Process for producing terephthalate derivatives by transesterification of dimethyl terephthalate

Abstract

This invention relates to a method for producing terephthalic acid ester derivatives using dimethyl terephthalate, and more particularly to a method for producing terephthalic acid ester derivatives in high yields using dimethyl terephthalate by means of simple engineering, which improves the efficiency and economy of the process by optimizing the reaction conditions and the catalyst used in the transesterification reaction.

Description

Technical Field

[0001] This invention relates to a transesterification reaction that can produce high-value-added derivatives from dimethyl terephthalate (DMT) by means of a transesterification reaction, in which the functional groups bound to the terephthalate are replaced in other forms, and a method for efficiently depolymerizing polymers containing ester functional groups through the transesterification reaction. In particular, it relates to an efficient conversion method that can produce high-value-added terephthalate derivatives in high yield by using one or more catalysts selected from alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine organic compounds as catalysts in a transesterification reaction using DMT and mono- and / or polyols as raw materials, and performing the transesterification reaction at room temperature (25°C) to below the boiling point of the applicable alcohol. It also relates to a depolymerization reaction engineering method for polymers containing ester functional groups that can be linked to a methanol decomposition reaction to obtain the high-value-added terephthalate derivatives in high yield while improving the engineering efficiency and economy of the transesterification reaction. Background Technology

[0002] Plastic is an inexpensive and durable material used in the production of a wide variety of products due to its ease of molding and processing. Because of these advantages, the consumption of plastics in various industrial and consumer sectors has increased dramatically over the past few decades. However, unmanaged plastic waste is dumped into the environment, causing pollution, and the microplastics that break down into small pieces cycle through ecosystems and accumulate in organisms, ultimately being re-ingested by humans through pathways such as fine dust, drinking water, and food. In particular, more than 50% of plastics are used for single-purpose, single-use applications such as packaging, agricultural films, and disposable consumables, or as short-term products to be discarded within one year of manufacture.

[0003] Most discarded plastics end up randomly in designated landfills or natural habitats where natural purification is difficult, leading to increasingly serious environmental pollution problems. Even naturally degradable or biodegradable plastics may persist for decades depending on local environmental factors such as UV exposure levels, temperature, and the presence or absence of degrading microorganisms.

[0004] To address the issues mentioned above, various research activities are being actively conducted, including the development of new plastic materials with shorter decomposition cycles in their natural state, with the aim of minimizing the accumulation of plastics and their environmental impact from the chemical decomposition of existing petroleum-based plastics to their physical recycling and processing.

[0005] Polymers containing ester functional groups can be monomerized through depolymerization, for which various chemical reaction pathways have been developed. The monomers generated through depolymerization can theoretically possess the same properties as the raw materials used in the initial polymer synthesis. Depolymerization pathways used in the industrial reuse of polyesters include hydrolysis, glycolysis, methanolysis, and ammonolysis, and various chemical depolymerization methods, including composite engineering that leverages the advantages of different processes through combination, are widely used.

[0006] Next, we will describe in more detail the depolymerization methods for the polymers containing ester functional groups listed above. It is known that, in the case of hydrolysis, decomposition can be carried out through various reaction pathways in the presence of acid, base, or metal salt catalysts. For the use of acid as a catalyst, extremely high concentrations of sulfuric acid solution are required to achieve high reaction yields, and there are also disadvantages such as economic issues related to engineering design, operation, and post-processing. For reaction systems using bases and metal salt catalysts, the efficiency is low because the decomposition reaction rate is extremely slow, the product purity is low, and catalyst recovery is difficult.

[0007] Glycolysis is a depolymerization reaction in which a glycol is added as a reactant. One of the most common examples of glycolysis is the production of bis(2-hydroxyethyl) terephthalate (BHET) by adding an excess of ethylene glycol, one of the monomeric raw materials. Because ethylene glycol, a raw material used in the synthesis of polyethylene terephthalate (PET) polymers, is used as a reactant, the product produced through depolymerization will have a chemical structure in which ethylene glycol is already bonded to both ends of the terephthalate ester. This allows for highly favorable reaction kinetics even when only a portion of the raw materials in existing polycondensation processes using terephthalic acid is replaced.

[0008] Furthermore, since the products obtained from glycolysis can be directly used as raw materials for the synthesis of polyethylene terephthalate (PET), it has the advantage of not requiring excessive additional equipment investment; rather, only a portion of the existing PET production line needs to be modified for polymer material manufacturing. Glycolysis is typically performed under reflux conditions with the reactants, i.e., glycols. Because the decomposition step from oligomers to monomers is slow and an equilibrium is reached between compounds even with extended reaction times, the product purity is low, and it is difficult to separate the final product, i.e., monomers, from the reactants with high purity or high yield. Generally, metal salts such as zinc acetate or lithium acetate are used as reaction catalysts. The metal ions constituting these catalysts are not completely removed during purification and remain in the product. Therefore, the recycled monomers may contain small amounts of metals harmful to human health, making it difficult to apply products produced by reprocessing these recycled monomers to reprocessing materials for food, medical, and other consumer goods applications. Furthermore, although glycolysis is carried out at relatively high temperatures, the recovery and purification of the product usually employs recrystallization at lower temperatures. This results in higher energy consumption, higher costs depending on the heat source supply method in the production process, and reduced efficiency.

[0009] Methanol decomposition is a widely used commercial process in the past, applied from global chemical companies to small and medium-sized plastics industries. Theoretically, the final monomer product obtained through this process is dimethyl terephthalate (DMT), and along with the transesterification reaction, ethylene glycol is released in a molar equivalent to the decomposed terephthalate. In actual reactions, due to incomplete methanol decomposition, the equilibrium of the reaction with free ethylene glycol, and side reactions such as hydrolysis, compounds such as 1-(2-Hydroxyethyl)4-methyl terephthalate (HEMT) and monomethyl terephthalate (MMT) may be generated as byproducts. The target compound of the methanol decomposition reaction, dimethyl terephthalate (DMT), can be used as an intermediate feedstock in engineering processes or complex hybrid depolymerization processes (e.g., methanol decomposition-glycolysis) to produce other monomers with higher added value. Furthermore, due to its relatively low boiling point compared to other monomers and the ease of selective control over hydrogenation reactions, it can be used as a gas-phase reactant for producing high-value-added diol monomers (e.g., 1,4-cyclohexanediethanol). Moreover, because it can be easily purified through recrystallization or distillation, it can also be used as a raw material for the polymerization of polyethylene terephthalate (PET) requiring high purity and quality. However, because methanol is used as the reaction solvent, stringent reaction conditions of high temperature and pressure are required. The initial costs may be excessive to equip it with reactors that fully meet the operating environment described above, as well as related high-durability auxiliary equipment. Furthermore, the investment may be high due to the need for additional unit processes for reactant recovery and product purification. As a representative catalyst, depolymerization catalysts commonly used in glycolysis reactions, such as magnesium acetate, cobalt acetate, and lead dioxide, which contain heavy metals, can be used for transesterification. However, the residual metal content in the product may induce problems such as human health hazards and environmental issues.

[0010] While methanol decomposition is widely used alongside hydrolysis or alkaline hydrolysis in the depolymerization of polymers containing ester functional groups, both reactions require significant high-temperature energy. Therefore, performing depolymerization at lower temperatures can lead to longer reaction times and limitations in the quality and quantity of the resulting product. When methanol decomposition is chosen as the reaction pathway for producing the depolymerized monomer, the yield and purity of the monomer product, dimethyl terephthalate (DMT), are significantly affected by the reactivity of the catalyst and the presence of impurities in the reaction. Therefore, to reduce the burden on the product purification process, effective methods for suppressing side reactions and high reactivity are required.

[0011] As prior art, Japanese Patent Publication No. JP1998-287741 (Patent Document 1) discloses a method for efficiently recovering monomethyl terephthalate and alkylene glycols separately by treating waste polyethylene terephthalate (PET) with methanol. Specifically, it describes a technique for recovering dimethyl terephthalate from the alkylene terephthalate polymer by continuously introducing methanol into at least a portion of the polymer in a molten state, while simultaneously generating dimethyl terephthalate (DMT) through a depolymerization reaction of the alkylene terephthalate, using a catalyst such as potassium carbonate at a depolymerization reaction temperature of 200–300°C. However, this patent suffers from problems due to the excessively high depolymerization temperature, resulting in high equipment investment costs and excessive energy consumption in the reaction process.

[0012] Therefore, when depolymerizing polymers containing ester functional groups using methanol decomposition, it may be advantageous to increase the rate of depolymerization without using excessive energy and to produce dimethyl terephthalate (DMT) in high yield by improving reaction selectivity. Moreover, if it can be used as an intermediate to form a continuous transesterification reaction, it is expected to achieve an efficient and economical process that can reduce energy consumption and produce bis(hydroxyethyl) terephthalate (BHET) or other forms of terephthalate derivatives in high yield.

[0013] As an example of the aforementioned reaction, in a transesterification reaction using dimethyl terephthalate (DMT) and ethylene glycol as starting materials and bis(hydroxyethyl) terephthalate (BHET) as the high-value monomer, methyl hydroxyethyl terephthalate (HEMT) can be generated as an intermediate product, in which the methyl terminal groups bound to the terephthalate are partially substituted. Furthermore, a compound in the form of a carboxylic acid functional group bound to the terephthalate can be generated as a byproduct through hydrolysis. To maximally suppress the byproduct pathways described above and to ensure that the 2 molar equivalents of methanol bound to DMT are completely replaced by ethylene glycol, a reaction pathway that promotes each step of the transesterification reaction is designed, and the optimal operating conditions that allow for the dominant generation of bis(hydroxyethyl) terephthalate (BHET) are determined and applied to engineering. It is anticipated that an efficient bis(hydroxyethyl) terephthalate (BHET) manufacturing process can be designed.

[0014] In the non-patent literature “Zn-and Ti-Modified Hydrotalcites for Transesterification of Dimethyl Terephthalate with Ethylene Glycol: Effect of the Metal Oxide and Catalyst Synthesis Method” (Amarsinh L. Jadhav, Radhika S. Malkar, and Ganapati D. Ya, ACS Omega 2020, 5, 2088-2096), an example is reported where, in the transesterification reaction using dimethyl terephthalate (DMT) and ethylene glycol, a composite metal planar structure is modified after introducing zinc and titanium into hydrotalcites, thereby increasing the selectivity of the high-value monomer, diethyl terephthalate (BHET), to 96.1%.

[0015] However, in the prior literature mentioned above, although the transesterification reaction was carried out at a high temperature of 180°C, the conversion rate of dimethyl terephthalate was only less than 70%. Moreover, the purification of diethyl terephthalate (BHET) from the obtained reaction mixture may require a lot of energy. Furthermore, due to the complexity of the catalyst manufacturing process, reproducibility issues may arise. Additionally, the metal introduced into the catalyst may be leached, which may limit its application in commercial engineering in terms of efficiency and economy.

