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, the method comprising the steps of: (1) washing a waste polyester with a washing solvent; (2) pre-treating the washed waste polyester with alcohol having 4 or more carbon atoms; (3) subjecting the pre-treated waste polyester to alcoholysis to obtain a liquid composition; and (4) subjecting the liquid composition to hydrolysis.

Description

Method for producing terephthalic acid and terephthalic acid produced therefrom

[0001] The present invention relates to a method for producing terephthalic acid energy-efficiently using waste polyester and to terephthalic acid produced from the method.

[0002] 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.

[0003] Due to the widespread use of polyester, the annual global volume of polyester waste with polyester resin applied to it is becoming increasingly unmanageable. Consequently, interest in recycling waste polyester or regeneration processes utilizing it is growing. Specifically, development is underway for processes that decompose (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).

[0004] As an example of the above process, there is a process in which waste polyester is washed and then the washed waste polyester is subjected to alcoholysis to produce terephthalic acid (regenerated terephthalic acid, r-TPA), a polymerization raw material. However, the above process has the problem that the yield and purity of the terephthalic acid are reduced due to the washing process of the waste polyester, and process troubles are caused.

[0005] Therefore, there is a need for a technology that can improve the recycling process of waste polyester to produce high-purity terephthalic acid at high yield.

[0006] [Prior Art Literature]

[0007] [Patent Document]

[0008] (Patent Document 1) Republic of Korea Publication Patent No. 1997-0042469

[0009] The present inventors have confirmed that by performing pretreatment of waste polyester using a specific alcohol, the depolymerization process of waste polyester for producing terephthalic acid can occur efficiently without going through a process for removing a solvent contained in the waste polyester (e.g., a drying process), thereby producing terephthalic acid with high purity at a high yield.

[0010] Accordingly, the object of the present invention is to provide a method for producing terephthalic acid capable of producing terephthalic acid having high purity at a high yield, and terephthalic acid (regenerated terephthalic acid) produced therefrom.

[0011] In order to solve the above problem, the present invention provides a method for producing terephthalic acid, comprising the steps of: (1) washing waste polyester with a washing solvent; (2) pretreating the washed waste polyester with an alcohol having 4 or more carbon atoms; (3) alcoholyzing the pretreated waste polyester to produce a liquid composition; and (4) hydrolyzing the liquid composition.

[0012] The present invention also provides terephthalic acid (regenerated terephthalic acid) produced by the above production method.

[0013] The present invention also provides a polyester resin comprising a component derived from the terephthalic acid.

[0014] The method for producing terephthalic acid according to the present invention produces terephthalic acid by pretreating waste polyester with a specific alcohol and then performing a depolymerization process including alcoholysis and hydrolysis. Therefore, even if the waste polyester contains moisture or solvent, the depolymerization process can be efficiently performed without a process for removing such moisture or solvent (e.g., a drying process). Accordingly, the present invention can contribute to providing high-purity terephthalic acid at a high yield.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0019]

[0020] The present invention has the feature of being able to produce terephthalic acid at a high yield even if waste polyester used in a process for producing terephthalic acid (regenerated terephthalic acid, rTPA) after undergoing separate alcoholysis and hydrolysis contains a large amount of moisture and alcohol components.

[0021] Discarded waste polyester, due to its nature, can contain a variety of contaminants. In particular, residual biochemical contaminants in polyester waste, such as food trays, can pose a safety risk to workers if they come into contact with them. To prevent this, raw materials for chemical recycling typically undergo various pre-cleaning processes.

[0022] In the above cleaning process, solvents such as water and alcohol are typically used, and as the alcohol, methanol, ethanol, and isopropyl alcohol, which are known to have antibacterial / disinfecting properties, are mainly selected.

[0023] Solvents used in excess for cleaning purposes rather than for depolymerization can reduce the purity of the products generated by the depolymerization reaction and sometimes cause process problems.

[0024] A typical process problem is process interruption due to filter clogging. If one or both sides of BHET, a product of the glycolysis reaction, are replaced by water to form carboxylic acid, this can cause problems in the glycolysis process. Furthermore, these solvent components have extremely low solubility in EG compared to BHET, making them highly susceptible to clogging the insoluble filter installed in the latter half of the reactor, potentially halting the entire process.

[0025] Meanwhile, the same phenomenon can occur in Methanoysis, which uses methanol as a depolymerization reaction material.

