Method for producing terephthalic acid and terephthalic acid produced therefrom

Abstract

The present invention relates to a method for producing terephthalic acid in an environmentally friendly manner using waste polyester. In particular, according to one embodiment of the present invention, the method for producing terephthalic acid includes the steps of (1) subjecting waste polyester to alcoholysis using C4 or higher alcohol to produce a liquid composition containing the compound represented by formula 1, and (2) subjecting the liquid composition to hydrolysis, and thus can produce terephthalic acid in an environmentally friendly manner, improve processability, and reduce process costs.

Description

Technical Field

[0001] Technical Field The present invention relates to a process for preparing terephthalic acid in an environmentally friendly manner using waste polyester and the recycled terephthalic acid prepared thereby.

Background Art

[0002] Background Art Polyester is widely used as a material for containers for filling beverages, packaging films, audio and video films, etc. or industrial materials such as medical fibers and tire cords due to its excellent mechanical strength, heat resistance, transparency and gas barrier properties. In particular, polyester sheets or plates have good transparency and excellent mechanical strength, so they are widely used as raw materials for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc.

[0003] Wastes of plastics such as polyester are generated in amounts that cannot be managed globally every year, so there is an increasing interest in the reuse of waste polyester or the recycling process using waste polyester. Furthermore, countries around the world are preparing regulations and plans regarding the reuse of waste plastic resources such as waste polyester. For example, regulations requiring the use of recycled resin at a ratio or more in packaging materials used in various fields are being discussed.

[0004] In particular, polyethylene terephthalate (PET) has excellent properties regarding heat resistance, processability, transparency and non-toxicity, so it is widely used in the manufacture of a wide range of products such as films, fibers, bottles and containers. However, most of these are landfilled or incinerated after use, so research on their reuse or recycling process continues.

[0005] For example, Korean Patent Application 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 an alkali metal salt and an alkaline earth metal salt of terephthalic acid and neutralizing it with an acid. As a result of the hydrolysis reaction, terephthalate is produced instead of terephthalic acid, and a neutralization step by adding an acid is required to convert it to terephthalic acid. There is a problem that environmental pollutants are generated from the by-products formed as a result, or a large amount of acid treatment waste liquid is generated.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, an object of the present invention is to provide a process for preparing terephthalic acid in an environmentally friendly manner by alcoholysis and hydrolysis of waste polyester using a special alcohol, and the recycled terephthalic acid prepared thereby.

Means for Solving the Problems

[0008] A process for preparing terephthalic acid according to an embodiment of the present invention includes: (1) subjecting waste polyester to alcoholysis using an alcohol having 4 or more carbon atoms to prepare a liquid composition containing a compound represented by Formula 1; and (2) subjecting the liquid composition to hydrolysis.

Chemical Formula

[0009] In Formula 1, R1 is an alkyl group having 4 or more carbon atoms.

[0010] The recycled terephthalic acid according to another embodiment of the present invention is prepared by the process for preparing terephthalic acid described above and has a total metal content of less than 100 ppm when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0011] The polyester resin according to another embodiment of the present invention contains recycled terephthalic acid.

Advantages of the Invention

[0012] In the process for preparing terephthalic acid according to one embodiment of the present invention, waste polyester is subjected to alcoholysis using an alcohol having 4 or more carbon atoms to prepare a liquid composition containing the compound represented by Formula 1, and then it is subjected to hydrolysis using water. Therefore, terephthalic acid can be prepared in an environmentally friendly manner, the process cost can be reduced, and the processability can be improved.

[0013] In particular, in the process for preparing terephthalic acid according to one embodiment of the present invention, waste polyester is subjected to alcoholysis using a special alcohol, particularly an alcohol having 4 or more carbon atoms, to prepare a liquid composition containing the compound represented by Formula 1, and then it is subjected to hydrolysis using water. In the process for preparing terephthalic acid according to one embodiment of the present invention, solid terephthalic acid can be directly produced without using an additional step, which is different from the conventional process in which a terephthalate is produced from waste polyester and an additional step of neutralizing it is performed. Therefore, this process is not only easily operable, but also can reduce the process cost and obtain excellent processability.

[0014] Furthermore, acids such as sulfuric acid or hydrochloric acid used to neutralize terephthalate have a problem of generating environmental pollutants such as Na2SO4 and NaCl or a large amount of acid treatment waste liquid as by-products. In contrast, in the process for preparing terephthalic acid according to an embodiment of the present invention, unlike the conventional process, solid terephthalic acid can be directly produced without performing an additional neutralization step, and therefore, it is environmentally friendly.

[0015] Furthermore, in the process for preparing terephthalic acid according to an embodiment of the present invention, an intermediate, i.e., a hydrolysis reactant, is prepared in a liquid form, and thus, insoluble impurities such as metal catalysts and coloring pigments that may be contained in the waste polyester and additives such as soluble colorants can be easily removed. Therefore, the purity and yield of terephthalic acid produced by a simple process can be further improved.

Mode for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail. The present invention is not limited to the present disclosure shown below and can be changed into various forms as long as the gist of the present invention does not change.

[0017] Throughout this specification, when a part refers to an element as "including", it should be understood that, unless otherwise specified, another element is not excluded, but another element may be included.

[0018] All numbers and expressions related to amounts of components, reaction conditions, etc. used in this specification should be understood to be modified by the term "about" unless otherwise indicated.

[0019] Throughout this specification, terms such as first, second, etc. are used to represent various components. However, these components are not limited by these terms. These terms are used only for the purpose of distinguishing one component from another.

[0020] The process for preparing terephthalic acid according to one embodiment of the present invention comprises: (1) subjecting waste polyester to alcoholysis using an alcohol having 4 or more carbon atoms to prepare a liquid composition containing a compound represented by Formula 1; and (2) subjecting the liquid composition to hydrolysis.

Chemical formula

[0021] In Formula 1, R1 is an alkyl group having 4 or more carbon atoms.

[0022] In a conventional method for preparing terephthalic acid from waste polyester, solid terephthalic acid is directly obtained using an acid catalyst, or dimethyl terephthalate (DMT) or bis(2-hydroxyethyl) terephthalate (BHET) is produced as an intermediate by methanolysis or glycolysis and then converted to terephthalic acid. In such cases, terephthalic acid, dimethyl terephthalate, and bis(2-hydroxyethyl) terephthalate are all solids at room temperature or relatively high temperatures.

[0023] When solid terephthalic acid is directly obtained using an acid catalyst, terephthalic acid precipitates as a solid immediately after formation, making it difficult to remove insoluble impurities or additives such as colorants and pigments that may be contained in the waste polyester during the manufacturing process. Therefore, the improvement of purity or yield is limited. For this reason, a method of preparing a terephthalate from waste polyester and then neutralizing it to obtain solid terephthalic acid is also used. In such cases, the purity and yield of terephthalic acid can be improved by removing insoluble impurities and the like, but there is a problem that environmental pollutants such as Na2SO4 and NaCl or a large amount of acid treatment waste liquid are generated as by-products during the neutralization process of the terephthalate.

[0024] Furthermore, when dimethyl terephthalate is prepared as an intermediate, a large amount of methanol needs to be used to produce dimethyl terephthalate. Therefore, very high-pressure conditions occur due to the methanol used, and additional heating and high-pressure processes are required to convert dimethyl terephthalate into the liquid phase to remove insoluble impurities, resulting in a decrease in processability. Furthermore, when bis(2-hydroxyethyl) terephthalate is prepared as an intermediate, it is difficult to separate and recover ethylene glycol produced as a by-product during the manufacturing process, and thus it is not desirable in terms of processability and process cost.

[0025] Furthermore, an environmentally friendly method of reusing waste polyester is used by adding a metal salt to the waste polyester and directly hydrolyzing it with water. However, it has low processability in that very high-temperature conditions of 300 °C or higher are required, and the reaction apparatus also needs to have high-pressure resistance.

