Method for producing terephthalic acid, and terephthalic acid produced therefrom

Abstract

The present invention relates to a method for producing terephthalic acid, and terephthalic acid produced therefrom. More specifically, according to one embodiment of the present invention, terephthalic acid can be produced in an eco-friendly manner while achieving high purity by introducing an alcohol with 4 or more carbon atoms, or a solvent immiscible with water, when hydrolyzing a compound produced by depolymerizing a waste polyester.

Description

Method for producing terephthalic acid and terephthalic acid produced therefrom

[0001] The present invention relates to an environmentally friendly method for producing terephthalic acid using waste polyester and to recycled terephthalic acid produced therefrom.

[0002] Polyester boasts excellent mechanical strength, heat resistance, transparency, and gas barrier properties, making it widely used in beverage containers, packaging films, audio and video films, and industrial materials such as medical fibers and tire cords. In particular, polyester sheets and boards, with their excellent transparency and mechanical strength, are widely used in cases, boxes, partitions, shelves, panels, packaging, building materials, and interior and exterior finishes.

[0003] As the annual global volume of polyester-based plastic waste grows to unmanageable levels, interest in recycling waste polyester or regeneration processes utilizing it is growing. Furthermore, countries around the world are developing regulations and measures for recycling waste plastic resources, including waste polyester. For example, regulations requiring a certain percentage of recycled resin in packaging materials used in various fields are being discussed.

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

[0005] For example, Korean Patent Publication No. 1997-0042469 discloses a technology for producing terephthalic acid by hydrolyzing waste polyethylene terephthalate with an alkaline aqueous solution to produce a slurry of terephthalic acid alkali metal and earth metal salts and neutralizing it with an acid. However, since a terephthalic acid salt, not terephthalic acid, is produced as a result of the hydrolysis reaction, a neutralization step of adding acid is required to convert it to terephthalic acid, and there is a problem that the resulting byproducts generate environmental pollutants or a large amount of acid treatment waste liquid.

[0006] [Prior Art Literature]

[0007] [Patent Document]

[0008] (Patent Document 1) Korean Patent Publication No. 1997-0042469

[0009] Accordingly, the present invention aims to provide a method for producing high-purity terephthalic acid by effectively removing impurities and by-products while being environmentally friendly using waste polyester, and a recycled terephthalic acid produced therefrom.

[0010] A method for producing terephthalic acid according to one embodiment of the present invention includes a step of hydrolyzing a compound produced by depolymerizing waste polyester, and in the hydrolysis step, an alcohol having 4 or more carbon atoms or a solvent immiscible with water is introduced.

[0011] A method for producing terephthalic acid according to one embodiment of the present invention includes a step of hydrolyzing a compound produced by depolymerizing waste polyester, and by introducing an alcohol having 4 or more carbon atoms or a solvent immiscible with water in the hydrolysis step, terephthalic acid can be produced in an environmentally friendly manner, and terephthalic acid with high purity can be produced.

[0012] Specifically, there was a problem that the purity of the manufactured recycled terephthalic acid was lowered due to various dyes, additives such as polymerization catalysts, and heavy metals derived from these contained in waste polyester, as well as diethylene glycol and isophthalic acid that can be generated as byproducts in the process of recycling waste polyester. In particular, diethylene glycol and isophthalic acid that can be generated as byproducts can lower the quality of the process of manufacturing polyester using the manufactured recycled terephthalic acid, and can also cause problems during the process, so they must be separated and removed. For example, when manufacturing polyester for fiber using recycled terephthalic acid, the impurity isophthalic acid can reduce the strength of the fiber and cause shrinkage exceeding the allowable limit. Additional processes such as purification processes have been performed to separate and remove these impurities, but these additional processes can reduce the processability or the yield of the desired main component, recycled terephthalic acid.

[0013] However, the present invention can easily separate and remove isophthalic acid, a by-product, without an additional process by introducing an alcohol having a carbon number of 4 or more or a solvent that is immiscible with water in the process of hydrolyzing a compound manufactured by depolymerizing waste polyester. More specifically, isophthalic acid has a higher solubility than terephthalic acid, and also has a high solubility in alcohols having a carbon number of 4 or more or in solvents that are immiscible with water. By utilizing these characteristics of isophthalic acid, by introducing an alcohol having a carbon number of 4 or more or a solvent that is immiscible with water in the hydrolysis step, isophthalic acid, an impurity, can be easily separated and removed.

[0014] In addition, the method for producing terephthalic acid according to one embodiment of the present invention can produce terephthalic acid in an environmentally friendly manner by hydrolyzing a compound produced by depolymerizing waste polyester using water, while also improving processability and reducing process costs.

[0015] In addition, unlike the conventional method of producing a terephthalic acid salt from waste polyester and then additionally performing a step of neutralizing it, the method for producing terephthalic acid of the present invention can directly produce solid terephthalic acid without an additional process, so the process is not only easy, but also the process cost can be reduced, and the processability is very excellent.

[0016] In addition, acids such as sulfuric acid or hydrochloric acid, which have been conventionally used to neutralize terephthalic acid salts, have the problem of generating environmental pollutants such as Na2SO4 and NaCl as byproducts or a large amount of acid treatment wastewater. However, the method for producing terephthalic acid of the present invention is environmentally friendly because, unlike conventional methods, solid terephthalic acid can be produced directly without performing an additional neutralization step.

[0017] In addition, the method for producing terephthalic acid of the present invention can easily remove insoluble impurities such as metal catalysts, coloring pigments, etc., or additives such as soluble coloring agents that may be included in waste polyester by producing an intermediate, i.e., a hydrolysis reactant, in a liquid phase, thereby further improving the purity and yield of terephthalic acid produced through a simple process.

[0018] The present invention is described in detail below. The present invention is not limited to the details disclosed below and may be modified in various ways without altering the spirit of the invention.

