METHOD FOR PRODUCING TEREPTALATE DERIVATIVES BY ESTER CONVERSION REACTION OF DIMTHYL TEREPTALATE

Abstract

The invention relates to a method for producing terephthalate derivatives from dimethyl terephthalate. The invention proposes an efficient and economical method for producing terephthalate derivatives from dimethyl terephthalate with high yield by optimizing reaction conditions, selecting an optimal ester conversion catalyst, and simplifying the procedures.

Description

Method for producing terephthalate derivatives by transesterification of dimethyl terephthalate

[0001] The present invention relates to an ester exchange reaction for producing a high value-added derivative in which a functional group bonded to terephthalate is substituted in a different form from dimethyl terephthalate (DMT) through an ester exchange reaction, and to an efficient depolymerization method of a polymer including an ester functional group thereby. The present invention relates to an efficient conversion method for producing a high value-added terephthalate derivative in a high yield by performing an ester exchange reaction using the DMT and a monohydric and / or polyhydric alcohol as raw materials at a temperature from room temperature (25°C) to a temperature below the boiling point of the applied alcohol using at least one selected from alkali metal carbonate, alkali hydroxide, alkali metal alkoxide, alkaline earth metal oxide, and guanidine-based organic compound as a catalyst, and to a depolymerization reaction process of a polymer including an ester functional group, which can obtain the high value-added terephthalate derivative in a high yield while improving the process efficiency and economic feasibility of the ester exchange reaction by linking the process with a methanolysis reaction.

[0002] Plastics are inexpensive, durable materials that are easy to mold and process, making them a versatile material for the production of a wide range of products. These advantages have led to a dramatic increase in plastic consumption across industry and daily life for decades. However, improperly managed plastic waste can lead to environmental pollution, or microplastics, broken down into small pieces, can float throughout the ecosystem, accumulating in living organisms and ultimately entering the human body through fine dust, drinking water, and food. Furthermore, more than 50% of these plastics are used for single-use, disposable purposes, such as packaging, agricultural films, and disposable consumer goods, or for short-term products discarded within a year of manufacture.

[0003] Most discarded plastics are randomly disposed of in designated landfills or natural habitats where natural decomposition is difficult, increasing the severity of environmental pollution. Even plastics that are biodegradable or biodegradable can persist for decades, depending on local environmental factors such as UV exposure, temperature, and the presence of decomposing microorganisms.

[0004] To address these issues, various research efforts are underway to minimize the accumulation of plastics or reduce their environmental impact, ranging from the chemical degradation of existing petroleum-based plastics to the physical regeneration and reprocessing of plastics, including the development of new plastic materials with short decomposition cycles in nature.

[0005] Polymers containing ester functional groups can be depolymerized into monomers through depolymerization, and various chemical reaction pathways have been developed. The monomers produced through decomposition can theoretically possess properties equivalent to those of the raw materials used in the initial polymer synthesis. Depolymerization pathways used industrially for polyester recycling include hydrolysis, glycolysis, methanolysis, and ammonolysis. Various chemical depolymerization methods are widely used, ranging from combinations of these processes to hybrid processes that leverage the strengths of each process.

[0006] More specifically, the method for depolymerizing polymers containing the ester functional groups listed above is described. In the case of hydrolysis, it is known that decomposition can proceed through various reaction pathways in the presence of acid, base, or metal salt catalysts. In the case of reactions applying acid as a catalyst, a very high concentration of sulfuric acid solution is required to obtain a high reaction yield, and thus, there are disadvantages such as economic issues due to process design, operation, and post-treatment. In the case of reaction systems applying base and metal salt catalysts, the decomposition reaction rate is very slow, the product purity is low, and catalyst recovery is difficult, so it is inefficient.

[0007] Glycolysis is a depolymerization reaction that involves adding glycol as a reactant. A common example of glycolysis is the process of producing bis(2-hydroxyethyl) terephthalate (BHET) by adding an excess of ethylene glycol, a monomer raw material. Because ethylene glycol, a raw material for the synthesis of polyethylene terephthalate (PET), is used as a reactant, the products produced by this depolymerization reaction have a chemical structure in which ethylene glycol is already bound to both ends of the terephthalate. Therefore, even replacing only a portion of the raw materials in a conventional polycondensation process using terephthalic acid can yield highly advantageous results from a kinetic perspective.

[0008] Furthermore, since the product obtained from the glycolysis reaction can be directly used as a raw material for PET synthesis, it has the advantage of being applicable to the production of polymer materials by modifying only a portion of the existing PET production line without excessive separate facility investment. Glycolysis is generally performed under reflux conditions of the reactant glycol, and has the problem that the process of decomposing oligomers into monomers is slow, and even if the reaction time is delayed, equilibrium between compounds is reached, which can result in low product purity. In addition, it is difficult to isolate the final product, the monomer, from the reactant with high purity or high yield. Metal salts such as zinc acetate or lithium acetate are typically used as reaction catalysts. The metal ions that make up these catalysts are not completely removed during the purification process and can remain in the product. In addition, even small amounts of metals that are harmful to the human body can be included in the recycled monomer, making it difficult to utilize them in products produced by reintroducing them, especially in the reprocessing of materials for food, medical, and other daily necessities. In addition, although glycolysis is a reaction that proceeds at high temperatures, the product recovery and purification process generally follows the low-temperature recrystallization method, which results in high energy consumption and low cost and efficiency depending on the method of supplying the heat source for the production process.

[0009] The methanolysis process is one of the most widely used commercial processes, not only in global chemical companies but also in small and medium-sized plastics industries. Theoretically, dimethyl terephthalate (DMT) is produced as the final monomer product. As the transesterification reaction progresses, ethylene glycol equivalent to the number of moles of decomposed terephthalate is liberated. In practice, partial methanolysis, reaction equilibrium with free ethylene glycol, and side reactions such as hydrolysis can lead to the formation of byproducts such as hydroxyethyl methyl terephthalate (1-(2-Hydroxyethyl) 4-methyl terephthalate (HEMT) and monomethyl terephthalate (MMT). The target compound of the methanolysis reaction, DMT, can be utilized as an intermediate in processes for producing other monomers with higher value or in complex hybrid depolymerization processes (e.g., methanolysis-glycolysis). In addition, it has a relatively low boiling point compared to other monomers and it is easy to control the selectivity for hydrogenation reaction, so it can be used as a gaseous reactant for producing high value-added diol monomers (e.g., 1,4-cyclohexanedimethanol), and it can be easily purified by recrystallization or distillation process, so it can also be used as a raw material for PET polymerization that requires high purity and high quality. However, since methanol is used as a reaction solvent, harsh reaction conditions of high temperature and high pressure are required, and the initial cost may be excessive to have a reactor that can meet such an operating environment and related auxiliary facilities with durability, and additional unit processes for reactant recovery and product purification are essential, so a high investment cost may be required.The catalyst used may be a typical ester exchange reaction catalyst containing heavy metals such as magnesium acetate, cobalt acetate, and lead dioxide, including zinc acetate, which is a depolymerization catalyst commonly used in glycolysis reactions. However, this may cause problems such as human health hazards and environmental problems due to the residual metal content in the product.

[0010] Methanolization, along with hydrolysis or alkaline decomposition, has been widely utilized as a depolymerization reaction process for polymers containing ester functional groups. However, both reactions are high-temperature and energy-intensive processes, and performing depolymerization at low temperatures can result in long reaction times and limited product quality and quantity. When methanolysis is selected as the reaction route for the production of depolymerizable monomers, the yield and purity of the monomer product, DMT, are significantly affected by the reactivity of the catalyst and reactive impurities. To reduce the burden of the product purification process, both effective methods for suppressing side reactions and high reactivity are required.

[0011] As a prior art, Japanese Patent Laid-Open No. JP1998-287741 (Patent Document 1) describes a method for treating waste PET with methanol to highly efficiently recover dimethyl terephthalate and alkylene glycol, wherein, when recovering dimethyl terephthalate from a polyalkylene terephthalate polymer, methanol is continuously introduced into the polymer, at least part of which is in a molten state, to produce DMT through a depolymerization reaction of the polyalkylene terephthalate, and the depolymerization reaction temperature is 200 to 300°C, and potassium carbonate or the like is used as a catalyst. However, the patent has a disadvantage in that the depolymerization temperature is too high, which increases the investment cost for equipment and the energy used in the reaction process.

[0012] Therefore, in depolymerizing a polymer containing an ester functional group by a methanolysis reaction, a method that can increase the depolymerization reaction rate without using excessive energy and improve the selectivity of the reaction to produce a high yield of DMT may be advantageous, and if this can be used as an intermediate to form a continuous transesterification reaction, it is expected that an efficient and economical process that can produce BHET or other forms of terephthalate derivatives in a high yield while reducing energy consumption can be realized.

[0013] As an example of the above reaction, in the transesterification reaction using DMT and ethylene glycol as starting materials and producing BHET, a high value-added monomer, as the final product, HEMT, in which the methyl end group bonded to terephthalate is partially substituted, is produced as a reaction intermediate, and a compound in which a carboxylic acid functional group is bonded to terephthalate through hydrolysis may be produced as a side reaction. It is expected that the design of a reaction path that can promote the step-by-step transesterification reaction so that all 2 molar equivalents of methanol bonded to DMT can be exchanged with ethylene glycol will be possible while suppressing this side reaction path as much as possible, and by identifying the optimal operating conditions under which BHET production can proceed dominantly and applying them to the process, it will be possible to design an efficient BHET manufacturing process.

[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), it was reported that in the transesterification reaction using DMT and ethylene glycol, a composite metal planar structure manufactured through modification after introducing zinc and titanium into hydrotalcites was used as a catalyst, which improved the selectivity of BHET, a high value-added monomer, to 96.1%.

[0015] However, in the case of the above-mentioned prior literature, even though the ester exchange reaction was performed at a high temperature of 180°C, the conversion rate of dimethyl terephthalate remained at a level of less than 70%, a lot of energy may be consumed in purifying BHET from the obtained reaction mixture, the catalyst manufacturing process is complicated, so there may be a problem with reproducibility, and the metal introduced into the catalyst may also be leached, so there may be limitations in the efficiency and economic feasibility of the process for application to commercial processes.

