Recycled terephthalic acid and manufacturing method thereof

Abstract

The present invention relates to recycled terephthalic acid having high purity and yield and improved color, and a manufacturing method thereof, the method comprising the steps of: depolymerizing a mixed fiber including cotton and a synthetic fiber with a depolymerization solvent to prepare a depolymerized product; filtering the depolymerized product to separate a filtrate; obtaining recycled dialkyl phthalate from the filtrate; and hydrolyzing the recycled dialkyl phthalate.

Description

Regenerated terephthalic acid and its production method

[0001] The present invention relates to recycled terephthalic acid and a method for producing the same.

[0002]

[0003] As plastic recycling becomes more important, the scope of plastics or polymer materials utilized as recycled materials is also expanding. Traditional recycling methods for waste plastics include: ① reusing them for the same or similar purpose after simple pretreatment such as washing; or ② mechanical recycling, or mechanical processing such as extrusion, which transforms waste plastics into polymer chips or pellets for other uses. However, true chemical recycling, distinct from pyrolysis, commonly referred to as chemical recycling, has recently emerged. Unlike conventional pyrolysis, chemical recycling involves sorting waste plastics and chemically treating them to recycle their individual raw materials.

[0004] This method is commonly called solvolysis because it uses a solvent to convert polymers into raw materials. Considering that most solvents used in this process are alcohols such as ethylene glycol (EG) and methanol, it is also called alcoholysis. More specifically, it is also called glycolysis or methanolysis based on the chemical names of each alcohol.

[0005] The advantages of this solvolysis-based chemical regeneration method compared to the traditional methods mentioned above - reuse / mechanical regeneration - are the quality advantage of being able to regenerate to the same quality as new products, and the great positive effect from an environmental perspective of suppressing the massive amount of carbon emissions that start from the mining of raw materials consumed when producing new plastics.

[0006] Chemical recycling methods are not applicable to all waste plastics. For chemical recycling to be feasible, the recycling process, such as solvolysis, must be environmentally friendly and economical. For example, chemical recycling (also known as depolymerization) requires at least as much energy as polymerization, making it difficult. Furthermore, it is advantageous for the materials produced through recycling to be readily reusable in the polymerization process for the same plastic. If the material structure or properties of the recycled raw material differ from the original raw material, new facilities will be required to recycle it into the existing plastic polymerization process, making it difficult to reduce new plastic production through chemical recycling.

[0007] For example, polyurethane is a plastic that undergoes a very easy chemical regeneration process, allowing the urethane bonds to be broken at relatively low temperatures. However, the resulting material is often different from the raw materials used in the urethane polymerization process, making regeneration difficult.

[0008] In contrast, polyester (e.g. PET (Polyethylene terephthalate)) is evaluated as a raw material very suitable for chemical recycling because the chemical recycling process itself is easy and the resulting materials can be obtained in the same form as the raw material.

[0009] However, it is generally not easy to obtain feedstock consisting of 100% pure waste polyethylene terephthalate (PET). PET feedstock, typically used for chemical recycling, is obtained from bottles or textiles. Bottles contain a variety of polyolefin components, such as polyethylene (PE) and polypropylene (PP), derived from bottle caps, while textiles contain a large amount of natural polymer materials for clothing, such as cotton. In particular, the content of materials other than PET in textiles is significantly higher than that in bottles. For example, waste clothing is highly likely to contain approximately 30-50% cotton without a separate collection and sorting (screening) process.

[0010] Process problems that arise when materials are not used alone are quite diverse. Adhesive materials mixed in can cause filter or pipe blockages, resulting in various process economical losses. While the nature of these problems differs slightly, the chemical regeneration of waste textiles can also present complex challenges.

[0011] The only way to prevent these various problems in advance is through sorting. Sorting involves selecting only raw materials with extremely high polyethylene terephthalate (PET) content and feeding them into a chemical recycling process. However, many waste materials with low or at least indeterminate PET content are inevitably subject to traditional disposal methods like landfill or incineration, making it difficult to pursue environmental friendliness.

[0012] To improve these shortcomings and achieve complete chemical regeneration, a recycling method encompassing the entire composition of raw materials, consisting of polymers with different chemical structures, must first be established. To achieve this, the development of recycling methods for other polymers, beyond polyethylene terephthalate (PET), for which chemical regeneration methods have not been actively developed or are inadequate, is crucial.

[0013] As mentioned above, representative non-PET polymers that can be discharged mixed with polyethylene terephthalate (PET) include natural fibers, especially cotton.

[0014] Cotton can generally be classified as cellulose based on its chemical structure. Depending on its molecular weight, cellulose can be used as a raw material for clothing or industrial applications, as rayon for clothing, or as a raw material for paper. Cotton typically has the highest molecular weight, followed by paper and pulp, and finally, as a raw material for rayon. Rayon has recently been required to have higher molecular weights to impart mechanical strength, and with the development of appropriate solvents, molecular weights exceeding cellulose for paper applications are now being utilized. Representative examples of high-molecular-weight rayon include Tencel, Lyocell, Modal, and Polynosic.

[0015] The best way to remove one material from a mixed feedstock of polyethylene terephthalate (PET) and cellulose may be to utilize the difference in solubility. However, neither polyethylene terephthalate (PET) nor cellulose can achieve a level of solubility that allows separation without using extremely polar solvents. Furthermore, the available solvents are either ultra-expensive ionic liquids, or extremely polar substances such as dimethyl sulfoxide (DMSO) and chloroform, which can cause health problems for users or pose serious economical issues. Therefore, separation using existing commercial solvents (so-called selective dissolution or selective solvation) is still difficult to apply due to economic issues.

[0016] Therefore, a progressive approach is needed to recycle synthetic fiber and cotton blended fabrics, which have been used in diverse fields such as clothing and industrial materials, beyond existing methods. This approach offers economic feasibility, process convenience, and user safety. Furthermore, technologies for depolymerizing cotton-polyethylene terephthalate (PET) blended fibers and post-recycling utilization are also needed.

[0017]

[0018] Accordingly, the present invention aims to provide a regenerated terephthalic acid and a method for producing the same, which obtains regenerated dialkyl phthalate from a blended fiber and hydrolyzes it while optimizing process conditions to have high purity and yield and improved color.

