Method for preparing recycled materials using waste copolyesters and recycled material compositions

Abstract

The present invention relates to a method for preparing recycled feedstock using waste copolyester, the method for preparing recycled feedstock includes the steps of: (1) depolymerizing waste copolyester to obtain a first reactant; (2) removing impurities present in the first reactant to obtain a second reactant; (3) distilling the second reactant to obtain a third reactant containing crude recycled bis-2-hydroxyethyl terephthalate and a fourth reactant containing recycled diol-ester; and (4) mixing the third reactant with an aqueous solvent and recrystallizing it to obtain a fifth reactant containing recycled bis-2-hydroxyethyl terephthalate and a filtrate.

Description

[Technical Field]

[0001] The present invention relates to a method for preparing various types of recycled materials with high efficiency using waste copolyesters, and to recycled material compositions obtained from waste copolyesters. [Background technology]

[0002] Among the commonly used polymers in modern life, polyesters are widely used as materials for beverage and food containers, various packaging films, interior and exterior materials such as panels, shelves and partitions, etc., thanks to their excellent mechanical strength, heat resistance, transparency and gas barrier properties.

[0003] As a result, unmanageable levels of plastic waste, including polyester, are generated worldwide each year. In recent years, countries around the world have developed regulations and programs to recycle waste plastic resources, including waste polyester.

[0004] Physical and chemical recycling methods are used to recycle waste polyester, but physical recycling is not widely used because it cannot guarantee purity. Chemical recycling, on the other hand, involves depolymerizing the waste polyester by cleaving its ester bonds. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among these, glycolysis involves decomposing waste polyester by adding glycols such as ethylene glycol or diethylene glycol at high temperatures. The resulting reaction product is primarily bis-2-hydroxyethyl terephthalate (BHET).

[0005] However, there is a large amount of waste polyester that is actually discarded in the form of copolymer and homopolymer, and when the waste polyester in the form of copolymer is depolymerized by the above-mentioned chemical recycling method, there is a limitation in recycling various kinds of raw materials (e.g., comonomers or oligomers, etc.). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Application Publication No. 2022-0138819 Summary of the Invention [Problem to be solved by the invention]

[0007] The reaction results (products) obtained by depolymerization of waste copolyesters include bis-2-hydroxyethyl terephthalate (BHET), as well as diethylene glycol, oligomers such as diethylene glycol esters, and comonomers used in the preparation of copolyesters.

[0008] Diethylene glycol and diethylene glycol esters are side reactants that are considered impurities. Their presence reduces the purity and color of bis-2-hydroxyethyl terephthalate (BHET), and therefore reduces the physical properties of recycled polyester when it is prepared using bis-2-hydroxyethyl terephthalate (BHET).

[0009] On the other hand, comonomers can be used as recycled raw materials together with bis-2-hydroxyethyl terephthalate (BHET), so it is necessary to recycle them efficiently.

[0010] Therefore, the present inventors have conducted various studies with the aim of developing a technology that can increase the comonomer recycling rate while minimizing the generation (residue) of side reaction substances such as diethylene glycol and diethylene glycol esters when waste copolyesters are depolymerized. As a result, they have discovered that the above-mentioned objective can be achieved by analyzing the substances generated during the depolymerization process, identifying the physical and chemical behavior of each substance, and separating each substance accordingly.

[0011] Therefore, an object of the present invention is to provide a method for preparing recycled materials that can efficiently produce various types of recycled materials by using waste copolyesters, while increasing the recycling rate of comonomers and minimizing the production of side reaction products.

[0012] Furthermore, another object of the present invention is to provide a recycled raw material composition obtained from waste copolyester. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention provides a method for preparing a recycled raw material, comprising the steps of: (1) depolymerizing a waste copolyester to obtain a first reactant; (2) removing impurities present in the first reactant to obtain a second reactant; (3) distilling the second reactant to obtain a third reactant containing crude recycled bis-2-hydroxyethyl terephthalate and a fourth reactant containing recycled diol-ester; and (4) mixing the third reactant with an aqueous solvent and recrystallizing it to obtain a fifth reactant containing recycled bis-2-hydroxyethyl terephthalate and a filtrate.

[0014] Furthermore, the present invention provides a recycled raw material composition obtained by depolymerizing a waste copolyester, which, when analyzed by high performance liquid chromatography (HPLC), has a peak area fraction of bis-2-hydroxyethyl terephthalate of 70% or less and a peak area fraction of diol ester of 10% or more.

[0015] Furthermore, the present invention provides a recycled raw material composition obtained by depolymerizing a waste copolyester, which, when analyzed by high performance liquid chromatography (HPLC), has a peak area fraction of bis-2-hydroxyethyl terephthalate of 95% or more and a peak area fraction of diol ester of less than 1.5%. [Effects of the Invention]

[0016] According to the present invention, waste copolyester is depolymerized and subjected to thin-film evaporation and recrystallization processes to prepare recycled raw materials, so that various types of recycled raw materials can be efficiently prepared together with recycled bis-2-hydroxyethyl terephthalate while minimizing the production (residual) of diethylene glycol and diethylene glycol esters, which are considered as impurities.

[0017] Therefore, the present invention can solve the conventional problem of difficulty in recycling waste copolyesters, and as a result, it is possible to give high value to waste copolyesters as recyclable resources.

[0018] Furthermore, since the present invention can produce various types of recycled raw materials (e.g., recycled bis-2-hydroxyethyl terephthalate, recycled cyclohexanedimethanol, recycled isosorbide, etc.) with high purity, it is possible to use the recycled raw materials to provide excellent quality recycled polyester (recycled copolyester) and products prepared using the same. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a flow chart illustrating a method for preparing recycled feedstock according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be described in detail below. The present invention is not limited to the disclosure shown below in this specification, and may be modified in various forms as long as the gist of the present invention is not changed.