[0019] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0020] All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification should be understood to be modified by the term “about” in all cases unless otherwise specified.

[0021] In this specification, the terms "first," "second," etc. are used to describe various components, and the components are not limited by the terms. The terms are used only to distinguish one component from another.

[0022]

[0023] Method for producing terephthalic acid

[0024] A method for producing terephthalic acid according to one embodiment of the present invention includes a step of hydrolyzing a compound produced by depolymerizing waste polyester, and in the hydrolysis step, an alcohol having 4 or more carbon atoms or a solvent immiscible with water is introduced.

[0025] As a specific example, a compound manufactured by depolymerizing waste polyester is hydrolyzed into water and an alcohol having 4 or more carbon atoms.

[0026] As a specific example, a compound manufactured by depolymerizing waste polyester is hydrolyzed with water and a solvent immiscible with water.

[0027] As a specific example, waste polyester is depolymerized with an alcohol having at least 1 carbon number, and the depolymerization reaction product is hydrolyzed into water and an alcohol having at least 4 carbon numbers.

[0028] As a specific example, waste polyester is depolymerized with an alcohol having at least 1 carbon atom, and the depolymerization reaction product is hydrolyzed with water and a solvent immiscible with water.

[0029]

[0030] depolymerization

[0031] The method for producing terephthalic acid of the present invention includes a step of producing a compound by depolymerizing waste polyester.

[0032] The above-mentioned waste polyester may be a waste polyester product that has been crushed or melted. For example, the waste polyester may be a polyester product that has been crushed and recovered and separated after use through consumption, or may be converted into pellet form (PCR, post-consumer recycled material), or may be polyester waste such as defective products or scraps that may be generated in processes such as forming polyester films, fibers, containers, etc. (PIR, post-industrial recycled material), but is not limited thereto.

[0033] Additionally, the depolymerization may include alcoholysis.

[0034] Specifically, the alcoholysis can be performed using an alcohol, more specifically a mono- or di-alcohol. In particular, when the compound is prepared by alcoholysis of waste polyester with an alcohol having one or more carbon atoms, the compound can be liquid at room temperature. More specifically, the compound can be liquid at room temperature, and the terephthalic acid can be solid at room temperature.

[0035] When producing a compound by alcoholysis of waste polyester using an alcohol having 1 or more carbon atoms, the compound is liquid at room temperature, so it is easy to remove insoluble impurities or additives such as colorants and pigments that may be included in the waste polyester, thereby improving the purity and yield of the produced terephthalic acid.

[0036] In addition, unlike conventional methods, solid terephthalic acid can be manufactured directly without performing an additional neutralization step, so the process is excellent and environmentally friendly.

[0037] For example, the alcoholysis can be carried out by first introducing waste polyester, alcohol, and a trace amount of alcoholysis catalyst into a first high-pressure reactor. As the alcoholysis reaction progresses, by-products such as ethylene glycol and unreacted alcohol (alcohol present in excess) can be recovered and reused through a separate fractional distillation device after the reaction is completed.

[0038] In addition, there is also a method of discharging ethylene glycol and unreacted alcohol generated during the reaction in the form of a real-time gaseous mixture during the reaction, and condensing and recovering them using an external cooling device. At this time, alcohol can be continuously injected into the high-pressure reactor at the same capacity and injection rate as the capacity and discharge rate of the discharged gaseous mixture. Since the discharged gaseous mixture can be used to separate the unreacted alcohol through a simple process such as fractional distillation or layer separation, the separated unreacted alcohol can be fed back into the first high-pressure reactor, and ethylene glycol can be recovered therefrom.

[0039] Thereafter, the alcoholysis product obtained through the alcoholysis reaction is cooled, filtered, and then introduced into a second high-pressure reactor together with water to carry out a hydrolysis reaction. Thereafter, a slurry-like solution is obtained, which is filtered to obtain solid terephthalic acid. At this time, a small amount of hydrolysis catalyst may be additionally introduced together with water before the hydrolysis reaction, and the hydrolysis catalyst may be the same as or different from the alcoholysis catalyst.

[0040] In addition, by additionally performing one or more steps of recovering unreacted components after the hydrolysis reaction is completed and reintroducing them into the alcoholysis or hydrolysis reaction, the yield of the final terephthalic acid produced can be improved, and the amount of waste generated can be reduced accordingly, making it environmentally friendly. For example, the filtrate obtained by filtering the excess unreacted alcohol and the byproduct ethylene glycol using a filter or the like can be reintroduced into the hydrolysis reaction.

[0041] The above alcoholysis reaction can be carried out smoothly without the use of an alcoholysis catalyst, making it environmentally friendly. In particular, when the content of insoluble metals in waste polyester is high, a non-catalytic reaction may be advantageous for the efficient treatment and removal of impurities. Alternatively, an alcoholysis catalyst may be added to the alcoholysis reaction. Specifically, an alcoholysis catalyst may be added from an energy perspective, which enhances reactivity and thus processability.

[0042] The above alcohol decomposition catalyst may be a metal acetate salt, an alkali metal salt, or a hydroxy salt.

[0043] More specifically, the alcohol decomposition catalyst is Li + , Na + , K + or Cs + Alkali metal ions, Be 2+ , Mg 2+ , Ca 2+ or Ba 2+ Alkaline earth metal ions, NH 4+ or NR 4+ Ammonium ion of (R is alkyl), and Zn 2+ One or more cations selected from the group consisting of; and OH - , OR - (R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2- ), may include at least one anion selected from the group consisting of 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion. The R may be an alkyl having 1 to 10 carbon atoms or an alkyl having 1 to 5 carbon atoms.

[0044] For example, the above 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)2·2H2O, Co(OAc)2·4H2O, Pb(OAc)2, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Pd(OAc)2, It may include at least one selected from the group consisting of Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, dibutyltin(IV) oxide, tin octoate, titanium phosphate, and terephthalic acid.