[0016] Therefore, when producing high-value-added terephthalate derivatives via the transesterification reaction of dimethyl terephthalate (DMT), it is crucial to ensure economic efficiency by using low-cost catalysts and simplifying the process while minimizing energy consumption and utilizing environmentally friendly materials with lower toxicity. Furthermore, there is a need to develop an integrated reaction and purification engineering technology that simultaneously improves the conversion rate of DMT and yields terephthalate derivatives in high quantities, thereby enhancing both engineering efficiency and economics. The resulting derivatives can be used as recycled monomers for recycling waste plastics, as additives such as plasticizers, and as polymer raw materials for synthesizing materials in which some or all of the glycols are modified to improve physical properties—all with high application value in various industrial sectors. Summary of the Invention

[0017] Technical issues

[0018] The purpose of this invention is to solve the problems described above by providing a transesterification reaction method that can produce high-value-added monomers in high yield while simplifying the process, namely, a method for producing other forms of terephthalic acid ester derivatives from dimethyl terephthalate (DMT).

[0019] Furthermore, the object of the present invention is to provide a method for expanding and applying the conversion method from dimethyl terephthalate (DMT) to other forms of terephthalic acid derivatives, applicable to the production of terephthalic acid ester derivative products in high yield by using reaction products generated from the depolymerization of polymers containing ester functional groups and mono- and / or polyols as reactants at room temperature (25°C) to below the boiling point of the applicable alcohol. In other words, it is an efficient and economical depolymerization method for producing high-value-added terephthalic acid derivatives from polymer raw materials containing ester functional groups through multiple transesterification reactions.

[0020] Technical solution

[0021] To address the aforementioned issues, the present invention provides a method for producing terephthalic acid ester derivatives from dimethyl terephthalate (DMT), characterized by comprising: (a) a step of carrying out an ester exchange reaction while applying a transport gas stream, after adding a monohydric and / or polyhydric alcohol as a solvent for ester exchange to dimethyl terephthalate, in the presence of one or more catalysts for ester exchange reactions selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine organic compounds; and (b) a step of separating and obtaining the terephthalic acid ester derivatives produced by said reaction.

[0022] In one embodiment of the present invention, the transesterification reaction in step (a) can be carried out in a temperature range between room temperature and the boiling point of the reactants, i.e., the monohydric and / or polyhydric alcohol solvents, and the molar ratio of the catalyst used for the transesterification reaction to each mole of dimethyl terephthalate can be from 0.00005 to 1.0.

[0023] In one embodiment of the present invention, the alcohol in step (a) may be ethylene glycol.

[0024] Furthermore, the present invention provides a method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups, characterized by comprising: (A) a step of depolymerization by introducing an alcohol, a polar aprotic solvent, and potassium carbonate (K2CO3) into the polymer containing ester functional groups; (B) a step of performing an ester exchange reaction while applying a transport gas stream to the depolymerization product obtained by step (A); and (C) a step of separating and obtaining the terephthalic acid ester derivatives produced by the reaction.

[0025] In one embodiment of the present invention, after step (A), a step of separating a portion of the compound from the depolymerization product may be performed. The portion of the compound separated to the outside may include one or more selected from polymers containing unreacted ester functional groups, insoluble catalysts, polar aprotic solvents, and reaction byproducts.

[0026] Furthermore, the polar aprotic solvent in step (A) is an inert solvent that does not participate in the depolymerization reaction of polymers containing ester functional groups and can reduce the solubility of the catalyst in alcohols. The organic compound is a compound with a chain-like and / or cyclic skeletal structure. The organic compound contains one or more of the following elements: halogen, oxygen, and nitrogen. It may be selected from one or more of the following: toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propionitrile, aminopropionitrile, methylaminopropionitrile, iminodipropionitrile, butyronitrile, methylbutenonitrile, butanenitrile, methyl ethyl ether, diethyl ether, ethyl phenyl ether, dimethoxybenzene, trimethoxybenzene, methoxyphenol, tetrahydrofuran, methyltetrahydrofuran, dioxane, chloromethane, dichloromethane, chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, and trichlorobenzene.

[0027] Furthermore, in one embodiment of the present invention, the number of moles of the alcohol and the number of moles of the polar aprotic solvent in step (A), compared to the number of repeating units of the polymer raw material containing ester functional groups, may be in the range of 0.1 to 5,000 times the number of repeating units of the polymer raw material containing ester functional groups.

[0028] Furthermore, in one embodiment of the present invention, prior to performing the transesterification reaction in step (B), as reactants for transesterification, the molar number of mono- and / or polyol reactants; and / or one or more transesterification catalysts selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine organic compounds can be adjusted to a specific range compared to the molar amount of dimethyl terephthalate contained in the depolymerization product, and the methanol recovered in step (C) can be reused as the depolymerization feedstock in step (A).

[0029] Furthermore, in one embodiment of the invention, the number of moles of the catalyst used for the transesterification reaction adjusted in step (B) is 0.00005 to 1.0 times that of each mole of dimethyl terephthalate contained in the depolymerization product.

[0030] Technical effect

[0031] This invention provides a method for obtaining high-value-added terephthalate derivatives from dimethyl terephthalate (DMT) in high yields using a small amount of transesterification catalyst and a simple engineering configuration with low energy consumption. Specifically, it utilizes a method that modifies the reaction equilibrium achievable in a closed system by altering the monomer feedstock, the added mono- and / or polyols, and the methanol free in the transesterification reaction. For example, it provides a method for producing terephthalate derivatives in high yields by selectively venting only methanol to the outside, thereby suppressing methanol decomposition (equivalent to the reverse reaction) and promoting the transesterification reaction (equivalent to the forward reaction).

[0032] As a catalyst prepared in the reactants according to an example of the invention, a catalyst effective for transesterification can be used. This catalyst is designed to induce a transesterification reaction that does not require methanol decomposition or derivative formation, and requires only a trace amount (1 / 1000 to 1 / 10 of the mass of catalyst used in the depolymerization of polymers containing ester functional groups) to achieve sufficient reactivity and maintain selective, efficient transesterification. Therefore, the transesterification reaction can be performed using only all or part of the catalyst remaining in the reaction products discharged from the previously executed methanol decomposition system. The vapor discharged is high-purity methanol equivalent to dimethyl terephthalate (DMT), almost entirely of which can be concentrated / recovered. The recovered methanol can be 100% reused as a reactant in the methanol decomposition reaction for the depolymerization of polymers containing ester functional groups. Therefore, by integrating the methanol reaction and the transesterification reaction for derivative formation, theoretically, a perfect methanol recycling technology can be achieved.

[0033] Furthermore, the present invention can provide a method for producing terephthalic acid ester derivatives in high yield by using dimethyl terephthalate (DMT) obtained from the depolymerization of a polymer containing ester functional groups and ethylene glycol as reaction intermediates. For example, a method can be provided to produce diethyl terephthalate (BHET) by adding ethylene glycol to the generated dimethyl terephthalate (DMT) after producing dimethyl terephthalate (DMT) and ethylene glycol in high yield from a low-temperature methanol decomposition reaction that can be performed in the presence of methanol, a polar solvent, and a transesterification catalyst, thereby ultimately producing the product BHET. In an embodiment of the present invention, when performing the depolymerization of a polymer containing ester functional groups, even without using the high-temperature reaction conditions (190–280°C) of conventional glycolysis, the high-value-added monomer BHET can be produced in high yield. Diethyl terephthalate (BHET) can be selectively produced in high yields by a series of reaction processes at near-room temperature, below or even below the boiling point of methanol, of the applicable diol reactant (e.g., ethylene glycol). This means that low-temperature and low-energy glycolytic depolymerization technology can be achieved.

[0034] According to the method of the present invention, compared with existing high-temperature glycolysis reactions, a relatively low amount of dimer or oligomers can be maintained, thereby obtaining a relatively high concentration of diethyl terephthalate (BHET). At the same time, the temperature of the reactants can be maintained at a temperature similar to the operating range of purification processes used to remove impurities (dimers or oligomers). Moreover, no preheating or cooling process with energy consumption is required during the transfer of reactants; instead, the process is directly used for purification. Therefore, continuous reaction and post-processing processes can be easily achieved while minimizing energy loss.

[0035] The transesterification reaction performed according to the present invention is applicable not only to the manufacture of diethyl terephthalate (BHET) used in the repolymerization of polyethylene terephthalate (PET), but also to the manufacture of recycled monomers or terephthalate derivatives used in the synthesis of many other types of materials. As an example, because the manufactured monomer has a geometrical property different from that of estrogen, it is applicable to materials that can replace phthalate plasticizers known to cause hormonal imbalances in humans. Furthermore, it is applicable to the manufacture of various types of raw materials for improving the properties of plastics. Although polyethylene terephthalate (PET) has excellent thermal and mechanical properties, its low final crystallization temperature and slow crystallization rate make it difficult to achieve injection molding in short cycles, and its applications are relatively limited due to the characteristics described above. Therefore, market demand for polymers with various properties that can be improved according to purpose and application continues to increase. For example, methods to modify a portion of the diol used in copolymerization or polycondensation by introducing new monomers into the diol units of polyethylene terephthalate (PET) and thereby improving the properties of the final product are widely used in industry. As an example, when butanediol is used instead of ethylene glycol in the polycondensation process, polybutylene terephthalate (PBT) materials with excellent injection molding polymer form can be produced due to the flexible chain structure. Furthermore, various forms of polymer materials can be synthesized by introducing different types of diols. That is, according to an example of the invention, when performing the transesterification reaction of dimethyl terephthalate (DMT), various forms of terephthalate derivatives can be easily produced by modifying the reactants of mono- and / or polyols and applying similar reaction conditions. In particular, when using reaction products generated from the methanol decomposition of waste polyethylene terephthalate (PET) as direct raw materials, recycled monomers can be economically manufactured through a very simple and easy reaction engineering process. Moreover, by injecting different raw materials, a variety of high-value-added terephthalate derivatives can be flexibly manufactured, thus forming a variety of upgrading and remanufacturing projects. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating a method for supplying transport gas to the outside of a reactor for discharging methanol generated from the transesterification reaction of dimethyl terephthalate (DMT) according to an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram illustrating an example of an engineering combination according to an embodiment of the present invention for obtaining a product, namely a terephthalate derivative, in high yield by depolymerizing a polymer feedstock containing ester functional groups.

[0038] Figure 3 This is a schematic diagram illustrating an example of the configuration of a test apparatus for performing a transesterification reaction of dimethyl terephthalate (DMT) according to an embodiment of the present invention. Detailed Implementation

[0039] Unless otherwise expressly defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Generally speaking, the nomenclature used in this specification follows nomenclature methods that are well-known and commonly used in the art.

[0040] Throughout this specification, when a part is described as "including" a constituent element, unless otherwise expressly stated to the contrary, it does not mean that other constituent elements are excluded, but rather that other constituent elements may be included.

[0041] The present invention provides an optimal catalyst for obtaining high-value-added terephthalate derivatives in high yield when using dimethyl terephthalate (DMT) as a raw material and adding monomethyl and / or dimethyl alcohol to perform transesterification reaction.

[0042] One aspect of the present invention provides a transesterification reaction method, which, as a catalyst for converting dimethyl terephthalate (DMT) into terephthalic acid ester derivatives in high yield via transesterification reaction, uses one or more selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine organic compounds.

