes the steps of (1) alcoholizing waste polyester with an alcohol having 4 or more carbon atoms to prepare a liquid composition containing the compound represented by Formula 1; and (2) hydrolyzing the liquid composition.

[Formula 1]

In Formula 1,

R ₁ is alkyl having 4 or more carbon atoms.

Regenerated terephthalic acid according to another embodiment of the present invention is manufactured according to the above method for producing terephthalic acid, and has a total metal content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of less than 100 ppm.

A polyester resin according to another embodiment of the present invention includes the recycled terephthalic acid.

The method for producing terephthalic acid according to an embodiment of the present invention involves alcoholizing waste polyester with an alcohol having 4 or more carbon atoms to prepare a liquid composition containing the compound represented by Formula 1, and hydrolyzing it using water, In addition to being able to produce terephthalic acid in an environmentally friendly manner, processability can be improved and process costs can also be reduced.

Specifically, the method for producing terephthalic acid according to an embodiment of the present invention involves alcoholizing waste polyester using a specific alcohol, more specifically, an alcohol having 4 or more carbon atoms to produce a composition containing the compound represented by Formula 1 in a liquid form. It is manufactured and hydrolyzed. Unlike the conventional method of producing terephthalic acid salt from waste polyester and then performing an additional step of neutralizing it, the method for producing terephthalic acid according to an embodiment of the present invention can directly produce solid terephthalic acid without additional processing, so the process Not only is this easy to do, but process costs can also be reduced, so fairness is excellent.

In addition, acids such as sulfuric acid or hydrochloric acid, which have been conventionally used to neutralize terephthalic acid salts, have had the problem of generating environmental pollutants such as Na ₂ SO ₄ and NaCl or large amounts of acid treatment waste liquid as by-products. However, the method for producing terephthalic acid according to an embodiment of the present invention is environmentally friendly because, unlike the prior art, solid terephthalic acid can be directly produced without performing an additional neutralization step.

In addition, the method for producing terephthalic acid according to an embodiment of the present invention is to prepare intermediates, that is, hydrolysis reactants, in a liquid phase, thereby removing insoluble impurities such as metal catalysts, coloring pigments, etc. or waste polyester. Since additives such as soluble colorants can be easily removed, the purity and yield of terephthalic acid produced through a simple process can be further improved.

Hereinafter, the present invention will be described in detail. The present invention is not limited to the content disclosed below, and may be modified into various forms as long as the gist of the invention is not changed.

In this specification, 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.

All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification should be understood as being modified by the term “about” in all cases unless otherwise specified.

In this specification, terms such as first and second are used to describe various components, and the components are not limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

A method for producing terephthalic acid according to an embodiment of the present invention includes the steps of (1) alcoholizing waste polyester with an alcohol having 4 or more carbon atoms to prepare a liquid composition containing a compound represented by the following formula (1); and (2) hydrolyzing the liquid composition.

[Formula 1]

In Formula 1,

R ₁ is alkyl having 4 or more carbon atoms.

Conventional methods for producing terephthalic acid from waste polyester include directly obtaining solid terephthalic acid using an acid catalyst, or dimethyl terephthalate (DMT) as an intermediate through methanolysis or glycolysis. , dimethyl terephthalate) or bis-2-hydroxyethyl terephthalate (BHET) was manufactured and then converted to terephthalic acid. At this time, the terephthalic acid, dimethyl terephthalate, and bis-2-hydroxyethyl terephthalate are all solid even at room temperature or relatively high temperature.

In this way, when solid terephthalic acid is directly obtained using an acid catalyst, etc., terephthalic acid precipitates as a solid immediately after being formed, making it difficult to remove insoluble impurities or additives such as colorants and pigments that may be included in waste polyester during the manufacturing process. There are limits to improving the purity or yield of manufactured terephthalic acid. Accordingly, a method of producing a terephthalic acid salt from waste polyester and then neutralizing it to obtain solid terephthalic acid has been used. However, in this case, the purity or yield of terephthalic acid can be improved by removing insoluble impurities, etc., while neutralizing the terephthalic acid salt There is a problem that environmental pollutants such as Na ₂ SO ₄ and NaCl or large amounts of acid treatment waste fluid are generated as by-products in the process.

In addition, when producing dimethyl terephthalate as an intermediate, a large amount of methanol must be used to produce the dimethyl terephthalate. Accordingly, very high pressure conditions are generated due to the methanol used, and in order to remove insoluble impurities, etc. Because an additional heating and high-pressure process is required to convert dimethyl terephthalate into a liquid phase, processability is low. In addition, when producing bis-2-hydroxyethyl terephthalate as an intermediate, it is difficult to separate and recover ethylene glycol generated as a by-product during the manufacturing process, which is undesirable in terms of processability and process cost.

In addition, an environmentally friendly method of recycling waste polyester has been used by adding metal salts to waste polyester and directly hydrolyzing it with water, but it requires very high temperature conditions of over 300℃ and the reaction device must also have high pressure resistance. Fairness is low.

However, in the method for producing terephthalic acid according to an embodiment of the present invention, it is easy to remove insoluble impurities or additives such as colorants and pigments that may be contained in waste polyester by producing intermediates, that is, hydrolysis reactants, in a liquid phase. , the purity and yield of produced terephthalic acid can be improved.

In addition, unlike the conventional method, solid terephthalic acid can be produced directly without performing an additional neutralization step, thus providing excellent processability and being environmentally friendly. Furthermore, not only is it easy to separate and recover ethylene glycol, which may be generated as a by-product in the manufacturing process, but also the alcohol with carbon atoms of 4 or more used in the alcoholysis reaction can be simply separated and reused, resulting in excellent process cost reduction. . In addition, fairness and economic efficiency can be further improved in that purification or transfer processes other than reaction can be performed at room temperature or low temperature.

For example, in the method for producing terephthalic acid according to an embodiment of the present invention, waste polyester, alcohol with a carbon number of 4 or more, and a very small amount of alcohol decomposition catalyst are first introduced into a first high pressure reactor, and alcohol decomposition reaction can be carried out. . Ethylene glycol and unreacted alcohol (alcohol present in excess), which are by-products generated as the alcohol decomposition reaction proceeds, can be recovered through a separate fractional distillation device after completion of the reaction and reused.

In addition, there is also a method of discharging ethylene glycol and unreacted alcohol generated during the reaction in the form of a real-time gaseous mixture during the reaction and condensing and recovering it using an external cooling device. At this time, alcohol may be continuously injected into the high-pressure reactor at the same volume and injection rate as the volume and discharge rate of the gaseous mixture being discharged. Since the unreacted alcohol can be separated from the discharged gaseous mixture through a simple process such as fractional distillation or layer separation, the separated unreacted alcohol can be put back into the first high pressure reactor, from which ethylene glycol is produced. It can be recovered.

Thereafter, the liquid alcoholysis product obtained through the alcoholysis reaction can be cooled, adsorbed, and filtered to purify it. The purified alcoholysis reaction composition is added together with water to a second high-pressure reactor to undergo a hydrolysis reaction, and then a slurry-type solution is obtained and filtered to obtain solid terephthalic acid. At this time, a small amount of hydrolysis catalyst may be additionally added along with water before the hydrolysis reaction, and the hydrolysis catalyst may be the same as or different from the alcoholization catalyst.

In addition, after the hydrolysis reaction is completed, the yield of the finally produced terephthalic acid can be improved by additionally performing the step of recovering unreacted components and reintroducing them to the alcoholization or hydrolysis reaction and reacting them one or more times. , it is environmentally friendly because it can reduce the amount of waste generated. For example, the filtrate obtained by filtering excess unreacted alcohol (having 4 or more carbon atoms) and ethylene glycol as a by-product using a filter or the like can be reintroduced into the hydrolysis reaction.

Method for producing terephthalic acid

A method for producing terephthalic acid according to an embodiment of the present invention includes (1) alcoholizing waste polyester with an alcohol having 4 or more carbon atoms to prepare a liquid composition containing the compound represented by Formula 1; steps; and (2) hydrolyzing the liquid composition.

[Formula 1]

In Formula 1,

R ₁ is alkyl having 4 or more carbon atoms.