[0045] In addition, the amount of the alcoholysis catalyst may be 10 ppm to 10,000 ppm relative to the total weight of the waste polyester. For example, the amount of the alcoholysis catalyst may be 10 ppm to 9,000 ppm, 100 ppm to 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 relative to the total weight of the waste polyester.

[0046] According to another embodiment of the present invention, waste polyester is depolymerized with an alcohol having 1 or more carbon atoms.

[0047] The carbon number of the alcohol may be 1 or more, 6 or more, 8 or more, 10 or more or 12 or more, and may be 1 to 14, 1 to 13, 1 to 10, 1 to 8, 6 to 12, 8 to 14 or 8 to 13.

[0048] By performing depolymerization of waste polyester using an alcohol having the above carbon number, depolymerization can be performed at lower temperature and pressure than the conventional waste polyester manufacturing process conditions that are performed at high temperature and high pressure, and an intermediate, i.e., a depolymerization product, can be manufactured in a liquid phase. In addition, since the carbon number of the alcohol satisfies the above range, the speed of the depolymerization reaction can be improved. In addition, since isophthalic acid, which may be manufactured as a byproduct in a subsequent hydrolysis step, is dissolved in the alcohol, isophthalic acid can be separated and removed through simple layer separation without an additional process. Therefore, the purity of the final terephthalic acid can be improved.

[0049] In addition, the boiling point of the alcohol may be 50°C to 290°C. For example, the boiling point of the alcohol may be 55°C to 280°C, 60°C to 260°C, 62°C to 230°C, 64°C to 190°C, or 64.7°C to 290°C. Since the boiling point of the alcohol satisfies the above range, ethylene glycol, a by-product generated in the depolymerization, can be more easily removed or recovered in a subsequent process, thereby further improving the processability. In particular, since there is a recent trend of using various monomer materials in fields that use polyester as a raw material, it can also be easily applied to removing various dialcohol-type monomers used in waste polyester products, such as waste plastic products.

[0050] The weight ratio of the waste polyester and the alcohol may be 1:1 to 10. For example, the weight ratio of the waste polyester and the alcohol 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.

[0051] Additionally, the alcoholysis reaction can be performed at a temperature of 160°C to 280°C and a pressure of 1 bar to 40 bar for 0.5 to 24 hours. For example, the alcoholysis reaction 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.

[0052] According to one embodiment of the present invention, the compound manufactured by depolymerizing the waste polyester may include a compound represented by the following chemical formula 1.

[0053] [Chemical Formula 1]

[0054]

[0055] In the above chemical formula 1,

[0056] R1 is alkyl or aryl, which is unsubstituted or substituted with hydroxy.

[0057] Specifically, the compound may include a compound represented by the following chemical formula 1-1 or the following chemical formula 1-2.

[0058] [Chemical Formula 1-1]

[0059]

[0060] [Chemical Formula 1-2]

[0061]

[0062] R1 may be alkyl substituted or unsubstituted with hydroxy, or aryl having 3 or more carbon atoms or 6 to 30 carbon atoms. For example, the above R1 is methyl, ethyl, propyl, n-propyl, isopropyl, 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, cyclohexyl, 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, It may be isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, decanyl, undecanyl, dodecanyl, tridecanyl, tetradecanyl, phenyl, biphenyl, terphenyl, quaterphenyl, naphthyl, anthracenyl, phenanthryl, triphenyl or fluorenyl.

[0063] In addition, the compound may include at least one selected from the group consisting of dimethyl terephthalate (DMT), dibutyl terephthalate (DBTP), diisooctyl terephthalate (DOTP), bis-2-hydroxyethyl terephthalate (BHET), dimethyl isophthalate (DMIP), dibutyl isophthalate (DBIP), and diisooctyl isophthalate (DOIP).

[0064] According to another embodiment of the present invention, after the depolymerization, a step of discharging unreacted alcohol and ethylene glycol as a by-product may be included.

[0065] Specifically, alcohol is separated from the mixture of the discharged alcohol and ethylene glycol, and the separated alcohol can be recycled as a raw material for the alcoholysis. For example, ethylene glycol and unreacted alcohol (alcohol present in excess), which are byproducts produced through alcoholysis, can be discharged in real time in the form of a gaseous mixture during the alcoholysis reaction and separated by fractional distillation or layer separation, and / or alcohol and ethylene glycol can be separated by fractional distillation after the reaction is completed, and the separated alcohol can be fed back into the alcoholysis and reused. At this time, the capacity and feeding rate of the alcohol fed for reuse can be the same as the capacity and feeding rate of the mixture of the discharged alcohol and ethylene glycol.

[0066] In addition, after the depolymerization, a step of recovering ethylene glycol, a by-product of the depolymerization, may be included. For example, ethylene glycol, a by-product of the alcoholysis, may be recovered by fractional distillation or layer separation of the mixture of the discharged alcohol and ethylene glycol, and may be recovered by fractional distillation or layer separation of the compound produced in the alcoholysis.

[0067] As a specific example, during the alcohol decomposition reaction, the unreacted alcohol and the by-product ethylene glycol can be discharged in real time in the state of a gaseous mixture, and the ethylene glycol can be recovered by condensing the mixture using an external cooling device.

[0068] According to one embodiment of the present invention, not only can unreacted alcohol and ethylene glycol be separated through a simple process such as fractional distillation or layer separation, but the separated unreacted alcohol can be recycled as a raw material for the alcoholysis, and the recovered ethylene glycol can be utilized in another process, so the processability and process cost reduction effects are excellent.

[0069] The recovery rate of the ethylene glycol may be 65% or more. For example, the recovery rate of the ethylene glycol may be 70% or more, 76% or more, 85% or more, 90% or more, 93% or more, 95% or more, 97% or more, 98% or more, 99% or more, or 99.5% or more.

[0070] According to another embodiment of the present invention, no purification step is included.

