Method for producing terephthalic acid by pet depolymerization using paper sludge incineration ash

Abstract

The present invention relates to a method for producing terephthalic acid by PET depolymerization using paper sludge incineration ash as a hydrolysis catalyst and, specifically, to a method for producing terephthalic acid, wherein a portion of a basic hydrolysis catalyst for waste PET is replaced with paper sludge incineration ash, thereby reducing the amount of catalyst used, maintaining the pKa of a hydrolysis reaction, and recycling, in an environmentally friendly manner, paper sludge incineration ash, which is a conventionally buried waste resource.

Description

Method for producing terephthalic acid from PET depolymerization using paper mill sludge incineration ash

[0001] The present invention relates to a method for producing terephthalic acid from PET depolymerization using paper mill sludge incineration ash, and more particularly, to a method for producing terephthalic acid which reduces the amount of catalyst used, maintains the pKa of the hydrolysis reaction, and can environmentally recycle paper mill sludge incineration ash, a waste resource that has been landfilled in the past, by adding paper mill sludge incineration ash during basic hydrolysis of waste PET.

[0002] Polyester is a type of plastic used in various applications such as films, containers, paints, machine parts, and fibers. A representative example of this is PET (Polyethylene terephthalate). PET can be manufactured by polymerizing terephthalic acid (TPA) or dimethyl terephthalate (DMT) with ethylene glycol (EG). Since PET is widely used industrially, it generates a lot of waste, so it is a material that is recycled due to regulations in each country. Research and development are being conducted on depolymerization methods to convert it into monomers.

[0003] There are various known chemical reaction pathways for PET depolymerization methods, including hydrolysis, methanolysis, and glycolysis. Among the above depolymerization methods, the hydrolysis method has the advantage of being able to hydrolyze waste PET containing up to 40 wt% of impurities.

[0004] The above hydrolysis method involves depolymerization under high-temperature conditions in the presence of a high concentration of acid or base catalyst, with TPA ultimately obtained as the depolymerization product. In the case of alkaline hydrolysis using the base catalyst, sodium hydroxide (NaOH) or potassium hydroxide (KOH) are known to be used as the base catalyst.

[0005] However, since the TPA produced in basic hydrolysis forms a salt with the basic catalyst, which reduces the pH of the reaction system, there is a problem that an excessive amount of catalyst must be added to maintain basic reaction conditions, and in the case where the raw material is a PET composite material, the catalyst is consumed as the mixed amide, carbamate, etc. are hydrolyzed, so there is a problem that the amount of catalyst used increases and the process efficiency decreases.

[0006] In addition, there is a problem that the unit price of raw materials increases economically and causes environmental problems due to the increase in waste after the catalyst is deactivated due to the strong acid used to protonate terephthalate salt into TPA, and there is a problem that it is difficult to commercialize TPA due to the low purity of TPA caused by impurities such as pigments, adhesives, and minerals contained in waste PET raw materials.

[0007] As a prior art, Korean Patent No. 10-0983349 (announced on September 20, 2010) discloses a technology for obtaining a product by hydrolyzing PET with KOH or NaOH, adding water to the product to separate the aqueous phase and the organic phase, and converting the terephthalate into TPA by adding sulfuric acid to the aqueous phase, and Korean Patent No. 10-2269702 (announced on June 28, 2021) discloses a technology for obtaining a solution in which disodium terephthalate (Na2-TPA) is dissolved by adding water to the product by hydrolyzing PET in the presence of sodium carbonate (Na2CO3) and zinc acetate, decolorizing the solution by adding a coagulant, and then obtaining TPA using sulfuric acid.

[0008] Nevertheless, in order to reduce the amount of base catalyst used in the basic hydrolysis of PET, a method for recycling waste resources is needed, and in addition, research and development is needed for a PET depolymerization method that can recover TPA with a purity of 99% or higher from the depolymerization product while also allowing the recovery of the base catalyst from the depolymerization product.

[0009] Meanwhile, paper sludge is a sediment generated during the sewage treatment or water purification process in the papermaking process. It was previously disposed of by dehydration and landfilling, but due to the enormous amount of sludge, some of the paper sludge was dehydrated and incinerated to be disposed of in the form of paper sludge incineration ash.