[0026] Currently, the only way to prevent this is to completely dry the entire waste polyester using separate energy sources. However, this drying method also has several drawbacks.

[0027] First, if the temperature and time are maintained at a high temperature sufficiently high for complete drying, the water and alcohol used for washing can be dried, but solid-state polymerization of the waste polyester occurs, which has the effect of increasing the molecular weight, and as a result, the difficulty of depolymerization increases.

[0028] To prevent this, if the waste polyester is not sufficiently dried, there is a risk that the entire process itself will be halted due to filter clogging after reaction by the component having Carboxylic Acid as a substituent as described above.

[0029] However, the present invention allows the depolymerization of waste polyester to proceed with a higher alcohol having 4 or more carbon atoms, so that the main product, a compound represented by chemical formula 1 (e.g., dibutyl terephthalate (DBTP)), or the like, acts as a solvent for the problematic mono-acid type substance, thereby allowing the entire product to be smoothly fed into the next step, hydrolysis, without causing filter clogging.

[0030] In addition, even if high-temperature drying is performed after the washing process, there are situations where it is extremely difficult to prevent water from mixing due to the basic process moisture content of waste polyester. Therefore, the process of the present invention, which can proceed with depolymerization without drying water and can input the product (liquid composition) into hydrolysis, which is a process for manufacturing terephthalic acid (regenerated terephthalic acid, r-TPA), is an extremely energy-efficient process that can drastically reduce process troubles.

[0031] Specifically, the present invention compares the fairness of a case where the water is only filtered and not completely dried, a case where a significant portion of the water is physically removed by dipping or additional washing in an alcohol to be used for depolymerization, such as butanol, after filtration, and a case where the water is completely dried to completely control side reactions in the depolymerization reaction due to water, depending on the water content of the waste polyester raw material to be used for depolymerization. The comparison of the fairness can be performed by checking the time taken for the insoluble filter process of the depolymerization reaction mixture to determine whether the process is easy.

[0032] For example, waste polyethylene terephthalate (w-PET) requires cleaning and drying during the pre-screening process. This is because when non-dried waste PET flakes are used, solid terephthalic acid (Solid TPA) is generated instead of a liquid composition (or liquid intermediate) in the alcoholysis reaction due to residual moisture, which can reduce the yield of terephthalic acid. In particular, when solid terephthalic acid is generated, side effects such as clogging of the filter at the post-reaction stage, reduced yield, and increased cost occur. However, the present invention can remove water contained in non-dried waste PET flakes by dipping them in an alcohol bath or spraying alcohol, and the used alcohol can be easily removed with an azeotrope.

[0033] Meanwhile, the present invention also has the characteristic of conducting a depolymerization process by controlling the moisture content of waste polyester. Specifically, the present invention can conduct a depolymerization process on waste polyester with a moisture content of 0 to 20% without performing a drying process for the waste polyester and without process problems, thereby producing terephthalic acid with high purity and yield.

[0034]

[0035] Method for producing terephthalic acid

[0036] A method for producing terephthalic acid according to the present invention comprises: (1) a step of washing waste polyester with a washing solvent; (2) a step of pretreating the washed waste polyester with an alcohol having 4 or more carbon atoms; (3) a step of alcoholyzing the pretreated waste polyester to produce a liquid composition; and (4) a step of hydrolyzing the liquid composition.

[0037]

[0038] Step (1): Cleansing

[0039] According to the present invention, step (1) is a step of cleaning waste polyester with a cleaning solvent. The cleaning is intended to remove foreign substances present in the waste polyester and can be performed using a conventionally known method. The cleaning solvent is not particularly limited, but may be water or alcohol (e.g., methanol, ethanol, isopropyl alcohol, etc.).

[0040] 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 (flaking) the above or converting the above 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.

[0041] The waste polyester may contain polyethylene terephthalate (PET) in an amount of 50 wt% or more, based on the total weight of the waste polyester, when considering the yield of terephthalic acid, and specifically, may contain 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%).

[0042]

[0043] Step (2): Preprocessing

[0044] According to the present invention, step (2) is a step of pretreating the washed waste polyester with an alcohol having a carbon number of 4 or more (first alcohol). The pretreatment method is not particularly limited, but may be performed by dipping the waste polyester in a bath containing an alcohol having a carbon number of 4 or more, or spraying the alcohol having a carbon number of 4 or more onto the waste polyester so that the waste polyester is showered.

