Method for depolymerization of waste polyester

Abstract

The present invention relates to a method for depolymerization of waste polyester. The depolymerization method comprises the steps of: (1) subjecting waste polyester to alcoholysis with alcohol having 4 or more carbon atoms; (2) obtaining a product by recovering a product derived from the alcoholysis reaction in a gas phase; and (3) obtaining a polymerization raw material by hydrolyzing the product.

Description

Depolymerization method of waste polyester

[0001] The present invention relates to a method for depolymerizing waste polyester, which can depolymerize waste polyester with high efficiency and thereby produce a polymerization raw material (recycled polymerization raw material) having high purity.

[0002]

[0003] Among polymer types, polyester resins are widely used as materials for beverage or food containers; various packaging films or sheets; and various interior and exterior materials such as panels, shelves, and partitions.

[0004] Due to the widespread use of polyester, the annual global volume of polyester waste with polyester resins is now overwhelming. Consequently, interest in recycling or regeneration processes utilizing waste polyester is growing. Specifically, development is underway for processes that depolymerize waste polyester to produce polymerization raw materials (recycled raw materials), and further utilize these polymerization raw materials to produce polyester resin (recycled polyester resin).

[0005] As an example of the above process, there is a process of depolymerizing waste polyester through alcoholysis, thereby producing polymerization raw materials such as terephthalic acid.

[0006] However, the above process has the problem of low process efficiency (energy efficiency) of waste polyester because it requires a separate recovery process and large-scale facilities to process by-products / products generated from the alcoholysis reaction of waste polyester. In addition, the above process has limitations in controlling the depolymerization reaction of waste polyester as a reversible reaction showing a reaction conversion rate of 100%. In addition, in order to obtain polymerization raw materials such as terephthalic acid through the above process, a neutralization step that adds acid is required, which generates a large amount of acid treatment waste liquid, etc., and is therefore not environmentally friendly.

[0007] Therefore, there is a need for a technology that can improve the depolymerization process of waste polyester to enhance the depolymerization process efficiency (energy efficiency) and thereby produce high-purity polymer raw materials in an environmentally friendly manner.

[0008]

[0009] [Prior Art Literature]

[0010] [Patent Document]

[0011] (Patent Document 1) Republic of Korea Publication Patent No. 2022-0102882

[0012] The present inventors have confirmed that by alcoholyzing waste polyester into a specific alcohol, recovering the product derived therefrom through a specific process, and then recycling it, the efficiency of the depolymerization process for waste polyester is significantly improved, and the purity of the polymerization raw material (recycled polymerization raw material) obtained as a result of the depolymerization process can be improved.

[0013] Accordingly, the object of the present invention is to provide a method for depolymerizing waste polyester, which can obtain a polymer raw material as a result of the depolymerization process with high purity, high yield, and in an environmentally friendly manner while exhibiting improved depolymerization process efficiency.

[0014]

[0015] To solve the above problem, the present invention provides a method for depolymerizing waste polyester, comprising: (1) a step of alcoholyzing waste polyester into an alcohol having 4 or more carbon atoms; (2) a step of recovering a product derived from the alcoholysis reaction in a gaseous form to obtain a product; and (3) a step of hydrolyzing the product to obtain a polymerization raw material.

[0016] In addition, the present invention provides a polymerization raw material obtained from the depolymerization method of the above waste polyester.

[0017]

[0018] The depolymerization method according to the present invention includes a process of alcoholyzing waste polyester into a specific alcohol and recovering in real time in a gaseous state a product derived from the alcoholysis reaction process, so that even if a separate recovery process and large-scale equipment are not provided (the scale of the recovery equipment can be reduced), components such as ethylene glycol, unreacted alcohol, and products (hydrolysis reaction raw materials) contained in the product can be recovered and reused very easily.

[0019] Specifically, the depolymerization method according to the present invention can enable the depolymerization reaction of waste polyester, which is a reversible reaction, to exhibit a 100% reaction conversion rate by recovering ethylene glycol, a byproduct, in real time in the vapor phase.

[0020] In addition, since by-products that must be extracted through separate recovery processes such as distillation / concentration and products that are raw materials for hydrolysis reactions (e.g., dibutyl terephthalate (DBTP)) are recovered in real time, the efficiency (energy efficiency) of the depolymerization process can be improved.

[0021] In addition, since a product (hydrolysis reaction raw material) with a minimized content of various impurities (waste) such as color can be supplied to the hydrolysis reaction, the purity of the polymerization raw material (e.g., regenerated terephthalic acid, etc.) obtained as a result of the depolymerization method can be significantly increased.

[0022] In addition, in order to obtain the above polymerization raw material, a neutralization step of adding an acid such as sulfuric acid or hydrochloric acid does not need to be performed, so the polymerization raw material can be manufactured in an environmentally friendly manner because no environmental pollutants or large amounts of acid treatment waste are generated.

[0023]

[0024] Figure 1 is a schematic diagram showing the flow of a depolymerization process of waste polyester according to one embodiment of the present invention.

[0025]

[0026] Hereinafter, the present invention will be described in detail. Herein, the present invention is not limited to the contents described below, and may be modified in various forms as long as the gist of the invention is not changed.

[0027] The word "comprising" or "including" in this specification is intended to specify particular features, regions, steps, processes, elements and / or components, and does not exclude the presence or addition of other features, regions, steps, processes, elements and / or components, unless specifically stated to the contrary.

[0028] All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification can be understood to be modified by the term “about” in all cases unless otherwise specified.

[0029] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0030]

[0031] The present invention introduces a vapor alcoholysis process in depolymerizing waste polyester, thereby reducing the equipment size of the depolymerization process and significantly improving the ease of recovery and reusability of byproducts (ethylene glycol, unreacted alcohol, etc.).