Alcohol decomposition step (1)

A method for producing terephthalic acid according to an embodiment of the present invention includes the step of alcoholizing waste polyester with an alcohol having 4 or more carbon atoms to prepare a liquid composition containing a compound represented by the following formula (1).

The waste polyester may be obtained by pulverizing or melting waste polyester products. For example, the waste polyester may be pulverized polyester products that have been used up and recovered and separated, or converted into pellets (Post Consumer Recycled material; PCR). , It may be polyester waste (Post Industrial Recycled material; PIR) such as defective products or scraps that may be generated in processes such as molding of polyester films, fibers, containers, etc., but is not limited to this.

In addition, the carbon number of the alcohol may be 4 or more, 6 or more, 8 or more, 10 or more, or 12 or more, and may be 4 to 14, 4 to 13, 4 to 10, 4 to 8, 6 to 12, 8 to 14, or 8 to 8. It could be 13.

By performing the alcoholysis of waste polyester using an alcohol having the above carbon number, the alcoholysis can be carried out at a lower temperature and pressure compared to the waste polyester production process conditions that were conventionally performed at high temperature and high pressure. , the intermediate, that is, the alcohol decomposition product, can be produced in liquid form. In addition, when the carbon number of the alcohol satisfies the above range, the speed of the alcohololysis reaction can be improved.

Additionally, the boiling point of the alcohol may be 100°C to 290°C. For example, the boiling point of the alcohol may be 100°C to 280°C, 100°C to 260°C, 100°C to 230°C, 110°C to 190°C, or 180°C to 290°C. When the boiling point of alcohol satisfies the above range, ethylene glycol, a by-product generated from the alcohol decomposition, can be more easily removed or recovered in the subsequent process, thereby further improving processability. In particular, since there is a recent trend of using various monomer materials in fields that use polyester as a raw material, it can be easily applied to remove various dialcohol-type monomers used in waste polyester products such as waste plastic products.

The weight ratio of the waste polyester and the alcohol may be 1:1 to 10. For example, the weight ratio of the waste polyester and the alcohol is 1:1 to 8, 1:1 to 6, 1:1 to 4, 1:1 to 3.5, 1:1.1 to 3.3, 1:2 to 4, or It may be 1:2 to 3.5.

Additionally, the alcoholysis reaction may be performed at a temperature of 160°C to 280°C and a pressure of 1 bar to 40 bar for 0.5 to 24 hours. For example, the alcoholysis reaction is performed at 165°C to 280°C, 165°C to 270°C, 180°C to 270°C, 190°C to 250°C, 200°C to 265°C, 220°C to 265°C, 240°C to 260°C. °C or a temperature of 245°C to 260°C, and 1 bar to 38 bar, 1 bar to 33 bar, 1 bar to 28 bar, 1 bar to 24 bar, 2 bar to 40 bar, 3 bar to 35 bar or 5 bar. It may be carried out at a pressure of 30 bar for 0.5 hours to 22 hours, 1 hour to 15 hours, 1.5 hours to 10 hours, 2 hours to 8 hours or 2 hours to 6 hours.

In step (1), an alcohol decomposition catalyst may be added. Specifically, the alcohol decomposition reaction can be smoothly performed as a non-catalytic reaction without using an alcohol decomposition catalyst, making it environmentally friendly. In particular, when the content of insoluble metals in waste polyester is high, a non-catalytic reaction may be advantageous for efficient treatment and removal of impurities. In addition, an alcohol decomposition catalyst can be added in step (1) from an energy perspective to improve processability by improving reactivity.

The alcohol decomposition catalyst may be a metal acetate salt, an alkali metal salt, or a hydroxy salt.

More specifically, the alcohol decomposition catalyst is an alkali metal ion of Li ⁺ , Na ⁺ , K ⁺ or Cs ⁺ , an alkaline earth metal ion of Be ²⁺ , Mg ²⁺ , Ca ²⁺ or Ba ²⁺ , NH ⁴⁺ or an ammonium ion of NR ⁴⁺ (R is alkyl), and at least one cation selected from the group consisting of Zn ²⁺ ; and OH ^- , OR ^- (R is alkyl), HCO ₃ ^- , CO ₃ ^2- , benzoate ion (C ₇ H ₅ O ₂ ^- ), 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion. It may contain one or more anions selected from the group consisting of. R may be alkyl having 1 to 10 carbon atoms or alkyl having 1 to 5 carbon atoms.

For example, the alcohol decomposition catalyst is Zn(OAC) ₂ , Co(OAc) ₂ , Mn(OAc) ₂ , Mg(OAc) ₂ , Ca(OAc) ₂ , Ba(OAc) ₂ , LiOAc, NaOAc, KOAc, Zn(OAC) ₂ ·2H ₂ O, Co(OAc) ₂ ·4H ₂ O, Pb(OAc) ₂ , Mn(OAc) ₂ ·4H ₂ O, Mg(OAc) ₂ ·4H ₂ O, Pd( OAc) ₂ , A group consisting of Ti(OBu) ₄ , Ti(OiPr) ₄ , GeO ₂ , Al(OiPr) ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , dibutyltin(IV) oxide, stannous octoate, titanium phosphate and terephthalic acid. It may include one or more types selected from.

Additionally, the input amount of the alcohol decomposition catalyst may be 10 ppm to 10,000 ppm based on the total weight of the waste polyester. For example, the input amount of the alcohol decomposition catalyst is 10 ppm to 9,000 ppm, 15 ppm to 8,000 ppm, 20 ppm to 6,000 ppm, 50 ppm to 3,500 ppm, 100 ppm to 1,500 ppm, 150 ppm, based on the total weight of the waste polyester. It may be from ppm to 1,000 ppm, 180 ppm to 500 ppm, or 200 ppm to 450 ppm.

According to one embodiment of the present invention, a liquid composition containing a compound represented by the following formula (1) is prepared through alcoholysis. Specifically, the composition is liquid at room temperature, and the liquid composition is a composition produced through an alcohololysis reaction.

The liquid composition includes a compound represented by the following formula (1).

[Formula 1]

In Formula 1,

R ₁ is alkyl having 4 or more carbon atoms.

Specifically, R is butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl. , hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, hexyl, 1-methylhexyl, 2-ethyl-1- Hexyl, heptyl, n-heptyl, 1-methylheptyl, octyl, n-octyl, isooctyl, tert-octyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl-propyl, 1, It may be 1-dimethyl-propyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, decanyl, undecanyl, dodecanyl, tridecanyl or tetradecanyl.

Specifically, the liquid composition may include unreacted alcohol and ethylene glycol (EG), a by-product. More specifically, the liquid composition may include the compound represented by Formula 1, ethylene glycol (EG), a by-product produced by the alcoholysis reaction, unreacted alcohol, and oligomers.

For example, the liquid composition may include a compound represented by Formula 2 below, and the oligomer may include a compound represented by Formula 3 below.

[Formula 2]

[Formula 3]

In Formulas 2 and 3,

R ₁ is alkyl having 4 or more carbon atoms,

n is an integer greater than or equal to 1.

According to one embodiment of the present invention, the liquid composition may include unreacted alcohol and ethylene glycol as a by-product, and the content of the compound represented by Formula 1 in the liquid composition may be 70 mol% or more. For example, with respect to the liquid composition prepared through alcoholysis, the content of the compound represented by Formula 1 in the liquid composition is 72 mol% or more, 75 mol% or more, 80 mol% or more, and 75 mol% or more. , 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, 92 mol% or more, 92.5 mol% or more, 93 mol% or more, 95 mol% or more, 97 mol% or more, 99 mol% or more Or it may be 99.5 mol% or more.

Additionally, the content of oligomers in the liquid composition may be 15 mol% or less. For example, the oligomer content in the composition is 11 mol% or less, 8.5 mol% or less, 7 mol% or less, 5 mol% or less, 3 mol% or less, 1 mol% or less, 0.8 mol% or less, 0.4 mol% or less. Or it may be 0.1 mol% or less.

According to another embodiment of the present invention, step (1) may include discharging unreacted alcohol and ethylene glycol as a by-product.

