A method for producing terephthalic acid and terephthalic acid produced thereby

Abstract

The present invention relates to a method for producing terephthalic acid in an environmentally friendly manner using waste polyester. Specifically, according to one embodiment of the present invention, the method for producing terephthalic acid includes the steps of: (1) alcoholysis of waste polyester using a C4 or higher alcohol to produce a liquid composition containing a compound represented by Formula 1; and (2) hydrolysis of the liquid composition, thereby producing terephthalic acid in an environmentally friendly manner and improving processability and reducing processing costs.

Description

Technical Field

[0001] This invention relates to a process for preparing terephthalic acid from waste polyester in an environmentally friendly manner, and the recycled terephthalic acid prepared therefrom. Background Technology

[0002] Polyester, with its excellent mechanical strength, heat resistance, transparency, and gas barrier properties, is widely used in materials such as beverage filling containers, packaging films, and audio-visual films, as well as industrial materials such as medical fibers and tire cords. In particular, polyester sheets or plates have good transparency and excellent mechanical strength, so they are widely used as raw materials for boxes, containers, partitions, shelves, panels, packaging materials, building materials, and internal and external materials.

[0003] Given the difficulty in controlling the amount of polyester and other plastic waste generated globally each year, there is a growing interest in recycling waste polyester or using waste polyester recycling processes. Furthermore, countries worldwide have developed regulations and plans for recycling, including waste plastic resources. For example, regulations currently under discussion require that packaging materials used in various sectors must utilize recycled resins at a certain or higher percentage.

[0004] In particular, polyethylene terephthalate (PET) is widely used in the manufacture of various products such as films, fibers, bottles, and containers due to its excellent properties in terms of heat resistance, processability, transparency, and non-toxicity. However, most of them end up in landfills or incinerators after use; therefore, research on recycling or regeneration processes using them continues.

[0005] For example, Korean Patent Application Publication No. 1997-0042469 discloses a technique for preparing terephthalic acid, which involves hydrolyzing waste polyethylene terephthalate with an alkaline aqueous solution to obtain a slurry of alkali metal and alkaline earth metal salts of terephthalic acid, followed by neutralization with acid. The hydrolysis reaction produces terephthalate salts, not terephthalic acid, and requires a neutralization step with acid to convert it back to terephthalic acid. The problem is that the resulting byproducts can generate environmental pollutants or produce large amounts of acid treatment wastewater.

[0006] [Existing Technical Documents]

[0007] [Patent Documents]

[0008] (Patent Document 1) Korean Patent Publication No. 1997-0042469. Summary of the Invention

[0009] Technical issues

[0010] Therefore, the present invention aims to provide a process for preparing terephthalic acid in an environmentally friendly manner by using specific alcohols to perform alcoholysis and hydrolysis on waste polyester, and the recycled terephthalic acid thereby prepared.

[0011] Solution to the problem

[0012] According to one embodiment of the present invention, the process for preparing terephthalic acid includes: (1) alcoholystolysis of waste polyester with an alcohol having four or more carbon atoms to prepare a liquid composition comprising the compound shown in Formula 1; and (2) hydrolysis of the liquid composition.

[0013] [Formula 1]

[0014]

[0015] In Formula 1, R1 is an alkyl group having four or more carbon atoms.

[0016] According to another embodiment of the invention, the recovered terephthalic acid is prepared according to the process for preparing terephthalic acid described above, and its total metal content is less than 100 ppm when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0017] According to another embodiment of the invention, the polyester resin comprises recycled terephthalic acid.

[0018] Beneficial effects of the invention

[0019] According to one embodiment of the present invention, in the process for preparing terephthalic acid, waste polyester is alcoholyzed with an alcohol having four or more carbon atoms to prepare a liquid composition comprising a compound shown in Formula 1, which is then hydrolyzed with water. Therefore, the preparation of terephthalic acid can be carried out in an environmentally friendly manner, improving processability while reducing processing costs.

[0020] Specifically, according to one embodiment of the present invention, in the process for preparing terephthalic acid, waste polyester is alcoholyzed with a specific alcohol, more specifically, an alcohol having four or more carbon atoms, to prepare a liquid composition comprising the compound shown in Formula 1, which is then hydrolyzed with water. According to one embodiment of the present invention, in the process for preparing terephthalic acid, solid terephthalic acid can be produced directly without additional steps, unlike conventional processes that produce terephthalates from waste polyester and involve additional neutralization steps. Therefore, this method is not only easy to operate but also reduces process costs and has excellent processability.

[0021] Furthermore, another issue is that acids used to neutralize terephthalates, such as sulfuric acid or hydrochloric acid, can produce environmentally polluting byproducts like Na₂SO₄ and NaCl, or large amounts of acid treatment waste liquid. In contrast, according to one embodiment of the invention, the process for preparing terephthalic acid differs from conventional processes in that solid terephthalic acid can be produced directly without the need for an additional neutralization step, thus being very environmentally friendly.

[0022] Furthermore, according to one embodiment of the present invention, in the process for preparing terephthalic acid, the intermediate (i.e., the hydrolysis agent) is prepared in liquid form; therefore, insoluble impurities (such as metal catalysts and coloring pigments) and additives (such as soluble colorants) that may be present in the waste polyester can be easily removed. Thus, the purity and yield of terephthalic acid produced by this simple process can be further improved. Detailed Implementation

[0023] Best Implementation of the Invention

[0024] The present invention will be described in detail below. The present invention is not limited to the contents disclosed below; it can be modified in various forms as long as the essential points of the invention are not altered.

[0025] Throughout this specification, when a component is referred to as "containing" an element, it should be understood that, unless otherwise specifically stated, other elements may be included, rather than excluded.

[0026] Unless otherwise stated, all numbers and expressions relating to the quantities of components, reaction conditions, etc., used herein should be understood to be modified by the term “about”.

[0027] Throughout this specification, the terms "first," "second," etc., are used to describe various components. However, these components should not be limited by these terms. These terms are only used to distinguish one component from another.

[0028] According to one embodiment of the present invention, the process for preparing terephthalic acid includes: (1) alcoholystolysis of waste polyester with an alcohol having four or more carbon atoms to prepare a liquid composition comprising the compound shown in Formula 1; and (2) hydrolysis of the liquid composition.

[0029] [Formula 1]

[0030]

[0031] In Formula 1, R1 is an alkyl group having four or more carbon atoms.

[0032] In traditional methods for preparing terephthalic acid from waste polyester, solid terephthalic acid is obtained directly using an acidic catalyst, or by producing dimethyl terephthalate (DMT) or bis(2-hydroxyethyl) terephthalate (BHET) as intermediates via methanololysis or glycolysis, which are then converted into terephthalic acid. In these cases, terephthalic acid, dimethyl terephthalate, and bis(2-hydroxyethyl) terephthalate are all solids at room temperature or relatively high temperatures.

[0033] When solid terephthalic acid is obtained directly using an acid catalyst, it precipitates immediately upon formation, making it difficult to remove insoluble impurities or additives, such as colorants and pigments, that may be present in the waste polyester during manufacturing. Therefore, improvements in purity or yield are limited. For this reason, a method has also been employed to prepare terephthalates from waste polyester and then neutralize them to obtain solid terephthalic acid. In this case, although the purity and yield of terephthalic acid can be improved by removing insoluble impurities, a problem exists: a large amount of environmental pollutants, such as Na₂SO₄ and NaCl, are generated during the neutralization of terephthalates.

[0034] Furthermore, when preparing dimethyl terephthalate as an intermediate, a large amount of methanol must be used to produce it. Therefore, the use of methanol creates very high-pressure conditions, requiring additional heating and high-pressure processes to convert dimethyl terephthalate into a liquid phase to remove insoluble impurities, resulting in low processability. Moreover, when bis(2-hydroxyethyl) terephthalate is used as an intermediate, it is difficult to separate and recover ethylene glycol generated as a byproduct during production; therefore, it is undesirable in terms of processability and cost.

[0035] In addition, an environmentally friendly method for recycling waste polyester is employed, which involves adding metal salts to the waste polyester and directly hydrolyzing it with water. However, this method has low processability due to the need for high-temperature conditions of 300°C or higher, and the requirement that the reaction apparatus be pressure-resistant.