[0010] However, with the emergence of a circular economy that encourages efficient use of resources, technologies have been developed to recycle high-carbon paper sludge into organic fertilizer (Korean Patent No. 10-1996-0001497 (announced on January 31, 1996)), lightweight aggregate (Korean Patent No. 10-0186278 (announced on April 15, 1999)), solidifying agent for manufacturing artificial soil (Korean Patent No. 10-1055317 (announced on August 9, 2011)), adsorbent (Korean Patent No. 10-1563984 (announced on October 28, 2015)), and solid fuel (Korean Patent Publication No. 10-2018-0046384 (announced on May 8, 2018)), and paper sludge containing SiO2, Al2O3, CaO, etc. A technology has been developed to extract components that are easy to store CO2 from paper slude incineration ash (PSA) (Korean Patent No. 10-1650126 (announced on August 22, 2016)) or extract components of papermaking raw materials (Korean Patent No. 10-2521806 (announced on April 17, 2023)).

[0011] Nevertheless, in order to diversify the uses of paper sludge incineration ash for environmentally friendly treatment of paper sludge amounting to 1.4 million tons as of 2016, research and development on technology to utilize it as a basic hydrolysis catalyst for PET is necessary.

[0012] The purpose of the present invention is to provide a method for producing terephthalic acid having a purity of 99% or higher while reducing the amount of catalyst used by replacing part of the basic hydrolysis catalyst with waste paper sludge incineration ash.

[0013] In order to solve the above problem, the present invention provides a method for producing TPA from PET depolymerization using paper mill sludge incineration ash, comprising the steps of: (a) depolymerizing a PET-containing polymer in the presence of at least one selected from the group consisting of alkali metal hydroxides and alkali metal oxides, paper mill sludge incineration ash, and a reaction solvent to obtain a PET depolymerization product containing a terephthalate metal salt; (b) filtering the PET depolymerization product to obtain a cake, and then adding water to the cake to elute an aqueous solution containing a terephthalate metal salt; (c) adding an organic solvent for purification to the aqueous solution containing the terephthalate metal salt of step (b) to separate it into an aqueous phase and an organic phase, and then obtaining a solution of an aqueous phase containing a terephthalate metal salt; And (d) a step of reacting a strong acid with a solution containing the terephthalate metal salt to precipitate the terephthalate metal salt as a solid terephthalic acid, and obtaining a solution containing a salt in which a conjugate base of a metal derived from a hydrolysis catalyst and a strong acid are combined.

[0014] The above paper sludge incineration ash is characterized by having a pH of 10 or higher by incinerating sludge generated during paper manufacturing, and containing 10 to 50 wt% of SiO2, 10 to 45 wt% of Al2O3, 1 to 15 wt% of MgO, and 1 to 35 wt% of CaO relative to the total weight of the incineration ash.

[0015] The paper sludge incineration ash of the above step (a) can be injected so that the pH of the reaction system becomes 7.1 or higher.

[0016] In the above step (a), the alkali metal hydroxide may be at least one selected from potassium hydroxide, sodium hydroxide, and lithium hydroxide, and the alkali metal oxide may be at least one selected from potassium oxide, sodium oxide, and lithium oxide.

[0017] The reaction solvent of the above step (a) is characterized in that it includes at least one solvent selected from methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, heptylene glycol, octylene glycol, nonylene glycol, decylene glycol, undecylene glycol, dodecylene glycol, glycerin, diethyl ether, methyl-t-butyl ether, tetrahydrofuran, acetone, methyl isobutyl ketone, methyl ethyl ketone, toluene, xylene, phenol, benzyl alcohol, methoxybenzene, ethoxybenzene, propoxybenzene, butoxybenzene, and pentoxybenzene. Can be.

[0018] In the above step (a), water may be added together with the reaction solvent.

[0019] The organic solvent for purification in the above step (c) may be at least one selected from among methyl isobutyl ketone, methyl ethyl ketone, acetone, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane.

[0020] According to the present invention, by replacing part of the basic hydrolysis reaction catalyst of waste PET with waste paper sludge incineration ash, the amount of catalyst used is reduced, basic reaction conditions are easily maintained, and waste paper sludge incineration ash that is to be landfilled can also be utilized.

[0021] In addition, the present invention has the effect of increasing the purity of the final TPA by reducing the amount of impurities produced by adding paper sludge to the impurities in the PET depolymerization product.