Specifically, alcohol is separated from the discharged mixture of alcohol and ethylene glycol, and the separated alcohol can be recycled as a raw material for alcohol decomposition. For example, ethylene glycol and unreacted alcohol (alcohol in excess), which are by-products produced through alcohol decomposition, are discharged in real time in the form of a gaseous mixture during the alcohol decomposition reaction and separated by fractional distillation or layer separation, and/ Alternatively, after completion of the reaction, alcohol and ethylene glycol can be separated by fractional distillation, and the separated alcohol can be reused by adding it to the alcohol decomposition in step (1). At this time, the volume and discharge rate of alcohol introduced for reuse may be the same as the volume and discharge rate of the mixture of alcohol and ethylene glycol discharged.

Additionally, step (1) may include recovering ethylene glycol, which is a by-product of alcohol decomposition. Specifically, ethylene glycol, a by-product of alcohol decomposition, can be recovered by fractional distillation or layer separation of the discharged mixture of alcohol and ethylene glycol, and by fractional distillation or layer separation of the composition prepared in step (1). It can be recovered.

For example, during the alcohol decomposition reaction, the unreacted alcohol and the by-product ethylene glycol can be discharged as a gaseous mixture in real time, and the ethylene glycol can be recovered by condensing it using an external cooling device.

According to one embodiment of the present invention, unreacted alcohol and ethylene glycol can be separated by a simple process such as fractional distillation or layer separation, and the separated unreacted alcohol can be recycled as a raw material for alcohol decomposition. Since the recovered ethylene glycol can be used in other processes, fairness and process cost reduction effects are excellent.

The recovery rate of ethylene glycol may be 65% or more. For example, the recovery rate of ethylene glycol may be 70% or more, 76% or more, 85% or more, 90% or more, 93% or more, 95% or more, 97% or more, 98% or more, 99% or more, or 99.5% or more. there is.

purification steps

A method for producing terephthalic acid according to another embodiment of the present invention may further include the step of purifying the liquid composition before step (2).

Specifically, the purifying step may include adding one or more adsorbents selected from the group consisting of activated carbon, silica gel, alumina, zeolite, and activated clay, or adsorbing through bed adsorption. More specifically, the adsorbent may be activated carbon or a mixture of activated carbon and silica gel. For example, the adsorbent may be a mixture of activated carbon and silica gel in a weight ratio of 1:0.5 to 1.5 or 1:0.8 to 1.2. , but is not limited to this.

The amount of the adsorbent may be 0.1% by weight to 20% by weight based on the total weight of the liquid composition. For example, the amount of the adsorbent added is 0.1% to 18% by weight, 0.1% to 15% by weight, 0.1% to 10% by weight, 0.1% to 5% by weight, or 0.1% by weight, based on the total weight of the liquid composition. It may be from % to 2% by weight.

Purity and yield can be further improved by further purifying the liquid composition using the adsorbent, specifically using a specific adsorbent that satisfies the dosage within the above numerical range. Specifically, by performing the step of purifying the liquid composition, which is the alcoholysis reaction composition, colorants and pigments that may be contained in the alcoholysis reaction composition, more specifically, insoluble impurities such as metals or waste polyester, may be contained. Since additives such as the like can be removed more effectively, the purity and yield of the final manufactured terephthalic acid can be further improved.

In addition, the method for producing terephthalic acid according to another embodiment of the present invention may further include a step of concentrating after the purification step.

The concentration may be performed at a temperature of 50°C to 120°C for 0.5 to 6 hours. For example, the concentration is performed at a temperature of 55°C to 115°C, 60°C to 110°C, 65°C to 105°C, or 75°C to 100°C for 1 hour to 5 hours, 1.5 hours to 4 hours, or 2 hours to 4 hours. The purified alcoholysis may be performed by stirring the reaction composition.

According to one embodiment of the present invention, the purified composition may have a pigment residual rate (%) of 15% or less according to the following formula A. For example, the colorant residual rate of the purified alcoholysis reaction composition is 13% or less, 11% or less, 10% or less, 8% or less, 6% or less, 5.5% according to the formula A below. % or less, 5% or less, 4.3% or less, or 4% or less.

[Formula A]

In formula A,

A1 diluted the purified alcoholysis reaction composition to a concentration of 5% using dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP), respectively, and then measured it using a UV-vis spectrophotometer. is the area of the absorbance curve obtained from 400 nm to 800 nm using,

A2 is the area of the absorbance curve obtained by preparing an alcoholysis reaction composition without purification and obtaining it in the same manner as above.

The description of purification in Formula A is the same as described above.

The colorant residual rate refers to the content of additives such as colorants, pigments, dyes, etc. remaining in the composition. The lower the colorant residual rate, the lower the content of additives such as colorants, pigments, dyes, etc., and thus the higher the purity. You can.

Additionally, the purified composition may have a low content of insoluble impurities such as metals. Specifically, the purified liquid composition may have a total metal content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of 100 ppm or less relative to the total weight of the purified alcoholysis reaction composition.

For example, the purified alcoholysis reaction composition may contain insoluble impurities such as metals, and the total amount of metals in the purified alcoholysis reaction composition measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) The content may be 80 ppm or less, 70 ppm or less, 60 ppm or less, 50 ppm or less, 40 ppm or less, or less than 30 ppm relative to the total weight of the purified alcoholysis reaction composition. In particular, the total content of Sb, Ti and Zn in the purified alcoholysis reaction composition is less than 30 ppm, less than 25 ppm, less than 20 ppm, less than 15 ppm, less than 10 ppm, less than 5 ppm, less than 3 ppm, or less than 1 ppm. It may be below.

Sb is known to be a widely used catalyst in general polyester polymerization due to its excellent stability, reaction speed, and cost, but as regulations are being strengthened due to the impact of Sb on the human body and the environment, it is a substance that must be removed during the chemical regeneration process. am.

In addition, Ti can be used as a polyester polymerization catalyst or as an additive in the polyester processing process in the form of TiO ₂ , but if it is contained in more than a certain amount, the quality of recycled terephthalic acid manufactured from it or polyester resin using it may be reduced, limiting its use. there is.

Zn is also a component used as a PET polymerization catalyst, and if it remains, it may affect the control of reactivity in the manufacturing process of recycled terephthalic acid or polyester resin using it, so it is desirable to remove it. In particular, since it is widely used in the chemical regeneration process, it is a material that requires sufficient removal of not only the amount contained in waste plastic, which is the raw material for this process, but also the amount separately added as a catalyst during the regeneration process.

According to one embodiment of the present invention, by further performing the purification, the total content of metals, especially Sb, Ti and Zn as described above, in the purified alcoholysis reaction composition is very low at 30 ppm or less.

For example, the Sb content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) may be 30 ppm or less, 20 ppm or less, 10 ppm or 1 ppm or less based on the total weight of the purified composition.

The Ti content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) may be 30 ppm or less, 20 ppm or less, 10 ppm or 1 ppm or less based on the total weight of the purified composition.

The Zn content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) may be 30 ppm or less, 20 ppm or less, 10 ppm or 1 ppm or less based on the total weight of the purified composition.

Hydrolysis reaction step (2)

A method for producing terephthalic acid according to an embodiment of the present invention includes the step of hydrolyzing the composition. Specifically, step (2) hydrolyzes the alcoholysis reaction composition (liquid composition containing the compound represented by Formula 1) or the purified alcoholysis reaction composition prepared in step (1) to produce regenerated terephthalic acid. It can be manufactured.

The hydrolysis can be performed by adding water to the composition. For example, in the hydrolysis, water is added to the alcoholysis reaction composition or the purified alcoholysis reaction composition, and the reaction temperature is 180°C to 280°C, 185°C to 280°C, 200°C to 275°C, and 220°C to 270°C. It may be carried out at a temperature of ℃ or 240 ℃ to 265 ℃ for 0.5 hours to 24 hours, 1 hour to 20 hours, 2.5 hours to 12 hours or 3 hours to 8 hours.

Conventionally, the process of adding metal catalysts such as iron, cobalt, manganese, nickel, etc. to waste polyester and directly hydrolyzing it with water is environmentally friendly, but requires extremely high temperature conditions of over 300℃ and the reaction device must also have high pressure resistance. fairness is low. However, the method for producing terephthalic acid according to an embodiment of the present invention has excellent processability because the process conditions are relaxed compared to the conventional method as described above.