[0021] As used herein, the term "comprising" is intended to specify certain features, regions, steps, processes, elements and / or components. This does not exclude the presence or addition of any other features, regions, steps, processes, elements and / or components, unless specifically stated to the contrary.

[0022] Throughout this specification, the terms first, second, etc. are used to distinguish one element from another, but the components are not limited by these terms.

[0023] All numbers and expressions used herein regarding quantities of ingredients, reaction conditions, and the like, will be understood to be modified by the term "about" unless otherwise indicated.

[0024] Method for preparing recycled materials The present invention provides a method for preparing recycled raw materials by analyzing the substances produced during the depolymerization of waste copolyester and conducting appropriate separation processes based on the physical and chemical behavior of each substance. Specifically, the method for preparing recycled raw materials according to the present invention includes the steps of: (1) depolymerizing waste copolyester to obtain a first reactant; (2) removing impurities present in the first reactant to obtain a second reactant; (3) distilling the second reactant to obtain a third reactant containing crude recycled bis-2-hydroxyethyl terephthalate and a fourth reactant containing recycled diol-ester; and (4) mixing the third reactant with an aqueous solvent and recrystallizing it to obtain a fifth reactant containing recycled bis-2-hydroxyethyl terephthalate and a filtrate.

[0025] The present invention makes it possible to efficiently separate comonomers, such as cyclohexanedimethanol (CHDM) and isosorbide (ISB), which are difficult to separate from reactants containing crude recycled bis-2-hydroxyethyl terephthalate obtained by depolymerization of waste copolyester. For example, the present invention is characterized in that cyclohexanedimethanol (CHDM), which competes with glycol-based compounds (e.g., monoethylene glycol (MEG)) introduced into the depolymerization reaction of waste copolyester in the transesterification reaction, is separated and concentrated by thin-film evaporation in the form of cyclohexanedimethanol ester (CHDM ester) and recovered from the bottom of the reactor; and isosorbide (ISB), which is inferior to glycol-based compounds and cyclohexanedimethanol in the transesterification reaction, is separated and concentrated by thin-film evaporation and recovered from the upper section (top) of the reactor, and then recrystallized and recovered in monomolecular form.

[0026] On the other hand, the recycled raw material in the present invention refers to a recycled monomer or recycled oligomer derived from waste copolyester. Specifically, the recycled raw material may include at least one selected from the group consisting of recycled bis-2-hydroxyethyl terephthalate (r-BHET), recycled cyclohexanedimethanol (r-CHDM), recycled tetramethylcyclobutanediol (r-TMCBD), recycled neopentyl glycol (r-NPG), recycled isosorbide (r-ISB), recycled cyclohexanedimethanol ester (r-CHDM ester), recycled tetramethylcyclobutanediol ester (r-TMCBD ester), recycled neopentyl glycol ester (r-NPG ester), and recycled isosorbide ester (r-ISB ester).

[0027] Hereinafter, each step of the method will be described in detail with reference to FIG. 1 as follows:

[0028] Step (1): Depolymerization According to the present invention, step (1) is a step of depolymerizing the waste copolyester by a chemical recycling method (e.g., glycolysis) to obtain a first reactant. Specifically, the first reactant can be obtained by carrying out a chemical reaction to cleave the polymer chain of the waste copolyester with a glycol-based compound.

[0029] The waste copolyester can be obtained by pre-processing post-consumer discarded waste products, such as beverage bottles, fabrics, films, cases, boxes, partitions, shelves, protective panels, packaging materials, building materials, and interior and exterior materials, which contain the copolyester.

[0030] The copolyesters contained in various waste products can be obtained by a conventional (co)polymerization reaction of one or more commonly known acid components and one or more commonly known alcohol components. The acid component may specifically include at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethylterephthalic acid, naphthalenedicarboxylic acid, orthophthalic acid, adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid. Specifically, the alcohol component may include at least one selected from the group consisting of ethylene glycol, 1,3-propanediol, 1,2-octanediol, 1,3-octanol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,1-dimethyl-1,5-pentanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol.

[0031] The pre-treatment may be carried out by removing other plastics, metals, and the aforementioned materials mixed in the waste, washing it, and then crushing it with a crusher. As a result of the pre-treatment, the waste copolyester may have a flake morphology. Furthermore, the waste copolyester may have a fiber-like microstructure.

[0032] The step (1) of depolymerizing the waste copolyester may include: (1-1) a first depolymerization step of depolymerizing the waste copolyester to obtain a 1-1 reactant; and (1-2) a second depolymerization step of depolymerizing the 1-1 reactant to obtain a first reactant.

[0033] The step (1-1) may include a procedure of carrying out a first chemical reaction to cleave a polymer chain of the waste copolyester with a first glycol-based compound to obtain a 1-1 reactant.

[0034] The first glycol compound used in the first depolymerization in step (1-1) is not particularly limited, but specifically may contain at least one selected from the group consisting of ethylene glycol (monoethylene glycol), propylene glycol, and diethylene glycol.

[0035] The supply amount of the first glycol-based compound (the amount used in the first depolymerization) is not particularly limited, but specifically may be 100 to 700 parts by weight, 100 to 600 parts by weight, 100 to 500 parts by weight, 200 to 500 parts by weight, 200 to 400 parts by weight, or 200 to 300 parts by weight, relative to 100 parts by weight of the waste copolyester. When the supply amount of the first glycol-based compound is within the above range, the first depolymerization of the waste copolyester is carried out smoothly, and it is possible to prevent excessive unreacted glycol-based compound from remaining.