[0043] Furthermore, the present invention provides a transesterification reaction method for producing terephthalic acid ester derivatives derived from dimethyl terephthalate (DMT). When converting dimethyl terephthalate (DMT) into terephthalic acid ester derivatives by means of glycolysis, the terephthalic acid ester derivatives can be obtained in high yield by setting optimal reaction conditions other than the optimal transesterification reaction catalyst.

[0044] The method of the present invention comprises: (a) after adding a monohydric and / or polyhydric alcohol as a reactant for transesterification to dimethyl terephthalate (DMT), performing a transesterification reaction while applying a gas stream in the presence of one or more transesterification reaction catalysts selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides and guanidine organic compounds; and (b) separating and obtaining the terephthalate derivative produced by the reaction.

[0045] In this invention, the addition of the catalyst and the flow of the transport gas in step (a) can be supplied to the reactants without restriction before or after the reactants reach the target temperature, and can be carried out under batch reaction conditions or continuous flow conditions. The catalyst and the mono- and / or polyols as additional reactants can also be added in a form mixed with dimethyl terephthalate (DMT) before the reaction is prepared.

[0046] The gas flow used to expel methanol to the outside can be formed by forced circulation of the gas phase with a pressure gradient. Alternatively, a continuous flow of gas can be used, where the methanol gas is condensed outside the reactor and then recirculated in a state of almost rarefied vapor concentration. Figure 2 (a) or by using a method that vents methanol to the outside by continuously supplying inert gas from the outside. Figure 2 (b)

[0047] During the transesterification reaction in step (a), dimethyl terephthalate, monohydric and / or polyhydric alcohols, and a catalyst for the transesterification reaction can be introduced into the reactor. To induce direct gas-liquid contact between the transport gas and the reactants within the reactor, bubbles can be ejected from the transfer tube positioned below the water level of the reactants. During this process, a certain concentration of methanol vapor will be formed in the gas phase and can be continuously discharged to the outside by means of the flow of the transport gas. Considering reactivity, it is preferable that mass transfer occurs when the methanol vapor diffused by the transport gas reaches a concentration above saturation; however, if the transport gas is supplied at a sufficient rate, the amount of methanol discharged can be adjusted according to the rate of the transesterification reaction.

[0048] Regarding the temperature of the transesterification reaction, it can be maintained within a range where the methanol generated or present in the reactants during the gas-liquid contact process reaches a certain evaporation rate, i.e., from room temperature to the boiling point of the monohydric and / or polyhydric alcohols suitable as reactants, and the pressure can be maintained from 0.1 torr to 5 atm based on absolute pressure, but it can also be varied within the range while taking into account both the temperature and pressure range used to perform the transesterification reaction and the rate at which methanol is removed by transporting the gas.

[0049] The temperature range can be varied depending on the catalyst used in the transesterification reaction, preferably ranging from room temperature to the boiling point of the alcohol suitable as a reactant. As for the pressure, operating at near atmospheric pressure will facilitate stable and continuous operation. Furthermore, the reaction time in step (a) can be varied depending on the type and amount of catalyst used in the reaction, as well as the amount of dimethyl terephthalate (DMT) and alcohol supplied.

[0050] Firstly, in step (a), the amount of catalyst added for the transesterification reaction, compared to each mole of the raw material, dimethyl terephthalate (DMT), can be from 0.00005 to 1.0 moles, preferably from 0.0001 to 0.2 moles. If the amount of catalyst for the transesterification reaction is less than 0.00005 moles per mole of the raw material, DMT, the transesterification reaction of DMT with mono- and / or polyols may proceed slowly, leading to a decrease in process efficiency. If the amount exceeds 1.0 moles, the improvement in efficiency may be insufficient compared to the increased catalyst content, resulting in decreased economic efficiency and increased byproducts. Furthermore, the excess catalyst may remain as an impurity during the separation of terephthalic acid ester derivatives, affecting the separation and purification efficiency.

[0051] The catalyst used for the transesterification reaction is selected from one or more compounds chosen from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine organic compounds. Preferably, it is selected from one or more compounds chosen from K2CO3, KHCO3, Na2CO3, NaHCO3, NaOH, KOH, MgO, CaO, CH3OK, CH3ONa, and triazabicyclodecene (TBD). The amount and combination of the catalyst should be able to improve both the conversion rate of dimethyl terephthalate (DMT) and the yield of terephthalate derivatives.

[0052] In step (a), the amount of ethylene glycol relative to each mole of dimethyl terephthalate (DMT) can be in the range of 1 to 50 moles. The esterification reaction can be carried out most efficiently when the amount of ethylene glycol is within this range.

[0053] The monohydric and polyhydric alcohols can be straight-chain, branched, cyclic, or mixed forms of alcohols with 1 to 20 carbon atoms, and the polyhydric alcohols have two or more OH functional groups. As an example of the alcohols, methanol, ethanol, n-propanol, isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, glycerol, or 1,2,4-butanetriol can be used, with ethylene glycol being preferred.

[0054] In step (a) of the transesterification reaction by adding a monohydric and / or polyhydric alcohol to dimethyl terephthalate (DMT) in the presence of the catalyst described above, a terephthalate derivative and methanol are generated. Furthermore, in order to continue the forward reaction to produce the terephthalate derivative product above the equilibrium concentration, the reaction is carried out under conditions where a transport gas stream is configured inside the reactor while methanol vapor is continuously discharged to the outside of the reaction system. As a method for supplying the transport gas, such as... Figure 2 As shown, a method using a unidirectional airflow can be used to discharge methanol vapor to the outside after it has been separated by a condenser. Figure 2 (b) or a method of recirculation after removal of methanol vapor ( Figure 2 (a) in the middle.

[0055] Regarding the transport gas injected into the reactor, maintaining a low concentration of methanol in the reactants to prevent or inhibit recombination of methanol incidentally generated during the transesterification reaction due to the reverse reaction will help improve the conversion rate of dimethyl terephthalate (DMT) and the yield of terephthalate derivative products. In this case, any gas that will not affect the alcohol-added transesterification reaction of dimethyl terephthalate (DMT) or the chemical action of the catalyst can be used as the transport gas without limitation. Preferably, air, nitrogen, argon, and helium can be used, and more preferably, an inert gas that is substantially free of moisture can be used.

[0056] In this invention, step (b) is the step of separating and obtaining the terephthalate derivative formed by the reaction. Specifically, it is the step of separating and obtaining the terephthalate derivative formed by step (a) in high yield from a reaction mixture containing unreacted residual dimethyl terephthalate (DMT), ethylene glycol, and residual catalyst, etc. It can be carried out according to generally known purification methods, and the method is not limited. Physical methods such as filtration, crystallization, centrifugation, evaporation, and distillation, and chemical methods such as adsorption, neutralization, and salting out can be carried out in parallel.

[0057] This invention manufactures high-value-added terephthalate derivatives by using dimethyl terephthalate (DMT) as a starting material and adding a transesterification reaction of mono- and / or polyols. The dimethyl terephthalate (DMT) can be obtained from the depolymerization of polymers containing ester functional groups, and the terephthalate derivatives are manufactured by transesterifying the depolymerization product with mono- and / or polyols, with or without a pretreatment process.

[0058] The transesterification reaction by adding monohydric and / or polyhydric alcohols to dimethyl terephthalate (DMT) can also be applied to a two-stage tandem reaction in which a polymeric raw material containing ester functional groups is first used to produce a reaction product by methanol decomposition, and then the reaction product is directly used as a raw material for a second transesterification reaction, thereby producing terephthalate derivatives in high yield.

[0059] That is, the present invention includes a method for producing terephthalic acid ester derivatives from the depolymerization of a polymer containing ester functional groups as a final product, and provides a method for producing high-value-added terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups, characterized by comprising: (A) a step of depolymerization by introducing an alcohol, a polar aprotic solvent and potassium carbonate (K2CO3) into the polymer containing ester functional groups; (B) a step of performing a transesterification reaction while applying a transport gas stream to the depolymerization product obtained by step (A); and (C) a step of separating and obtaining the terephthalic acid ester derivative product produced by the reaction.

[0060] Figure 1 This is a schematic diagram illustrating a conceptual process for producing terephthalate derivatives from polymer feedstocks containing ester functional groups via transesterification. First, step (A) 100 involves depolymerization by introducing the polymer containing ester functional groups, an alcohol, a polar aprotic solvent, and potassium carbonate (K₂CO₃) into a depolymerization reactor. The polymer containing ester functional groups can contact the alcohol, the polar aprotic solvent, and potassium carbonate (K₂CO₃) and produce alcohol-added monomers via transesterification, effectively achieving low-temperature depolymerization of the polymer. This process is very simple and can yield dimethyl terephthalate (DMT) in high yields of over 90%, and its economic efficiency is excellent due to low energy consumption.

[0061] The polymer containing ester functional groups can be a single or mixed form of waste plastics, such as polyethylene, high-density polyethylene, low-density polyethylene, polypropylene, or a combination thereof mixed with the polymer containing ester functional groups. Other polymers exemplified above as mixtures with the polymer containing ester functional groups are merely illustrative and not limited to those listed above.

[0062] Furthermore, polymers containing ester functional groups can be polymers formed by the condensation polymerization of dicarboxylic acids and diols, wherein the dicarboxylic acid is selected from the group consisting of terephthalic acid, naphthalenedicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, diphenoxyethane dicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, decane dicarboxylic acid, cyclohexane dicarboxylic acid, trimellitic acid, pyromellitic acid, and combinations thereof, and the diol is selected from the group consisting of ethylene glycol, propylene glycol, ... The group consisting of 1,2-propanediol, butanediol, neopentyl glycol, hexanediol, decanediol, dodecaethylene glycol, 1,4-cyclohexanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, di(tetramethylene) glycol, tri(tetramethylene) glycol, polytetramethylene glycol, pentaerythritol, 2,2-bis(4-(3-hydroxyethoxyphenyl)propane), and combinations thereof.

[0063] For example, the polymer containing ester functional groups may be selected from polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polyglycolic acid or polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCX), polyhydroxyalkanoates (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), polyethylene naphthalate (PEN), Vectran, and combinations thereof.

[0064] The most common example of a polymer containing ester functional groups is polyethylene terephthalate (PET), in which the starting material used to manufacture the polymer is terephthalic acid or a derivative monomer and ethylene glycol.

[0065] The polymers containing ester functional groups used in this invention may be in a state containing various impurities rather than a pure state. For example, in addition to polymers containing ester functional groups, mixtures containing fragments such as bottle caps, adhesives, paper, residual liquids, dust, or combinations thereof, but not limited thereto, may also be used as depolymerization raw materials.

[0066] The alcohol is a reactant, preferably a straight-chain primary alcohol, such as methanol, ethanol, propanol, butanol, or a combination thereof.

[0067] Regarding the alcohol, the number of moles of alcohol relative to the polymer raw material containing ester functional groups per repeating unit mole can be in the range of 0.1 to 5,000, preferably in the range of 1 to 500.