[0036] In contrast, according to one embodiment of the present invention, in the process for preparing terephthalic acid, the intermediate (i.e., the hydrolysis agent) is prepared in liquid form; therefore, insoluble impurities and additives, such as colorants and pigments, that may be present in the waste polyester can be easily removed. Thus, the purity and yield of the produced terephthalic acid can be improved.

[0037] Furthermore, unlike traditional processes, solid terephthalic acid can be produced directly without an additional neutralization step, resulting in excellent processability and environmental friendliness. In addition, ethylene glycol, a byproduct that may be formed during the preparation process, can be easily separated and recovered, and alcohols containing four or more carbon atoms used in the alcoholysis reaction can also be easily separated and reused, thus significantly reducing process costs. Moreover, since purification and transfer processes outside the reaction can be carried out at room temperature or low temperature, processability and economic efficiency can be further improved.

[0038] For example, according to one embodiment of the present invention, in the process for preparing terephthalic acid, waste polyester, an alcohol containing four or more carbon atoms, and a trace amount of alcoholysis catalyst are first loaded into a first high-pressure reactor, and then an alcoholysis reaction is carried out. The byproduct ethylene glycol and unreacted alcohol (excess alcohol) formed during the alcoholysis reaction can be recovered and reused by a separate fractionation unit after the reaction is completed.

[0039] Furthermore, the ethylene glycol and unreacted alcohols formed during the reaction can be discharged in real time as a gaseous mixture, then condensed and recovered using an external cooling device. In this case, the alcohols can be continuously fed into the high-pressure reactor at the same feed rate and volume as the volume and discharge rate of the discharged gas mixture. Unreacted alcohols can be separated from the discharged gas mixture through simple processes, such as fractionation or layer separation. The separated unreacted alcohols can then be fed back into the first high-pressure reactor, from which ethylene glycol can be recovered.

[0040] Subsequently, the liquid alcoholysis product obtained through the alcoholysis reaction can be purified by cooling, adsorption, and filtration. The purified alcoholysis reaction composition is fed together with water into a second high-pressure reactor for hydrolysis, resulting in a slurry solution, which is then filtered to obtain solid terephthalic acid. In this case, a small amount of hydrolysis catalyst can be added with water before the hydrolysis reaction. The hydrolysis catalyst can be the same as or different from the alcoholysis catalyst.

[0041] Furthermore, after the hydrolysis reaction is complete, the unreacted components are recovered and reintroduced into the alcoholysis or hydrolysis reaction for one or more subsequent reactions, thereby increasing the yield of the final terephthalic acid. Additionally, waste generation can be reduced, making it more environmentally friendly. For example, the filtrate obtained after filtering excess unreacted alcohols (with four or more carbon atoms) and the byproduct ethylene glycol using a filter or similar device can be reused in the hydrolysis reaction.

[0042] Process for preparing terephthalic acid

[0043] According to one embodiment of the present invention, the process for preparing terephthalic acid includes: (1) alcoholystolysis of waste polyester with an alcohol having four or more carbon atoms to prepare a liquid composition comprising the compound shown in Formula 1; and (2) hydrolysis of the liquid composition.

[0044] [Formula 1]

[0045]

[0046] In Formula 1, R1 is an alkyl group having four or more carbon atoms.

[0047] Alcohololysis step (1)

[0048] According to one embodiment of the present invention, the process for preparing terephthalic acid includes: alcoholysis of waste polyester with an alcohol having four or more carbon atoms to prepare a liquid composition comprising the compound shown in Formula 1.

[0049] Waste polyester can be obtained by crushing or melting waste polyester products. For example, waste polyester can be obtained by crushing used polyester products and recycling and separating them, or by converting them into pellets (post-consumer recycled materials; PCR) or polyester waste (post-industrial recycled materials; PIR), such as defective products or waste that may be formed during the molding process of polyester films, fibers, containers, etc., but not limited to these.

[0050] In addition, the number of carbon atoms in an alcohol can be 4 or more, 6 or more, 8 or more, 10 or more, or 12 or more, and can also be 4 to 14, 4 to 13, 4 to 10, 4 to 8, 6 to 12, 8 to 14, or 8 to 13.

[0051] Since the alcoholysis of waste polyester uses alcohols with the aforementioned number of carbon atoms, it can be carried out at lower temperatures and pressures compared to traditional processes using waste polyester that operate under high temperature and pressure. Furthermore, it can produce intermediates, i.e., the alcoholysis products, in liquid form. Additionally, when the number of carbon atoms in the alcohol meets the aforementioned range, the alcoholysis reaction rate can be increased.

[0052] Furthermore, the boiling points of alcohols can range from 100°C to 290°C. For example, the boiling points of alcohols can 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 an alcohol falls within the above range, ethylene glycol, which is formed as a byproduct during alcoholysis, can be more easily removed or recovered in subsequent processes, thereby further improving processability. In particular, in recent years, the use of various monomer materials has become a trend in the field of polyester as raw material; therefore, it can be conveniently used to remove various glycol-type monomers used in waste polyester products, such as waste plastic products.

[0053] The weight ratio of waste polyester to alcohol can be from 1:1 to 10. For example, the weight ratio of waste polyester to alcohol can be from 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 1:2 to 3.5.

[0054] Furthermore, the alcoholysis reaction can be carried out at temperatures ranging from 160°C to 280°C and pressures ranging from 1 bar to 40 bar for 0.5 hours to 24 hours. For example, the alcoholysis reaction can be carried out at temperatures ranging from 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, or 245°C to 260°C, and at pressures ranging from 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 to 30 bar, for durations ranging from 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.

[0055] In step (1), an alcoholysis catalyst can be added. Specifically, the alcoholysis reaction can proceed smoothly as a non-catalytic reaction without the use of an alcoholysis catalyst, making it environmentally friendly. In particular, when the content of insoluble metals in waste polyester is high, the non-catalytic reaction may be beneficial for the effective treatment and removal of impurities. In addition, from an energy perspective, the addition of an alcoholysis catalyst in step (1) can enhance processability by increasing the reactivity.

[0056] The alcoholysis catalyst can be a metal acetate, alkali metal salt, or hydroxyl salt.

[0057] More specifically, the alcoholysis catalyst may contain at least one cation selected from alkali metal ions such as Li. + Na + K + and Cs + Alkaline earth metal ions such as Be 2+ Mg 2+ Ca 2+ and Ba 2+ Ammonium ions, such as NH4+ 4+ and NR 4+ (where R is an alkyl group), and Zn 2+ The group consists of; or contains at least one anion selected from OH-. - OR - (where R is an alkyl group), HCO3 - CO3 2- Benzoate ions (C7H5O2) -The group consisting of 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion. R can be an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 5 carbon atoms.

[0058] For example, the alcoholysis catalyst may include at least one selected from the group consisting of Zn(OAC)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Zn(OAC)2·2H2O, Co(OAc)2·4H2O, Pb(OAc)2, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Pd(OAc)2, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, di-n-butyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid.

[0059] Furthermore, the amount of alcoholysis catalyst added can be from 10 ppm to 10,000 ppm, depending on the total weight of the waste polyester. For example, the amount of alcoholysis catalyst added can be 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 to 1,000 ppm, 180 ppm to 500 ppm, or 200 ppm to 450 ppm, depending on the total weight of the waste polyester.

[0060] According to one embodiment of the invention, a liquid composition comprising the compound shown in Formula 1 is prepared by alcoholysis. Specifically, the composition is liquid at room temperature, and the liquid composition is produced by an alcoholysis reaction.

[0061] The liquid composition comprises a compound represented by Formula 1.

[0062] [Formula 1]

[0063]

[0064] In Formula 1, R1 is an alkyl group having four or more carbon atoms.

[0065] Specifically, R1 can be butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methylbutyl, 1-ethylbutyl, 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-ethylpropyl, 1,1-dimethylpropyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, decyl, undecyl, dodecyl, tridecyl, or tetradecyl.