[0026] In contrast, in the process for preparing terephthalic acid according to an embodiment of the present invention, the intermediate, i.e., the hydrolysis reactant, is prepared in liquid form, and thus insoluble impurities such as metal catalysts and coloring pigments that may be contained in the waste polyester, as well as additives such as soluble colorants, can be easily removed. Therefore, the purity and yield of the produced terephthalic acid can be further improved.

[0027] Furthermore, since solid terephthalic acid can be directly produced without performing an additional neutralization step, it is environmentally friendly and has excellent processability, unlike conventional processes. Furthermore, not only is it easy to separate and recover ethylene glycol that may be formed as a by-product during the preparation process, but the alcohol having 4 or more carbon atoms used during the alcoholysis reaction can also be easily separated and reused, resulting in an excellent process cost reduction effect. Furthermore, the processability and economic efficiency can be further improved in that the purification and transfer processes other than the reaction can be performed at room temperature or low temperature.

[0028] For example, in the process of preparing terephthalic acid according to an embodiment of the present invention, first, waste polyester, an alcohol having 4 or more carbon atoms, and a very small amount of an alcoholysis catalyst are charged into a first high-pressure reactor, and then an alcoholysis reaction is carried out. Ethylene glycol and unreacted alcohol (the alcohol present in excess), which are by-products formed when the alcoholysis reaction is carried out, can be recovered by another fractionation device after the completion of the reaction and reuse.

[0029] Furthermore, ethylene glycol and unreacted alcohol formed during the reaction can be discharged immediately in the form of a gas mixture during the reaction, and then this is condensed and recovered using an external cooling device. In such a case, alcohol can be continuously supplied to the high-pressure reactor at the same volume and supply rate as the volume and discharge rate of the discharged gas mixture. Unreacted alcohol can be separated from the discharged gas mixture through a simple process such as fractionation or phase separation. The unreacted alcohol thus separated can be supplied again to the first high-pressure reactor, and then ethylene glycol can be recovered.

[0030] Thereafter, the liquid alcoholysis product obtained by the alcoholysis reaction can be purified by cooling, adsorption, and filtration. The purified alcoholysis reaction composition is supplied to a second high-pressure reactor together with water, and a hydrolysis reaction is carried out, and then a slurry-type solution is obtained, and filtered to obtain solid terephthalic acid. In such a case, a small amount of hydrolysis catalyst can be further supplied together with water before the hydrolysis reaction. The hydrolysis catalyst can be the same as or different from the alcoholysis catalyst.

[0031] Furthermore, after the completion of the hydrolysis reaction, the unreacted components are recovered and reintroduced for one or more reactions in the alcoholysis or hydrolysis reaction, thereby improving the yield of terephthalic acid finally produced. Furthermore, the amount of waste generated can be reduced, thereby making it more environmentally friendly. For example, the filtrate obtained by filtering excess unreacted alcohol (having 4 or more carbon atoms) and ethylene glycol as a by-product using a filter or the like can be reintroduced into the hydrolysis reaction.

[0032] Process for preparing terephthalic acid A process for preparing terephthalic acid according to an embodiment of the present invention includes (1) subjecting waste polyester to alcoholysis using an alcohol having 4 or more carbon atoms to prepare a liquid composition containing a compound represented by Formula 1, and (2) subjecting the liquid composition to hydrolysis.

Chemical formula

[0033] In Formula 1, R1 is an alkyl group having 4 or more carbon atoms.

[0034] Alcoholysis step (1) A process for preparing terephthalic acid according to an embodiment of the present invention includes subjecting waste polyester to alcoholysis using an alcohol having 4 or more carbon atoms to prepare a liquid composition containing a compound represented by Formula 1.

[0035] Waste polyester can be obtained by crushing or melting waste polyester products. For example, waste polyester can be obtained by crushing used, recovered, and separated polyester products or converting them into pellets (post-consumer recycled materials, PCR), or can be polyester waste such as defective products or scraps formed during processes such as the molding of polyester films, fibers, containers, etc. (post-industrial recycled materials, PIR), and is not limited thereto.

[0036] Furthermore, the number of carbon atoms of the alcohol can be 4 or more, 6 or more, 8 or more, 10 or more, or 12 or more, and can be 4 to 14, 4 to 13, 4 to 10, 4 to 8, 6 to 12, 8 to 14, or 8 to 13.

[0037] When 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 lower temperature and pressure than the conventional process using waste polyester, which is carried out at high temperature and high pressure, and the intermediate, i.e., the alcoholysis product, can be produced in liquid form. Furthermore, when the number of carbon atoms of the alcohol satisfies the above range, the reaction rate of alcoholysis can be improved.

[0038] Furthermore, the alcohol can have a boiling point of 100°C to 290°C. For example, the boiling point of the alcohol 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 the alcohol satisfies the above range, ethylene glycol formed as a by-product during alcoholysis can be more easily removed or recovered during subsequent processes, thereby further improving processability. In particular, in the fields where polyester is used as a raw material, there has been a tendency to use various monomer materials in recent years, and therefore, the removal of various dialcohol-type monomers used in waste polyester such as waste plastic products can be easily adopted.

[0039] The weight ratio of the waste polyester to the alcohol can be from 1:1 to 10. For example, the weight ratio of the waste polyester to the alcohol can 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.

[0040] Furthermore, the alcoholysis reaction can be carried out at a temperature of 160°C to 280°C and a pressure of 1 bar to 40 bar for 0.5 hour to 24 hours. For example, the alcoholysis reaction can 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 hour 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.

[0041] In step (1), an alcoholysis catalyst can be added. In particular, the alcoholysis reaction can be smoothly carried out as a non-catalytic reaction without using an alcoholysis catalyst, thereby being environmentally friendly. In particular, when the content of insoluble metals in the waste polyester is high, the non-catalytic reaction can be advantageous for efficient treatment and impurity removal. Furthermore, the alcoholysis catalyst can be added to step (1) from the perspective of energy in order to improve processability by improving reactivity.

[0042] The alcoholysis catalyst can be a metal acetate, an alkali metal salt or a hydroxy salt.

[0043] In particular, the alcoholysis catalyst is Li + , Na + , K + and Cs + such alkali metal ions as, Be 2+ , Mg 2+ , Ca 2+ and Ba 2+Alkaline earth metal ions such as, NH 4+ and NR 4+ (wherein R is alkyl), ammonium ions such as Zn 2+ and at least one cation selected from the group consisting of OH - , OR - (wherein R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - ), 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion, and may contain at least one anion selected from the group consisting of. R may be an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 5 carbon atoms.

[0044] For example, the alcoholysis catalyst may contain 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.

[0045] 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, the amount of the alcoholysis catalyst added may 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 based on the total weight of the waste polyester.

[0046] According to one embodiment of the present invention, a liquid composition containing a compound represented by Formula 1 is prepared by alcoholysis. In particular, this composition is liquid at room temperature, and this liquid composition is a composition produced by an alcoholysis reaction.

[0047] The liquid composition contains a compound represented by Formula 1. [Chemical formula]

[0048] In Formula 1, R1 is an alkyl group having 4 or more carbon atoms.

[0049] In particular, R1 can be butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, hexyl, 1-methylhexyl, 2-ethyl-1-hexyl, heptyl, n-heptyl, 1-methylheptyl, octyl, n-octyl, isooctyl, tert-octyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl-propyl, 1,1-dimethyl-propyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, decanyl, undecanyl, dodecanyl, tridecanyl or tetradecanyl.

[0050] In particular, the liquid composition may contain unreacted alcohol and ethylene glycol (EG) as a by-product. In particular, this liquid composition may contain a compound represented by Formula 1, ethylene glycol (EG) formed as a by-product of the alcoholysis reaction, unreacted alcohol and oligomers.