[0071] In general, a purification step may be performed prior to the hydrolysis step below for the compound produced by the above-described depolymerization. For example, the purification step may include a step of introducing one or more adsorbents selected from the group consisting of activated carbon, silica gel, alumina, zeolite, and activated clay, or adsorbing through bed adsorption. The adsorbent may be activated carbon or a mixture of activated carbon and silica gel, but is not limited thereto.

[0072] In the past, the purity and yield of terephthalic acid produced could be further improved by controlling the input amount or type of adsorbent through the above purification step, but this may result in a decrease in the yield of the desired main component, regenerated terephthalic acid.

[0073] The method for producing terephthalic acid of the present invention has excellent processability because it can improve the purity and yield of regenerated terephthalic acid produced without an additional process such as the above purification process.

[0074]

[0075] hydrolysis

[0076] A method for producing terephthalic acid according to one embodiment of the present invention includes a step of hydrolyzing a compound produced by depolymerizing waste polyester.

[0077] As a specific example, the compound can be hydrolyzed with an alcohol having 4 or more carbon atoms or a solvent that is immiscible with water to produce terephthalic acid.

[0078] The description of the alcohols having 4 or more carbon atoms is as described above. More specifically, alcohols have different boiling points and polarities depending on the number of carbon atoms, and their affinity for water also varies, so these characteristics are utilized.

[0079] According to one embodiment of the present invention, the solvent is immiscible with water. For example, the solvent may have a solubility in water of 30% or less, 30% or less, or 10% or less at 90°C or lower. By performing depolymerization of waste polyester using a solvent having a solubility in water satisfying the above range, isophthalic acid, which may be produced as a byproduct, is dissolved in the solvent, allowing separation and removal of isophthalic acid through simple layer separation without additional processes. Therefore, the purity of the final terephthalic acid can be improved.

[0080] The solvent may include at least one selected from the group consisting of toluene, cyclohexane, cyclopentane, benzene, dichloromethane, chloroform, ethyl acetate, butyl acetate, isopropyl acetate, 3-methoxy-3-methyl butyl acetate, pentane, hexane, heptane, 1,4-dioxane, dichloromethane, dichloroethylene, trichloroethylene, chloroform, chlorobenzene, dichlorobenzene, and xylene.

[0081] In addition, the amount of the alcohol or the solvent added relative to the total weight of the compound may be 1 wt% to 50 wt%. For example, an alcohol having 4 or more carbon atoms or a solvent that is immiscible with water may be added in the hydrolysis step, and at this time, the amount of the alcohol or the solvent added in the hydrolysis step may be 1 wt% to 50 wt%, 1 wt% to 20 wt%, or 20 wt% to 50 wt% relative to the total weight of the compound.

[0082] The hydrolysis step may produce isophthalic acid as a byproduct. For example, if waste polyester contains isophthalic acid, depolymerization may produce dialkyl isophthalates, which are difficult to separate due to mixing with liquid dimethyl terephthalate, dibutyl terephthalate, bis-2-hydroxyethyl terephthalate, and other compounds produced through the depolymerization of terephthalic acid. Furthermore, when hydrolyzing these compounds with water, a purification process must be performed under specific crystallization process conditions.

[0083] However, according to one embodiment of the present invention, when adding an alcohol having a carbon number of 4 or more or a solvent immiscible with water to the compound and performing hydrolysis, isophthalic acid has a higher solubility than terephthalic acid and has a high solubility in the alcohol having a carbon number of 4 or more or the solvent immiscible with water, so that only isophthalic acid is dissolved in the alcohol having a carbon number of 4 or more or the solvent immiscible with water, and isophthalic acid can be easily removed by a simple process such as layer separation without an additional process having special process conditions.

[0084] The isophthalic acid may be 1 wt% or less based on the total weight of the terephthalic acid. For example, after the hydrolysis is completed, the recovered isophthalic acid may be 0.5 wt% or less, 0.1 wt% or less, 800 ppm or less, 500 ppm or less, 250 ppm or less, 100 ppm or less, 50 ppm or less, 10 ppm or less, or 5 ppm or less based on the total weight of the terephthalic acid.

[0085] In addition, the content of the organic dye contained in the terephthalic acid may be 5 wt% or less. For example, the organic dye may include additives such as a colorant, a pigment, etc., and the content of the organic dye may be 3 wt% or less, 1.5 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.4 wt% or less, 0.2 wt% or less, or 0.1 wt% or less, based on the total weight of the terephthalic acid after the hydrolysis is completed.

[0086] Additionally, water may be introduced in the hydrolysis step. Specifically, water may be introduced in an amount of 1 to 500 times the weight of the compound, i.e., the hydrolysis reactant, in the hydrolysis step. For example, the amount of water introduced 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, i.e., the hydrolysis reactant.

[0087] Additionally, the hydrolysis may be performed at 180°C to 280°C for 0.5 to 24 hours. For example, the hydrolysis may be performed at a temperature of 185°C to 280°C, 200°C to 275°C, 220°C to 270°C, or 240°C to 265°C for 1 to 20 hours, 2.5 to 12 hours, or 3 to 8 hours.

[0088] Conventionally, a process 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 extremely high temperatures of over 300°C, and the reaction apparatus must also have high pressure resistance, resulting in low processability. However, the method for producing terephthalic acid according to one embodiment of the present invention exhibits superior processability due to relaxed process conditions compared to conventional methods, as described above.

[0089] Additionally, a hydrolysis catalyst may be added in the hydrolysis step. Specifically, hydrolysis may be performed by adding a hydrolysis catalyst to a mixture of the compound, i.e., a hydrolysis reactant, and water.

[0090] The hydrolysis catalyst may be a metal acetate salt, an alkali metal salt, or a hydroxy salt.