[0066] Specifically, the liquid composition may comprise unreacted alcohol and ethylene glycol (EG) as a byproduct. More specifically, the liquid composition may comprise the compound represented by Formula 1, ethylene glycol (EG) formed as a byproduct through alcoholysis, unreacted alcohol, and oligomers.

[0067] For example, the liquid composition may contain the compound shown in Formula 2, and the oligomer may contain the compound shown in Formula 3.

[0068] [Equation 2]

[0069]

[0070] [Formula 3]

[0071]

[0072] In Formulas 2 and 3, R1 is an alkyl group having 4 or more carbon atoms, and n is an integer of 1 or greater.

[0073] According to one embodiment of the invention, the liquid composition may comprise unreacted alcohol and ethylene glycol as a byproduct, and the content of the compound represented by Formula 1 in the liquid composition may be 70 mol% or higher. For example, the content of the compound represented by Formula 1 in a liquid composition prepared by alcoholysis may be 72 mol% or higher, 75 mol% or higher, 80 mol% or higher, 85 mol% or higher, 90 mol% or higher, 91 mol% or higher, 92 mol% or higher, 92.5 mol% or higher, 93 mol% or higher, 95 mol% or higher, 97 mol% or higher, 99 mol% or higher, or 99.5 mol% or higher.

[0074] Furthermore, the content of oligomers in the liquid composition may be 15 mol% or less. For example, the content of oligomers in the liquid composition may be 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 0.1 mol% or less.

[0075] According to another embodiment of the invention, step (1) may include discharging unreacted alcohols and ethylene glycols as byproducts.

[0076] Specifically, the alcohol is separated from the discharged mixture of alcohol and ethylene glycol, and the separated alcohol can be recycled as feedstock for alcoholysis. For example, the byproduct ethylene glycol formed during alcoholysis and the unreacted alcohol (excess alcohol) are discharged in real time as a gaseous mixture during the alcoholysis reaction for fractionation or layer separation, and / or fractionation after the reaction to separate them into alcohol and ethylene glycol. The separated alcohol can be reintroduced into the alcoholysis of step (1) and reused. In this case, the volume and feed rate of the alcohol introduced for reuse can be the same as the volume and discharge rate of the discharged mixture of alcohol and ethylene glycol.

[0077] Furthermore, step (1) may include recovering ethylene glycol as a byproduct of alcoholysis. Specifically, ethylene glycol as a byproduct of alcoholysis can be recovered by fractionation or layer separation of the discharged alcohol and ethylene glycol mixture, and can also be recovered by fractionation or layer separation of the composition prepared in step (1).

[0078] For example, during the alcoholysis reaction, unreacted alcohol and the byproduct ethylene glycol are discharged as a gaseous mixture in real time, which is then condensed using an external cooling device to recover the ethylene glycol.

[0079] According to one embodiment of the invention, not only can unreacted alcohols and ethylene glycol be separated by simple processes such as fractionation or layer separation, but the separated unreacted alcohols can also be recycled as feedstock for alcoholysis, and the recovered ethylene glycol can be used in other processes. Therefore, both processability and processing cost reduction are excellent.

[0080] Ethylene glycol recovery rates can reach 65% or higher. For example, ethylene glycol recovery rates can be 70% or higher, 76% or higher, 85% or higher, 90% or higher, 93% or higher, 95% or higher, 97% or higher, 98% or higher, 99% or higher, or 99.5% or higher.

[0081] Purification steps

[0082] According to another embodiment of the present invention, the process for preparing terephthalic acid may further include purification of the liquid composition prior to step (2).

[0083] Specifically, the purification step may include adding an adsorbent selected from the group consisting of activated carbon, silica gel, alumina, zeolite, and activated clay, or adsorption via 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 thereto.

[0084] The content of the added adsorbent can be from 0.1 wt% to 20 wt% based on the total weight of the liquid composition. For example, the content of the added adsorbent can be from 0.1 wt% to 18 wt%, 0.1 wt% to 15 wt%, 0.1 wt% to 10 wt%, 0.1 wt% to 5 wt%, or 0.1 wt% to 2 wt% based on the total weight of the liquid composition.

[0085] As the purification of the liquid composition using an adsorbent continues, particularly with the use of an adsorbent at a specific feed amount within the aforementioned numerical range, purity and yield can be further improved. Specifically, as the purification of the liquid composition (which is an alcoholysis composition) proceeds, insoluble impurities, such as metals that may be present in the alcoholysis composition, or additives that may be present in the waste polyester, such as colorants and pigments, can be removed more effectively. Therefore, the purity and yield of the finally prepared terephthalic acid can be further improved.

[0086] Furthermore, according to another embodiment of the present invention, the process for preparing terephthalic acid may further include a concentration step after the purification step.

[0087] Concentration can be carried out at temperatures ranging from 50°C to 120°C for 0.5 to 6 hours. For example, concentration can be carried out at temperatures ranging from 55°C to 115°C, 60°C to 110°C, 65°C to 105°C, or 75°C to 100°C, by stirring the purified alcoholysis composition for 1 to 5 hours, 1.5 to 4 hours, or 2 to 4 hours.

[0088] According to one embodiment of the invention, the purified composition may have a pigment residue rate (%) of 15% or less, according to Equation A. For example, according to Equation A, the pigment residue rate (%) of the purified alcoholysis composition may be 13% or less, 11% or less, 10% or less, 8% or less, 6% or less, 5.5% or less, 5% or less, 4.3% or less, or 4% or less.

[0089] [Equation A]

[0090]

[0091] In equation A,

[0092] A1 is the area of ​​the absorbance curve obtained using a UV-Vis spectrophotometer in the wavelength range of 400 nm to 800 nm for a purified alcoholysis reaction composition diluted to a concentration of 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP), and A2 is the area of ​​the absorbance curve obtained in the same manner for an unpurified alcoholysis reaction composition.

[0093] The explanation of purification in Equation A is as described above.

[0094] Pigment residue rate refers to the content of residual colorants, pigments, dyes, and other additives in a composition. The lower the pigment residue rate, the lower the content of colorants, pigments, dyes, and other additives, and the higher the purity.

[0095] Furthermore, the purified composition may contain fewer insoluble impurities, such as metals. Specifically, when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the total metal content of the purified liquid composition relative to the total weight of the purified alcoholysis composition may be 100 ppm or less.

[0096] For example, the purified alcoholysis composition may contain insoluble impurities, such as metals. When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the total metal content in the purified alcoholysis composition relative to its total weight 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. In particular, the total content of Sb, Ti, and Zn in the purified alcoholysis composition may be less than 30 ppm, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less.

[0097] Sb is widely used as a catalyst in common polyester polymerization due to its excellent stability, reaction rate, and cost. However, due to the increasing regulations on Sb's impact on human health and the environment, it is a substance that must be removed during chemical recycling.

[0098] In addition, Ti can be used as a catalyst for polyester polymerization or as an additive in polyester processing in the form of TiO2. If it contains a certain amount or more, the quality of the recycled terephthalic acid prepared from it or the polyester resin using it may decrease, thus limiting its use.

[0099] Zinc (Zn) is also a component of the polymerization catalyst used in polyesters, such as PET. If it remains, it may affect the reactivity control in the preparation of recycled terephthalic acid or polyester resins using it. Therefore, it is best to remove it. In particular, because it is widely used in chemical recycling processes, it is necessary to thoroughly remove this substance from waste plastics (which are the raw materials for this process) and from its separate addition as a catalyst in the recycling process.

[0100] According to one embodiment of the invention, as purification proceeds further, the total content of metals in the purified alcoholysis composition, particularly the total content of Sb, Ti and Zn as described above, is very low, at 30 ppm or less.

[0101] For example, when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the Sb content relative to the total weight of the purified alcoholysis composition can be 30 ppm or less, 20 ppm or less, 10 ppm or less, or 1 ppm or less.

[0102] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the Ti content relative to the total weight of the purified alcoholysis composition can be 30 ppm or less, 20 ppm or less, 10 ppm or less, or 1 ppm or less.

[0103] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the Zn content relative to the total weight of the purified alcoholysis composition can be 30 ppm or less, 20 ppm or less, 10 ppm or less, or 1 ppm or less.