[0032] Specifically, when the above waste polyester is subjected to alcoholysis, a specific alcohol, such as butanol, octanol, etc., is introduced, and when ethylene glycol, unreacted butanol, unreacted octanol, etc. are generated as by-products (outputs), the recovery of the by-products can be very easy by recovering them in real time in the gas phase (for example, when vapor butanolysis is applied, the equipment size can be reduced / when vapor octanolysis is applied, the boiling points (bp) of ethylene glycol (EG) and octanol are the same, and there is almost no distribution of octanol and water, so complete separation of ethylene glycol and octanol is possible by adding a small amount of water (for example, about twice the amount of EG) to the ethylene glycol (EG) and octanol discharged as by-products (outputs) and distilling them).

[0033] In addition, since specific products obtained through the above alcoholysis (e.g., dibutyl terephthalate (DBTP), dioctyl terephthalate (DOTP), etc.) are directly introduced as hydrolysis reaction raw materials without purification, it is possible to achieve improved efficiency of the depolymerization process while obtaining polymerization raw materials having high purity.

[0034]

[0035] Depolymerization method of waste polyester

[0036] The method for depolymerizing waste polyester resin according to the present invention comprises the steps of (1) alcoholyzing waste polyester with an alcohol having 4 or more carbon atoms; (2) recovering a product derived from the alcoholysis reaction in a gaseous form to obtain a product; and (3) hydrolyzing the product to obtain a polymerization raw material.

[0037] According to the present invention, in the step (2), the product may include at least one selected from the group consisting of ethylene glycol, unreacted alcohol, and a compound represented by the following chemical formula 1:

[0038] [Chemical Formula 1]

[0039]

[0040] In the above chemical formula 1,

[0041] R1 is alkyl having 4 or more carbon atoms.

[0042] In the compound represented by the above chemical formula 1, R1 is specifically, 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, It can be 4-methylhexyl, 5-methylhexyl, decanyl, undecanyl, dodecanyl, tridecanyl or tetradecanyl.

[0043] According to the present invention, the product obtained in the step (2) may include a compound (liquid compound or concentrated compound) represented by the chemical formula 1.

[0044] According to the present invention, the supply of the waste polyester for alcoholysis in the step (1) and the gaseous recovery in the step (2) can be performed simultaneously and continuously (in real time) from the time point at which the gaseous recovery of the product in the step (2) begins.

[0045] According to the present invention, the alcohol in step (1) may have 4 to 13 carbon atoms. Specifically, the alcohol may have 4 to 12, 4 to 10, 4 to 8, 4 to 7, or 4 to 6 carbon atoms. By performing alcoholysis of waste polyester using an alcohol having the above carbon atoms, alcoholysis can be performed at a relatively lower temperature and pressure than in the past, while increasing the reaction rate of alcoholysis.

[0046] According to the present invention, a step of purifying the product of step (2) may not be included. Specifically, the product obtained in step (2) may be supplied as an unpurified product to the hydrolysis reaction of step (3) without purification. This is possible because purification of the product occurs naturally during the process of recovering the product in the gas phase in step (2).

[0047] According to the present invention, the polymerization raw material obtained in the step (3) may be terephthalic acid (specifically, regenerated terephthalic acid (r-TPA) having a solid phase).

[0048] The method for depolymerizing waste polyester according to the present invention may include, for example, a process in which waste polyester (e.g., waste PET) is fed into an alcoholysis reactor and an alcoholysis reaction is performed, a mixture of unreacted alcohol (e.g., butanol, octanol, etc.), ethylene glycol (EG), and a compound represented by chemical formula 1 (e.g., DBTP, DOTP, etc.), excluding waste polyester and oligomers, among the substances present in the alcoholysis reactor, is continuously discharged in real time as a gaseous phase to the outside of the alcoholysis reactor during the depolymerization process, the gaseous mixture discharged to the outside undergoes a real-time distillation / separation process, and the unreacted alcohol obtained through this is fed back into the alcoholysis reactor, ethylene glycol (EG) is recovered in a separate T / K, and the compound represented by chemical formula 1 is fed into the hydrolysis reactor in a liquid phase without undergoing a purification process or after undergoing a purification process.

[0049]

[0050] The present invention is described in detail as follows.

[0051]

[0052] Step (1): Alcohololysis

[0053] A depolymerization method according to one embodiment of the present invention includes a step of alcoholyzing waste polyester into an alcohol having 4 or more carbon atoms.

[0054] The above waste polyester may be a waste polyester product, or a product obtained by crushing or melting waste. Specifically, the waste polyester may include at least one selected from the group consisting of waste polyethylene terephthalate fibers, waste polyethylene terephthalate containers, waste polyethylene terephthalate films, and polyester waste (Post Industrial Recycled Material; PIR), and may be a product obtained by crushing the same or converting the same into a pellet form (post consumer recycled material; PCR). The above polyester waste (PIR) may refer to defective products or scraps generated in the molding process of films, fibers, containers, etc.

[0055] The waste polyester may contain polyethylene terephthalate (PET) in an amount of 50 wt% or more, specifically 55 wt% or more, 60 wt% or more, 65 wt% or more, 70 wt% or more, 75 wt% or more, 80 wt% or more, 85 wt% or more, 90 wt% or more, or 95 wt% or more (e.g., 50 to 100 wt%, 60 to 97 wt%, 70 to 95 wt%, or 80 to 90 wt%), based on the total weight of the waste polyester.

[0056] The alcohol used in the alcoholysis reaction may have a carbon number of 4 or more, 6 or more, 8 or more, 10 or more, 12 or more, or 14 or more. Specifically, the alcohol may have a carbon number of 4 to 13, 4 to 10, 4 to 8, 4 to 7, or 4 to 6. By performing alcoholysis of waste polyester using an alcohol having the above carbon number, alcoholysis can be performed at a relatively lower temperature and pressure than in the past, while increasing the reaction rate of alcoholysis.