[0045] The above immersion or spraying conditions are not particularly limited and can be appropriately adjusted depending on the amount, condition, etc. of the waste polyester. For example, the temperature at which the immersion is performed may be 150°C or less, 130°C or less, 120°C or less, 110°C or less, or 100°C or less.

[0046] Through the above pretreatment, the cleaning solvent remaining in the waste polyester can be removed, and as a result, a liquid composition rather than solid terephthalic acid (Solid TPA) is well produced in the alcohol reaction, thereby solving problems such as clogging of the filter at the post-reaction stage, reduction in the yield of terephthalic acid, and increase in cost.

[0047] Meanwhile, the alcohol having 4 or more carbon atoms used for the above pretreatment is an azeotrope and can be easily removed through a separate distillation process, etc. Specifically, the carbon atoms of the alcohol (first alcohol) may be 4 or more, 6 or more, 8 or more, 10 or more, 12 or more, or 14 or more. Specifically, the carbon atoms of the alcohol (first alcohol) may be 4 to 13, 4 to 10, 4 to 9, 4 to 8, or 4 to 6.

[0048]

[0049] Step (3): Alcohololysis

[0050] According to the present invention, step (3) is a step of producing a liquid composition by alcoholyzing the pretreated waste polyester. Specifically, the pretreated waste polyester is alcoholyzed with an alcohol having 4 or more carbon atoms (second alcohol) to obtain a liquid composition containing a compound represented by the following chemical formula 1. Through the alcoholyzation, a liquid composition having a liquid phase rather than a solid phase and containing a high content of the compound represented by the following chemical formula 1 as a hydrolysis target substance is obtained, thereby producing terephthalic acid in a high yield.

[0051] [Chemical Formula 1]

[0052]

[0053] In the above chemical formula 1,

[0054] R1 is alkyl having 4 or more carbon atoms.

[0055] The carbon number of the alcohol (second alcohol) introduced into the alcoholysis reaction may be 4 or more, 6 or more, 8 or more, 10 or more, 12 or more, or 14 or more. Specifically, the carbon number of the alcohol may be 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 low temperature and pressure compared to the prior art, and a liquid composition including only liquid components and not solid components can be obtained. In addition, the reaction rate of the alcoholysis can be increased.

[0056] The boiling point of the alcohol may be 100 to 290°C, and specifically, 110 to 280°C, 120 to 260°C, 130 to 230°C, 140 to 190°C, or 150 to 180°C. Since the boiling point of the alcohol is within the above range, by-products such as ethylene glycol and diethylene glycol generated in the alcoholysis process can be more easily removed or recovered in a subsequent process, thereby improving processability.

[0057] The reaction ratio of the waste polyester and the alcohol for the above alcohol decomposition is not particularly limited, but may be a weight ratio of 1:1 to 10. Specifically, the weight ratio 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.

[0058] Through the alcoholysis, a liquid composition containing a high content of the compound represented by the chemical formula 1 is produced. Specifically, the liquid composition may contain 45 to 99.9 mol% of the compound represented by the chemical formula 1 based on the total molar number of the liquid raw material. For example, the content of the compound represented by the chemical formula 1 may be 50 to 99.9 mol%, 55 to 99.5 mol%, 60 to 99.5 mol%, 65 to 99 mol%, 68 to 99 mol%, 70 to 98 mol%, 73 to 97 mol%, 75 to 96 mol%, 78 to 95 mol%, 80 to 93 mol%, 83 to 92 mol%, or 85 to 90 mol% based on the total molar number of the liquid composition. When the content of the compound represented by the above chemical formula 1 is within the above range, terephthalic acid can be produced in high yield through a hydrolysis reaction of the liquid composition.

[0059] 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.

[0060] According to the present invention, the alcoholysis can be carried out at a temperature of 160 to 280°C for 0.5 to 24 hours. Specifically, the alcoholysis reaction can be carried out at a temperature of 165 to 270°C, 170 to 260°C, 175 to 250°C, 180 to 240°C, or 180 to 230°C for 1 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 can be carried out at a reaction pressure set according to the reaction temperature and / or reaction time. Specifically, the pressure during the alcoholysis reaction may be 1 to 40 bar, 1 to 38 bar, 1.5 to 33 bar, 2 to 28 bar, 2.5 to 24 bar, 3 to 40 bar, 4 to 35 bar, or 5 to 30 bar.

