Method for preparing terephthalic acid and terephthalic acid prepared by said method

Abstract

The present invention relates to a method for preparing terephthalic acid and the terephthalic acid prepared by the method.Specifically, according to one embodiment of the present invention, the method includes a step of hydrolyzing a compound prepared by depolymerizing waste polyester using a specific hydrolysis catalyst, thereby preparing terephthalic acid in an environmentally friendly manner, and providing high purity terephthalic acid.

Description

[Technical Field]

[0001] The present invention relates to a process for preparing terephthalic acid in an environmentally friendly manner using waste polyester, and to recycled terephthalic acid prepared by the process. [Background technology]

[0002] Due to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties, polyester is widely used as a material for beverage containers, packaging films, audio / video films, etc., as well as industrial materials such as medical fibers and tire cords. In particular, polyester sheets and boards have good transparency and excellent mechanical strength, making them widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, and interior and exterior materials.

[0003] Plastic waste, including polyester, is generated at levels that exceed the capacity of the global waste stream each year, leading to growing interest in recycling waste polyester and in regeneration processes using waste polyester. Furthermore, countries around the world are establishing regulations and plans for the recycling of waste plastic resources, including waste polyester. For example, regulations requiring the use of a certain percentage of recycled resin in packaging materials used in various fields are being considered.

[0004] In particular, polyethylene terephthalate (PET) has excellent properties in terms of heat resistance, processability, transparency, and non-toxicity, and is therefore widely used in the manufacture of a wide range of products such as films, fibers, bottles, and containers. However, most of these products are landfilled or incinerated after use, so research into recycling or regeneration processes using these products is ongoing.

[0005] For example, Korean Patent Publication No. 1997-0042469 discloses a technique for preparing terephthalic acid by hydrolyzing waste polyethylene terephthalate with an aqueous alkali solution to obtain a slurry of alkali metal salts and alkaline earth metal salts of terephthalic acid, and then neutralizing the slurry with acid. As a result of the hydrolysis reaction, terephthalic acid salts are produced instead of terephthalic acid, and a neutralization step involving the addition of acid is required to convert the salts into terephthalic acid. This process has problems, such as the generation of environmental pollutants from by-products and the generation of large amounts of acid treatment waste liquid. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Publication No. 1997-0042469 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, an object of the present invention is to provide a process for preparing high-purity terephthalic acid in an environmentally friendly manner by hydrolyzing a compound prepared by depolymerizing waste polyester using a specific hydrolysis catalyst, and to provide recycled terephthalic acid prepared by the process. [Means for solving the problem]

[0008] The process for preparing terephthalic acid according to one embodiment of the present invention includes depolymerizing waste polyester to prepare a compound, and hydrolyzing the compound. The hydrolysis catalyst used in the hydrolysis step is Li + , Na + , K. + , and Cs + Alkali metal ions, Be 2+ , Mg 2+ , Ca 2+ , and Ba 2+ alkaline earth metal ions, NH 4+ , and NR4+ (wherein R is alkyl), and Zn 2+ At least one cation selected from the group consisting of: - , OR - (wherein R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - ), 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion.

[0009] Recycled terephthalic acid according to another embodiment of the present invention is prepared according to the above process for preparing terephthalic acid and has a total metal content of less than 100 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0010] A polyester resin according to another embodiment of the present invention comprises recycled terephthalic acid. [Effects of the Invention]

[0011] A process for preparing terephthalic acid according to one embodiment of the present invention includes hydrolyzing a compound prepared by depolymerizing waste polyester using a hydrolysis catalyst, wherein the hydrolysis catalyst is Li + , Na + , K. + , and Cs + Alkali metal ions such as Be 2+ , Mg 2+ , Ca 2+ , and Ba 2+ alkaline earth metal ions such as NH 4+ , and NR 4+ where R is alkyl, and ammonium ions such as Zn 2+ At least one cation selected from the group consisting of: - , OR - (wherein R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2- ), 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion, not only can terephthalic acid be produced in an environmentally friendly manner, but also can produce highly pure terephthalic acid.

[0012] Specifically, in conventional alkaline hydrolysis reactions, solid terephthalic acid is not immediately produced, but a terephthalic acid salt is produced, necessitating an additional step of neutralizing the salt. Furthermore, the acids used to neutralize the terephthalic acid salt, such as sulfuric acid and hydrochloric acid, generate environmental pollutants such as NaSO and NaCl as by-products, and a large amount of acid treatment waste liquid.

[0013] In contrast, in a process for preparing terephthalic acid according to one embodiment of the present invention, Li + , Na + , K. + , Cs + Alkali metal ions such as Be 2+ , Mg 2+ , Ca 2+ , and Ba 2+ alkaline earth metal ions such as NH 4+ , and NR 4+ where R is alkyl, and ammonium ions such as Zn 2+ At least one cation selected from the group consisting of: - , OR - (wherein R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 -Unlike conventional processes, the use of a trace amount of a hydrolysis catalyst containing at least one anion selected from the group consisting of 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion allows for direct production of solid terephthalic acid without any additional steps. Therefore, not only can the process be easily operated, but the process cost can also be reduced. Furthermore, since no environmental pollutants are generated, terephthalic acid can be prepared in a very environmentally friendly manner.

[0014] Another process for producing terephthalic acid involves preparing dimethyl terephthalate (DMT) or bis(2-hydroxyethyl) terephthalate (BHET) from waste polyester and then hydrolyzing it. Metal catalysts, such as iron, cobalt, manganese, or nickel, are used for the hydrolysis. Because some of the terephthalic acid produced acts as an acid catalyst, the alcohol produced as a by-product of the hydrolysis reaction can decompose. This results in problems such as increased process costs and the generation of non-recyclable waste.