[0016] Therefore, when manufacturing high-value-added terephthalate derivatives through the transesterification of DMT, it is crucial to avoid excessive energy consumption, utilize environmentally friendly materials with low toxicity, and ensure economic feasibility through the use of low-cost catalysts and process simplification. Furthermore, the development of an integrated reaction and purification process technology that improves both process efficiency and economic feasibility, enabling the production of terephthalate derivatives in high yields as well as the conversion rate of DMT, is required. The manufactured derivatives can be utilized as various upcycled raw materials with high industrial value, such as recycled monomers for the recycling of waste plastic resources, additives such as plasticizers, and polymerization raw materials for the synthesis of materials in which some or all of the glycol is modified to improve physical properties.

[0017] In order to solve the above problems, the present invention aims to provide a method for producing a high-yield, high-value-added monomer by a simple process through an ester exchange reaction, that is, a method for producing another form of terephthalate derivative from dimethyl terephthalate (DMT).

[0018] In addition, the present invention expands and applies the method for converting the DMT into another form of terephthalate derivative, and provides a method for manufacturing a terephthalate derivative in a high yield as a product at a temperature from room temperature (25°C) to the boiling point of the applied alcohol by applying a monohydric and / or polyhydric alcohol as a reactant with a reaction product generated from the depolymerization of a polymer containing an ester functional group, that is, an efficient and economical depolymerization method for manufacturing a high value-added terephthalate derivative through a multiple ester exchange reaction using a polymer raw material containing an ester functional group as a starting material.

[0019] In order to solve the above problem, the present invention provides a method for producing a terephthalate derivative from DMT, characterized by comprising the steps of: (a) adding a monohydric and / or polyhydric alcohol to dimethyl terephthalate as a solvent for ester exchange, and performing an ester exchange reaction while applying a flow of a carrier gas in the presence of at least one catalyst for ester exchange selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds; and (b) obtaining a terephthalate derivative produced by the above reaction by separating the same.

[0020] In one embodiment of the present invention, the ester exchange reaction of step (a) may be carried out at a temperature range between room temperature and the boiling point of the monohydric and / or polyhydric alcohol solvent as the reactant, and the catalyst for the ester exchange reaction may have a molar ratio of 0.00005 to 1.0 per mole of dimethyl terephthalate.

[0021] In one embodiment of the present invention, the alcohol in step (a) may be ethylene glycol.

[0022] In addition, the present invention provides a method for producing a terephthalate derivative by depolymerizing a polymer containing an ester functional group, characterized by comprising the steps of: (A) depolymerizing a polymer containing an ester functional group by adding an alcohol, a polar aprotic solvent, and potassium carbonate (K2CO3); (B) performing an ester exchange reaction while adding a flow of a carrier gas to the depolymerization result obtained in step (A); and (C) separating and obtaining a terephthalate derivative produced by the reaction.

[0023] In one embodiment of the present invention, after step (A), a step of separating some compounds from the depolymerization result may be further performed, and some compounds separated to the outside may include one or more selected from a polymer including an unreacted ester functional group, an insoluble catalyst, a polar aprotic solvent, a reaction byproduct, etc.

[0024] In addition, the polar aprotic solvent of the above step (A) is an inert solvent that does not participate in the depolymerization reaction of a polymer containing an ester functional group, and is a solvent that can lower the solubility of a catalyst for alcohol, and the skeletal structure of the organic compound is a compound in a chain form and / or a ring form, and at least one of a halogen element, oxygen, and nitrogen is bonded to the organic compound, and is selected from the group consisting of toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propionitrile, aminopropionitrile, methylaminopropionitrile, iminodipropionitrile, butyronitrile, methylbutenenitrile, butanenitrile, methyl ethyl ether, diethyl ether, ethylphenyl ether, dimethoxybenzene, trimethoxybenzene, methoxyphenol, tetrahydrofuran, methyltetrahydrofuran, dioxane, chloromethane, dichloromethane, It may be one or more selected from chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, and trichlorobenzene.

[0025] Additionally, in one embodiment of the present invention, in the step (A), the number of moles of the alcohol and the number of moles of the polar aprotic solvent relative to the number of moles of repeating units of the polymer raw material including an ester functional group may be in a ratio range of 0.1 to 5,000 times the number of moles of repeating units of the polymer raw material including an ester functional group.

[0026] In addition, in one embodiment of the present invention, before performing the ester interchange reaction in step (B), a monohydric and / or polyhydric alcohol reactant and / or one or more ester interchange reaction catalysts selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds may be added as reactants for ester interchange to the depolymerization result in step (A), such that the mole number of the catalyst is within a predetermined range per mole of dimethyl terephthalate contained in the depolymerization result, and the methanol recovered in step (C) may be reused as a depolymerization raw material in step (A).

[0027] In addition, in one embodiment of the present invention, the catalyst for the ester exchange reaction controlled in step (B) is characterized in that the molar number is 0.00005 to 1.0 times per mol of dimethyl terephthalate included in the depolymerization result.

[0028] The present 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 process configuration that requires little energy consumption. More specifically, the present invention utilizes a method for altering the reaction equilibrium that can be reached within a closed system between monomer raw materials, added monohydric and / or polyhydric alcohols, and methanol liberated by the transesterification reaction. For example, the present invention provides a method for producing terephthalate derivatives in high yields by selectively discharging only methanol to the outside, thereby suppressing methanolysis, which corresponds to the reverse reaction, and promoting the transesterification reaction, which corresponds to the forward reaction.

[0029] According to an example of the present invention, a catalyst in a reactant can be used that is effective in ester interchange, and there is no need to distinguish between the reaction selectivity of methanolysis and the ester interchange reaction that produces a derivative. It can exhibit sufficient reactivity even with a trace amount of 1 / 1000 to 1 / 10th of the mass of the catalyst used in the depolymerization reaction of a polymer containing a general ester functional group, and can be used to induce an effective and efficient ester interchange reaction that can maintain selectivity. Therefore, the ester interchange reaction can be performed using only all or a portion of the catalyst remaining in the reaction product discharged from the methanolysis reaction system that has been performed previously. The vapor discharged to the outside is high-purity methanol equivalent to the amount of DMT, and almost all of it can be concentrated / recovered. The recovered methanol can be 100% recycled as a reactant for methanolysis for the depolymerization of a polymer containing an ester functional group. Therefore, if methanolysis and the ester interchange reaction that produces a derivative are configured together, it corresponds to a technology that theoretically enables perfect methanol recycling.

[0030] In addition, the present invention can provide a method for producing a high yield of a terephthalate derivative using DMT and ethylene glycol obtained from the depolymerization of a polymer containing an ester functional group as reaction intermediates. For example, a method can be provided for producing a high yield of DMT and ethylene glycol through a low-temperature methanolysis reaction that can be performed in the presence of methanol, a polar solvent, and an ester exchange reaction catalyst, and then producing BHET as a final product through an ester exchange reaction in which ethylene glycol is added to the produced DMT. According to an example of the present invention, when depolymerization of a polymer containing an ester functional group is performed, it is possible to produce BHET, a high-value monomer, in a high yield even without using the high-temperature reaction conditions (190 to 280°C) of conventional glycolysis. For example, high yields of BHET can be selectively produced by a series of reaction processes maintained at temperatures close to room temperature, below the boiling point of the applied diol reactant (e.g., ethylene glycol), and even below the boiling point of methanol, which means that low-temperature, low-energy glycolysis depolymerization technology can be implemented.

[0031] The method according to the present invention can maintain the amount of dimer or oligomer produced lower than that of the existing high-temperature glycolysis reaction, thereby obtaining a relatively high concentration of BHET, while maintaining the temperature of the reactant similar to the operating range of the purification process for removing impurities (including dimers or oligomers), and can be directly applied to the purification process without going through a preheating or cooling process that involves energy consumption when transporting the reactant, thereby minimizing energy loss and facilitating the implementation of continuous reaction and post-treatment processes.

[0032] The transesterification reaction performed according to the present invention can be applied to the production of recycled monomers or terephthalate derivatives, which can be applied to the synthesis of various materials other than BHET, which can be used in the repolymerization of PET. For example, because the monomer produced has geometrical characteristics different from the structure of estrogen hormones, it can be applied to materials that can replace phthalate plasticizers known to cause hormone disruption in the human body. Furthermore, it can be utilized in the production of raw materials for improving the properties of various types of plastics. While PET possesses excellent thermal and mechanical properties, its low final crystallization temperature and slow crystallization rate make it difficult to perform injection molding within a short cycle, limiting its applications. Therefore, the market demand for various types of polymer resins with improved properties tailored to specific purposes and applications is steadily increasing. For example, methods for improving the properties of the final product by introducing new monomers into the diol units of PET for copolymerization or by modifying some of the diols used during polycondensation are already widely used in industry. For example, if ethylene glycol is replaced with butylene glycol during the condensation polymerization process and polymerization is performed, polybutylene terephthalate (PBT), a polymer with excellent injection molding properties due to its more flexible chain structure, can be produced. In addition, if different types of diols are introduced, it can be applied to the synthesis of various types of polymer materials. That is, in performing the transesterification reaction of DMT according to an example of the present invention, by modifying the reactants of monohydric and / or polyhydric alcohols and applying similar reaction conditions, various types of terephthalate derivatives can be easily produced.In particular, if the reaction product manufactured from the methanolysis of waste PET is directly utilized as a raw material, a recycled monomer can be manufactured economically through a very simple and easy reaction process, and a wide range of upcycling processes can be configured to flexibly manufacture various high value-added terephthalate derivatives by varying the raw material injection.

[0033] FIG. 1 is a diagram illustrating a method for supplying a carrier gas to discharge methanol generated from an ester exchange reaction of DMT to the outside of a reactor according to one embodiment of the present invention.

[0034] FIG. 2 is a diagram illustrating an example of a process combination that can be configured to obtain a terephthalate derivative, a product, in high yield through depolymerization from a polymer raw material containing an ester functional group according to one embodiment of the present invention.

[0035] FIG. 3 is a schematic diagram illustrating an example configuration of an experimental device for performing an ester exchange reaction of DMT according to one embodiment of the present invention.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In general, the nomenclature used herein is well known and commonly used in the art.