[0068] Potassium carbonate is used as the catalyst. Potassium carbonate, represented by the chemical formula K₂CO₃, is a white crystalline solid soluble in water. It is preferable to use the anhydrous form of potassium carbonate rather than the hydrated form, and it is advisable to dry it before use. Regarding the amount of potassium carbonate used, it can be at least 0.01 times the repeating molar number of the polymer containing ester functional groups, preferably 0.01 to 100 times, and more preferably 0.1 to 10 times.

[0069] As the polar aprotic solvent, an organic liquid-phase compound that can be used to reduce the activation energy of the decomposition reaction of ester functional groups or the transesterification reaction is preferred. From the perspective of reaction thermodynamics, it is preferable to use a non-reactive, inert solvent that does not directly participate in the reaction and can induce heterogeneous catalytic reactions and dissolve the generated monomers by reducing the solubility of the catalyst (potassium carbonate) in the reactants (ethanol).

[0070] The organic compound in the polar aprotic solvent may be a compound with a chain-like or cyclic skeletal structure, or a compound in which halogen elements are directly bonded to or linked to each other by means of oxygen or nitrogen. As a specific example, one or more of the following can be used: toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propionitrile, aminopropionitrile, methylaminopropionitrile, iminodipropionitrile, butyronitrile, methylbutenonitrile, butanenitrile, methyl ethyl ether, diethyl ether, ethyl phenyl ether, dimethoxybenzene, trimethoxybenzene, methoxyphenol, tetrahydrofuran, methyltetrahydrofuran, dioxane, chloromethane, dichloromethane, chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, trichlorobenzene, methylphenyl ether, and ethylphenyl ether.

[0071] Furthermore, the polar aprotic solvent can be used in a molar ratio range of 0.1 to 5,000 times that of the repeating unit molars of the polymer raw material containing ester groups, preferably in a molar ratio range of 1 to 500 times.

[0072] Because step (A) involves alcohol-added depolymerization of polymers containing ester functional groups in the range of 0–80°C, preferably in the range of 10–60°C, in some examples of step (A), complete decomposition of the polymer can be induced under near-normal pressure and temperature conditions, and the reaction system can be realized through a simple structure and composition. This can significantly reduce investment costs compared to existing technologies or existing functions, and can also manage energy efficiently and stably.

[0073] Furthermore, since water-soluble, multiphase, low-cost catalysts are typically used in the depolymerization of step (A), the catalysts can be easily recovered and reused, and the monomers produced can be recovered in a high proportion by lowering the temperature of the reactants themselves to below room temperature. Moreover, since the solvents used can be reused as depolymerization feedstocks for new polymer raw materials, the economic efficiency of the recycling process can be further improved.

[0074] Furthermore, in the depolymerization of the polymer in step (A), no additional heat source is required; sufficient energy for depolymerization can be obtained solely from the heat of mixing and heat of solution generated during the preparation of the mixed solution for the depolymerization reaction. In the case described above, the depolymerization can be carried out in an insulated reactor. Additionally, as in a specific embodiment of the invention, depolymerization can also be carried out simultaneously with the supply of an external heat source.

[0075] Furthermore, the depolymerization of the polymer can be performed under conditions above atmospheric pressure. Specifically, it can be performed under pressure conditions greater than 1 atm to 6.5 atm.

[0076] Furthermore, the depolymerization of the polymer can be performed in the form of exposure to the atmosphere or in the form of a closed system, or it can be performed by reflux of the solvent by equipping a condenser.

[0077] Furthermore, the depolymerization reaction time in step (A) may vary depending on the amount of polymer used. The monomer can be obtained in a sufficiently high yield within 24 hours at room temperature without any energy applied. Moreover, since no significant chemical changes occur in substances other than the reactants, most of the monomers can be recycled and reused in the project.

[0078] Following step (A), a step 200 can be performed to separate a portion of the compound from the depolymerization product obtained through depolymerization. Specifically, the step of separating the portion of the compound from the depolymerization product is a step of separating a mixture containing dimethyl terephthalate (DMT) and ethylene glycol, as well as residual unreacted products, methanol, polar aprotic solvents, catalysts, or byproducts such as monomethyl terephthalate (MMT) and terephthalic acid (TPA) derivatives, from a reaction mixture 10 obtained after the completion of the depolymerization reaction. This separation involves selecting one or more of the polymer, insoluble catalyst, polar aprotic solvent, and reaction byproducts. This step can be carried out according to commonly known methods and is not particularly limited in its application.

[0079] As an example of separation, when the insoluble catalyst and unreacted polymer are separated from the depolymerization product by filtration, the depolymerization product can exhibit a homogeneous liquid phase. Subsequently, by increasing the temperature or reducing the pressure, some or all of the polar aprotic solvent or methanol can be evaporated or distilled, thereby crystallizing the dimethyl terephthalate (DMT) in the depolymerization product. As a method for removing foreign matter and increasing the concentration of dimethyl terephthalate (DMT), a washing solution can be added, and additional methods such as recrystallization, physical filtration, distillation, evaporation, and drying can be used to prepare a raw material for the ethylene glycol-added transesterification reaction. The solvent and catalyst separated from the depolymerization product can be reused as raw materials in step (A) 100, as described previously.

[0080] Furthermore, step 200, which separates a portion of the compound, may be a step performed in preparation for the transesterification reaction step 300, which involves adding a monohydric and / or polyhydric alcohol to the generated dimethyl terephthalate (DMT), but it is not mandatory. That is, step 200, which separates the depolymerization product obtained from the depolymerization step of the polymer containing ester functional groups in step (A), may be omitted, and the product may be used directly as a starting material for step (B).

[0081] In this invention, step (B) 300 is a step in which a transesterification reaction is carried out while a transport gas flow 3 is applied to the depolymerization product obtained in step (A). The method of carrying out the transesterification reaction in step (B) is the same as the method for producing terephthalic acid ester derivatives from dimethyl terephthalate (DMT) described above, and therefore, detailed descriptions related thereto will be omitted. The dimethyl terephthalate (DMT) in step (B) is obtained by depolymerization of a polymer containing ester functional groups. This depolymerization can be carried out by a simple process under ambient temperature and pressure conditions, and the depolymerization product contains high yields of dimethyl terephthalate (DMT) and polyols. By reusing this product to produce terephthalic acid ester derivatives from the original dimethyl terephthalate (DMT), the final product, i.e., the terephthalic acid ester derivative, can be obtained directly from the polymer containing ester functional groups.

[0082] Before performing the transesterification reaction in step (B), the number of moles of monovalent and / or polyvalent alcohols and / or one or more transesterification catalysts selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine organic compounds may be adjusted to a specific range compared with the mole of dimethyl terephthalate contained in the depolymerization product, as the solvent used for the transesterification reaction in step (A).

[0083] The molar number of the alcohol and / or transesterification catalyst can be adjusted by adding the alcohol and / or transesterification catalyst to the depolymerization product or removing a portion of it, or by adding a new monohydric and / or polyhydric alcohol after removing a portion. In this case, the removal and addition processes can also be carried out in step 200, as described above, to separate a portion of the compound.

[0084] The newly added mono- and / or polyols can be straight-chain, branched, cyclic, or mixed forms of alcohols with 1 to 20 carbon atoms, and the polyols have two or more OH functional groups.

[0085] The number of moles of the adjusted ethylene glycol can be in the range of 0.1 to 100 moles compared to each mole of dimethyl terephthalate contained in the depolymerization product, and preferably in the range of 1 to 50 moles.

[0086] Furthermore, the number of moles of catalyst used in the adjusted transesterification reaction can be in the range of 0.00005 to 1.0 moles compared to the mole of dimethyl terephthalate contained in the depolymerization product, and preferably in the range of 0.0001 to 0.2 moles.

[0087] In the transesterification reaction 300, in order to continuously carry out the additional reaction of mono- and / or polyols in the direction of product formation while suppressing the reverse reaction caused by methanol, methanol can be discharged to the outside of the reactor by means of a gas flow 3 40, and the methanol recovered by the condenser 400, which maintains a low temperature, can be reused as a raw material for the depolymerization reaction in step (A) 60. When compared with the existing glycolysis method for the production of diethyl terephthalate (BHET) using high-temperature reaction conditions (typically in the range of 200 to 280°C), the terephthalate derivative product can be obtained more efficiently because the reaction can be carried out rapidly at low temperatures far below the boiling points of mono- and / or polyols. Moreover, because of the different reaction temperature range and the reaction pathway for obtaining the product, the product (dimer or oligomer) generated due to internal decomposition (or depolymerization) can be generated at a lower concentration or not at all, but the terephthalate derivative can be obtained in a high yield.

[0088] The method of this invention can improve reactivity in the low-temperature range and efficiency in the purification process, thereby significantly reducing energy consumption compared with existing methods, and ultimately providing a more economical method for manufacturing high-value-added terephthalate derivatives.

[0089] In this invention, step (C) is step 500, which is to separate and obtain dimethyl terephthalate in high yield produced by the reaction. This step can be performed in the same manner as the method for producing terephthalic acid ester derivatives using dimethyl terephthalate (DMT) described above, and therefore detailed descriptions thereof will be omitted.

[0090] Next, detailed information about the process of the present invention will be described through comparative examples and embodiments. However, the following content is merely representative examples used to illustrate the present invention, and the scope of the present invention is not limited by the following embodiments.

[0091] Raw material 1 (dimethyl terephthalate raw material)

[0092] The raw material 1 is prepared by uniformly pulverizing dimethyl terephthalate (Sigma-Aldrich, catal.#185124, purity >99.0%) supplied by the reagent manufacturer using a pestle and mortar.

[0093] Raw material 2 (polymer raw material containing ester functional groups)

[0094] As a polymer material containing ester functional groups, the waste polyethylene terephthalate material bottles were washed until no foreign matter remained and dried. Then, they were crushed using a continuous pulverizer (manufacturer and model: IKAMF10.1). Next, only plastic fragments with a length and width of 1 to 3 mm and a thickness of less than 0.5 mm on the wider side were collected using a standard sieve as raw material 2.

[0095] <Example 1>

[0096] After adding approximately 14.5 g of dimethyl terephthalate (DMT) feedstock prepared according to the process of feedstock 1 and approximately 55.6 g of ethylene glycol (Sigma-Aldrich; purity ≥99.8%) (equivalent to 12 times the molar number of feedstock 1) into a three-necked flask and assembling a distillation apparatus equipped with a cooler, stirring was started using a magnetic stirrer at a speed of 1,200 rpm.

[0097] To effectively remove the reaction product, methanol, high-purity nitrogen (Central Industrial Gases; 99.9992%) was used as the inert transport gas. The gas flow rate in contact with the liquid in the reactor was adjusted to 200 sccm using a mass flow controller, or normalized to the initial reaction mixture volume under standard conditions and converted to gas hourly space velocity (GHSV). -1 The setting value remained stable at 240.