[0015] Specifically, when a metal catalyst such as iron, cobalt, manganese, or nickel is used for hydrolysis, a portion of terephthalic acid produced during the hydrolysis reaction dissolves in water and acts as an acid catalyst, which may dehydrate the alcohol produced as a by-product of the hydrolysis reaction to produce additional by-products such as dialkyl ethers and alkenes, resulting in a decrease in the alcohol recovery rate, generation of non-recyclable waste, or the need for a process to remove additional by-products in order to recycle the alcohol, thereby increasing process costs.

[0016] [ka]

[0017] In contrast, in a process for preparing terephthalic acid according to one embodiment of the present invention, Li + , Na + , K.+ , Cs + Alkali metal ions such as Be 2+ , Mg 2+ , Ca 2+ , and Ba 2+ alkaline earth metal ions such as NH 4+ , and NR 4+ where R is alkyl, and ammonium ions such as Zn 2+ At least one cation selected from the group consisting of: - , OR - (wherein R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - By using a hydrolysis catalyst containing at least one anion selected from the group consisting of benzoyl benzoate ion, 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion, a portion of the terephthalic acid produced during the hydrolysis reaction does not act as an acid catalyst, and therefore the decomposition rate of the alcohol can be reduced. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention is described in detail below. The present invention is not limited to the disclosure shown below, and can be modified in various forms without departing from the gist of the present invention.

[0019] In this specification, when a part is described as "comprising" certain elements, it is understood that other elements may be included, rather than excluding other elements, unless otherwise specified.

[0020] All numerical values ​​and expressions relating to amounts of ingredients, reaction conditions, and the like used herein are understood to be modified by the term "about" unless otherwise specified.

[0021] Throughout this specification, terms such as first, second, etc. are used to describe various components, but should not be construed as limiting the components; they are used solely to distinguish one component from another.

[0022] Process for preparing terephthalic acid The process for preparing terephthalic acid according to one embodiment of the present invention includes depolymerizing waste polyester to prepare a compound, and hydrolyzing the compound. The hydrolysis catalyst used in the hydrolysis step is Li + , Na + , K. + , and Cs + Alkali metal ions such as Be 2+ , Mg 2+ , Ca 2+ , and Ba 2+ alkaline earth metal ions such as NH 4+ , and NR 4+ where R is alkyl, and ammonium ions such as Zn 2+ At least one cation selected from the group consisting of: - , OR - (wherein R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - ), 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion.

[0023] R may be an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 5 carbon atoms.

[0024] The waste polyester may be obtained by shredding or melting waste polyester products. For example, but not limited to, waste polyester may be obtained by shredding, recovering, separating, or pelletizing used polyester products (post-consumer recycled material; PCR), or by polyester waste materials such as rejects and off-cuts that may be formed during processes such as molding polyester film, fiber, containers, etc. (post-industrial recycled material; PIR).

[0025] Specifically, the hydrolysis catalyst may include at least one selected from the group consisting of NaOH, NaHCO3, Na2CO3, NaOMe, KOH, K2CO3, KOtBu, CsOH, Ca(OH)2, LiOH, and NH4OH.

[0026] By using the specific hydrolysis catalysts listed above, a portion of the produced terephthalic acid does not act as an acid catalyst, thereby reducing the decomposition rate of alcohol. For example, when a hydrolysis catalyst such as NaOH is used, unlike the prior art in which a portion of the produced terephthalic acid acts as an acid catalyst, the terephthalic acid is converted into TPA-Na salt, which dissolves in the water used in the hydrolysis reaction. Therefore, it is possible to effectively prevent the decomposition of alcohol, which is a by-product of the hydrolysis reaction.

[0027] In the process for preparing terephthalic acid according to one embodiment of the present invention, an alcohol of R1-OH (where R is an alkyl group having 2 or more carbon atoms) may also be formed as a by-product of the hydrolysis reaction. In the case of dimethyl terephthalate, methanol may be formed. In the case of bis(2-hydroxyethyl) terephthalate, ethylene glycol may be formed. However, in the process for preparing terephthalic acid according to one embodiment of the present invention, a specific hydrolysis catalyst is used, so the decomposition rates of alcohol, methanol, and ethylene glycol are very low compared to the prior art, and therefore the production rate of alcohol by-products is low.

[0028] The amount of the hydrolysis catalyst used may be 0.01 mol to 1.0 mol based on 1 mol of the compound. For example, the amount of the hydrolysis catalyst used may be 0.02 mol to 1.0 mol, 0.02 mol to 0.8 mol, 0.03 mol to 0.5 mol, 0.05 mol to 0.4 mol, or 0.05 mol to 0.2 mol based on 1 mol of the compound prepared by depolymerizing waste polyester.

[0029] Furthermore, water may be added in the hydrolysis step. Specifically, water may be added in an amount of 1 to 500 times the weight of the compound in the hydrolysis step. For example, the amount of water added in the hydrolysis step may be 1 to 450 times, 1 to 400 times, 1 to 250 times, 1 to 100 times, 1.2 to 50 times, or 1.5 to 30 times the weight of the compound.

[0030] Alternatively, the hydrolysis may be carried out for 0.5 to 24 hours at 180 to 280°C. For example, the hydrolysis may be carried out at a temperature of 185 to 280°C, 200 to 275°C, 220 to 270°C, or 240 to 265°C for 1 to 20 hours, 2.5 to 12 hours, or 3 to 8 hours.

[0031] The conventional method of adding a metal catalyst such as iron, cobalt, manganese, or nickel to waste polyester and then directly hydrolyzing it with water is environmentally friendly. However, it requires an ultra-high temperature of 300°C or higher and requires a reactor that can withstand high pressure, making it difficult to process. In contrast, the process for preparing terephthalic acid according to one embodiment of the present invention has improved process conditions compared to the prior art, making it easy to process.