[0037] Whenever it is said throughout this specification that a part "includes" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0038] The present invention provides an optimal catalyst for obtaining a high value-added terephthalate derivative in high yield in performing an ester exchange reaction that can be performed by using DMT as a raw material and adding a monohydric and / or polyhydric alcohol.

[0039] In one aspect, the present invention provides a method for an ester interchange reaction, wherein at least one selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds is selected as a catalyst for converting DMT into a terephthalate derivative in a high yield through an ester interchange reaction.

[0040] In addition, the present invention provides a method for producing a terephthalate derivative derived from DMT, which can obtain a terephthalate derivative in high yield by setting optimal reaction conditions in addition to the optimal ester exchange reaction catalyst in converting DMT into a terephthalate derivative by a glycolysis reaction.

[0041] The method of the present invention comprises the steps of (a) adding a monohydric and / or polyhydric alcohol to DMT as a reactant for an ester interchange reaction, and performing an ester interchange reaction while applying a flow of a carrier gas in the presence of at least one ester interchange reaction catalyst selected from the group consisting of an alkali carbonate, an alkali hydroxide, an alkali alkoxide, an alkaline earth metal oxide, and a guanidine-based organic compound; and (b) obtaining a terephthalate derivative produced by the reaction by separating it.

[0042] In the present invention, the introduction of the catalyst and the flow of the carrier gas in step (a) can be supplied to the reactants without limitation before or after the reactants reach the target temperature, and can be performed under batch reaction conditions or continuous flow conditions. The catalyst and the additional reactants, i.e., monohydric and / or polyhydric alcohols, can also be introduced in a mixed form with DMT prior to preparing the reaction.

[0043] The above-mentioned carrier gas flow is used as a means for discharging methanol to the outside, and a flow by forced circulation of a gas phase with a pressure gradient can be used. In addition, a continuous flow of gas that is condensed outside the reactor and then recirculated with a nearly diluted vapor concentration (Fig. 2a) can be used, or a method of discharging methanol to the outside by continuously supplying an inert gas from the outside (Fig. 2b) can also be used.

[0044] In performing the ester interchange reaction according to the step (a) above, dimethyl terephthalate, a monohydric and / or polyhydric alcohol, and a catalyst for ester interchange reaction are introduced into the reactor, and a transport pipe is placed below the level of the reactants so that the carrier gas can induce direct gas-liquid contact with the reactants in the reactor, thereby allowing bubbles to be sprayed. In this process, a concentration of methanol vapor in the gas phase is formed, and it can be continuously discharged to the outside through a flow to the outside by the carrier gas. It may be advantageous for the reactivity of the methanol vapor diffusing into the carrier gas if mass transfer occurs above the saturation concentration, but if a carrier gas is supplied at a sufficient rate, the amount of methanol discharged can be controlled by the rate of the ester interchange reaction.

[0045] The temperature of the above ester exchange reaction can be maintained within a range in which the evaporation rate of methanol generated from the reaction or present in the reactants occurs during the gas-liquid contact process, that is, a temperature between room temperature and the boiling point of the monohydric and / or polyhydric alcohol applied as the reactant, and a pressure of 0.1 torr to 5 atm in absolute pressure, but can be changed within the above range in consideration of the range of temperature and pressure for carrying out the ester exchange reaction and the rate of methanol removal by the carrier gas.

[0046] The above temperature range may vary depending on the catalyst for the transesterification reaction being introduced, and is preferably a temperature between room temperature and the boiling point of the alcohol used as the reactant. Furthermore, it may be advantageous for the process to be stable and continuous to proceed at a pressure near atmospheric pressure. Furthermore, the reaction time in step (a) may vary depending on the type and amount of catalyst used in the reaction, as well as the amounts of DMT and alcohol supplied.

[0047] First, in the step (a), the catalyst for the transesterification reaction may be added in a molar ratio of 0.00005 to 1.0, preferably 0.0001 to 0.2, per unit mole of the raw material DMT. When the catalyst for the transesterification reaction is included in a molar ratio of less than 0.00005 per unit mole of the raw material DMT, the transesterification reaction of DMT with monohydric and / or polyhydric alcohols may proceed slowly, thereby reducing process efficiency. When the catalyst is included in a molar ratio exceeding 1.0, the degree of improvement in effect is not great compared to the increased catalyst content, which is uneconomical, and by-products may rather increase. In addition, when separating a terephthalate derivative, the excess catalyst remains as an impurity, which may affect separation and purification efficiency.

[0048] The catalyst for the above ester exchange reaction is at least one selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds, preferably at least one selected from K2CO3, KHCO3, Na2CO3, NaHCO3, NaOH, KOH, MgO, CaO, CH3OK, CH3ONa, and TBD, and the amount and combination of the catalysts should be such that the conversion rate of DMT can be significantly improved, while also significantly improving the yield for terephthalate derivatives.

[0049] (a) The amount of ethylene glycol in step may range from 1 to 50 moles per mole of DMT. The esterification reaction can occur most efficiently when the amount of ethylene glycol is within the above range.

[0050] The above monohydric and polyhydric alcohols may be alcohols having 1 to 20 carbon atoms in a straight chain, branched chain, cyclic chain, or a mixture thereof, and the polyhydric alcohols have two or more OH functional groups. Examples of the alcohols include at least one of methanol, ethanol, n-propanol, isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, glycerol, and 1,2,4-butanetriol, and preferably, ethylene glycol may be used.

[0051] In the step (a) of adding a monohydric and / or polyhydric alcohol to DMT under the catalyst for the above-described transesterification reaction to carry out the transesterification reaction, a terephthalate derivative and methanol are produced, and the forward reaction to the produced terephthalate derivative product is carried out under the condition that the flow of carrier gas is maintained inside the reactor and the methanol vapor is continuously discharged to the outside of the reaction system so that the forward reaction can continue above the equilibrium concentration. As a method for supplying the carrier gas, a method using a unidirectional flow (b in FIG. 2) in which methanol vapor is separated by a condenser and then discharged to the outside, or a method (a in FIG. 2) in which methanol vapor is removed and then recycled can be used.

[0052] The carrier gas injected into the reactor may be advantageous in terms of improving the DMT conversion rate and the yield of terephthalate derivative products by maintaining the concentration of methanol in the reactants at a low level so as to prevent or suppress the methanol by-product from the ester exchange reaction from being recombined through a reverse reaction. At this time, the carrier gas may be used without limitation as long as it does not chemically react with the alcohol addition ester exchange reaction of DMT or the catalyst, and preferably, air, nitrogen, argon, helium, etc. may be used, and preferably, an inert gas that does not substantially contain moisture may be advantageous.

[0053] In the present invention, step (b) is a step of obtaining a terephthalate derivative formed by the above reaction by separating it, and specifically, a step of obtaining a terephthalate derivative formed in step (a) with high purity by separating it from a reaction mixture containing unreacted residual DMT, ethylene glycol, residual catalyst, etc., and can be performed by a generally known purification method, and the method is not limited thereto, but can be performed in parallel with physical methods such as filtration, crystallization, centrifugation, evaporation, and distillation, or chemical methods such as adsorption, neutralization, and salting out.

[0054] The present invention relates to a method for producing a high value-added terephthalate derivative through an ester exchange reaction in which a monohydric and / or polyhydric alcohol can be added using DMT as a starting material, wherein the DMT may be obtained from the depolymerization of a polymer containing an ester functional group, and a terephthalate derivative may be produced by subjecting the depolymerization product to an ester exchange reaction with a monohydric and / or polyhydric alcohol with or without a pretreatment process.

[0055] The above-mentioned transesterification reaction by monovalent and / or polyvalent alcohol addition of DMT can also be applied to a reaction process for producing a high yield of terephthalate derivatives through a two-step serial reaction in which a reaction product produced through a methanolysis reaction from a polymer raw material containing an ester functional group is directly used as a raw material for a second transesterification reaction.

[0056] That is, the present invention includes a method for initiating depolymerization of a polymer including an ester functional group to produce a terephthalate derivative as a final product, and provides a method for producing a high value-added terephthalate derivative by depolymerization of a polymer including an ester functional group, characterized by comprising the steps of: (A) adding an alcohol, a polar aprotic solvent, and potassium carbonate (K2CO3) to a polymer including an ester functional group to depolymerize the polymer; (B) performing an ester exchange reaction while applying a flow of a carrier gas to the depolymerization result obtained in step (A); and (C) obtaining a terephthalate derivative product by separating the product.

[0057] Figure 1 conceptually diagrams a process for producing a terephthalate derivative through an ester exchange reaction from a polymer raw material containing the ester functional group. First, step (100) of (A) is a step of introducing a polymer containing an ester functional group, an alcohol, a polar aprotic solvent, and potassium carbonate (K2CO3) into a depolymerization reactor to depolymerize the polymer. The polymer containing the ester functional group comes into contact with the alcohol, the polar aprotic solvent, and potassium carbonate (K2CO3) to produce an alcohol addition monomer through an ester exchange reaction, and low-temperature depolymerization of the polymer effectively proceeds. The process is very simple, can obtain DMT in a high yield of 90% or more, and is very economical because of low energy consumption.

[0058] Here, the polymer containing the ester functional group may be in the form of a single or mixed waste plastic, such as polyethylene, high-density polyethylene, low-density polyethylene, polypropylene, or a combination thereof mixed with the polymer containing the ester functional group. Other polymers mixed with the polymer containing the ester functional group listed as examples above are merely examples and are not limited to those listed above.

[0059] In addition, the polymer including an ester functional group may be a polymer formed by polycondensation of a dicarboxylic acid and a dialcohol, wherein the dicarboxylic acid is selected from the group consisting of terephthalic acid, naphthalene dicarboxylic acid, diphenyldicarboxylic acid, diphenyl ether dicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, trimellitic acid, pyromellitic acid, and combinations thereof, and the dialcohol is selected from the group consisting of ethylene glycol, trimethylene glycol, 1,2-propanediol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, decanedicarboxylic acid, dodecamethylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, and dipropylene. selected from the group consisting of glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, di(tetramethylene) glycol, tri(tetramethylene) glycol, polytetramethylene glycol, pentaerythritol, 2,2-bis(4-β-hydroxyethoxyphenyl)propane and combinations thereof.