[0057] The boiling point of the alcohol may be 100 to 290°C. For example, the boiling point of the alcohol may be 100 to 280°C, 100 to 260°C, 100 to 230°C, 110 to 190°C, or 180 to 290°C. Since the boiling point of the alcohol satisfies the above range, ethylene glycol, a by-product generated from the alcoholysis, can be more easily removed or recovered in a subsequent process, thereby further improving the processability. In particular, since there is a recent trend in the field of using polyester as a raw material to use various monomer materials, it can also be easily applied to removing various dialcohol-type monomers used in waste polyester products, such as waste plastic products.

[0058] 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.

[0059] According to the present invention, the alcoholysis can be performed at a temperature of 160 to 300°C for 0.5 to 24 hours. Specifically, the alcoholysis reaction may be performed at a temperature of 170 to 300°C, 180 to 300°C, 190 to 300°C, 200 to 300°C, 210 to 300°C, 220 to 300°C, 230 to 300°C, 240 to 295°C, 250 to 290°C, 260 to 290°C, 270 to 290°C, or 275 to 285°C for 0.5 to 22 hours, 1.5 to 20 hours, 2 to 15 hours, 2.5 to 10 hours, 3 to 8 hours, or 3 to 6 hours. Meanwhile, the alcoholysis may be performed at a reaction pressure depending on the reaction temperature and / or reaction time. Specifically, the pressure during the alcoholysis reaction may be normal pressure or 0.1 to 3 bar, 1 to 3 bar, 1.5 to 3 bar, 2 to 3 bar, or 2.5 to 3 bar.

[0060] The above alcoholysis reaction may or may not involve a catalyst. If the alcoholysis reaction is a non-catalytic reaction that does not involve a catalyst, the removal process for insoluble metals and the like can be omitted, thereby ensuring environmental friendliness and producing a polymerization raw material with high purity. Furthermore, if the alcoholysis reaction is a catalytic reaction that involves a catalyst, the activity of the alcoholysis reaction can be increased, thereby improving processability (economic feasibility).

[0061] As a catalyst to be used in the above alcohol decomposition reaction, metal acetate salts, alkali metal salts, hydroxyl salts, etc. may be used. Specifically, the catalyst may be Li + , Na + , K + , or Cs + Alkali metal ions, Be 2+ , Mg 2+ , Ca 2+ , or Ba2+ Alkaline earth metal ions, NH 4+ , and Zn 2+ One or more cations selected from the group consisting of; and / or OH - , OR - , 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.

[0062] For example, the catalyst may include at least one selected from the group consisting of Zn(OAC)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Pb(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Pd(OAc)2, Zn(OAC)2·2H2O, Co(OAc)2·4H2O, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, dibutyltin(IV) oxide, tin octoate, titanium phosphate, and terephthalic acid.

[0063] The amount of the catalyst added may be 10 to 10,000 ppm, 10 to 9,000 ppm, 15 to 8,000 ppm, 20 to 6,000 ppm, 50 to 3,500 ppm, 100 to 1,500 ppm, 300 to 1,400 ppm, 500 to 1,300 ppm, 800 to 1,200 ppm, or 900 to 1,100 ppm, based on the total weight of the waste polyester.

[0064] According to one embodiment of the present invention, a liquid composition comprising a compound represented by the following chemical formula 1 can be prepared through the alcoholysis. Specifically, the composition is liquid at room temperature, and the liquid composition may refer to a composition produced through the alcoholysis reaction.

[0065] The above liquid composition comprises a compound represented by the following chemical formula 1.

[0066] [Chemical Formula 1]

[0067]

[0068] In the above chemical formula 1,

[0069] R1 is alkyl having 4 or more carbon atoms.

[0070] Specifically, the R1 is butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methyl-butyl, 1-ethyl-butyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, hexyl, 1-methylhexyl, 2-ethyl-1-hexyl, heptyl, n-heptyl, 1-methylheptyl, octyl, n-octyl, isooctyl, tert-octyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethyl-propyl, 1,1-dimethyl-propyl, isohexyl, 2-methylpentyl, 4-methylhexyl, It can be 5-methylhexyl, decanyl, undecanyl, dodecanyl, tridecanyl or tetradecanyl.

[0071] Specifically, the liquid composition may include unreacted alcohol and ethylene glycol (EG), which is a by-product. More specifically, the liquid composition may include the compound represented by the chemical formula 1, ethylene glycol (EG), which is a by-product produced by the alcoholysis reaction, unreacted alcohol, and oligomers.

[0072] For example, the liquid composition may include a compound represented by the following chemical formula 2, and the oligomer may include a compound represented by the following chemical formula 3.

[0073] [Chemical Formula 2]

[0074]

[0075] [Chemical Formula 3]

[0076]

[0077] In the above chemical formulas 2 and 3,

[0078] R2 and R3 are each independently an alkyl having 4 or more carbon atoms, and n is an integer of 1 or more.

[0079] Specifically, in the compounds represented by the above chemical formulas 2 and 3, R2 and R3 are each independently an alkyl having 4 to 12 carbon atoms, and n may be an integer of 1 to 3.

[0080]

[0081] Step (2): Weather recovery

[0082] A depolymerization method according to one embodiment of the present invention includes a step of recovering a product by vaporizing a product derived from the alcoholysis reaction of step (1). Specifically, unreacted alcohol, byproduct ethylene glycol, and a compound represented by the chemical formula 1 derived from the alcoholysis reaction of step (1) are discharged into a vapor phase and recovered through a distillation / separation process, thereby obtaining unreacted alcohol, ethylene glycol, and a compound represented by the chemical formula 1 as a product.

[0083] More specifically, the mixture of unreacted alcohol, ethylene glycol, and the compound represented by the formula 1 generated or discharged in the step (1) is recovered in a gaseous state, and these are separated into unreacted alcohol, ethylene glycol, and the compound represented by the formula 1, respectively, so that the separated unreacted alcohol can be circulated (recycled) as a raw material for the alcoholysis, the separated ethylene glycol can be circulated (recycled) in a separate process, and the separated compound represented by the formula 1 can be circulated (recycled) as a raw material for the hydrolysis reaction of the step (3) described below as a product. Here, the mixture can be discharged in real time in the form of a gaseous mixture, condensed, and then subjected to a process of fractional distillation or layer separation, thereby being separated and recovered into unreacted alcohol, ethylene glycol, and the compound represented by the formula 1, respectively. At this time, the capacity and the charging speed of the alcohol charged for reuse can be the same as the capacity and the discharge speed of the mixture of the discharged unreacted alcohol and ethylene glycol.