[0032] According to one embodiment of the present invention, solid terephthalic acid can be prepared by hydrolysis. Specifically, the process may further include filtering, washing, and drying the hydrolysis reaction product prepared by the hydrolysis reaction after the hydrolysis step. That is, solid terephthalic acid can be produced by filtering, washing, and drying the hydrolysis reaction product prepared by the hydrolysis reaction.

[0033] For example, the hydrolysis reaction product can be cooled to an appropriate temperature at which water does not evaporate, for example, room temperature to less than 100°C, to obtain a slurry solution, and the solution can be filtered to obtain a solid, which can be washed and dried under vacuum to obtain solid terephthalic acid.

[0034] Washing can be carried out using protic solvents such as alcohols having 4 or more carbon atoms and / or water, isopropanol, and acetic acid, or mixtures of aprotic solvents such as acetone, dichloromethane, chloroform, tetrahydrofuran (THF), and toluene.

[0035] Residual pigments or impurities generated by decomposition of pigments during hydrolysis, especially yellow impurities, can be effectively removed by washing, improving the yellow index or color properties. In addition, the use of water for washing removes mineral salts, improving quality.

[0036] For example, the solid obtained by filtration can be washed with a mixture of alcohol at 80°C to 150°C and / or water at 70°C to 95°C.

[0037] According to one embodiment of the present invention, the compound prepared by depolymerizing waste polyester may be a compound represented by Formula 1:

[0038] [ka]

[0039] In Formula 1, R1 is a substituted or unsubstituted alkyl group.

[0040] Specifically, R1 may be an unsubstituted or hydroxy-substituted alkyl group. For example, the compound may be dimethyl terephthalate (DMT), dibutyl terephthalate (DBTP), diisooctyl terephthalate (DOTP), or bis(2-hydroxyethyl) terephthalate (BHET).

[0041] For example, dimethyl terephthalate can be prepared by methanolysis of waste polyester. Bis(2-hydroxyethyl) terephthalate can be prepared by glycolysis of waste polyester. Commercially available dimethyl terephthalate and bis(2-hydroxyethyl) terephthalate can also be used.

[0042] Alternatively, in Formula 1, R1 may be a substituted or unsubstituted alkyl group having two or more carbon atoms.

[0043] For example, R1 can be methyl, ethyl, propyl, n-propyl, isopropyl, 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-methylhex ... The alkyl group may be xyl, 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, 1,1-dimethyl-propyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, decanyl, undecanyl, dodecanyl, tridecanyl, or tetradecanyl.

[0044] According to one embodiment of the present invention, alcohol may be produced as a by-product in the hydrolysis step. Specifically, the alcohol decomposition rate may be less than 10%. For example, the alcohol decomposition rate (%) may be calculated by filtering the slurry-like hydrolysis reaction product obtained by hydrolysis and analyzing the components of the filtrate obtained by gas chromatography. The alcohol decomposition rate may be 9% or less, 6% or less, 5% or less, 4.5% or less, 4% or less, 3% or less, or 2% or less. In the process for preparing terephthalic acid according to one embodiment of the present invention, not only is the alcohol decomposition rate low, but the alcohol can also be recovered and reused, making it environmentally friendly and reducing process costs.

[0045] According to another embodiment of the present invention, the depolymerization may comprise alcoholysis.

[0046] Specifically, the alcoholysis can be carried out using an alcohol having 4 or more carbon atoms. In particular, when the compound is prepared by subjecting waste polyester to alcoholysis using an alcohol having 4 or more carbon atoms, the compound can be liquid at room temperature.

[0047] When waste polyester is subjected to alcoholysis using an alcohol having four or more carbon atoms to prepare a compound, the compound is liquid at room temperature. Therefore, insoluble impurities and additives such as colorants and pigments that may be contained in the waste polyester can be easily removed. Therefore, the purity and yield of the produced terephthalic acid can be improved.

[0048] In addition, since solid terephthalic acid can be produced directly without an additional neutralization step as in conventional processes, this method is easy to process and environmentally friendly. Furthermore, not only is it easy to separate and recover ethylene glycol, which may be formed as a by-product during the preparation process, but the alcohols with four or more carbon atoms used in the alcoholysis reaction can also be easily separated and reused, resulting in excellent process cost reduction. Furthermore, the purification and transfer processes other than the reaction can be carried out at room temperature or low temperatures, further improving processability and economy.

[0049] For example, alcoholysis can be carried out first by charging waste polyester, an alcohol having 4 or more carbon atoms, and a trace amount of an alcoholysis catalyst into a first high-pressure reactor. Ethylene glycol, which is a by-product formed during the alcoholysis reaction, and unreacted alcohol (excess alcohol) may be recovered and reused in a separate fractional distillation apparatus after the reaction is completed.

[0050] Alternatively, the ethylene glycol and unreacted alcohol formed during the reaction may be discharged as a gaseous mixture in real time during the reaction and then condensed and recovered using an external cooling device. In such a case, the alcohol may be continuously fed to the high-pressure reactor at the same amount and rate as the amount and rate of the discharged gaseous mixture. The unreacted alcohol may be separated from the discharged gaseous mixture by a simple process such as fractional distillation or layer separation. The unreacted alcohol thus separated may be fed back to the first high-pressure reactor, from which ethylene glycol can be recovered.

[0051] The liquid alcoholysis product obtained by the alcoholysis reaction can then be purified by cooling, adsorption, and filtration. The purified alcoholysis reaction composition is supplied to a second high-pressure reactor together with water to carry out a hydrolysis reaction, and a slurry solution is obtained, which is then filtered to obtain solid terephthalic acid. In this case, a small amount of a hydrolysis catalyst can be additionally supplied together with water before the hydrolysis reaction. The hydrolysis catalyst may be the same as or different from the alcoholysis catalyst.