[0051] For example, the liquid composition may contain a compound represented by Formula 2, and the oligomer may contain a compound represented by Formula 3. [Chemical formula]

[0052] In Formulas 2 and 3, R1 is an alkyl group having 4 or more carbon atoms, and n is an integer of 1 or more.

[0053] According to one embodiment of the present invention, the liquid composition may contain unreacted alcohol and ethylene glycol as a by-product, and the content of the compound represented by Formula 1 in the liquid composition may be 70 mol% or more. For example, the content of the compound represented by Formula 1 in the liquid composition prepared by alcoholysis may be 72 mol% or more, 75 mol% or more, 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, 92 mol% or more, 92.5 mol% or more, 93 mol% or more, 95 mol% or more, 97 mol% or more, 99 mol% or more, or 99.5 mol% or more.

[0054] Furthermore, the content of the oligomer in the liquid composition may be 15 mol% or less. For example, the content of the oligomer 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.

[0055] According to another embodiment of the present invention, step (1) may include discharging unreacted alcohol and ethylene glycol as a by-product.

[0056] In particular, the alcohol is separated from the mixture of the discharged alcohol and ethylene glycol, and the separated alcohol can be reused as a raw material for alcoholysis. For example, ethylene glycol as a by-product formed in alcoholysis and unreacted alcohol (alcohol present in excess) are immediately discharged in the form of a gas mixture during the alcoholysis reaction, and fractional distillation or layer separation is performed, and / or fractional distillation is performed after the completion of the reaction to separate into alcohol and ethylene glycol. The separated alcohol can be reintroduced and reused in the alcoholysis in step (1). In such a case, the volume and supply rate of the alcohol introduced for reuse can be the same as the volume and discharge rate of the mixture of the discharged alcohol and ethylene glycol.

[0057] Furthermore, step (1) may include recovering ethylene glycol as a by-product of alcoholysis. In particular, ethylene glycol as a by-product of alcoholysis can be recovered by fractional distillation or layer separation of the mixture of the discharged alcohol and ethylene glycol, and can be recovered by fractional distillation or layer separation of the composition prepared in step (1).

[0058] For example, unreacted alcohol and ethylene glycol as a by-product are immediately discharged as a gas mixture during the alcoholysis reaction, and this is condensed using an external cooling device to recover ethylene glycol.

[0059] According to one embodiment of the present invention, unreacted alcohol and ethylene glycol can not only be separated by a simple process such as fractional distillation or layer separation, but also the separated unreacted alcohol can be reused as a raw material for alcoholysis, and the recovered ethylene glycol can be used in another process. Therefore, it is excellent in processability and process cost reduction.

[0060] The recovery rate of ethylene glycol can be 65% or more. For example, the recovery rate of ethylene glycol can be 70% or more, 76% or more, 85% or more, 90% or more, 93% or more, 95% or more, 97% or more, 98% or more, 99% or more, or 99.5% or more.

[0061] Purification step The process for preparing terephthalic acid according to another embodiment of the present invention may further include purifying the liquid composition before step (2).

[0062] In particular, 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 adsorption through bed adsorption. In particular, 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 with a weight ratio of 1:0.5 to 1.5 or 1:0.8 to 1.2, but is not limited thereto.

[0063] The content of the adsorbent added can be 0.1% by weight to 20% by weight based on the total weight of the liquid composition. For example, the content of the adsorbent added can be 0.1% by weight to 18% by weight, 0.1% by weight to 15% by weight, 0.1% by weight to 10% by weight, 0.1% by weight to 5% by weight, or 0.1% by weight to 2% by weight based on the total weight of the liquid composition.

[0064] When the step of purifying the liquid composition using an adsorbent, particularly an adsorbent satisfying a specific supply amount within the above numerical range, is further performed, the purity and yield can be further improved. In particular, when the step of purifying the liquid composition which is an alcoholysis reaction composition is performed, it becomes possible to more efficiently remove insoluble impurities such as metals that may be contained in the alcoholysis reaction composition or additives such as coloring agents and pigments that may be contained in waste polyester. Therefore, the purity and yield of the finally prepared terephthalic acid can be further improved.

[0065] Furthermore, a process for preparing terephthalic acid according to another embodiment of the present invention may further include a concentration step after the purification step.

[0066] This concentration can be carried out at a temperature of 50°C to 120°C for 0.5 hours to 6 hours. For example, the concentration can be carried out by stirring the purified alcoholysis reaction composition at a temperature of 55°C to 115°C, 60°C to 110°C, 65°C to 105°C or 75°C to 100°C for 1 hour to 5 hours, 1.5 hours to 4 hours or 2 hours to 4 hours.

[0067] According to one embodiment of the present invention, the purified composition may have a pigment residue rate (%) of 15% or less according to Formula A. For example, the pigment residue rate (%) of the purified alcoholysis reaction composition according to Formula A 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.

Number

[0068] In Formula A, A1 is the area of the absorbance curve obtained at 400 nm to 800 nm using a UV-vis spectrophotometer for the purified alcoholysis reaction composition diluted to a concentration of 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF) or N-methylpyrrolidone (NMP), and A2 is the area of the absorbance curve obtained in the same manner as above for the unpurified alcoholysis reaction composition.

[0069] The description regarding purification in Formula A is as described above.

[0070] The pigment residue rate means the content of additives such as colorants, pigments, dyes remaining in the composition. The lower the pigment residue rate, the lower the content of additives such as colorants, pigments, dyes, indicating higher purity.

[0071] Furthermore, the content of insoluble impurities such as metals in the purified composition can be reduced. In particular, when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the purified liquid composition can have a total metal content of 100 ppm or less based on the total weight of the purified alcoholysis reaction composition.

[0072] For example, the purified alcoholysis reaction 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 reaction composition can 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 alcoholysis reaction composition. In particular, the total content of Sb, Ti, and Zn in the purified alcoholysis reaction composition can 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.

[0073] Sb is known to be a catalyst widely used in the polymerization of common polyesters due to its excellent stability, reaction rate, and cost. However, due to the strengthening of regulations regarding the impact of Sb on the human body and the environment, this is a substance that needs to be removed during the chemical recycling process.

[0074] Furthermore, Ti can be used as a catalyst for polyester polymerization or as an additive for polyester processing in the form of TiO2. When contained in a specific amount or more, the quality of the recycled terephthalic acid prepared therefrom or the polyester resin using it may deteriorate, thereby limiting its use.

[0075] Zn is also a component used as a polymerization catalyst for polyesters such as PET. If this remains, it can affect the control of reactivity in the preparation process of recycled terephthalic acid or polyester resin that uses it. Therefore, it is preferable to remove this. In particular, since it is widely used in chemical recycling processes, this is a substance that needs to sufficiently remove the amount contained in waste plastics, which are the raw materials of this process, and the amount separately added as a catalyst during the recycling process.

[0076] According to one embodiment of the present invention, when further purification is carried out, the total content of metals, particularly Sb, Ti, and Zn mentioned above, in the purified alcoholysis reaction composition becomes very small, 30 ppm or less.

[0077] For example, when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the content of Sb 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 alcoholysis reaction composition.

[0078] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the content of Ti 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 alcoholysis reaction composition.

[0079] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the content of Zn 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 alcoholysis reaction composition.

[0080] Hydrolysis reaction step (2) The process for preparing terephthalic acid according to one embodiment of the present invention includes subjecting the composition to hydrolysis. In particular, in step (2), the alcoholysis reaction composition (liquid composition containing the compound represented by formula I) prepared in step (1) or the purified alcoholysis reaction composition can be subjected to hydrolysis to prepare recycled terephthalic acid.