[0104] Hydrolysis reaction step (2)

[0105] According to one embodiment of the present invention, the process for preparing terephthalic acid includes hydrolyzing the composition. Specifically, in step (2), the alcoholysis composition (a liquid composition comprising the compound shown in Formula 1) or the purified alcoholysis composition prepared in step (1) may be hydrolyzed to prepare recovered terephthalic acid.

[0106] Hydrolysis can be carried out by adding water to the composition. For example, hydrolysis can be carried out by adding water to the alcoholysis composition or purified alcoholysis composition at temperatures of 180°C to 280°C, 185°C to 280°C, 200°C to 275°C, 220°C to 270°C, or 240°C to 265°C for 0.5 hours to 24 hours, 1 hour to 20 hours, 2.5 hours to 12 hours, or 3 hours to 8 hours.

[0107] Traditional methods involve adding metal catalysts, such as iron, cobalt, manganese, or nickel, to waste polyester, followed by direct hydrolysis with water. This method is very environmentally friendly. However, it suffers from low processability due to the need for high-temperature conditions of 300°C or higher and the requirement for high-pressure-resistant reaction equipment. In contrast, according to one embodiment of the present invention, the process for preparing terephthalic acid offers improved process conditions compared to existing technologies, thus exhibiting excellent processability.

[0108] Furthermore, the weight ratio of the composition to water can be from 1:1 to 500. For example, in hydrolysis, the weight ratio of the alcoholysis composition (purified or concentrated alcoholysis composition) to water can be from 1:1 to 450, 1:1 to 400, 1:1 to 250, 1:1 to 100, 1:1 to 50, 1:1.2 to 20, or 1:1.5 to 10.

[0109] In addition, a hydrolysis catalyst may be added in step (2). Specifically, the hydrolysis catalyst may be added to the mixture of the alcoholysis reaction composition and water to carry out hydrolysis.

[0110] Hydrolysis can proceed smoothly as a non-catalytic reaction without the need for a hydrolysis catalyst, making it environmentally friendly. In particular, when the content of insoluble metals in waste polyester is high, non-catalytic reactions may be beneficial for the effective treatment and removal of impurities. Furthermore, from an energy perspective, a hydrolysis catalyst can be added in step (2) to enhance processability by increasing the reactivity.

[0111] Hydrolysis catalysts can be metal acetates, alkali metal salts, or hydroxyl salts.

[0112] More specifically, the hydrolysis catalyst may contain at least one cation selected from alkali metal ions such as Li. + Na + K + and Cs + Alkaline earth metal ions such as Be 2+ Mg 2+ Ca 2+ and Ba 2+ Ammonium ions, such as NH4+ 4+ and NR 4+ (where R is an alkyl group), and Zn 2+ The group consists of; or contains at least one anion selected from OH-. - OR - (where R is an alkyl group), HCO3 - CO3 2- Benzoate ions (C7H5O2) -The group consisting of 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion. R can be an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 5 carbon atoms.

[0113] For example, the hydrolysis catalyst may include at least one selected from the group consisting of Zn(OAC)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Zn(OAC)2·2H2O, Co(OAc)2·4H2O, Pb(OAc)2, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Pd(OAc)2, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, di-n-butyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid.

[0114] Additionally, the amount of hydrolysis catalyst added can be from 10 ppm to 10,000 ppm, based on the total weight of the composition. For example, based on the total weight of the alcoholysis composition (purified or purified concentrated alcoholysis composition), the amount of hydrolysis catalyst added can be 15 ppm to 8,000 ppm, 20 ppm to 5,500 ppm, 30 ppm to 3,000 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.

[0115] According to one embodiment of the present invention, solid terephthalic acid can be prepared by a hydrolysis reaction. Specifically, the process may further include filtering, washing, and drying the hydrolysis product prepared by the hydrolysis reaction after the hydrolysis step. That is, solid terephthalic acid can be generated from the hydrolysis product prepared by the hydrolysis reaction after filtration, washing, and drying.

[0116] For example, the hydrolysis product can be cooled to a suitable temperature, such as from room temperature to below 100°C where water does not evaporate, to obtain a slurry solution. After filtration, a solid is obtained, which is then washed and vacuum dried to obtain solid terephthalic acid.

[0117] Washing can be performed using alcohols and / or water having four or more carbon atoms, protic solvents such as isopropanol and acetic acid, or non-protic solvents such as acetone, dichloromethane, chloroform, tetrahydrofuran (THF), and toluene.

[0118] Here, the description of alcohols having four or more carbon atoms is as described above. The alcohol with four or more carbon atoms used in the washing process can be the same as or different from the alcohol with four or more carbon atoms used in step (1). For example, when 1-butanol is used as the alcohol in step (1) to produce terephthalic acid, the prepared solid terephthalic acid can be washed with a mixture of 1-butanol and water. Furthermore, the number of carbon atoms in the alcohol used in the washing process can be the same as the number of carbon atoms in the alcohol used in step (1).

[0119] Washing effectively removes residual pigments or impurities produced during pigment hydrolysis, especially yellow impurities, thereby enhancing the yellow index or color characteristics. Furthermore, the use of water for washing removes mineral salts, thus improving quality.

[0120] Furthermore, the yield of terephthalic acid can be 65% or higher. For example, the final yield of regenerated terephthalic acid can be 68% or higher, 70% or higher, 75% or higher, 80% or higher, 85% or higher, 90% or higher, or 95% or higher.

[0121] Recycled terephthalic acid

[0122] According to another embodiment of the invention, the recovered terephthalic acid is prepared according to the process for preparing terephthalic acid described above, and its total metal content is less than 100 ppm when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0123] Specifically, the recovered terephthalic acid can be prepared according to the process used to prepare terephthalic acid.

[0124] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the total metal content of the recovered terephthalic acid can be less than 100 ppm, 90 ppm or lower, 80 ppm or lower, 65 ppm or lower, 50 ppm or lower, 35 ppm or lower, less than 30 ppm, 15 ppm or lower, 9 ppm or lower, 7 ppm or lower, 5 ppm or lower, or 1 ppm or lower.

[0125] Furthermore, when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the total content of Sb, Ti, and Zn in the recovered terephthalic acid can be less than 30 ppm. For example, the total content of Sb, Ti, and Zn in the recovered terephthalic acid may be harmful to human health, or may contain catalysts that can act as reactants or side reactions in subsequent polymerization processes, and its content may be 25 ppm or lower, 20 ppm or lower, 15 ppm or lower, 10 ppm or lower, 5 ppm or lower, 3 ppm or lower, or 1 ppm or lower.

[0126] For example, when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the Sb content in the recovered terephthalic acid may be 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less, relative to the total weight of the recovered terephthalic acid.

[0127] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the Ti content in the recovered terephthalic acid can be 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less, relative to the total weight of the recovered terephthalic acid.

[0128] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the Zn content in the recovered terephthalic acid can be 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less, relative to the total weight of the recovered terephthalic acid.

[0129] When measured with a colorimeter, the colorimetric value -b of the recovered terephthalic acid can be less than 2, 1.6 or lower, 1.4 or lower, 1.3 or lower, or 1 or lower. Since the above colorimetric value range corresponds to the colorimetric value range of virgin terephthalic acid typically produced in petrochemical processes, the recovered terephthalic acid meeting these colorimetric value ranges not only has a low yellow index but also exhibits excellent quality due to its high monomer purity.

[0130] Chromaticity-b (Col-b) is a color coordinate system defined by the International Commission on Illumination (CIE), where color is represented by L (luminance), a (complementary color from green to red), and b (complementary color from yellow to blue). It can be measured using a colorimeter.

[0131] Furthermore, according to Equation B, the residual pigment content of the recovered terephthalic acid can be 10% or less. For example, the residual pigment content of the recovered terephthalic acid can be 10% or less, 8% or less, 7% or less, 5% or less, or 4% or less.