[0091] More specifically, the hydrolysis catalyst is Li + , Na + , K + or Cs + Alkali metal ions, Be 2+ , Mg 2+ , Ca 2+ or Ba 2+ Alkaline earth metal ions, NH 4+ or NR 4+ Ammonium ion of (R is alkyl), and Zn 2+ One or more cations selected from the group consisting of; and OH - , OR - (R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - ), may include at least one anion selected from the group consisting of 4-alkoxycarbonylbenzoate ion, acetate ion, and terephthalate ion. The R may be an alkyl having 1 to 10 carbon atoms or an alkyl having 1 to 5 carbon atoms.

[0092] For example, the hydrolysis catalyst may be 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, It may include at least one selected from the group consisting of Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, dibutyltin(IV) oxide, tin octoate, titanium phosphate, and terephthalic acid.

[0093] The amount of the hydrolysis catalyst may be 10 ppm to 10,000 ppm relative to the total weight of the compound, i.e., the hydrolysis reactant. For example, the amount of the hydrolysis catalyst may be 15 ppm to 8,000 ppm, 20 ppm to 5,500 ppm, 30 ppm to 3,000 ppm, 50 ppm to 1,600 ppm, 100 ppm to 1,200 ppm, 150 ppm to 1,100 ppm, 300 ppm to 1,000 ppm, 350 ppm to 950 ppm, 400 ppm to 850 ppm, 420 ppm to 700 ppm, or 450 ppm to 650 ppm relative to the total weight of the compound, i.e., the hydrolysis reactant.

[0094] According to one embodiment of the present invention, solid terephthalic acid can be produced through the hydrolysis reaction. Specifically, after the hydrolysis step, a step of filtering, washing, and drying the hydrolysis reaction product produced by the hydrolysis reaction can be additionally included. That is, solid terephthalic acid can be produced by filtering, washing, and drying the hydrolysis reaction product produced by the hydrolysis reaction.

[0095] For example, the hydrolysis reaction product can be cooled to an appropriate temperature, such as room temperature to less than 100°C, at which water does not vaporize, to obtain a slurry-like solution, which can be filtered to obtain a solid, which can then be washed and vacuum-dried to obtain solid terephthalic acid.

[0096] The above washing can be performed using a mixture of alcohol having 4 or more carbon atoms and / or water, a protic solvent such as isopropanol or acetic acid, or an aprotic solvent such as acetone, dichloromethane, chloroform, tetrahydrofuran (THF), or toluene.

[0097] By effectively removing residual pigments and impurities resulting from pigment decomposition during hydrolysis, the above-mentioned washing process can improve yellowness and color characteristics. Furthermore, using water for washing can also remove inorganic salts, thereby improving quality.

[0098] For example, the solid obtained by the above filtration can be washed with a mixture of alcohol at 80°C to 150°C and / or water at 70°C to 95°C.

[0099] At this time, the alcohol having 4 or more carbon atoms used in the washing may have the same carbon number as the alcohol used in the hydrolysis.

[0100] Additionally, the yield of the terephthalic acid may be 65% or greater. For example, the yield of the final manufactured recycled terephthalic acid may be 68% or greater, 70% or greater, 75% or greater, 80% or greater, 85% or greater, 90% or greater, or 95% or greater.

[0101]

[0102] Recycled terephthalic acid

[0103] According to another embodiment of the present invention, a regenerated terephthalic acid is produced according to the method for producing terephthalic acid, and has a total content of metals of less than 100 ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0104] Specifically, the above-mentioned recycled terephthalic acid can be manufactured according to the above-mentioned method for manufacturing terephthalic acid.

[0105] The above-mentioned recycled terephthalic acid may have a total metal content of less than 100 ppm, less than 90 ppm, less than 80 ppm, less than 65 ppm, less than 50 ppm, less than 35 ppm, less than 30 ppm, less than 15 ppm, less than 9 ppm, less than 7 ppm, less than 5 ppm, or less than 1 ppm as measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0106] Additionally, 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 spectrometry (ICP-AES). For example, the recycled terephthalic acid may have a total content of Sb, Ti, and Zn of 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, which are harmful to the human body or may be utilized as reaction or side reaction catalysts in a future polymerization process.

[0107] For example, the recycled terephthalic acid may have a Sb content measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) of 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less relative to the total weight of the recycled terephthalic acid.

[0108] The above-mentioned recycled terephthalic acid may have a Ti content measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) of 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less relative to the total weight of the above-mentioned recycled terephthalic acid.

[0109] The above-mentioned recycled terephthalic acid may have a Zn content measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) of 30 ppm or less, 25 ppm or less, 20 ppm or less, 15 ppm or less, 10 ppm or less, 5 ppm or less, 3 ppm or less, or 1 ppm or less relative to the total weight of the above-mentioned recycled terephthalic acid.

[0110] The above-mentioned recycled terephthalic acid may have a color-b value of less than 2, 1.6 or less, 1.4 or less, 1.3 or less, or 1 or less as measured by a colorimeter. The numerical range of the color-b is equivalent to that of a typical new terephthalic acid produced in a petrochemical process, so that the color-b of the recycled terephthalic acid satisfies the above range, so that not only is the yellowness low, but also the monomer is well purified, resulting in excellent quality.

[0111] The above color-b is a color system established by the International Standard Color Measurement Organization (CIE (Commission International d'Eclairage), and expresses color by indicating Color as L (brightness), a (complementary color from green to red), and b (complementary color from yellow to blue), and can be measured using a colorimeter.

[0112] The above contents are explained in more detail with the following examples. However, the following examples are only intended to illustrate the present invention, and the scope of the examples is not limited to these examples.

[0113] Manufacturing Example 1-1

[0114] 1 kg of waste polyethylene terephthalate (waste PET) and 4.0 kg of 1-butanol were charged into a first high-pressure reactor with a capacity of 7 L, and 200 mg of Zn(OAC)2·2H2O (200 ppm based on the total weight of the waste PET) was added as an alcoholysis catalyst.