[0098] Next, the flask containing the reactants was heated, and when the final temperature of the reaction solution reached 80°C, approximately 0.05 g (equivalent to 0.005 moles of the initial feedstock 1) of potassium carbonate (K₂CO₃, Sigma-Aldrich, ACS reagent) was added as a catalyst to initiate the reaction. The high-value-added depolymerization monomer, diethyl terephthalate (BHET), was then obtained by performing a transesterification reaction for a total of 8 hours. As the reaction proceeded, the generated methanol was degassed from the reactants and discharged outside the reactor using a gas transport stream, and collected using a trap maintained below 0°C.

[0099] During the reaction process, trace amounts (less than 50 mg) of the liquid reactants were collected at specific time intervals and quantified using a high-performance liquid chromatograph (HPLC) with an Optimapak C18 Column (250 mm, 5 micron), UV detector (λ = 254 nm) calibrated with standard samples. This allowed for the estimation of product distribution and concentration, and subsequently, the conversion rate and product yield were calculated. For analysis using HPLC, a methanol:water mixture with a volume ratio of 70:30 was used as the mobile phase, and the total flow rate was maintained at 0.7 ml / min.

[0100] The conversion rate of dimethyl terephthalate (DMT) in the transesterification reaction and the yields of intermediate products from dimethyl terephthalate (DMT) undergoing partial transesterification with alcohol reactants (e.g., ethyl hydroxy terephthalate (HEMT) in ethylene glycol-added transesterification), monomer products from complete transesterification (e.g., bis(hydroxyethyl) terephthalate (BHET) in ethylene glycol-added transesterification), dimers, potassium monomethyl terephthalate (K-MMT) as a by-reactant, and dipotassium terephthalate (K2-TPA) were calculated using the formulas shown below.

[0101] Dimethyl terephthalate (DMT) conversion rate = (N0-N) / N0 (Formula 1)

[0102] Monomer yield = (N monomer / N0)×100%(Formula 2)

[0103] Intermediate yield = (N intermediate / N0)×100%(Formula 3)

[0104] Monomethyl terephthalate (MMT) yield = (N MMT / N0)×100%(Formula 4)

[0105] Terephthalic acid (TPA) yield = (N TPA / N0)×100%(Formula 5)

[0106] Dimer yield = (N dimer / N0)×100%(Formula 6)

[0107] In the formula, N0 is the initial input of the raw material, namely dimethyl terephthalate (DMT), in moles, and N, N intermedmte N monomer N MMT N TPA and N dimerIt is the number of moles of terephthalic acid esters contained in unconverted dimethyl terephthalate (DMT), intermediate products, monomer products, monomethyl terephthalate (MMT), terephthalic acid (TPA), and dimers.

[0108] <Comparative Example 1>

[0109] Except that potassium carbonate was not added in Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0110] <Example 2>

[0111] Except that approximately 0.001 g (equivalent to 0.0001 moles of raw material 1) of potassium carbonate was used in accordance with Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0112] <Example 3>

[0113] Except that approximately 0.01 g of potassium carbonate (equivalent to 0.001 times the molar amount of raw material 1) was used in accordance with Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0114] <Example 4>

[0115] Except that approximately 0.1 g (equivalent to 0.01 times the molar amount of raw material 1) of potassium carbonate was used in the same manner as in Example 1, the transesterification reaction was carried out and evaluated.

[0116] <Example 5>

[0117] Except that approximately 0.5 g (equivalent to 0.05 times the molar amount of raw material 1) of potassium carbonate was used in accordance with Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0118] <Example 6>

[0119] Except that approximately 2.1 g (equivalent to 0.2 times the molar amount of raw material 1) of potassium carbonate was used in accordance with Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0120] <Comparative Example 2>

[0121] Except that no inert transport gas was used in Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0122] <Example 7>

[0123] In addition to maintaining the gas as an inert transport gas for 50 sccm (GHSV = 60 h) based on Example 1, -1 In addition to high-purity nitrogen, transesterification was carried out and evaluated in the same manner as in Example 1.

[0124] <Example 8>

[0125] In addition to maintaining the gas as an inert transport gas at 100 sccm (GHSV = 120 h) based on Example 1, -1 In addition to high-purity nitrogen, transesterification was carried out and evaluated in the same manner as in Example 1.

[0126] <Example 9>

[0127] In addition to maintaining the gas as an inert transport gas at 500 sccm (GHSV = 600 h) based on Example 1, -1 In addition to high-purity nitrogen, transesterification was carried out and evaluated in the same manner as in Example 1.

[0128] <Example 10>

[0129] Except that the temperature of the reaction solution was maintained at 50°C in the same manner as in Example 1, the transesterification reaction was carried out and evaluated.

[0130] <Example 11>

[0131] Except that the temperature of the reaction solution was maintained at 65°C in the same manner as in Example 1, the transesterification reaction was carried out and evaluated.

[0132] <Example 12>

[0133] Except that the temperature of the reaction solution was maintained at 100°C in the same manner as in Example 1, the transesterification reaction was carried out and evaluated.

[0134] <Example 13>

[0135] Except that the temperature of the reaction solution was maintained at 110°C based on Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0136] <Example 14>

[0137] Except that the temperature of the reaction solution was maintained at 120°C based on Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0138] <Example 15>

[0139] Except that the temperature of the reaction solution was maintained at 130°C based on Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0140] <Example 16>

[0141] Except that the temperature of the reaction solution was maintained at 140°C based on Example 1, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0142] <Example 17>

[0143] Except that approximately 0.008 g (equivalent to 0.001 times the molar amount of raw material 1) of potassium bicarbonate (KHCO3) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0144] <Example 18>

[0145] Except that approximately 0.008 g (equivalent to 0.001 times the molar amount of raw material 1) of sodium carbonate (Na2CO3) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0146] <Example 19>

[0147] Except that approximately 0.006 g (equivalent to 0.001 times the molar amount of raw material 1) of sodium bicarbonate (NaHCO3) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0148] <Comparative Example 3>

[0149] Except that approximately 0.007 g (equivalent to 0.001 moles of raw material 1) of potassium acetate (KOAc) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0150] <Comparative Example 4>

[0151] Except that approximately 0.006 g (equivalent to 0.001 moles of sodium acetate (NaOAc) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0152] <Comparative Example 5>

[0153] Except that approximately 0.01 g (equivalent to 0.001 moles of raw material 1) of zinc acetate (Zn(OAc)2·2H2O) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0154] <Example 20>

[0155] Except that approximately 0.004 g (equivalent to 0.001 times the molar amount of raw material 1) of potassium hydroxide (KOH) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0156] <Example 21>

[0157] Except that approximately 0.003 g (equivalent to 0.001 times the molar amount of raw material 1) of sodium hydroxide (NaOH) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0158] <Example 22>

[0159] Except that approximately 0.005 g (equivalent to 0.001 times the molar amount of raw material 1) of potassium methoxide (CH3OK) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0160] <Example 23>

[0161] Except that approximately 0.004 g (equivalent to 0.001 times the molar amount of raw material 1) of sodium methoxide (CH3ONa) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0162] <Example 24>

[0163] Except that approximately 0.003 g of magnesium oxide (MgO) was used as a catalyst (equivalent to 0.001 times the molar amount of raw material 1) in accordance with Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0164] <Example 25>

[0165] Except that approximately 0.004 g of calcium oxide (CaO) was used as a catalyst (equivalent to 0.001 times the molar amount of raw material 1) in accordance with Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0166] <Example 26>

[0167] Except that approximately 0.01 g (equivalent to 0.001 moles of raw material 1) of triazabicyclodecene (TBD) was used as a catalyst in the same manner as in Example 1 and the reaction time was maintained at 3 hours, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0168] <Comparative Example 6: Depolymerization of polyethylene terephthalate (PET) via high-temperature glycolysis>

[0169] As the feedstock for the glycolysis reaction, approximately 10 g of polyethylene terephthalate (PET) feedstock 2 was prepared. Approximately 38.75 g (12 mol per mole of repeating monomer) of ethylene glycol, a polar diol solvent, was added to a three-necked flask. After installing a reflux condenser at atmospheric pressure, the flask was heated and stirred using a heated magnetic stirrer. Next, at a temperature of 177°C, the prepared 10 g of polymer feedstock was added, and stirring continued while the temperature was increased. When the reaction mixture reached 197°C or the reflux temperature, the catalytic reaction was initiated by adding approximately 0.571 g (0.05 mol per mole of repeating monomer) of zinc acetate catalyst. The reaction was then carried out using a condenser with one end exposed to atmospheric pressure while continuously stirring for 2 hours and maintaining the reaction temperature stably within ±0.5°C. After the reaction, unreacted substances in the product were separated and quantified by filtration. The decomposed monomers, dimers, mono(hydroxyethyl) terephthalate (MHET) as by-reactions, and oligomers were quantified by high-performance liquid chromatography (HPLC) calibrated with standard samples beforehand, following a method similar to that used to quantify the reactants in Example 1.

[0170] <Example 27: Depolymerization of polyethylene terephthalate (PET) via room temperature methanol decomposition and low temperature glycolysis>

[0171] Approximately 3 g of polyethylene terephthalate (PET) prepared according to ingredient 2, along with approximately 66.3 g (equivalent to 50 moles of repeating units of the polymer in ingredient 2) of dichloromethane (Samchun Chemicals; 99.5%), 24.96 g (equivalent to 50 moles of repeating units of the polymer in ingredient 2) of methanol (Samchun Chemicals; 99.9%), and approximately 0.43 g (equivalent to 0.2 moles of repeating units of the polymer in ingredient 2) of K₂CO₃ (potassium carbonate; Sigma-Aldrich, ACS reagent) as a catalyst, were added to a three-necked flask. Double-distilled water was then added to adjust the initial moisture content of the reactants to 0.4 moles of repeating units of the polymer in ingredient 2. The reaction was carried out using a magnetic stirrer at 25°C and atmospheric pressure at 500 rpm for 24 hours.

[0172] After the reaction, the product is filtered to separate it into a filtrate containing a portion of potassium terephthalate (K-MMT), potassium terephthalate (K-MMT), ethylene glycol, and potassium terephthalate (MTT), as well as organic solvents, and a solid component (filter cake) containing unreacted polyethylene terephthalate (PET), K2CO3 catalyst, and potassium terephthalate (K-MMT).

[0173] Samples were prepared by diluting trace amounts (less than 50 mg) of the filtrate and potassium salts from the solid component in an aqueous mobile phase. The product distribution and concentration in each sample were estimated using quantitative analysis with Optimapak C18 Column (250 mm, 5 micron), UV detector (X = 254 nm). Unreacted polyethylene terephthalate (PET) in the solid component was quantified gravimetrically. The conversion rate of PET in the depolymerization reaction, and the yields of dimethyl terephthalate (DMT), ethyl hydroxymethyl terephthalate (HEMT), terephthalic acid (TPA), and monomethyl terephthalate (MMT) were then calculated using the quantified values. For HPLC analysis, a methanol:water mixture with a volume ratio of 70:30 was used as the mobile phase, and the total flow rate was maintained at 0.7 mL / min.

[0174] The conversion rate of polyethylene terephthalate (PET) and the yield of dimethyl terephthalate (DMT) in the depolymerization reaction were calculated using the formulas shown below.