[0036] The conditions for the first depolymerization in step (1-1) are not particularly limited, but may be, for example, at 180 to 200°C for 1 to 4 hours. More specifically, the first depolymerization temperature may be 180 to 195°C, 180 to 193°C, 180 to 190°C, 180 to 188°C, or 180 to 185°C. Furthermore, the first depolymerization time may be 1 to 4 hours, 1 to 3 hours, or 1 to 2 hours from the time when the temperature required for the first depolymerization is reached. By keeping the temperature and time of the first depolymerization within the above ranges, the first depolymerization of the waste copolyester is carried out smoothly while minimizing the formation of side reaction products such as diethylene glycol and diethylene glycol esters.

[0037] The first depolymerization in step (1-1) may be carried out in the presence of a catalyst that activates the depolymerization reaction. The catalyst is not particularly limited as long as it is a commonly known catalyst, and specifically, it may include a metal acetate, its anhydride, or its hydride. More specifically, the catalyst may be at least one acetate selected from the group consisting of zinc acetate, sodium acetate, cobalt acetate, and manganese acetate, its hydride, or its anhydride.

[0038] The amount of catalyst supplied (used) in step (1-1) is not particularly limited, but specifically, it may be 0.01 to 5 parts by weight, 0.05 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.2 to 1 part by weight per 100 parts by weight of the waste copolyester.

[0039] Step (1-2) may include a procedure of carrying out a second chemical reaction in which the 1-1 reactant obtained in step (1-1) is cleaved with a second glycol-based compound to obtain a first reactant.

[0040] The second glycol-based compound used in the second depolymerization in step (1-2) is not particularly limited, but may specifically include at least one selected from the group consisting of ethylene glycol (monoethylene glycol), propylene glycol, and diethylene glycol. The second glycol-based compound may be derived from the first depolymerization procedure in step (1-1), or may be further added during the second depolymerization procedure in step (1-2).

[0041] The supply amount of the second glycol-based compound (the amount used in the second depolymerization) is not particularly limited, but specifically may be 100 to 700 parts by weight, 100 to 600 parts by weight, 100 to 500 parts by weight, 200 to 500 parts by weight, 200 to 400 parts by weight, or 200 to 300 parts by weight per 100 parts by weight of the waste copolyester. When the supply amount of the second glycol-based compound is within the above range, the second depolymerization of the 1-1 reactant is carried out smoothly, and it is possible to prevent excessive unreacted glycol-based compound from remaining.

[0042] The conditions for the second depolymerization in step (1-2) are not particularly limited, but may be, for example, at 150 to 170°C for 1 to 4 hours. More specifically, the second depolymerization temperature may be 150 to 165°C, 150 to 163°C, 150 to 160°C, 150 to 158°C, or 150 to 155°C. Furthermore, the second depolymerization time may be 1 to 4 hours, 1 to 3 hours, or 1 to 2 hours from the time when the temperature required for the second depolymerization is reached. By keeping the temperature and time of the second depolymerization within the above ranges, the second depolymerization of the 1-1 reactant is carried out smoothly while minimizing the formation of side reactants such as diethylene glycol and diethylene glycol esters.

[0043] The second depolymerization in step (1-2) may be carried out in the presence of a catalyst that activates the depolymerization reaction. The catalyst may be derived from the first depolymerization step in step (1-1), or may be further added during the second depolymerization step in step (1-2). The description of the catalyst is the same as that of the catalyst in step (1-1) above, and therefore a detailed description thereof will be omitted.

[0044] As described above, the method for preparing recycled raw materials according to the present invention includes the steps of first depolymerization and second depolymerization of waste copolyester, which allows the production of side reaction substances such as diethylene glycol and diethylene glycol esters to be relatively minimized compared to the case where only the first depolymerization is carried out by applying the same amount of raw materials for the same time.

[0045] On the other hand, the method for preparing recycled raw materials according to the present invention may further include a step of cooling the first reactant obtained in step (1) and subjecting it to solid-liquid separation before the impurity removal step in step (2) described below. Specifically, in the cooling and solid-liquid separation step, the first reactant is cooled by vacuum flashing and then subjected to solid-liquid separation by pressure filtration using a filter aid. As a result, the first reactant can be converted into a liquid reactant. By further performing the cooling and solid-liquid separation step, solid foreign matter such as particulate matter and insoluble organic matter contained in the first reactant can be removed, thereby increasing the yield and purity of the final recycled raw material obtained.

[0046] The temperature to which the first reactant is cooled by the reduced pressure flash is not particularly limited, but may specifically be 135°C or lower, 130°C or lower, 125°C or lower, 120°C or lower, or 115°C or lower and 100°C or higher, 105°C or higher, or 110°C or higher (for example, 100 to 135°C, 105 to 125°C, or 110 to 120°C).

[0047] The pressure of the decompression flash is not particularly limited, but may specifically be 200 Torr or less, 150 Torr or less, 100 Torr or less, 50 Torr or less, or 30 Torr or less and 5 Torr or more, 8 Torr or more, 10 Torr or more, or 15 Torr or more (for example, 5 to 200 Torr, 10 to 100 Torr, or 15 to 50 Torr).

[0048] The filter aid used for solid-liquid separation is not particularly limited as long as it is a commonly known one, but specifically, it may contain at least one selected from the group consisting of diatomaceous earth, perlite, and asbestos powder.

[0049] The amount of filter aid supplied (amount used) is not particularly limited, but specifically may be 0.01 to 2 parts by weight, 0.05 to 2 parts by weight, 0.05 to 1 part by weight, or 0.1 to 1 part by weight per 100 parts by weight of the first reactant.

[0050] Step (2): Removal of impurities According to the present invention, step (2) is a step of removing impurities present in the first reactant obtained in step (1) to obtain a second reactant. Here, when the first reactant is further subjected to a cooling and solid-liquid separation step, the first reactant is in the state of a liquid reactant from which solid impurities have been removed. The removal of impurities may be performed on the liquid reactant.