[0060] As an example, the polymer comprising the ester functional group may be selected from polyethylene terephthalate (PET), polypropylene terephthalate (PPT), polyglycolide or polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyhydroxyalkanoate (PHA), polyhydroxybutyrate (PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), Vectran, and combinations thereof.

[0061] The most common example of a polymer containing the above ester functional group is polyethylene terephthalate (PET), wherein the starting materials for producing the polymer are terephthalic acid or a derivative monomer thereof and ethylene glycol.

[0062] The polymer containing an ester functional group used in the present invention may not be pure, but may contain various impurities. For example, in addition to the polymer containing an ester functional group, a mixture of debris, including but not limited to bottle caps, adhesives, paper, residual liquid, dust, or combinations thereof, may be used as a raw material for depolymerization.

[0063] The alcohol as a reactant is preferably a straight-chain primary alcohol, and may be, for example, methanol, ethanol, propanol, butanol or a combination thereof.

[0064] The above alcohol can be used in a ratio range of 0.1 to 5,000, preferably 1 to 500, per mole of repeating unit of the polymer raw material containing the ester functional group.

[0065] Potassium carbonate is used as the catalyst. Potassium carbonate is expressed by the chemical formula K2CO3 and is a white crystal that dissolves in water. It is preferable to use the potassium carbonate in an anhydrous form rather than a hydrate form, and it is even more preferable to dry it before use. The amount of potassium carbonate used may be 0.01 times or more the number of moles of the polymer repeating unit containing the ester functional group, preferably 0.01 to 100 times, and more preferably 0.1 to 10 times.

[0066] The above polar aprotic solvent is used as an organic liquid compound that can be applied to lower the activation energy of a decomposition reaction or an ester exchange reaction of an ester functional group, and is a non-reactive, inert solvent that does not directly participate in the reaction, and lowers the solubility of a catalyst (potassium carbonate) in a reactant (alcohol) to induce a heterogeneous catalytic reaction, and it may be thermodynamically desirable to be able to dissolve the monomer produced.

[0067] The skeletal structure of the organic compound in the above polar aprotic solvent may be a chain-shaped or ring-shaped compound, or a halogen element may be directly bonded to the organic compound, or the organic compounds may be connected to each other or to themselves by oxygen or nitrogen. As a specific example, at least one selected from among toluene, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, tetrahydrofuran, dichloro methane, chloroform, chlorobenzene, methyl phenyl ether, and ethyl phenyl ether may be used.

[0068] In addition, the polar aprotic solvent can be used in a molar ratio range of 0.1 to 5,000 times the number of moles of repeating units of the polymer raw material containing the ester group, preferably in a molar ratio range of 1 to 500 times.

[0069] Since the above step (A) depolymerizes a polymer containing an ester functional group by alcohol addition in the range of 0 to 80°C, preferably 10 to 60°C, according to some examples according to the above (A), complete decomposition of the polymer can be induced near ambient pressure and ambient temperature, and since the reaction system can be implemented through a simple structure and configuration, the investment cost can be much lower than that of existing technologies or existing processes, and efficient and stable energy management is also possible.

[0070] Meanwhile, since the depolymerization of the above step (A) basically uses a water-soluble, heterogeneous, inexpensive catalyst, the recovery and reuse of the catalyst after the reaction is easy, and the temperature of the reactant itself can be lowered below room temperature to recover the manufactured monomer at a high rate, and the used solvent can be reintroduced as a depolymerization raw material for a new polymer raw material, so the economic feasibility of the recycling process can be further improved.

[0071] Furthermore, in the above step (A), the depolymerization of the polymer can be achieved by obtaining sufficient energy necessary for depolymerization solely from the heat of mixing, heat of dissolution, etc. generated during the process of preparing the mixed solution for the depolymerization reaction without the input of an additional heat source. In this case, the depolymerization can be performed within an insulated reactor. Furthermore, as in some specific examples according to the present invention, depolymerization can be performed while supplying an external heat source.

[0072] Additionally, the depolymerization of the polymer can be performed at a pressure higher than atmospheric pressure. Specifically, it can be performed at a pressure of about 1 atm to 6.5 atm.

[0073] In addition, the depolymerization of the polymer can be performed in a form exposed to the atmosphere or in a closed system, and can also be performed by refluxing the solvent using a condenser.

[0074] In addition, the depolymerization reaction time of step (A) may vary depending on the amount of polymer used, but at room temperature with no energy applied, the monomer can be obtained in a sufficiently high yield within 24 hours, and since the substances other than the reactants do not undergo significant chemical changes, most of them can be recovered and reintroduced into the process.

[0075] After the step (A), a step (200) of separating some compounds from the depolymerization result obtained by depolymerization may be further performed. Specifically, the step of separating some compounds from the depolymerization result is a step of separating a flow including at least one selected from the polymer, an insoluble catalyst, a polar aprotic solvent, a reaction byproduct, etc. from a reaction mixture (10) including DMT and ethylene glycol obtained after completion of the depolymerization reaction in the step (A) and byproducts such as unreacted substances, methanol, a polar aprotic solvent, a catalyst, or monomethyl terephthalate (MMT), terephthalic acid (TPA) derivatives, etc., to the outside, and can be performed by a generally known method, and the method is not limited thereto.

[0076] As an example of separation, if an insoluble catalyst and unreacted polymer are separated from the depolymerization result through filtration, the depolymerization result can take on a uniform liquid form, and if temperature is applied or pressure is reduced to evaporate or distill part or all of the concentration of the polar aprotic solvent or methanol, crystallization of DMT in the depolymerization result can occur. Here, a washing solution may be additionally added as a method for removing foreign substances and increasing the concentration of DMT, and methods such as recrystallization, physical filtration, distillation, evaporation, and drying may be additionally used to prepare the result as a raw material for ethylene glycol addition transesterification. The solvent and catalyst separated from the depolymerization result can be reintroduced (20) as a raw material for the methanolysis depolymerization (100) of the previous step (A).

[0077] Meanwhile, the step (200) of separating some of the compounds may be a step performed to prepare for the ester exchange reaction step (300) performed by adding monovalent and / or polyvalent alcohols to the produced DMT, but this does not necessarily mean that it must be performed. That is, the depolymerization product obtained from the depolymerization step of the polymer including the ester functional group of the step (A) may be directly used as a raw material of the step (B) without going through the step (200) of separating the depolymerization product.

[0078] In the present invention, step (B) (300) is a step of performing an ester interchange reaction while adding a flow of carrier gas (3) to the depolymerization result obtained in step (A). The method for performing the ester interchange reaction in step (B) is the same as the method for producing a terephthalate derivative from DMT described above, and thus a detailed description thereof will be omitted. The DMT in step (B) is obtained by depolymerization of a polymer containing an ester functional group (30), and the depolymerization can be performed by a simple process at room temperature and pressure, and the product of the depolymerization contains a high yield of DMT and a polyhydric alcohol. By using the method for producing a terephthalate derivative from DMT of the present disclosure, a terephthalate derivative can be directly obtained as a final product from a polymer containing an ester functional group.

[0079] Before performing the ester interchange reaction in the above step (B), the depolymerization result in step (A) may be subjected to the ester interchange reaction by adding one or more ester interchange reaction catalysts selected from the group consisting of monohydric and / or polyhydric alcohols and / or alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds as a solvent for the ester interchange reaction, after adjusting the mole number to a predetermined range per mole of dimethyl terephthalate contained in the depolymerization result.

[0080] The molar number of the alcohol and / or ester exchange reaction catalyst is controlled by adding the alcohol and / or ester exchange reaction catalyst to the depolymerization product, removing a portion of the alcohol and / or ester exchange reaction catalyst from the depolymerization product, or adding a new monohydric and / or polyhydric alcohol after the partial removal. In this case, the removal and addition processes may also be performed in the step (200) of separating some of the compounds described above.

[0081] The newly added monohydric and / or polyhydric alcohols may be linear, branched, cyclic or mixed alcohols having 1 to 20 carbon atoms, and the polyhydric alcohols have two or more OH functional groups.

[0082] The mole number of ethylene glycol after the above adjustment may be in the range of 0.1 to 100 moles per mole of dimethyl terephthalate contained in the depolymerization result, and preferably in the range of 1 to 50 moles.

[0083] Additionally, the mole number of the catalyst for the transesterification reaction after adjustment may be in the range of 0.00005 to 1.0 mole per mole of dimethyl terephthalate contained in the depolymerization result, preferably in the range of 0.0001 to 0.2 mole.

[0084] In the above ester interchange reaction (300), in order to suppress the reverse reaction by methanol and at the same time continue the addition reaction of monohydric and / or polyhydric alcohols in the direction of product generation, methanol can be discharged (40) outside the reactor by the flow of carrier gas (3), and the methanol recovered through the condenser (400) maintained at a low temperature can be reused (60) as a depolymerization reaction raw material in step (A). Compared to the conventional BHET production method by the glycolysis method using high-temperature reaction conditions (typically in the range of 200 to 280°C), the reaction can proceed rapidly even at a low temperature much lower than the boiling point of the monohydric and / or polyhydric alcohols, so that terephthalate derivative products can be effectively obtained, and since the reaction temperature range and the reaction path to the product are different, products (dimers or oligomers) that are generated due to less decomposition (or depolymerization) within the product are generated in a relatively low concentration or not generated at all, whereas terephthalate derivatives can be obtained in a high yield.

[0085] According to the method of the present invention, the reactivity in the low-temperature region and the efficiency of the purification process are improved, thereby significantly reducing energy consumption compared to existing processes, and consequently providing a means for economically producing high-value-added terephthalate derivatives.

[0086] In the present invention, step (C) is a step (500) of separating and obtaining a high yield of terephthalate derivatives manufactured by the above reaction, and can be performed in the same manner as the method for manufacturing terephthalate derivatives from DMT described above, so a detailed description thereof is omitted.

[0087] Below, the details of the process of the present invention will be explained through comparative examples and examples. These examples are merely representative examples for illustrating the present invention, and the scope of application of the present invention is not limited to the examples below.