[0175] Polyethylene terephthalate (PET) conversion rate = (M0 - M) / M0 × 100% (Formula 7)

[0176] Dimethyl terephthalate (DMT) yield = (M DMT / M0)×100% (Formula 8)

[0177] In the formula, M0 and M represent the number of repeating moles of the added raw material polymer (polyethylene terephthalate, PET) and the unreacted polymer, respectively, while M DMT This represents the number of moles of dimethyl terephthalate (DMT) produced.

[0178] The filtrate of the depolymerization product was used as a raw material in a transesterification reaction with added ethylene glycol. The transesterification reaction was performed under the same conditions as in Example 1, but the filtrate of the depolymerization product was used instead of raw material 1, and most of the methanol and polar aprotic solvent were removed using a vacuum evaporator. Next, the molar amount of dimethyl terephthalate (DMT) was adjusted to the same state as in Example 1, and the total amount of ethylene glycol generated by depolymerization and the additional ethylene glycol was adjusted to approximately 55.6 g (12 times the molar amount of dimethyl terephthalate (DMT)). The transesterification reaction was then carried out without the addition of a catalyst and evaluated.

[0179] The molar amounts of catalyst and potassium monomethyl terephthalate (K-MMT) in the recovered solid fraction after filtration were quantified using gravimetric analysis and high-performance liquid chromatography (HPLC), respectively (the measured results were molar ratios of 0.126 and 0.024 compared to the number of moles of the starting material). The residual catalyst molars in the filtrate of the depolymerization product were estimated by subtracting the number of moles recovered in the solid phase (based on the molar number of potassium cations) from the initial catalyst input. This confirmed that the amount of catalyst (K₂CO₃) in the starting material for the ethylene glycol-added transesterification reaction was approximately 0.054 molar ratio compared to each mole of dimethyl terephthalate (DMT).

[0180] The conversion rate of dimethyl terephthalate (DMT), the yield of bis(hydroxyethyl) terephthalate (BHET), methyl hydroxy terephthalate (HEMT), and the yield of the BHET dimer were calculated using Formulas 1 to 4 as described above, and the results are shown in Table 5.

[0181] <Example 28>

[0182] Except that, in addition to replacing ethylene glycol with the same number of 1,3-propanediol (Sigma-Aldrich; purity ≥98%) as a reactant as in Example 1 (a molar ratio of 12 times that of dimethyl terephthalate (DMT) per unit molar), and maintaining the temperature of the reaction solution at 100°C, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0183] <Example 29>

[0184] In addition to using the same number of 1,4-butanediol (Sigma-Aldrich) as a reactant as described in Example 1 (a molar ratio of 12 times compared to a unit molar number of dimethyl terephthalate (DMT)); The transesterification reaction was carried out using a solution of ethylene glycol (purity ≥ 99%) instead of ethylene glycol, and the temperature of the reaction solution was maintained outside 100°C. The reaction was evaluated in the same manner as in Example 1.

[0185] <Example 30>

[0186] Except that, in addition to replacing ethylene glycol with the same number of 1,6-hexanediol (Sigma-Aldrich; purity ≥99%) as a reactant as in Example 1 (a molar ratio of 12 times that of dimethyl terephthalate (DMT) per unit mole), and maintaining the temperature of the reaction solution at 100°C, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0187] <Example 31>

[0188] In addition to using the same number of 1,2-propanediol (Sigma-Aldrich) as a reactant as described in Example 1 (a molar ratio of 12 times compared to a unit molar number of dimethyl terephthalate (DMT)); The transesterification reaction was carried out using a solution of ethylene glycol (purity ≥ 99%) instead of ethylene glycol, and the temperature of the reaction solution was maintained outside 100°C. The reaction was evaluated in the same manner as in Example 1.

[0189] <Example 32>

[0190] Except that, in addition to replacing ethylene glycol with the same molar amount of 1,3-butanediol (Sigma-Aldrich; Anhyrous, purity ≥99%) as a reactant as in Example 1, and maintaining the temperature of the reaction solution at 100°C, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0191] <Example 33>

[0192] Except that, in addition to replacing ethylene glycol with the same molar amount of 1,4-cyclohexanedimethanol (Sigma-Aldrich; a mixture of cis and trans, purity ≥99%) as a reactant as in Example 1, and maintaining the temperature of the reaction solution at 100°C, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0193] <Example 34>

[0194] Except that, in addition to replacing ethylene glycol with the same molar amount of 2-ethyl-1-hexanol (Sigma-Aldrich; purity ≥99.6%) as a reactant as in Example 1 (a molar ratio of 12 times that of dimethyl terephthalate (DMT) per unit molar amount) and maintaining the temperature of the reaction solution at 100°C, the transesterification reaction was carried out and evaluated in the same manner as in Example 1.

[0195] [Comparison of the characteristics of transesterification reactions based on the amount of catalyst used]

[0196] Table 1 shows the results of adjusting the amount of potassium carbonate (K2CO3) used as a catalyst in the examples of the present invention and observing its reaction effect when performing transesterification reactions in Examples 1 to 6 and Comparative Example 1 (reaction temperature 80°C, GHSV = 240 h). -1 Unlike the examples using a catalyst, in Comparative Example 1, where no catalyst was added, the yields of diethyl terephthalate (BHET) after 2 hours and 8 hours were approximately 0.0% and 2.4%, respectively, confirming that the transesterification reaction was very slow. These results, as described above, demonstrate that a catalyst is necessary to facilitate the ethylene glycol-added transesterification reaction of dimethyl terephthalate (DMT) under low-temperature conditions exemplified in this invention.

[0197] Table 1

[0198]

[0199] DMT: Dimethyl terephthalate; EG: Ethylene glycol.

[0200] BHET: Bis(2-hydroxyethyl)terephthalate

[0201] HEMT: 1-(2-Hydroxyethyl)4-methyl terephthalate; K2-TPA: Dipotassium terephthalate.

[0202] K-MMT: Potassium monomethyl terephthalate

[0203] Examples 1 to 4 are results of reactions using potassium carbonate equivalent to 0.00001 to 0.01 moles per mole of dimethyl terephthalate (DMT) as a catalyst. It can be confirmed that the formation rate and yield of bis(hydroxyethyl) terephthalate (BHET) are significantly improved when the amount of potassium carbonate is increased.

[0204] Furthermore, Examples 5 and 6, which used potassium carbonate equivalent to 0.05 and 0.2 moles per mole of dimethyl terephthalate (DMT) as catalyst, respectively, showed a tendency for a decrease in the formation rate and yield of diethyl terephthalate (BHET). Conversely, the final yield of the reaction byproduct, dipotassium terephthalate (K2-TPA), tended to increase to 6.0% and 18.5%, respectively. These results indicate that using an excess of catalyst compared to the molar amount of dimethyl terephthalate (DMT) not only increases catalyst consumption but also promotes side reactions such as hydrolysis or alkaline hydrolysis. Therefore, appropriately adjusting the amount of catalyst will help improve the performance and economy of the transesterification reaction.

[0205] [Comparison of the characteristics of transesterification reactions based on gas hourly space velocity (GHSV)]

[0206] When the transesterification reaction of dimethyl terephthalate (DMT) is carried out in the presence of excess ethylene glycol solvent, a very high rate of product formation, namely diethyl terephthalate (BHET), can be observed initially. Furthermore, the rate of methanol formation, which is incidentally generated during the transesterification reaction, increases proportionally to the molar amount of BHET produced. In a closed system, the transesterification reaction described above is not an irreversible reaction in which all the initially added dimethyl terephthalate (DMT) is converted into BHET. The incidentally generated methanol and the reverse transesterification reaction involving BHET also proceed at a certain rate. Once the forward and reverse reactions reach equilibrium, the concentration of the compounds will not change further, and even with changes in reaction conditions, improvements in product yield remain limited. However, the reverse reaction can be suppressed by effectively removing some of the reaction products from the reaction mixture or by removing them from the reaction system. The characteristics of the reaction will depend on the amount of change in the concentration of the corresponding substances, i.e., the rate of mass transfer to the outside.

[0207] In the transesterification reaction performed according to an example of the present invention, the methanol produced is the substance with the lowest boiling point among the input raw materials and products (130°C higher than ethylene glycol). Therefore, in addition to increasing the temperature of the reaction system or reducing the pressure, methanol can be selectively discharged to the outside by continuously injecting transport gas flowing in from the outside, thereby inhibiting the re-formation of dimethyl terephthalate (DMT) caused by the reverse transesterification reaction.

[0208] Table 2

[0209]

[0210] DMT: Dimethyl terephthalate; EG: Ethylene glycol.

[0211] BHET: Bis(2-hydroxyethyl)terephthalate

[0212] HEMT: 1-(2-Hydroxyethyl)4-methyl terephthalate

[0213] K2-TPA: Dipotassium terephthalate

[0214] K-MMT: Potassium monomethyl terephthalate

[0215] Table 2 shows the results of observations on the characteristics of the transesterification reaction performed at a reaction temperature of 80°C, with the flow rate of the inert transport gas (high-purity nitrogen) injected to remove methanol from the reaction products, i.e., to make gas-liquid contact with the reactants inside the reactor.

[0216] In the absence of a transport gas flow (Comparative Example 2), a low yield of approximately 58.4% of diethyl terephthalate (BHET) was observed after a transesterification reaction at 80°C for 3 hours. Even with prolonged exposure to the reaction conditions for approximately 8 hours, only a negligible increase in yield of approximately 0.9% was observed. This is presumably because, even with the reactor in an open system configuration and the internal temperature maintained above the boiling point of methanol, the methanol generated during some of the transesterification reaction did not actively diffuse into the unfilled gas phase (headspace) or outside the reactor, but rather remained at a high concentration inside the reactants.

[0217] Furthermore, for transesterification reactions (Examples 1 and 7 to 9) performed under continuous gas flow conditions with varying flow rates of the transport gas, i.e., nitrogen, the conversion rate and the yield of diethyl terephthalate (BHET) were significantly improved. In particular, it was found that in the reactions performed in Examples 1 and 9, where the gas hourly space velocity (GHSV) exceeded 200, a yield of diethyl terephthalate (BHET) of over 92% could be achieved when the reaction time exceeded 3 hours.

[0218] Furthermore, it was found that maintaining excessively high gas flow rates and prolonged exposure to reaction conditions resulted in a slight increase in the yields of both dimers and oligomers, thus failing to improve the yield of bis(hydroxyethyl) terephthalate (BHET). In Example 1, no oligomers were observed in the reactants even after a reaction lasting more than 3 hours. Conversely, when the transesterification reaction was performed according to Example 9, oligomer formation was observed starting after 6 hours, leading to a decrease in the selectivity of bis(hydroxyethyl) terephthalate (BEHT). Even with the formation of less than 3% oligomers, the viscosity of the reaction mixture increased significantly, and a rapid turbidity of the reactants was observed due to the formation of a heterogeneous phase in some of the products. Therefore, in order to maximize the yield of the polymer depolymerization monomer, bis(hydroxyethyl) terephthalate (BHET), it is beneficial to improve the final yield of bis(hydroxyethyl) terephthalate (BHET) by using the appropriate gas flow and selecting the optimal gas flow conditions that can effectively remove methanol generated through transesterification while dominantly carrying out the additional ethylene glycol reaction.