[0052] In addition, after the hydrolysis reaction is completed, the unreacted components are recovered and reintroduced into the alcoholysis or hydrolysis reaction for one or more reactions, thereby improving the yield of the final terephthalic acid. Furthermore, this method is environmentally friendly because it reduces the amount of waste generated. For example, the filtrate obtained by filtering the excess unreacted alcohol (having 4 or more carbon atoms) and the by-product ethylene glycol can be reintroduced into the hydrolysis reaction.

[0053] The alcoholysis reaction can be carried out smoothly as a non-catalytic reaction without the use of an alcoholysis catalyst, making it environmentally friendly. In particular, when the waste polyester contains a high content of insoluble metals, a non-catalytic reaction can be advantageous for efficient treatment and removal of impurities. Alternatively, an alcoholysis catalyst can be added to the alcoholysis reaction. Specifically, from an energy perspective, an alcoholysis catalyst can be added to improve reactivity and processability.

[0054] The alcoholysis catalyst may be a metal acetate, alkali metal salt, or hydroxy salt.

[0055] More specifically, the alcoholysis catalyst is Li + , Na + , K. + , and Cs + Alkali metal ions such as Be 2+ , Mg 2+ , Ca 2+ , and Ba 2+alkaline earth metal ions such as NH 4+ , and NR 4+ where R is alkyl, and ammonium ions such as Zn 2+ At least one cation selected from the group consisting of: - , OR - (wherein R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - ), 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion. R may be an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 5 carbon atoms.

[0056] For example, the alcoholysis catalyst may comprise 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, dibutyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid.

[0057] Furthermore, the amount of the alcoholysis catalyst added may be 10 ppm to 10,000 ppm based on the total weight of the waste polyester, for example, 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 based on the total weight of the waste polyester.

[0058] According to another embodiment of the present invention, alcoholysis may include draining off unreacted alcohol and by-product ethylene glycol.

[0059] Specifically, the alcohol can be separated from the discharged mixture of alcohol and ethylene glycol, and the separated alcohol can be recycled as a raw material for alcoholysis. For example, during and / or after the completion of the alcoholysis reaction, ethylene glycol, which is a by-product of alcoholysis, and unreacted alcohol (excess alcohol) are subjected to fractional distillation or layer separation to separate the alcohol. The separated alcohol can be fed to alcoholysis for reuse. In this case, the amount and feed rate of the alcohol fed for reuse may be the same as the amount and discharge rate of the discharged mixture of alcohol and ethylene glycol.

[0060] The number of carbon atoms in the alcohol used for alcoholysis may be 4 or more, 6 or more, 8 or more, 10 or more, or 12 or more, or may be 4 to 14, 4 to 13, 4 to 10, 4 to 8, 6 to 12, 8 to 14, or 8 to 13.

[0061] Since the alcoholysis of waste polyester is carried out using an alcohol having the above number of carbon atoms, the alcoholysis can be carried out at a low temperature and pressure, compared to conventional processes using waste polyester, which are carried out at a high temperature and pressure, and the alcoholysis product, i.e., the above compound, can be produced in a liquid state. Furthermore, by using an alcohol with the above number of carbon atoms within the above range, the alcoholysis reaction rate can be improved.

[0062] The alcohol may have a boiling point of 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 alcohol boiling point is within the above range, ethylene glycol formed as a by-product in alcoholysis can be more easily removed and recovered in a subsequent process, further improving processability. In particular, in recent years, there has been a trend toward using various monomer materials in fields using polyester as a raw material, and this method can be easily adopted for removing various dialcohol-based monomers used in waste polyester products such as waste plastic products.

[0063] The weight ratio of waste polyester to alcohol may be 1:1 to 10. For example, the weight ratio of waste polyester to alcohol may be 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.

[0064] Alternatively, the alcoholysis reaction may be carried out at a temperature of 160° C. to 280° C. and a pressure of 1 bar to 40 bar for 0.5 hours to 24 hours. For example, the alcoholysis reaction may be carried out at a temperature of 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 a pressure of 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 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.

[0065] In the alcoholysis reaction, an alcoholysis catalyst can be added. Specifically, before the alcoholysis reaction, an alcoholysis catalyst can be added to a mixture of waste polyester and alcohol in order to improve reactivity and enhance processability from the viewpoint of energy.

[0066] The alcoholysis catalyst may be a metal acetate, alkali metal salt, or hydroxy salt.

[0067] More specifically, the alcoholysis catalyst is Li + , Na + , K. + , and Cs + Alkali metal ions such as Be 2+ , Mg 2+ , Ca 2+ , and Ba 2+ alkaline earth metal ions such as NH 4+ , and NR 4+ where R is alkyl, and ammonium ions such as Zn 2+ At least one cation selected from the group consisting of: - , OR - (wherein R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - ), 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion. R may be an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 5 carbon atoms.

[0068] For example, the alcoholysis catalyst may comprise 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, dibutyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid.

[0069] Furthermore, the amount of the alcoholysis catalyst added may be 10 ppm to 10,000 ppm based on the total weight of the waste polyester, for example, 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 based on the total weight of the waste polyester.

[0070] The alcoholysis reaction can be carried out smoothly as a non-catalytic reaction without the use of an alcoholysis catalyst, making it environmentally friendly. In particular, when the waste polyester contains a high content of insoluble metals, the non-catalytic reaction can be advantageous for the efficient treatment and removal of impurities.

[0071] According to another embodiment of the present invention, the process may further comprise purifying the compound prior to the hydrolysis step.

[0072] Specifically, the purification step may include 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. 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 1:0.5-1.5 or 1:0.8-1.2, but is not limited thereto.

[0073] The content of the added adsorbent may be 0.1% to 20% by weight based on the total weight of the compound, for example, 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% to 2% by weight based on the total weight of the compound.