[0081] Hydrolysis can be carried out by adding water to the composition. For example, hydrolysis can be carried out by adding water to the alcoholysis reaction composition or the purified alcoholysis reaction composition at a temperature 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 hour to 24 hours, 1 hour to 20 hours, 2.5 hours to 12 hours or 3 hours to 8 hours.

[0082] The conventional method in which a metal catalyst such as iron, cobalt, manganese or nickel is added to the waste polyester and then directly hydrolyzed with water is environmentally friendly. However, it has low processability in that very high temperature conditions of 300 °C or higher are required and the reaction apparatus also needs to have high pressure resistance. In contrast, the process for preparing terephthalic acid according to one embodiment of the present invention has excellent processability because the process conditions are improved compared to the prior art.

[0083] Furthermore, the weight ratio of the composition to water can be 1:1 to 500. For example, the weight ratio of the alcoholysis reaction composition (purified or purified and concentrated alcoholysis reaction composition) used during hydrolysis to water can be 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.

[0084] Furthermore, in step (2), a hydrolysis catalyst can be added. In particular, a hydrolysis catalyst can be added to the mixture of the alcoholysis reaction composition and water in order to carry out hydrolysis.

[0085] The hydrolysis reaction can be smoothly carried out as a non-catalytic reaction without using a hydrolysis catalyst, and thus it is environmentally friendly. In particular, when the content of insoluble metals in the waste polyester is high, the non-catalytic reaction can be advantageous with respect to efficient treatment and impurity removal. Furthermore, the hydrolysis catalyst can be added to step (2) from the viewpoint of energy in order to improve processability by improving reactivity.

[0086] The hydrolysis catalyst can be a metal acetate, an alkali metal salt or a hydroxy salt.

[0087] In particular, the hydrolysis catalyst is Li + , Na + , K + and Cs + and other alkali metal ions such as Be 2+ , Mg 2+ , Ca 2+ and Ba 2+ and other alkaline earth metal ions such as NH 4+ and NR 4+ (where R is alkyl), and other ammonium ions such as Zn 2+ and at least one cation selected from the group consisting of or OH - , OR - (where R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - ), 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.

[0088] For example, the hydrolysis catalyst can 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, dibutyltin(IV) oxide, stannous octoate, titanium phosphate and terephthalic acid.

[0089] Furthermore, the amount of the hydrolysis catalyst added can be from 10 ppm to 10,000 ppm based on the total weight of the composition. For example, the amount of the hydrolysis catalyst added can be from 15 ppm to 8,000 ppm, from 20 ppm to 5,500 ppm, from 30 ppm to 3,000 ppm, from 50 ppm to 1,600 ppm, from 100 ppm to 1,200 ppm, from 150 ppm to 1,100 ppm, from 300 ppm to 1,000 ppm, from 350 ppm to 950 ppm, from 400 ppm to 850 ppm, from 420 ppm to 700 ppm or from 450 ppm to 650 ppm based on the total weight of the alcoholysis reaction composition (purified or purified and concentrated alcoholysis reaction composition).

[0090] According to one embodiment of the present invention, solid terephthalic acid can be prepared by a hydrolysis reaction. In particular, this process may further include filtration, washing and drying of the hydrolysis reaction product prepared by the hydrolysis reaction after the hydrolysis step. That is, the hydrolysis reaction product prepared by the hydrolysis reaction can be filtered, washed and dried to produce solid terephthalic acid.

[0091] For example, the hydrolysis reaction product can be cooled to an appropriate temperature, for example, from room temperature to less than 100 °C, at which temperature water does not evaporate and a solution in the form of a slurry is obtained. When this is filtered, a solid is obtained, which is washed and dried under reduced pressure to obtain solid terephthalic acid.

[0092] The washing can be carried out using a mixture of an alcohol having 4 or more carbon atoms and / or water, a protic solvent such as isopropanol and acetic acid, or an aprotic solvent such as acetone, dichloromethane, chloroform, tetrahydrofuran (THF) and toluene.

[0093] Here, the description regarding the alcohol having 4 or more carbon atoms is as described above. The alcohol having 4 or more carbon atoms used for washing may be the same as or different from the alcohol having 4 or more carbon atoms used in step (1). For example, when 1-butanol is used as the alcohol in step (1) for producing terephthalic acid, the prepared solid terephthalic acid can be washed with a mixture of 1-butanol and water. Further, the number of carbon atoms in the alcohol used for washing can be the same as the number of carbon atoms in the alcohol used in step (1).

[0094] Residual pigments or impurities generated by the decomposition of pigments during hydrolysis, particularly yellow impurities, can be efficiently removed by washing, thereby improving the yellowness index or color characteristics. Further, when water is used for washing, inorganic salts can be removed, thereby improving the quality.

[0095] Furthermore, the yield of terephthalic acid can be 65% or more. For example, the yield of the finally produced recycled terephthalic acid can be 68% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more.

[0096] Recycled terephthalic acid The recycled terephthalic acid according to another embodiment of the present invention is prepared by the process for preparing terephthalic acid as described above and has a total metal content of less than 100 ppm when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0097] In particular, the recycled terephthalic acid can be prepared by the process for preparing terephthalic acid.

[0098] Recycled terephthalic acid can have a total metal 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, 15 ppm or less, 9 ppm or less, 7 ppm or less, 5 ppm or less or 1 ppm or less when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0099] Furthermore, recycled terephthalic acid can have a total content of Sb, Ti and Zn of less than 30 ppm when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). For example, the total content of Sb, Ti and Zn in recycled terephthalic acid, which can be harmful to the human body or function as a catalyst for reactions or side reactions in subsequent polymerization processes, can 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.

[0100] For example, when measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the content of Sb in recycled 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 based on the total weight of the recycled terephthalic acid.

[0101] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the content of Ti in recycled 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 based on the total weight of the recycled terephthalic acid.

[0102] When measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), the content of Zn in recycled 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 based on the total weight of the recycled terephthalic acid.

[0103] The recycled terephthalic acid can have a color - b of less than 2, 1.6 or less, 1.4 or less, 1.3 or less, or 1 or less as measured using a colorimeter. Since the above numerical ranges of color - b are equivalent to those of virgin terephthalic acid generally produced in petrochemical processes, the recycled terephthalic acid that meets the above range of color - b not only has a low yellowness index but also has excellent quality because the monomers are sufficiently purified.

[0104] Col - b is a color coordinate established by the International Commission on Illumination (CIE), and color is represented by L (brightness), a (complementary color from green to red), and b (complementary color from yellow to blue). This can be measured using a colorimeter.

[0105] Furthermore, the recycled terephthalic acid can have a pigment residue rate according to formula B of 10% or less. For example, the pigment residue rate of the recycled terephthalic acid can be 10% or less, 8% or less, 7% or less, 5% or less, or 4% or less.

Number

[0106] In formula B, B1 is the area of the absorbance curve obtained at 400 nm - 800 nm using a UV - vis spectrophotometer for recycled terephthalic acid diluted to a concentration of 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or N - methylpyrrolidone (NMP), and B2 is the area of the absorbance curve obtained in the same manner for recycled terephthalic acid that has not been purified during its preparation process.

[0107] B1 can be measured for recycled terephthalic acid produced by performing a purification step or purification and concentration steps in the process of preparing the recycled terephthalic acid. B2 can be measured for recycled terephthalic acid produced without performing a purification step in the process of preparing the recycled terephthalic acid or produced by performing only a concentration step.

[0108] Furthermore, when measuring by diluting the recycled terephthalic acid to a concentration of 5% in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and N-methylpyrrolidone (NMP) respectively, the yellowness index (Y.I.) can be less than 2, 1.8 or less, or 1.7 or less. The yellowness index can be measured for the recycled terephthalic acid produced by performing a purification step in the process of preparing the recycled terephthalic acid, or by performing purification and concentration steps.