[0022] Figure 1 is a drawing showing the appearance and HPLC spectrum of TPA obtained according to comparative examples and examples of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0024] Throughout this specification, whenever a part is said to “include” a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0025] Basic catalysts such as KOH and NaOH have been used as basic hydrolysis catalysts for PET, but there is a constant problem that an excessive amount of catalyst must be added due to the nature of basic hydrolysis, and there is also a problem that a larger amount of catalyst is required when performing basic hydrolysis of composite plastic materials that are mixed with plastics such as amide and carbamate in addition to PET.

[0026] To solve this problem, the applicant has completed the present invention regarding a method for producing high-yield, high-purity TPA by utilizing waste paper sludge incineration ash, which has been discarded, as a basic hydrolysis catalyst for PET, thereby partially replacing existing basic catalysts and improving hydrolysis efficiency.

[0027] Hereinafter, we will examine a method for producing terephthalic acid from PET depolymerization using paper sludge incineration ash as a hydrolysis catalyst.

[0028] A method for producing TPA from PET depolymerization using paper mill sludge incineration ash as a hydrolysis catalyst of the present invention, comprising the steps of: (a) depolymerizing a PET-containing polymer in the presence of at least one selected from the group consisting of alkali metal hydroxides and alkali metal oxides, paper mill sludge incineration ash, and a reaction solvent to obtain a PET depolymerization product containing a terephthalate metal salt; (b) filtering the PET depolymerization product to obtain a cake, and then adding water to the cake to elute an aqueous solution containing a terephthalate metal salt; (c) adding an organic solvent for purification to the aqueous solution containing a terephthalate metal salt of step (b) to separate it into an aqueous phase and an organic phase, and then obtaining a solution of an aqueous phase containing a terephthalate metal salt; And (d) a step of reacting a strong acid with a solution containing the terephthalate metal salt to precipitate the terephthalate metal salt as a solid terephthalic acid, and obtaining a solution containing a salt in which a conjugate base of a metal derived from a hydrolysis catalyst and a strong acid are combined.

[0029] The above step (a) is a step of depolymerizing a polymer including PET in the presence of a hydrolysis catalyst including paper sludge incineration ash and a base catalyst and a reaction solvent.

[0030] In the step (a), the paper mill sludge incineration ash as the hydrolysis catalyst of the present invention is technically characterized by having a pH of 10 or higher by incinerating sludge generated during papermaking, and the paper mill sludge incineration ash is a mixture of various components, and the main components thereof may have a composition including SiO2 10 to 50 wt%, Al2O3 10 to 45 wt%, MgO 1 to 15 wt%, CaO 1 to 35 wt%, etc. based on the total weight of the incineration ash. In addition, the paper mill sludge incineration ash may further include Fe2O3, K2O, Na2O, TiO2, phosphorus, carbon, moisture, etc.

[0031] There is no limitation on the amount of the above-mentioned paper sludge incinerator ash to be added so that the pH of the reaction system becomes 7.1 or higher, and the amount and composition of the polymer including PET to be depolymerized, the amount and composition of another hydrolysis catalyst including at least one of alkali metal hydroxide and alkali metal oxide, etc. may be taken into consideration.

[0032] The hydrolysis catalyst to be introduced together with the above-mentioned paper sludge incineration ash includes at least one of an alkali metal hydroxide including potassium hydroxide, sodium hydroxide, and lithium hydroxide; an alkali metal oxide including potassium oxide, sodium oxide, and lithium oxide; and preferably, at least one of KOH and NaOH.

[0033] The depolymerization in step (a) above includes alkaline hydrolysis, and a saponification reaction can be performed together with the hydrolysis reaction using water generated from the reaction of the hydrolysis catalyst and the reaction solvent as a medium.

[0034] The above reaction solvent includes, for example, alcohol solvents including methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, heptylene glycol, octylene glycol, nonylene glycol, decylene glycol, undecylene glycol, dodecylene glycol, and glycerin; ether solvents including diethyl ether, methyl-t-butyl ether, and tetrahydrofuran; ketone solvents including acetone, methyl isobutyl ketone, and methyl ethyl ketone; An aromatic solvent including toluene, xylene, phenol, benzyl alcohol, methoxybenzene, ethoxybenzene, propoxybenzene, butoxybenzene, and pentoxybenzene may include at least one of the following; and preferably, at least one of ethanol, methyl isobutyl ketone (MIBK), and methoxybenzene.

