Depolymerization product of polyester and mechanochemical depolymerization method for polyester

Abstract

The present invention relates to a depolymerization product of polyester and a mechanochemical depolymerization method for polyester, the depolymerization product of polyester comprising: 0 wt% to 10 wt% of undegraded polyester; 60 wt% to 99 wt% of a dibasic acid; 1 wt% to 25 wt% of alkylene glycol; and 0 wt% to 15 wt% of an unreacted degrader, impurities, or a combination thereof.

Description

Polyester depolymer and mechanochemical depolymerization method of polyester

[0001] This invention relates to a mechanochemical depolymerization method of polyester and a depolymerized polyester.

[0002] Polyesters, represented by polyethylene terephthalate (PET), have excellent chemical stability and are used in fibers, fabrics, clothing, films, sheets, and beverage bottles.

[0003] As the use of polyester increases rapidly, various methods are being considered to recover and reuse its waste. One such method is the so-called chemical recycling method, which involves depolymerizing waste such as polyester to convert it into monomers for recovery, and then using these monomers as raw materials to repolymerize and manufacture recycled polyesters such as polyethylene terephthalate.

[0004] Chemical recycling of polyester is expected to be a means of realizing resource reuse because it enables the separation of impurities and its quality as a raw material does not differ significantly from that of virgin.

[0005] Broadly speaking, the depolymerization methods of polyester into monomers are typically divided into three main types: the hydrolysis method using water as a solvent, the alcohollysis method using alcohol as a solvent, and the glycolysis method using glycol as a solvent.

[0006] Hydrolysis methods include, for example, a method of decomposing a melt of polyethylene terephthalate into terephthalic acid and ethylene glycol by reacting it with water and then reacting it with ammonium hydroxide (see Patent Document 1). This method has the advantage of not using glycol or alcohol for the reaction, but requires a special high-pressure depolymerization reactor because the reaction is carried out under high pressure conditions.

[0007] The alcoholylysis method is a method of depolymerizing polyester by heating, for example, in an alcohol solvent (a catalyst is added as needed) (see Patent Documents 2 and 3). This method has the advantage that, for example, when depolymerizing polyethylene terephthalate using methanol as a solvent, dimethyl terephthalate (DMT), a useful and easy-to-handle monomer, is directly produced by the depolymerization reaction, and the depolymerization reaction is relatively fast. However, the alcohol used as a solvent has a low boiling point, and pressurization is required to carry out the reaction (for example, reacting in supercritical or subcritical methanol), so a special high-pressure depolymerization reactor is required.

[0008] The glycolysis method is a method for producing bis(β-hydroxyalkyl) terephthalate and ethylene glycol by depolymerizing a polyester by heating it in an excess alkylene glycol solvent with a depolymerization catalyst such as sodium carbonate (see Patent Documents 4 and 5). For example, when ethylene glycol is used as the solvent, bis(β-hydroxyethyl) terephthalate (BHET) is produced by the depolymerization reaction, and dimethyl terephthalate (DMT) can be recovered by adding methanol in the presence of an ester exchange catalyst to carry out an ester exchange reaction. Although the glycolysis method can be carried out at atmospheric pressure, the reaction time is relatively long, so a reduction in the reaction time is required, and there is a problem that the glycol in the solvent deteriorates when heated for a long time.

[0009] These known depolymerization methods for polyester require a reaction time of at least several hours, which poses difficulties in the mass disposal of polyester waste. Furthermore, since the reaction must be carried out under high temperature or high pressure conditions, special equipment capable of withstanding such conditions is required, which is why commercialization has not yet been achieved.

[0010] To address the aforementioned problems, a non-solvent mechanochemical depolymerization technology is being proposed. Since the mechanochemical depolymerization method depolymerizes polyester using the heat generated simultaneously with the grinding of the polyester, there is no need to perform additional processes such as washing, grinding, crushing, cutting, or processing (flaking, popcorning) to feed waste collected from industry or households into chemical processes, and all types of waste can be used as feedstock.

[0011] Among them, Patent Document 1 discloses a method of depolymerizing polyester into a dibasic acid and an alkylene glycol while generating heat by grinding polyester in the presence of a decomposing agent. The decomposing agent disclosed is an alkali, an acid, a salt thereof, a monoalcohol, a polyalcohol, or a mixture thereof, and disclosed that these may be in a solid state or an aqueous solution state. However, according to the depolymerization method of Patent Document 1, when a decomposing agent in a solid state is used, the decomposing agent is not evenly distributed, resulting in a low decomposition rate of polyester. Additionally, when an aqueous decomposing agent is used, the grinding proceeds with the decomposing agent added in advance before grinding, and the temperature is not raised above a certain level due to the aqueous decomposing agent, resulting in a low decomposition rate of polyester.

[0012] [Prior Art Literature]

[0013] (Patent Document 0001) Japanese Patent Publication No. 2003-527363 (Publication Date: September 16, 2003)

[0014] According to one embodiment, a depolymerization of polyester and a mechanochemical depolymerization method of polyester are provided, which are environmentally advantageous due to process shortening and thermal energy reduction, can reduce manufacturing costs, and have an excellent decomposition rate.

[0015] According to one embodiment, a polyester mechanochemical depolymer is provided, comprising 0% to 10% by weight of undissolved polyester; 60% to 99% by weight of a dibasic acid; 1% to 25% by weight of an alkylene glycol; and 0% to 15% by weight of unreacted decomposer, impurities, or a combination thereof.

[0016] According to another embodiment, a method for mechanochemical depolymerization of polyester is provided, comprising the steps of: introducing a polyester raw material into a depolymerization reactor; generating heat by rotating a disk located inside the reaction section of the depolymerization reactor; and introducing a decomposition agent into the depolymerization reactor to depolymerize the polyester.

[0017] The polyester depolymer and the polyester mechanochemical depolymerization method according to one embodiment are environmentally advantageous due to process shortening and thermal energy reduction, can reduce manufacturing costs, and can have an excellent decomposition rate.

[0018] FIG. 1 is a schematic diagram illustrating the structure of a depolymerization reactor according to one embodiment.

[0019] FIG. 2 is a drawing for specifically explaining the reaction section of a depolymerization reactor according to one embodiment.

[0020] Hereinafter, embodiments of the present disclosure are described in detail so that those skilled in the art to which the present disclosure pertains can easily implement them. However, the present disclosure may be embodied in various different forms and is not limited to the embodiments described herein.

[0021] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Furthermore, the singular form includes the plural form unless specifically stated otherwise in the text.

[0022] Polyester depolymer

[0023] A depolymer of polyester according to one embodiment comprises 0% to 10% by weight of undissolved polyester; 60% to 99% by weight of a dibasic acid; 1% to 25% by weight of an alkylene glycol; and 0% to 15% by weight of unreacted decomposer, impurities, or a combination thereof.

[0024] Here, the depolymer of the polyester refers to a composition obtained by depolymerizing the polyester. The depolymer of the polyester may further include the dibasic acid and alkylene glycol to be obtained by depolymerizing the polyester, as well as unreacted products, by-products, etc. The depolymer of the polyester may be obtained according to a known depolymerization method, or may be prepared according to a depolymerization method of the polyester according to an embodiment described below. The polyester may be a polyester formed by polymerizing a dibasic acid and an alkylene glycol, for example, polyethylene terephthalate (PET), polybutylene terephthalate, or polyethylene naphthalate, or may be polycaprolactone formed by polymerizing caprolactone.