[0051] The removal of impurities in step (2) may be carried out specifically using an ion exchange resin. More specifically, the removal of impurities may be carried out by passing the first reactant (liquid reactant) through an ion exchange resin or by adding an ion exchange resin to the first reactant (liquid reactant). By carrying out such an impurity removal step, ionic impurities (e.g., catalysts and foreign metals) contained in the first reactant can be removed, and the second reactant can be obtained with high purity.

[0052] The ion exchange resin used to remove impurities may be a commonly known cation exchange resin, anion exchange resin, amphoteric ion exchange resin, or chelating resin.

[0053] Specifically, the cation exchange resin may include a strongly acidic cation exchange resin having a sulfonic acid group (-SO3H) or a weakly acidic cation exchange resin having a carboxyl group (-COOH). The anion exchange resin may include a strongly basic anion exchange resin in the form of a quaternary ammonium salt or a weakly basic anion exchange resin having primary, secondary, or tertiary amino groups. The chelating resin may be a polymer resin having reactive functional groups, such as acetate or phosphate, that chelate metal ions such as sodium, copper, nickel, zinc, and manganese.

[0054] When impurity removal is carried out by adding an ion exchange resin to the first reactant, the amount of ion exchange resin supplied (used) is not particularly limited, and may be 1 time or more, 2 times or more, 3 times or more, or 5 times or more and 20 times or less, 15 times or less, 10 times or less, or 8 times or less (e.g., 1 to 20 times, 2 to 15 times, 3 to 10 times, or 5 to 8 times) the weight of the catalyst used in depolymerization in step (1). Furthermore, the amount of ion exchange resin supplied (used) may be 1 part by weight or more, 2 parts by weight or more, 3 parts by weight or more, or 5 parts by weight or more and 50 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, or 7 parts by weight or less (e.g., 1 to 50 parts by weight, 3 to 20 parts by weight, or 5 to 10 parts by weight) per 100 parts by weight of the waste copolyester in step (1).

[0055] On the other hand, when the impurity removal is carried out by passing the first reactant through an ion exchange resin, the ion exchange resin may be in the form of particles having a predetermined size. Specifically, the impurity removal may be carried out by passing the first reactant through a column packed with ion exchange resin particles having a particle size of 0.3 to 1.5 mm, 0.5 to 1.3 mm, or 0.7 to 1.0 mm.

[0056] Step (3): Distillation According to the present invention, step (3) is a step of distilling the second reactant to obtain a third reactant containing crude recycled bis-2-hydroxyethyl terephthalate and a fourth reactant containing recycled diol-ester. Step (3) may include: (3-1) a first distillation step of distilling the second reactant to obtain a 2-1 reactant; and (3-2) a second distillation step of distilling the 2-1 reactant to obtain a third reactant containing crude recycled bis-2-hydroxyethyl terephthalate and a fourth reactant containing recycled diol-ester.

[0057] Step (3-1) may include a procedure of performing a first distillation of the second reactant by a commonly known distillation process to obtain a 2-1 reactant. Specifically, the first distillation may be performed as a vacuum distillation so that unreacted glycol-based compounds contained in the second reactant can be efficiently removed. As a result, a 2-1 reactant from which unreacted glycol-based compounds have been removed can be obtained.

[0058] A glass distillation apparatus or a rotary evaporator may be used for the first vacuum distillation in step (3-1).

[0059] The conditions for the first vacuum distillation in step (3-1) are not particularly limited, but may be, for example, a pressure of 0.1 to 200 Torr and a temperature of 150°C or lower. More specifically, the pressure of the first vacuum distillation may be 0.1 to 150 Torr, 0.2 to 100 Torr, 0.3 to 50 Torr, or 0.5 to 30 Torr. Furthermore, the temperature of the first vacuum distillation may be 90°C or higher, 100°C or higher, or 110°C or higher and 145°C or lower, 140°C or lower, or 135°C or lower (e.g., 90 to 150°C, 100 to 145°C, or 120 to 135°C).

[0060] The unreacted glycolic compounds removed by the first vacuum distillation may be recovered and reused in the depolymerization procedure of step (1), thereby increasing the economic efficiency of the depolymerization process.

[0061] Meanwhile, in the method for preparing recycled raw materials according to the present invention, step (3) may further include a step of subjecting the 2-1 reactant obtained by the first vacuum distillation in step (3-1) to solid-liquid separation before the second distillation in step (3-2). Specifically, the solid-liquid separation may be carried out using a pressure filter, an absorbent (e.g., activated carbon), a centrifuge, a filter press, or a belt press. As a result, insoluble foreign matter contained in the 2-1 reactant can be removed.

[0062] Step (3-2) may include a procedure of performing a second distillation of the second-first reactant by a commonly known distillation process to obtain a third reactant and a fourth reactant. Specifically, the second distillation may be performed by thin-film evaporation to efficiently separate the crude recycled bis-2-hydroxyethyl terephthalate and the recycled diol-ester from the recycled comonomers (e.g., recycled cyclohexanedimethanol and recycled isosorbide) contained in the second-first reactant. More specifically, the second distillation may be performed by thin-film evaporation using a thin-film evaporator. By performing the thin-film evaporation, the third reactant (distillate) containing the crude recycled bis-2-hydroxyethyl terephthalate can be obtained from the top of the thin-film evaporator, and the fourth reactant (residue after removal of the distillate) containing the recycled diol-ester can be obtained from the bottom of the thin-film evaporator.

[0063] The recycled diol-ester contained in the fourth reactant may be any compound having two hydroxy groups (OH) and an ester structure (C=O). Specifically, the recycled diol-ester may include at least one selected from the group consisting of recycled cyclohexanedimethanol ester (r-CHDM-ester), recycled isosorbide ester (r-ISB-ester), recycled tetramethylcyclobutanediol ester (r-TMCBD-ester), and recycled neopentyl glycol ester (r-NPG-ester). Preferably, the recycled diol-ester may be recycled cyclohexanedimethanol ester (r-CHDM-ester). Here, examples of recycled diol-esters may exclude (or not include) diethylene glycol ester (recycled diethylene glycol ester), which is considered an impurity.