[0132] [Equation B]

[0133]

[0134] In equation B,

[0135] B1 is the area of ​​the absorbance curve obtained using a UV-Vis spectrophotometer in the wavelength range of 400 nm to 800 nm for recovered terephthalic acid diluted to a 5% concentration in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP); and B2 is the area of ​​the absorbance curve obtained in the same manner for recovered terephthalic acid that was not purified during its preparation.

[0136] In the preparation of recovered terephthalic acid, B1 can be measured on the recovered terephthalic acid produced through a purification step or a purification and concentration step. In the preparation of recovered terephthalic acid, B2 can be measured on the recovered terephthalic acid produced without a purification step or with only a concentration step.

[0137] Furthermore, when the recovered terephthalic acid is diluted to a concentration of 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP) and measured, the yellow index (YI) can be less than 2, 1.8, or lower, or 1.7 or lower. During the preparation of the recovered terephthalic acid, the yellow index can be measured for the recovered terephthalic acid produced through a purification step or a purification and concentration step.

[0138] Polyester resin and its preparation process

[0139] According to another embodiment of the invention, the polyester resin comprises recycled terephthalic acid.

[0140] Specifically, the polyester resin may include recycled terephthalic acid, diol compounds or derivatives thereof, and optionally dicarboxylic acid compounds or derivatives thereof.

[0141] For example, the diol component or its derivative may include at least one selected from the group consisting of ethylene glycol, monoethylene glycol, diethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,4-cyclohexanediol, and neopentyl glycol. The dicarboxylic acid component or its derivative may include at least one selected from the group consisting of terephthalic acid (TPA), isophthalic acid (IPA), 2,6-naphthalenedicarboxylic acid (2,6-NDA), dimethyl terephthalate (DMT), dimethyl isophthalate (DMI), and dimethyl 2,6-naphthalenedicarboxylic acid (2,6-NDC). However, they are not limited thereto.

[0142] According to another embodiment of the present invention, the process for preparing the polyester resin includes mixing recycled terephthalic acid with a diol compound or a derivative thereof and optionally a dicarboxylic acid compound or a derivative thereof, and then carrying out an esterification reaction; and subjecting the esterification reaction product to a polycondensation reaction.

[0143] Esterification reactions can be carried out at temperatures ranging from 200°C to 350°C, 220°C to 320°C, or 250°C to 290°C. Furthermore, esterification reactions can be carried out under pressure exceeding normal levels, up to 0 kg / cm². 2 Up to 10kg / cm 2 (0 mmHg to 7,355.6 mmHg), 0 kg / cm 2 Up to 5kg / cm 2 (0 mmHg to 3,677.8 mmHg) or 0 kg / cm 2 Up to 2.0 kg / cm 2 (0 mmHg to 1,471.1 mmHg). For example, esterification reactions can be carried out for 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 6 hours, but are not limited to these.

[0144] Furthermore, the polycondensation reaction can be carried out at temperatures ranging from 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 can be carried out under reduced pressures of 0.01 mmHg to 400 mmHg, 0.05 mmHg to 100 mmHg, or 0.1 mmHg to 100 mmHg. Moreover, the polycondensation reaction can be carried out for the desired time until the desired intrinsic viscosity is reached. For example, it can be carried out for 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 4 hours.

[0145] In addition, catalysts and / or stabilizers can be added during esterification and polycondensation reactions.

[0146] For example, catalysts for esterification reactions can be sodium and magnesium formates; acetates, borates, fatty acid salts, and carbonates of zinc (Zn), cadmium (Cd), manganese (Mn), cobalt (Co), calcium (Ca), and barium (Ba); as well as metallic magnesium (Mg); and oxides of lead (Pb), Zn, antimony (Sb), and germanium (Ge).

[0147] In addition, the catalysts for the polycondensation reaction can be, for example, titanium-based catalysts such as tetraethyl titanate, tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, 2-ethylhexyl titanate, octyl glycol titanate, lactate titanate, triethanolamine titanate, acetylacetone titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, titanium dioxide / silica copolymer, titanium dioxide / zirconium dioxide copolymer; germanium-based catalysts such as germanium dioxide and copolymers using germanium dioxide; or tin-based catalysts such as butyltin oxide, dibutyltin oxide, and butyltin hydroxyoxide.

[0148] In addition, stabilizers can be phosphorus-based compounds, such as phosphoric acid, trimethyl phosphate, and triethyl phosphate, but are not limited to these.

[0149] According to another embodiment of the invention, the process for preparing the polyester resin may further include carrying out a solid-state polymerization reaction. For example, solid-state polymerization may be carried out at a temperature of 190°C to 230°C under vacuum conditions of 0.2 Torr to 2.0 Torr or in a nitrogen atmosphere after the polycondensation reaction.

[0150] Invention Model

[0151] The present invention will now be described in more detail with reference to the following embodiments. However, these embodiments are for illustrative purposes only, and the scope of the invention is not limited thereto.

[0152] [Example]

[0153] Preparation of liquid compositions

[0154] Example 1-1

[0155] 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as an alcohol were loaded into a first high-pressure reactor with a capacity of 7 liters. Then, 200 mg of Zn(OAC)2·2H2O was added as an alcoholysis catalyst (200 ppm relative to the total weight of waste PET).

[0156] Then, tighten and seal all connections of the first high-pressure reactor, raise the temperature to 250°C within 1 hour, and carry out the alcoholysis reaction for 3 hours with stirring, while maintaining the temperature at 250°C and the pressure at 24 bar.

[0157] After the alcoholysis reaction was completed, the mixture was cooled to room temperature to obtain a liquid alcoholysis composition. The components and contents of the alcoholysis composition were analyzed by nuclear magnetic resonance (NMR). The alcoholysis composition contained the compound represented by Formula 1 (R1: (CH2)3CH3), residual ethylene glycol (EG), an alcohol (1-butanol), and oligomers.

[0158] Subsequently, the alcoholysis reaction composition was placed in a separate flask, and the excess unreacted 1-butanol and the produced ethylene glycol (EG) were recovered separately using a fractionation apparatus.

[0159] [Formula 1]

[0160]

[0161] Examples 1-2

[0162] 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as an alcohol were loaded into a first high-pressure reactor with a capacity of 7 liters. Then, 200 mg of Zn(OAC)2·2H2O was added as an alcoholysis catalyst (200 ppm relative to the total weight of waste PET).

[0163] Then, tighten and seal all connections of the first high-pressure reactor, raise the temperature to 250°C within 1 hour, and carry out the alcoholysis reaction for 3 hours with stirring, while maintaining the temperature at 250°C and the pressure at 24 bar.

[0164] Specifically, one hour after the start of the alcoholysis reaction, the valve of the pre-installed back pressure regulator is adjusted to discharge the gaseous mixture of ethylene glycol (EG), a byproduct of the alcoholysis reaction, and excess 1-butanol present in the reactor. In this case, the internal temperature of the first high-pressure reactor is maintained at 250°C, and the gaseous mixture of ethylene glycol (EG) and 1-butanol discharged through the back pressure regulator is condensed using an external cooling device. Furthermore, the discharge rate of the ethylene glycol (EG) and 1-butanol gaseous mixture is adjusted to 3 kg / h, while 1-butanol is continuously fed into the first high-pressure reactor. In this case, the volume and feed rate of the newly supplied 1-butanol to the first high-pressure reactor are adjusted to be the same as the volume and discharge rate of the discharged ethylene glycol (EG) and 1-butanol gaseous mixture. The alcoholysis reaction is carried out while the discharge and feed processes are maintained for 3 hours.

[0165] After the alcoholysis reaction was completed, the mixture was cooled to room temperature to obtain a liquid alcoholysis composition. The components and contents of the alcoholysis composition were analyzed by nuclear magnetic resonance (NMR). The alcoholysis composition contained the compound represented by Formula 1 (R1: (CH2)3CH3), residual ethylene glycol (EG), an alcohol (1-butanol), and oligomers.

[0166] The alcoholysis reaction composition was then placed in a separate flask, and the excess unreacted 1-butanol and the produced ethylene glycol were recovered separately using a fractionation apparatus.