[0109] Polyester resin and its preparation process A polyester resin according to another embodiment of the present invention contains recycled terephthalic acid.

[0110] In particular, the polyester resin may contain recycled terephthalic acid, a diol compound or its derivative, and optionally a dicarboxylic acid compound or its derivative.

[0111] 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-cyclohexanedimethanol, and neopentyl glycol. The dicarboxylic acid 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-naphthalenedicarboxylate (2,6-NDC). However, it is not limited thereto.

[0112] 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 its derivative and optionally a dicarboxylic acid compound or its derivative, and then performing an esterification reaction and subjecting the esterification reaction product to a polycondensation reaction.

[0113] 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. Further, the esterification reaction can be carried out at a pressure higher than the standard pressure by 0 kg / cm 2 to 10 kg / cm 2 (0 mmHg to 7,355.6 mmHg), 0 kg / cm 2 to 5 kg / cm 2 (0 to 3,677.8 mmHg), or 0 kg / cm 2 to 2.0 kg / cm 2 (0 to 1,471.1 mmHg). Further, the esterification reaction can be carried out over a period of 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 6 hours.

[0114] Furthermore, the polycondensation reaction can 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. Further, the polycondensation reaction can be carried out under a reduced pressure of 0.01 mmHg to 400 mmHg, 0.05 mmHg to 100 mmHg, or 0.1 mmHg to 100 mmHg. Further, the polycondensation reaction can be carried out over the time required to reach the desired intrinsic viscosity. For example, this can be carried out over a period of 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 4 hours.

[0115] Furthermore, a catalyst and / or a stabilizer can be further added to the esterification reaction and the polycondensation reaction.

[0116] For example, the catalyst for the esterification reaction can be methylates of sodium and magnesium, acetates, borates, fatty acid salts, and carbonates of Zn, Cd, Mn, Co, Ca, and Ba, metallic Mg, and oxides of Pb, Zn, Sb, and Ge.

[0117] Furthermore, the catalyst for the polycondensation reaction can 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, lactate titanate, triethanolamine titanate, acetylacetonate titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, titanium dioxide / silicon dioxide copolymer, titanium dioxide / zirconium dioxide copolymer, a germanium-based catalyst such as germanium dioxide and a copolymer using the same, or a tin-based catalyst such as monobutyltin oxide, dibutyltin oxide, and monobutylhydroxytin oxide.

[0118] Furthermore, the stabilizer can be a phosphorus-based compound, and for example, phosphoric acid, trimethyl phosphate, and triethyl phosphate can be used, but are not limited thereto.

[0119] The process for preparing the polyester resin according to another embodiment of the present invention may further include performing a solid-phase polymerization reaction. For example, the solid-phase polymerization can be carried out after the polycondensation reaction under a temperature of 190°C to 230°C and a vacuum condition of 0.2 Torr to 2.0 Torr or in a nitrogen atmosphere.

[0120] Aspects of the Invention Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these examples are described for illustrative purposes of the present invention, and the scope of the present invention is not limited thereto.

Examples

[0121] Preparation of Liquid Composition Example 1-1 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as an alcohol were charged into a first high-pressure reactor with a capacity of 7 liters, and then 200 mg of Zn(OAC)2·2H2O (200 ppm based on the total weight of the waste PET) as an alcoholysis catalyst was added thereto.

[0122] After that, all the connections of the first high-pressure reactor were tightened and sealed, the temperature was raised to 250 °C in 1 hour, and the alcoholysis reaction was carried out with stirring for 3 hours while maintaining the temperature of 250 °C and the pressure of 24 bar.

[0123] After completion of the alcoholysis reaction, it was cooled to room temperature to obtain a liquid alcoholysis reaction composition. Here, the components and contents of the alcoholysis reaction composition were analyzed by NMR. The alcoholysis reaction composition contained a compound represented by Formula 1 (R1: (CH2)3CH3), residual ethylene glycol (EG), alcohol (1-butanol), and oligomers.

[0124] After that, the alcoholysis reaction composition was put into another flask, and excess unreacted 1-butanol and the generated ethylene glycol (EG) were respectively recovered using a fractional distillation apparatus.

Chemical formula

[0125] Example 1-2 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as alcohol were charged into a first high-pressure reactor with a capacity of 7 liters, and then 200 mg of Zn(OAC)2·2H2O (200 ppm based on the total weight of the waste PET) as an alcoholysis catalyst was added thereto.

[0126] After that, all the connections of the first high-pressure reactor were tightened and sealed, the temperature was raised to 250 °C in 1 hour, and the alcoholysis reaction was carried out with stirring for 3 hours while maintaining the temperature of 250 °C and the pressure of 24 bar.

[0127] Specifically, one hour after the start of the alcoholysis reaction, the valve of the pre-attached backpressure control device was adjusted to discharge the gas mixture of ethylene glycol (EG), a by-product generated by the alcoholysis reaction, and the excess 1-butanol present. In such a case, the internal temperature of the first high-pressure reactor was maintained at 250 °C, and the gas mixture of ethylene glycol (EG) and 1-butanol discharged from the backpressure control device was condensed using an external cooling device. Further, the discharge rate of the gas mixture of ethylene glycol (EG) and 1-butanol was adjusted to 3 kg / h, and at the same time, 1-butanol was continuously supplied to the first high-pressure reactor. In such a case, the volume and supply rate of the newly supplied 1-butanol to the first high-pressure reactor were adjusted to be the same as the volume and discharge rate of the discharged gas mixture of ethylene glycol (EG) and 1-butanol. The alcoholysis reaction was carried out while maintaining the discharge and supply processes for 3 hours.

[0128] After completion of the alcoholysis reaction, it was cooled to room temperature to obtain a liquid alcoholysis reaction composition. Here, the components and contents of the alcoholysis reaction composition were analyzed by NMR. The alcoholysis reaction composition contained a compound represented by Formula 1 (R1: (CH2)3CH3), residual ethylene glycol (EG), alcohol (1-butanol), and oligomers.

[0129] Thereafter, the alcoholysis reaction composition was put into another flask, and the excess unreacted 1-butanol and the generated ethylene glycol were respectively recovered using a fractional distillation apparatus.

Chemical formula

[0130] Examples 1-3 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-butanol as alcohol were charged into a first high-pressure reactor with a capacity of 7 liters, and then 200 mg of Zn(OAC)2·2H2O (200 ppm based on the total weight of the waste PET) as an alcoholysis catalyst was added thereto.

[0131] Thereafter, all the connections of the first high-pressure reactor were tightened and sealed, the temperature was raised to 250°C in 1 hour, and the alcoholysis reaction was carried out with stirring for 3 hours while maintaining a temperature of 250°C and a pressure of 24 bar.

[0132] Specifically, 1 hour after the start of the alcoholysis reaction, the valve of the pre-attached backpressure control device was adjusted to discharge the gas mixture of ethylene glycol (EG), a by-product generated by the alcoholysis reaction, and the excess 1-butanol. In such a case, the internal temperature of the first high-pressure reactor was maintained at 250°C, and the gas mixture of ethylene glycol (EG) and 1-butanol discharged from the backpressure control device was condensed using an external cooling device. Furthermore, the discharge rate of the gas mixture of ethylene glycol (EG) and 1-butanol was adjusted to 3 kg / h, and at the same time, 1-butanol was continuously supplied to the first high-pressure reactor. In such a case, the volume and supply rate of the newly supplied 1-butanol to the first high-pressure reactor were adjusted to be the same as the volume and discharge rate of the discharged gas mixture of ethylene glycol (EG) and 1-butanol.