Additionally, the weight ratio of the composition and the water may be 1:1 to 500. For example, the weight ratio of the alcoholysis reaction composition (purified or purified and concentrated alcoholysis reaction composition) and the water used in the hydrolysis is 1:1 to 450, 1:1 to 400, 1:1. It may be 1 to 250, 1:1 to 100, 1:1 to 50, 1:1.2 to 20, or 1:1.5 to 10.

Additionally, a hydrolysis catalyst may be added in step (2). Specifically, hydrolysis may be performed by adding a hydrolysis catalyst to the mixture of the alcoholysis reaction composition and water.

The hydrolysis reaction can be smoothly performed as a non-catalytic reaction without using a hydrolysis catalyst, making it environmentally friendly. In particular, when the content of insoluble metals in waste polyester is high, a non-catalytic reaction may be advantageous for efficient treatment and removal of impurities. Additionally, a hydrolysis catalyst may be added in step (2) from an energy perspective to improve processability by improving reactivity.

The hydrolysis catalyst may be a metal acetate salt, an alkali metal salt, or a hydroxy salt.

More specifically, the hydrolysis catalyst is an alkali metal ion of Li ⁺ , Na ⁺ , K ⁺ or Cs ⁺ , an alkaline earth metal ion of Be ²⁺ , Mg ²⁺ , Ca ²⁺ or Ba ²⁺ , NH ⁴⁺ or NR ⁴⁺ (R is alkyl) ammonium ion, and at least one cation selected from the group consisting of Zn ²⁺ ; and OH ^- , OR ^- (R is alkyl), HCO ₃ ^- , CO ₃ ^2- , benzoate ion (C ₇ H ₅ O ₂ ^- ), 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion. It may contain one or more anions selected from the group consisting of. R may be alkyl having 1 to 10 carbon atoms or alkyl having 1 to 5 carbon atoms.

For example, the hydrolysis catalyst is Zn(OAC) ₂ , Co(OAc) ₂ , Mn(OAc) ₂ , Mg(OAc) ₂ , Ca(OAc) ₂ , Ba(OAc) ₂ , LiOAc, NaOAc, KOAc , Zn(OAC) ₂ ·2H ₂ O, Co(OAc) ₂ ·4H ₂ O, Pb(OAc) ₂ , Mn(OAc) ₂ ·4H ₂ O, Mg(OAc) ₂ ·4H ₂ O, Pd(OAc ) ₂ , A group consisting of Ti(OBu) ₄ , Ti(OiPr) ₄ , GeO ₂ , Al(OiPr) ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , dibutyltin(IV) oxide, stannous octoate, titanium phosphate and terephthalic acid. It may include one or more types selected from.

The dosage of the hydrolysis catalyst may be 10 ppm to 10,000 ppm based on the total weight of the composition. For example, the input amount of the hydrolysis catalyst is 15 ppm to 8,000 ppm, 20 ppm to 5,500 ppm, and 30 ppm to 3,000 based on the total weight of the alcohololysis reaction composition (purified or purified and concentrated alcohololysis reaction composition). ppm, 50 ppm to 1,600 ppm, 100 ppm to 1,200 ppm, 150 ppm to 1,100 ppm, 300 ppm to 1,000 ppm, 350 ppm to 950 ppm, 400 ppm to 850 ppm, 420 ppm to 700 ppm or 450 ppm to 650 ppm. You can.

According to one embodiment of the present invention, solid terephthalic acid can be produced through the hydrolysis reaction. Specifically, after the hydrolysis step, the step of filtering, washing, and drying the hydrolysis reaction product prepared by the hydrolysis reaction may be further included. That is, solid terephthalic acid can be produced by filtering, washing, and drying the hydrolysis reaction product prepared through the hydrolysis reaction.

For example, a slurry-type solution can be obtained by cooling the hydrolysis reaction product to an appropriate temperature, such as room temperature to less than 100° C., to a temperature that does not vaporize water, and filtering the solution to wash the resulting solid. Solid terephthalic acid can be obtained by vacuum drying.

The washing may be performed using a mixture of alcohol and/or water having 4 or more carbon atoms, a protic solvent such as isopropanol, acetic acid, etc., or an aprotic solvent such as acetone, dichloromethane, chloroform, tetrahydrofuran (THF), and toluene. .

At this time, the description of the alcohol having 4 or more carbon atoms is as described above, and the alcohol with 4 or more carbon atoms used in the washing may be the same as or different from the alcohol with 4 or more carbon atoms used in step (1). For example, when 1-butanol is used as alcohol in step (1) for producing terephthalic acid, the prepared solid terephthalic acid can be washed with a mixture of 1-butanol and water. Additionally, the carbon number of the alcohol used in the washing may be the same as the carbon number of the alcohol used in step (1).

Through the washing, residual pigments or impurities generated by pigment decomposition during hydrolysis, especially yellow impurities, can be effectively removed, thereby improving yellowness or color characteristics. Additionally, by using water for washing, inorganic salts can be removed, thereby improving quality.

Additionally, the yield of terephthalic acid may be 65% or more. For example, the yield of the finally produced recycled terephthalic acid may be 68% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more.

Regenerated Terephthalic Acid

Regenerated terephthalic acid according to another embodiment of the present invention is manufactured according to the above method for producing terephthalic acid, and has a total metal content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of less than 100 ppm.

Specifically, the recycled terephthalic acid can be produced according to the method for producing terephthalic acid.

The regenerated terephthalic acid has a total metal content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of less than 100 ppm, less than 90 ppm, less than 80 ppm, less than 65 ppm, less than 50 ppm, less than 35 ppm, less than 30 ppm. , may be 15 ppm or less, 9 ppm or less, 7 ppm or less, 5 ppm or less, or 1 ppm or less.

Additionally, the regenerated terephthalic acid may have a total content of Sb, Ti, and Zn of less than 30 ppm, as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). For example, the recycled terephthalic acid has a total content of Sb, Ti, and Zn, which are harmful to the human body or may be used as reaction or side reaction catalysts in future polymerization processes, of 25 ppm or less, 20 ppm or less, 15 ppm or less, and 10 ppm or less. , may be 5 ppm or less, 3 ppm or less, or 1 ppm or less.

For example, the recycled terephthalic acid has a Sb content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, and 10 ppm relative to the total weight of the recycled terephthalic acid. It may be 5 ppm or less, 3 ppm or less, or 1 ppm or less.

The recycled terephthalic acid has a Ti content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, and 5 ppm relative to the total weight of the recycled terephthalic acid. It may be less than or equal to 3 ppm or less than or equal to 1 ppm.

The recycled terephthalic acid has a Zn content measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, and 5 ppm relative to the total weight of the recycled terephthalic acid. It may be less than or equal to 3 ppm or less than or equal to 1 ppm.

The recycled terephthalic acid may have a color-b measured with a colorimeter of less than 2, less than 1.6, less than 1.4, less than 1.3, or less than 1. The numerical range of color-b is equivalent to the general new terephthalic acid produced in the petrochemical process, so the color-b of recycled terephthalic acid satisfies the above range, so not only is the yellowness low, but the monomer is well purified, improving the quality. great.

The color-b is a color system established by the International Standard Color Measuring Organization (CIE (Commission International d'Eclairage)), where the colors are L (lightness), a (complementary color from green to red), and b (complementary color from yellow to blue). ) and can be measured using a colorimeter.

In addition, the regenerated terephthalic acid may have a pigment residual rate of 10% or less according to the formula B below. For example, the pigment residual rate of the recycled terephthalic acid may be 10% or less, 8% or less, 7% or less, 5% or less, or 4% or less.

[Formula B]

In formula B above,

B1 is obtained by diluting the regenerated terephthalic acid in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP) to a concentration of 5%, and then measuring the regenerated terephthalic acid at 400 nm to 800 nm using a UV-vis spectrophotometer. is the area of the absorbance curve obtained from,

B2 is the area of the absorbance curve obtained by preparing a composition manufactured without performing a purification process during the process of producing the recycled terephthalic acid, and obtained in the same manner as above.