[0035] As an example of the present invention, water may be introduced together with the reaction solvent in step (a). By introducing water separately from the reaction solvent, the speed, purification, and conversion rate of the hydrolysis reaction may be improved. In this case, the amount of water introduced is not limited, but may preferably be in the range of 1 to 4 times the weight of the incinerator ash.

[0036] The hydrolysis reaction of the above step (a) is basic hydrolysis, and conditions such as temperature and pressure can be applied without limitation to conditions applied to conventional hydrolysis methods.

[0037] The above terephthalate metal salt is a compound in which an alkali metal derived from a hydrolysis catalyst is combined with terephthalate. The type of metal depends on the type of metal of the hydrolysis catalyst, and may be, for example, one or more of dipotassium terephthalate (K2-TPA), disodium terephthalate (Na2-TPA), and dilithium terephthalate (Li2-TPA).

[0038] The above step (b) is a step of eluting an aqueous solution containing a terephthalate metal salt from the PET depolymerization product obtained in step (a).

[0039] In the above step (b), in order to remove foreign substances contained in the PET depolymerization product of step (a), the depolymerization product is filtered to remove the filtrate containing the reaction solvent and impurities dissolved therein, and a cake containing terephthalate metal salt and paper sludge incineration ash is obtained. Although organic impurity components such as pigments and adhesives are present in the cake, the contents of these may be reduced when paper sludge incineration ash is added. Next, water is added and filtered to extract an aqueous solution containing the primary purified terephthalate metal salt.

[0040] The amount of water added to the cake can be 4 to 10 times the weight of the polymer, including the raw PET. If the amount of water added is less than 4 times the weight of the raw PET, the PET will become supersaturated. If it exceeds 10 times, it is not economical and has a negative impact on the environment.

[0041] The above step (c) is a step of extracting an aqueous phase after adding an organic solvent for purification and performing phase separation to purify a terephthalate metal salt of higher purity from an aqueous solution containing a terephthalate metal salt.

[0042] In the above step (c), the organic solvent for purification can be a hydrophobic solvent alone or a mixture of hydrophobic solvents of different components, and in some cases, a water-soluble solvent can be mixed or a water-soluble solvent can be used alone. Any type that does not undergo an additional reaction can be preferably used. The organic solvent for purification that can be used in the present invention is used for the purpose of removing impurities and reaction solvents present in trace amounts in the aqueous layer obtained in step (b), and therefore can be changed depending on the type and ratio of the impurities and reaction solvents.

[0043] As the organic solvent for purification, one or more of a ketone solvent, an alcohol solvent, and an alkane solvent, or one or more thereof, may be used alone.

[0044] For example, the organic solvent for purification may be one or more of a ketone solvent including at least one of methyl isobutyl ketone, methyl ethyl ketone, and acetone; an alcohol solvent including butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, and dodecanol; and an alkane solvent including pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane.

[0045] The amount of the organic solvent for purification may be 1 to 4 times the weight of the water introduced in step (b). If the amount of the organic solvent for purification is less than 1 time the weight of the water, there is a problem that the purity of the TPA finally obtained is reduced due to the emulsion layer located in the middle, and if it exceeds 4 times, some of the TPA is separated into the organic phase, reducing the purity of the TPA, and the amount of the organic solvent for purification that is discarded is excessive, which causes a problem of poor economic efficiency.

[0046] The above step (d) is a step of reacting the terephthalate metal salt in the water phase of step (c) with a strong acid to finally obtain terephthalic acid.

[0047] In the above step (d), a strong acid is reacted to convert the terephthalate metal salt into terephthalic acid. A strong acid including hydrochloric acid and sulfuric acid used in a conventional hydrolysis method can be used, and is not limited to the type of the strong acid described, but sulfuric acid can be preferably used.

[0048] From the above reaction, high purity terephthalic acid of 99% or more that can be commercialized can be obtained.

[0049] Hereinafter, preferred embodiments of a method for producing terephthalic acid from PET depolymerization using paper sludge incinerator ash as a hydrolysis catalyst according to the present invention will be described. It should be noted that the following examples are provided to illustrate one or more preferred embodiments of the present invention, but the present invention is not limited to these embodiments. Numerous modifications to the examples described below may be made within the scope of the present invention.