[0167] [Formula 1]

[0168]

[0169] Examples 1-3

[0170] 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as an alcohol were loaded into a first high-pressure reactor with a capacity of 7 liters. Then, 200 mg of Zn(OAC)2·2H2O was added as an alcoholysis catalyst (200 ppm relative to the total weight of waste PET).

[0171] Then, tighten and seal all connections of the first high-pressure reactor, raise the temperature to 250°C within 1 hour, and carry out the alcoholysis reaction for 3 hours with stirring, while maintaining the temperature at 250°C and the pressure at 24 bar.

[0172] Specifically, one hour after the start of the alcoholysis reaction, the valve of the pre-installed back pressure regulator is adjusted to discharge the gaseous mixture of ethylene glycol (EG), a byproduct of the alcoholysis reaction, and excess 1-butanol present in the reactor. In this case, the internal temperature of the first high-pressure reactor is maintained at 250°C, and the gaseous mixture of ethylene glycol (EG) and 1-butanol discharged through the back pressure regulator is condensed using an external cooling device. Furthermore, the discharge rate of the gaseous mixture of ethylene glycol (EG) and 1-butanol is adjusted to 3 kg / h, while 1-butanol is continuously supplied to the first high-pressure reactor. In this case, the volume and feed rate of the newly supplied 1-butanol to the first high-pressure reactor are adjusted to be the same as the volume and discharge rate of the discharged gaseous mixture of ethylene glycol (EG) and 1-butanol.

[0173] The condensed gas mixture of ethylene glycol (EG) and 1-butanol was transferred to a 5-liter layer separator filled with 3 kg of water. The process of stirring for 10 minutes and separating the layers for 2 minutes was repeated to separate the 1-butanol layer from the water and ethylene glycol (EG) layers. The separated 1-butanol was then pumped back into the first high-pressure reactor in real time using a high-pressure pump. The alcoholysis reaction was then carried out while maintaining stirring, layer separation, and reintroduction for 3 hours.

[0174] After the alcoholysis reaction was completed, the mixture was cooled to room temperature to obtain a liquid alcoholysis composition. The components and contents of the alcoholysis composition were analyzed by nuclear magnetic resonance (NMR). The alcoholysis composition contained the compound represented by Formula 1 (R1: (CH2)3CH3), residual ethylene glycol (EG), an alcohol (1-butanol), and oligomers.

[0175] The alcoholysis reaction composition was then placed in a separate flask, and the excess unreacted 1-butanol and the produced ethylene glycol were recovered separately using a fractionation apparatus.

[0176] [Formula 1]

[0177]

[0178] Examples 1-4

[0179] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-1, except that 3.3 kg of 1-pentanol was used as the alcohol and the pressure was maintained at 13 bar.

[0180] Examples 1-5

[0181] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-2, except that 3.3 kg of 1-pentanol was used as the alcohol and the pressure was maintained at 13 bar.

[0182] Examples 1-6

[0183] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-3, except that 3.3 kg of 1-pentanol was used as the alcohol and the pressure was maintained at 13 bar.

[0184] Examples 1-7

[0185] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-1, except that 3.3 kg of 1-octanol was used as the alcohol and the pressure was maintained at 3.4 bar.

[0186] Examples 1-8

[0187] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-2, except that 3.3 kg of 1-octanol was used as the alcohol and the pressure was maintained at 3.4 bar.

[0188] Examples 1-9

[0189] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-3, except that 3.3 kg of 1-octanol was used as the alcohol and the pressure was maintained at 3.4 bar.

[0190] Examples 1-10

[0191] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-1, except that 3.3 kg of 2-ethyl-1-hexanol was used as the alcohol and the pressure was maintained at 4.1 bar.

[0192] Examples 1-11

[0193] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-2, except that 3.3 kg of 2-ethyl-1-hexanol was used as the alcohol and the pressure was maintained at 4.1 bar.

[0194] Examples 1-12

[0195] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-3, except that 3.3 kg of 2-ethyl-1-hexanol was used as the alcohol and the pressure was maintained at 4.1 bar.

[0196] Examples 1-13

[0197] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-1, except that 3.3 kg of 1-decyl alcohol was used as the alcohol and the pressure was maintained at 1.6 bar.

[0198] Examples 1-14

[0199] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-2, except that 3.3 kg of 1-decyl alcohol was used as the alcohol and the pressure was maintained at 1.6 bar.

[0200] Examples 1-15

[0201] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-3, except that 3.3 kg of 1-decyl alcohol was used as the alcohol and the pressure was maintained at 1.6 bar.

[0202] Examples 1-16

[0203] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-1, except that 3.3 kg of 1-decyl alcohol was used as the alcohol and the pressure was maintained at 1.0 bar.

[0204] Examples 1-17

[0205] 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-dodecanoic acid as an alcohol were loaded into a first high-pressure reactor with a capacity of 7 liters. Then, 200 mg of Zn(OAC)2·2H2O was added as an alcoholysis catalyst (200 ppm relative to the total weight of waste PET).

[0206] Then, tighten and seal all connections of the first high-pressure reactor, raise the temperature to 250°C within 1 hour, and carry out alcoholysis reaction for 3 hours with stirring, while maintaining a temperature of 250°C and a pressure of 1 bar.

[0207] Specifically, one hour after the start of the alcoholysis reaction, the valve of the pre-installed back pressure regulator is adjusted to release the vapor of ethylene glycol (EG), a byproduct of the alcoholysis reaction. In this case, the internal temperature of the first high-pressure reactor is maintained at 250°C, and the ethylene glycol (EG) vapor is condensed using an external cooling device.

[0208] In addition, 1-dodecyl alcohol is continuously supplied to the first high-pressure reactor in an amount equivalent to the amount of ethylene glycol (EG) discharged and condensed in vapor form. In this case, the volume and feed rate of the newly supplied 1-dodecyl alcohol to the first high-pressure reactor are adjusted to match the volume and discharge rate of the discharged ethylene glycol (EG) vapor. The alcoholysis reaction is carried out while the feed and discharge processes are maintained for 3 hours.

[0209] After the alcoholysis reaction was completed, the mixture was cooled to room temperature to obtain a liquid alcoholysis composition. The components and contents of the alcoholysis composition were analyzed by nuclear magnetic resonance. The alcoholysis composition contained the compound represented by Formula 1 (R1: (CH2)). 11 CH3), residual ethylene glycol (EG), alcohol (1-dodecyl alcohol), and oligomers.

[0210] Subsequently, the alcoholysis reaction composition was placed in a separate flask, and the excess unreacted 1-dodecyl alcohol and the produced ethylene glycol (EG) were recovered separately using a fractionation apparatus.

[0211] [Formula 1]

[0212]

[0213] Examples 1-18

[0214] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-1, except that 3.3 kg of 1-tetradecaneol was used as the alcohol and the pressure was maintained at 1.0 bar.

[0215] Examples 1-19

[0216] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-17, except that 3.3 kg of 1-tetradecyl alcohol was used as the alcohol.

[0217] Comparative Example 1-1

[0218] The liquid alcoholysis composition was prepared in the same manner as in Examples 1-1, except that 3.3 kg of methanol was used as the alcohol and the pressure was maintained at 83 bar.

[0219] Comparative Examples 1-2

[0220] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-2, except that 3.3 kg of methanol was used as the alcohol and the pressure was maintained at 83 bar.

[0221] Comparative Examples 1-3

[0222] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-1, except that 3.3 kg of ethanol was used as the alcohol and the pressure was maintained at 64 bar.

[0223] Comparative Examples 1-4

[0224] The liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-2, except that 3.3 kg of ethanol was used as the alcohol and the pressure was maintained at 64 bar.

[0225] [Table 1]

[0226]

[0227] As can be seen from Table 1 above, since the liquid alcoholysis compositions of Examples 1-1 to 1-19 are prepared using alcohols having four or more carbon atoms, they can be prepared under very low process pressures compared to Comparative Examples 1-1 to 1-4. The compounds shown in Formula 1 have high content, i.e., high yield and high purity, and the recovery rate of ethylene glycol is also high.