[0084] According to one embodiment of the present invention, unreacted alcohol, ethylene glycol, and the compound represented by chemical formula 1 can be separated by a simple process such as fractional distillation or layer separation, and the separated unreacted alcohol can be recycled as a raw material for the alcoholysis, the recovered ethylene glycol can be utilized in another process, and the compound (product) represented by chemical formula 1 can be directly input into the hydrolysis reaction described below without purification, so the processability and process cost reduction effects are excellent.

[0085] 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.

[0086]

[0087] Step (3): Hydrolysis reaction

[0088] A depolymerization method according to one embodiment of the present invention includes a step of hydrolyzing the product to obtain a polymerization raw material. Specifically, step (3) may be a step of hydrolyzing the product containing the compound represented by Chemical Formula 1 obtained in step (2) to produce regenerated terephthalic acid.

[0089] The hydrolysis can be performed by adding water to the product. Specifically, the hydrolysis reaction can be performed by adding water to the product and at a temperature of 180 to 280°C, 185 to 280°C, 200 to 275°C, 220 to 270°C, or 240 to 265°C for 0.5 to 24 hours, 1 to 20 hours, 2.5 to 12 hours, or 3 to 8 hours.

[0090] The weight ratio of the product and the water may be specifically 1:1 to 500, 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.

[0091] The above hydrolysis reaction may or may not involve a catalyst. If the hydrolysis reaction is a non-catalytic reaction, in which no catalyst is added, the removal process for insoluble metals and the like can be omitted, thereby ensuring environmental friendliness and producing a high-purity polymerization raw material. Furthermore, if the hydrolysis reaction is a catalytic reaction, in which a catalyst is added, the activity of the hydrolysis reaction is increased, thereby improving processability (economic feasibility).

[0092] As a catalyst to be used in the above hydrolysis reaction, metal acetate salts, alkali metal salts, hydroxyl salts, etc. may be used. Specifically, the 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+ , and Zn 2+ One or more cations selected from the group consisting of; and / or OH - , OR - , 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.

[0093] For example, the catalyst may include at least one selected from the group consisting of Zn(OAC)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Pb(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Pd(OAc)2, Zn(OAC)2·2H2O, Co(OAc)2·4H2O, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, dibutyltin(IV) oxide, tin octoate, titanium phosphate, and terephthalic acid.

[0094] The amount of the catalyst added may be 15 to 8,000 ppm, 20 to 5,500 ppm, 30 to 3,000 ppm, 50 to 1,600 ppm, 100 to 1,200 ppm, 150 to 1,100 ppm, 300 to 1,000 ppm, 350 to 950 ppm, 400 to 850 ppm, 420 to 700 ppm, or 450 to 650 ppm, based on the total weight of the product.

[0095] According to one embodiment of the present invention, solid terephthalic acid as a polymerization raw material 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 cooling the product formed by the hydrolysis reaction may be additionally included. That is, solid terephthalic acid as a polymerization raw material can be produced by filtering, washing, and drying the hydrolysis reaction product produced by cooling the product formed by the hydrolysis reaction.

[0096] For example, the hydrolysis reaction product can be obtained as a slurry solution by cooling to an appropriate temperature, for example, a temperature at which water does not evaporate, such as room temperature to less than 100°C, and the solid obtained by filtering can be washed and then vacuum-dried to obtain solid terephthalic acid. Specifically, the product formed by the hydrolysis reaction can be cooled to a temperature of 80 to 99°C, 81 to 99°C, 82 to 99°C, 83 to 98°C, 84 to 97°C, 84 to 96°C, 85 to 95°C, 86 to 94°C, 87 to 93°C, 88 to 92°C, or 89 to 91°C to obtain a slurry solution, the solid obtained by filtering can be washed and then vacuum-dried to obtain solid terephthalic acid.

[0097] The washing may be performed using a mixture of an alcohol having 4 or more carbon atoms and / or water having a temperature of 80 to 99°C, 81 to 99°C, 82 to 99°C, 83 to 98°C, 84 to 97°C, 84 to 96°C, 85 to 95°C, 86 to 94°C, 87 to 93°C, 88 to 92°C, or 89 to 91°C, a protic solvent such as isopropanol, acetic acid, or the like, or an aprotic solvent such as acetone, dichloromethane, chloroform, tetrahydrofuran (THF), toluene, or the like.

[0098] The above washing effectively removes residual pigments and impurities resulting from pigment decomposition during hydrolysis, particularly yellow impurities, thereby improving yellowness and color characteristics. Furthermore, by using water for the washing, inorganic salts can be removed, thereby improving the quality of the terephthalic acid produced.

[0099] The yield of the above terephthalic acid may be specifically 65% ​​or more, 68% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more.

[0100]

[0101] Polymerization raw materials (recycled polymerization raw materials)

[0102] The polymerization raw material according to the present invention is obtained through the depolymerization method of the waste polyester. Specifically, the polymerization raw material may be solid terephthalic acid (recycled terephthalic acid).

[0103] According to one embodiment of the present invention, the terephthalic acid may 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 as measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0104] Additionally, the terephthalic acid may have a total content of Sb, Ti, and Zn of 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 as measured by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0105] Specifically, the 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 based on the total weight of the terephthalic acid.

[0106] Additionally, the 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 based on the total weight of the terephthalic acid.

[0107] In addition, the 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 based on the total weight of the terephthalic acid.

[0108] Meanwhile, the 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 general virgin terephthalic acid produced in a petrochemical process, and since the color-b of the terephthalic acid satisfies the above range, it can be seen that not only is the yellowness low, but also that the purification is well done and the quality is excellent.