[0019]

[0020] An embodiment of the present invention provides a method for producing regenerated terephthalic acid, comprising the steps of: depolymerizing a blended fiber including cotton and synthetic fibers with a depolymerization solvent to produce a depolymerized product; filtering the depolymerized product to separate a filtrate; obtaining a regenerated dialkyl phthalate from the filtrate; and hydrolyzing the regenerated dialkyl phthalate.

[0021] In addition, an embodiment of the present invention provides a recycled terephthalic acid manufactured according to the above manufacturing method, having a purity of 98.5% or more, a yellowness of 10 or less, and a color b of 2 or less.

[0022]

[0023] The regenerated terephthalic acid manufactured according to the manufacturing method of the present invention has excellent properties such as high purity and yield and color by performing optimal process conditions for blended fibers including cotton and synthetic fibers.

[0024]

[0025] If it is determined that a detailed description of a related public configuration or function in this specification may obscure the gist of the present invention, the detailed description is omitted.

[0026] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0027] All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification should be understood to be modified by the term “about” in all cases unless otherwise specified.

[0028] In the following description, the description that one component is formed above / below another component or is connected or joined to each other includes all of the components being formed, connected or joined directly or indirectly through another component.

[0029] In this specification, when a numerical range with a limited upper limit and a numerical range with a limited lower limit are described to illustrate the size, physical properties, etc. of a component, it should be understood that a numerical range in which these upper and lower limits are combined is also included in the exemplary range of the present invention.

[0030] In this specification, singular expressions should be interpreted to include the singular or plural as interpreted in the context, unless otherwise stated.

[0031] The present invention is not limited to the contents disclosed below, and may be modified in various forms as long as the gist of the invention is not changed.

[0032]

[0033] Method for producing recycled terephthalic acid

[0034] The method for producing regenerated terephthalic acid according to the present invention comprises the steps of: depolymerizing a blended fiber including cotton and synthetic fibers with a depolymerization solvent to produce a depolymerized product; filtering the depolymerized product to separate a filtrate; obtaining a regenerated dialkyl phthalate from the filtrate; and hydrolyzing the regenerated dialkyl phthalate.

[0035]

[0036] A step of producing a depolymerized product by depolymerizing a blended fiber containing cotton and synthetic fibers with a depolymerization solvent.

[0037] A method for producing regenerated terephthalic acid according to an embodiment of the present invention comprises the step of producing a depolymerized product by depolymerizing a blended fiber including cotton and synthetic fibers with a depolymerization solvent.

[0038] The above-mentioned blended fiber (waste blended fiber) includes cotton. The cotton refers to a fiber extracted from a plant (cotton) of the genus Botrytis and the family Malvaceae. The cotton contains 90 to 95 wt% of cellulose, and the cellulose is derived from the cell wall of cotton. In addition to the cellulose, the cotton may include other components such as wax, protein, pectin, and fat. In the present invention, the cotton may include cotton of various colors such as black, navy, brown, red, and gray.

[0039] The above-mentioned blended fiber comprises a synthetic fiber, and the synthetic fiber may comprise polyethylene terephthalate (PET). In addition, the synthetic fiber may comprise, in addition to the polyethylene terephthalate, at least one selected from the group consisting of polyamide, polyurethane, polypropylene, polyethylene, and polyether. In summary, the synthetic fiber may comprise at least one selected from the group consisting of polyethylene terephthalate, polyamide, polyurethane, polypropylene, polyethylene, and polyether.

[0040] At this time, the blended fiber may contain 0.1 wt% or more, 1 wt% or more, 2 wt% or more, 3 wt% or more, 4 wt% or more, or 5 wt% or more of the cotton based on the total weight, and may contain 99.9 wt% or less, 99 wt% or less, 98 wt% or less, 97 wt% or less, 96 wt% or less, or 95 wt% or less. For example, the blended fiber may contain 0.1 wt% to 99.9 wt%, 5 wt% to 95 wt%, 20 wt% to 80 wt%, 20 wt% to 60 wt%, 40 wt% to 80 wt%, 20 wt% to 40 wt%, 40 wt% to 60 wt%, or 60 wt% to 80 wt% of the cotton based on the total weight.

[0041] At this time, the blended fiber may contain the synthetic fiber in an amount of 0.1 wt% or more, 1 wt% or more, 2 wt% or more, 3 wt% or more, 4 wt% or more, or 5 wt% or more, based on the total weight, and may contain 99.9 wt% or less, 99 wt% or less, 98 wt% or less, 97 wt% or less, 96 wt% or less, or 95 wt% or less. For example, the blended fiber may contain the synthetic fiber in an amount of 0.1 wt% to 99.9 wt%, 5 wt% to 95 wt%, 20 wt% to 80 wt%, 20 wt% to 60 wt%, 40 wt% to 80 wt%, 20 wt% to 40 wt%, 40 wt% to 60 wt%, or 60 wt% to 80 wt%, based on the total weight.

[0042] When a blended fiber having a cotton and synthetic fiber content controlled within a given range is depolymerized using a depolymerization solvent, the yield, purity, color, etc. of the regenerated terephthalic acid obtained from the blended fiber can be improved.

[0043] The above depolymerization solvent may be any solvent used in the depolymerization reaction of synthetic fibers, such as glycolysis, hydrolysis, methanolysis, and aminolysis. For example, the depolymerization solvent may include a monoalcohol having 1 to 14 carbon atoms or a polyhydric alcohol having 2 or more carbon atoms. For example, the depolymerization solvent may include a monoalcohol having 1 to 14 carbon atoms, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, 1-unadecanol, 1-dodecanol, 1-tridecanol, and 1-tetradecanol, and may include a polyhydric alcohol having 2 or more carbon atoms, such as ethylene glycol, propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, glycerol, erythritol, and sorbitol. More specifically, the depolymerization solvent may be at least one selected from the group consisting of methanol, n-butanol, and ethylene glycol. When the above depolymerization solvent is used, the yield, purity, color, etc. of the regenerated terephthalic acid obtained from the blended fiber can be improved.

[0044] The total amount of the depolymerization solvent added may be 1, 2, or 3 times the weight of the blended fiber, and may also be 7, 5, or 4 times or less. For example, the amount of the depolymerization solvent added may be 1 to 7 times the weight of the blended fiber, specifically 2 to 5 times, and more specifically 3 to 4 times. When the depolymerization solvent is added in the amount of the added weight, the yield, purity, color, etc. of the regenerated terephthalic acid obtained from the blended fiber may be improved.