[0061] The above alcoholysis reaction may or may not involve a catalyst. If the alcoholysis reaction is a non-catalytic reaction in which no catalyst is introduced, the removal process for insoluble metals, etc. can be omitted, thereby ensuring environmental friendliness and producing high-purity terephthalic acid. Furthermore, if the alcoholysis reaction is a catalytic reaction in which a catalyst is introduced, the activity of the alcoholysis reaction can be increased, thereby improving processability (economic feasibility).

[0062] 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 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.

[0063] 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.

[0064] 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, 150 to 1,000 ppm, 180 to 500 ppm, or 200 to 450 ppm, based on the total weight of the waste polyester.

[0065] Meanwhile, the liquid composition may contain terephthalic acid in an amount of 10 wt% or less based on the total weight of the liquid composition. Specifically, the liquid composition may contain no solid terephthalic acid (terephthalic acid content of 0 wt%), 0.01 to 10 wt%, 0.1 to 8 wt%, 1 to 5 wt%, or 1 to 3 wt%.

[0066] In addition, the liquid composition may further include at least one selected from the group consisting of alcohol derivatives and oligomers. Specifically, the liquid composition may include the alcohol derivative and not include the oligomer, or may not include the alcohol derivative and include the oligomer, or may include both the alcohol derivative and the oligomer. The alcohol derivative and / or the oligomer may be present in a liquid phase within the liquid composition.

[0067] The content of each of the alcohol derivative and the oligomer included in the liquid composition may not be particularly limited. Specifically, the liquid composition may contain 0.01 to 50 mol% of the alcohol derivative and 0.01 to 50 mol% of the oligomer, based on the total molar number of the liquid composition. For example, the content of the alcohol derivative may be 0.1 to 40 mol%, 0.1 to 35 mol%, 0.5 to 30 mol%, 0.5 to 25 mol%, 1 to 23 mol%, 1 to 22 mol%, 1.5 to 21 mol%, 1.5 to 20 mol%, 2 to 18 mol%, 2.5 to 17 mol%, 3 to 15 mol%, or 5 to 10 mol%, based on the total molar number of the liquid composition. In addition, the content of the oligomer may be 0.05 to 40 mol%, 0.05 to 35 mol%, 0.1 to 30 mol%, 0.1 to 25 mol%, 0.5 to 20 mol%, 0.5 to 15 mol%, 1 to 10 mol%, 1 to 8 mol%, 1.5 to 5 mol%, 1.5 to 4 mol%, 2 to 4 mol%, or 2 to 3 mol%, based on the total mole number of the liquid composition. When the contents of the alcohol derivative and the oligomer are each within the above range, the hydrolysis reaction of the liquid composition can be efficiently performed.

[0068] According to the present invention, the alcohol derivative 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.

[0069] [Chemical Formula 2]

[0070]

[0071] [Chemical Formula 3]

[0072]

[0073] In the above chemical formulas 2 and 3,

[0074] R2 and R3 are each independently an alkyl having 4 or more carbon atoms, and n is an integer of 1 or more.

[0075] 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.

[0076] Meanwhile, according to the present invention, the liquid composition may further include at least one selected from the group consisting of ethylene glycol and unreacted alcohol. Specifically, the liquid composition may include the ethylene glycol and not include the unreacted alcohol, or may not include the ethylene glycol and include the unreacted alcohol, or may include both the ethylene glycol and the unreacted alcohol.

[0077] The above ethylene glycol may refer to a by-product produced by the alcoholysis reaction, and the unreacted alcohol may refer to residual alcohol remaining after the alcohol having 4 or more carbon atoms added for the alcoholysis reaction does not participate in the alcoholysis reaction.

[0078] The content of the unreacted alcohol included in the liquid composition may not be particularly limited. Specifically, the liquid composition may contain 0.01 to 50 mol% of the unreacted alcohol based on the total molar number of the liquid composition. For example, the content of the unreacted alcohol may be 0.01 to 40 mol%, 0.01 to 35 mol%, 0.01 to 30 mol%, 0.02 to 25 mol%, 0.02 to 20 mol%, 0.02 to 15 mol%, 0.03 to 10 mol%, 0.03 to 5 mol%, 0.03 to 1 mol%, 0.04 to 0.5 mol%, 0.04 to 0.1 mol%, or 0.05 to 0.07 mol% based on the total molar number of the liquid raw material.