[0025] The depolymerization of the polyester above contains 0% to 10% by weight of undegraded polyester. For example, the depolymerization of the polyester above may contain 0.5% to 9% by weight, 1% to 8% by weight, 1.5% to 7% by weight, 1.5% to 6% by weight, 1.5% to 5% by weight, 1.5% to 4% by weight, 1.5% to 3% by weight, or 1.5% to 2.5% by weight of undegraded polyester. The content of the undegraded polyester may be relative to 100% by weight of the depolymerization of the polyester, and the content of the undegraded polyester may be calculated according to the evaluation method of Test Example 1 below. In Test Example 1 below, the depolymerization of the polyester may be the same as the discharged salt, and the undegraded polyester may be the same as undegraded PET. When the content of undegraded polyester in the depolymerization of the above polyester satisfies the above range, the degradation rate of the polyester may be high, and most of the polyester may be depolymerized while a small amount of undegraded polyester may be included.

[0026] The depolymer of the polyester above contains 60% to 99% by weight of a dibasic acid. For example, the depolymer of the polyester above may contain 65% to 98% by weight, 67% to 97% by weight, or 69% to 96% by weight of a dibasic acid. The content of the dibasic acid may be relative to 100% by weight of the depolymer of the polyester, and the content of the dibasic acid may be calculated according to the evaluation method of Test Example 1 below. In Test Example 1 below, the depolymer of the polyester may be identical to the discharged salt, and the dibasic acid may be identical to TPA-salt. When the content of the dibasic acid in the depolymer of the polyester above satisfies the above range, the decomposition rate of the polyester may be high, and most of the polyester may be depolymerized and most of it may decompose into dibasic acid. In the disclosed alkali hydrolysis depolymerization method, the content of alkylene glycol is included in excess, so the content of dibasic acid in the depolymer may not satisfy the above range.

[0027] The depolymer of the polyester above contains 1% to 25% by weight of alkylene glycol. For example, the depolymer of the polyester above may contain 1% to 24% by weight, 1% to 23% by weight, 1% to 22% by weight, 1% to 21% by weight, or 1.5% to 21% by weight of alkylene glycol. The content of the alkylene glycol may be relative to 100% by weight of the depolymer of the polyester, and the content of the alkylene glycol may be calculated according to the evaluation method of Test Example 1 below. In Test Example 1 below, the depolymer of the polyester may be the same as the discharged salt, and the alkylene glycol may include ethylene glycol (EG), diethylene glycol (DEG), or a combination thereof. If the content of alkylene glycol in the depolymer of the above polyester satisfies the above range, it can be environmentally friendly, reduce energy costs, or be efficient. In addition, there is a process advantage as there is no additional solvent removal process. In known alkali hydrolysis depolymerization methods, the content of alkylene glycol is included in excess, so the content of alkylene glycol in the depolymer may not satisfy the above range and may exceed it.

[0028] The depolymer of the polyester comprises 0% to 15% by weight of unreacted decomposers, impurities, or a combination thereof. For example, the depolymer of the polyester may comprise 0% to 12% by weight, 0% to 10% by weight, 0% to 5% by weight, 0.5% to 2% by weight, or 0.5% to 1% by weight of unreacted decomposers, impurities, or a combination thereof. The unreacted decomposer refers to a compound remaining among the decomposers used in the depolymerization reaction of the polyester that does not participate in the reaction, and may include, for example, alkalis, acids, salts thereof, monoalcohols, polyalcohols, or mixtures thereof. The impurities refer to unintended components that may be incorporated into the raw material, reaction system, or process, and may include, for example, heteropolymers other than polyester and additives such as dyes. The content of the above unreacted decomposer, impurities, or combinations thereof may be based on 100% by weight of the depolymerization of the polyester and may be calculated according to the evaluation method of Test Example 1 below. The above depolymerization of the polyester may contain an unreacted decomposer, and the unreacted decomposer may include, for example, NaOH, and in Test Example 1 below, the depolymerization of the polyester may be the same as the discharged salt, and the unreacted decomposer may include unreacted NaOH.

[0029] The depolymer of the polyester may contain the dibasic acid and the alkylene glycol in a weight ratio of 2:1 to 100:1. For example, the depolymer of the polyester may contain the dibasic acid and the alkylene glycol in a weight ratio of 2:1 to 90:1, 2:1 to 80:1, 2:1, 70:1, or 3:1 to 65:1. When the weight ratio of the dibasic acid and the alkylene glycol in the depolymer of the polyester satisfies the above range, it may be environmentally friendly, reduce energy costs, or be efficient. In addition, there is a process advantage as there is no additional solvent removal process. In known alkali hydrolysis depolymerization methods, the content of alkylene glycol is included in excess, so the content of alkylene glycol in the depolymer may not satisfy the above range and may exceed it.

[0030] The depolymer of the polyester may contain the alkylene glycol and the undegraded polyester in a weight ratio of 10:1 to 1:5, for example, in a weight ratio of 10:1 to 1:4, 10:1 to 1:3, 10:1 to 1:2, 9.5:1 to 1:2, or 9.5:1 to 1:1.5. When the weight ratio of the alkylene glycol and the undegraded polyester satisfies the above range and is included in the depolymer of the polyester, the depolymer of the polyester satisfies the above range, so the alkylene glycol content of the depolymer of the polyester is environmentally friendly, can reduce energy costs, or is efficient. In addition, there is a process advantage as there is no additional solvent removal process. In the disclosed alkali hydrolysis depolymerization method, the content of alkylene glycol is included in excess, so the content of alkylene glycol in the depolymer may not satisfy the above range.

[0031] The depolymer of the above polyester may be in powder form.

[0032] The above dibasic acid may include a dicarboxylic acid or an aliphatic dicarboxylic acid. Examples of the dicarboxylic acids include terephthalic acid, phthalic acid (ortho), isophthalic acid, dibromoisophthalic acid, sodium sulfoisophthalate, phenylenediooxydicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenylketone dicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, 2,6-naphthalene dicarboxylic acid, trimellitic acid, or pyromellitic acid. In addition, the above aliphatic dicarboxylic acids include aliphatic cyclic dicarboxylic acids such as aliphatic dicarboxylic acid hexahydroterephthalic acid or hexahydroisophthalic acid, and succinic acid, glutaric acid, adipic acid, pimetic acid, souveric acid, azelaic acid, sebacic acid, undecadicarboxylic acid, or dodeca dicarboxylic acid.

[0033] The depolymer of the above polyester may contain a dibasic acid in the form of a salt.

[0034] The above alkylene glycol may include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, polytetramethylene glycol, 1,4-cyclohexanediol, 1,4-benzenediol, or a combination thereof. For example, if the polyester is polyethylene terephthalate, ethylene glycol can be recovered as the alkylene glycol, and if the polyester is polybutylene terephthalate, butylene glycol can be recovered as the monomer.

[0035] The above alkylene glycol may include ethylene glycol, diethylene glycol, or a combination thereof. The above diethylene glycol may be included in an amount of 0% to 5% by weight relative to 100% by weight of the polyester depolymer, for example, 0% to 4% by weight, 0% to 3% by weight, 0% to 2% by weight, 0% to 1% by weight, or 0% to 0.6% by weight. The content of diethylene glycol in the polyester depolymer may be calculated according to the evaluation method of Test Example 1 below. If the content of diethylene glycol in the polyester depolymer satisfies the above range, it may be environmentally friendly, reduce energy costs, or be efficient. In addition, there is a process advantage as there is no additional solvent removal process. In the disclosed alkali hydrolysis depolymerization method, the content of alkylene glycol is included in excess, so the content of alkylene glycol in the depolymer may not satisfy the above range.