[0115] Afterwards, all the connecting parts of the first high-pressure reactor were fastened and sealed, and the temperature was raised to 250°C over 1 hour. While maintaining the temperature at 250°C, the reactor was stirred for 4 hours to carry out the alcoholysis reaction, and after the alcoholysis reaction was completed, the reactor was cooled to room temperature.

[0116] Thereafter, the product of the alcoholysis reaction was stirred at 100°C for 3 hours, filtered, concentrated, and fractionally distilled using a Buchner funnel to obtain 1.31 kg (yield 90%) of a mixture of dibutyl terephthalate (DBTP) and dibutyl isophthalate (DBIP). The composition of the purified mixture was analyzed by HPLC and is shown in Table 1.

[0117]

[0118] Manufacturing Example 1-2

[0119] A mixture of diisooctyl terephthalate (DOTP, diisooctyl terephthlate) and diisooctyl isophthalate (DOIP, diisooctyl isophthalate) (1.79 kg, yield 88%) was obtained in the same manner as in Manufacturing Example 1-1, except that 4.0 kg of 2-ethyl-1-hexanol was used instead of 1-butanol. The composition of the purified mixture was analyzed by HPLC and is shown in Table 1.

[0120]

[0121] Manufacturing Example 1-3

[0122] 1 kg of waste polyethylene terephthalate (waste PET) and 4.0 kg of methanol were charged into a first high-pressure reactor with a capacity of 7 L, and 200 mg of Zn(OAC)2·2H2O (200 ppm based on the total weight of the waste PET) was added as an alcoholysis catalyst.

[0123] Afterwards, all the connecting parts of the first high-pressure reactor were fastened and sealed, and the temperature was raised to 200°C over 1 hour. While maintaining the temperature at 200°C, the reactor was stirred for 4 hours to carry out an alcoholysis reaction, and the alcoholysis product was filtered, concentrated, and fractionally distilled to obtain 0.94 kg (yield 93%) of a mixture of dimethyl terephthalate (DMT) and dimethyl isophthalate (DMIP). The composition of the purified mixture was analyzed by HPLC and is shown in Table 1.

[0124]

[0125] Manufacturing Example 1-4

[0126] A mixture of diethyl terephthalate (DET, diethyl terephthlate) and diethyl isophthalate (DEIP, diethyl isophthalate) (1.01 kg, yield 87%) was obtained in the same manner as in Manufacturing Example 1-3, except that 4.0 kg of ethanol was used instead of methanol. The composition of the purified mixture was analyzed by HPLC and is shown in Table 1.

[0127]

[0128] Manufacturing Example 1-5

[0129] A mixture of bis(2-hydroxyethyl) terephthalate (BHET, bis(2-hydroxyethyl) terephthalate) and bis(2-hydroxyethyl) isophthalate (BHIP, bis(2-hydroxyethyl) isophthalate) (1.22 kg, yield 93%) was obtained in the same manner as in Manufacturing Example 1-3, except that 4.0 kg of ethylene glycol was used instead of methanol. The composition of the purified mixture was analyzed by HPLC and is shown in Table 1.

[0130]

[0131] Chemical Formula 1 Yield (%) Chemical Formula 1-1 Content of compound (%) Chemical Formula 1-2 Content of compound (%) Production Example 11-butanol 90 94.15.9 Production Example 22-ethyl-1-hexanol 88 94.9 5.1 Production Example 3 methanol 93 95.4 4.6 Production Example 4 ethanol 87 95.14.9 Production Example 5 ethylene glycol 93 94.2 5.8

[0132]

[0133] [Manufacture of terephthalic acid]

[0134] Example 1

[0135] Into a second high-pressure reactor with a capacity of 1 L, 100 g of dibutyl terephthalate (DBTP) and dibutyl isophthalate (DBIP), 400 g of water, and 77 g of butanol prepared in 1-1 were charged, and 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the DBTP and DBIP) was added as a hydrolysis catalyst.

[0136] Afterwards, all the connecting parts of the second high-pressure reactor were fastened and sealed, and the temperature was raised to 260°C, and the hydrolysis reaction was performed for 8 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The hydrolysis product was filtered, and the obtained solid was washed with 90°C butanol and 90°C water, and vacuum-dried to obtain 53.7 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was less than 1 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0137]

[0138] Example 2

[0139] Into a second high-pressure reactor with a capacity of 1 L, 100 g of dibutyl terephthalate (DBTP) and dibutyl isophthalate (DBIP), 400 g of water, and 77 g of toluene prepared in 1-1 were charged, and 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the DBTP and DBIP) was added as a hydrolysis catalyst.

[0140] Afterwards, all the connecting parts of the second high-pressure reactor were fastened and sealed, and the temperature was raised to 260°C, and the hydrolysis reaction was performed for 8 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The hydrolysis product was filtered, and the obtained solid was washed with 90°C toluene and 90°C water and vacuum-dried to obtain 52.3 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 10 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0141]

[0142] Example 3

[0143] Into a second high-pressure reactor with a capacity of 1 L, 100 g of dibutyl terephthalate (DBTP) and dibutyl isophthalate (DBIP), 400 g of water, and 77 g of cyclohexane prepared in 1-1 were charged, and 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the DBTP and DBIP) was added as a hydrolysis catalyst.

[0144] Afterwards, all the connecting parts of the second high-pressure reactor were fastened and sealed, and the temperature was raised to 260°C, and the hydrolysis reaction was performed for 8 hours while maintaining 260°C, and then cooled to 90°C to obtain a slurry-type hydrolysis reaction product. The hydrolysis product was filtered, and the obtained solid was washed with cyclohexane at 90°C and water at 90°C and vacuum-dried to obtain 54.1 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 5 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0145]

[0146] Example 4

[0147] Into a second high-pressure reactor with a capacity of 1 L, 100 g of diisooctyl terephthalate (DOTP) and diisooctyl isophthalate (DOIP), 400 g of water, and 77 g of 2-ethyl-1-hexanol prepared in 1-1 were charged, and 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the DOTP and the DOIP) was added as a hydrolysis catalyst.