[0045] Meanwhile, a depolymerization catalyst may be introduced in the step of preparing the depolymerization product. A catalyst may be used. The depolymerization catalyst may be a metal catalyst, for example, a metal salt catalyst or a metallic organic catalyst. Specifically, the depolymerization catalyst may be a metal acetate, carbonate, oxide, hydroxide, etc., and the metal may be an alkali metal, an alkaline earth metal, a transition metal, etc. As a specific example, the depolymerization catalyst includes a metal acetate, an anhydride or a hydrate thereof, and more specifically, it may be at least one selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, and manganese acetate, or a hydrate or anhydride thereof.

[0046] In addition, the input weight of the catalyst may be 0.01 part by weight or more, 0.1 part by weight or more, 0.2 part by weight or more, or 0.3 part by weight or more, and may also be 5 parts by weight or less, 1 part by weight or less, 0.7 part by weight or less, 0.6 part by weight or less, or 0.5 part by weight or less, relative to 100 parts by weight of the blended fiber. For example, the input weight of the catalyst may be 0.1 part by weight to 1 part by weight, and specifically, 0.2 part by weight to 0.7 part by weight. More specifically, the catalyst may be used in an amount of 0.2 part by weight to 0.5 part by weight relative to 100 parts by weight of the blended fiber. By using the catalyst under the above content conditions, the yield, purity, color, etc. of the regenerated terephthalic acid obtained from the blended fiber may be improved.

[0047] The above depolymerization can be carried out at a temperature of 180°C or higher, 185°C or higher, 190°C or higher, 195°C or higher, or 200°C or higher, and can be carried out at a temperature of 280°C or lower, 270°C or lower, 260°C or lower, 250°C or lower, 240°C or lower, 230°C or lower, or 220°C or lower. For example, the depolymerization can be carried out at a temperature of 180°C to 280°C or 200°C to 220°C. By carrying out the depolymerization under the corresponding temperature conditions, the yield, purity, color, etc. of the regenerated terephthalic acid obtained from the blended fiber can be improved.

[0048] Pretreatment process

[0049] Meanwhile, according to an embodiment of the present invention, prior to performing the step of manufacturing a depolymerized product, a step of pretreating the blended fiber comprising the cotton and synthetic fibers with a pretreatment agent may be further included. In this case, the pretreatment step may be a step of removing impurities including chromophores and polyurethane from the blended fiber.

[0050] The pretreatment agent used for pretreatment of the above-mentioned blended fiber may include at least one selected from the group consisting of an organic solvent, an oxidizing agent, and a reducing agent. Pretreatment may be performed by extracting pigments, dyes, etc. contained in the above-mentioned blended fiber with the organic solvent or decomposing and removing them with the oxidizing agent and / or reducing agent.

[0051] According to the present invention, the organic solvent may include at least one selected from the group consisting of cyclohexanone (CH), ethylene glycol (EG), 1-butanol (1-BD), dimethyl sulfoxide (DMSO), dimethylacetamide (DMAC), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), benzyl alcohol (BA), toluene, and xylene.

[0052] The organic solvent may have a boiling point of 100°C or higher. Specifically, the organic solvent may have a boiling point of 105°C or higher, 110°C or higher, 115°C or higher, 120°C or higher, 130°C or higher, 150°C or higher, 170°C or higher, 180°C or higher, or 200°C or higher (e.g., 100 to 220°C, 110 to 210°C, 130 to 205°C, 150 to 200°C, or 155 to 190°C).

[0053] According to the present invention, the oxidizing agent may include at least one selected from the group consisting of sodium hypochlorite, potassium hypochlorite, hydrogen peroxide, ozone, and potassium permanganate. Specifically, the oxidizing agent may be sodium hypochlorite.

[0054] Additionally, the reducing agent may include at least one selected from the group consisting of sodium hydrosulfite and thiourea dioxide. Specifically, the reducing agent may be sodium hydrosulfite.

[0055] By pretreating the blended fiber with the above pretreatment agent, the safety of the user can be ensured, damage to the fiber can be prevented, and pigments, dyes, etc. can be efficiently removed.

[0056] The proportion of the pretreatment agent to be added is not particularly limited, but considering process safety, economic feasibility, and foreign substance removal efficiency (decolorization efficiency), it may be added in an amount of 5 to 100 ml per 1 g of the blended fiber. Specifically, it may be 50 to 2,000 parts by weight, 100 to 1,800 parts by weight, 500 to 1,700 parts by weight, 700 to 1,500 parts by weight, 800 to 1,300 parts by weight, or 900 to 1,000 parts by weight, based on 100 parts by weight of the blended fiber.

[0057] According to the present invention, the pretreatment of the blended fiber can be performed at a temperature of 40 to 180°C. Specifically, the pretreatment can be performed at a temperature of 50 to 170°C, 60 to 160°C, 70 to 150°C, 75 to 140°C, or 80 to 135°C. By performing the pretreatment at the above temperature, foreign substances contained in the blended fiber (specifically, cellulose) can be efficiently removed while preventing damage to the blended fiber.

[0058]

[0059] A step of filtering the above-mentioned depolymerization product and separating the filtrate

[0060] A method for producing regenerated terephthalic acid according to an embodiment of the present invention includes a step of filtering a depolymerized product to separate a filtrate.

[0061] First, the depolymerization product is cooled to a certain temperature. The depolymerization product is cooled to 95°C or lower, 90°C or lower, or 85°C or lower.

[0062] Next, impurities are separated through a filter to obtain a filtrate. The filtration can be performed using various methods, such as gravity filtration, vacuum filtration, pressurized filtration, and membrane filtration.

[0063]

[0064] A step of obtaining a regenerated dialkyl phthalate from the above filtrate

[0065] A method for producing regenerated terephthalic acid according to an embodiment of the present invention includes a step of obtaining regenerated dialkyl phthalate from a filtrate.

[0066] The above filtrate may refer to a filtrate obtained by filtering out impurities in a step of filtering the depolymerized product and separating the filtrate.

[0067] In the step of obtaining the above-mentioned regenerated dialkyl phthalate, the filtrate is concentrated using a reduced pressure distiller to remove excess unreacted methanol, and then fractionally distilled to obtain the regenerated dialkyl phthalate.

[0068] The step of obtaining the above-mentioned regenerated dialkyl phthalate may include a process of distillation under reduced pressure using a vacuum distillation unit, wherein moisture or residual solvent in the filtrate can be removed and concentrated through the distillation under reduced pressure. Since unreacted solvents such as methanol, ethanol, and ethylene glycol may remain in the filtrate, it is necessary to remove these from the filtrate prior to the subsequent step.