[0036] In addition, if the depolymer of the polyester contains both ethylene glycol and diethylene glycol, the depolymer of the polyester may contain the ethylene glycol and the diethylene glycol in a weight ratio of 100:1 to 1:1. For example, the depolymer of the polyester may contain the ethylene glycol and the diethylene glycol in a weight ratio of 90:1 to 1:1, 80:1 to 1:1, 70:1 to 1:1, 60:1 to 1:1, 50:1 to 1:1, or 40:1 to 1:1. The content of ethylene glycol and diethylene glycol in the depolymer of the polyester may be calculated according to the evaluation method of Test Example 1 below. If the weight ratio of ethylene glycol and diethylene glycol in the depolymer of the above polyester satisfies the above range, it can be environmentally friendly, reduce energy costs, or be efficient. In addition, there is a process advantage as there is no additional solvent removal process. In known alkali hydrolysis depolymerization methods, the content of alkylene glycol is included in excess, so the content of alkylene glycol in the depolymer may not satisfy the above range.

[0037] The depolymer of the polyester may further contain water. The depolymer of the polyester may contain water in an amount greater than 0 wt% to 10 wt% or less, greater than 0 wt% to 9 wt% or less, greater than 0 wt% to 8 wt% or less, or greater than 0 wt% to 7 wt% or less. The water content in the depolymer of the polyester can be calculated according to the evaluation method of Test Example 1 below.

[0038] Mechanochemical depolymerization method of polyester

[0039] Another embodiment provides a method for mechanochemical depolymerization of polyester, comprising the steps of: introducing a polyester raw material into a depolymerization reactor; generating heat by rotating a disk located inside the reaction section of the depolymerization reactor; and introducing a decomposition agent into the depolymerization reactor to depolymerize the polyester.

[0040] Hereinafter, the steps of a mechanochemical depolymerization method of polyester according to one embodiment will be described sequentially.

[0041] Step of feeding polyester raw materials into a depolymerization reactor

[0042] In the above step, the polyester raw material is fed into a depolymerization reactor. Here, the polyester may be a polyester formed by polymerizing a dibasic acid and an alkylene glycol, for example, polyethylene terephthalate (PET), polybutylene terephthalate, or polyethylene naphthalate, or may be polycaprolactone formed by polymerizing caprolactone.

[0043] As the above polyester raw material, molded articles containing polyester, particularly waste, may be used. Waste may include waste generated after using molded articles containing polyester, as well as residues generated during the manufacture of molded articles or defective products. For example, it may be used PET bottles, cups, strings, packaging packs, etc., or burrs, sprues, sheets, fibers, fabrics, clothes, films, or sheets produced during molding, or cups after vacuum forming and cutting.

[0044] At this time, the polyester content in the polyester waste may be 60% to 100% by weight relative to 100% by weight of the polyester waste. If the polyester content is less than 60% by weight, the amount of by-products and non-recyclable separated purification waste relative to the raw materials obtained through the depolymerization process is too large, so it may not be practically economically viable.

[0045] When using polyester waste as a polyester raw material, a pretreatment step may be performed to wash the waste and remove contaminants attached to the waste, such as dyes, contents, or soil, before feeding the polyester raw material into the depolymerization reactor.

[0046] In addition, since the mechanochemical depolymerization method of polyester involves depolymerization occurring simultaneously with grinding, the recovered polyester waste can be depolymerized as is or into relatively large pieces, but optionally, the waste can be mechanically cut, ground, or processed into a suitable size. The grinding treatment can be performed using known suitable means, and for example, by grinding using a hammer mill, the polyester waste can be ground into fine pieces of 2 mm to 8 mm in size and then provided to the depolymerization reaction.

[0047] In addition, if necessary, the polyester can be immersed in a solvent to extract and remove dyes, or components lighter than the solvent can be separated, or only a certain size can be recovered by blowing it with wind or using a sieve and provided for a depolymerization reaction.

[0048] However, as mentioned above, since the mechanochemical depolymerization method of polyester depolymerizes the polyester using heat generated simultaneously with the crushing of the polyester, there is no need to additionally perform washing, crushing, shredding, cutting, or processing (flaking, popcorning) to feed waste collected from industry or general households into the chemical process, and all waste of various forms can be used as feedstock.

[0049] The mechanochemical depolymerization method for polyester does not require a high-pressure reactor because it generates heat by grinding the polyester within a depolymerization reactor and then uses the generated heat to depolymerize the polyester, allowing the apparatus to be configured as a batch or continuous reactor.

[0050] The type of the above-mentioned depolymerization reactor is not specifically limited, provided that it is a depolymerization reactor that includes equipment capable of grinding polyester.

[0051] FIG. 1 is a schematic diagram illustrating the structure of a depolymerization reactor according to one embodiment. In the mechanochemical depolymerization method of polyester according to one embodiment, the depolymerization reactor shown in FIG. 1 may be used. Hereinafter, the depolymerization reactor of each step is described on the premise of the depolymerization reactor shown in FIG. 1, but is not limited thereto.

[0052] Referring to FIG. 1, the depolymerization reactor (10) may include a reaction section (100), a raw material input device (200), a decomposition agent input device (300), a nitrogen supply device (400), an exhaust tank (500), an exhaust pipe (520), a dryer (600), a condenser (700), and a main motor (800).

[0053] The above reaction section (100) may refer to a configuration in which the depolymerization of a polymer occurs, and the reaction section (100) may include a reaction section body (110), a disk rotation axis (120), a disk (130), a blade section support (140), and a blade section (150). Since the elements constituting the above reaction section (100) are described in detail in the 'heat generation step' described later, they are omitted below.

[0054] The raw material input device (200) may refer to a device for inputting raw materials into the reaction section (100). In the above step, the polyester raw material is input into the raw material input device (200) of the depolymerization reactor (10) and stored, and then can be supplied into the main body (110) of the reaction section.

[0055] The decomposition agent injection device (300) may refer to a device that supplies a decomposition agent to the reaction unit (100). Since the decomposition agent injection device (300) can perform a major role in supplying the decomposition agent into the reaction unit during the 'step of depolymerizing polyester by injecting a decomposition agent' described later, it will be explained in detail during the 'step of depolymerizing polyester by injecting a decomposition agent'.

[0056] The nitrogen supply device (400) may refer to a device that supplies nitrogen to the reaction unit (100). The nitrogen supply device (400) may be positioned below the reaction unit (100). The nitrogen supply device (400) may be positioned to surround the disk rotation axis (120). That is, the disk rotation axis (120) may be located inside the nitrogen supply device (400).

[0057] The nitrogen supply device (400) can supply nitrogen gas from the bottom to the top of the reaction section (100). The disc rotation axis (120) can be positioned to penetrate the body of the reaction section (110), and the nitrogen supply device (400) can prevent unnecessary gas from entering through the gap located between the disc rotation axis (120) and the body of the reaction section (110).

[0058] The discharge tank (500) may be configured to store the depolymerized product discharged from the reaction section (100). To transfer the depolymerized product from the reaction section (100) to the discharge tank (500), a discharge pipe (510) providing a passage and other additional transfer devices may be used.

[0059] Additionally, an exhaust pipe (520) providing a passage to transfer the gas generated during the polyester depolymerization process to the exhaust tank (500) may be used. For example, gases and dust such as ethylene glycol, water vapor, and polyester dust may be transferred through the exhaust pipe (520).

[0060] The screw conveyor (530) may be configured to convey the depolymerized material stored in the discharge tank (500) to the dryer (600). For example, the screw conveyor (530) may be configured to convey the depolymerized material by rotating a blade in the form of a screw.

[0061] The screw motor (540) is connected to the screw conveyor (530) and can provide the necessary rotational power to the screw conveyor (530).

[0062] The dryer (600) may be configured to dry the polymer transferred from the discharge tank (500).

[0063] The condenser (700) can perform the function of condensing the gas stored in the discharge tank (500). For example, the condenser (700) can cool the gas generated during the depolymerization process or condense the gas by compressing it.