[0079] In addition, the liquid composition may not contain ethylene glycol and unreacted alcohol. Specifically, the liquid raw material may optionally undergo further steps of fractional distillation, adsorption purification, and concentration, which will be described later, before being subjected to a hydrolysis reaction, thereby removing (or recovering) ethylene glycol and unreacted alcohol, thereby not containing ethylene glycol and unreacted alcohol (for example, the content of each of ethylene glycol and unreacted alcohol is 0 mol%).

[0080] That is, according to the present invention, the method for producing terephthalic acid may further include a step of fractionally distilling the liquid composition prior to the hydrolysis reaction described below. The fractional distillation may be performed using a commonly known fractional distillation method, through which unreacted alcohol and ethylene glycol, a by-product, can be removed and recovered. At this time, the recovered unreacted alcohol is reused as a raw material for the alcoholysis reaction, and the ethylene glycol can be reused as a raw material for polymerization of a polyester resin or utilized in another process, thereby ensuring processability (economic feasibility). Meanwhile, by-products such as diethylene glycol can also be removed through the fractional distillation.

[0081] In addition, according to the present invention, the method for producing terephthalic acid may further include a step of adsorbent purification of the liquid composition prior to the hydrolysis reaction described below. Specifically, the adsorbent purification may be performed using one or more adsorbents selected from the group consisting of activated carbon, silica gel, alumina, zeolite, and activated clay, or through bed adsorption.

[0082] The above adsorbent may be specifically activated carbon or a mixture of activated carbon and silica gel. For example, the adsorbent may be a mixture of activated carbon and silica gel in a weight ratio of 1:0.5 to 1.5, or 1:0.8 to 1.2.

[0083] The amount of the adsorbent added is not particularly limited, but may be 0.1 to 20 wt%, 0.1 to 18 wt%, 0.2 to 15 wt%, 0.2 to 10 wt%, 0.3 to 5 wt%, or 0.3 to 2 wt% based on the total weight of the liquid composition. By adding the adsorbent to the liquid composition in the above amount and performing adsorption purification, insoluble impurities such as metals, or impurities such as colorants and pigments derived from waste polyester can be effectively removed, thereby producing terephthalic acid with excellent purity and quality.

[0084] Additionally, according to the present invention, the method for producing terephthalic acid may further include a step of concentrating the liquid composition prior to the hydrolysis reaction described below. Specifically, the step of concentrating may be further performed after the liquid composition has been adsorbed and purified. The concentration may be performed using a conventionally known concentration method, through which unreacted alcohol and ethylene glycol, a byproduct, can be removed and recovered.

[0085] Specifically, the concentration can be performed by stirring and filtering the adsorption-purified liquid composition at a temperature of 55 to 115°C, 60 to 110°C, 65 to 105°C, or 75 to 100°C for 1 to 5 hours, 1.5 to 4 hours, or 2 to 4 hours.

[0086] The liquid composition that has undergone the above adsorption purification may have a pigment residue rate (%) according to the following formula A of 15% or less, 13% or less, 11% or less, 10% or less, 8% or less, 6% or less, 5.5% or less, 5% or less, 4.3% or less, or 4% or less.

[0087] [Formula A]

[0088]

[0089] In the above formula A,

[0090] A1 is the area of ​​the absorbance curve obtained at 400 to 800 nm using a UV-vis spectrophotometer after diluting the adsorption-purified liquid composition to a concentration of 5% using dimethyl sulfoxide (DMSO), dimethylformamide (DMF), or methylpyrrolidone (NMP), respectively.

[0091] A2 is the area of ​​the absorbance curve obtained by the same method as above for a liquid composition that has not undergone adsorption purification.

[0092] According to the present invention, the liquid composition may have a filtering time of 30 minutes or less for passing through a filter having a pore size of 0.5 ㎛ or less, and specifically, may be 20 minutes or less, 10 minutes or less, 5 minutes or less, 3 minutes or less, or 1 minute or less, thereby significantly improving the yield and processability of terephthalic acid.

[0093]

[0094] Step (4): Hydrolysis reaction

[0095] According to the present invention, step (4) is a step of hydrolyzing the liquid composition. Specifically, by hydrolyzing the liquid composition, terephthalic acid (regenerated terephthalic acid) can be produced.