[0074] The purity and yield can be further improved by further performing a step of purifying the compound using an adsorbent, specifically an adsorbent with a specific supply amount within the above numerical range. Specifically, by performing a step of purifying the compound, it is possible to more effectively remove insoluble impurities such as metals that may be contained in the compound, or additives such as colorants and pigments that may be contained in the waste polyester. Therefore, the purity and yield of the finally prepared terephthalic acid can be further improved.

[0075] In addition, a concentration step may be further carried out after the purification step.

[0076] Concentration may be carried out for 0.5 to 6 hours at a temperature of 50 to 120° C. For example, concentration may be carried out by stirring the purified compound at a temperature of 55 to 115° C., 60 to 110° C., 65 to 105° C., or 75 to 100° C. for 1 to 5 hours, 1.5 to 4 hours, or 2 to 4 hours.

[0077] The purified compound may also have a low content of insoluble impurities, such as metals. Specifically, the purified compound may have a total metal content of 100 ppm or less, based on the total weight of the purified compound, as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0078] For example, the purified compound may contain insoluble impurities such as metals. The total content of metals in the purified compound 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, based on the total weight of the purified compound, as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES). In particular, the total content of Sb, Ti, and Zn 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.

[0079] Sb is a catalyst widely used in the polymerization of general polyesters due to its excellent stability, reaction rate, and cost. However, due to the effects of Sb on the human body and the environment, regulations are being tightened, and Sb must be removed during chemical recycling processes.

[0080] Ti is sometimes used in the form of TiO2 as a polyester polymerization catalyst or an additive in polyester processing. If Ti is contained in an amount exceeding a certain level, the quality of recycled terephthalic acid prepared from the polyester or polyester resin using the polyester may deteriorate, limiting their use.

[0081] Zn is also a component used as a polymerization catalyst for PET. Residual Zn can affect the control of reactivity in the preparation process of recycled terephthalic acid or polyester resins using recycled terephthalic acid. Therefore, it is preferable to remove Zn. In particular, Zn is widely used in chemical recycling processes, so it is a substance that must be sufficiently removed from the amount contained in the waste plastics that are the raw material for this process, and from the amount added separately as a catalyst during the recycling process.

[0082] According to an embodiment of the present invention, further purification is carried out so that the total content of metals in the purified compound, particularly the above-mentioned Sb, Ti, and Zn, is very low, at 30 ppm or less.

[0083] For example, the Sb content can be 30 ppm or less, 20 ppm or less, 10 ppm or less, or 1 ppm or less, based on the total weight of the purified compound, as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0084] The Ti content may be 30 ppm or less, 20 ppm or less, 10 ppm or less, or 1 ppm or less, based on the total weight of the purified compound, as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0085] The Zn content may be 30 ppm or less, 20 ppm or less, 10 ppm or less, or 1 ppm or less, based on the total weight of the purified compound, as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0086] The yield of terephthalic acid may be 80% or more based on the total weight of the compound prepared by depolymerizing the waste polyester. For example, the yield of terephthalic acid may be 82% or more, 85% or more, 87% or more, 88% or more, 89% or more, 90% or more, 91% or more, 92% or more, 94% or more, 95% or more, or 96% or more based on the total weight of the compound prepared by depolymerizing the waste polyester.

[0087] Recycled Terephthalic Acid Recycled terephthalic acid according to another embodiment of the present invention is prepared according to the above process for preparing terephthalic acid and has a total metal content of less than 100 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0088] Specifically, recycled terephthalic acid can be prepared according to a process for preparing terephthalic acid.

[0089] The recycled terephthalic acid can have a total metals content of less than 100 ppm, 90 ppm or less, 80 ppm or less, 65 ppm or less, 50 ppm or less, 35 ppm or less, less than 30 ppm, less than 20 ppm, 15 ppm or less, 9 ppm or less, 7 ppm or less, 5 ppm or less, or 1 ppm or less, as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0090] Furthermore, the recycled 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 total content of Sb, Ti, and Zn in the recycled terephthalic acid, which may be harmful to humans or may be used as a reaction catalyst or a side reaction catalyst in a subsequent polymerization process, may be 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.

[0091] For example, when measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), the Sb content in the recycled terephthalic acid may be 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 6 ppm or less, 5 ppm or less, 4 ppm or less, 3 ppm or less, 2 ppm or less, or 1 ppm or less, relative to the total weight of the recycled terephthalic acid.

[0092] When measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), the Ti content in the recycled 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, based on the total weight of the recycled terephthalic acid.

[0093] When measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES), the Zn content in the recycled terephthalic acid may be 30 ppm or less, 25 ppm or less, 15 ppm or less, 10 ppm or less, 6 ppm or less, 5 ppm or less, 4 ppm or less, 3 ppm or less, 2 ppm or less, or 1 ppm or less, based on the total weight of the recycled terephthalic acid.

[0094] When measured with a colorimeter, recycled terephthalic acid may have a color-b of less than 2, 1.6 or less, 1.4 or less, 1.3 or less, or 1 or less. The above numerical range of color-b is equivalent to that of virgin terephthalic acid typically produced in petrochemical processes. Therefore, recycled terephthalic acid that satisfies the above numerical range of color-b not only has a low yellow index, but also has excellent quality due to well-purified monomers.

[0095] Col-b is a color coordinate system established by the International Commission on Illumination (CIE) that expresses color in terms of L (lightness), a (complementary color of green to red), and b (complementary color of yellow to blue). Col-b can be measured using a colorimeter.

[0096] Furthermore, the recycled terephthalic acid may have a yellow index (YI) of less than 2, 1.8 or less, or 1.7 or less when diluted to a 5% concentration with dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP), respectively.