[0088] Raw material 1 (dimethyl terephthalate raw material)

[0089] Dimethyl terephthalate (Sigma-Aldrich, cat.# 185124, purity > 99.0%) supplied from a reagent manufacturer was evenly ground using a mortar and pestle to prepare a fine powder as raw material 1.

[0090] Raw material 2 (polymer raw material containing ester functional group)

[0091] As a polymer material containing an ester functional group, a bottle made of waste polyethylene terephthalate material discharged after consumption was washed and dried to remove any remaining foreign substances, and then crushed using a continuous crushing mill (manufacturer and model: IKA MF10.1), and then only plastic chips having a width and length of 1 to 3 mm and a thickness of 0.5 mm or less were collected using a standard sieve to prepare raw material 2.

[0092] <Example 1>

[0093] About 14.5 g of DMT raw material prepared according to the process of raw material 1 and about 55.6 g of ethylene glycol (Sigma-Aldrich; purity ≥ 99.8%), a dihydric alcohol polar solvent (corresponding to 12 times the mole number of raw material 1), were placed in a 3-neck flask, and after equipping a distillation device with a condenser, stirring was started at a speed of 1,200 rpm using a magnetic stirrer.

[0094] To effectively remove methanol, a reaction product, high-purity nitrogen (Central Industrial Gas; 99.9992%) was used as an inert carrier gas, and the gas flow rate in contact with the liquid in the reactor was regulated using a mass flow controller so that the set value could be maintained constant at 200 sccm, or 240 when converted to gas hourly space velocity (GHSV(hr-1)) by normalizing it to the volume of the initial reaction mixture under standard conditions.

[0095] After that, the flask containing the reactants was started to be heated, and when the final temperature of the reaction solution reached 80℃, about 0.05 g of potassium carbonate (K2CO3; Sigma-Aldrich, ACS reagent) as a catalyst (corresponding to 0.005 times the mole number of the introduced raw material 1) was added to initiate the reaction, and then the ester exchange reaction was performed for a total of 8 hours to obtain BHET, a high value-added depolymerization monomer. As the reaction progressed, the generated methanol was degassed from the reactants by the flow of carrier gas, discharged to the outside of the reactor, and collected by an external trap maintained at 0℃ or lower.

[0096] During the above reaction, a small amount (less than 50 mg) of the liquid reactant was collected at each time point and quantified using high-performance liquid chromatography (HPLC with Optimapak C18 Column (250 mm, 5 micron), UV detector (λ=254 nm)) pre-calibrated with a standard sample, and the product distribution and concentration were estimated from this, and the conversion rate and product yield were calculated, respectively. During HPLC analysis, a mixed solution of methanol:water 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.

[0097] The conversion rate of DMT by the transesterification reaction and the yields of intermediate products in which the transesterification reaction from DMT to alcohol reactant has partially progressed (e.g., HEMT in the case of ethylene glycol addition transesterification reaction), monomer products produced when the transesterification reaction has completely progressed (e.g., BHET in the case of ethylene glycol addition transesterification reaction), dimers, and side products such as potassium monomethyl terephthalate (K-MMT) and dipotassium terephthalate (K2-TPA) were calculated using the following formulas.

[0098] DMT conversion rate = (N0- N) / N0 (Formula 1)

[0099] Monomer yield = (N monomer / N0) × 100% (Formula 2)

[0100] Intermediate yield = (N intermediate / N0) × 100% (Formula 3)

[0101] MMT yield = (N MMT / N0) × 100% (Formula 4)

[0102] TPA yield = (N TPA / N0) × 100% (Formula 5)

[0103] Dimer yield = (N dimer / N0) × 100% (Formula 6)

[0104] In the above formula, N0 is the number of moles of DMT, which is the initial input raw material, and N, N intermediate , N monomer , N MMT , N TPA and N dimer is the mole number of terephthalate contained in the unconverted DMT, intermediates, monomer products, MMT, TPA and dimer.

[0105] <Comparative Example 1>

[0106] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that potassium carbonate was not added.

[0107] <Example 2>

[0108] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.001 g (corresponding to 0.0001 times the mole of raw material 1) of potassium carbonate was used in Example 1.

[0109] <Example 3>

[0110] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.01 g of potassium carbonate (corresponding to 0.001 times the mole of raw material 1) was used in Example 1.

[0111] <Example 4>

[0112] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.1 g of potassium carbonate (corresponding to 0.01 times the mole of raw material 1) was used in Example 1.

[0113] <Example 5>

[0114] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.5 g of potassium carbonate (corresponding to 0.05 times the mole of raw material 1) was used.

[0115] <Example 6>

[0116] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 2.1 g of potassium carbonate (corresponding to 0.2 times the mole number of raw material 1) was used in Example 1.

[0117] Comparative Example 2

[0118] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that an inert carrier gas was not used in the above Example 1.

[0119] <Example 7>

[0120] An ester exchange reaction was performed and evaluated by the same method as in Example 1, except that high-purity nitrogen was maintained as an inert carrier gas at 50 sccm (GHSV=60 h-1).

[0121] <Example 8>

[0122] An ester exchange reaction was performed and evaluated by the same method as in Example 1, except that high-purity nitrogen was maintained as an inert carrier gas at 100 sccm (GHSV=120 h-1).

[0123] <Example 9>

[0124] An ester exchange reaction was performed and evaluated by the same method as in Example 1, except that high-purity nitrogen was maintained as an inert carrier gas at 500 sccm (GHSV=600 h-1).

[0125] <Example 10>

[0126] The ester exchange reaction was performed and evaluated by the same method as in Example 1, except that the temperature of the reaction solution was maintained at 50°C.

[0127] <Example 11>

[0128] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that the temperature of the reaction solution was maintained at 65°C.

[0129] <Example 12>

[0130] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that the temperature of the reaction solution was maintained at 100°C.

[0131] <Example 13>

[0132] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that the temperature of the reaction solution was maintained at 110°C.

[0133] <Example 14>

[0134] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that the temperature of the reaction solution was maintained at 120°C.

[0135] <Example 15>

[0136] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that the temperature of the reaction solution was maintained at 130°C.

[0137] <Example 16>

[0138] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that the temperature of the reaction solution was maintained at 140°C.

[0139] <Example 17>

[0140] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.008 g (corresponding to 0.001 times the mole 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.

[0141] <Example 18>

[0142] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.008 g (corresponding to 0.001 times the mole of raw material 1) of sodium carbonate (Na2CO3) was used as a catalyst and the reaction time was maintained at 3 hours.

[0143] <Example 19>

[0144] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that about 0.006 g (corresponding to 0.001 times the mole 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.

[0145] <Comparative Example 3>

[0146] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that about 0.007 g (corresponding to 0.001 times the mole of raw material 1) of potassium acetate (KOAc) was used as a catalyst and the reaction time was maintained at 3 hours.

[0147] Comparative Example 4

[0148] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that about 0.006 g (corresponding to 0.001 times the mole of raw material 1) of sodium acetate (NaOAc) was used as a catalyst and the reaction time was maintained at 3 hours.

[0149] Comparative Example 5

[0150] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that about 0.01 g (corresponding to 0.001 times the mole 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.

[0151] <Example 20>

[0152] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.004 g (corresponding to 0.001 times the mole of raw material 1) of potassium hydroxide (KOH) was used as a catalyst and the reaction time was maintained at 3 hours.

[0153] <Example 21>

[0154] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.003 g (corresponding to 0.001 times the mole of raw material 1) of sodium hydroxide (NaOH) was used as a catalyst and the reaction time was maintained at 3 hours.

[0155] <Example 22>

[0156] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that about 0.005 g (corresponding to 0.001 times the mole of raw material 1) of potassium methoxide (CH3OK) was used as a catalyst and the reaction time was maintained at 3 hours.

[0157] <Example 23>

[0158] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that about 0.004 g (corresponding to 0.001 times the mole 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.

[0159] <Example 24>

[0160] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.003 g (corresponding to 0.001 times the mole of raw material 1) of magnesium oxide (MgO) was used as a catalyst and the reaction time was maintained at 3 hours.

[0161] <Example 25>

[0162] An ester exchange reaction was performed and evaluated using the same method as in Example 1, except that about 0.004 g (corresponding to 0.001 times the mole number of raw material 1) of calcium oxide (CaO) was used as a catalyst and the reaction time was maintained at 3 hours.

[0163] <Example 26>

[0164] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that about 0.01 g (corresponding to 0.001 times the mole of raw material 1) of triazabicyclodecene (TBD) was used as a catalyst in Example 1 and the reaction time was maintained at 3 hours.

[0165] <Comparative Example 6: PET Depolymerization by High-Temperature Glycolysis Reaction>

[0166] About 10 g of PET raw material 2 was prepared as a raw material for the glycolysis reaction. About 38.75 g of ethylene glycol (12 mol per mol of polymer repeating unit), a dihydric alcohol polar solvent, was charged into a 3-neck flask, and after equipping a reflux condenser at atmospheric pressure, it was heated and stirred using a heated magnetic stirrer. When the temperature reached 177℃, 10 g of the prepared polymer raw material was added, and stirring was continued while raising the temperature. When the reaction mixture reached 197℃ or the reflux temperature, about 0.571 g of zinc acetate catalyst (0.05 mol per mol of polymer repeating unit) was added to initiate the catalytic reaction, and the reaction was performed using a condenser with one end exposed to atmospheric pressure while continuously stirring for 2 hours, while maintaining the reaction temperature constant within a range of ±0.5℃. After the reaction, the unreacted products among the results were separated and quantified through filtration, and the decomposed monomers, dimers, side products such as mono(hydroxyethyl) terephthalate (MHET) and oligomers were quantified using high-performance liquid chromatography calibrated in advance with standard samples in a manner similar to the method used to quantify the reactants of Example 1, and then the product distribution and concentration were estimated.

[0167] <Example 27: PET depolymerization by room temperature methanolysis and low temperature glycolysis>

[0168] About 3 g of the PET raw material prepared according to Raw Material 2, about 66.3 g of dichloromethane (Samchun Pure Chemicals; purity 99.5%) (corresponding to 50 times the mole number of the repeating unit of the Raw Material 2 polymer), 24.96 g of methanol (Samchun Pure Chemicals; 99.9%) (corresponding to 50 times the mole number of the repeating unit of the Raw Material 2 polymer), and about 0.43 g of K2CO3 (potassium carbonate; Sigma-Aldrich, ACS reagent) as a catalyst (corresponding to 0.2 times the mole number of the repeating unit of the Raw Material 2 polymer) were placed in a 3-neck flask, and double-distilled water was added to adjust the initial moisture content of the reactants to have an initial mole number of 0.4 per mole number of the repeating unit of the Raw Material polymer. The reaction was carried out using a magnetic stirrer at 500 rpm for 24 hours at 25℃ and atmospheric pressure.