[0228] Purification and concentration of liquid compositions

[0229] Example 2-1

[0230] In Example 1-1, before recovering excess unreacted alcohol and produced ethylene glycol using the fractionation equipment, 0.1 g of activated carbon as an adsorbent was added to 100 g of liquid alcoholysis reaction composition, which was then purified, stirred at 100°C for 3 hours, and then filtered to concentrate the alcoholysis reaction composition.

[0231] Examples 2-2 to 2-23, and Comparative Examples 2-1 and 2-2

[0232] The purification and concentration of the liquid alcoholysis reaction composition were performed in the same manner as in Example 2-1, but the changes in the liquid composition and process conditions are shown in Table 2 below. Here, in Comparative Examples 2-1 and 2-2, it precipitated in an undissolved state and was not purified.

[0233] Examples 2-24 to 2-26

[0234] In each of Examples 1-1, 1-4, and 1-10, after recovering excess unreacted alcohol and produced ethylene glycol using a fractionation apparatus, 0.1 g of activated carbon as an adsorbent is added to 100 g of liquid alcoholysis reaction composition, which is then purified, stirred at 100°C for 3 hours, and then filtered to concentrate the alcoholysis reaction composition.

[0235] Comparative Examples 2-3 to 2-21

[0236] In each of Examples 1-1 to 1-19, no adsorbent is added to the liquid alcoholysis composition before using a fractionation apparatus to recover excess unreacted alcohol and the produced ethylene glycol. The mixture is stirred at 100°C for 3 hours and then concentrated by filtration.

[0237] Test Example 1-1: Pigment Residue Rate

[0238] The pigment residue rate (%) of the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21 was measured respectively.

[0239] Specifically, the compositions of Examples 2-1 were diluted to 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP), respectively, and the areas of the absorbance curves (A1) in the range of 400 nm to 800 nm were obtained using a UV-Vis spectrophotometer. Furthermore, for the compositions of Comparative Examples 2-3 (the compositions of Examples 1-1 were used in the same manner as those of Examples 2-1, but without purification and concentration by adding an adsorbent), the areas of the absorbance curves (A2) in the range of 400 nm to 800 nm were obtained in the same manner as described above. The pigment residue rate (%) was calculated based on the measured areas of the absorbance curves according to the following equation A.

[0240] [Equation A]

[0241]

[0242] The pigment residue rate (%) of the compositions of Examples 2-2 to 2-26 and Comparative Examples 2-1 to 2-21 was measured in the same manner as described above.

[0243] Test Example 1-2: Yellow Index

[0244] The yellow index (YI) of the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21 was measured respectively.

[0245] Specifically, the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21 were diluted to a concentration of 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP), respectively, and then the yellow index was measured using a ColorFlex EZ instrument (manufacturer: HunterLab).

[0246] Test Examples 1-3: Metal Content

[0247] The metal content (ppm) in each composition of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21 was measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). ND indicates that the content was too low, less than one part per million (1 ppm), to be measured.

[0248] [Table 2]

[0249]

[0250]

[0251] As can be seen from Table 2 above, the purified and concentrated alcoholysis reaction compositions of Examples 2-1 to 2-26 have very low pigment residue rates and very low contents of metals such as Sb, Ti and Zn.

[0252] Preparation of terephthalic acid

[0253] Example 3-1

[0254] 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 with a capacity of 600 ml. Then 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added to it.

[0255] The temperature of the second high-pressure reactor was then raised to 260°C, and the hydrolysis reaction was carried out at 260°C for 4 hours. The mixture was then cooled to 90°C to obtain a slurry of the hydrolysis product. The slurry was filtered to obtain a solid, which was washed with butanol and water at 90°C and dried under vacuum to give 53.7 g (yield: 90%) of solid terephthalic acid (TPA).

[0256] Example 3-2

[0257] 100g (0.30 mol) of the purified and concentrated alcoholysis reaction composition of Examples 2-5 and 200g (11.10 mol) of water were added to a second high-pressure reactor with a capacity of 600ml. Then, 50mg of Zn(OAC)2·2H2O (500ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added.

[0258] The temperature of the second high-pressure reactor was then raised to 260°C, and the hydrolysis reaction was carried out at 260°C for 4 hours. The mixture was then cooled to 90°C to obtain a slurry of the hydrolysis product. The slurry was filtered to obtain a solid, which was washed with pentanol and water at 90°C and dried under vacuum to give 43.9 g (yield: 81%) of solid terephthalic acid (TPA).

[0259] Example 3-3

[0260] 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 with a capacity of 600 ml. Then 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added to it.

[0261] The temperature of the second high-pressure reactor was then raised to 260°C, and the hydrolysis reaction was carried out at 260°C for 4 hours. The mixture was then cooled to 90°C to obtain a slurry of the hydrolysis product. The slurry was filtered to obtain a solid, which was washed with 2-ethyl-1-hexanol and water at 90°C and dried under vacuum to give 38.0 g (yield: 88%) of solid terephthalic acid (TPA).

[0262] Examples 3-4

[0263] 35.4 g (yield: 82%) of solid terephthalic acid (TPA) was obtained in the same manner as in Examples 3-3, except that 100 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Examples 2-13 was used.

[0264] Examples 3-5

[0265] 36.7 g (yield: 85%) of solid terephthalic acid (TPA) was obtained in the same manner as in Examples 3-3, except that 100 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Examples 2-14 was used.

[0266] Examples 3-6

[0267] 114 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Examples 2-18 and 200 g (11.10 mol) of water were charged into a second high-pressure reactor with a capacity of 600 ml. Then 57 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added to it.

[0268] The temperature of the second high-pressure reactor was then raised to 260°C, and the hydrolysis reaction was carried out at 260°C for 4 hours. The mixture was then cooled to 90°C to obtain a slurry of the hydrolysis product. The slurry was filtered to obtain a solid, which was washed with decanol and water at 90°C and vacuum dried to give 36.1 g (yield: 85%) of solid terephthalic acid (TPA).

[0269] Examples 3-7

[0270] 54.3 g (yield: 91%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-1, except that no hydrolysis catalyst was added.

[0271] Examples 3-8

[0272] 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 with a capacity of 600 ml. Then 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added to it.

[0273] The temperature of the second high-pressure reactor was then raised to 260°C, and the hydrolysis reaction was carried out at 260°C for 4 hours. The mixture was then cooled to 90°C to obtain a slurry of the hydrolysis product. Acetone was added to the solid obtained by filtering the slurry, and the mixture was stirred at 50°C for 4 hours. The mixture was then filtered, washed with acetone and water at 50°C, and vacuum dried to obtain 55.6 g (yield: 93%) of solid terephthalic acid (TPA).

[0274] Examples 3-9

[0275] 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 with a capacity of 600 ml. Then 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the purified and concentrated alcoholysis reaction composition) was added to it.

[0276] The temperature of the second high-pressure reactor was then raised to 260°C, and the hydrolysis reaction was carried out at 260°C for 4 hours. The mixture was then cooled to 90°C to obtain a slurry of the hydrolysis product. Butanol was added to the solid obtained by filtering the slurry of the hydrolysis product, and the mixture was stirred at 90°C for 4 hours. The mixture was then filtered, washed with butanol and water at 50°C, and vacuum dried to obtain 53.1 g (yield: 89%) of solid terephthalic acid (TPA).

[0277] Examples 3-10

[0278] 59.2 g (yield: 99%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-1, except that the filtrate separated in the filtration step of Example 3-1 was further used.

[0279] Specifically, the filtrate separated in the filtration step of Example 3-1 was added back into the second high-pressure reactor, heated to 260°C, and subjected to a hydrolysis reaction at 260°C for 4 hours. The mixture was then cooled to 90°C to obtain a slurry-like hydrolysis product. The slurry-like hydrolysis product was filtered to obtain a solid, which was washed with butanol and water at 90°C and vacuum dried to obtain 5.5 g of solid terephthalic acid (TPA).

[0280] Comparative Example 3-1

[0281] 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 Examples 2-4 was used.

[0282] Comparative Example 3-2

[0283] 40.4 g (yield: 81%) of solid terephthalic acid (TPA) was obtained in the same manner as in Examples 3-2, except that 100 g (0.30 mol) of the composition of Comparative Examples 2-7 was used.