[0064] The main motor (800) can perform the role of providing rotational power to cause the disk rotation axis (120) to rotate. The main motor (800) and the reaction unit (100) may be located on the frame (830), and the disk rotation axis (120) of the main motor (800) and the reaction unit (100) may exchange rotational power through a rotating belt (820) located within the frame (830), but are not limited thereto. Since the main motor (800) can perform the primary role of rotating the disk (130) in the 'heat generation step' described later, it will be explained in detail in the 'heat generation step'.

[0065] The above depolymerization reactor (10) may be a closed type, and the inside of the depolymerization reactor (10) may be replaced with nitrogen (N2) to suppress side reactions after the raw material is introduced, and the reaction may proceed in a nitrogen (N2) atmosphere for the entire process time. That is, after the step of introducing the polyester raw material into the depolymerization reactor (10), and before the step of generating heat by rotating the disk (130) located inside the reaction section (100) of the depolymerization reactor (10) described later, the process may further include a step of replacing the inside of the depolymerization reactor with nitrogen (N2) to suppress side reactions. The step of replacing the inside of the depolymerization reactor with nitrogen may be carried out by supplying nitrogen into the inside of the reaction section body (110) through a nitrogen supply device (400) to replace the inside with nitrogen. That is, the inside of the reaction section body (110) can maintain a nitrogen atmosphere by means of the nitrogen supply device (400).

[0066] heat generation stage

[0067] Next, heat is generated by rotating a disk (130) located inside the reaction section (100) of the depolymerization reactor (10). Inside the reaction section (100), a reaction can occur in which a polymer polyester is depolymerized into a dibasic acid and an alkylene glycol.

[0068] A mechanochemical depolymerization method of polyester according to one embodiment may have the best grinding efficiency when using a depolymerization reactor comprising a reaction part having a specific structure, and furthermore, grinding heat, frictional heat, or a combination thereof can be generated more easily.

[0069] FIG. 2 is a drawing for specifically explaining the reaction section of a depolymerization reactor according to one embodiment. The reaction section of the depolymerization reactor used in the mechanochemical depolymerization method of polyester according to one embodiment is not limited to the configuration shown in FIG. 2 and the configuration described below, provided that heat can be generated by rotating a disk.

[0070] The reaction unit (100) may include a disk (130) located within the reaction unit body (110), a disk rotation axis (120) connected to the center of the disk (130), one or more blade support members (140) located on the disk, and one or more blade members (150) supported by the one or more blade support members (140).

[0071] The rotation of the disk (130) placed inside the reaction unit (100) can be achieved by transmitting rotational power generated from a rotational power generating device, such as a main motor (800), through the disk rotation shaft (120).

[0072] Inside the reaction section (100), as the disk (130) rotates, the blade support (140) and the blade section (150) can also rotate together, and the polyester raw materials supplied to the reaction section body (110) generate crushing heat through the crushing of the polyester, and frictional heat can be generated through friction between the polyester and the inner wall of the depolymerization reactor. For example, the heat may include crushing heat generated by the crushing of the polyester raw materials, frictional heat generated by friction between the polyester raw materials and the depolymerization reactor, or both.

[0073] A blade support (140) may be positioned on the disc (130). Additionally, a plurality of blade sections (150) may be arranged on the blade support (140). The plurality of blade sections (150) may be arranged at different heights due to the step difference of the blade support (140). The disc (130), the blade support (140), and the blade section (150) may be positioned at a certain distance from the inner side wall of the reaction body (110). Furthermore, the disc (130) may be positioned at a certain distance from the inner bottom of the reaction body (110).

[0074] The total radial length (L1) of the blade portion (150) may be shorter than the radius (R) of the disk (130). For example, the total radial length (L1) of the blade portion (150) may be 30% to 70% of the radius (R) of the disk (130). Additionally, the total radial length (L1) of the blade portion (150) may be 40% to 60% of the radius (R) of the disk (130), and for example, 50%.

[0075] When the configuration of the reaction unit (100) constituting the depolymerization reactor (10) according to one embodiment is controlled as described above, the heat, particularly frictional heat, can be generated very easily, so that the polyester can ultimately be decomposed with very high efficiency.

[0076] As such, the mechanochemical depolymerization method of polyester can proceed as a solvent-free reaction without adding a large amount of solvent, as the polyester is crushed and the heat generated therefrom is used to depolymerize the polyester, and can be carried out without applying additional heat from the outside other than the heat generated internally. For example, the mechanochemical depolymerization method of polyester can be carried out without adding a solvent such as water or ethylene glycol.

[0077] Furthermore, the mechanochemical depolymerization method for polyester does not require separate heat control, the addition of large amounts of solvent to increase reaction uniformity, or a separate heat source. This results in a simple equipment configuration and low investment costs, and is also environmentally advantageous as there is no separate treatment or disposal of solvents. Additionally, the dibasic acid produced by depolymerization can be obtained as a salt in the form of paste, powder, or pellets, which reduces volume and facilitates storage and transportation.

[0078] In order to generate crushing heat and frictional heat, the rotational speed of the disk (130) located inside the reaction section (100) in the depolymerization reactor (10) can be appropriately adjusted. In the step of generating heat, the rotational speed of the disk (130) may be 500 rpm to 5000 rpm, for example, 700 rpm to 3000 rpm, or 1000 rpm to 2000 rpm. In the step of generating heat, if the rotational speed of the disk (130) located inside the reaction section (100) in the depolymerization reactor is less than 500 rpm, crushing is not effective, so the generation of heat by crushing and heat by friction may be insufficient, and if the rotational speed of the disk (130) located inside the reaction section (100) in the depolymerization reactor is more than 5000 rpm, the generation of heat by crushing and friction may be excessive.

[0079] In the step of generating heat, the temperature inside the reaction section (100) of the depolymerization reactor (10) can be raised to an appropriate range due to the heat (crushing heat, frictional heat, or a combination thereof) generated by the rotation of the disk (130). For example, the internal temperature of the reaction section (100) may be 130°C to 300°C. If the internal temperature of the reaction section (100) is less than 130°C, the depolymerization efficiency may be reduced, and if the internal temperature of the reaction section (100) exceeds 300°C, depolymerization by-products may be generated. In addition, according to the mechanochemical depolymerization method of polyester according to one embodiment, the decomposition agent is not introduced before generating heat inside the reaction section (100), but is introduced after generating heat as described below, thereby raising the internal temperature of the reaction section (100) to the above range.

[0080] Step of depolymerizing polyester by adding a decomposition agent

[0081] Next, a decomposition agent is introduced into the depolymerization reactor (10) to depolymerize the polyester. In the mechanochemical depolymerization method of polyester according to one embodiment, since the polyester is depolymerized in the presence of a decomposition agent by using the heat generated therefrom to crush the polyester, there is no need to additionally perform washing, crushing, shredding, cutting, or processing (flaking, popcorning) processes to feed waste collected from industry or general households into a chemical process, and all waste of various forms can be used as feedstock.

[0082] The decomposition agent is introduced into the decomposition reactor (10) after generating heat through grinding heat, frictional heat, or a combination thereof by rotating the disk (130) so that the internal temperature of the reaction section (100) in the decomposition reactor (10) satisfies the above range. In one embodiment, the mechanochemical decomposition method of polyester can further increase the decomposition rate of the polyester raw material by proceeding in the order of introducing the decomposition agent first and then rotating the disk (130) to generate heat, rather than proceeding in the order of rotating the disk (130) to generate heat and raising the temperature so that the internal temperature of the reaction section (100) satisfies the above range, and then introducing the decomposition agent into the decomposition reactor.