[0097] Polyester resin and process for preparing same A polyester resin according to another embodiment of the present invention comprises recycled terephthalic acid.

[0098] Specifically, the polyester resin may include recycled terephthalic acid, a diol compound or a derivative thereof, and optionally a dicarboxylic acid compound or a derivative thereof.

[0099] For example, the diol component or a derivative thereof 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-cyclohexanedimethanol, and neopentyl glycol. The dicarboxylic acid or a derivative thereof 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-naphthalenedicarboxylate (2,6-NDC). However, the dicarboxylic acid or a derivative thereof is not limited thereto.

[0100] A process for preparing a polyester resin according to another embodiment of the present invention includes mixing recycled terephthalic acid with a diol compound or a derivative thereof, and optionally a dicarboxylic acid compound or a derivative thereof, carrying out an esterification reaction, and subjecting the esterification reaction product to a polycondensation reaction.

[0101] The esterification reaction can be carried out at a temperature of 200°C to 350°C, 220°C to 320°C, or 250°C to 290°C. The esterification reaction can be carried out at a pressure lower than atmospheric pressure and 0 kg / cm 2 ~10kg / cm 2 (0mmHg~7,355.6mmHg), 0kg / cm 2 ~5kg / cm 2 (0 to 3,677.8 mmHg), or 0 kg / cm 2 ~2.0kg / cm 2 The esterification reaction may be carried out under a high pressure (0 to 1,471.1 mmHg) for 1 to 24 hours, 1 to 10 hours, or 1 to 6 hours.

[0102] The polycondensation reaction may be carried out 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. The polycondensation reaction may be carried out under reduced pressure of 0.01 mmHg to 400 mmHg, 0.05 mmHg to 100 mmHg, or 0.1 mmHg to 100 mmHg. The polycondensation reaction may be carried out for a time required to reach the desired intrinsic viscosity. For example, the polycondensation reaction may be carried out for 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 4 hours.

[0103] In the esterification reaction and polycondensation reaction, a catalyst and / or a stabilizer may be further added.

[0104] For example, the catalyst for the esterification reaction may be sodium, magnesium methylates, acetates, borates, fatty acid salts, carbonates of Zn, Cd, Mn, Co, Ca, Ba, metallic Mg, and oxides of Pb, Zn, Sb, and Ge.

[0105] Furthermore, the catalyst for the polycondensation reaction may be, for example, a titanium-based catalyst such as tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, titanium lactate, triethanolamine titanate, acetylacetonate titanate, ethylacetoacetic ester titanate, isostearyl titanate, titanium dioxide, titanium dioxide / silicon dioxide copolymer, or titanium dioxide / zirconium dioxide copolymer; a germanium-based catalyst such as germanium dioxide or a copolymer using the same; or a tin-based catalyst such as monobutyltin oxide, dibutyltin oxide, or monobutylhydroxytin oxide.

[0106] The stabilizer may also be a phosphorus-based compound such as, but not limited to, phosphoric acid, trimethyl phosphate, and triethyl phosphate.

[0107] The process for preparing a polyester resin according to another embodiment of the present invention may further include carrying out a solid-state polymerization reaction. For example, the solid-state polymerization may be carried out after the polycondensation reaction at a temperature of 190°C to 230°C under a vacuum condition of 0.2 Torr to 2.0 Torr or in a nitrogen atmosphere.

[0108] Aspects of the invention The present invention will now be described in more detail with reference to the following examples, which are provided for illustrative purposes only and are not intended to limit the scope of the present invention. [Example]

[0109] Preparation Example 1-1 A first high-pressure reactor with a capacity of 7 liters was charged with 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol, followed by the addition of 200 mg of Zn(OAC)2·2H2O (200 ppm relative to the total weight of the waste PET) as an alcoholysis catalyst.

[0110] Thereafter, all connections of the first high-pressure reactor were sealed, and the temperature was raised to 250°C over 1 hour. While maintaining the temperature at 250°C, the alcoholysis reaction was carried out for 4 hours with stirring. After completion of the alcoholysis reaction, the mixture was cooled to room temperature.

[0111] Then, 5 g of activated carbon was added as an adsorbent to 500 g of the alcoholysis reaction product, and the mixture was stirred at 100°C for 3 hours. The mixture was then filtered using a Buchner funnel and concentrated to obtain liquid dibutyl terephthalate (DBTP).

[0112] Preparation Example 1-2 Liquid diisooctyl terephthalate (DOTP) was obtained in the same manner as in Preparation Example 1-1, except that 2-ethyl-1-hexanol was used instead of 1-butanol.

[0113] Preparation of terephthalic acid Example 1 A second high-pressure reactor having a capacity of 600 ml was charged with 72.4 g (0.26 mol) of the liquid dibutyl terephthalate (DBTP) prepared in Preparation Example 1-1 and 200 g (11.10 mol) of water, and then 1.02 g (0.026 mol, 0.1 mol based on 1 mol of DBTP) of NaOH was added as a hydrolysis catalyst.

[0114] The temperature of the second high-pressure reactor was then raised to 260°C, and the hydrolysis reaction was carried out for 4 hours while maintaining the temperature at 260°C. The reaction mixture was then cooled to room temperature to obtain a slurry hydrolysis reaction product. The slurry hydrolysis reaction product was filtered to obtain a solid, which was washed with butanol (approximately 90°C) and water (approximately 90°C), and dried under vacuum to obtain 40.6 g (yield: 94%) of solid terephthalic acid (TPA). The components of the filtrate were analyzed using gas chromatography to calculate the decomposition rate (%).

[0115] Example 2 In the same manner as in Example 1, except that 100 g (0.26 mol) of diisooctyl terephthalate (DOTP) prepared in Preparation Example 1-2 was used instead of the liquid dibutyl terephthalate (DBTP) prepared in Preparation Example 1-1, and octanol (about 80°C) was used instead of butanol (about 80°C) in washing, 36.7 g (yield: 85%) of solid terephthalic acid (TPA) was obtained.