[0219] [Characteristic changes in transesterification reaction based on reaction temperature]

[0220] Table 3 records the reaction results observed under varying reaction temperatures when performing an ethylene glycol transesterification reaction using dimethyl terephthalate (DMT) according to the method of the present invention (GHSV = 240 h). -1 ).

[0221] It has been confirmed that by maintaining a temperature above the boiling point of methanol (Example 1 and Examples 12 to 16), a high yield of diethyl terephthalate (BHET) obtained via transesterification can be maintained from the initial stage of the reaction, and a yield of over 95% of BHET can be achieved when the reaction time exceeds 4 hours. It is estimated that the increased yield described above is due to the increased mass transfer rate of methanol at reaction temperatures above the boiling point, and also to an increased rate of glycolysis catalytic reactions, which sequentially convert dimethyl terephthalate (DMT) to ethyl hydroxymethyl terephthalate (HEMT) and then to BHET.

[0222] Table 3

[0223]

[0224] DMT: Dimethyl terephthalate; EG: Ethylene glycol.

[0225] BHET: Bis(2-hydroxyethyl)terephthalate

[0226] HEMT: 1-(2-Hydroxyethyl)4-methyl terephthalate

[0227] K2-TPA: Dipotassium terephthalate

[0228] K-MMT: Potassium monomethyl terephthalate

[0229] Furthermore, when the transesterification reaction was carried out while maintaining the reaction temperature below the boiling point of methanol (Examples 10 and 11), the yields of diethyl terephthalate (BHET) based on the reaction time were 45.4% and 73.9% after a reaction time of 2 hours, respectively, and 68.1% and 86.8% after a reaction time of 4 hours, respectively, showing a relatively low rate of increase.

[0230] Furthermore, although not recorded in the table, oligomers were detected after prolonged exposure to the reaction conditions (after 7 hours of reaction time), and after 8 hours of reaction time, approximately 11.2% and 3.3% of the applicable dimethyl terephthalate (DMT) feedstock were converted into oligomers. At this point, the viscosity of the reactants increased significantly, and a non-uniform suspension was observed.

[0231] That is, it can be seen that in order to increase the conversion rate of dimethyl terephthalate (DMT) and the yield of monomer bis(hydroxyethyl) terephthalate (BHET) without generating oligomers in a shorter reaction time or residence time, it would be more advantageous to control the reaction temperature above the boiling point of methanol.

[0232] [Comparison of the characteristics of transesterification reactions based on the selected reaction catalysts]

[0233] Existing glycolysis reactions for producing diethyl terephthalate (BHET) from polymers containing ester functional groups are performed at high temperatures, thus requiring significant energy consumption. To overcome these issues, a novel reaction pathway can be considered to produce BHET in high yields at low temperatures.

[0234] As an example of the reaction pathway described above, the methanol decomposition reaction for producing dimethyl terephthalate (DMT) using polymer feedstocks containing ester functional groups can be carried out at room temperature, and it is expected that diethyl terephthalate (BHET) can be produced in high yields, provided that low-temperature reaction conditions that allow for continuous and dominant ethylene glycol addition are provided.

[0235] If a separate separation process is not performed after the first reaction, namely methanol decomposition, some catalyst residue may remain in the resulting reaction mixture. Therefore, it is necessary to design or consider a new catalyst system that can perform well in continuous transesterification reactions.

[0236] As catalysts commonly used in transesterification reactions, acidic, basic, and metal salt catalysts can be employed. However, acidic catalysts have a slower reaction rate compared to basic catalysts and are usually carried out at high temperatures (above 100°C). Furthermore, to prevent corrosion, acid-resistant designs are required in the reactor and auxiliary equipment, which may lead to excessive initial investment costs.

[0237] Therefore, in this invention, the reaction performance and effectiveness of basic catalysts and metal salt catalysts that are expected to exhibit reactivity and selectivity in the ethylene glycol-assisted transesterification reaction of dimethyl terephthalate (DMT) were evaluated and reviewed.

[0238] To compare the relative performance of the catalysts, except for the type of catalyst, the reaction conditions were maintained at the same level: 0.001 moles of ester reaction catalyst were added per mole of dimethyl terephthalate (DMT), and the transport gas flow was GHSV for 240 h⁻¹. -1 The reaction was carried out for 3 hours at a reaction temperature of 80°C.

[0239] As catalysts used for performance evaluation, metal acetate salts (e.g., zinc acetate), alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine organic compounds were selected, which are expected to exhibit the best performance in transesterification reactions. Their reactivity and acid dissociation equilibrium constants (pKa) are shown in Table 4 (reaction temperature 80 °C, reaction time 3 h, GHSV = 240 h). -1 ).

[0240] Table 4

[0241]

[0242] DMT: Dimethyl terephthalate; EG: Ethylene glycol.

[0243] BHET: Bis(2-hydroxyethyl)terephthalate

[0244] HEMT: 1-(2-Hydroxyethyl)4-methyl terephthalate, KOAc: CH3COOK, NaOAc: CH3COONa, Zn(OAc)2: Zn(CH3COO)·2H2O, TBD: Triazabicyclodecene.

[0245] K2-TPA: Dipotassium terephthalate

[0246] K-MMT: Potassium monomethyl terephthalate

[0247] In general high-temperature reaction processes for producing bis(hydroxyethyl) terephthalate (BHET) by depolymerization of polymers containing ester functional groups, metal acetate salts are used as catalysts. In particular, zinc acetate (Zn(CH3COO)2·2H2O) is most commonly used in commercial processes due to its high polymer depolymerization reactivity and excellent selectivity for BHET. To confirm the catalytic effectiveness of metal acetate salts in the transesterification reaction according to the present invention, reaction tests were performed after replacing the catalysts with potassium acetate, sodium acetate, and zinc acetate.

[0248] In Comparative Examples 3 and 4, where the catalyst was replaced with potassium acetate and sodium acetate under the same conditions, the yield of diethyl terephthalate (BHET) after 3 hours was only below 4%, exhibiting extremely low reaction performance. Furthermore, in Comparative Example 5, where zinc acetate was used as a catalyst, the yield of BHET was only 0.7%, the same as in Comparative Example 1 where no catalyst was used, with almost no BHET being formed. Therefore, it can be confirmed that metal acetate salts, which are effective in conventional high-temperature (≥190°C) glycolysis reactions, cannot be used as effective catalysts in the transesterification reaction performed according to the present invention.

[0249] When comparing the reaction results of Examples 3 and 17 to 19 using metal salt catalysts composed of anions of carbonate and bicarbonate, it can be confirmed that when the reaction is carried out for 3 hours using K2CO3 and sodium carbonate (Na2CO3) as catalysts, the yields of diethyl terephthalate (BHET) are 92.0% and 92.3%, respectively. Compared with the cases where potassium bicarbonate (KHCO3) and sodium bicarbonate (NaHCO3) are used as catalysts, the yield of diethyl terephthalate (BHET) is increased by more than 13%.

[0250] Alkali metal hydroxides (or alkali metal hydroxides) are used as representative raw materials in the depolymerization of polymers containing ester functional groups in alkaline hydrolysis. In alkaline hydrolysis, because the alkali metal hydroxide is directly used as a reactant for the decomposition of ester bonds, an excess of the ester bonds in the polymer is required. Water or alcohol is used as the reaction medium, while ethylene glycol is discharged as a reaction product.

[0251] In this application, the function of alkali metal hydroxides as catalysts, rather than as reactants for alkaline hydrolysis, was observed. Under the reaction conditions of this application—namely, supplying an excess of ethylene glycol and adding trace amounts of alkali metal hydroxide within a temperature range between room temperature (25°C) and the boiling point of ethylene glycol—it exhibits the function of a catalyst for transesterification. When transesterification was carried out with trace amounts of potassium hydroxide and sodium hydroxide (Examples 20 and 21) added at 0.001 mol per mole of dimethyl terephthalate (DMT), all of the dimethyl terephthalate (DMT) was converted, and the yield of diethyl terephthalate (BHET) reached over 91% after 3 hours of reaction.

[0252] Next, the performance of using alkoxide metal salts as alternative catalysts in the transesterification reaction was confirmed. When the catalyst was replaced with potassium methoxide (CH3OK) or sodium methoxide (CH3ONa) (Examples 22 and 23), not only was higher reactivity observed, but the yields of diethyl terephthalate (BHET) reached high levels of 90.6% and 83.6%, respectively, after 3 hours of reaction. These catalysts showed a significant improvement in the rate of the first additional reaction from dimethyl terephthalate (DMT) to the first ethylene glycol reaction (to produce methyl hydroxyethyl terephthalate (HEMT)) compared to the previous use of alkali metal carbonate catalysts (Examples 3 and 18), but exhibited a slightly lower reaction rate in the second additional reaction (to produce BHET).

[0253] High transesterification performance was also observed when alkaline earth metal oxide catalysts were used. When the catalysts were replaced with magnesium oxide and calcium oxide (Examples 24 and 25), conversion rates of over 96% were observed, with yields of diethyl terephthalate (BHET) of 77.4% and 90.6% after 3 hours of reaction, respectively.

[0254] Finally, the reaction characteristics of metal-free organocatalysts were compared. In Example 26, triazabicyclodecene (TBD), a guanidine compound commonly used as a catalyst for organic synthesis due to its strong base properties, was used as a catalyst for the transesterification reaction. Similar to Example 3, where potassium carbonate (K₂CO₃) was used as a catalyst, after a reaction time of 3 hours, almost all of the added dimethyl terephthalate (DMT) participated in the glycolysis reaction, and a high yield of 90.5% of diethyl terephthalate (BHET) was observed.

[0255] A comparison of the reaction performance in Table 4 based on the acid dissociation equilibrium constant (pKa) of the catalyst used confirms that, in order to obtain bis(hydroxyethyl) terephthalate (BHET) in high yield by performing a low-temperature (≤100°C) glycolysis reaction, a catalyst with a pKa value of 6 or higher is preferred.

[0256] [BHET terephthalate is produced by transesterification of polymers containing ester functional groups]

[0257] The glycolysis reaction for the direct production of bis(hydroxyethyl) terephthalate (BHET) from polymer feedstocks containing ester functional groups is typically carried out at high temperatures of 190–300 °C. As reported in several prior studies, high-temperature glycolysis reactions generally use metal acetates as catalysts and are carried out at temperatures close to or above the boiling point of the additional reactant, ethylene glycol. In the corresponding catalytic reactions, the yield of the monomer product (bis(hydroxyethyl) terephthalate (BHET)) obtained by glycolysis can reach over 80%, higher than that of other compounds. However, in addition to byproducts generated through side reactions such as hydrolysis (e.g., methyl(hydroxyethyl) terephthalate (MHET) and terephthalic acid), a certain proportion of dimers or oligomers are also generated at reaction equilibrium. In contrast, in an embodiment of the invention, when depolymerization is performed using a low-temperature methanol decomposition-glycolysis tandem reaction pathway with a different temperature range and a different mechanism for the formation of diethyl terephthalate (BHET), high-purity diethyl terephthalate (BHET) containing only small amounts of reaction intermediates (e.g., methyl hydroxy terephthalate (HEMT)) and dimers can be obtained in high yield.