[0083] Before introducing a decomposition agent into the depolymerization reactor (10), the rotation speed of the disk (130) can be adjusted according to the internal temperature of the reaction section (100). For example, if the internal temperature of the reaction section (100) is 220°C or higher, or between 220°C and 300°C, the decomposition agent can be introduced directly into the depolymerization reactor without adjusting the rotation speed of the disk (130). Meanwhile, if the internal temperature of the reaction section (100) is less than 220°C, between 130°C and 200°C, between 130°C and 180°C, or between 130°C and 160°C, the rotation speed of the disk (130) can be adjusted before introducing the decomposition agent into the depolymerization reactor, and at this time, the step of adjusting the rotation speed of the disk (130) to 500 rpm or less may be further included.

[0084] The above steps may be carried out by introducing a decomposition agent into a decomposition agent injection device (300) and supplying the decomposition agent from the decomposition agent injection device (300) to the reaction unit (100). In this case, the decomposition agent may be supplied in the form of spray injection or direct injection through a nozzle, etc., separately provided inside the main body (110) of the reaction unit, but is not limited thereto. A pump (310) may be used to supply the decomposition agent from the decomposition agent injection device (300) to the reaction unit (100).

[0085] The above-mentioned decomposition agent may include alkalis, acids, salts thereof, monoalcohols, polyalcohols, or mixtures thereof. Additionally, as described above, when the mechanochemical depolymerization of polyester proceeds as a solvent-free reaction, the above-mentioned decomposition agent may be introduced in a solid state or an aqueous solution state.

[0086] For example, the alkali may include hydroxides of alkali metals or alkaline earth metals, ammonia, or a mixture thereof. Here, the alkali metal may be a monovalent metal such as lithium, sodium, potassium, rubidium, or cesium, among which relatively inexpensive sodium or potassium may be used. The alkaline earth metal may be beryllium, magnesium, calcium, strontium, barium, radium, etc. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, or lithium hydroxide. Among these, sodium hydroxide exhibits excellent reaction speed and reaction rate when used in combination with ethylene glycol, etc.

[0087] The acid may be an organic acid or an inorganic acid, and may include, for example, hydrochloric acid, nitric acid, sulfuric acid, carbonic acid, phosphoric acid, acetic acid, hypochlorous acid (HClO), or a mixture thereof.

[0088] The salt may include inorganic salts such as carbonates, bicarbonates, phosphates, sulfates, sulfites, nitrates, silicates, and hypochlorites, organic salts such as formates, acetates, citrates, and oxalates, or mixtures thereof, and may include, for example, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, tripotassium phosphate (hydrate), sodium hypochlorite, or mixtures thereof.

[0089] Polyhydric alcohols may include ethylene glycol, n-propylene glycol, isopropylene glycol, diethylene glycol, polyethylene glycol, triethylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, glycerin, benzyl alcohol, polypropylene glycol, pentaerythritol, trimethylenepropane, or mixtures thereof. Among these polyhydric alcohols, ethylene glycol, n-propylene glycol, isopropylene glycol, diethylene glycol, polyethylene glycol, triethylene glycol, or glycerin, which have high boiling points and relatively high reactivity, may be used.

[0090] Monoalcohols may include methanol, ethanol, propanol, butanol, or mixtures thereof, and alkyl ether compounds of polyhydric alcohols such as the diols or triols exemplified above, such as diethylene glycol monomethyl ether, benzyl alcohol, or 2-ethylhexanol.

[0091] Since the decomposition agent reacts with both the polyester and the dye, the amount of decomposition agent added can be 0.75 to 3 moles per 1 mole of dibasic acid contained in the polyester, for example, in the case of a monovalent decomposition agent (e.g., sodium hydroxide), it can be added in the amount of 1.5 to 3 moles, and in the case of a divalent decomposition agent (e.g., calcium carbonate), it can be added in the amount of 0.75 to 1.5 moles.

[0092] For example, when depolymerizing polyester, more specifically polyethylene terephthalate, using sodium hydroxide as the decomposition agent, the reaction equation is as shown in Reaction Equation 1 below, and 2 moles of NaOH (420 g) per mole of TPA is required to decompose 1 kg of polyethylene terephthalate (PET).

[0093] [Reaction Equation 1]

[0094] PET + 2NaOH → TPA salt + EG

[0095] In the above reaction scheme 1, PET is polyethylene terephthalate, NaOH is sodium hydroxide, TPA salt is sodium terephthalate, and EG is ethylene glycol.

[0096] In addition, when the polyester raw material introduced into the depolymerization reactor (10) is a fiber, the amount of dye introduced during processing varies from 0.5% by weight to 20% by weight (based on the weight of fabric (owf)) of the weight of the polyester fiber, so the amount of decomposition agent introduced may be 2 moles or more per 1 mole of dibasic acid contained in the polyester so that both the dye and the polyester fiber can be decomposed.

[0097] The above depolymerization can be carried out for 5 to 120 minutes, for example, 5 to 60 minutes, or 10 to 40 minutes. The depolymerization reaction time can be increased within the range of 120 minutes as the concentration of impurities including the dye of the polyester increases, as the throughput of the polyester increases, and as the temperature inside the reaction section (100) in the depolymerization reactor (10) decreases.

[0098] Meanwhile, in the above depolymerization process, the generated alkylene glycol and water can be separated and recovered by vaporizing them using the generated heat. The mechanochemical depolymerization method of polyester can proceed as a solvent-free reaction by crushing the polyester and depolymerizing the polyester using the heat generated therefrom. Since the internal temperature of the reaction section (100) in the depolymerization reactor (10) can reach up to 300°C due to the crushing heat, frictional heat, or a combination thereof generated during the depolymerization process, the generated alkylene glycol and water can be separated and recovered by vaporizing them. In a method of mechanochemical depolymerization of polyester according to one embodiment, since a decomposition agent is introduced after generating heat including crushing heat, frictional heat, or a combination thereof by rotating a disk (130), the internal temperature of the reaction section (100) in the depolymerization reactor (10) can be raised higher than in the case where heat is generated by crushing the polyester with the decomposition agent introduced beforehand, and as a result, the products, alkylene glycol and water, can be vaporized and recovered without receiving heat from the outside.

[0099] Meanwhile, the conventional alkali hydrolysis depolymerization method involves introducing a large amount of depolymerization solvent and depolymerizing polyester in a high-temperature reactor. In this case, a separate process is required to separate the liquid alkylene glycol and the solid dibasic acid salt from the depolymerization product obtained during depolymerization, and a large amount of energy is consumed because the depolymerization solvent and polyester must be raised to the reaction temperature. Additionally, although the used depolymerization solvent can be separated from the product and reused, this requires a separate purification process, which incurs high costs. Furthermore, there is a problem in that it is difficult to control impurities because by-products are added depending on the type of depolymerization solvent used.

[0100] However, according to a mechanochemical depolymerization method of a polyester according to one embodiment, alkylene glycol that can be recovered during the depolymerization process can be recovered by vaporizing 0% or more, or 100% or less, for example, 30% to 95%, or 50% to 98% by weight, relative to 100% by weight of alkylene glycol recoverable during the depolymerization process. When the content of alkylene glycol that can be recovered by vaporizing during depolymerization is 0% by weight, a separate process for separation before dissolution is required because the alkylene glycol is discharged mixed with the dibasic acid; however, when the content of alkylene glycol that can be recovered by vaporizing during depolymerization is 100% by weight, the alkylene glycol is not mixed with the generated dibasic acid, so the dibasic acid can be dissolved immediately and the next process can proceed.

[0101] The above depolymerization reactor (10) may further include an outlet for discharging vaporized alkylene glycol and water. The vaporized alkylene glycol and water may be under atmospheric pressure conditions, and nitrogen (N2) may be introduced to liquefy the alkylene glycol and water in a condenser as a gas flow and recover them. Afterward, they may be cooled to near room temperature under a nitrogen (N2) atmosphere.