[0050] <Example 1: Depolymerization of polyester sheet fabric for automobiles in the presence of a hydrolysis catalyst in which a portion of KOH is replaced with paper sludge incineration ash>

[0051] Polyester sheet fabric for automobiles is crushed to prepare polymer raw materials. In a 250 mL round-bottomed flask, a reaction solvent containing 14 g of water, 60 g of ethanol, and 60 g of MIBK is added, 7.29 g of KOH, and 8.75 g of paper sludge incineration ash. Then, 10 g of the crushed fabric is added and stirred at 60°C for 1 hour. As a result of component analysis of the paper sludge incineration ash, it was analyzed as SiO2 [34%], Al2O3 [22%], Fe2O3 [0.6%], CaO [11%], MgO [5%], Na2O [0.4%], K2O [1.8%], TiO2 [1.8%], and other components, along with carbon and moisture. After the reaction is completed, the reaction product is filtered to obtain a cake, and 80 g of water is added to the cake to obtain an aqueous solution from which dipotassium terephthalate is eluted. 80 g of an organic solvent for purification, a 1:1 mixture of methyl isobutyl ketone (MIBK) and octanol, is added to the aqueous solution to separate the phases, and only the aqueous phase is recovered. Sulfuric acid is added to the recovered aqueous phase to adjust the pH to 3 or lower, and a white solid is obtained, which is then filtered. The solid is washed five times with 80 g of water and then dried to obtain white terephthalic acid (8.2 g) (yield: 95%, purity: 99.81% (HPLC), see Fig. 1). The yield of terephthalic acid in the following examples and comparative examples was calculated as the ratio of the mole number of the obtained terephthalic acid to the mole number of PET.

[0052] <Example 2: Depolymerization of a film for manufacturing electronic products in the presence of a hydrolysis catalyst in which a portion of KOH is replaced with paper sludge incineration ash>

[0053] A polymer raw material is prepared by crushing a film for manufacturing automotive electronic products. In a 250 mL round-bottomed flask, 7.29 g of KOH and 8.75 g of the paper sludge incinerator ash from Example 1 are added to a reaction solvent consisting of 14 g of water, 60 g of ethanol, and 60 g of MIBK. Then, 10 g of the finely crushed raw material is added and stirred at 60°C for 1 hour. After the reaction is complete, the reaction product is filtered to obtain a cake, and 80 g of water is added to the cake to obtain an aqueous solution from which dipotassium terephthalate has been eluted. 80 g of a purification organic solvent consisting of a 1:1 mixture of methyl isobutyl ketone (MIBK) and octanol is added to the aqueous solution, phase separation is performed, and only the aqueous phase is recovered. The recovered aqueous phase is adjusted to a pH of 3 or lower by adding sulfuric acid to obtain a white solid, which is then filtered. After washing five times with 80 g of water and drying, white terephthalic acid (6.2 g) was obtained (yield: 95%, purity: 99.78% (HPLC), see Figure 1).

[0054] <Comparative Example 1: Depolymerization of polyester sheet fabric for automobiles in the presence of a hydrolysis catalyst containing only KOH without replacing paper sludge incineration ash>

[0055] The same method as Example 1 was performed except that the paper sludge incinerator ash was not added and 16.04 g of KOH was added.

[0056] As a result, milky white terephthalic acid (8.3 g) was obtained (yield: 95%, purity: 97.66% (HPLC), see Figure 1).

[0057] <Comparative Example 2: Depolymerization of a film for manufacturing electronic products in the presence of hydrolysis containing only KOH without replacing paper sludge incineration ash>

[0058] The same method as Example 2 was performed except that the paper sludge incinerator ash was not added and 16.04 g of KOH was added.

[0059] As a result, gray terephthalic acid (6.1 g) was obtained (yield: 94%, purity: 98.21% (HPLC), see Figure 1).

[0060] <Comparative Example 3: Depolymerization of polyester sheet fabric for automobiles in the presence of a hydrolysis catalyst containing only paper sludge incineration ash>

[0061] The same method as Example 1 was performed except that KOH was not added and 16.04 g of paper sludge incineration ash was added.

[0062] As a result, white terephthalic acid (5.6 g) was obtained (yield: 65%, purity: 99.99% (HPLC), see Figure 1).

[0063] <Comparative Example 4: Depolymerization of a film for manufacturing electronic products in the presence of hydrolysis containing only paper sludge incineration ash>

[0064] The same method as Example 2 was performed except that KOH was not added and 16.04 g of paper sludge incineration ash was added.

[0065] As a result, white terephthalic acid (4.5 g) was obtained (yield: 69%, purity: 99.97% (HPLC), see Fig. 1).