[0069] The reduced pressure distillation for removing the unreacted solvent can be performed at a known appropriate temperature to improve the purity of the regenerated dialkyl phthalate. For example, the reduced pressure distillation for removing the unreacted solvent can be performed at 190°C or lower, 180°C or lower, or 170°C or lower, and can also be performed at 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher. Specifically, the temperature during the reduced pressure distillation for removing the unreacted solvent can be 60°C to 190°C or 80°C to 180°C. As a more specific example, the distillation for removing the unreacted solvent can be performed at a temperature of 90°C to 170°C. The pressure during the reduced pressure distillation for removing the unreacted solvent may be, for example, 0.1 Torr to 760 Torr, 0.1 Torr to 200 Torr, or 0.5 Torr to 30 Torr, and more specifically, the reduced pressure distillation may be performed under stepwise reduced pressure conditions from 760 torr to 0.8 torr.

[0070] Meanwhile, the step of obtaining the regenerated dialkyl phthalate may include a fractional distillation step. The regenerated dialkyl phthalate may be obtained by performing a reduced pressure distillation step and performing a fractional distillation step on the concentrated filtrate. Alternatively, the step of obtaining the regenerated dialkyl phthalate may include a step of adding water and an adsorbent to the concentrated filtrate and performing adsorption. For example, a carbon-based inorganic adsorbent may be used as the adsorbent, and specifically, activated carbon or the like may be used. The adsorption step may be performed under stirring at a temperature of 75°C to 95°C or 80°C to 90°C for 1 to 4 hours or 1 to 3 hours. After performing the adsorption step on the filtrate, the regenerated dialkyl phthalate may be obtained by performing a crystallization step.

[0071]

[0072] Step of hydrolyzing recycled dialkyl phthalate

[0073] A method for producing regenerated terephthalic acid according to an embodiment of the present invention includes a step of hydrolyzing regenerated dialkyl phthalate.

[0074] In the step of hydrolyzing the above-mentioned regenerated dialkyl phthalate, a solvent containing water is added to the regenerated dialkyl phthalate, and a hydrolysis reaction is performed at a certain temperature for a certain period of time to obtain regenerated terephthalic acid.

[0075] The weight ratio of the above-mentioned regenerated dialkyl phthalate and the hydrolysis solvent may be 1:1 to 500, 1:1 to 400, 1:1 to 300, 1:1 to 200, or 1:1 to 100. When the weight ratio of the above-mentioned regenerated dialkyl phthalate and the hydrolysis solvent is controlled within the corresponding range, the yield, purity, and color characteristics of the finally produced regenerated terephthalic acid may be improved.

[0076] Additionally, after the hydrolysis reaction, the reaction solution may be cooled to room temperature, filtered, and washed with a solvent, and then subjected to a drying process.

[0077] The hydrolysis may be carried out at a temperature of 15°C or higher, 20°C or higher, 30°C or higher, 40°C or higher, 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher, and may be carried out at a temperature of 280°C or lower, 270°C or lower, 260°C or lower, 250°C or lower, 240°C or lower, 230°C or lower, 220°C or lower, or 210°C or lower. For example, the hydrolysis may be carried out under temperature conditions of 15°C to 280°C. In addition, the hydrolysis may be carried out for 1 hour or longer, 2 hours or longer, or 3 hours or longer, and may be carried out for 10 hours or shorter, 9 hours or shorter, 8 hours or shorter, or 7 hours or shorter. For example, the hydrolysis may be carried out for 1 hour to 10 hours, or 3 hours to 7 hours. When the temperature and time conditions of the above hydrolysis are controlled within the relevant range, the yield, purity, and color characteristics of the final produced recycled terephthalic acid can be improved.

[0078] Meanwhile, the hydrolysis may include alkaline hydrolysis or neutral hydrolysis.

[0079] The above alkaline hydrolysis is a hydrolysis process that is carried out under alkaline conditions. Water and basic components such as sodium hydroxide, potassium hydroxide, and lithium hydroxide are added to the regenerated dialkyl phthalate, and hydrolysis is carried out by a hydrolysis reaction at a certain temperature for a certain period of time. At this time, the alkaline hydrolysis may be carried out at a temperature of 15°C or higher, 20°C or higher, 30°C or higher, 40°C or higher, 50°C or higher, 60°C or higher, 70°C or higher, 80°C or higher, or 90°C or higher, and may be carried out at a temperature of 150°C or lower, 140°C or lower, 130°C or lower, 120°C or lower, or 110°C or lower. For example, the alkaline hydrolysis may be carried out at a temperature of 15°C to 150°C or 90°C to 110°C. In addition, the alkaline hydrolysis may be carried out for 1 hour or more, 2 hours or more, or 3 hours or more, or 8 hours or less, 7 hours or less, 6 hours or less, or 5 hours or less. For example, the alkaline hydrolysis may be carried out for 1 to 8 hours or 3 to 5 hours. When the temperature and time conditions of the alkaline hydrolysis are controlled within the corresponding ranges, the yield, purity, and color characteristics of the finally produced regenerated terephthalic acid may be improved. Meanwhile, when the hydrolysis is carried out through alkaline hydrolysis, it is preferable to cool the reaction solution to room temperature, neutralize it with an acidic component such as hydrochloric acid, and then filter it and wash it repeatedly with a solvent such as water.

[0080] The above neutral hydrolysis is a hydrolysis carried out under neutral conditions, in which water is added to the regenerated dialkyl phthalate and hydrolysis is carried out by a hydrolysis reaction at a certain temperature for a certain period of time. At this time, the neutral hydrolysis may be carried out at a temperature of 150°C or higher, 160°C or higher, 170°C or higher, 180°C or higher, or 190°C or higher, and may be carried out at a temperature of 280°C or lower, 270°C or lower, 260°C or lower, 250°C or lower, 240°C or lower, 230°C or lower, 220°C or lower, or 210°C or lower. For example, the neutral hydrolysis may be carried out under temperature conditions of 150°C to 280°C or 190°C to 210°C. In addition, the neutral hydrolysis may be carried out for 3 hours or more, 4 hours or more, or 5 hours or more, or 10 hours or less, 9 hours or less, 8 hours or less, or 7 hours or less. For example, the neutral hydrolysis may be carried out for 3 to 10 hours or 5 to 7 hours. When the temperature and time conditions of the neutral hydrolysis are controlled within the corresponding ranges, the yield, purity, and color characteristics of the finally produced regenerated terephthalic acid may be improved. Meanwhile, when the hydrolysis is carried out as neutral hydrolysis, it is preferable to cool the reaction solution to room temperature, filter it, and wash it with a solvent such as butanol.