[0102] Among the products resulting from the depolymerization reaction, the alkylene glycol is separated, and the remaining dibasic acid can be obtained in the form of a solid salt.

[0103] However, depending on the rotational speed of the disk (130), the alkylene glycol may not be recovered at all or may be recovered only partially, and in this case, the depolymerization product may contain a mixture of the dibasic acid salt and the remaining alkylene glycol. As an example, the mechanochemical depolymerization method of polyester may optionally further include a process of separating the alkylene glycol and the dibasic acid salt from the depolymerization product and then recovering the alkylene glycol. As an example, the method of separating the alkylene glycol and the dibasic acid salt produced by the depolymerization reaction is not specifically limited, and a known method may be selected depending on the target compound, and separation may be performed, for example, by distillation concentration. As a means for distillation concentration, all conventional distillation concentration devices, such as a vacuum continuous distillation device or a vacuum batch distillation device, may be used. Subsequently, the dibasic acid salt in a solid state can be obtained through a drying process.

[0104] In addition, depending on the type of decomposition agent used during depolymerization, it can be divided into hydrolysis using alkali, alcohollysis using alcohol, and glycolysis using glycol, and the type of dibasic acid obtained varies accordingly.

[0105] When depolymerizing polyester using the glycolysis method, the resulting product may vary depending on the type of decomposition agent used in the depolymerization reaction. For example, when polyethylene terephthalate is depolymerized using ethylene glycol as the decomposition agent, bis(β-hydroxyethyl) terephthalate (BHET) can be obtained as the monomer, and when depolymerization is performed using propylene glycol as the decomposition agent, bis(β-hydroxyethyl isopropyl) terephthalate (BHEPT) can be obtained as the monomer.

[0106] In addition, when benzyl alcohol and tripotassium phosphate are used as decomposition agents, the ester compounds of the obtained oligomers have very good solubility in chloroform, etc., so they can be efficiently recovered using solvent extraction. Alternatively, dibasic acids or oligomer ester compounds can be recovered using means such as filtration or distillation.

[0107] In this way, the obtained ester compound of the dibasic acid or oligomer (e.g., BHET) can also be recovered as a methyl ester of the dibasic acid or oligomer (e.g., DMT) by performing an ester exchange reaction with methanol. Known methods can be appropriately used for the ester exchange reaction, for example, by performing an ester exchange reaction between a depolymerization reaction concentrate and methanol at 65°C to 85°C for 0.5 to 5 hours in the presence of an ester exchange reaction catalyst (such as an alkali metal compound), a slurry in which solid DMT is dispersed in a mixture of methanol and alkylene glycol can be obtained. Additionally, purified DMT can be recovered by separating the cake containing DMT using a solid-liquid separation device or the like and performing distillation purification.

[0108] Meanwhile, when depolymerizing polyester using the hydrolysis method, dibasic acid salts such as dibasic acids or dialkali metal salts of oligomers may be produced, and these products may vary depending on the type of alkali metal used in the depolymerization reaction. For example, when polyethylene terephthalate is depolymerized using sodium hydroxide as a decomposition agent, sodium terephthalate is produced along with ethylene glycol.

[0109] Among these, dibasic acid salts (e.g., sodium terephthalate) do not dissolve in alkylene glycol and form solid crystals, so they can be easily separated from the solvent by filtration methods such as solid-liquid separation. In addition, alcohols attached to the obtained powdered crystals can be removed by washing with alcohols such as methanol or ethanol.

[0110] Salt can be collected and recovered at room temperature from the discharge tank (500) of the above depolymerization reactor (10). Here, room temperature may refer to a temperature range of 20°C to 30°C. Subsequently, the crystals of the dibasic acid salt are dissolved in water, and then an acid is mixed to neutralize the reaction, thereby precipitating a dibasic acid (e.g., terephthalic acid). The precipitated dibasic acid can be recovered by separating the solid from the liquid using methods such as centrifugal separation.

[0111] The amount of water added during the recovery process may be 300 to 1,000 parts by weight per 100 parts by weight of the dibasic acid salt. The amount of acid supplied to separate the dibasic acid may be equimolar or greater with respect to the alkali metal contained in the dibasic acid salt. The type of acid used may be an inorganic acid such as hydrochloric acid, sulfuric acid, or phosphoric acid, which is a strong acid with a pH of 2, or an organic acid such as formic acid, acetic acid, or oxalic acid. Among these, inorganic acids, particularly hydrochloric acid or sulfuric acid, are suitable as they can reduce impurities in the monomers produced. The neutralization reaction temperature may be 20°C to 85°C, and the neutralization reaction can typically be completed within 10 minutes to 5 hours.

[0112] Meanwhile, the mechanochemical depolymerization method of polyester may optionally further include a step of removing impurities contained in the polyester molded product or waste, etc., in an aqueous solution of a dibasic acid salt.

[0113] The means for removing impurities are not particularly limited, and any appropriate techniques or devices may be utilized. For example, solid components such as resins other than polyester (polyethylene, polypropylene, polyvinyl chloride, etc.) remaining in an unreacted state, and decomposers such as undissolved alkali metals, can be removed using a mesh. Additionally, since dyes, fillers, etc., cannot be removed by a mesh, they can be removed by centrifugation or filtration using adsorbents such as activated carbon.

[0114] In addition, since the obtained dibasic acid crystals exhibit a particle size distribution characteristic of several µm to several hundred µm, the method may optionally include an additional step of recrystallizing the dibasic acid crystals to a commercially viable particle size (100 µm or more). The recrystallization method is not particularly limited and, for example, can be carried out under high temperature and high pressure conditions after mixing the dibasic acid crystals with water.

[0115] The dibasic acid and alkylene glycol obtained by the mechanochemical depolymerization method of polyester can be recycled as monomers for polymerizing recycled polyester. Specifically, recycled polyester can be produced by esterifying and polycondensing the depolymerized polyester containing the dibasic acid and alkylene glycol obtained by the mechanochemical depolymerization method of polyester.

[0116] Esterification involves reacting the recovered monomer, a dibasic acid, with an alkylene glycol, for example, terephthalic acid and ethylene glycol. This reaction can proceed without a catalyst, but it may also be carried out in the presence of catalysts well known as transesterification catalysts, such as alkaline earth metal compounds like magnesium and calcium, or metal compounds like titanium, zinc, and manganese.

[0117] Subsequently, a recycled polyester resin can be produced by polycondensing the product of the esterification process. At this time, both dissolution polymerization and solid-state polymerization can be used.

[0118] In addition, for quality control after solid-state polymerization, a compound that promotes water treatment and / or crystallization may be added as needed, and a polycondensation catalyst or stabilizer may be added at the start or during the polycondensation process.

[0119] Here, water treatment can be performed by contacting the recycled polyester resin, manufactured in the form of solid particles, with, for example, water, steam, a steam-containing inert gas, steam-containing air, etc. Compounds that promote crystallization may include, for example, polyhexamethylene terephthalate, inorganic compounds, higher aliphatic compounds, polyether compounds, polyolefin-based thermoplastic resins such as polypropylene and polyethylene, and these compounds may be added to the recycled polyester resin in an amount of 1 ppm to 100 ppm.

[0120] Compounds such as germanium, antimony, titanium, and aluminum can be used as polycondensation catalysts. The amount of polycondensation catalyst added can be 2 ppm to 800 ppm as the weight of the catalyst metal element relative to the total weight of the dibasic acid component, and, for example, 4 ppm to 500 ppm.