[0169] After the reaction, the resultant product was filtered and separated into a filtrate containing organic solvents, etc., along with some of DMT, HEMT, ethylene glycol, and K-MMT, a potassium salt of MMT, and a solid (filter cake) containing unreacted PET, K2CO3 catalyst, and K-MMT.

[0170] The potassium salts in the above filtrate and solid were each taken in trace amounts (less than 50 mg) and diluted in a mobile phase aqueous solution to prepare samples. The product distribution and concentration in each sample were estimated through quantitative analysis using high-performance liquid chromatography (HPLC with Optimapak C18 Column (250 mm, 5 micron), UV detector (λ=254 nm)). Unreacted PET in the solid was quantified by the gravimetric method. The conversion rate of PET and the yields of DMT, HEMT, TPA, and MMT according to the depolymerization reaction were calculated from the quantified values. During HPLC analysis, a mixed solution of methanol:water 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.

[0171] The conversion rate of PET and the yield of DMT by depolymerization reaction were calculated using the following formula.

[0172] PET conversion rate = (M0- M) / M0× 100% (Formula 7)

[0173] DMT yield = (M DMT / M0) × 100% (Formula 8)

[0174] In the above formula, M0 and M represent the number of moles of repeating units of the initially introduced raw polymer (PET) and the unreacted polymer, respectively, and M DMT represents the number of moles of DMT produced.

[0175] The filtrate of the above depolymerization resultant was used as a raw material for an ester interchange reaction in which ethylene glycol was added. The ester interchange reaction was performed under the same conditions as in Example 1, except that the filtrate of the depolymerization resultant was used instead of Raw Material 1 as a raw material, and most of the methanol and polar aprotic solvent were removed using a vacuum evaporator. Thereafter, the mole number of DMT was adjusted to be the same as in Example 1, and the ethylene glycol was added to the amount produced from the depolymerization and the additional amount so that the total amount was approximately 55.6 g (a mole ratio of 12 times the mole number per mole of DMT), and the ester interchange reaction was performed and evaluated without additionally adding a catalyst.

[0176] The mole numbers of catalyst and K-MMT in the solid recovered after filtration were quantified gravimetrically and HPLC, respectively (measured at a mole ratio of 0.126 and 0.024 compared to the mole number of repeating units of raw materials), and the mole number excluding that recovered in the solid phase from the mole number of initially introduced catalyst (based on the mole balance of potassium cations) was estimated as the mole number of residual catalyst in the filtrate of the depolymerization result. From this, it was found that the amount of catalyst (K2CO3) in the raw material for the ester interchange reaction in which ethylene glycol is added exists in a ratio of approximately 0.054 mole per unit mole of DMT.

[0177] The conversion rate of DMT by ester exchange reaction and the yields of BHET, HEMT, and BHET dimer were calculated using the above-mentioned equations 1 to 4, and the results are shown in Table 5.

[0178] <Example 28>

[0179] An ester interchange reaction was performed and evaluated in the same manner as in Example 1, except that 1,3-propanediol (Sigma-Aldrich; purity ≥ 98%) was used in the same molar ratio (12 times the molar ratio of DMT units) instead of ethylene glycol as the reactant in Example 1 and that the temperature of the reaction solution was maintained at 100°C.

[0180] <Example 29>

[0181] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that 1,4-butanediol (Sigma-Aldrich; ReagentPlus®, purity ≥ 99%) was used in an equimolar amount (12 times the molar ratio of DMT unit moles) instead of ethylene glycol as a reactant in Example 1 and that the temperature of the reaction solution was maintained at 100°C.

[0182] <Example 30>

[0183] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that 1,6-hexanediol (Sigma-Aldrich; purity ≥ 99%) was used in an equimolar amount (12 times the molar ratio of DMT unit moles) instead of ethylene glycol as a reactant in Example 1 and that the temperature of the reaction solution was maintained at 100°C.

[0184] <Example 31>

[0185] An ester exchange reaction was performed and evaluated in the same manner as in Example 1, except that 1,2-propanediol (Sigma-Aldrich; ReagentPlus®, purity ≥ 99%) was used in an equimolar amount (12 times the molar ratio of DMT unit moles) instead of ethylene glycol as a reactant in Example 1 and that the temperature of the reaction solution was maintained at 100°C.

[0186] <Example 32>

[0187] An ester interchange reaction was performed and evaluated in the same manner as in Example 1, except that 1,3-butanediol (Sigma-Aldrich; Anhyrous, purity ≥ 99%) was used in an equimolar amount (12 times the molar ratio of DMT unit moles) instead of ethylene glycol as a reactant in Example 1 and that the temperature of the reaction solution was maintained at 100°C.

[0188] <Example 33>

[0189] An ester interchange reaction was performed and evaluated in the same manner as in Example 1, except that 1,4-cyclohexanedimethanol (Sigma-Aldrich; mixture of cis and trans, purity ≥ 99%) was used in an equimolar amount (12 times the molar ratio of DMT unit moles) instead of ethylene glycol as a reactant in Example 1 and that the temperature of the reaction solution was maintained at 100°C.

[0190] <Example 34>

[0191] An ester interchange reaction was performed and evaluated in the same manner as in Example 1, except that 2-Ethyl-1-hexanol (Sigma-Aldrich; purity ≥ 99.6%) was used in an equimolar amount (12 times the molar ratio of DMT unit moles) instead of ethylene glycol as a reactant in Example 1 and that the temperature of the reaction solution was maintained at 100°C.

[0192] [Comparison of transesterification reaction characteristics according to catalyst usage]

[0193] [Table 1] shows the results of observing the effect of the reaction by adjusting the amount of potassium carbonate (K2CO3) used as a catalyst according to the example of the present invention in performing the ester exchange reaction in Examples 1 to 6 and Comparative Example 1 (reaction temperature 80°C, GHSV = 240h) -1 ). Unlike the examples in which a catalyst was used, in Comparative Example 1 in which no catalyst was added at all, the yields of BHET after 2 hours and 8 hours were approximately 0.0% and 2.4%, respectively, indicating that the rate of the transesterification reaction was very low. This is a result that explains that the use of a catalyst is essential to promote the addition transesterification reaction of ethylene glycol to DMT at low temperatures as exemplified in the present invention.

[0194] [Table 1]

[0195]

[0196] Examples 1 to 4 are the results of reactions conducted using potassium carbonate as a catalyst in an amount of 0.0001 to 0.01 mole per mole of DMT of raw material 1, and show that the production speed and yield of BHET are greatly improved as the amount of potassium carbonate increases.

[0197] Meanwhile, Examples 5 and 6 used potassium carbonate in amounts of 0.05 and 0.2 moles per mole of DMT, respectively, but the production rate and yield of BHET tended to decrease. On the other hand, the final yield of K2-TPA, a by-product of the reaction, tended to increase to 6.0% and 18.5%, respectively. This result explains that if an excessive amount of catalyst is used compared to the mole number of DMT introduced, not only catalyst consumption but also side reactions such as hydrolysis and alkali decomposition may be promoted. Therefore, appropriately controlling the amount of catalyst can help improve the performance and economic feasibility of the ester interchange reaction.

[0198] [Comparison of transesterification reaction characteristics according to gas space velocity (GHSV)]

[0199] When the transesterification reaction of DMT is performed in the presence of an excess of ethylene glycol solvent, the production rate of the product BHET is observed to be very high in the early stages of the reaction, and the production rate of methanol by-product by the exchange reaction also increases in proportion to the mole number of BHET produced. In a closed system, this transesterification reaction is not an irreversible reaction in which all of the initially introduced DMT is converted to BHET, and the reverse transesterification reaction involving the by-product methanol and BHET can also have a rate. When the forward and reverse reactions reach equilibrium, the concentration of the compound no longer changes, and even if the reaction conditions are changed, there may be a limit to improving the product yield. However, the reverse reaction can be suppressed by effectively removing some of the reaction products within the reaction product mixture or discharging them to the outside of the reaction system, and the characteristics of the reaction can be determined by the amount of change in the concentration of the corresponding substance, i.e., the mass transfer rate discharged to the outside.

[0200] Methanol produced from the ester exchange reaction performed according to an example of the present invention is a substance with the lowest boiling point among the raw materials and products introduced (130°C or higher than ethylene glycol). In addition to raising the temperature of the reaction system or lowering the pressure, if a carrier gas introduced from outside is continuously flowed, selective external discharge of methanol occurs and regeneration of DMT by the ester exchange reverse reaction can be suppressed.

[0201] [Table 2]

[0202]

[0203] [Table 2] shows the characteristics of the ester exchange reaction performed by varying the flow rate of the inert carrier gas (high purity nitrogen) introduced to cause gas-liquid contact with the reactants inside the reactor to remove methanol from the reaction product (reaction temperature 80℃).

[0204] In the absence of carrier gas flow (Comparative Example 2), a relatively low yield of about 58.4% of BHET was observed when the transesterification reaction was performed at 80℃ for 3 hours, and a slight increase of about 0.9% was observed in the reaction yield even after exposure to the reaction conditions for a long time of about 8 hours. Although the reactor exists in the form of an open system and the internal temperature is maintained above the boiling point of methanol, it can be expected that this is because the methanol produced as some of the transesterification reaction progressed did not dominantly diffuse to the headspace where the reactants were not filled or to the outside of the reactor, but rather existed at a high concentration within the reactants.

[0205] Meanwhile, in the case of the ester exchange reaction performed under continuous flow conditions with different flow rates of nitrogen as a carrier gas (Examples 1 and 7 to 9), it can be seen that the conversion rate and the yield of BHET are greatly improved. In particular, in the reactions performed according to Examples 1 and 9 in which the GHSV exceeds 200, it can be seen that a BHET yield of 92% or more is obtained when the reaction time exceeds 3 hours.