The B1 may be measured for recycled terephthalic acid produced by purification or purification and concentration in the process for producing recycled terephthalic acid, and B2 may be measured for recycled terephthalic acid produced by performing a purification or concentration process in the process for producing recycled terephthalic acid. It may have been measured on recycled terephthalic acid produced by only performing the process.

In addition, the yellowness index (Y.I.) measured after diluting the regenerated terephthalic acid to a concentration of 5% using dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP), respectively, was It may be less than 2, less than or equal to 1.8, or less than or equal to 1.7. The yellowness may be measured for recycled terephthalic acid produced by performing a purification or purification and concentration process in the process for producing recycled terephthalic acid.

Polyester resin and method for producing the same

A polyester resin according to another embodiment of the present invention includes the recycled terephthalic acid.

Specifically, the polyester resin may include the recycled terephthalic acid, a diol compound or a derivative thereof, and optionally a dicarboxylic acid compound or a derivative thereof.

For example, the diol compound or its derivative is a group consisting of ethylene glycol, monoethylene glycol, diethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,4-cyclohexanedimethanol, and neopentyl glycol. It may include one or more types selected from, and the dicarboxylic acid compound and its derivatives include terephthalic acid (TPA), isophthalic acid (IPA), and naphthalene 2,6-dicarboxylic acid (2,6-naphthalenedicarboxylic acid). acid; 2,6-NDA), dimethyl terephthalate (DMT), dimethylisophthalate (DMI), and dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC). It may include one or more types selected from the group consisting of, but is not limited to this.

A method for producing a polyester resin according to another embodiment of the present invention includes mixing the recycled terephthalic acid with a diol compound or a derivative thereof, and optionally a dicarboxylic acid compound or a derivative thereof, and then performing an esterification reaction; and subjecting the esterification reaction product to a polycondensation reaction.

The esterification reaction may be performed at a temperature of 200°C to 350°C, 220°C to 320°C, or 250°C to 290°C. In addition, the esterification reaction is performed at a pressure of 0 kg/cm ² to 10 kg/cm ² (0 mmHg to 7355.6 mmHg), 0 kg/cm ² to 5 kg/cm ² (0 to 3677.8 mmHg), or 0 kg/cm 2 compared to normal pressure. It can be performed under pressurization as high as cm ² to 2.0 kg/cm ² (0 to 1471.1 mmHg). Additionally, the esterification reaction may be performed for 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 6 hours.

Additionally, the polycondensation reaction may be performed at a temperature of 150°C to 400°C, 200°C to 370°C, 250°C to 350°C, or 270°C to 300°C. Additionally, the polycondensation reaction may be performed under reduced pressure conditions of 0.01 mmHg to 400 mmHg, 0.05 mmHg to 100 mmHg, or 0.1 mmHg to 100 mmHg. In addition, the polycondensation reaction may be performed for the necessary time until the desired intrinsic viscosity is reached, for example, 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 4 hours.

Additionally, a catalyst and/or stabilizer may be additionally added in the esterification reaction and the polycondensation reaction.

For example, the esterification reaction catalyst includes methylates of sodium and magnesium; Acetate, borate, fatty acid salt, carbonate such as Zn, Cd, Mn, Co, Ca, Ba, etc.; metal Mg; It may be an oxide such as Pb, Zn, Sb, or Ge.

In addition, the polycondensation reaction catalyst is, for example, tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate. , lactate titanate, triethanolamine titanate, acetyl acetonate titanate, ethyl acetoacetic ester titanate, isostearyl titanate, titanium dioxide, titanium dioxide/silicon dioxide copolymer, titanium dioxide/zirconium dioxide copolymer, etc. The same titanium-based catalyst; Germanium-based catalysts such as germanium dioxide and copolymers using it; Alternatively, it may be a tin-based catalyst such as monobutyl tin oxide, dibutyl tin oxide, or monobutyl hydroxy tin oxide.

Additionally, the stabilizer may be a phosphorus-based compound such as phosphoric acid, trimethyl phosphate, or triethyl phosphate, but is not limited thereto.

A method for producing a polyester resin according to another embodiment of the present invention may further include the step of performing a solid-state polymerization reaction. For example, the solid-state polymerization may be performed after the polycondensation reaction step, and may be performed at a temperature of 190°C to 230°C, and may be performed under vacuum conditions of 0.2 torr to 2.0 torr or under a nitrogen atmosphere. there is.

The above will be explained in more detail by the following examples. However, the following examples are only for illustrating the present invention, and the scope of the examples is not limited to these only.

[Example]

Preparation of liquid composition

Example 1-1

Into the first high pressure reactor with a capacity of 7 L, 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as alcohol were added, and 200 mg of Zn(OAC) ₂ ·2H ₂ O (the waste 200 ppm relative to the total weight of PET) was added.

Afterwards, the temperature was raised to 250°C over 1 hour while all connections of the first high pressure reactor were tightened and sealed, and then stirred while maintaining the temperature of 250°C and pressure of 24 bar for 3 hours. An alcohololysis reaction was performed.

After the alcoholysis reaction was completed, it was cooled to room temperature to obtain a liquid alcoholysis reaction composition. At this time, the components and their contents of the alcoholysis reaction composition were analyzed through NMR. The alcoholysis reaction composition contained a compound represented by the following formula (R ₁ : (CH ₂ ) ₃ CH ₃ ), residual ethylene glycol (EG), alcohol (1-butanol), and oligomer.

Thereafter, the alcoholysis reaction composition was added to a separate flask, and excess unreacted 1-butanol and produced ethylene glycol (EG) were respectively recovered using a fractional distillation device.

[Formula 1]

Example 1-2

Into the first high pressure reactor with a capacity of 7 L, 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as alcohol were added, and 200 mg of Zn(OAC) ₂ ·2H ₂ O (the waste 200 ppm relative to the total weight of PET) was added.

Afterwards, the temperature was raised to 250°C over 1 hour while all connections of the first high pressure reactor were tightened and sealed, and then stirred while maintaining the temperature of 250°C and pressure of 24 bar for 3 hours. An alcohololysis reaction was performed.

Specifically, 1 hour after the alcohol decomposition reaction starts, the valve of the pre-installed back pressure regulator is adjusted to control ethylene glycol (EG), a by-product produced by the alcohol decomposition reaction. A gaseous mixture of 1-butanol present in excess was discharged. At this time, the internal temperature of the first high pressure reactor was maintained at 250°C, and the gaseous mixture of ethylene glycol (EG) and 1-butanol discharged through the reverse pressure regulator was condensed using an external cooling device. In addition, the discharge rate of the gaseous mixture of ethylene glycol (EG) and 1-butanol was adjusted to 3 kg/h, and at the same time, 1-butanol was continuously supplied to the first high pressure reactor. At this time, the volume and input rate of 1-butanol newly supplied to the first high pressure reactor were adjusted to be the same as the volume and discharge rate of the gaseous mixture of ethylene glycol (EG) and 1-butanol discharged. Alcohol decomposition reaction was carried out while maintaining the discharge and supply process for 3 hours.

After the alcoholysis reaction was completed, it was cooled to room temperature to obtain a liquid alcoholysis reaction composition. At this time, the components and their contents of the alcoholysis reaction composition were analyzed through NMR. The alcoholysis reaction composition contained a compound represented by the following formula (R ₁ : (CH ₂ ) ₃ CH ₃ ), residual ethylene glycol (EG), alcohol (1-butanol), and oligomer.

Thereafter, the alcoholysis reaction composition was added to a separate flask, and excess unreacted 1-butanol and produced ethylene glycol were respectively recovered using a fractional distillation device.

[Formula 1]

Example 1-3

Into the first high pressure reactor with a capacity of 7 L, 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as alcohol were added, and 200 mg of Zn(OAC) ₂ ·2H ₂ O as an alcohol decomposition catalyst (the waste 200 ppm relative to the total weight of PET) was added.

Afterwards, the temperature was raised to 250°C over 1 hour while all connections of the first high pressure reactor were tightened and sealed, and then stirred while maintaining the temperature of 250°C and pressure of 24 bar for 3 hours. An alcohololysis reaction was performed.