[0081] After filtering and washing, it may be dried for 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, or 5 hours or more at a temperature condition of 70℃ or higher, 80℃ or higher, or 90℃ or higher, or 130℃ or lower, 120℃ or lower, or 110℃ or lower, or for 10 hours or less, 9 hours or less, 8 hours or less, or 7 hours or less. For example, after filtering and washing, it may be dried for 1 hour to 10 hours, or 5 hours to 7 hours at a temperature of 70℃ to 130℃ or 90℃ to 110℃.

[0082]

[0083] Recycled terephthalic acid

[0084] According to an embodiment of the present invention, a regenerated terephthalic acid manufactured according to the above manufacturing method is provided.

[0085] The above recycled terephthalic acid may have a purity of 98.5% or more, 98.6% or more, 98.7% or more, 98.8% or more, 98.9% or more, 99.0% or more, 99.1% or more, 99.2% or more, 99.3% or more, 99.4% or more, or 99.5% or more, and may be less than or equal to 100%. For example, the above recycled terephthalic acid may have a purity of 98.5% to 100% or 99.5% to 100%.

[0086] The above-mentioned recycled terephthalic acid may have a yellowness of 10 or less, 9 or less, 8 or less, 7 or less, or 6 or less, or may be 0 or more. The above-mentioned recycled terephthalic acid may have a yellowness of 0 to 10 or 0 to 6.

[0087] The above-mentioned recycled terephthalic acid may have a color b of 2 or less, a color b of 1.9 or less, a color b of 1.8 or less, or a color b of 1.7 or less, and may be 0 or greater. For example, the above-mentioned recycled terephthalic acid may have a color b of 0 to 2 or 0 to 1.7.

[0088] The above-mentioned recycled terephthalic acid is advantageous for application to various products as its purity, yellowness, and Color b value satisfy the above ranges.

[0089]

[0090] The above contents are explained in more detail with the following examples. However, the following examples are only intended to illustrate the present invention, and the scope of the examples is not limited to these examples.

[0091]

[0092] Example

[0093] Example 1

[0094] <Example 1-1>

[0095] In a 1 L high-pressure reactor, 100 g of a black cotton 5 wt% / PET 95 wt% blended fiber, 400 ml of methanol, and 100 mg of Zn(OAc)2·2H2O were charged and reacted at 200 ° C. for 4 hours. The reaction solution was cooled to 50 ° C. and filtered to obtain brown regenerated cellulose (r-cellulose). The regenerated cellulose (r-cellulose) was washed three times with 100 ml of methanol and dried at 100 ° C. for 6 hours. Meanwhile, the filtrate was concentrated in a reduced pressure distillation unit to remove excess unreacted methanol, and then fractionally distilled to obtain regenerated dimethyl terephthalate (r-DMT).

[0096]

[0097] <Example 1-2>

[0098] Regenerated cellulose (r-cellulose) and regenerated dimethyl terephthalate (r-DMT) were obtained through the same process as Example 1-1, except that a blended fiber of 30 wt% black cotton / 70 wt% PET (cut to about 1×1 cm) was used.

[0099]

[0100] <Example 1-3>

[0101] Regenerated cellulose (r-cellulose) and regenerated dimethyl terephthalate (r-DMT) were obtained through the same process as Example 1-1, except that a blended fiber of 50 wt% black cotton / 50 wt% PET (cut to about 1×1 cm) was used.

[0102]

[0103] <Example 1-4>

[0104] Regenerated cellulose (r-cellulose) and regenerated dimethyl terephthalate (r-DMT) were obtained through the same process as Example 1-1, except that a blended fiber of 70 wt% black cotton / 30 wt% PET (cut to about 1×1 cm) was used.

[0105]

[0106] <Example 1-5>

[0107] Regenerated cellulose (r-cellulose) and regenerated dimethyl terephthalate (r-DMT) were obtained through the same process as Example 1-1, except that a blended fiber of 95 wt% black cotton / 5 wt% PET (cut to about 1×1 cm) was used.

[0108]

[0109] <Example 1-6>

[0110] In a 1 L high-pressure reactor, 100 g of a black cotton 5 wt% / PET 95 wt% blended fiber, 400 ml of n-butanol, and 100 mg of Zn(OAc)2·2H2O were charged and reacted at 220 ° C. for 4 hours. The reaction solution was cooled to room temperature and filtered to obtain brown regenerated cellulose (r-cellulose). The regenerated cellulose (r-cellulose) was washed three times with 100 ml of n-butanol and dried at 100 ° C. for 6 hours. Meanwhile, the filtrate was concentrated in a reduced pressure distillation unit to remove excess unreacted butanol, and then fractionally distilled to obtain regenerated dibutyl terephthalate (r-DBTP).

[0111]

[0112] <Example 1-7>

[0113] Regenerated cellulose (r-cellulose) and regenerated dibutyl terephthalate (r-DBTP) were obtained through the same process as in Example 1-6, except that a blended fiber of 30 wt% black cotton / 70 wt% PET (cut to about 1×1 cm) was used.

[0114]

[0115] <Example 1-8>

[0116] Regenerated cellulose (r-cellulose) and regenerated dibutyl terephthalate (r-DBTP) were obtained through the same process as in Example 1-6, except that a blended fiber of 50 wt% black cotton / 50 wt% PET (cut to about 1×1 cm) was used.

[0117]

[0118] <Example 1-9>

[0119] Regenerated cellulose (r-cellulose) and regenerated dibutyl terephthalate (r-DBTP) were obtained through the same process as Example 1-6, except that a blended fiber of 70 wt% black cotton / 30 wt% PET (cut to about 1×1 cm) was used.

[0120]

[0121] <Example 1-10>

[0122] Regenerated cellulose (r-cellulose) and regenerated dibutyl terephthalate (r-DBTP) were obtained through the same process as in Example 1-6, except that a blended fiber of 95 wt% black cotton and 5 wt% PET (cut to about 1×1 cm) was used.