[0096] The hydrolysis may be performed by adding water to the liquid composition. Specifically, the hydrolysis reaction may be performed by adding water to the liquid composition 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.

[0097] The weight ratio of the liquid composition 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.

[0098] 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 high-purity terephthalic acid. 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).

[0099] 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.

[0100] 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.

[0101] 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 liquid composition.

[0102] 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 the hydrolysis reaction can be additionally included. That is, the hydrolysis reaction product produced by the hydrolysis reaction can be filtered, washed, and dried to produce solid terephthalic acid as a polymerization raw material.

[0103] 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.

[0104] 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, acetic acid, etc., or an aprotic solvent such as acetone, dichloromethane, chloroform, tetrahydrofuran (THF), toluene, etc.

[0105] 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.

[0106] 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.

[0107]

[0108] Terephthalic acid (recycled terephthalic acid)

[0109] The terephthalic acid according to the present invention is obtained through the above method for producing terephthalic acid.

[0110] According to 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).

[0111] 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).

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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 color-b value range 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 range, it can be seen that not only is the yellowness low, but also that the purification is good and the quality is excellent.

[0116] 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.

[0117] 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, or a purification and concentration process, in a process for manufacturing terephthalic acid.

[0118]

[0119] Polyester resin and method for producing the same

[0120] The polyester resin according to the present invention is manufactured using the above-described terephthalic acid. Specifically, the polyester resin comprises a component derived from the above-described terephthalic acid and a component derived from a diol compound.

[0121] 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.

[0122] 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).

[0123] The method for producing a polyester resin according to the present invention comprises the steps of: subjecting a polymerization raw material composition in which the terephthalic acid, the diol compound, and / or optionally the dicarboxylic acid compound are mixed to an esterification reaction; and the step of subjecting the esterification reaction product to a polycondensation reaction.

[0124] The esterification reaction may 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 may 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] The above stabilizer is not particularly limited, but may include phosphorus compounds such as phosphoric acid, trimethyl phosphate, and triethyl phosphate.

[0132] Meanwhile, the method for producing a polyester resin according to the present invention may further include a step of subjecting the polymer obtained through the polycondensation reaction to a solid-state polymerization reaction in order to control the intrinsic viscosity (IV), molecular weight, etc. of the polymer, 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.

[0133]

[0134] 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.

[0135]

[0136] [Example 1]

[0137] Step (1): Cleaning of waste polyester

[0138] Collected waste polyethylene terephthalate (PET) bottles were fed into a crusher to produce waste PET flakes measuring 1 to 30 mm in size. The produced waste PET flakes were washed with water to obtain washed waste PET flakes.

[0139] Step (2): Preprocessing

[0140] 1 kg of the above-mentioned washed waste PET flakes were immersed in a bath containing 1.5 kg of 1-butanol, and the waste PET flakes were pretreated at 100°C for 30 minutes to remove water remaining in the waste PET flakes.

[0141] Step (3): Alcohololysis

[0142] Into a first high-pressure reactor with a capacity of 7 L, 1 kg of the pretreated waste PET flakes, 3.3 kg of 1-butanol, and 1 g of Zn(OAC)2·2H2O (catalyst) (1000 ppm based on the total weight of the waste PET) were charged. Next, all the connecting parts of the first high-pressure reactor were fastened and sealed, and the temperature of the first high-pressure reactor was increased to 250 ° C. over 1 hour. Then, the alcoholysis reaction was performed by stirring while maintaining a pressure of 24 bar at 250 ° C. for 3 hours. After the alcoholysis reaction was completed, the reactor was cooled to room temperature and concentrated under reduced pressure to remove 1-butanol and ethylene glycol (EG) generated during the reaction, and the insoluble matter and solid products contained in the waste polyethylene terephthalate (PET) were removed by filtering under reduced pressure, thereby obtaining a liquid composition.

[0143] Step (4): Hydrolysis

[0144] Into a second high-pressure reactor with a capacity of 600 ml, 60 g (0.22 mol) of the above liquid composition, 240 g (13.3 mol) of water, and 12 mg (200 ppm based on the total weight of the concentrated liquid composition) of Zn(OAC)2·2H2O (catalyst) were charged. Next, the temperature of the second 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 reaction product. The slurry-type hydrolysis reaction product was filtered, and the obtained solid was washed with 1-butanol and water at 90°C and vacuum-dried to obtain solid terephthalic acid (TPA).