Specifically, 1 hour after the alcohol decomposition reaction starts, the valve of the pre-installed back pressure regulator is adjusted to control ethylene glycol (EG), a by-product produced by the alcohol decomposition reaction. A gaseous mixture of 1-butanol present in excess was discharged. At this time, the internal temperature of the first high pressure reactor was maintained at 250°C, and the gaseous mixture of ethylene glycol (EG) and 1-butanol discharged through the reverse pressure regulator was condensed using an external cooling device. In addition, the discharge rate of the gaseous mixture of ethylene glycol (EG) and 1-butanol was adjusted to 3 kg/h, and at the same time, 1-butanol was continuously supplied to the first high pressure reactor. At this time, the volume and input rate of 1-butanol newly supplied to the first high pressure reactor were adjusted to be the same as the volume and discharge rate of the gaseous mixture of ethylene glycol (EG) and 1-butanol discharged.

The condensed gaseous mixture of ethylene glycol (EG) and 1-butanol was transferred to a 5 L capacity layer separation device filled with 3 kg of water, and then the process of stirring for 10 minutes and layer separation for 2 minutes was repeated. It was separated into a 1-butanol layer and a water/ethylene glycol (EG) layer. The separated 1-butanol was re-introduced to the first high-pressure reactor in real time using a high-pressure pump. Alcohol decomposition reaction was performed while the stirring, layer separation, and reintroduction processes were maintained for 3 hours.

After the alcoholysis reaction was completed, it was cooled to room temperature to obtain a liquid alcoholysis reaction composition. At this time, the components and their contents of the alcoholysis reaction composition were analyzed through NMR. The alcoholysis reaction composition contained a compound represented by the following formula (R ₁ : (CH ₂ ) ₃ CH ₃ ), residual ethylene glycol (EG), alcohol (1-butanol), and oligomer.

Thereafter, the alcoholysis reaction composition was added to a separate flask, and excess unreacted 1-butanol and produced ethylene glycol were respectively recovered using a fractional distillation device.

[Formula 1]

Example 1-4

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-1, except that 3.3 kg of 1-pentanol was used as alcohol and the pressure was maintained at 13 bar.

Examples 1-5

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-2, except that 3.3 kg of 1-pentanol was used as alcohol and the pressure was maintained at 13 bar.

Example 1-6

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-3, except that 3.3 kg of 1-pentanol was used as alcohol and the pressure was maintained at 13 bar.

Example 1-7

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-1, except that 3.3 kg of 1-octanol was used as alcohol and the pressure was maintained at 3.4 bar.

Examples 1-8

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-2, except that 3.3 kg of 1-octanol was used as alcohol and the pressure was maintained at 3.4 bar.

Example 1-9

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-3, except that 3.3 kg of 1-octanol was used as alcohol and the pressure was maintained at 3.4 bar.

Examples 1-10

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-1, except that 3.3 kg of 2-ethyl-1-hexanol was used as alcohol and the pressure was maintained at 4.1 bar.

Example 1-11

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-2, except that 3.3 kg of 2-ethyl-1-hexanol was used as alcohol and the pressure was maintained at 4.1 bar.

Examples 1-12

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-3, except that 3.3 kg of 2-ethyl-1-hexanol was used as alcohol and the pressure was maintained at 4.1 bar.

Example 1-13

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-1, except that 3.3 kg of 1-decanol was used as alcohol and the pressure was maintained at 1.6 bar.

Example 1-14

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-2, except that 3.3 kg of 1-decanol was used as alcohol and the pressure was maintained at 1.6 bar.

Example 1-15

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-3, except that 3.3 kg of 1-decanol was used as alcohol and the pressure was maintained at 1.6 bar.

Example 1-16

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-1, except that 3.3 kg of 1-dodecanol was used as alcohol and the pressure was maintained at 1.0 bar.

Example 1-17

Into the first high pressure reactor with a capacity of 7 L, 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-dodecanol as alcohol were added, and 200 mg of Zn(OAC) ₂ ·2H ₂ O as an alcohol decomposition catalyst (as described above) 200 ppm relative to the total weight of waste PET) was added.

Afterwards, the temperature was raised to 250°C over 1 hour while all connections of the first high pressure reactor were fastened and sealed, and then stirred while maintaining the temperature of 250°C and pressure of 1.0 bar for 3 hours. An alcohololysis reaction was performed.

Specifically, 1 hour after the alcohol decomposition reaction starts, the valve of the pre-installed back pressure regulator is adjusted to control ethylene glycol (EG), a by-product produced by the alcohol decomposition reaction. of vapor was discharged. At this time, the internal temperature of the first high pressure reactor was maintained at 250°C, and the discharged vapor of ethylene glycol (EG) was condensed using an external cooling device.

Additionally, 1-dodecanol was continuously supplied to the first high pressure reactor in an amount equal to the amount of ethylene glycol (EG) discharged as vapor and condensed. At this time, the volume and input rate of 1-dodecanol newly supplied to the first high pressure reactor were adjusted to be the same as the volume and discharge rate of ethylene glycol (EG) discharged. The alcohol decomposition reaction was performed while maintaining the discharge and supply process for 3 hours.

After the alcohol decomposition reaction was completed, it was cooled to room temperature to obtain a liquid alcohol decomposition reaction composition. At this time, the components and their contents of the alcoholysis reaction composition were analyzed through NMR. The alcoholysis reaction composition contained a compound represented by the following formula (R ₁ : (CH ₂ ) ₁₁ CH ₃ ), residual ethylene glycol (EG), alcohol (1-dodecanol), and oligomer.

Thereafter, the alcoholysis reaction composition was added to a separate flask, and excess unreacted 1-dodecanol and produced ethylene glycol (EG) were respectively recovered using a fractional distillation device.

[Formula 1]

Example 1-18

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-1, except that 3.3 kg of 1-tetradecanol was used as alcohol and the pressure was maintained at 1.0 bar.

Example 1-19

A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-17, except that 3.3 kg of 1-tetradecanol was used as alcohol.

Comparative Example 1-1

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-1, except that 3.3 kg of methanol was used as alcohol and the pressure was maintained at 83 bar.

Comparative Example 1-2

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-2, except that 3.3 kg of methanol was used as alcohol and the pressure was maintained at 83 bar.

Comparative Example 1-3

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-1, except that 3.3 kg of ethanol was used as alcohol and the pressure was maintained at 64 bar.

Comparative Example 1-4

A liquid alcoholysis reaction composition was prepared in the same manner as Example 1-2, except that 3.3 kg of ethanol was used as alcohol and the pressure was maintained at 64 bar.

As shown in Table 1, the liquid alcoholysis reaction compositions of Examples 1-1 to 1-19 were prepared using alcohol having 4 or more carbon atoms, so the process was very low compared to Comparative Examples 1-1 to 1-4. While it can be manufactured under pressure, the content of the compound represented by Chemical Formula 1, that is, the yield and purity, is high, and the recovery rate of ethylene glycol is also excellent.

Purification and concentration of liquid compositions

Example 2-1

In Example 1-1, 0.1 g of activated carbon was added as an adsorbent to 100 g of the liquid alcoholization reaction composition before recovering the excess unreacted alcohol and produced ethylene glycol using a fractional distillation device, and purified, and 100 g of activated carbon was added as an adsorbent. After stirring at ℃ for 3 hours, the alcoholysis reaction composition was concentrated by filtration.

Examples 2-2 to 2-23, and Comparative Examples 2-1 and 2-2

The liquid alcoholysis reaction composition was purified and concentrated in the same manner as in Example 2-1, except that the liquid composition and process conditions were different as shown in Table 2 below. However, Comparative Examples 2-1 and 2-2 precipitated in an undissolved state and were not purified.

Examples 2-24 to 2-26

Activated carbon as an adsorbent was added to 100 g of the liquid alcoholysis reaction composition after recovering the excess unreacted alcohol and produced ethylene glycol using a fractional distillation apparatus in Examples 1-1, 1-4, and 1-10, respectively. 0.1 g was added and purified, stirred at 100°C for 3 hours, and then filtered to concentrate the alcoholysis reaction composition.