[0133] The condensed gas mixture of ethylene glycol (EG) and 1-butanol was transferred to a layer separation device having a capacity of 5 liters and filled with 3 kg of water, and the procedures of stirring for 10 minutes and layer separation for 2 minutes were repeated to separate the 1-butanol layer and the water and ethylene glycol (EG) layer. Immediately, the separated 1-butanol was supplied again to the first high-pressure reactor using a high-pressure pump. The alcoholysis reaction was carried out while maintaining the procedures of stirring, layer separation, and re-introduction for 3 hours.

[0134] After completion of the alcoholysis reaction, the reaction mixture was cooled to room temperature to obtain a liquid alcoholysis reaction composition. Here, the components and contents of the alcoholysis reaction composition were analyzed by NMR. The alcoholysis reaction composition contained a compound represented by Formula 1 (R1: (CH2)3CH3), residual ethylene glycol (EG), alcohol (1-butanol), and oligomers.

[0135] Thereafter, the alcoholysis reaction composition was transferred to another flask, and excess unreacted 1-butanol and the generated ethylene glycol were recovered using a fractional distillation apparatus, respectively.

Chemical formula

[0136] Examples 1-4 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-1, except that 3.3 kg of 1-pentanol was used as the alcohol and the pressure was maintained at 13 bar.

[0137] Example 1-5 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-2, except that 3.3 kg of 1-pentanol was used as the alcohol and the pressure was maintained at 13 bar.

[0138] Example 1-6 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-3, except that 3.3 kg of 1-pentanol was used as the alcohol and the pressure was maintained at 13 bar.

[0139] Example 1-7 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-1, except that 3.3 kg of 1-octanol was used as the alcohol and the pressure was maintained at 3.4 bar.

[0140] Example 1-8 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-2, except that 3.3 kg of 1-octanol was used as the alcohol and the pressure was maintained at 3.4 bar.

[0141] Example 1-9 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-3, except that 3.3 kg of 1-octanol was used as the alcohol and the pressure was maintained at 3.4 bar.

[0142] Example 1-10 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 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.

[0143] Example 1-11 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 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.

[0144] Example 1-12 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 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.

[0145] Example 1-13 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-1, except that 3.3 kg of 1-decanol was used as the alcohol and the pressure was maintained at 1.6 bar.

[0146] Example 1-14 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-2, except that 3.3 kg of 1-decanol was used as the alcohol and the pressure was maintained at 1.6 bar.

[0147] Example 1-15 A liquid alcoholysis reaction composition was prepared in the same manner as in Examples 1-3, except that 3.3 kg of 1-decanol was used as the alcohol and the pressure was maintained at 1.6 bar.

[0148] Examples 1-16 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-1, except that 3.3 kg of 1-dodecanol was used as the alcohol and the pressure was maintained at 1.0 bar.

[0149] Example 1-17 1 kg of waste polyethylene terephthalate (waste PET) and 3.3 kg of 1-dodecanol as the alcohol were charged into a first high-pressure reactor with a capacity of 7 liters. Subsequently, 200 mg of Zn(OAC)2·2H2O (200 ppm based on the total weight of the waste PET) as the alcoholysis catalyst was added thereto.

[0150] Subsequently, all connections of the first high-pressure reactor were tightened and sealed, and the temperature was raised to 250°C in 1 hour. While maintaining the temperature of 250°C and the pressure of 1.0 bar, the alcoholysis reaction was carried out with stirring for 3 hours.

[0151] In particular, 1 hour after the start of the alcoholysis reaction, the valve of a pre-installed backpressure control device was adjusted to discharge the vapor of ethylene glycol (EG), which is a by-product generated by the alcoholysis reaction. In such a case, the internal temperature of the first high-pressure reactor was maintained at 250°C, and the vapor of ethylene glycol (EG) was condensed using an external cooling device.

[0152] Furthermore, an amount of 1-dodecanol equal to the amount of ethylene glycol (EG) discharged as vapor and condensed was continuously supplied to the first high-pressure reactor. In such a case, the volume and supply rate of the newly supplied 1-dodecanol to the first high-pressure reactor were adjusted to be the same as the volume and discharge rate of the vapor of the discharged ethylene glycol (EG). The alcoholysis reaction was carried out while maintaining the discharge and supply processes for 3 hours.

[0153] After completion of the alcoholysis reaction, the reaction mixture was cooled to room temperature to obtain a liquid alcoholysis reaction composition. Here, the components and contents of the alcoholysis reaction composition were analyzed by NMR. The alcoholysis reaction composition contained a compound represented by Formula 1 (R1: (CH2) 11 CH3), residual ethylene glycol (EG), alcohol (1-dodecanol), and oligomers.

[0154] Thereafter, the alcoholysis reaction composition was transferred to another flask, and the excess unreacted 1-dodecanol and the generated ethylene glycol (EG) were recovered using a fractional distillation apparatus, respectively.

Chemical formula

[0155] Example 1-18 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-1, except that 3.3 kg of 1-tetradecanol was used as the alcohol and the pressure was maintained at 1.0 bar.

[0156] Example 1-19 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-17, except that 3.3 kg of 1-tetradecanol was used as the alcohol.

[0157] Comparative Example 1-1 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-1, except that 3.3 kg of methanol was used as the alcohol and the pressure was maintained at 83 bar.

[0158] Comparative Example 1-2 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-2, except that 3.3 kg of methanol was used as the alcohol and the pressure was maintained at 83 bar.

[0159] Comparative Example 1-3 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-1, except that 3.3 kg of ethanol was used as the alcohol and the pressure was maintained at 64 bar.

[0160] Comparative Example 1-4 A liquid alcoholysis reaction composition was prepared in the same manner as in Example 1-2, except that 3.3 kg of ethanol was used as the alcohol and the pressure was maintained at 64 bar.

[0161] [Table 1]

[0162] As can be seen from Table 1 above, when the liquid alcoholysis reaction compositions of Examples 1-1 to 1-19 were prepared using alcohols having 4 or more carbon atoms, these could be prepared at a very low process pressure as compared with Comparative Examples 1-1 to 1-4. The content of the compound represented by Formula 1, that is, the yield and purity were high, and the recovery rate of ethylene glycol was also excellent.

[0163] Purification and Concentration of Liquid Composition Example 2-1 Using the fractionation apparatus in Example 1-1, 0.1 g of activated carbon as an adsorbent was added to 100 g of the liquid alcoholysis reaction composition before recovering the excess unreacted alcohol and the produced ethylene glycol, and then the purification was carried out. This was stirred at 100 °C for 3 hours and then filtered to concentrate the alcoholysis reaction composition.

[0164] Examples 2-2 to 2-23 and Comparative Examples 2-1 and 2-2 As shown in Table 2 below, the liquid alcoholysis reaction compositions were each purified and concentrated in the same manner as in Example 2-1, except that the liquid composition and process conditions were changed. Here, in Comparative Examples 2-1 and 2-2, precipitation occurred in an undissolved state and this was not purified.

[0165] Examples 2-24 to 2-26 Using the fractionation apparatuses in Examples 1-1, 1-4, and 1-10 respectively, 0.1 g of activated carbon as an adsorbent was added to 100 g of the liquid alcoholysis reaction composition after recovering excess unreacted alcohol and the produced ethylene glycol, and then purification was carried out. This was stirred at 100 °C for 3 hours and then filtered to concentrate the alcoholysis reaction composition.

[0166] Comparative Examples 2-3 to 2-21 Using the fractionation apparatuses in Examples 1-1 to 1-19 respectively, no adsorbent was added to the liquid alcoholysis reaction composition before recovering excess unreacted alcohol and the produced ethylene glycol. This was stirred at 100 °C for 3 hours and then filtered to concentrate it.

[0167] Test Example 1-1: Pigment Residual Ratio The pigment residual ratio (%) was measured for each of the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21.