[0116] Example 3 In the same manner as in Example 1, except that 2.04 g (0.052 mol) of NaOH was used, 39.7 g (yield: 92%) of solid terephthalic acid (TPA) was obtained.

[0117] Example 4 In the same manner as in Example 1, except that 2.18 g (0.026 mol) of NaHCO3 was used instead of NaOH, 38.4 g (yield: 89%) of solid terephthalic acid (TPA) was obtained.

[0118] Example 5 The procedure of Example 1 was repeated except that 2.76 g (0.026 mol) of Na2CO3 was used instead of NaOH, to obtain 38.9 g (yield: 90%) of solid terephthalic acid (TPA).

[0119] Example 6 The procedure of Example 1 was repeated except that 1.40 g (0.026 mol) of NaOMe was used instead of NaOH, to obtain 35.4 g (yield: 82%) of solid terephthalic acid (TPA).

[0120] Example 7 The procedure of Example 1 was repeated except that 1.46 g (0.026 mol) of KOH was used instead of NaOH, to obtain 40.6 g (yield: 94%) of solid terephthalic acid (TPA).

[0121] Example 8 In the same manner as in Example 1, except that 3.59 g (0.026 mol) of K2CO3 was used instead of NaOH, 38.4 g (yield: 89%) of solid terephthalic acid (TPA) was obtained.

[0122] Example 9 In the same manner as in Example 1, except that 2.92 g (0.026 mol) of KOtBu was used instead of NaOH, 35.4 g (yield: 82%) of solid terephthalic acid (TPA) was obtained.

[0123] Example 10 39.7 g (yield: 92%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 1, except that 2.73 g (0.013 mol) of Na2TPA (disodium terephthalate) was used instead of NaOH.

[0124] Example 11 In the same manner as in Example 1, except that 6.35 g (0.026 mol) of sodium monobutyl terephthalate was used instead of NaOH, 37.1 g (yield: 86%) of solid terephthalic acid (TPA) was obtained.

[0125] Example 12 The same procedure as in Example 1 was repeated, except that 45.7 g (0.26 mol) of dimethyl terephthalate (DMT, manufacturer: Sigma Aldrich) was used instead of the liquid dibutyl terephthalate (DBTP) prepared in Preparation Example 1-1, and methanol (high temperature, approximately 110°C) was used instead of butanol for washing, to obtain 37.4 g (yield: 88%) of solid terephthalic acid (TPA).

[0126] Example 13 The same procedure as in Example 1 was repeated, except that 65.1 g (0.26 mol) of bis(2-hydroxyethyl) terephthalate (BHET, manufacturer: Sigma Aldrich) was used instead of the liquid dibutyl terephthalate (DBTP) prepared in Preparation Example 1-1, and ethylene glycol (high temperature) was used instead of butanol (high temperature) in washing, to obtain 40.8 g (yield: 96%) of solid terephthalic acid (TPA).

[0127] Example 14 A second high-pressure reactor having a capacity of 600 ml was charged with 100 g (0.26 mol) of the liquid diisooctyl terephthalate (DOTP) prepared in Preparation Example 1-2 and 200 g (11.10 mol) of water, followed by the addition of 1.02 g (0.026 mol, 0.1 mol based on 1 mol of DOTP) of NaOH as a hydrolysis catalyst.

[0128] The temperature of the second high-pressure reactor was then increased to 260°C, and the hydrolysis reaction was carried out for 4 hours while maintaining the temperature at 260°C. The mixture was then cooled to room temperature to obtain a slurry hydrolysis reaction product. The slurry hydrolysis reaction product was filtered, and the resulting filtrate was subjected to layer separation to obtain an aqueous layer (190 g). This aqueous layer was then fed back to the second high-pressure reactor, and 95 g (0.24 mol) of liquid diisooctyl terephthalate (DOTP) prepared in Preparation Example 1-2 was then fed to the reactor. The hydrolysis reaction was then carried out again at 260°C. The mixture was again cooled to room temperature to obtain a slurry hydrolysis reaction product. The product was filtered to obtain a solid. The solid was washed with octanol (approximately 150°C) and water (approximately 90°C), and dried under vacuum to obtain 36.8 g (yield: 91%) of solid terephthalic acid (TPA). The components of the filtrate were analyzed using gas chromatography to calculate the decomposition rate (%).

[0129] Example 15 A second high-pressure reactor having a capacity of 600 ml was charged with 20 g (0.051 mol) of the liquid diisooctyl terephthalate (DOTP) prepared in Preparation Example 1-2 and 400 g (22.20 mol) of water, followed by the addition of 0.20 g (0.0051 mol, 0.1 mol based on 1 mol of DOTP) of NaOH as a hydrolysis catalyst.

[0130] The temperature of the second high-pressure reactor was then raised to 260°C, and the hydrolysis reaction was carried out for 4 hours while maintaining the temperature at 260°C. The reaction mixture was then cooled to room temperature to obtain a slurry hydrolysis reaction product. The slurry hydrolysis reaction product was filtered to obtain a solid, which was washed with octanol (approximately 120°C) and water (approximately 80°C), and dried under vacuum to obtain 8.4 g (yield: 99%) of solid terephthalic acid (TPA). The components of the filtrate were analyzed using gas chromatography to calculate the decomposition rate (%).

[0131] Comparative Example 1 Solid terephthalic acid (TPA) (39.7 g, yield: 92%) was obtained in the same manner as in Example 1, except that 14 mg of Zn(OAC)2·2H2O was used as the hydrolysis catalyst.