[0066] Figure 1 is a drawing showing the appearance and HPLC spectrum of TPA obtained according to comparative examples and examples of the present invention.

[0067] Referring to Fig. 1, according to Examples 1 and 2, ultra-high purity terephthalic acid of 99% or more, which is commercially feasible, was obtained by adding paper sludge incineration ash, and it was confirmed that colored pigment impurities were completely removed from the pure white terephthalic acid in terms of appearance and HPLC spectrum.

[0068] On the other hand, Comparative Examples 1 and 2, in which only KOH was used as a hydrolysis catalyst, had yields equivalent to those of Examples 1 and 2, but were less economical because a large amount of KOH was consumed in hydrolyzing dye, polyurethane, and adhesive components, and the purity of 99% required for commercialization was found to be lower due to impurities.

[0069] In addition, Comparative Examples 3 and 4, in which only paper sludge incineration ash was used as a hydrolysis catalyst, were able to recover 99% of high-purity terephthalic acid, but the yield was poor at less than 70% because it was not used in combination with an existing hydrolysis catalyst.

[0070] While the present invention has been described above with reference to the embodiments described herein or illustrated in the accompanying drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent embodiments are possible. Accordingly, the technical protection scope of the present invention should be defined by the following claims.

Claims

1. (a) A step of depolymerizing a PET-containing polymer in the presence of at least one selected from the group consisting of alkali metal hydroxides and alkali metal oxides, paper sludge incinerator ash, and a reaction solvent to obtain a PET depolymerization product containing a terephthalate metal salt; (b) a step of filtering the PET depolymerization product to obtain a cake, and then adding water to the cake to elute an aqueous solution containing a terephthalate metal salt; (c) a step of adding an organic solvent for purification to the aqueous solution containing the terephthalate metal salt of step (b) to separate the solution into an aqueous phase and an organic phase, and then obtaining a solution of the aqueous phase containing the terephthalate metal salt; and (d) A method for producing TPA from PET depolymerization using paper sludge incinerator ash, characterized by comprising the step of reacting a strong acid with a solution containing the terephthalate metal salt to precipitate the terephthalate metal salt as a solid terephthalic acid, and obtaining a solution containing a salt in which a conjugate base of a metal and a strong acid derived from a hydrolysis catalyst are combined.

2. In paragraph 1, A method for producing TPA from PET depolymerization using paper mill sludge incineration ash, characterized in that the paper mill sludge incineration ash contains 10 to 50 wt% of SiO2, 10 to 45 wt% of Al2O3, 1 to 15 wt% of MgO, and 1 to 35 wt% of CaO relative to the total weight of the incineration ash.

3. In paragraph 1, A method for producing TPA from PET depolymerization using paper mill sludge incineration ash, characterized in that the paper mill sludge incineration ash of step (a) is introduced so that the pH of the reaction system becomes 7.1 or higher.

4. In paragraph 1, A method for producing TPA from PET depolymerization using paper sludge incineration ash, characterized in that in the step (a), the alkali metal hydroxide is at least one selected from potassium hydroxide, sodium hydroxide, and lithium hydroxide, and the alkali metal oxide is at least one selected from potassium oxide, sodium oxide, and lithium oxide.

5. In paragraph 1, The reaction solvent of the above step (a) is characterized in that it includes at least one solvent selected from methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, heptylene glycol, octylene glycol, nonylene glycol, decylene glycol, undecylene glycol, dodecylene glycol, glycerin, diethyl ether, methyl-t-butyl ether, tetrahydrofuran, acetone, methyl isobutyl ketone, methyl ethyl ketone, toluene, xylene, phenol, benzyl alcohol, methoxybenzene, ethoxybenzene, propoxybenzene, butoxybenzene, and pentoxybenzene. A method for producing TPA from PET depolymerization using paper sludge incineration ash.

6. In paragraph 1, A method for producing TPA from PET depolymerization using paper sludge incineration ash, characterized in that water is introduced together with a reaction solvent in the above step (a).

7. In paragraph 1, A method for producing TPA from PET depolymerization using paper sludge incineration ash, characterized in that the organic solvent for purification in the above step (c) is at least one selected from among methyl isobutyl ketone, methyl ethyl ketone, acetone, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, dodecanol, pentane, hexane, heptane, octane, nonane, decane, undecane, and dodecane.

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