[0168] Specifically, the composition of Example 2-1 was diluted to a concentration of 5% each in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and N-methylpyrrolidone (NMP), and the area (A1) of the absorbance curve at 400 nm to 800 nm was determined using a UV-vis spectrophotometer. Further, in the case of the composition of Comparative Example 2-3 (the composition of Example 1-1 was used in the same manner as the composition of Example 2-1 described above, but this composition was concentrated without purification by adding an adsorbent), the area (A2) of the absorbance curve at 400 nm to 800 nm was determined in the same manner as above. Using the measured area of the absorbance curve, the pigment residual ratio (%) was calculated by the following formula A.

Equation

[0169] For each of the compositions of Examples 2-2 to 2-26 and Comparative Examples 2-1 to 2-21, the pigment residual ratio (%) was measured in the same manner as above.

[0170] Test Example 1-2: Yellowness Index The yellowness index (Y.I.) was measured for each of the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21.

[0171] Specifically, each of the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21 was diluted to a concentration of 5% each in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and N-methylpyrrolidone (NMP), and the yellowness index was measured using a ColorFlex EZ (manufacturer: HunterLab) apparatus.

[0172] Test Example 1-3: Metal content Using inductively coupled plasma atomic emission spectrometry (ICP-AES), the metal content (ppm) present in each of the compositions of Examples 2-1 to 2-26 and Comparative Examples 2-1 to 2-21 was measured. N.D. means that the content is less than 1 ppm, which is too low to be measured as a specific value.

[0173] [Table 2-1]

[0174] [Table 2-2]

[0175] [Table 2-3]

[0176] As can be seen from Table 2 above, the purified and concentrated alcoholysis reaction compositions of Examples 2-1 to 2-26 had a very low pigment residue rate and a very low content of metals such as Sb, Ti, and Zn.

[0177] Preparation of terephthalic acid Example 3-1 100 g (0.36 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-2 and 200 g (11.10 mol) of water were charged into a second high-pressure reactor with a capacity of 600 ml, and then 50 mg of Zn(OAC)2·2H2O (500 ppm based on the total weight of the purified and concentrated alcoholysis reaction composition) was added thereto.

[0178] Thereafter, the temperature of the second high-pressure reactor was raised to 260°C, and the hydrolysis reaction was carried out for 4 hours while maintaining the temperature at 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. When this hydrolysis reaction product in the form of a slurry was filtered, a solid was obtained, which was washed with butanol and water at 90°C and dried under vacuum to obtain 53.7 g (yield: 90%) of solid terephthalic acid (TPA).

[0179] Example 3-2 100 g (0.30 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-5 and 200 g (11.10 mol) of water were charged into a second high-pressure reactor with a capacity of 600 ml, and then 50 mg of Zn(OAC)2·2H2O (500 ppm based on the total weight of the purified and concentrated alcoholysis reaction composition) was added thereto.

[0180] Thereafter, the temperature of the second high-pressure reactor was raised to 260°C, and the hydrolysis reaction was carried out for 4 hours while maintaining the temperature at 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. When this hydrolysis reaction product in the form of a slurry was filtered, a solid was obtained, which was washed with pentanol and water at 90°C and dried under vacuum to obtain 43.9 g (yield: 81%) of solid terephthalic acid (TPA).

[0181] Example 3-3 Into a second high-pressure reactor with a capacity of 600 ml, 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 charged, and then 50 mg of Zn(OAC)2·2H2O (500 ppm based on the total weight of the purified and concentrated alcoholysis reaction composition) was added thereto.

[0182] Thereafter, the temperature of the second high-pressure reactor was raised to 260°C, and while maintaining the temperature of 260°C, the hydrolysis reaction was carried out for 4 hours, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. Filtering this hydrolysis reaction product in the form of a slurry gave a solid, which was washed with 2-ethyl-1-hexanol and water at 90°C and dried under vacuum to obtain 38.0 g (yield: 88%) of solid terephthalic acid (TPA).

[0183] Example 3-4 Except that 100 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-13 was used, 35.4 g (yield: 82%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-3.

[0184] Example 3-5 Except that 100 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-14 was used, 36.7 g (yield: 85%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-3.

[0185] Example 3-6 Into a second high-pressure reactor with a capacity of 600 ml, 114 g (0.26 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-18 and 200 g (11.10 mol) of water were charged, and then 57 mg of Zn(OAC)2·2H2O (500 ppm based on the total weight of the purified and concentrated alcoholysis reaction composition) was added thereto.

[0186] Thereafter, the temperature of the second high-pressure reactor was raised to 260 °C, and while maintaining the temperature at 260 °C, the hydrolysis reaction was carried out for 4 hours, and then cooled to 90 °C to obtain a hydrolysis reaction product in the form of a slurry. Filtering the hydrolysis reaction product in the form of a slurry gave a solid, which was washed with decanol and water at 90 °C and dried under vacuum to obtain 36.1 g (yield: 85%) of solid terephthalic acid (TPA).

[0187] Example 3-7 54.3 g (yield: 91%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-1, except that no hydrolysis catalyst was added.

[0188] Example 3-8 100 g (0.36 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-2 and 200 g (11.10 mol) of water were charged into a second high-pressure reactor with a capacity of 600 ml, and then 50 mg of Zn(OAC)2·2H2O (500 ppm based on the total weight of the purified and concentrated alcoholysis reaction composition) was added thereto.

[0189] Thereafter, the temperature of the second high-pressure reactor was raised to 260 °C, and while maintaining the temperature at 260 °C, the hydrolysis reaction was carried out for 4 hours, and then cooled to 90 °C to obtain a hydrolysis reaction product in the form of a slurry. Acetone was added to the solid obtained by filtering the hydrolysis reaction product in the form of a slurry, and then stirred at 50 °C for 4 hours. This was filtered, then washed with acetone and water at 50 °C, and dried under vacuum to obtain 55.6 g (yield: 93%) of solid terephthalic acid (TPA).

[0190] Example 3-9 100 g (0.36 mol) of the purified and concentrated alcoholysis reaction composition of Example 2-2 and 200 g (11.10 mol) of water were charged into a second high-pressure reactor with a capacity of 600 ml, and then 50 mg of Zn(OAC)2·2H2O (500 ppm based on the total weight of the purified and concentrated alcoholysis reaction composition) was added thereto.

[0191] Thereafter, the temperature of the second high-pressure reactor was raised to 260°C, and while maintaining the temperature at 260°C, the hydrolysis reaction was carried out for 4 hours, followed by cooling to 90°C to obtain a hydrolysis reaction product in the form of a slurry. Butanol was added to the solid obtained by filtering this hydrolysis reaction product in the form of a slurry, and then stirred at 90°C for 4 hours. This was filtered, then washed with butanol and water at 50°C, and dried under vacuum to obtain 53.1 g (yield: 89%) of solid terephthalic acid (TPA).

[0192] Example 3-10 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 by the filtration step of Example 3-1 was further used.

[0193] Specifically, the filtrate separated in the filtration step of Example 3-1 was re-introduced into the second high-pressure reactor, the temperature was raised to 260°C, and while maintaining the temperature at 260°C, the hydrolysis reaction was carried out for 4 hours, followed by cooling to 90°C to obtain a hydrolysis reaction product in the form of a slurry. Filtering this hydrolysis reaction product in the form of a slurry gave a solid, which was washed with butanol and water at 90°C and dried under vacuum to obtain 5.5 g of solid terephthalic acid (TPA).

[0194] Comparative Example 3-1 54.4 g (yield: 91%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-1, except that 100 g (0.36 mol) of the composition of Comparative Example 2-4 was used.

[0195] Comparative Example 3-2 40.4 g (yield: 81%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-2, except that 100 g (0.30 mol) of the composition of Comparative Example 2-7 was used.

[0196] Comparative Example 3-3 Except for using 100 g (0.26 mol) of the composition of Comparative Example 2-13, 36.7 g (yield: 85%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-3.