[0121] In addition, recycled polyester may include phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, triphenyl phosphate, and triethyl phosphonoacetate; phosphoric acid esters such as triphenyl phosphite and trisdodecyl phosphite; methyl acid phosphate, dibutyl phosphate, monobutyl phosphate; phosphoric acid, phosphoric acid, hypophosphoric acid, and polyphosphoric acid as stabilizers. The amount of stabilizer added may be 1,000 ppm or less as the weight of the phosphorus element in the stabilizer relative to the total weight of the recycled polyester, for example, 500 ppm or less, or 300 ppm or less.

[0122] Meanwhile, as described above, since the mechanochemical depolymerization method of polyester according to one embodiment depolymerizes the polyester using heat generated by grinding the polyester at the same time, the color of the recycled polyester produced using the dibasic acid and alkylene glycol obtained by this method may have an L value of 70 or higher, for example, 75 or higher, or 80 to 95.

[0123] The L, a, and b color system is internationally used as a standard for evaluating the color of polyester. These color values ​​are one of the color systems designed to standardize color measurement and describe recognizable colors and color differences. In this system, L is the lightness factor, while a and b are color measurements. Specifically, the L value represents a numerical factor indicating brightness and is a very important figure in the manufacturing of fibers, fabrics, or clothing. Additionally, a positive b value indicates yellowing and a negative b value indicates blueing, while a positive a value indicates reddish discoloration and a negative a value indicates greenish discoloration.

[0124] The values ​​of L, a, and b are defined in Korean Industrial Standards (KS) related to color measurement, such as KS A 0061, 0063, 0064, 0065, 0066, 0067, 0084, 0085, 0089, 0114, etc. For example, the values ​​of L, a, and b can be determined by removing moisture from 50 g of polyester resin to be measured in the air, placing it in a colorimeter model SA-2000, measuring the color 10 times, and setting the average value as the standard value.

[0125] The L value of recycled polyester is related to the purity of the recycled dibasic acid and alkylene glycol. For example, the L value decreases as the amount of internal impurities or matting agents such as titanium dioxide (TiO2) increases. If the L value is less than 70, the impurity content is too high, which may result in a colored appearance after polymerization and fiber formation or cause many side reactions during polymerization, making it unsuitable for use as a high-value-added material; furthermore, since its primary application is the same as that of mechanically recycled polyester, it may be meaningless. On the other hand, if the L value exceeds 95, the material exhibits properties that are difficult to achieve even with existing virgin materials. Achieving this value through recycling may result in reduced economic feasibility due to increased unit production volume and process costs, such as the need for additional decolorization and purification processes or increased residence time.

[0126] Hereinafter, embodiments are described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0127]

[0128] [Preparation Example: Depolymer of Polyester]

[0129] Example 1

[0130] 3.6 kg of waste polyethylene terephthalate (waste PET) was fed into a depolymerization reactor as a raw material.

[0131] After the raw materials were added, the inside of the depolymerization reactor was replaced with nitrogen (N2) to suppress side reactions, and the reaction was carried out in a nitrogen (N2) atmosphere for the entire process time.

[0132] The disk of the depolymerization reactor was rotated at 1500 rpm to generate heat through grinding and friction caused by the rotation of the disk, and then the rotation speed of the disk was lowered to 500 rpm.

[0133] Waste polyethylene terephthalate (waste PET) was depolymerized into terephthalic acid (TPA) salt and ethylene glycol (EG) by uniformly injecting 3 kg of a 50% sodium hydroxide aqueous solution (aq) by spraying while rotating the disk at 500 rpm.

[0134] After the reaction was completed, the polyester was naturally cooled to room temperature (25°C) under a nitrogen (N2) atmosphere to obtain a depolymerized polyester inside the depolymerization reactor.

[0135]

[0136] Example 2

[0137] 3.6 kg of waste polyethylene terephthalate (waste PET) was fed into a depolymerization reactor as a raw material.

[0138] After the raw materials were added, the inside of the depolymerization reactor was replaced with nitrogen (N2) to suppress side reactions, and the reaction was carried out in a nitrogen (N2) atmosphere for the entire process time.

[0139] After generating heat through crushing and friction caused by the rotation of the disc of the depolymerization reactor by rotating the disc at 1500 rpm, 3 kg of a 50% aqueous sodium hydroxide solution (aq) was uniformly injected by a spray method while rotating the disc to depolymerize waste polyethylene terephthalate (waste PET) into terephthalic acid (TPA) salt and ethylene glycol (EG).

[0140] At the same time, ethylene glycol (EG) and water (H2O) were vaporized and recovered using heat generated by grinding and friction.

[0141] The vaporized ethylene glycol (EG) was at atmospheric pressure, and nitrogen (N2) was introduced during the process to liquefy the ethylene glycol (EG) and water (H2O) in a condenser using a gas flow and recover them.

[0142] After recovering ethylene glycol (EG) and water (H2O), the polyester depolymer was obtained by naturally cooling to (25°C) under a nitrogen (N2) atmosphere.

[0143]

[0144] Comparative Example 1

[0145] 3.6 kg of waste polyethylene terephthalate (waste PET) and 1.5 kg of 98% solid sodium hydroxide as an alkali catalyst were dissolved in 21.6 kg of ethylene glycol (EG) and fed into a high-temperature, high-pressure reactor.

[0146] After the raw materials were introduced, the inside of the reactor was replaced with nitrogen (N2) to suppress side reactions, and the reaction was carried out in a nitrogen (N2) atmosphere for the entire process time.

[0147] The disc of the reactor was rotated at 1500 rpm, and the temperature was raised to 180°C by heat generated by grinding and friction caused by the rotation of the disc, and then the depolymerization reaction was carried out at 180°C for 30 minutes.

[0148] After the reaction was completed, the polyester depolymer was obtained from the reactor by naturally cooling to room temperature (25°C) under a nitrogen (N2) atmosphere.

[0149]

[0150] Test Example 1: Quantitative Analysis

[0151] Quantitative analysis was performed using the depolymers of the polyesters of Examples 1 and 2 and Comparative Example 1.

[0152] (1) Measure conversion rate

[0153] 15g of each was taken from the depolymerization of the polyesters of Examples 1 and 2 and Comparative Example 1, completely dissolved in 135g of water, and then the undegraded solid PET (undegraded PET) was removed by filtration. Afterward, the solution from which the undegraded PET had been removed was titrated with 1N sulfuric acid as a standard solution using a potentiometric titrator, and the pH graph was observed.

[0154] In the pH graph, the acid consumption was calculated based on the inflection points where all residual NaOH is neutralized (approx. pH 7) and where TPA-salt is precipitated as TPA (approx. pH 3). Accordingly, 'V1' was defined as the volume of sulfuric acid consumed for the neutralization of residual NaOH and 'V2-V1' as the volume of sulfuric acid consumed for the precipitation of TPA salt, and the actual quantitative values ​​of TPA salt and NaOH were calculated based on each.

[0155] The number of moles consumed was calculated by applying the molar concentration, density, and molecular weight of 1N sulfuric acid to the acid consumption amount, and based on this, the actual masses of NaOH (39.9 g / mol) and TPA salt (210.1 g / mol) were calculated, respectively. By substituting these values ​​into Equations 1 and 2 below, the unknown PET input amount was inversely calculated, and then the conversion rate was calculated by substituting the PET input amount back into the equations.

[0156] [Equation 1]

[0157] Conversion Rate = Mass of TPA Salt (g) ÷ [(Amount of PET Input ÷ Molecular Weight of PET (192.17 g / mol)) × Molecular Weight of TPA Salt]

[0158] [Equation 2]

[0159] Conversion Rate = 1 - [Mass of NaOH (g) ÷ {(Amount of PET Added ÷ Molecular Weight of PET) × Molecular Weight of NaOH × 2 mol}]

[0160] The PET input amount was inversely calculated by setting the equations 1 and 2 above to match, and the conversion rate was calculated from the corresponding value. Each sample was repeated three times to calculate the average value, and the results are shown in Table 1 below. In addition, based on the conversion rate and the calculated PET input amount, the content of TPA-salt, unreacted NaOH, and undegraded PET in the 15g sample was inversely calculated.