[0123]

[0124] <Example 1-11>

[0125] In a 1 L high-pressure reactor, 100 g of a black cotton 5 wt% / PET 95 wt% blended fiber, 400 ml of ethylene glycol, and 100 mg of Zn(OAc)2·2H2O were added and reacted at 200 ° C. for 4 hours. The reaction solution was cooled to 80 ° C. and filtered to obtain brown regenerated cellulose (r-cellulose). The regenerated cellulose (r-cellulose) was washed three times with water and 100 ml of acetone, and then dried at 100 ° C. for 6 hours. Meanwhile, the filtrate was concentrated in a reduced pressure distillation unit to remove excess unreacted ethylene glycol, and then 200 ml of water was added. Activated carbon was added, stirred at 85 ° C. for 2 hours, filtered, and recrystallized to obtain regenerated bis(2-hydroxyethyl) terephthalate (r-BHET).

[0126]

[0127] <Example 1-12>

[0128] Regenerated cellulose (r-cellulose) and regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) were obtained through the same process as Example 1-11, except that a blended fiber of 30 wt% black cotton / 70 wt% PET (cut to about 1×1 cm) was used.

[0129]

[0130] <Example 1-13>

[0131] Regenerated cellulose (r-cellulose) and regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) were obtained through the same process as Example 1-11, except that a blended fiber of 50 wt% black cotton / 50 wt% PET (cut to about 1×1 cm) was used.

[0132]

[0133] <Example 1-14>

[0134] Regenerated cellulose (r-cellulose) and regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) were obtained through the same process as Example 1-11, except that a blended fiber of 70 wt% black cotton / 30 wt% PET (cut to about 1×1 cm) was used.

[0135]

[0136] <Example 1-15>

[0137] Regenerated cellulose (r-cellulose) and regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) were obtained through the same process as Example 1-11, except that a blended fiber of 95 wt% black cotton and 5 wt% PET (cut to about 1×1 cm) was used.

[0138]

[0139] <Examples 1-16 to 1-30>

[0140] Regenerated cellulose (r-cellulose) and dialkyl phthalate were obtained through the same process as in Examples 1-1 to 1-15, except that a navy colored blended fiber instead of a black blended fiber was used.

[0141]

[0142] Example 2

[0143] <Example 2-1>

[0144] 4.0 g of regenerated cellulose (r-cellulose) of Example 1-1 was added to 200 ml of a 20% NaOH aqueous solution and stirred at room temperature for 1 hour. After filtration, the obtained cotton was washed with a filter and water and then vacuum-dried to obtain mercerized regenerated cellulose.

[0145] 0.5 g of the above mercerized regenerated cellulose was mixed with 25 mL of acetic acid, 3.0 g of acetic anhydride, and 50 mg of sulfuric acid, and stirred at 40°C for 12 hours. The reaction product was added dropwise to water to obtain a precipitate, which was filtered and washed with water and vacuum-dried to obtain acetylated regenerated cellulose.

[0146]

[0147] <Examples 2-2 to 2-30>

[0148] Acetylated regenerated cellulose was obtained by performing the same procedure as in Example 2-1, except that the regenerated cellulose (r-cellulose) of Examples 1-2 to 1-30 was used instead of the regenerated cellulose (r-cellulose) of Example 1-1.

[0149]

[0150] <Example 1>

[0151] 1) Recovery rate of regenerated cellulose

[0152] The recovery rate of regenerated cellulose of Examples 2-1 to 2-30 was calculated using the following formula using the weight (g) of the cotton introduced into the reaction and the weight (g) of the recovered regenerated cellulose (r-Cellulose).

[0153] [Formula 1]

[0154]

[0155]

[0156] 2) Degree of polymerization (DP) of regenerated cellulose

[0157] The degree of polymerization of the regenerated cellulose of Examples 2-1 to 2-30 was calculated by measuring the viscosity in CED (Cupriethylene diamine) according to TAPPI T230.

[0158]

[0159] 3) PET depolymerization component content in regenerated cellulose (ppm)

[0160] The regenerated cellulose of Examples 2-1 to 2-30 was freeze-pulverized, cut, and diluted in methanol to 1 wt / v%. The filtrate was syringe filtered, and the remaining PET depolymerization component in the surface was quantified after HPLC measurement.

[0161]

[0162] 4) Molecular weight of regenerated cellulose

[0163] The molecular weight of the regenerated cellulose obtained in Examples 2-1 to 2-30 was measured through gel permeation chromatography (GPC, Chloroform / o-CP eluent) using chloroform (CHCl3) as the main solvent and orthochlorophenol (o-CP) added.

[0164]

[0165] 4) Dialkyl phthalate yield

[0166] The yield of the regenerated dialkyl phthalate obtained in Examples 1-1 to 1-30 was calculated using the following formula using the amount (mol) of polyethylene terephthalate (PET) introduced into the reaction and the amount (mol) of the dialkyl phthalate obtained after depolymerization.

[0167] [Formula 2]

[0168]

[0169]

[0170] 5) Dialkyl phthalate purity

[0171] The regenerated dialkyl phthalate obtained in Examples 1-1 to 1-30 was diluted to 1 wt / v% in methanol and then the purity was measured using high-performance liquid chromatography (HPLC).

[0172]

[0173] 6) Yellowness Index (YID)

[0174] The regenerated dialkyl phthalate obtained in Examples 1-1 to 1-30 was diluted to 10 wt% in a solvent and the yellowness index (YID) was measured using a colorimeter.

[0175]