Comparative Examples 2-3 to 2-21

In Examples 1-1 to 1-19, an adsorbent was not added to the liquid alcoholysis reaction composition before recovering the excess unreacted alcohol and produced ethylene glycol using a fractional distillation device, and the reaction mixture was distilled at 100°C. After stirring for 3 hours, it was filtered and concentrated.

Experimental Example 1-1: Pigment Residual Rate

The pigment residual rate (%) was calculated for the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21.

Specifically, the composition of Example 2-1 was diluted to a concentration of 5% using dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP), respectively, and then subjected to UV-vis spectroscopy. An absorbance curve was obtained from 400 nm to 800 nm using a photometer, and its area (A1) was measured. In addition, the same method as above was used for the composition of Comparative Example 2-3 (the composition of Example 1-1 was used in the same way as the composition of Example 2-1, but the composition was concentrated without purification by adding an adsorbent) An absorbance curve was obtained from 400 nm to 800 nm and its area (A2) was measured. The pigment residual rate (%) was calculated according to the following formula A using the area of the measured absorbance curve.

[Formula A]

The pigment residual rate (%) was calculated for the compositions of Examples 2-2 to 2-26 and Comparative Examples 2-1 to 2-21 in the same manner as above.

Experimental Example 1-2: Yellowness

For the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21, yellowness index (Y.I.) was measured.

Specifically, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP) were added to the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21. After diluting each to a concentration of 5%, the yellowness was measured using ColorFlex EZ (manufacturer: HunterLab) equipment.

Experimental Example 1-3: Metal content

The content of the metal present in the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21 was determined using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) ( ppm) was measured. N.D. means that the content is too low, less than 1 ppm, to be measured as a specific value.

As shown in Table 2, the purified and concentrated alcoholysis reaction compositions of Examples 2-1 to 2-26 had a very low colorant residual rate and also had a very low content of metals such as Sb, Ti, and Zn.

Preparation of terephthalic acid

Example 3-1

100 g (0.36 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-2 and 200 g (11.10 mol) of water were added to a second high pressure reactor of 600 ml capacity, and Zn (OAC) was added as a hydrolysis catalyst. ) 50 mg of ₂ ·2H ₂ O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added.

Thereafter, the temperature of the second high pressure reactor was raised to 260°C, the hydrolysis reaction was performed for 4 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The solid obtained by filtering the slurry-type hydrolysis reaction product was washed with butanol and water at 90°C and dried under vacuum to obtain 53.7 g of solid terephthalic acid (TPA) (yield: 90%).

Example 3-2

100 g (0.30 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-5 and 200 g (11.10 mol) of water were added to a second high pressure reactor of 600 ml capacity, and Zn (OAC) was used as a hydrolysis catalyst. ) 50 mg of ₂ ·2H ₂ O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added.

Thereafter, the temperature of the second high pressure reactor was raised to 260°C, the hydrolysis reaction was performed for 4 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The solid obtained by filtering the slurry-type hydrolysis reaction product was washed with pentanol and water at 90°C and dried under vacuum to obtain 43.9 g of solid terephthalic acid (TPA) (yield: 81%).

Example 3-3

100 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-11 and 1,000 g (55.50 mol) of water were added to a second high pressure reactor of 600 ml capacity, and Zn (OAC) was added as a hydrolysis catalyst. ) 50 mg of ₂ ·2H ₂ O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added.

Thereafter, the temperature of the second high pressure reactor was raised to 260°C, the hydrolysis reaction was performed for 4 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The solid obtained by filtering the slurry-type hydrolysis reaction product was washed with 2-ethyl-1-hexanol and water at 90°C and dried in vacuum to obtain 38.0 g (yield: 88%) of solid terephthalic acid (TPA).

Example 3-4

35.4 g of solid terephthalic acid (TPA) (yield: 82) was prepared in the same manner as in Example 3-3, except that 100 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-13 was used. %) was obtained.

Example 3-5

36.7 g of solid terephthalic acid (TPA) (yield: 85 g) in the same manner as in Example 3-3, except that 100 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-14 was used. %) was obtained.

Example 3-6

114 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-18 and 200 g (11.10 mol) of water were added to a second high pressure reactor of 600 ml capacity, and Zn (OAC) was added as a hydrolysis catalyst. ) 57 mg of ₂ ·2H ₂ O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added.

Thereafter, the temperature of the second high pressure reactor was raised to 260°C, the hydrolysis reaction was performed for 4 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The solid obtained by filtering the slurry-type hydrolysis reaction product was washed with decanol and water at 90°C and dried under vacuum to obtain 36.1 g (yield: 85%) of solid terephthalic acid (TPA).

Example 3-7

54.3 g (yield: 91%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-1, except that the hydrolysis catalyst was not added.

Example 3-8

100 g (0.36 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-2 and 200 g (11.10 mol) of water were added to a second high pressure reactor of 600 ml capacity, and Zn (OAC) was added as a hydrolysis catalyst. ) 50 mg of ₂ ·2H ₂ O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added.

Thereafter, the temperature of the second high pressure reactor was raised to 260°C, the hydrolysis reaction was performed for 4 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. Acetone was added to the solid obtained by filtering the slurry-type hydrolysis reaction product and stirred at 50°C for 4 hours. After filtering, washing with acetone and water at 50°C and drying under vacuum, 55.6 g (yield: 93%) of solid terephthalic acid (TPA) was obtained.

Example 3-9

100 g (0.36 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-2 and 200 g (11.10 mol) of water were added to a second high pressure reactor of 600 ml capacity, and Zn (OAC) was added as a hydrolysis catalyst. ) 50 mg of ₂ ·2H ₂ O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added.

Thereafter, the temperature of the second high pressure reactor was raised to 260°C, the hydrolysis reaction was performed for 4 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. Butanol was added to the solid obtained by filtering the slurry-type hydrolysis reaction product and stirred at 90°C for 4 hours. After filtering, washing with butanol and water at 50°C and drying in vacuum, 53.1 g (yield: 89%) of solid terephthalic acid (TPA) was obtained.

Example 3-10

59.2 g (yield: 99%) of terephthalic acid (TPA) was obtained in the same manner as in Example 3-1, except that the filtrate separated through the filtration process in Example 3-1 was additionally used.

Specifically, the filtrate separated through the filtration process of Example 3-1 was placed back into the second high pressure reactor, the temperature was raised to 260°C, and the hydrolysis reaction was performed for 4 hours while maintaining 260°C. Afterwards, it was cooled to 90°C to obtain a slurry-type hydrolysis reaction product. The solid obtained by filtering the slurry-type hydrolysis reaction product was washed with butanol and water at 90°C and dried in vacuum to obtain an additional 5.5 g of solid terephthalic acid (TPA).

Comparative Example 3-1

54.4 g (yield: 91%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-1, except that 100 g (0.36 mol) of the composition of Comparative Example 2-4 was used.

Comparative Example 3-2

40.4 g (yield: 81%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-2, except that 100 g (0.30 mol) of the composition of Comparative Example 2-7 was used.

Comparative Example 3-3

36.7 g (yield: 85%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-3, except that 100 g (0.26 mol) of the composition of Comparative Example 2-13 was used.

Comparative Example 3-4

34.4 g (yield: 81%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-6, except that 114 g (0.26 mol) of the composition of Comparative Example 2-16 was used.

Experimental Example 2-1: Pigment Residual Rate

The pigment residual rate (%) was calculated for the terephthalic acid of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4.

Specifically, the terephthalic acid of Example 3-1 was diluted to a concentration of 5% using dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP), respectively, and then subjected to UV-vis spectroscopy. An absorbance curve was obtained from 400 nm to 800 nm using a photometer, and its area (B1) was measured. In addition, the composition of Comparative Example 2-4 (the composition of Example 1-2 used for the production of terephthalic acid in Example 3-1 was used in the same manner, but concentrated without adding an adsorbent) was the same as above. Using this method, an absorbance curve was obtained from 400 nm to 800 nm and its area (B2) was measured. The pigment residual rate (%) was calculated according to the following formula B using the area of the measured absorbance curve.