[0148] Afterwards, all the connecting parts of the second high-pressure reactor were fastened and sealed, and the temperature was raised to 260°C, and the hydrolysis reaction was performed for 8 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The hydrolysis product was filtered, and the obtained solid was washed with 2-ethyl-1-hexanol at 90°C and water at 90°C, and vacuum-dried to obtain 37.4 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was less than 1 ppm, and this was quantified using high-performance liquid chromatography (HPLC).

[0149]

[0150] Example 5

[0151] Except that 100 g of dimethyl terephthalate (DMT) and dimethyl isophthalate (DMIP) manufactured in Manufacturing Example 1-3 were used instead of Manufacturing Example 1-1, the same procedure as in Example 1 was followed to obtain 78.8 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 7 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0152]

[0153] Example 6

[0154] Except that 100 g of dimethyl terephthalate (DMT) and dimethyl isophthalate (DMIP) manufactured in Manufacturing Example 1-3 were used instead of Manufacturing Example 1-1, the same procedure as in Example 2 was followed to obtain 77.1 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 9 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0155]

[0156] Example 7

[0157] Except that 100 g of dimethyl terephthalate (DMT) and dimethyl isophthalate (DMIP) manufactured in Manufacturing Example 1-3 were used instead of Manufacturing Example 1-1, the same procedure as in Example 3 was followed to obtain 77.3 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 11 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0158]

[0159] Example 8

[0160] Except that 100 g of diethyl terephthalate (DET) and diethyl isophthalate (DEIP) manufactured in Manufacturing Example 1-4 were used instead of Manufacturing Example 1-1, the same procedure as in Example 1 was followed to obtain 68.1 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 10 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0161]

[0162] Example 9

[0163] Except that 100 g of diethyl terephthalate (DET) and diethyl isophthalate (DEIP) manufactured in Manufacturing Example 1-4 were used instead of Manufacturing Example 1-1, the same procedure as in Example 2 was followed to obtain 67.3 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 10 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0164]

[0165] Example 10

[0166] Except that 100 g of diethyl terephthalate (DET) and diethyl isophthalate (DEIP) manufactured in Manufacturing Example 1-4 were used instead of Manufacturing Example 1-1, the same procedure as in Example 3 was followed to obtain 67.0 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 5 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0167]

[0168] Example 11

[0169] The same procedure as Example 1 was followed, except that 100 g of bis(2-hydroxyethyl) terephthalate (BHET) and bis(2-hydroxyethyl) isophthalate (BHIP) manufactured in Manufacturing Example 1-5 were used instead of Manufacturing Example 1-1, to obtain 62.3 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 3 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0170]

[0171] Example 12

[0172] Except that 100 g of bis(2-hydroxyethyl) terephthalate (BHET) and bis(2-hydroxyethyl) isophthalate (BHIP) manufactured in Manufacturing Example 1-5 were used instead of Manufacturing Example 1-1, the same procedure as in Example 2 was followed to obtain 61.1 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 13 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0173]

[0174] Example 13

[0175] Except that 100 g of bis(2-hydroxyethyl) terephthalate (BHET, bis(2-hydroxyethyl) terephthalate) and bis(2-hydroxyethyl) isophthalate (BHIP, bis(2-hydroxyethyl) isophthalate) manufactured in Manufacturing Example 1-5 were used instead of Manufacturing Example 1-1, the same procedure as in Example 3 was carried out to obtain 62.0 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 13 ppm based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0176]

[0177] Comparative Example 1

[0178] Into a second high-pressure reactor with a capacity of 1 L, 100 g of dimethyl terephthalate (DMT) and dimethyl isophthalate (DMIP) manufactured in the above Manufacturing Example 1-3 and 400 g of water were charged, and 50 mg of Zn(OAC)2·2H2O (500 ppm relative to the total weight of the DBTP and DBIP) was added as a hydrolysis catalyst.

[0179] Afterwards, all the connecting parts of the second high-pressure reactor were fastened and sealed, and the temperature was raised to 260°C, and the hydrolysis reaction was performed for 8 hours while maintaining 260°C, and then cooled to 90°C to obtain a hydrolysis reaction product in the form of a slurry. The hydrolysis product was filtered, and the obtained solid was washed with methanol and 90°C water and vacuum-dried to obtain 78.0 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 1.8% of the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0180]

[0181] Comparative Example 2

[0182] Using 100 g of diethyl terephthalate (DET) and diethyl isophthalate (DEIP) manufactured in Manufacturing Example 1-4, 67.1 g of solid terephthalic acid (TPA) was obtained in the same manner as in Comparative Example 1, except that ethanol was used instead of methanol for washing. At this time, the by-product isophthalic acid (IPA) was 1.5% of the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0183]

[0184] Comparative Example 3

[0185] Using 100 g of bis(2-hydroxyethyl) terephthalate (BHET, bis(2-hydroxyethyl) terephthalate) and bis(2-hydroxyethyl) isophthalate (BHIP, bis(2-hydroxyethyl) isophthalate) manufactured in Manufacturing Example 1-5, the same procedure as in Comparative Example 1 was performed except that ethylene glycol was used instead of methanol for washing, thereby obtaining 62.2 g of solid terephthalic acid (TPA). At this time, the by-product isophthalic acid (IPA) was 1.1% based on the total weight of the solid terephthalic acid, and this was quantified using high-performance liquid chromatography (HPLC).