[0206] On the other hand, it was found that maintaining an excessively high carrier gas flow rate and exposing the reaction conditions for a long time did not improve the BHET yield as the yield of dimers and oligomers slightly increased. In the case of Example 1, no oligomers were observed in the reactants even when the reaction was performed for more than 3 hours. On the other hand, when the transesterification reaction was performed according to Example 9, it was observed that oligomers began to be formed after 6 hours and the selectivity of BHET decreased. Even when only a small amount of oligomers, less than 3%, was produced, the viscosity of the reaction mixture increased significantly, and some of the products formed a heterogeneous phase, causing the reactants to rapidly become suspended. Therefore, in order to maximize the yield of BHET, a high-molecular-weight depolymerization monomer, it may be desirable to apply the flow of the carrier gas, but select the optimal carrier gas flow conditions that can efficiently remove methanol produced from the transesterification reaction while also allowing the addition reaction of ethylene glycol to occur dominantly, which may improve the final yield of BHET.

[0207] [Changes in the characteristics of transesterification reaction according to reaction temperature]

[0208] [Table 3] shows the results of the reaction observed by performing the ester exchange reaction by adding ethylene glycol from DMT according to the method of the present invention at different reaction temperatures (GHSV = 240 h -1 ).

[0209] When the temperature was maintained above the boiling point of methanol (Example 1 and Examples 12 to 16), the BHET yield obtained from the ester interchange reaction could be maintained high from the beginning of the reaction, and it was found that a BHET yield of 95% or more was obtained when the reaction time exceeded 4 hours. It can be assumed that this improvement in yield was contributed by the increase in the mass transfer rate of methanol when the reaction temperature exceeded the boiling point of methanol, as well as the enhancement of the sequential glycolysis catalytic reaction rate in which DMT is converted to HEMT and then to BHET.

[0210] [Table 3]

[0211]

[0212] Meanwhile, when the ester exchange reaction was performed while maintaining the reaction temperature below the boiling point of methanol (Examples 10 and 11), the BHET yield according to the reaction time was observed to increase at a somewhat slower rate, reaching 45.4% and 73.9% after 2 hours of reaction time, and 68.1% and 86.8% after 4 hours of reaction time, respectively.

[0213] In addition, although not shown in the table, oligomers began to be detected upon exposure to reaction conditions for a long period of time (after 7 hours of reaction time), and approximately 11.2% and 3.3% of the applied DMT raw materials were converted to oligomers after 8 hours of reaction time, respectively. At this time, the viscosity of the reaction solution significantly increased, and it was also observed that it changed into a non-uniform suspension.

[0214] In summary, it was found that controlling the reaction temperature to a temperature exceeding the boiling point of methanol was more advantageous in order to increase the conversion of DMT within a short reaction time or residence time and to improve the yield of BHET, a monomer, without forming oligomers.

[0215] [Comparison of transesterification reaction characteristics according to reaction catalyst selection]

[0216] Conventional glycolysis reactions for producing BHET from polymers containing ester functional groups are performed at high temperatures, resulting in significant energy consumption. To overcome this issue, novel reaction pathways capable of producing high-yield BHET at low temperatures can be considered.

[0217] As an example of such a reaction pathway, the methanolysis reaction for producing DMT from a polymer raw material containing an ester functional group can be performed at room temperature, and if low-temperature reaction conditions can be provided in which continuous ethylene glycol addition can occur dominantly, it can be expected that a high yield of BHET can be produced.

[0218] If a separate separation process is not performed after the first reaction, methanolysis, some of the catalyst may remain in the resulting reaction mixture. However, it may be necessary to design or consider a new catalyst system that can exhibit sufficient performance for the subsequent transesterification reaction.

[0219] Catalysts commonly used in ester exchange reactions include acidic, basic, and metal salt catalysts. However, since acidic catalysts progress more slowly than basic catalysts, the reaction is usually performed at high temperatures (over 100°C). In addition, acid-resistant design of the reactor and auxiliary equipment is required to prevent corrosion, which may result in excessive initial investment costs.

[0220] Therefore, in the present invention, the reaction performance and usefulness of a basic catalyst and a metal salt catalyst expected to have reactivity and selectivity for the ethylene glycol addition transesterification reaction of DMT were evaluated.

[0221] In order to compare the relative performance of the catalysts, the same reaction conditions were used except for the type of catalyst, i.e., the amount of ester reaction catalyst added was 0.001 mol per 1 mol of DMT, the flow of carrier gas was maintained at GHSV 240 h-1, and the reaction temperature was maintained at 80°C, and the reaction was performed for 3 hours.

[0222] As catalysts for performance evaluation, metal acetates (e.g., zinc acetate), alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds, which are expected to show the best performance in the ester interchange reaction, were selected and used, and their reaction performances and acid dissociation equilibrium constants (pKa) are shown in [Table 4] (reaction temperature 80°C, reaction time 3 h, GHSV = 240 h). -1 ).

[0223] [Table 4]

[0224]

[0225] In a typical high-temperature reaction process for producing BHET through the depolymerization of polymers containing ester functional groups, metal acetate salts are used as catalysts. In particular, zinc acetate (Zn(CH3COO)2·2H2O) is the most commonly used in commercial processes due to its high polymer depolymerization reactivity and excellent selectivity for BHET. In order to confirm the catalytic effectiveness of metal acetate salts for the transesterification reaction according to the present invention, reaction experiments were performed after replacing potassium acetate, sodium acetate, and zinc acetate as catalysts.

[0226] In Comparative Examples 3 and 4, where potassium acetate and sodium acetate were substituted as catalysts under the same conditions and the reaction was performed, very low reaction performance was observed with a BHET yield of less than 4% after 3 hours. In addition, in Comparative Example 5, where zinc acetate was used as a catalyst, the BHET yield was 0.7%, and as in Comparative Example 1, which was performed without adding a catalyst, almost no BHET was produced. Therefore, it was confirmed that metal acetate salts that can be usefully used in conventional high-temperature (≥190°C) glycolysis reactions cannot be used as efficient catalysts for the transesterification reaction performed according to the present invention.

[0227] Comparing the reaction results of Example 3 and Examples 17 to 19 using a metal salt catalyst composed of carbonic acid and bicarbonate as anions, when potassium carbonate (K2CO3) and sodium carbonate (Na2CO3) were applied as catalysts and the reaction was performed for 3 hours, the yields of BHET were 92.0% and 92.3%, respectively, which was 13% higher than the yield of BHET obtained when potassium bicarbonate (KHCO3) and sodium bicarbonate (NaHCO3) were used as catalysts.

[0228] Alkali hydroxides (or alkali metal hydroxides) are typically used as raw materials for alkaline decomposition reactions in the depolymerization of polymers containing ester functional groups. In alkaline decomposition reactions, alkali hydroxides directly participate as reactants in the decomposition of ester bonds. Therefore, they are supplied in excess of the moles of ester bonds present in the polymer. Water or alcohol serves as a reaction medium, and ethylene glycol is released as a reaction product.

[0229] In this application, the function of alkali hydroxide as a catalyst rather than a reactant for alkali decomposition was observed. Under the reaction conditions of this application, that is, supplying ethylene glycol in excess and adding a small amount of alkali hydroxide in a temperature range between room temperature (25°C) and the boiling point of ethylene glycol, the function as a catalyst for the transesterification reaction can be expressed. When potassium hydroxide and sodium hydroxide (Examples 20 and 21) were added in small amounts of 0.001 mol per 1 mol of DMT and the transesterification reaction was performed, all DMT was converted, and the BHET yield reached a value of more than 91% after 3 hours of reaction.

[0230] Next, the performance of the transesterification reaction was confirmed when alkoxide metal salts were used as alternative catalysts. When potassium methoxide (CH3OK) or sodium methoxide (CH3ONa) was used as a catalyst (Examples 22 and 23), relatively high values ​​of 90.6% and 83.6% in BHET yields after 3 hours of reaction were observed along with high reactivity. Compared to the cases where alkali metal carbonate catalysts were applied previously (Examples 3 and 18), these catalysts were effective in increasing the rate of the first ethylene glycol addition reaction (HEMT production) from DMT, but showed somewhat lower reaction rates in the second addition (BHET production).

[0231] High performance of the ester exchange reaction was also observed when an alkaline earth metal oxide catalyst was applied. When the reaction was performed by replacing magnesium oxide and calcium oxide as catalysts (Examples 24 and 25), the conversion rate was observed to be over 96%, and the yields of BHET were 77.4% and 90.6%, respectively, after 3 hours of reaction.

[0232] Finally, the reaction characteristics for metal-free organic catalysts were compared. In Example 26, triazabicyclodecene (TBD), a guanidine compound with strong basic properties and commonly used as an organic synthesis catalyst, was used as a catalyst for the transesterification reaction. Similar to Example 3, which used potassium carbonate (K2CO3) as a catalyst, after 3 hours of reaction, almost all of the DMT introduced was involved in the glycolysis reaction, and the yield of BHET was observed to be relatively high at 90.5%.

[0233] When comparing the reaction performance according to the acid dissociation equilibrium constant (pKa) of the catalysts used in Table 4, it is confirmed that a catalyst having a pKa value of 6 or more is suitable for performing the low-temperature (≤100°C) glycolysis reaction of the present invention to obtain a high yield of BHET.

[0234] [Production of BHET by transesterification of polymers containing ester functional groups]

[0235] The glycolysis reaction, which directly produces BHET by depolymerizing a polymer containing an ester functional group as a raw material, is usually performed at a high temperature of 190–300°C. As reported in many previous literature, high-temperature glycolysis reactions typically utilize metal acetates as catalysts and are performed at temperatures near or above the boiling point of the adduct, ethylene glycol. In this catalytic reaction, the monomer product (BHET) from glycolysis is obtained at a higher rate than other compounds, at over 80%. However, in addition to by-products generated from side reactions such as hydrolysis (e.g., monohydroxyethyl terephthalate (MHET), terephthalic acid), dimers and oligomers are observed to be produced at a certain rate depending on the reaction equilibrium. On the other hand, when depolymerization is performed by adopting a low-temperature methanolysis-glycolysis serial reaction route with different temperature ranges and BHET production mechanisms according to an example of the present invention, high-purity BHET containing only a small amount of reaction intermediates (e.g., HEMT) and dimers can be obtained in high yield.