[0176] Alcohol (product) Raw material Fiber color L / a / b Example Regenerated cellulose Example Regenerated dialkyl phthalate Recovery rate (%) DPPET derived depolymerization component Molecular weight Mw (g / mol) Yield (%) Purity (%) Color YID Methanol (DMT) Black 33.0 / 2.20 / -0.152-194620 N.D. 6.1Ⅹ10 4 1-19599.23.72-295660N.D.6.3Ⅹ10 4 1-29298.94.52-395750N.D.6.7Ⅹ10 4 1-39598.74.52-497640N.D.6.1Ⅹ10 4 1-49499.14.82-594590N.D.5.9Ⅹ10 4 1-59698.93.5 Butanol (DBTP)2-695550 N.D.5.7Ⅹ10 4 1-69599.23.82-794580N.D.5.4Ⅹ10 4 1-79298.93.62-896500N.D.5.2Ⅹ10 4 1-89598.72.72-997550N.D.5.5Ⅹ10 4 1-99499.13.62-1095590N.D.5.7Ⅹ10 4 1-109698.93.5 Ethylene glycol (BHET) 2-1195710 N.D. 6.3Ⅹ10 4 1-119299.43.32-1294620N.D.6.1Ⅹ10 4 1-129199.35.82-1396650N.D.6.0Ⅹ10 4 1-139299.14.72-1496580N.D.5.8Ⅹ10 4 1-149299.43.62-1595630N.D.6.1Ⅹ10 4 1-159099.04.5 Methanol (DMT) Navy 33.2 / 0.31 / -5.002-1696640 N.D. 6.1Ⅹ10 4 1-169599.13.22-1797690N.D.5.4Ⅹ10 4 1-179297.94.12-1897720N.D.6.3Ⅹ10 41-189499.23.62-1995600N.D.5.7Ⅹ10 4 1-199498.93.52-2096620N.D.6.1Ⅹ10 4 1-209599.24.0 Butanol (DBTP) 2-2196570 N.D. 5.8Ⅹ10 4 1-219598.73.62-2295580N.D.5.8Ⅹ10 4 1-229799.53.22-2394540N.D.5.4Ⅹ10 4 1-239499.22.82-2497550N.D.5.5Ⅹ10 4 1-249599.33.52-2596570N.D.5.8Ⅹ10 4 1-259599.02.9 Ethylene glycol (BHET) 2-2695690 N.D.6.2Ⅹ10 4 1-269299.33.22-2795650N.D.6.0Ⅹ10 4 1-279099.23.62-2897660N.D.6.3Ⅹ10 4 1-289299.04.72-2995570N.D.5.8Ⅹ10 4 1-299299.24.52-3096650N.D.6.0Ⅹ10 4 1-309199.43.9

[0177] Referring to Table 1 above, the recovery rate of regenerated cellulose (r-Cellulose) of Examples 2-1 to 2-30 is 64% to 97%, the degree of polymerization (DP) is 500 to 750, and the molecular weight is 5.2×10 4 g / mol to 6.7×10 4 It was confirmed that the yield of the regenerated dialkyl phthalate of Examples 1-1 to 1-30 was 90% to 97%, the purity was 97.9% to 99.6%, and the yellowness was 2.7 to 5.8.

[0178]

[0179] Example 3

[0180] <Example 3-1> (Neutral)

[0181] In a 1 L high-pressure reactor, 100 g (0.51 mol) of the regenerated dimethyl terephthalate (r-DMT) obtained in Example 1-2 and 400 ml (22.20 mol) of water were added and reacted at 200 ° C. for 6 hours. The reaction solution was cooled to room temperature, filtered, washed with methanol, and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0182]

[0183] <Example 3-2> (Neutral)

[0184] In a 1 L high-pressure reactor, 100 g (0.36 mol) of the regenerated dibutyl terephthalate (r-DBTP) obtained in Example 1-7 and 400 ml (22.20 mol) of water were charged and reacted at 220 ° C. for 6 hours. The reaction solution was cooled to room temperature, filtered, washed with butanol, and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0185]

[0186] <Example 3-3> (Neutral)

[0187] In a 1 L high-pressure reactor, 100 g (0.39 mol) of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) obtained in Example 1-12 and 400 ml (22.20 mol) of water were added and reacted at 200 ° C. for 6 hours. The reaction solution was cooled to room temperature, filtered, washed with butanol, and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0188]

[0189] <Example 3-4> (Alkaline)

[0190] In a 1 L flask, 100 g (0.51 mol) of the regenerated dimethyl terephthalate (r-DMT) obtained in Example 1-2, 51 g (1.28 mol) of NaOH, and 400 ml of water were added and reacted at 100 ° C. for 4 hours. The reaction solution was cooled to room temperature and neutralized with hydrochloric acid. After filtering, it was washed three times with water and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0191]

[0192] <Example 3-5> (Alkaline)

[0193] In a 1 L high-pressure reactor, 100 g (0.36 mol) of the regenerated dibutyl terephthalate (r-DBTP) obtained in Example 1-7, 36 g (0.90 mol) of NaOH, and 400 ml of water were added and reacted at 100 ° C. for 8 hours. The reaction solution was cooled to room temperature and neutralized with hydrochloric acid. After filtering, the solution was washed three times with water and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0194]

[0195] <Example 3-6> (Alkaline)

[0196] In a 1 L high-pressure reactor, 100 g (0.39 mol) of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) obtained in Example 1-12, 39 g (0.98 mol) of NaOH, and 400 ml of water were charged and reacted at 100 ° C. for 4 hours. The reaction solution was cooled to room temperature and neutralized with hydrochloric acid. After filtering, it was washed three times with water and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0197]

[0198] <Example 3-7> (Neutral)

[0199] In a 1 L high-pressure reactor, 100 g (0.51 mol) of the regenerated dimethyl terephthalate (r-DMT) obtained in Example 1-5 and 400 ml (22.20 mol) of water were charged and reacted at 200 ° C. for 6 hours. The reaction solution was cooled to room temperature, filtered, washed with methanol, and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0200]

[0201] <Example 3-8> (Neutral)

[0202] In a 1 L high-pressure reactor, 100 g (0.36 mol) of the regenerated dibutyl terephthalate (r-DBTP) obtained in Example 1-10 and 400 ml (22.20 mol) of water were charged and reacted at 220 ° C. for 6 hours. The reaction solution was cooled to room temperature, filtered, washed with butanol, and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0203]

[0204] <Example 3-9> (Neutral)

[0205] In a 1 L high-pressure reactor, 100 g (0.39 mol) of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) obtained in Example 1-15 and 400 ml (22.20 mol) of water were charged and reacted at 200 ° C. for 6 hours. The reaction solution was cooled to room temperature, filtered, washed with butanol, and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0206]

[0207] <Example 3-10> (Alkaline)

[0208] In a 1 L flask, 100 g (0.51 mol) of the regenerated dimethyl terephthalate (r-DMT) obtained in Example 1-5, 51 g (1.28 mol) of NaOH, and 400 ml of water were added and reacted at 100 ° C. for 4 hours. The reaction solution was cooled to room temperature and neutralized with hydrochloric acid. After filtering, the solution was washed three times with water and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0209]

[0210] <Example 3-11> (Alkaline)

[0211] In a 1 L high-pressure reactor, 100 g (0.36 mol) of the regenerated dibutyl terephthalate (r-DBTP) obtained in Example 1-10, 36 g (0.90 mol) of NaOH, and 400 ml of water were charged and reacted at 100 ° C. for 8 hours. The reaction solution was cooled to room temperature and neutralized with hydrochloric acid. After filtering, the solution was washed three times with water and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0212]

[0213] <Example 3-12> (Alkaline)

[0214] In a 1 L high-pressure reactor, 100 g (0.39 mol) of the regenerated bis(2-hydroxyethyl) terephthalate (r-BHET) obtained in Example 1-15, 39 g (0.98 mol) of NaOH, and 400 ml of water were added and reacted at 100 ° C. for 4 hours. The reaction solution was cooled to room temperature and neutralized with hydrochloric acid. After filtering, the solution was washed three times with water and dried at 100 ° C. for 6 hours to produce regenerated terephthalic acid (r-TPA). The yield and quality of the obtained regenerated terephthalic acid (r-TPA) are shown in Table 2.