[0186]

[0187] Example Input Raw Material Input SolventTPA Purity (%)IPA ContentExample 1DBTP / DBIPbutanol99.9+<1 ppmExample 2DBTP / DBIPtoluene99.9+10 ppmExample 3DBTP / DBIPcyclohexane99.9+5 ppmExample 4DOTP / DOIP2-ethyl-1-hexanol99.9+<1 ppmExample 5DMT / DMIPbutanol99.9+7 ppmExample 6DMT / DMIPtoluene99.9+9 ppmExample 7DMT / DMIPcyclohexane99.9+11 ppmExample 8DET / DEIPbutanol99.9+3 ppmExample 9DET / DEIPtoluene99.9+10 ppmExample 10DET / DEIPcyclohexane99.9+5 ppmExample 11 BHET / BHIP butanol 99.9 + 3 ppmExample 12 BHET / BHIP toluene 99.9 + 13 ppmExample 13 BHET / BHIP cyclohexane 99.9 + 8 ppmComparative Example 1 DMT / DMIPX 98.2 1.8%Comparative Example 2 DET / DEIPX 98.5 1.5%Comparative Example 3 BHET / BHIPX 98.9 1.1%

[0188]

[0189] Experimental Example 1: Metal content

[0190] The content (ppm) of metals present in the terephthalic acid of Examples 1 to 13 and Comparative Examples 1 to 3 was measured using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). ND means that the content is less than 1 ppm, which is too low to be measured as a specific numerical value.

[0191]

[0192] Experimental Example 2: color-b

[0193] For the terephthalic acid of Examples 1 to 13 and Comparative Examples 1 to 3, the color characteristic color-b was measured using a colorimeter.

[0194]

[0195] Metal content (ppm) (Sb / Ti / Zn) Color-b Example 1 N.D. / ND / ND0.9 Example 2 N.D. / ND / 11.1 Example 3 N.D. / ND / ND1.2 Example 4 1 / ND / ND1.3 Example 5 N.D. / ND / ND1.4 Example 6 N.D. / ND / 11.3 Example 7 N.D. / ND / 11.2 Example 8 N.D. / ND / ND1.3 Example 9 1 / ND / ND1.4 Example 10 N.D. / ND / ND1.3 Example 11 N.D. / ND / 11.2 Example 12 1 / ND / ND1.1 Example 13 N.D. / ND / ND1.3 Comparative Example 148 / 12 / 243.8 Comparative Example 245 / 13 / 234.2 Comparative example 363 / 11 / 223.3

[0196]

[0197] As shown in Table 3 above, the terephthalic acid of Examples 1 to 15 not only had a very low content of metal impurities but also had a very low Color b according to the colorimeter. In contrast, it was confirmed that the terephthalic acid of Comparative Examples 1 to 3 had relatively high values ​​for the metal content and Color b according to the colorimeter.

Claims

1. A step of hydrolyzing a compound manufactured by depolymerizing waste polyester, A method for producing terephthalic acid, wherein an alcohol having 4 or more carbon atoms or a solvent immiscible with water is added in the hydrolysis step.

2. In paragraph 1, A method for producing terephthalic acid, wherein the alcohol has 4 to 14 carbon atoms.

3. In paragraph 1, A method for producing terephthalic acid, wherein the solvent has a solubility in water of 30% or less at a temperature of 90°C or less.

4. In paragraph 1, A method for producing terephthalic acid, wherein the solvent comprises at least one selected from the group consisting of toluene, cyclohexane, cyclopentane, benzene, dichloromethane, chloroform, ethyl acetate, butyl acetate, isopropyl acetate, 3-methoxy-3-methyl butyl acetate, pentane, hexane, heptane, 1,4-dioxane, dichloromethane, dichloroethylene, trichloroethylene, chloroform, chlorobenzene, dichlorobenzene, and xylene.

5. In paragraph 1, A method for producing terephthalic acid, wherein the amount of the alcohol or the solvent added is 15 wt% to 95 wt% relative to the total weight of the compound.

6. In paragraph 1, In the above hydrolysis step, water is added, A method for producing terephthalic acid, wherein the water is added in an amount of 1 to 500 times the weight of the compound.

7. In paragraph 1, In the above hydrolysis step, a hydrolysis catalyst is added, The above hydrolysis catalyst is Li + , Na + , K + or Cs + Alkali metal ions, Be 2+ , Mg 2+ , Ca 2+ or Ba 2+ Alkaline earth metal ions, NH 4+ or NR 4+ Ammonium ion of (R is alkyl), and Zn 2+ One or more cations selected from the group consisting of; and OH - , OR - (R is alkyl), HCO3 - , CO3 2- , benzoate ion (C7H5O2 - ), comprising at least one anion selected from the group consisting of 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion, A method for producing terephthalic acid, wherein the amount of the hydrolysis catalyst added is 10 ppm to 10,000 ppm relative to the total weight of the compound.

8. In paragraph 1, A method for producing terephthalic acid, wherein the compound comprises a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R1 is alkyl or aryl, which is unsubstituted or substituted with hydroxy.

9. In paragraph 1, A method for producing terephthalic acid, wherein the compound comprises at least one selected from the group consisting of dimethyl terephthalate (DMT), dibutyl terephthalate (DBTP), diisooctyl terephthalate (DOTP), bis-2-hydroxyethyl terephthalate (BHET), dimethyl isophthalate (DMIP), dibutyl isophthalate (DBIP), and diisooctyl isophthalate (DOIP).

10. In paragraph 1, In the above hydrolysis step, isophthalic acid, a by-product, is produced, A method for producing terephthalic acid, wherein the isophthalic acid is 1 wt% or less based on the total weight of the terephthalic acid.

11. In paragraph 1, A method for producing terephthalic acid, wherein the content of organic dye contained in the terephthalic acid is 5 wt% or less.

12. In paragraph 1, The above depolymerization includes alcoholysis, A method for producing terephthalic acid, wherein the weight ratio of waste polyester and the alcohol in the above alcohol decomposition is 1:1 to 10.

13. In paragraph 1, A method for producing terephthalic acid, wherein the above terephthalic acid is a solid at room temperature.

14. In paragraph 1, A process for producing terephthalic acid, which does not include a purification step.

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