[0109] 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.

[0110] The above terephthalic acid may have a yellowness index (YI) of less than 2, 1.8 or less, or 1.7 or less, measured after being diluted to a concentration of 5% using dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP). The above yellowness index may be measured for terephthalic acid manufactured by performing a purification process in a process for manufacturing terephthalic acid.

[0111]

[0112] Polyester resin and method for producing the same

[0113] A polyester resin according to one embodiment of the present invention is manufactured using the polymerization raw material described above. Specifically, the polyester resin comprises a component derived from the polymerization raw material described above and a component derived from a diol compound.

[0114] The above diol compound may specifically include at least one selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and isosorbide.

[0115] In addition, the polyester resin may further include a component derived from a dicarboxylic acid compound. Specifically, the dicarboxylic acid compound may include at least one selected from the group consisting of isophthalic acid (IPA), 2,6-naphthalenedicarboxylic acid (2,6-NDA), dimethyl terephthalate (DMT), dimethylisophthalate (DMI), and dimethyl naphthalene 2,6-dicarboxylic acid (dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC).

[0116] A method for producing a polyester resin according to one embodiment of the present invention comprises the steps of: subjecting a polymerization raw material composition in which the polymerization raw material (e.g., terephthalic acid), the diol compound, and / or optionally the dicarboxylic acid compound are mixed to an esterification reaction; and subjecting the esterification reaction product to a polycondensation reaction.

[0117] The above esterification reaction can be carried out at a temperature of 200 to 350°C, 220 to 320°C, or 250 to 290°C. In addition, the esterification reaction can be carried out at a pressure of 0 to 10 kg / cm compared to atmospheric pressure. 2 (0 to 7355.6 mmHg), 0 to 5 kg / cm 2 (0 to 3677.8 mmHg), or 0 to 2.0 kg / cm 2 (0 to 1471.1 mmHg). In addition, the esterification reaction can be performed for 1 to 24 hours, 1 to 10 hours, or 1 to 6 hours.

[0118] The polycondensation reaction may be carried out at a temperature of 150 to 400°C, 200 to 370°C, 250 to 350°C, or 270 to 300°C. In addition, the polycondensation reaction may be carried out under reduced pressure conditions of 0.01 to 400 mmHg, 0.05 to 100 mmHg, or 0.1 to 100 mmHg. This polycondensation reaction may be carried out for a necessary time until the desired intrinsic viscosity is reached, and specifically, may be carried out for 1 to 24 hours, 1 to 10 hours, or 1 to 4 hours.

[0119] In the above esterification reaction and / or the above polycondensation reaction, one or more additives selected from the group consisting of an oxidation stabilizer, a branching agent, a coloring agent, a crystallizer, a catalyst, a stabilizer, and an ultraviolet absorber may be further added.

[0120] The above-mentioned oxidation stabilizer is not particularly limited, but may include at least one selected from the group consisting of hindered phenol compounds, phosphite compounds, and thioether compounds.

[0121] The branching agent may be a compound having three or more functional groups, and specifically may include at least one selected from the group consisting of trimellitic anhydride, trimellitic acid, pyromelletic dianhydride, glycerol, trimethylol propane, pentaerythritol, citric acid, tartaric acid, and 3-hydroxyglutaric acid.

[0122] The coloring agent is not particularly limited, but may include at least one selected from the group consisting of cobalt compounds, anthraquionone compounds, perinone compounds, azo compounds, and methine compounds. Specifically, cobalt acetate, cobalt propionate, Clarient's Polysynthren Blue RLS toner, Clarient's Solvaperm Red BB toner, etc. may be used as the coloring agent.

[0123] The catalyst is not particularly limited, but may include methylates of sodium and magnesium; acetates, borates, fatty acid salts, or carbonates of Zn, Cd, Mn, Co, Ca, Ba, etc.; or oxides or hydrates of Mg, Pb, Mn, Ti, Sb, Sn, Al, Ge, etc. Specifically, the catalyst may include tetraethyl titanate, acetyltripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, triethanolamine titanate, acetylacetonate titanate, ethylacetoacetic ester titanate, isostearyl titanate, titanium dioxide, germanium dioxide, germanium tetrachloride, germanium ethylene glycoside, germanium acetate, or a combination thereof.

[0124] The above stabilizer is not particularly limited, but may include phosphorus compounds such as phosphoric acid, trimethyl phosphate, and triethyl phosphate.

[0125] Meanwhile, the method for manufacturing a polyester resin according to one embodiment of the present invention may further include a step of subjecting the polymer to a solid-state polymerization reaction to control the intrinsic viscosity (IV), molecular weight, etc. of the polymer obtained through the polycondensation reaction, if necessary. The solid-state polymerization reaction conditions are not particularly limited and may be appropriately set depending on the intrinsic viscosity, molecular weight, etc. of the desired polyester resin.

[0126]

[0127] The present invention is described in more detail through the following examples. However, the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0128]

[0129] [Example 1-1]

[0130] Alcohololysis reaction and gas phase recovery

[0131] 300 g of waste polyethylene terephthalate (waste PET) and 300 mg of Zn(OAC)2·2H2O (1000 ppm based on the total weight of the waste PET) as an alcohol decomposition catalyst were added to a high-pressure reactor with a capacity of 1 L.