[0064] The recycled cyclohexanedimethanol-ester may specifically comprise at least one selected from the group consisting of 1-(2-hydroxyethyl) 4-[[4-(hydroxymethyl)cyclohexyl]methyl] terephthalate (CHDM-ester-1); 1,1'-[1,4-cyclohexanediylbis(methylene)] 4,4'-bis(2-hydroxyethyl) terephthalate (dimer-2 and dimer-3); and 1,4-benzenedicarboxylic acid, 1-[2-[[4-[(2-hydroxyethoxy)carbonyl]benzoyl]oxy]ethyl]-4-[2-[[4-[([(hydroxymethyl)cyclohexyl]methoxy)carbonyl]benzoyl]oxy]ethyl] ester (trimer-2).

[0065] In addition to the recycled diol-ester, the fourth reactant may further include a recycled comonomer, specifically, at least one selected from the group consisting of recycled cyclohexanedimethanol, recycled tetramethylcyclobutanediol, recycled neopentyl glycol, and recycled isosorbide.

[0066] For example, the fourth reactant may comprise at least one selected from the group consisting of recycled cyclohexanedimethanol-ester and recycled cyclohexanedimethanol.

[0067] Such recycled diol-ester and / or recycled comonomer can be recovered by additional purification processes of the fourth reactant.

[0068] On the other hand, the recycled diol-ester and / or recycled comonomer may be contained in the third reactant in addition to the fourth reactant, and the description thereof is the same as above and therefore omitted.

[0069] The thin film evaporator for the second thin film evaporation in step (3-2) may include an evaporator, a wiper rotor, and a condenser.

[0070] The conditions for the second thin-film evaporation in step (3-2) are not particularly limited, but may be carried out at 180 to 235°C under a pressure of 0.005 to 5 Torr. More specifically, the pressure of the second thin-film evaporation may be 0.01 to 4 Torr, 0.05 to 3 Torr, or 0.07 to 1.5 Torr. Furthermore, the temperature of the second thin-film evaporation (internal thin-film temperature of the thin-film evaporator) may be 185 to 230°C, 190 to 225°C, 195 to 220°C, or 200 to 215°C. By keeping the temperature and pressure of the second thin-film evaporation within the above ranges, it is possible to maximize the efficiency of separating the third reactant containing crude recycled bis-2-hydroxyethyl terephthalate and the fourth reactant containing recycled diol-ester. In particular, the recovery concentration index (RCI) of the recycled diol-ester (e.g., recycled cyclohexanedimethanol-ester) described below can be controlled within a desired range to ensure the required level of separation efficiency.

[0071] The third reactant obtained in step (3) may have a peak area fraction of bis-2-hydroxyethyl terephthalate of 90% or more, specifically 90-99%, 90-98%, 90-97%, or 90-96%, when analyzed by high performance liquid chromatography (HPLC).Furthermore, the third reactant may have a peak area fraction of diol ester (e.g., cyclohexanedimethanol ester) of 4% or less, specifically 0.5-4%, 0.8-3.5%, 1-3.2%, or 1.5-2.5%, when analyzed by high performance liquid chromatography (HPLC).

[0072] Furthermore, the fourth reaction product obtained in step (3) may have a peak area fraction of bis-2-hydroxyethyl terephthalate of 70% or less, specifically 20-70%, 25-67%, 30-65%, or 40-50%, when analyzed by high performance liquid chromatography (HPLC). Furthermore, the fourth reaction product may have a peak area fraction of diol ester (e.g., cyclohexanedimethanol ester) of 10% or more, specifically 10-40%, 11-38%, 15-35%, or 20-30%, when analyzed by high performance liquid chromatography (HPLC).

[0073] On the other hand, in the method for preparing recycled raw materials according to the present invention, the recovery concentration index (RCI) according to the following formula 1 may be 0.5 to 0.99. Specifically, the recovery concentration index (RCI) may be 0.55 to 0.99, 0.6 to 0.99, 0.65 to 0.99, 0.7 to 0.98, 0.75 to 0.98, or 0.8 to 0.97. The recovery concentration index refers to the distribution coefficient of the recycled diol-ester (e.g., recycled cyclohexanedimethanol-ester (r-CHDM-ester)) separated according to the second thin-film evaporation conditions in step (3-2). If the recovery concentration index is within the above range, it may indicate that the separation of the third reactant and the fourth reactant was very successful. [Formula 1] RCI=CE2 / (CE1+CE2) In Equation 1, CE1 is the peak area fraction of the diol-ester (total peak area fraction of diol-esters) identified when the third reactant is analyzed by high performance liquid chromatography (HPLC), and CE2 is the peak area fraction of the diol-ester (total peak area fraction of diol-esters) identified when the fourth reactant is analyzed by high performance liquid chromatography (HPLC).

[0074] Step (4): Recrystallization According to the present invention, step (4) is a step of mixing the third reactant obtained in step (3) with an aqueous solvent and recrystallizing it to obtain a fifth reactant containing recycled bis-2-hydroxyethyl terephthalate and a filtrate. Step (4) may include the steps of (4-1) mixing the third reactant with an aqueous solvent to obtain an aqueous solution; and (4-2) cooling the aqueous solution, recrystallizing it, and subjecting it to solid-liquid separation to obtain a fifth reactant containing recycled bis-2-hydroxyethyl terephthalate (r-BHET) and a filtrate.

[0075] Step (4-1) may include adding an aqueous solvent to the third reactant, mixing, and dissolving the third reactant to obtain an aqueous solution. The temperature at which the third reactant is dissolved is not particularly limited, but may be, for example, 50 to 90°C, 55 to 85°C, 60 to 80°C, or 65 to 75°C. A dissolution temperature within the above range may increase the yield of recycled bis-2-hydroxyethyl terephthalate (r-BHET). The aqueous solvent may be, for example, water, distilled water, deionized water, or pure water.