[0284] Comparative Example 3-3

[0285] 36.7 g (yield: 85%) of solid terephthalic acid (TPA) was obtained in the same manner as in Examples 3-3, except that 100 g (0.26 mol) of the composition used in Comparative Examples 2-13 was employed.

[0286] Comparative Examples 3-4

[0287] 34.4 g (yield: 81%) of solid terephthalic acid (TPA) was obtained in the same manner as in Examples 3-6, except that 114 g (0.26 mol) of the compositions of Comparative Examples 2-16 was used.

[0288] Test Example 2-1: Pigment Residue Rate

[0289] The pigment residue rate (%) of terephthalic acid in Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4 was measured.

[0290] Specifically, the terephthalic acid of Example 3-1 was diluted to a concentration of 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP), respectively, and the area of ​​the absorbance curve in the range of 400 nm to 800 nm was obtained using a UV-Vis spectrophotometer (B1). Furthermore, for the compositions of Comparative Examples 2-4 (the compositions of Examples 1-2 were used in the same manner as those used to prepare the terephthalic acid of Example 3-1, but without the addition of an adsorbent during concentration), the area of ​​the absorbance curve in the range of 400 nm to 800 nm was obtained in the same manner as described above (B2). The pigment residue rate (%) was calculated based on the measured area of ​​the absorbance curve according to the following equation B.

[0291] [Equation B]

[0292]

[0293] The pigment residue rate (%) of terephthalic acid in Examples 3-2 to 3-10 and Comparative Examples 3-1 to 3-4 was measured in the same manner as described above. Specifically, for B2 of Formula 1 above, Examples 3-2 were measured using the compositions of Comparative Examples 2-7, Examples 3-3 to 3-5 were measured using the compositions of Comparative Examples 2-13, Examples 3-3 to 3-5 were measured using the compositions of Comparative Examples 2-13, and Examples 3-6 were measured using the compositions of Comparative Examples 2-16. Furthermore, 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.

[0294] Test Example 2-2: Yellow Index

[0295] The yellow index (YI) of the recovered terephthalic acid in Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4 was determined.

[0296] Specifically, the recovered terephthalic acid from Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4 was diluted to a concentration of 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP), respectively, and then the yellow index was measured using a ColorFlex EZ instrument (manufacturer: HunterLab).

[0297] Test Example 2-3: Metal Content

[0298] The metal content (ppm) in terephthalic acid in Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-10 was measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). ND indicates that the content was too low, less than one part per million (1 ppm), to be measured.

[0299] Test Example 2-4: Chromaticity -b

[0300] The chromaticity-b, i.e. color characteristic, of terephthalic acid in each of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4 was measured using a colorimeter.

[0301] [Table 3]

[0302]

[0303] As can be seen from Table 3 above, the terephthalic acid (recovered terephthalic acid) prepared in Examples 3-1 to 3-6 not only has a low pigment residue rate and a low yellow index, but also a very low content of metal impurities. In particular, in Examples 3-10, the filtrate separated by the filtration step, i.e., the unreacted material, was used to obtain recovered terephthalic acid in a very high yield.

Claims

1. A process for preparing terephthalic acid, comprising: (1) Alcohololysis of waste polyester with an alcohol having 4 to 14 carbon atoms to prepare a liquid composition comprising a compound of Formula 1, wherein the alcohololysis is carried out at a pressure of 1 bar to 28 bar; and (2) Hydrolyzing the liquid composition: [Formula 1] In Formula 1, R1 is an alkyl group having 4 to 14 carbon atoms.

2. The process for preparing terephthalic acid according to claim 1, wherein, The weight ratio of the waste polyester to the alcohol is 1:1 to 10.

3. The process for preparing terephthalic acid according to claim 1, wherein, The alcoholysis was carried out at a temperature of 160°C to 280°C and a pressure of 1 bar to 28 bar for 0.5 hours to 24 hours.

4. The process for preparing terephthalic acid according to claim 1, wherein, The liquid composition comprises unreacted alcohol and ethylene glycol as a byproduct, and the content of the compound represented by Formula 1 in the liquid composition is 70 mol% or higher.

5. The process for preparing terephthalic acid according to claim 1, wherein, Step (1) includes discharging unreacted alcohol and ethylene glycol as a byproduct, separating the alcohol from the mixture of discharged alcohol and ethylene glycol, and recovering the separated alcohol as a feedstock for alcoholysis.

6. The process for preparing terephthalic acid according to claim 1, wherein, Step (1) includes recovering ethylene glycol as a byproduct of alcoholysis, and the recovery rate of said ethylene glycol is 65% or higher.

7. The process for preparing terephthalic acid according to claim 1, wherein, In step (1), an alcoholysis catalyst is added. The alcoholysis catalyst comprises at least one cation, which is selected from Li + Na + K + and Cs + Alkali metal ions, Be 2+ Mg 2+ Ca 2+ and Ba 2+ Alkaline earth metal ions, NH 4+ and NR 4+ Where R is an ammonium ion of an alkyl group and Zn 2+ The group consisting of; or containing at least one anion, said anion being selected from OH- - OR - Where R is an alkyl group or HCO3 - CO3 2- The group consisting of benzoate ion, 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion, and Based on the total weight of the waste polyester, the amount of alcoholysis catalyst added is from 10 ppm to 10,000 ppm.

8. The process for preparing terephthalic acid according to claim 1, wherein, In step (1), an alcoholysis catalyst is added. The alcoholysis catalyst comprises at least one selected from the group consisting of Zn(OAc)₂, Co(OAc)₂, Mn(OAc)₂, Mg(OAc)₂, Ca(OAc)₂, Ba(OAc)₂, LiOAc, NaOAc, KOAc, Zn(OAc)₂·2H₂O, Co(OAc)₂·4H₂O, Pb(OAc)₂, Mn(OAc)₂·4H₂O, Mg(OAc)₂·4H₂O, Pd(OAc)₂, Ti(OBu)₄, Ti(OiPr)₄, GeO₂, Al(OiPr)₃, Na₂CO₃, K₂CO₃, di-n-butyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid. Based on the total weight of the waste polyester, the amount of alcoholysis catalyst added is from 10 ppm to 10,000 ppm.

9. The process for preparing terephthalic acid according to claim 1, further comprising purifying the liquid composition prior to step (2).

10. The process for preparing terephthalic acid according to claim 9, wherein, The purification step includes adding at least one adsorbent selected from the group consisting of activated carbon, silica gel, alumina, zeolite and activated clay, or adsorbing by bed adsorption, and the content of the added adsorbent is from 0.1% to 20% by weight based on the total weight of the liquid composition.

11. The process for preparing terephthalic acid according to claim 1, wherein, The hydrolysis is carried out by adding water to the liquid composition at a temperature of 180°C to 280°C for 0.5 hours to 24 hours.

12. The process for preparing terephthalic acid according to claim 11, wherein, The liquid composition has a weight ratio of water of 1:1 to 500.

13. The process for preparing terephthalic acid according to claim 1, wherein, In step (2), a hydrolysis catalyst is added. The hydrolysis catalyst contains at least one cation, which is selected from Li. + Na + K + and Cs + Alkali metal ions, Be 2+ Mg 2+ Ca 2+ and Ba 2+ Alkaline earth metal ions, NH 4+ and NR 4+ Where R is an ammonium ion of an alkyl group and Zn 2+ The group consisting of; or containing at least one anion, said anion being selected from OH- - OR - Where R is an alkyl group or HCO3 - CO3 2- The group consisting of benzoate ion, 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion, and The amount of hydrolysis catalyst added is from 10 ppm to 10,000 ppm, based on the total weight of the liquid composition.

14. The process for preparing terephthalic acid according to claim 1, wherein, In step (2), a hydrolysis catalyst is added, wherein the hydrolysis catalyst is selected from at least one of the following groups: Zn(OAc)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Zn(OAc)2·2H2O, Co(OAc)2·4H2O, Pb(OAc)2, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Pd(OAc)2, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, di-n-butyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid. The amount of hydrolysis catalyst added is from 10 ppm to 10,000 ppm, based on the total weight of the liquid composition.

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