[0197] Comparative Example 3-4 Except for using 114 g (0.26 mol) of the composition of Comparative Example 2-16, 34.4 g (yield: 81%) of solid terephthalic acid (TPA) was obtained in the same manner as in Example 3-6.

[0198] Test Example 2-1: Pigment Residual Rate The pigment residual rate (%) was measured for each of the terephthalic acids of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4.

[0199] Specifically, the terephthalic acid of Example 3-1 was diluted to a concentration of 5% each in dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and N-methylpyrrolidone (NMP), and the area (B1) of the absorbance curve at 400 nm to 800 nm was determined using a UV-vis spectrophotometer. Further, in the case of the composition of Comparative Example 2-4 (the same composition as Example 1-2 used in the preparation of the terephthalic acid of Example 3-1, but this composition was concentrated without adding an adsorbent), the area (B2) of the absorbance curve at 400 nm to 800 nm was determined in the same manner as above. Using the measured area of the absorbance curve, the pigment residual rate (%) was calculated by the following formula B.

Equation

[0200] For each of the terephthalic acids of Examples 3-2 to 3-10 and Comparative Examples 3-1 to 3-4, the pigment residual rate (%) was measured in the same manner as above. In particular, regarding B2 of the above formula 1, for Example 3-2, it was measured using the composition of Comparative Example 2-7, for Examples 3-3 to 3-5, it was measured using the composition of Comparative Example 2-13, and for Example 3-6, it was measured using the composition of Comparative Example 2-16. Further, 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.

[0201] Test Example 2-2: Yellowness Index For each of the recycled terephthalic acids of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4, the yellowness index (Y.I.) was measured.

[0202] Specifically, each of the recycled terephthalic acids of 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 N-methylpyrrolidone (NMP), respectively, and the yellowness index was measured using a ColorFlex EZ (manufacturer: HunterLab) device.

[0203] Test Example 2-3: Metal Content Using inductively coupled plasma atomic emission spectrometry (ICP-AES), the metal content (ppm) present in each of the terephthalic acids of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 10 was measured. N.D. means that the content is less than 1 ppm, which is too low to be measured as a specific value.

[0204] Test Example 2-4: Color - b For each of the terephthalic acids of Examples 3-1 to 3-10 and Comparative Examples 3-1 to 3-4, the color - b of the color characteristics was measured using a colorimeter.

[0205] [Table 3]

[0206] As can be seen from Table 3 above, the terephthalic acids (recycled terephthalic acids) prepared in Examples 3-1 to 3-6 not only have a low pigment retention rate and a low yellowness index, but also have a very low metal content as impurities. In particular, in Example 3-10, a recycled terephthalic acid was obtained in a very high yield using the filtrate, i.e., the unreacted material separated by the filtration step.

Claims

1. A process for preparing terephthalic acid, comprising: Step (1): subjecting waste polyester to alcoholysis using an alcohol having 4 or more carbon atoms to prepare a liquid composition containing a compound represented by Formula 1; Step (2): subjecting the liquid composition to hydrolysis 【Chemical 1】 [In Formula 1, R １ is an alkyl group having 4 or more carbon atoms] A process comprising the above steps.

2. The process for preparing terephthalic acid according to Claim 1, wherein the number of carbon atoms of the alcohol is 4 to 14.

3. 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.

4. The process for preparing terephthalic acid according to Claim 1, wherein the alcoholysis is carried out at a temperature of 160°C to 280°C and a pressure of 1 bar to 40 bar for 0.5 hour to 24 hours.

5. The process for preparing terephthalic acid according to Claim 1, wherein the liquid composition contains unreacted alcohol and ethylene glycol as a by-product, and the content of the compound represented by Formula 1 in the liquid composition is 70 mol% or more.

6. The liquid composition contains unreacted alcohol and ethylene glycol as a by-product. Step (1) includes discharging the unreacted alcohol and ethylene glycol as a by-product. The alcohol is separated from the discharged mixture of alcohol and ethylene glycol, and the separated alcohol is reused as a raw material for the alcoholysis. The process for preparing terephthalic acid according to Claim 1.

7. The process for preparing terephthalic acid according to Claim 1, wherein Step (1) includes recovering ethylene glycol as a by-product of the alcoholysis, and the recovery rate of ethylene glycol is 65% or more.

8. In Step (1), an alcoholysis catalyst is added. The alcoholysis catalyst is Li ＋ , Na ＋ , K ＋ and Cs ＋ alkali metal ions of, Be ２＋ , Mg ２＋ , Ca ２＋ and Ba ２＋ alkaline earth metal ions of, NH ４＋ and NR ４＋ (wherein, R is alkyl) ammonium ions and Zn ２＋ at least one cation selected from the group consisting of; or OH － , OR － (wherein, R is alkyl), HCO ３ － , CO ３ ２－ , benzoate ion (C ７ H ５ O ２ － ), 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion at least one anion selected from the group consisting of, and The process for preparing terephthalic acid according to Claim 1, wherein the amount of the alcoholysis catalyst added is 10 ppm to 10,000 ppm based on the total weight of the waste polyester.

9. In Step (1), an alcoholysis catalyst is added. The alcoholysis catalyst is Zn(OAc) ２ , Co(OAc) ２ , Mn(OAc) ２ , Mg(OAc) ２ , Ca(OAc) ２ , Ba(OAc) ２ , LiOAc, NaOAc, KOAc, Zn(OAC) ２ ·2H ２ O, Co(OAc) ２ ·4H ２ O, Pb(OAc) ２ , Mn(OAc) ２ ·4H ２ O, Mg(OAc) ２ ·4H ２ O, Pd(OAc) ２ , Ti(OBu) ４ , Ti(O i Pr) ４ , GeO ２ , Al(O i Pr) ３ , Na ２ CO ３ , K ２ CO ３ , and contains at least one selected from the group consisting of dibutyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid, and The process for preparing terephthalic acid according to claim 1, wherein the amount of the alcoholysis catalyst added is 10 ppm to 10,000 ppm based on the total weight of the waste polyester.

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

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

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

13. The weight ratio of the liquid composition to water is 1:1 to 500. The process for preparing terephthalic acid according to claim 12.

14. In step (2), a hydrolysis catalyst is added, The hydrolysis catalyst is Li ＋ , Na ＋ , K ＋ and Cs ＋ alkali metal ions of, Be ２＋ , Mg ２＋ , Ca ２＋ and Ba ２＋ alkaline earth metal ions of, NH ４＋ and NR ４＋ (wherein, R is alkyl) ammonium ions and Zn ２＋ at least one cation selected from the group consisting of; or OH － , OR － (wherein, R is alkyl), HCO ３ － , CO ３ ２－ , benzoate ion (C ７ H ５ O ２ － ), 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion, and The process for preparing terephthalic acid according to claim 1, wherein the amount of the hydrolysis catalyst added is 10 ppm to 10,000 ppm based on the total weight of the liquid composition.

15. In step (2), a hydrolysis catalyst is added, The hydrolysis catalyst is Zn(OAc) ２ , Co(OAc) ２ , Mn(OAc) ２ , Mg(OAc) ２ , Ca(OAc) ２ , Ba(OAc) ２ , LiOAc, NaOAc, KOAc, Zn(OAC) ２ ·2H ２ O, Co(OAc) ２ ·4H ２ O, Pb(OAc) ２ , Mn(OAc) ２ ·4H ２ O, Mg(OAc) ２ ·4H ２ O, Pd(OAc) ２ , Ti(OBu) ４ , Ti(O iPr) ４ , GeO ２ , Al(O iPr) ３ , Na ２ CO ３ , K ２ CO ３ , and includes at least one selected from the group consisting of dibutyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid, and The process for preparing terephthalic acid according to claim 1, wherein the amount of the hydrolysis catalyst added is 10 ppm to 10,000 ppm based on the total weight of the liquid composition.

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