[Formula B]

The pigment residual rate (%) of terephthalic acid was calculated for Examples 3-2 to 3-10 and Comparative Examples 3-1 to 3-4 in the same manner as above. Specifically, with respect to B2 of Formula 1, Example 3-2 was measured using the composition of Comparative Example 2-7, and Examples 3-3 to 3-5 were measured using the composition of Comparative Example 2-13. and Example 3-6 was measured using the composition of Comparative Example 2-16. In addition, in Comparative Examples 3-1 to 3-4, B2 of Formula 1 was measured using the compositions of Comparative Examples 2-4, 2-7, 2-13, and 2-16, respectively.

Experimental Example 2-2: Yellowness

For the regenerated terephthalic acid of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4, the yellowness index (Y.I.) was measured.

Specifically, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP) were added to the regenerated terephthalic acid of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4. After each dilution to a concentration of 5%, the yellowness was measured using ColorFlex EZ (manufacturer: HunterLab) equipment.

Experimental Example 2-2: Metal content

The content of the metal present in the terephthalic acid of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4 was determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES) ( ppm) was measured. N.D. means that the content is too low, less than 1 ppm, to be measured as a specific value.

Experimental Example 2-3: color-b

For the terephthalic acid of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4, color-b, a color characteristic, was measured using a colorimeter.

As shown in Table 3, the terephthalic acid (regenerated terephthalic acid) prepared in Examples 3-1 to 3-6 not only had low pigment retention rate and low yellowness, but also had a very low content of metal as an impurity. In particular, Example 3-10 was able to obtain regenerated terephthalic acid in very high yield by using the filtrate, that is, the unreacted material, separated through the filtration process.

Claims (19)

(1) preparing a liquid composition containing a compound represented by the following formula (1) by alcoholizing waste polyester with an alcohol having 4 or more carbon atoms; and
(2) A method for producing terephthalic acid, comprising the step of hydrolyzing the liquid composition:
[Formula 1]

In Formula 1,
R ₁ is alkyl having 4 or more carbon atoms. According to claim 1,
A method for producing terephthalic acid, wherein the alcohol has 4 to 14 carbon atoms. According to claim 1,
A method for producing terephthalic acid, wherein the weight ratio of the waste polyester and the alcohol is 1:1 to 10. According to claim 1,
A method for producing terephthalic acid, wherein the alcoholysis is performed at a temperature of 160°C to 280°C and a pressure of 1 bar to 40 bar for 0.5 to 24 hours. According to claim 1,
The liquid composition contains unreacted alcohol and ethylene glycol as a by-product,
A method for producing terephthalic acid, wherein the content of the compound represented by Formula 1 in the liquid composition is 70 mol% or more. According to claim 1,
Step (1) includes discharging unreacted alcohol and ethylene glycol as a by-product from the alcohol decomposition,
A method for producing terephthalic acid, wherein alcohol is separated from the mixture of the discharged alcohol and ethylene glycol, and the separated alcohol is recycled as a raw material for the alcoholysis. According to claim 1,
Step (1) includes recovering ethylene glycol, a by-product of alcohol decomposition,
A method for producing terephthalic acid, wherein the recovery rate of ethylene glycol is 65% or more. According to claim 1,
In step (1), an alcohol decomposition catalyst is added,
The alcohol decomposition catalyst is an alkali metal ion of Li ⁺ , Na ⁺ , K ⁺ or Cs ⁺ , an alkaline earth metal ion of Be ²⁺ , Mg ²⁺ , Ca ²⁺ or Ba ²⁺ , NH ⁴⁺ or NR ⁴⁺ ( R is alkyl) ammonium ion, and at least one cation selected from the group consisting of Zn ²⁺ ; and OH ^- , OR ^- (R is alkyl), HCO ₃ ^- , CO ₃ ^2- , benzoate ion (C ₇ H ₅ O ₂ ^- ), 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion. Contains one or more anions selected from the group consisting of,
A method for producing terephthalic acid, wherein the input amount of the alcohol decomposition catalyst is 10 ppm to 10,000 ppm based on the total weight of the waste polyester. According to claim 1,
In step (1), an alcohol decomposition catalyst is added,
The alcohol decomposition catalyst is Zn(OAC) ₂ , Co(OAc) ₂ , Mn(OAc) ₂ , Mg(OAc) ₂ , Ca(OAc) ₂ , Ba(OAc) ₂ , LiOAc, NaOAc, KOAc, Zn ( OAC) ₂ ·2H ₂ O, Co(OAc) ₂ ·4H ₂ O, Pb(OAc) ₂ , Mn(OAc) ₂ ·4H ₂ O, Mg(OAc) ₂ ·4H ₂ O, Pd(OAc) ₂ , A group consisting of Ti(OBu) ₄ , Ti(OiPr) ₄ , GeO ₂ , Al(OiPr) ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , dibutyltin(IV) oxide, stannous octoate, titanium phosphate and terephthalic acid. Contains one or more types selected from,
A method for producing terephthalic acid, wherein the input amount of the alcohol decomposition catalyst is 10 ppm to 10,000 ppm relative to the total weight of the waste polyester. According to claim 1,
A method for producing terephthalic acid, further comprising the step of purifying the liquid composition before step (2). According to claim 10,
The purifying step includes adding at least one adsorbent selected from the group consisting of activated carbon, silica gel, alumina, zeolite, and activated clay or adsorbing through bed adsorption,
A method for producing terephthalic acid, wherein the amount of the adsorbent added is 0.1% to 20% by weight based on the total weight of the liquid composition. According to claim 1,
A method for producing terephthalic acid, wherein the hydrolysis is performed by adding water to the liquid composition and performing it at 180°C to 280°C for 0.5 to 24 hours. According to claim 11,
A method for producing terephthalic acid, wherein the weight ratio of the liquid composition and the water is 1:1 to 500. According to claim 1,
In step (2), a hydrolysis catalyst is added,
The hydrolysis catalyst is an alkali metal ion of Li ⁺ , Na ⁺ , K ⁺ or Cs ⁺ , an alkaline earth metal ion of Be ²⁺ , Mg ²⁺ , Ca ²⁺ or Ba ²⁺ , NH ⁴⁺ or NR ⁴⁺ (R is an alkyl) ammonium ion, and at least one cation selected from the group consisting of Zn ²⁺ ; and OH ^- , OR ^- (R is alkyl), HCO ₃ ^- , CO ₃ ^2- , benzoate ion (C ₇ H ₅ O ₂ ^- ), 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion. Contains one or more anions selected from the group consisting of,
A method for producing terephthalic acid, wherein the input amount of the hydrolysis catalyst is 10 ppm to 10,000 ppm based on the total weight of the liquid composition. According to claim 1,
The hydrolysis catalyst is Zn(OAC) ₂ , Co(OAc) ₂ , Mn(OAc) ₂ , Mg(OAc) ₂ , Ca(OAc) ₂ , Ba(OAc) ₂ , LiOAc, NaOAc, KOAc, Zn(OAC) ) ₂ ·2H ₂ O, Co(OAc) ₂ ·4H ₂ O, Pb(OAc) ₂ , Mn(OAc) ₂ ·4H ₂ O, Mg(OAc) ₂ ·4H ₂ O, Pd(OAc) ₂ , A group consisting of Ti(OBu) ₄ , Ti(OiPr) ₄ , GeO ₂ , Al(OiPr) ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , dibutyltin(IV) oxide, stannous octoate, titanium phosphate and terephthalic acid. Contains one or more types selected from,
A method for producing terephthalic acid, wherein the input amount of the hydrolysis catalyst is 10 ppm to 10,000 ppm based on the total weight of the liquid composition. Prepared according to the method for producing terephthalic acid of claim 1,
Regenerated terephthalic acid with a total metal content of less than 100 ppm as determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). According to claim 16,
The regenerated terephthalic acid has a total content of Sb, Ti and Zn of less than 30 ppm, as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). According to claim 16,
The regenerated terephthalic acid is diluted to a concentration of 5% using dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP), and the yellowness index (YI) measured is less than 2. , recycled terephthalic acid. A polyester resin comprising the recycled terephthalic acid of claim 16.