[0076] Step (4-2) may include cooling the aqueous solution to crystallize (recrystallize) it, and then subjecting it to conventional solid-liquid separation to obtain a fifth reactant containing recycled bis-2-hydroxyethyl terephthalate (r-BHET) and a filtrate. The temperature to which the aqueous solution is cooled is not particularly limited, but may be 20 to 30°C, 22 to 28°C, or 24 to 26°C.

[0077] By converting the third reactant into an aqueous solution in step (4-1) and cooling and recrystallizing the aqueous solution in step (4-2), it is possible to maximize the separation efficiency of recycled bis-2-hydroxyethyl terephthalate (r-BHET) and comonomer (e.g., recycled isosorbide) while increasing the yield of recycled bis-2-hydroxyethyl terephthalate (r-BHET).

[0078] The fifth reactant obtained in step (4) may have a peak area fraction of bis-2-hydroxyethyl terephthalate of 95% or more, specifically 95 to 99.5%, 95.5 to 99%, 96 to 98%, or 97 to 98%, when analyzed by high performance liquid chromatography (HPLC).Furthermore, the fifth reactant may have a peak area fraction of diol ester (e.g., cyclohexanedimethanol ester) of less than 1.5%, specifically 0.2 to 1.4%, 0.3 to 1.3%, 0.4 to 1.2%, or 0.5 to 1.1%, when analyzed by high performance liquid chromatography (HPLC).

[0079] On the other hand, in the method for preparing the recycled raw material according to the present invention, when the fourth reactant in step (3) and the fifth reactant in step (4) are each analyzed by high performance liquid chromatography (HPLC), the total peak area fraction (PA) of the diol-ester (e.g., cyclohexanedimethanol-ester) is T Specifically, the total peak area fraction (PA) according to the following formula 2 may be 0.1 to 70%. T ) may be 1 to 70%, 5 to 60%, 10 to 50%, or 15 to 45%. [Formula 2] PA T =PA1+PA2 (In Equation 2, PA1 is the peak area fraction of a diol-ester (e.g., cyclohexanedimethanol-ester) identified when the fourth reactant is analyzed by high performance liquid chromatography (HPLC), and PA2 is the peak area fraction of a diol-ester (e.g., cyclohexanedimethanol-ester) identified when the fifth reactant is analyzed by high performance liquid chromatography (HPLC).

[0080] On the other hand, the filtrate obtained in step (4) may contain recycled isosorbide (r-ISB) in an amount of 0.1 to 30 wt % based on the total weight of the filtrate. Specifically, the content of recycled isosorbide contained in the filtrate may be 0.2 to 15 wt %, 0.25 to 13 wt %, 0.3 to 10 wt %, 0.35 to 8 wt %, or 0.4 to 7 wt % based on the total weight of the filtrate. Here, if the content of recycled isosorbide is within the above range, this may mean that the recovery rate of isosorbide is high.

[0081] Specifically, according to the present invention, the recovery rate of isosorbide (ISB) according to the following formula 3 can be calculated. R ) may be 80% or more, 82% or more, 84% or more, 86% or more, or 88% or more (e.g., 80 to 99.5%, 82 to 99%, 84 to 98.5%, or 86 to 98%). [Formula 3] ISB R =(ISB B / ISB A ) x 100 (In formula 3, ISB A is the weight of isosorbide fed to the waste copolyester (introduced during the preparation of the waste copolyester), and ISB B is the weight of isosorbide contained in the filtrate)

[0082] The fifth reactant obtained in step (4) may be subjected to a drying process using a vacuum oven or the like, thereby recovering recycled bis-2-hydroxyethyl terephthalate. Furthermore, the filtrate obtained in step (4) may be subjected to an additional purification process, thereby recovering recycled isosorbide.

[0083] As described above, various recycled materials can be prepared according to the present invention, and the recycled materials obtained according to the preparation method of the present invention may have significantly superior purity and quality. Therefore, the recycled materials obtained according to the present invention can be efficiently used as raw materials for preparing recycled polyesters (recycled copolyesters).

[0084] Recycled raw material composition The present invention provides a recycled raw material composition obtained from waste copolyester. The description of the waste copolyester is the same as above, so it will be omitted. The recycled raw material composition according to the present invention may be a reaction material (product) obtained by the above-mentioned preparation method.

[0085] Specifically, the recycled raw material composition according to the present invention is obtained by depolymerizing waste copolyester, and when analyzed by high performance liquid chromatography (HPLC), the peak area fraction of bis-2-hydroxyethyl terephthalate is 70% or less, and the peak area fraction of diol ester is 10% or more.

[0086] More specifically, the recycled raw material composition (A) according to the present invention may be obtained by depolymerization and thin-film evaporation of a waste copolyester (e.g., the fourth reactant). When analyzed by high-performance liquid chromatography (HPLC), the recycled raw material composition (A) may have a peak area fraction of bis-2-hydroxyethyl terephthalate of 20 to 70%, 25 to 67%, 30 to 65%, or 40 to 50%, and a peak area fraction of a diol ester (e.g., cyclohexanedimethanol ester) of 10 to 40%, 11 to 38%, 15 to 35%, or 20 to 30%.

[0087] On the other hand, the recycled raw material composition (B) according to the present invention is obtained by depolymerizing waste copolyester, and when analyzed by high performance liquid chromatography (HPLC), the peak area fraction of bis-2-hydroxyethyl terephthalate is 95% or more, and the peak area fraction of diol ester is less than 1.5%.