[0258] Table 5 records the results of methanol decomposition at high temperature (190°C) and low temperature (25°C) transesterification reactions using raw material 2 as a common raw material, as well as the results of ethylene glycol-added transesterification reactions at 80°C.

[0259] In the table below, the molar amounts of ethylene glycol (EG) and catalyst in Comparative Example 6 are based on repeating units of polyethylene terephthalate (PET), and the molar amounts of ethylene glycol (EG) and catalyst in Example 27 are based on dimethyl terephthalate (DMT).

[0260] Table 5

[0261]

[0262] DMT: Dimethyl terephthalate; EG: Ethylene glycol.

[0263] BHET: Bis(2-hydroxyethyl)terephthalate

[0264] HEMT: 1-(2-Hydroxyethyl)4-methyl terephthalate

[0265] MHET: Mono(hydroxyethyl) terephthalate

[0266] K2-TPA: Dipotassium terephthalate

[0267] K-MMT: Potassium monomethyl terephthalate

[0268] When zinc acetate was used and the depolymerization reaction was carried out at high temperature (Comparative Example 6), polymer decomposition occurred rapidly from the initial stage of the reaction (within 2 hours), and the yield of diethyl terephthalate (BHET) reached 80.6%. However, when exposed to the reaction conditions for a longer period (about 8 hours), the increase in the yield of diethyl terephthalate (BHET) was not significant, and a high concentration of undecomposed compounds, such as approximately 4.1% dimer and 10-15% oligomer yield, was observed.

[0269] In Example 27, the previously used polyethylene terephthalate (PET) feedstock (feedstock 2) was used again. A portion of the catalyst was removed by filtration in the liquid reaction mixture obtained through room temperature (25°C) depolymerization based on methanol decomposition using a suitable co-solvent. Then, after removing the solvent by increasing the temperature, ethylene glycol was added to perform a second reaction, namely glycolysis. In the reaction described above, significantly different reaction characteristics and product distribution were observed compared to the high-temperature glycolysis of Comparative Example 6.

[0270] In Example 27, an extremely high dimethyl terephthalate (DMT) conversion rate was observed from the initial stage of the reaction, and a yield of over 92% of bis(hydroxyethyl) terephthalate (BHET) was observed after the reaction conditions were left for a sufficiently long time (more than 8 hours). Observation of the distribution of reaction byproducts revealed that in the high-temperature glycolysis of Comparative Example 6, mono(hydroxyethyl) terephthalate (MHET) was generated as a reaction byproduct, but in Example 27, ethylene glycol-added ethyl terephthalate (HEMT) was obtained as an intermediate product, and the reaction rate was relatively fast; after 8 hours of reaction, only a very small amount of ethyl terephthalate (HEMT) concentration of less than 0.5% was observed remaining.

[0271] The results described above confirm that the same catalyst can be used continuously in each reaction when producing bis(hydroxyethyl) terephthalate (BHET) from polymers containing ester functional groups via methanol decomposition-glycolysis reaction.

[0272] [Characteristics of transesterification reactions with different alcohol reactant types and comparison of monomer product yields]

[0273] Table 6 records the results of observations on transesterification reactions conducted by adding different types of mono- or poly-ols to replace ethylene glycol, the raw material for glycolysis, during the production of polymer monomers containing ester functional groups (reaction temperature 100℃, GHSV = 240h). -1 ).

[0274] Table 6

[0275]

[0276]

[0277] DMT: Dimethyl terephthalate, K2-TPA: Dipotassium terephthalate, K-MMT: Potassium monomethyl terephthalate, EG: Ethylene glycol, PDO: Propanediol, BDO: Butanediol, HDO: Hexanediol, CHDM: 1,4-cyclohexanediol, 2E1H: 2-Ethyl-1-hexanol

[0278] Monomer product: Both methyl groups in dimethyl terephthalate (DMT) are completely replaced by diol reactants.

[0279] Intermediate: Only one methyl group in dimethyl terephthalate (DMT) is replaced by transesterification.

[0280] When using chain diols (Examples 12 and 28 to 32) and cyclic diols (Example 33) as additional reactants in transesterification reactions, it was observed that the initial conversion rate of dimethyl terephthalate (DMT) slowed down with increasing carbon number. This is presumably because steric hindrance may occur with increasing diol molecular size, and the reactivity in the transesterification reaction decreases with increasing carbon number. In the case where 1,3-propanediol was used as a reactant in Example 28, the first transesterification reaction of dimethyl terephthalate (DMT) to the intermediate methyl 1-(3-hydroxypropyl)-4-terephthalate (HBMT) was faster than in the case where 1,4-butanediol was used as a reactant in Example 29, but the second transesterification reaction from the intermediate to the product bis(3-hydroxypropyl) terephthalate (BHPT) was relatively slower. This indicates that the structural characteristics of the diol compound substituted by the first transesterification reaction affect the rate of the second transesterification reaction.

[0281] When the transesterification reaction was carried out using a structural isomer (1,2-propanediol) (Example 31) that was expected to directly affect the transesterification reaction due to the adjacent arrangement of the second alcohol functional group, replacing 1,3-propanediol (Example 28) with diols (α,ω-diol) at both ends of the chain, the rates of both the first and second transesterification reactions were significantly limited. However, comparing the results of transesterification reactions using a structural isomer of butanediol, which has a relatively long chain structure, as a reactant (Examples 29 and 32), it was found that the rates of both the first and second transesterification reactions were not significantly limited due to the flexibility of the chain. In the case of using 1,4-cyclohexanediethanol, which contains a relatively large cyclic hydrocarbon structure, as a reactant (Example 33), the transesterification reaction rate became slower due to the steric hindrance of the diol molecule itself. Furthermore, it was observed that only the first transesterification reaction occurred selectively in the early stages of the reaction, and the results described above indicate that monomer structures with different ester bond pairs can be designed by using different types of mono- or poly-alcohol reactants in the first and second transesterification reactions.

[0282] In the case of transesterification using 2-ethylhexanol, the main raw material for plasticizers, as an additional reactant (Example 34), a relatively fast conversion rate of dimethyl terephthalate (DMT) was observed from the initial stage of the reaction. Thus, most of the conversion of dimethyl terephthalate (DMT) was completed within 2 hours. Moreover, even when the reaction conditions were maintained at high temperature for the next 8 hours, no by-products were generated, and the monomer product, dioctyl terephthalate (DOTP), could be stably maintained.

[0283] In summary, by changing the type of alcohol added according to an example of this application and applying it to the transesterification reaction conditions, monomers with functional groups of various structures can be produced by means of ester bonds to the form of terephthalic acid esters.

[0284] While specific aspects of the invention have been described in detail above, those skilled in the art will understand that these specific descriptions are merely preferred embodiments and the scope of the invention is not limited thereto. Therefore, the essential scope of the invention should be defined by the appended claims and their equivalents.

Claims

1. A method for producing a terephthalic acid ester derivative from dimethyl terephthalate, characterized by, include: (a) After adding monohydric and / or polyhydric alcohols as reactants for transesterification to dimethyl terephthalate, the transesterification reaction is carried out in the presence of one or more catalysts for transesterification selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides and guanidine organic compounds, while a flow of transport gas is applied. as well as, (b) The step of isolating and obtaining the terephthalate derivative produced by the reaction, The transesterification reaction in step (a) is carried out at 50-140°C.

2. The method for producing terephthalic acid ester derivatives from dimethyl terephthalate according to claim 1, characterized in that: The catalyst used for transesterification in step (a) is in the range of 0.00005 to 1.0 molar ratio compared to each mole of dimethyl terephthalate.

3. The method for producing terephthalic acid ester derivatives from dimethyl terephthalate according to claim 1, characterized in that: The alcohol in step (a) is ethylene glycol.

4. A method for producing terephthalate derivatives by depolymerization of a polymer comprising ester functional groups, characterized in that, include: (A) A step of depolymerization by introducing methanol, a polar aprotic solvent and potassium carbonate into a polymer containing ester functional groups, wherein the depolymerization product obtained by step (A) includes dimethyl terephthalate. (B) A step of adding a monohydric and / or polyhydric alcohol as a reactant for transesterification to a depolymerization product comprising dimethyl terephthalate, and then, in the presence of one or more catalysts for transesterification selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine organic compounds, while applying a transport gas stream to the depolymerization product; and, (C) The step of isolating and obtaining the terephthalate derivative produced by the reaction, The transesterification reaction in step (B) is carried out at 50-140°C.

5. The method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups according to claim 4, characterized in that: Following step (A), a step is performed to separate a portion of the compound from the depolymerization product to the outside.

6. The method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups according to claim 5, characterized in that: The portion of the compound isolated to the outside comprises one or more selected from polymers containing unreacted ester functional groups, insoluble catalysts, polar aprotic solvents, and reaction byproducts.

7. The method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups according to claim 4, characterized in that: The polar aprotic solvent in step (A) is an inert solvent that does not participate in the depolymerization reaction of polymers containing ester functional groups and can reduce the solubility of the catalyst in alcohol. The organic compound in the polar aprotic solvent is a compound with a chain-like and / or cyclic skeletal structure, and the organic compound contains one or more of halogen elements, oxygen, and nitrogen.

8. The method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups according to claim 4, characterized in that: The polar aprotic solvent in step (A) is selected from one or more of the following: toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propionitrile, aminopropionitrile, methylaminopropionitrile, iminodipropionitrile, butyronitrile, methylbutenyl nitrile, butane nitrile, methyl ethyl ether, diethyl ether, ethyl phenyl ether, dimethoxybenzene, trimethoxybenzene, methoxyphenol, tetrahydrofuran, methyltetrahydrofuran, dioxane, chloromethane, dichloromethane, chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, and trichlorobenzene.

9. The method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups according to claim 4, characterized in that: In step (A), the number of moles of the alcohol and the number of moles of the polar aprotic solvent, compared to the number of repeating moles of the polymer raw material containing the ester functional group, are in the range of 0.1 to 5,000 times the number of repeating moles of the polymer raw material containing the ester functional group.

10. The method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups according to claim 4, characterized in that: Prior to performing the transesterification reaction in step (B), as reactants for transesterification, the molar number of a monohydric and / or polyhydric alcohol; and / or one or more transesterification reactions selected from the group consisting of alkali metal carbonates, alkali metal hydroxides, alkali metal alkoxides, alkaline earth metal oxides and guanidine organic compounds in the depolymerization product of step (A) is adjusted to a specific range relative to the molar amount of dimethyl terephthalate contained in the depolymerization product.

11. The method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups according to claim 4, characterized in that: The methanol recovered in step (C) is reused as the depolymerization feedstock in step (A).

12. The method for producing terephthalic acid ester derivatives by depolymerization of a polymer containing ester functional groups according to claim 4, characterized in that: The number of moles of catalyst used in the transesterification reaction in step (B) is 0.00005 to 1.0 times that of each mole of dimethyl terephthalate contained in the depolymerization product.

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