[0132] Afterwards, all the connecting parts of the high-pressure reactor were fastened and sealed, the temperature was raised to 280 ℃, stirred, and maintained for 30 minutes. After that, 1-butanol as alcohol was introduced at a rate of 5 ml / min through the bottom of the high-pressure reactor. At this time, some of the 1-butanol introduced into the high-pressure reactor was used for the alcoholysis reaction, and the unreacted 1-butanol was vaporized and discharged outside the reactor, and condensed and recovered through an external condenser. About 30 minutes after the introduction of 1-butanol, ethylene glycol (EG) and dibutyl terephthalate, which are by-products of the alcoholysis reaction of waste PET, were generated and vaporized together with 1-butanol, and discharged outside the high-pressure reactor as an output (gaseous mixture), which was condensed and recovered through an external condenser. The production of ethylene glycol (EG) and dibutyl terephthalate was confirmed by analyzing the condensate through GC (gas chromatography). From the point at which the ethylene glycol (EG) and the dibutyl terephthalate began to vaporize and be discharged outside the reactor, the waste PET was additionally introduced into the high-pressure reactor. At this time, the waste PET was introduced into the high-pressure reactor through a quantitative pump in a molten state at a temperature of 280°C in an external melting tank, and the introduction speed was adjusted to 1.25 g / min. Through the above process, a process system was implemented in which continuous introduction of waste PET and continuous discharge of the product were performed in real time.

[0133] Product yield

[0134] After the gaseous phase was discharged outside the high-pressure reactor, the condensed liquid (liquid mixture) was separated using a fractional distillation device to sequentially obtain 1-butanol, ethylene glycol (EG), and dibutyl terephthalate as a product.

[0135]

[0136] [Example 1-2]

[0137] The same process as in Example 1-1 was performed except that 300 g of 1-pentanol was used as the alcohol, thereby obtaining 1-pentanol, ethylene glycol (EG), and the product.

[0138]

[0139] [Example 1-3]

[0140] The same process as in Example 1-1 was performed except that 300 g of 1-octanol was used as the alcohol, thereby obtaining 1-octanol, ethylene glycol (EG), and the product.

[0141]

[0142] [Example 1-4]

[0143] The same process as Example 1-1 was performed except that 300 g of 2-ethyl-1-hexanol was used as the alcohol, thereby obtaining 2-ethyl-1-hexanol, ethylene glycol (EG), and the product.

[0144]

[0145] [Example 1-5]

[0146] The same process as in Example 1-1 was performed except that 300 g of 1-decanol was used as the alcohol, thereby obtaining 1-decanol, ethylene glycol (EG), and the product.

[0147]

[0148] [Example 1-6]

[0149] The same process as Example 1-1 was performed, except that the internal pressure of the high-pressure reactor was maintained at 3 bar by pressurizing with nitrogen, to obtain 1-butanol, ethylene glycol (EG), and the product.

[0150]

[0151] [Example 1-7]

[0152] The same process as Example 1-1 was performed, except that the internal pressure of the high-pressure reactor was maintained at 3 bar by pressurizing with nitrogen and 300 g of 1-pentanol was used as the alcohol, to obtain 1-pentanol, ethylene glycol (EG), and the product.

[0153]

[0154] [Example 1-8]

[0155] The same process as Example 1-1 was performed, except that the internal pressure of the high-pressure reactor was maintained at 3 bar by pressurizing with nitrogen and 300 g of 1-octanol was used as the alcohol, to obtain 1-octanol, ethylene glycol (EG), and the product.

[0156]

[0157] [Example 1-9]

[0158] The same process as Example 1-1 was performed, except that the internal pressure of the high-pressure reactor was maintained at 3 bar by pressurizing with nitrogen and 300 g of 2-ethyl-1-hexanol was used as the alcohol, to obtain 2-ethyl-1-hexanol, ethylene glycol (EG), and the product.

[0159]

[0160] [Example 1-10]

[0161] The same process as Example 1-1 was performed, except that the internal pressure of the high-pressure reactor was maintained at 3 bar by pressurizing with nitrogen and 300 g of 1-decanol was used as the alcohol, to obtain 1-decanol, ethylene glycol (EG), and the product.

[0162]

[0163] [Comparative Example 1-1]

[0164] Alcohololysis reaction

[0165] In a 1 L high-pressure reactor, 300 g of waste polyethylene terephthalate (waste PET), 300 mg of Zn(OAC)2·2H2O as an alcohol decomposition catalyst (1000 ppm based on the total weight of the waste PET), and 400 ml of 1-butanol as an alcohol were added.

[0166] Afterwards, all the connecting parts of the high-pressure reactor were fastened and sealed, and the temperature was raised to 280°C over 1 hour. Then, the temperature was maintained at 280°C and the pressure at 40 bar for 4 hours, and the alcoholysis reaction was performed. However, the product (gaseous mixture) derived from the alcoholysis reaction was not discharged to the outside or recovered, but was allowed to remain within the high-pressure reactor.

[0167] After the above alcoholysis reaction was completed, the mixture was cooled to room temperature to obtain a liquid alcoholysis reaction composition.

[0168] Product yield

[0169] The liquid reaction composition obtained from the above alcoholysis reaction was separated using a fractional distillation device to sequentially obtain 1-butanol, ethylene glycol (EG), and dibutyl terephthalate as a product.

[0170]

[0171] [Comparative Example 1-2]

[0172] The same process as in Comparative Example 1-1 was performed except that 300 g of 1-pentanol was used as the alcohol, thereby obtaining 1-pentanol, ethylene glycol (EG), and the product.

[0173]

[0174] [Comparative Example 1-3]

[0175] The same process as in Comparative Example 1-1 was performed except that 300 g of 1-octanol was used as the alcohol, thereby obtaining 1-octanol, ethylene glycol (EG), and the product.

[0176]

[0177] [Comparative Example 1-4]

[0178] The same process as in Comparative Example 1-1 was performed except that 300 g of 2-ethyl-1-hexanol was used as the alcohol, thereby obtaining 2-ethyl-1-hexanol, ethylene glycol (EG), and the product.

[0179]

[0180] [Comparative Example 1-5]

[0181] The same process as in Comparative Example 1-1 was performed except that 300 g of 1-decanol was used as the alcohol, thereby obtaining 1-decanol, ethylene glycol (EG), and the product.