[0132] Comparative Example 2 Solid terephthalic acid (TPA) (34.1 g, yield: 79%) was obtained in the same manner as in Example 2, except that 20 mg of Zn(OAC)2·2H2O was used as the hydrolysis catalyst.

[0133] Comparative Example 3 Solid terephthalic acid (TPA) (36.2 g, yield: 84%) was obtained in the same manner as in Example 13, except that 9.1 mg of Zn(OAC)2·2H2O was used as the hydrolysis catalyst.

[0134] Comparative Example 4 Solid terephthalic acid (TPA) (34.6 g, yield: 80%) was obtained in the same manner as in Example 14, except that 13 mg of Zn(OAC)2·2H2O was used as the hydrolysis catalyst.

[0135] Comparative Example 5 Solid terephthalic acid (TPA) (39.3 g, yield: 91%) was obtained in the same manner as in Example 1, except that 5.7 g of Zn(OAC)2·2H2O was used as the hydrolysis catalyst.

[0136] Comparative Example 6 Solid terephthalic acid (TPA) (35.9 g, 83% yield) was obtained in the same manner as in Example 2, except that 5.7 g of Zn(OAC)2·2H2O was used as the hydrolysis catalyst.

[0137] Comparative Example 7 Solid terephthalic acid (TPA) (37.2 g, 86% yield) was obtained in the same manner as in Example 13, except that 5.7 g of Zn(OAC)2·2H2O was used as the hydrolysis catalyst.

[0138] Comparative Example 8 Solid terephthalic acid (TPA) (34.1 g, yield: 79%) was obtained in the same manner as in Example 14, except that 5.7 g of Zn(OAC)2·2H2O was used as the hydrolysis catalyst.

[0139] Test example: Metal content An inductively coupled plasma atomic emission spectrometer (ICP-AES) was used to measure the metal content (ppm) present in the terephthalic acid of each of Examples 1 to 15 and Comparative Examples 1 to 8. ND means that the content was too low, less than 1 ppm, and therefore could not be measured as a specific value.

[0140] [Table 1]

[0141] As can be seen from Table 1 above, the recycled terephthalic acid prepared in Examples 1 to 15 was prepared by hydrolysis using the hydrolysis catalyst of the present invention and water, and therefore was environmentally friendly, and had a lower alcohol decomposition rate and a very low content of metal impurities, resulting in a high yield, compared to Comparative Examples 1 to 8. In addition, the process for preparing terephthalic acid according to the present invention is environmentally friendly in that it allows the recovery and reuse of alcohol, and can reduce process costs.

Claims

1. The method comprises hydrolyzing a compound that is liquid at room temperature and is prepared by depolymerizing waste polyester or bis(2-hydroxyethyl) terephthalate (BHET), the depolymerization comprises alcoholysis, the alcoholysis being carried out using an alcohol having 4 or more carbon atoms; The hydrolysis catalyst used in the hydrolysis step is NaOH, NaHCO ３ , Na ２ CO ３ , NaOMe, KOH, K ２ CO ３ , KOtBu, CsOH, Ca(OH) ２ , LiOH, and NH ４ 1. A process for preparing terephthalic acid, comprising at least one selected from the group consisting of: OH.

2. 2. The process for preparing terephthalic acid according to claim 1, wherein the amount of the hydrolysis catalyst used is 0.01 mole to 1.0 mole based on 1 mole of the compound.

3. 10. The process for preparing terephthalic acid according to claim 1, wherein the hydrolysis is carried out at a temperature of 180°C to 280°C for 0.5 hours to 24 hours.

4. 2. The process for preparing terephthalic acid according to claim 1, wherein water is added in the hydrolysis step, and the amount of water is added is 1 to 500 times the weight of the compound.

5. 1. The compound of formula 1: 【Chemistry 1】 (In formula 1, R １ 2. The process for preparing terephthalic acid according to claim 1, wherein R is a substituted or unsubstituted alkyl group.

6. R １ 6. The process for preparing terephthalic acid of claim 5, wherein is an unsubstituted or hydroxy-substituted alkyl group, or a substituted or unsubstituted alkyl group having two or more carbon atoms.

7. 2. The process for preparing terephthalic acid according to claim 1, wherein the compound is dibutyl terephthalate (DBTP) or diisooctyl terephthalate (DOTP).

8. 2. The process for preparing terephthalic acid according to claim 1, wherein in the hydrolysis step, alcohol is produced as a by-product, and the decomposition rate of the alcohol is less than 10%.

9. 2. The process for preparing terephthalic acid according to claim 1, wherein the weight ratio of waste polyester to alcohol in the alcoholysis is 1:1-10, and the alcoholysis is carried out at a temperature of 160°C-280°C and a pressure of 1 bar-40 bar for 0.5 hours-24 hours.

10. 10. The process for preparing terephthalic acid according to claim 1, wherein the process further comprises purifying the compound prior to the hydrolysis step.

11. 11. The process for preparing terephthalic acid according to claim 10, wherein the purification step comprises 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 adsorbent added is 0.1 wt% to 20 wt% based on the total weight of the compound.

12. Prepared according to the process for preparing terephthalic acid of claim 1, the process further comprising purifying the compound prior to the hydrolysis step; 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 adsorbent added is 0.1 wt % to 20 wt % based on the total weight of the compound; A method for producing recycled terephthalic acid, the method having a total metal content of less than 100 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

13. The method for producing recycled terephthalic acid according to claim 12, having a total content of Sb, Ti and Zn of less than 30 ppm as measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

14. having a color-b of less than 2 when measured with a colorimeter; 13. The method for producing recycled terephthalic acid according to claim 12, wherein the recycled terephthalic acid has a yellow index (Y.I.) of less than 2 when measured after diluting to a 5% concentration with dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP).

15. A method for producing a polyester resin, comprising recycled terephthalic acid obtained by the method for producing recycled terephthalic acid according to claim 12.

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