[0215]

[0216] <Example 2>

[0217] 1) TPA purity

[0218] The purity (%) of the regenerated terephthalic acid (r-TPA) obtained in Examples 3-1 to 3-12 above is confirmed by diluting it in a solvent and measuring it by HPLC.

[0219]

[0220] 2) Color b measurement

[0221] The Color b value of powder TPA of the regenerated terephthalic acid (r-TPA) obtained in Examples 3-1 to 3-12 was measured using a colorimeter.

[0222]

[0223] Example Yield (%) Purity (%) Color b3-19599.21.73-29099.51.33-39899.41.23-49799.81.43-59899.81.23-69799.51.13-79499.71.43-89599.41.73-99599.31.33-109799.51.63-119899.81.33-129699.41.5

[0224] Referring to Table 3 above, Example 3-1 obtained recycled terephthalic acid with a yield of 95%, purity of 99.2%, and Color-b value of 1.7, Example 3-2 obtained recycled terephthalic acid with a yield of 90%, purity of 99.5%, and Color-b value of 1.3, Example 3-3 obtained recycled terephthalic acid with a yield of 98%, purity of 99.4%, and Color-b value of 1.2, Example 3-4 obtained recycled terephthalic acid with a yield of 97%, purity of 99.8%, and Color-b value of 1.4, Example 3-5 obtained recycled terephthalic acid with a yield of 98%, purity of 99.8%, and Color-b value of 1.2, and Example 3-6 obtained recycled terephthalic acid with a yield of 97%. Terephthalic acid was obtained, the purity was 99.5%, the Color-b value was 1.1, Example 3-7 obtained regenerated terephthalic acid with a yield of 94%, the purity was 99.7%, the Color-b value was 1.4, Example 3-8 obtained regenerated terephthalic acid with a yield of 95%, the purity was 99.4%, the Color-b value was 1.7, Example 3-9 obtained regenerated terephthalic acid with a yield of 95%, the purity was 99.3%, the Color-b value was 1.3, Example 3-10 obtained regenerated terephthalic acid with a yield of 97%, the purity was 99.5%, the Color-b value was 1.6, Example 3-11 obtained regenerated terephthalic acid with a yield of 98%, the purity was 99.8%, the Color-b value was 1.3, and Example 3-12 obtained recycled terephthalic acid with a yield of 96%, purity of 99.5%, and Color-b value of 1.5.

Claims

1. A step of producing a depolymerized product by depolymerizing a blended fiber including cotton and synthetic fibers with a depolymerization solvent; A step of filtering the above-mentioned depolymerization product and separating the filtrate; A step of obtaining a regenerated dialkyl phthalate from the above filtrate; and A method for producing regenerated terephthalic acid, comprising a step of hydrolyzing the above-mentioned regenerated dialkyl phthalate.

2. In paragraph 1, A method for producing recycled terephthalic acid, wherein the purity of the above-mentioned recycled terephthalic acid is 98.5% or more, the yellowness is 10 or less, and the color b is 2 or less.

3. In paragraph 1, A method for producing recycled terephthalic acid, wherein the synthetic oil comprises at least one selected from the group consisting of polyethylene terephthalate, polyamide, polyurethane, polypropylene, polyethylene, and polyether.

4. In paragraph 1, A method for producing regenerated terephthalic acid, wherein the above blended fiber contains 0.1 to 99.9 wt% of cotton based on the total weight.

5. In paragraph 1, A method for producing regenerated terephthalic acid, wherein the depolymerization solvent comprises a monoalcohol having 1 to 14 carbon atoms or a polyhydric alcohol having 2 or more carbon atoms, and the depolymerization is performed at a temperature of 180°C to 280°C.

6. In paragraph 1, A process for pretreating the blended fiber with a pretreatment agent prior to the above depolymerization is included. A method for producing regenerated terephthalic acid, wherein the above pretreatment process is a process for removing impurities including chromophores or polyurethane from the blended fiber.

7. In paragraph 6, A method for producing regenerated terephthalic acid, wherein the pretreatment agent comprises at least one selected from the group consisting of an organic solvent, an oxidizing agent, and a reducing agent.

8. In paragraph 7, A method for producing regenerated terephthalic acid, wherein the organic solvent comprises at least one selected from the group consisting of cyclohexanone, ethylene glycol, 1-butanol, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone, benzyl alcohol, toluene, and xylene.

9. In paragraph 7, A method for producing regenerated terephthalic acid, wherein the organic solvent has a boiling point of 100°C or higher.

10. In paragraph 7, A method for producing regenerated terephthalic acid, wherein the oxidizing agent comprises at least one selected from the group consisting of sodium hypochlorite, potassium hypochlorite, hydrogen peroxide, ozone, and potassium permanganate.

11. In paragraph 7, A method for producing regenerated terephthalic acid, wherein the reducing agent comprises at least one selected from the group consisting of sodium hydrosulfite and thiourea dioxide.

12. In paragraph 1, A method for producing regenerated terephthalic acid, wherein the hydrolysis comprises alkaline hydrolysis or neutral hydrolysis.

13. In paragraph 12, A method for producing regenerated terephthalic acid, wherein the alkaline hydrolysis is performed at 15°C to 150°C.

14. In paragraph 12, A method for producing regenerated terephthalic acid, wherein the above neutral hydrolysis is performed at 150°C to 280°C.

15. In paragraph 1, A method for producing recycled terephthalic acid, wherein the weight ratio of the above-mentioned recycled dialkyl phthalate and the hydrolysis solvent is 1:1 to 500.

16. Regenerated terephthalic acid manufactured according to the manufacturing method of paragraph 1, having a purity of 98.5% or more, a yellowness of 10 or less, and a color b of 2 or less.

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