[0182]

[0183] Alcohol Chemical Formula 1 Compound EG Recovery Rate (mol%) Process Pressure R Recovery Rate (mol%) Example 1 1-butanol (CH2) 3 CH 3 99.8 99.9 Atmospheric Pressure Example 2 1-pentanol (CH2) 4 CH 3 99.8 99.8 Atmospheric Pressure Example 3 1-octanol (CH2) 7 CH 3 99.9 99.8 Atmospheric Pressure Example 4 2-ethyl-1-hexanol 99.799.7Atmospheric pressure Example 51-decanol(CH2)9CH399.899.8Atmospheric pressure Example 61-butanol(CH2)3CH399.999.83bar Example 71-pentanol(CH2)4CH399.999.93bar Example 81-octanol(CH2)7CH399.799.93bar Example 92-ethyl-1-hexanol 99.899.73 bar Example 101-decanol(CH2)9CH3 99.999.83 bar Comparative Example 11-butanol(CH2)3CH3 87.376.540 bar Comparative Example 21-pentanol(CH2)4CH3 83.470.125 bar Comparative Example 31-octanol(CH2)7CH3 77.162.77 bar Comparative Example 42-ethyl-1-hexanol 76.363.27barComparative example 51-decanol(CH2)9CH373.558.34bar

[0184]

[0185] As a result, in the case of Examples 1 to 9, where the product (gaseous mixture) was recovered by condensing it through a condenser, the recovery rate of the compound according to Chemical Formula 1 and the recovery rate of ethylene glycol were high, whereas in the case of Comparative Examples 1 to 5, where the product (gaseous mixture) was not recovered by condensing it through a condenser, the recovery rate of the compound according to Chemical Formula 1 and the recovery rate of ethylene glycol were relatively low.

[0186] Furthermore, in the case of Examples 1 to 9, where the pressure of the high-pressure reactor was maintained at atmospheric pressure or 0.1 to 3 bar, the recovery rate of the compound according to Chemical Formula 1 and the recovery rate of ethylene glycol were high, whereas in the case of Comparative Examples 1 to 5, where the pressure of the high-pressure reactor was maintained at 4 to 40 bar, the recovery rate of the compound according to Chemical Formula 1 and the recovery rate of ethylene glycol were relatively low.

[0187]

[0188] [Example 2-1]

[0189] 60 g (0.22 mol) of the compound of chemical formula 1 obtained in Example 1-1 and 240 g (13.3 mol) of water were added to a high-pressure reactor with a capacity of 600 ml.

[0190] Thereafter, the temperature of the high-pressure reactor was raised to 260°C, and a hydrolysis reaction was performed for 4 hours while maintaining the temperature at 260°C, and then cooled to 90°C to obtain a slurry-type hydrolysis product. The slurry-type hydrolysis product was filtered, and the obtained solid was washed with 1-butanol and water at 90°C and vacuum-dried to obtain 32.2 g (yield: 90%) of solid terephthalic acid (TPA).

[0191]

[0192] [Example 2-2]

[0193] 60 g (0.20 mol) of the compound of chemical formula 1 obtained in Example 1-2 and 240 g (13.3 mol) of water were added to a high-pressure reactor with a capacity of 600 ml.

[0194] Thereafter, the temperature of the high-pressure reactor was raised to 260°C, and a hydrolysis reaction was performed for 4 hours while maintaining the temperature at 260°C, and then cooled to 90°C to obtain a slurry-type hydrolysis product. The slurry-type hydrolysis product was filtered, and the obtained solid was washed with 1-pentanol and water at 90°C and vacuum-dried to obtain 29.9 g (yield: 92%) of solid terephthalic acid (TPA).

[0195]

[0196] [Example 2-3]

[0197] 60 g (0.15 mol) of the compound of chemical formula 1 obtained in Example 1-3 and 240 g (13.3 mol) of water were added to a high-pressure reactor with a capacity of 600 ml.

[0198] Thereafter, the temperature of the high-pressure reactor was raised to 260°C, and a hydrolysis reaction was performed for 4 hours while maintaining the temperature at 260°C, and then cooled to 90°C to obtain a slurry-type hydrolysis product. The slurry-type hydrolysis product was filtered, and the obtained solid was washed with 1-octanol and water at 90°C and vacuum-dried to obtain 23.2 g (yield: 91%) of solid terephthalic acid (TPA).

[0199]

[0200] [Example 2-4]

[0201] 60 g (0.15 mol) of the compound of chemical formula 1 obtained in Example 1-4 and 240 g (13.3 mol) of water were added to a high-pressure reactor with a capacity of 600 ml.

[0202] Thereafter, the temperature of the high-pressure reactor was raised to 260°C, and a hydrolysis reaction was performed for 4 hours while maintaining the temperature at 260°C, and then cooled to 90°C to obtain a slurry-type hydrolysis product. The slurry-type hydrolysis product was filtered, and the obtained solid was washed with 2-ethyl-1-hexanol and water at 90°C and vacuum-dried to obtain 23.1 g (yield: 90%) of solid terephthalic acid (TPA).

[0203]

[0204] [Example 2-5]

[0205] 60 g (0.13 mol) of the compound of chemical formula 1 obtained in Example 1-5 and 240 g (13.3 mol) of water were added to a high-pressure reactor with a capacity of 600 ml.

[0206] Thereafter, the temperature of the high-pressure reactor was raised to 260°C, and a hydrolysis reaction was performed for 4 hours while maintaining the temperature at 260°C, and then cooled to 90°C to obtain a slurry-type hydrolysis product. The slurry-type hydrolysis product was filtered, and the obtained solid was washed with butanol and water at 90°C and vacuum-dried to obtain 20.3 g (yield: 91%) of solid terephthalic acid (TPA).

[0207]

[0208] [Example 2-6]

[0209] The same method as Example 2-1 was performed except that the compound of chemical formula 1 obtained in Example 1-6 was used, and the same amount of terephthalic acid as in Example 2-1 was obtained.

[0210]

[0211] [Example 2-7]

[0212] The same method as Example 2-2 was performed except that the compound of chemical formula 1 obtained in Example 1-7 was used, and the same amount of terephthalic acid as in Example 2-2 was obtained.