[0161] (2) Analysis of EG and DEG content

[0162] 0.3 g of each sample was placed in a 50 mL conical tube and dissolved and diluted in 3 g of methanol. At this time, TPA-salt and undegraded PET were not dissolved in methanol, and only EG and DEG were extracted. Each sample was sealed and sonicated for 15 minutes, after which fine particles were removed using a syringe filter, and the filtrate was analyzed by gas chromatography-mass spectrometry (GC-MS). Quantitative curves were constructed based on the integral values ​​of the EG and DEG peaks and sample concentrations, and based on this, the EG and DEG content (wt%) in the samples was calculated and is shown in Table 2.

[0163] (3) Analysis of water content

[0164] 0.1 g of the depolymerized polyesters of Examples 1 and 2 and Comparative Example 1 were taken, aliquoted into Karl Fischer vials, and heated to 160°C using a Karl Fischer Thermoprep instrument to release moisture. The released moisture was quantified by the Karl Fischer Coulometric Titration method to analyze the moisture content (weight%) in the samples. The results are shown in Table 2 below.

[0165] (4) Calculation of final content

[0166] Through the above analysis, TPA-salt, unreacted NaOH, and undegraded PET were indirectly calculated from the conversion rate calculation results, while EG, DEG, and moisture were calculated based on their respective direct analysis results. By synthesizing these results, the composition was organized so that the sum of the components in the depolymerization salt was 100 wt%, and the results are shown in Table 2.

[0167] (Unit: %) Example 1 Example 2 Comparative Example 1 Conversion Rate 96.59896

[0168] (Unit: weight%) Example 1 Example 2 Comparative Example 1 TPA-salt 699 5.9 3 3.1 EG 20.4 1.5 6 4.4 DEG 0.6 0 1.6 H2O 6.7 00 Undecomposed PET 2.3 1.8 0.6 Unreacted NaOH 1.0 0.8 0.3 Discharged salt (= Depolymerization of polyester) 100 100 100

[0169] Referring to Tables 1 and 2 above, it can be seen that although Examples 1 and 2 produce depolymers of polyester without adding a solvent, they have a higher conversion rate than the depolymer of polyester of Comparative Example 1 produced according to the conventional method of adding a solvent, and at the same time, the content of EG in the discharged salt is significantly reduced compared to the Comparative Example. Furthermore, unlike the prior art, the examples according to the present invention do not require an additional process for removing the solvent, so they are environmentally friendly, offer process advantages, and have excellent energy efficiency.

[0170] Although embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims also fall within the scope of the present invention.

[0171] [Explanation of the symbol]

[0172] 10: Depolymerization reactor

[0173] 100: Reaction part

[0174] 110: Reactor body

[0175] 120: Disk rotation axis

[0176] 130: Disk

[0177] 140: Blade support

[0178] 150: Blade part

[0179] 151: Blade

[0180] 200: Raw material input device

[0181] 300: Decomposer injection device

[0182] 310: Pump

[0183] 400: Nitrogen supply unit

[0184] 500: Discharge tank

[0185] 510: Discharge pipe

[0186] 520: Exhaust pipe

[0187] 530: Screw conveyor

[0188] 540: Screw motor

[0189] 600: Dryer

[0190] 700: Condenser

[0191] 800: Main motor

[0192] 810: Motor rotating shaft

[0193] 820: Rotating belt

[0194] 830: Frame

Claims

0% to 10% by weight of undegraded polyester; 60% to 99% by weight of dibasic acid; 1% to 25% by weight of alkylene glycol; and Containing 0 to 15 weight% of unreacted decomposition agents, impurities, or a combination thereof, Polyester depolymer. In paragraph 1, The depolymer of the above polyester comprises the above dibasic acid and the above alkylene glycol in a weight ratio of 2:1 to 100:1, Polyester depolymer. In paragraph 1, The depolymer of the polyester comprises the alkylene glycol and the undegraded polyester in a weight ratio of 10:1 to 1:

5. Polyester depolymer. In paragraph 1, The depolymer of the above polyester is in the form of a powder, Polyester depolymer. In paragraph 1, The above dibasic acid includes an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid, and Polyester depolymer. In paragraph 1, The above alkylene glycol comprises ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, polytetramethylene glycol, 1,4-cyclohexanediol, 1,4-benzenediol, or a combination thereof. Polyester depolymer. In paragraph 6, The above alkylene glycol includes ethylene glycol, diethylene glycol, or a combination thereof, and The above diethylene glycol is included in an amount of 0% to 5% by weight relative to 100% by weight of the depolymerization of polyester, Polyester depolymer. In Paragraph 7, The depolymer of the above polyester comprises the ethylene glycol and the diethylene glycol in a weight ratio of 100:1 to 1:

1. Polyester depolymer. In paragraph 1, The depolymer of the above polyester further contains water, and The above water is included in an amount greater than 0% by weight and less than or equal to 10% by weight with respect to 100% by weight of the depolymerization of polyester, Polyester depolymer. A step of introducing polyester raw materials into a depolymerization reactor; A step of generating heat by rotating a disk located inside the reaction section of the above depolymerization reactor; and A method comprising the step of depolymerizing the polyester by introducing a decomposition agent into the above depolymerization reactor. Mechanochemical depolymerization method of polyester. In Paragraph 10, The above depolymerization reactor is a closed type, Mechanochemical depolymerization method of polyester. In Paragraph 10, The above reaction unit is, A disk located within the main body of the above reaction unit, A disk rotation axis connected to the center of the above disk, One or more blade supports located on the above-mentioned disk, and It includes one or more blade portions supported by one or more blade portion supports, and The total radial length (L1) of the one or more blade portions is 30% to 70% of the radius (R) of the disk, Mechanochemical depolymerization method of polyester. In Paragraph 10, In the step of generating the heat mentioned above, The heat above includes grinding heat generated by grinding the polyester, frictional heat generated by friction between the polyester and the inner wall of the depolymerization reactor, or both. Mechanochemical depolymerization method of polyester. In Paragraph 10, In the step of generating the heat mentioned above, The rotational speed of the above disk is 500 rpm to 5000 rpm, Mechanochemical depolymerization method of polyester. In Paragraph 10, In the step of generating the heat mentioned above, The internal temperature of the above reaction section is 130 ℃ to 300 ℃, Mechanochemical depolymerization method of polyester. In Paragraph 10, In the step of depolymerizing polyester by introducing a decomposition agent into the above depolymerization reactor, If the internal temperature of the reaction section is less than 220 ℃, the method further includes the step of adjusting the rotation speed of the disk to 500 rpm or less before introducing a decomposition agent into the depolymerization reactor. Mechanochemical depolymerization method of polyester. In Paragraph 10, The above decomposition agent comprises alkali, acid, salts thereof, monoalcohols, polyalcohols, or mixtures thereof, Mechanochemical depolymerization method of polyester. In Paragraph 10, The above decomposition agent is in an aqueous solution or solid state, Mechanochemical depolymerization method of polyester. In Paragraph 10, In the above depolymerization step, Further comprising separating the depolymerized alkylene glycol by vaporizing it using the heat. Mechanochemical depolymerization method of polyester. In Paragraph 10, The above depolymerization is a solvent-free reaction that proceeds without the addition of a solvent, Mechanochemical depolymerization method of polyester.

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