[0145]

[0146] [Example 2]

[0147] Solid terephthalic acid (TPA) was obtained through the same process as Example 1, except that 1 kg of washed waste PET flakes was placed in a container and 1-butanol was sprayed onto the container containing the waste PET flakes at a rate of 0.05 kg / min for 30 minutes to pretreat the waste PET flakes.

[0148]

[0149] [Example 3]

[0150] Solid terephthalic acid (TPA) was obtained through the same process as Example 1, except that waste PET flakes were pretreated with 1-pentanol instead of 1-butanol and 1-pentanol was used for alcoholysis.

[0151]

[0152] [Comparative Example 1]

[0153] Solid terephthalic acid (TPA) was obtained through the same process as Example 1, except that the step of pretreating the washed waste PET flakes with 1-butanol was omitted.

[0154]

[0155] [Comparative Example 2]

[0156] Solid terephthalic acid (TPA) was obtained through the same process as Example 1, except that waste PET flakes were pretreated with toluene instead of 1-butanol.

[0157]

[0158] [Example 1]

[0159] The liquid composition obtained through the alcoholysis reaction was analyzed by NMR (JEOL analysis equipment) to identify the components contained in the liquid composition, and the results are shown in Table 1 below.

[0160]

[0161]

[0162]

[0163] [Example 2]

[0164] The liquid composition obtained through the alcoholysis reaction process and the vacuum concentration process was filtered under reduced pressure to check the filtering speed (time), and the results are shown in Table 2 below. Specifically, the reduced pressure was maintained at a constant 30 torr, and the filter used was a product purchased from Sigma-Aldrich (ZapCap-CR, PTFE membrane, pore size 0.45 ㎛). In addition, the time required to filter the entire liquid composition obtained through the vacuum concentration process after the alcoholysis reaction was measured.

[0165]

[0166] Distinctive filtering time (minutes) Example 11 Example 21 Example 31.5 Comparative example 131 Comparative example 243

[0167] [Example 3]

[0168] 0.1 g of the filtrate obtained in Test Example 2 was dissolved in 10 ml of dimethyl sulfoxide (DMSO) and analyzed by HPLC. The TPA content in the filtrate was confirmed by substituting it into a calibration curve calculated in advance using pure TPA (purity >99.9%). Thereafter, the yield of terephthalic acid (the amount of TPA produced in the hydrolysis reaction) was calculated according to Equation 1 below, and the results are shown in Table 3 below.

[0169] [Formula 1]

[0170]

[0171]

[0172] Amount of filter filtrate (g) (insoluble matter + TPA) TPA content in filter filtrate (wt%) TPA yield (mole%) Example 12.100 Example 22.200 Example 32.100 Comparative example 132943.0 Comparative example 235933.3

Claims

1. (1) A step of washing waste polyester with a washing solvent; (2) A step of pretreating the above-mentioned washed waste polyester with an alcohol having a carbon number of 4 or more; (3) A step of producing a liquid composition by alcoholyzing the pretreated waste polyester; and (4) A method for producing terephthalic acid, comprising a step of hydrolyzing the liquid composition.

2. In paragraph 1, A method for producing terephthalic acid, wherein the alcohol has 4 to 8 carbon atoms.

3. In paragraph 1, A method for producing terephthalic acid, wherein the above pretreatment is performed by dipping the waste polyester in the alcohol or spraying the alcohol onto the waste polyester.

4. In paragraph 3, A method for producing terephthalic acid, wherein the above immersion is performed at 150°C or lower.

5. In paragraph 1, A method for producing terephthalic acid, wherein the content of terephthalic acid contained in the above liquid composition is 10 wt% or less based on the total weight of the liquid composition.

6. In paragraph 1, A method for producing terephthalic acid, wherein the liquid composition has a filtering time of 30 minutes or less, through a filter having a pore size range of 0.5 ㎛ or less.

7. In paragraph 1, A method for producing terephthalic acid, wherein the above alcohol decomposition is performed by adding an alcohol having 4 or more carbon atoms to the waste polyester.

8. In paragraph 1, The above liquid composition is a method for producing terephthalic acid, comprising 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.

9. In paragraph 1, A method for producing terephthalic acid, wherein the yield of terephthalic acid is 70% or more.

10. Terephthalic acid produced by a production method according to any one of claims 1 to 9.

11. A polyester resin comprising a component derived from terephthalic acid of Article 10.

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