[0213]

[0214] [Example 2-8]

[0215] The same method as Example 2-3 was performed except that the compound of chemical formula 1 obtained in Example 1-8 was used, and the same amount of terephthalic acid as in Example 2-3 was obtained.

[0216]

[0217] [Example 2-9]

[0218] The same method as Example 2-4 was performed except that the compound of chemical formula 1 obtained in Example 1-9 was used, and the same amount of terephthalic acid as in Example 2-4 was obtained.

[0219]

[0220] [Example 2-10]

[0221] The same method as Example 2-5 was performed except that the compound of chemical formula 1 obtained in Example 1-10 was used, and the same amount of terephthalic acid as in Example 2-5 was obtained.

[0222]

[0223] [Comparative Example 2-1]

[0224] The same method as Example 2-1 was performed except that the compound of chemical formula 1 obtained in Comparative Example 1-1 was used, and the same amount of terephthalic acid as in Example 2-1 was obtained.

[0225]

[0226] [Comparative Example 2-2]

[0227] The same method as Example 2-2 was performed except that the compound of chemical formula 1 obtained in Comparative Example 1-2 was used, and the same amount of terephthalic acid as in Example 2-2 was obtained.

[0228]

[0229] [Comparative Example 2-3]

[0230] The same method as Example 2-3 was performed except that the compound of chemical formula 1 obtained in Comparative Example 1-3 was used, and the same amount of terephthalic acid as in Example 2-3 was obtained.

[0231]

[0232] [Comparative Example 2-4]

[0233] The same method as Example 2-4 was performed except that the compound of chemical formula 1 obtained in Comparative Example 1-4 was used, and the same amount of terephthalic acid as in Example 2-4 was obtained.

[0234]

[0235] [Comparative Example 2-5]

[0236] The same method as Example 2-5 was performed except that the compound of chemical formula 1 obtained in Comparative Example 1-5 was used, and the same amount of terephthalic acid as in Example 2-5 was obtained.

[0237]

[0238] Experimental Example 1: Metal content

[0239] The content (ppm) of metals present in the terephthalic acid of Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-5 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.

[0240]

[0241] Experimental Example 2: Color-b

[0242] For the terephthalic acid of Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-5, the color characteristic color-b was measured using a colorimeter.

[0243]

[0244] Experimental Example 3: Yellowness

[0245] For the terephthalic acid of Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-5, the yellowness index (YI) was measured.

[0246] Specifically, the terephthalic acid of Examples 2-1 to 2-10 and Comparative Examples 2-1 to 2-5 was diluted to a concentration of 5% using dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and methylpyrrolidone (NMP), and then the yellowness was measured using a ColorFlex EZ (manufacturer: HunterLab) device.

[0247]

[0248] Metal content (ppm) (Sb / Ti / Zn) Color-by-Y.I. DMSO / DMF / NMP Example 2-1 N.D. / ND / ND 0.8 0.9 / 1.1 / 0.8 Example 2-2 1 / ND / ND 1.3 1.1 / 1.3 / 1.4 Example 2-3 N.D. / ND / ND 1.2 1.3 / 1.4 / 1.2 Example 2-4 1 / ND / ND 1.1 1.2 / 1.3 / 1.2 Example 2-5 N.D. / ND / 11.4 1.3 / 1.4 / 1.2 Example 2-6 2 / ND / ND 1.2 1.4 / 1.4 / 1.3 Example 2-7 N.D. / ND / 11.3 1.3 / 1.3 / 1.2 Example 2-8N.D. / ND / 11.21.3 / 1.4 / 1.3Example 2-91 / ND / ND1.31.4 / 1.3 / 1.3Example 2-101 / ND / ND1.41.2 / 1.3 / 1.2Comparative Example 2-154 / 9 / 167.57.8 / 8.4 / 8.2Comparative Example 2-272 / 7 / 198.37.8 / 8.2 / 8.4Comparative Example 2-363 / 8 / 187.87.2 / 8.4 / 8.5Comparative Example 2-458 / 7 / 149.28.3 / 8.7 / 8.3Comparative Example 2-564 / 9 / 187.37.5 / 8.2 / 8.2

[0249]

[0250] As shown in Table 2 above, the terephthalic acid of Examples 2-1 to 2-10 not only had a very low content of metal impurities but also had very low Color b and yellowness according to the colorimeter. In contrast, it was confirmed that the terephthalic acid of Comparative Examples 2-1 to 2-5 had relatively high values ​​for the metal content and Color b and yellowness according to the colorimeter.

Claims

1. (1) A step of alcoholyzing waste polyester into an alcohol having 4 or more carbon atoms; (2) a step of obtaining a product by recovering the product derived from the alcoholysis reaction in a gaseous form; and (3) A method for depolymerizing waste polyester, comprising a step of hydrolyzing the above product to obtain a polymerization raw material.

2. In paragraph 1, A method for depolymerizing waste polyester, wherein the product comprises at least one selected from the group consisting of ethylene glycol, unreacted alcohol, and a compound represented by the following chemical formula 1: [Chemical Formula 1] In the above chemical formula 1, R1 is alkyl having 4 or more carbon atoms.

3. In paragraph 2, A method for depolymerizing waste polyester, wherein the product comprises a compound represented by the chemical formula 1.

4. In paragraph 1, A method for depolymerizing waste polyester, wherein the supply of the waste polyester for the alcoholysis and the gaseous recovery are performed simultaneously and continuously from the point in time when the gaseous recovery of the above-mentioned product begins.

5. In paragraph 1, A method for depolymerizing waste polyester, wherein the alcohol has 4 to 13 carbon atoms.

6. In paragraph 1, A method for depolymerizing waste polyester, which does not include a step of purifying the product of the above step (2).

7. In paragraph 1, A method for depolymerizing waste polyester, wherein the polymerization raw material comprises terephthalic acid.

8. A polymerization raw material obtained from a depolymerization method according to any one of paragraphs 1 to 7.

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