[0088] More specifically, the recycled raw material composition (B) according to the present invention may be obtained by depolymerization, thin-film evaporation, and recrystallization of a waste copolyester (e.g., the fifth reactant). When analyzed by high-performance liquid chromatography (HPLC), the recycled raw material composition (B) may have a peak area fraction of bis-2-hydroxyethyl terephthalate of 95 to 99.5%, 95.5 to 99%, 96 to 98%, or 97 to 98%, and a peak area fraction of a diol ester (e.g., cyclohexanedimethanol ester) of 0.2 to 1.4%, 0.3 to 1.3%, 0.4 to 1.2%, or 0.5 to 1.1%.

[0089] On the other hand, the diol-ester identified as a result of the analysis by high performance liquid chromatography (HPLC) may specifically include at least one selected from the group consisting of cyclohexanedimethanol-esters (CHDM-esters), tetramethylcyclobutanediol-esters (TMCBD-esters), neopentylglycol-esters (NPG-esters), and isosorbide-esters (ISB-esters).

[0090] When the recycled raw material compositions (A and B) according to the present invention are analyzed to contain bis-2-hydroxyethyl terephthalate and / or diol ester in the above-mentioned specific ratios, the present invention can efficiently provide various types of recycled raw materials together with recycled bis-2-hydroxyethyl terephthalate. [Example]

[0091] Hereinafter, the present invention will be described in more detail with reference to embodiments, however, these examples are provided for illustrative purposes only and the present invention is not limited thereto.

[0092] [Example 1] 1,000 g of waste copolyester having composition 1 shown in Table 1 below, 2,000 g of ethylene glycol, and 5.0 g of zinc acetate anhydride were charged into a first reactor made of stainless steel (SUS). The temperature inside the reactor was raised to 180°C, and a first depolymerization (first glycolysis reaction) was carried out for 2 hours. As a result, a reactant 1-1 was obtained.

[0093] Subsequently, the 1-1 reactant was transferred to a second reactor and cooled to 150°C. 2,000 g of ethylene glycol was further added thereto, and a second depolymerization (second glycolysis reaction) was carried out for 2 hours, during which the reactor temperature was maintained at 150°C. As a result, a first reactant was obtained.

[0094] Next, the first reaction mass was cooled to 120°C by vacuum flashing, and 16 g of a filter aid (Celite™ 545) was added thereto, followed by pressure filtration to perform solid-liquid separation.

[0095] The liquid reaction mass obtained by solid-liquid separation was passed through a column packed with ion exchange resin (Bonlite's BC107(H)) to remove ionic impurities, yielding a second reaction mass containing crude recycled bis-2-hydroxyethyl terephthalate (crude r-BHET) and unreacted ethylene glycol.

[0096] Next, the second reaction material was transferred to a 10-liter distillation apparatus and vacuum distilled at 130°C to recover unreacted ethylene glycol, thereby obtaining a 2-1 reaction material from which ethylene glycol had been removed.

[0097] Next, 7.8 g of activated carbon was added to 1,560 g of the 2-1 reactant. A solid-liquid separation was performed to remove residual chromophores, followed by separation using a thin-film evaporator (VTA VKL70-4S). Specifically, thin-film evaporation was performed at 210 °C and 0.08 Torr to obtain 952 g of the third reactant containing crude r-BHET and 608 g of the fourth reactant containing recycled diol-ester, respectively.

[0098] Next, the third reactant and distilled water equivalent to three times the weight of the third reactant were added to a glass reactor and dissolved at 70°C. Then, the mixture was cooled to room temperature, crystallized, filtered, and dried in a vacuum oven to obtain a fifth reactant containing recycled bis-2-hydroxyethyl terephthalate (r-BHET) with high purity. After cooling and crystallization, the filtrate obtained by filtration was collected as the sixth reactant.

[0099] [Examples 2 to 4] Each step was carried out in the same manner as in Example 1, except that waste copolyesters having compositions 2 to 4 in Table 1 below were used.

[0100] [Example 5] Each step was carried out according to the same procedure as in Example 1, except that the thin film evaporation was carried out at 240°C.

[0101] [Comparative Example 1] Each step was carried out in the same manner as in Example 1, except that waste polyester (waste polyester terephthalate (PET)) having composition 5 in Table 1 below was used.

[0102] [Table 1]

[0103] [Test Example 1] The reaction products obtained in each step were analyzed by high performance liquid chromatography (HPLC) under the following conditions. The results are shown in Tables 2 to 4 below.

[0104] Pretreatment: Approximately 0.01 g of each reactant was diluted in approximately 20 ml of methanol and then analyzed by high performance liquid chromatography (HPLC). HPLC analyzer (model): Waters e2695 Column: C18 (4.6 x 250 mm), 5 μm UV detector: 242 nm Injection volume: 10μl Eluent (gradient): A - H2O+H3PO4, B - acetonitrile Then, the peak area fraction (area %) of each component in the total peak area of ​​HPLC was obtained.

[0105] [Test Example 2] The recovery concentration index (RCI) was calculated according to the following formula 1. The results are shown in Tables 2 to 4 below. Here, CHDM-ester-1, dimer-2, dimer-3, and trimer-2 were defined as the diol-ester (cyclohexanedimethanol-ester) components in Tables 2 to 4 below. [Formula 1] RCI=CE2 / (CE1+CE2) In Equation 1, CE1 is the peak area fraction of the diol-ester identified when the third reactant is analyzed by high performance liquid chromatography (HPLC), and CE2 is the peak area fraction of the diol-ester identified when the fourth reactant is analyzed by high performance liquid chromatography (HPLC).

[0106] [Test Example 3] The filtrate collected as the sixth reactant was analyzed by gas chromatography (GC) under the following conditions. The results are shown in Tables 2 to 4 below.