[0236] [Table 5] shows the results of a comparison of high-temperature (190°C) and low-temperature ester exchange reaction (25°C methanolysis and 80°C ethylene glycol addition ester exchange reaction) manufactured using the same raw material as raw material 2.

[0237] In the table below, the mole numbers of EG and catalyst in Comparative Example 6 are based on the repeating unit of PET, and the mole numbers of EG and catalyst in Example 27 are based on DMT.

[0238] [Table 5]

[0239]

[0240] When the depolymerization reaction was performed at high temperature using zinc acetate (Comparative Example 6), the polymer decomposition occurred rapidly from the initial stage of the reaction (within 2 hours), and a yield of 80.6% of BHET was obtained. However, when exposed to long-term reaction conditions for approximately 8 hours, the increase in the yield of BHET was not remarkable, and the concentration of unreacted compounds was observed to be high, with the yields of dimers at approximately 4.1% and oligomers at 10-15%.

[0241] In Example 27, using the same PET raw material (raw material 2) used previously, a liquid reaction mixture (DMT yield: 91%) obtained by methanolysis-based depolymerization at room temperature (25°C) using a cosolvent was filtered to remove part of the catalyst, the temperature was raised to remove the solvent, and ethylene glycol was added to perform the second reaction, glycolysis. In the case of this reaction, very different reaction characteristics and product distributions were observed from those of the high-temperature glycolysis of Comparative Example 6.

[0242] In Example 27, a very high DMT conversion rate was observed from the beginning of the reaction, and when left under reaction conditions for a sufficient time (more than 8 hours), a BHET yield exceeding 92% was observed. Looking at the distribution of reaction by-products, MHET was obtained as a reaction by-product in the high-temperature glycolysis of Comparative Example 6, but in Example 27, HEMT, to which ethylene glycol addition was performed on only one side, was obtained as a reaction intermediate, and it was observed that the reaction proceeded relatively quickly, leaving only a very low HEMT concentration of less than 0.5% after 8 hours of reaction.

[0243] From these results, it can be confirmed that the same catalyst can be used continuously for each reaction in producing BHET from a polymer containing an ester functional group through a low-temperature methanolysis-glycolysis reaction.

[0244] [Comparison of the characteristics of transesterification reactions and the yield of monomer products by type of alcohol reactant]

[0245] [Table 6] shows the results of observing the characteristics of the ester exchange reaction performed by adding a different type of monohydric or polyhydric alcohol instead of ethylene glycol, which is the raw material for the glycolysis reaction, in the production of a polymer monomer containing an ester functional group (reaction temperature 100°C, GHSV = 240 h -1 ).

[0246] [Table 6]

[0247]

[0248] When transesterification reactions were performed using chain-like diols (Examples 12 and 28 to 32) and cyclic diols (Example 33) as adducts, it was observed that the initial conversion rate of DMT somewhat slowed down as the carbon number increased. This can be expected to be the result of steric hindrance that may occur as the molecular size of the diol increases, and the reaction activity for transesterification reactions decreases as the carbon number increases. When 1,3-propanediol was used as a reactant for the transesterification reaction (Example 28), the rate of the first transesterification reaction in which DMT is converted into the reaction intermediate 1-(3-hydroxypropyl) 4-methyl terephthalate (HBMT) was observed to be faster than when 1,4-butanediol was used as a reactant for the transesterification reaction (Example 29). However, the rate of the second transesterification reaction in which the reaction intermediate is converted into the product bis-(3-hydroxypropyl) terephthalate (BHPT) was observed to be relatively slow. This explains that the structural characteristics of the diol compound substituted by the first transesterification reaction affect the rate of the second transesterification reaction.

[0249] Meanwhile, when a structural isomer (1,2-propanediol), which is expected to have a direct effect on the transesterification reaction because the second alcohol functional group is positioned adjacently, was used as a reactant instead of 1,3-propanediol (Example 28) having a diol (α,ω-diol) at both ends of the chain as a reactant for the transesterification reaction (Example 31), it was observed that both the rates of the first and second transesterification reactions were significantly limited. When comparing the results of the transesterification reaction using structural isomers of butanediol with relatively long chain structures as reactants (Examples 29 and 32), it was observed that the rates of the first and second transesterification reactions were not significantly limited by the flexibility of the chain. When 1,4-cyclohexanedimethanol containing a cyclic hydrocarbon structure with a relatively large volume was used as a reactant (Example 33), the transesterification reaction proceeded slowly due to the steric hindrance of the diol molecular structure itself. Meanwhile, it was observed that only the first ester exchange reaction proceeded selectively in the early stage of the reaction, which is a result showing that it is possible to design a monomer structure having different ester bond pairs by applying different types of monohydric or polyhydric alcohol reactants to the first and second ester exchange reactions.

[0250] When 2-ethylhexanol, a main raw material of plastic plasticizers, was used as an additional reactant to carry out an ester exchange reaction (Example 34), the conversion rate of DMT was rapid from the beginning of the reaction, and most of the DMT was converted in 2 hours. Even when exposed to high-temperature reaction conditions for 8 hours thereafter, the monomer product dioctyl terephthalate (DOTP) remained stable without generating byproducts.

[0251] In summary, by applying the ester exchange reaction conditions by changing the type of alcohol added according to an example according to the present application, it is possible to produce a monomer in which functional groups of various structures are bonded to terephthalate through an ester bond.

[0252] While specific aspects of the present invention have been described in detail above, it will be apparent to those skilled in the art that these specific descriptions merely represent preferred embodiments and are not intended to limit the scope of the present invention. Therefore, the substantial scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for producing a terephthalate derivative from dimethyl terephthalate, (a) a step of adding a monohydric and / or polyhydric alcohol to dimethyl terephthalate as a reactant for ester exchange, and performing an ester exchange reaction while applying a flow of a carrier gas in the presence of at least one catalyst for ester exchange selected from the group consisting of an alkali carbonate, an alkali hydroxide, an alkali alkoxide, an alkaline earth metal oxide, and a guanidine-based organic compound; (b) a step of obtaining a terephthalate derivative by separating the terephthalate derivative produced by the above reaction; A method for producing a terephthalate derivative from dimethyl terephthalate, characterized by including the step.

2. In paragraph 1, A method for producing a terephthalate derivative from dimethyl terephthalate, characterized in that the catalyst for the ester exchange reaction per mole of dimethyl terephthalate in the step (a) is in the range of 0.00005 to 1.0 mol.

3. In paragraph 1, A method for producing a terephthalate derivative from dimethyl terephthalate, characterized in that the alcohol in the step (a) is ethylene glycol.

4. A method for producing a terephthalate derivative by depolymerization of a polymer containing an ester functional group, (A) Alcohol, polar aprotic solvent and potassium carbonate (K) are added to a polymer containing an ester functional group. 2 CO 3 ) and depolymerization step; (B) a step of performing an ester exchange reaction while adding a flow of carrier gas to the depolymerization result obtained in step (A); and (C) A method for producing a terephthalate derivative by depolymerization of a polymer containing an ester functional group, characterized by comprising a step of obtaining a terephthalate derivative produced by the above reaction; 5. In paragraph 4, A method for producing a terephthalate derivative by depolymerizing a polymer containing an ester functional group, characterized in that it further comprises a step of separating some compounds from the depolymerization result after the step (A) above.

6. In paragraph 5, A method for producing a terephthalate derivative by depolymerizing a polymer including an ester functional group, characterized in that some of the compounds separated to the outside include at least one selected from a polymer including an unreacted ester functional group, an insoluble catalyst, a polar aprotic solvent, and a reaction by-product.

7. In paragraph 4, A method for producing a terephthalate derivative by depolymerizing a polymer including an ester functional group, characterized in that the polar aprotic solvent of the step (A) is an inert solvent that does not participate in the depolymerization reaction of a polymer including an ester functional group and can lower the solubility of a catalyst for alcohol, and the skeletal structure of the organic compound is a chain-shaped and / or ring-shaped compound, and at least one of a halogen element, oxygen, and nitrogen is bonded to the organic compound.

8. In paragraph 4, A method for producing a terephthalate derivative by depolymerizing a polymer including an ester functional group, characterized in that the polar aprotic solvent of step (A) is at least one selected from toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propionitrile, aminopropionitrile, methylaminopropionitrile, iminodipropionitrile, butyronitrile, methylbutenenitrile, butanenitrile, methyl ethyl ether, diethyl ether, ethyl phenyl ether, dimethoxybenzene, trimethoxybenzene, methoxyphenol, tetrahydrofuran, methyltetrahydrofuran, dioxane, chloromethane, dichloromethane, chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, and trichlorobenzene.

9. In paragraph 4, A method for producing a terephthalate derivative by depolymerizing a polymer including an ester functional group, characterized in that in the step (A), the number of moles of the alcohol and the number of moles of the polar aprotic solvent relative to the number of moles of the repeating unit of the polymer raw material including an ester functional group are in a ratio range of 0.1 to 5,000 times relative to the number of moles of the repeating unit of the polymer raw material including an ester functional group.

10. In paragraph 4, A method for producing a terephthalate derivative by depolymerizing a polymer including an ester functional group, characterized in that, before performing the ester exchange reaction in the step (B), at least one ester exchange reaction catalyst selected from the group consisting of a monohydric and / or polyhydric alcohol and / or an alkali carbonate, an alkali hydroxide, an alkali alkoxide, an alkaline earth metal oxide, and a guanidine-based organic compound is added as a reactant for ester exchange to the depolymerization result in the step (A), so that the mole number of the catalyst is within a predetermined range per mole of dimethyl terephthalate contained in the depolymerization result.

11. In paragraph 4, A method for producing a terephthalate derivative by depolymerization of a polymer containing an ester functional group, characterized in that the methanol recovered in step (C) is reused as a depolymerization raw material in step (A).

12. In paragraph 4, A method for producing a terephthalate derivative by depolymerizing a polymer containing an ester functional group, characterized in that the ester exchange catalyst controlled in the step (B) has a molar number of 0.00005 to 1.0 times per mol of dimethyl terephthalate contained in the depolymerization result.

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