[0107] Pretreatment: About 0.1 g of the filtrate was diluted in about 10 ml of CHCl 3 , filtered through a 0.45 μm filter, and then analyzed by gas chromatography (GC). GC analyzer (model): Agilent 7890B Column: DB-624 (30 m x 0.25 mm x 1.4 μm) Oven temperature: 60°C (2 min), -10°C / min, -200°C (0 min), -20°C / min, -260°C (5 min). Water injector temperature: 250℃ Detector temperature: 250℃ Flow rate: 1.5 mL / min (N2), split ratio: 1 / 50

[0108] [Table 2]

[0109] [Table 3-1]

[0110] [Table 3-2]

[0111] [Table 4]

[0112] As shown in Tables 2 to 4, when the recycled materials (Examples 1 to 5) were prepared using the preparation method of the present invention, various recycled materials (r-BHET, r-CHDM, and r-ISB) could be prepared in high yields. In particular, the recovery concentration index (RCI) of CHDM-esters was 0.5 or higher, making it possible to prepare (recover) comonomers such as r-CHDM and r-ISB, which were difficult to recycle in the past.

Claims

1. 1. A method for preparing recycled feedstock, comprising: (1) depolymerizing waste copolyester to obtain a first reactant; (2) removing impurities present in the first reactant to obtain a second reactant; (3) distilling the second reactant to obtain a third reactant comprising crude recycled bis-2-hydroxyethyl terephthalate and a fourth reactant comprising recycled diol-ester; (4) combining the third reactant with an aqueous solvent and recrystallizing it to obtain a fifth reactant and a filtrate comprising recycled bis-2-hydroxyethyl terephthalate; A method comprising:

2. 2. The method for preparing a recycled raw material according to claim 1, wherein the step (1) comprises: (1-1) a first depolymerization step of depolymerizing the waste copolyester to obtain a first-1 reactant; and (1-2) a second depolymerization step of depolymerizing the first-1 reactant to obtain a first reactant.

3. The method for preparing recycled raw materials according to claim 2, wherein the first depolymerization in step (1-1) is carried out at 180 to 200°C.

4. 3. The method for preparing recycled raw materials according to claim 2, wherein the second depolymerization in step (1-2) is carried out at 150 to 170°C.

5. The method for preparing recycled feedstock according to claim 1, wherein step (3) comprises: (3-1) a first distillation step of distilling the second reactant to obtain a second-1 reactant; and (3-2) a second distillation step of distilling the second-1 reactant to obtain a third reactant and a fourth reactant.

6. The method for preparing recycled raw materials according to claim 5, wherein the first distillation in step (3-1) is carried out as a vacuum distillation at 150°C or less.

7. 6. The method for preparing recycled raw materials according to claim 5, wherein the second distillation in step (3-2) is carried out as a thin-film evaporation at 180 to 235°C.

8. 2. The method for preparing recycled feedstocks according to claim 1, wherein the fourth reactant in step (3) comprises at least one selected from the group consisting of recycled cyclohexanedimethanol-esters and recycled cyclohexanedimethanol.

9. 2. The method for preparing recycled feedstock according to claim 1, wherein the third reactant in step (3) has a peak area fraction of bis-2-hydroxyethyl terephthalate of 90% or more and a peak area fraction of diol-ester of 4% or less when analyzed by high performance liquid chromatography (HPLC).

10. 2. The method for preparing recycled feedstock according to claim 1, wherein the fourth reactant in step (3) has a peak area fraction of bis-2-hydroxyethyl terephthalate of 70% or less and a peak area fraction of diol-ester of 10% or more when analyzed by high performance liquid chromatography (HPLC).

11. The recovered concentration index (RCI) according to the following formula 1 is 0.5 to 0.99: [Formula 1] RCI=CE ２ / (E １ +CE ２ ) (In Formula 1, CE １ is the peak area fraction of the diol-ester identified when the third reactant was analyzed by high performance liquid chromatography (HPLC), and CE ２ is the peak area fraction of the diol-ester identified when the fourth reactant was analyzed by high performance liquid chromatography (HPLC).

10. A method for preparing the recycled material of claim 1.

12. The method for preparing recycled raw materials according to claim 1, wherein step (4) comprises: (4-1) mixing a third reactant with an aqueous solvent to obtain an aqueous solution; and (4-2) cooling the aqueous solution, recrystallizing it, and subjecting it to solid-liquid separation to obtain a fifth reactant and a filtrate.

13. 2. The method for preparing recycled feedstock according to claim 1, wherein the fifth reactant in step (4) has a peak area fraction of bis-2-hydroxyethyl terephthalate of 95% or more and a peak area fraction of diol-ester of less than 1.5% when analyzed by high performance liquid chromatography (HPLC).

14. 2. The method for preparing recycled raw materials according to claim 1, wherein when the fourth reactant in step (3) and the fifth reactant in step (4) are each analyzed by high performance liquid chromatography (HPLC), the total peak area fraction of the diol-ester is 0.1 to 70%.

15. 2. The method for preparing recycled feedstocks according to claim 1, wherein the filtrate of step (4) contains recycled isosorbide in an amount of 0.1 to 30 wt % based on the total weight of the filtrate.

16. A recycled raw material composition obtained by depolymerization of waste copolyester, wherein when analyzed by high performance liquid chromatography (HPLC), the peak area fraction of bis-2-hydroxyethyl terephthalate is 70% or less and the peak area fraction of diol-ester is 10% or more.

17. The recycled material composition according to claim 16, wherein the diol ester comprises at least one selected from the group consisting of cyclohexanedimethanol ester, tetramethylcyclobutanediol ester, neopentyl glycol ester, and isosorbide ester.

18. A recycled raw material composition obtained by depolymerization of waste copolyester, wherein when analyzed by high performance liquid chromatography, the peak area fraction of bis-2-hydroxyethyl terephthalate is 95% or more and the peak area fraction of diol-ester is less than 1.5%.

19. The recycled material composition according to claim 18, wherein the diol-ester comprises at least one selected from the group consisting of cyclohexanedimethanol-ester, tetramethylcyclobutanediol-ester, neopentyl glycol-ester, and isosorbide-ester.

Images