Method for producing terephthalate derivatives by transesterification of dimethyl terephthalate

Abstract

The present invention relates to a method for producing a terephthalate derivative from dimethyl terephthalate, and more particularly to a method for producing a terephthalate derivative from dimethyl terephthalate with improved process efficiency and economic efficiency, by optimizing reaction conditions and a catalyst for transesterification, thereby enabling the production of a terephthalate derivative in a high yield through a simple process.

Description

[Technical field]

[0001] The present invention relates to an ester exchange reaction of dimethyl terephthalate (DMT) to produce a highly-added derivative in which a functional group bonded to terephthalate is substituted into another form by an ester exchange reaction, and an efficient method for depolymerizing a polymer containing an ester functional group by the ester exchange reaction. The present invention relates to an efficient conversion method for producing a highly-added terephthalate derivative in high yield by carrying out the ester exchange reaction at room temperature (25° C.) or a temperature equal to or lower than the boiling point of the applied alcohol using at least one selected from alkali metal carbonates, alkali hydroxides, alkali metal alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds as a catalyst in the ester exchange reaction using the DMT and a monohydric and / or polyhydric alcohol as raw materials, and a depolymerization reaction process for a polymer containing an ester functional group, which can obtain the highly-added terephthalate derivative in high yield and improve the process efficiency and economy of the ester exchange reaction by combining the above with a methanolysis reaction. [Background technology]

[0002] Plastics are used in the production of various products because they are cheap, durable, and easy to mold and process. Due to these advantages, the consumption of plastics has increased dramatically over the past few decades in various fields of industry and daily life. However, problems have arisen in that improperly managed plastic waste is left in the environment, causing environmental pollution, and that microplastics that have broken down into small pieces float around the ecosystem and accumulate in living organisms, eventually reentering the human body through fine dust, drinking water, food, etc. Furthermore, more than 50% of such plastics are used for single-use disposable purposes such as packaging, agricultural films, disposable consumer goods, etc., or as short-term products that are discarded within one year of production.

[0003] Most discarded plastics are randomly dumped into designated landfills or natural habitats where natural purification is difficult, making the environmental pollution problem more serious by the day. Even naturally degradable or biodegradable plastics can persist for decades depending on local environmental factors such as the level of ultraviolet light exposure, temperature, and the presence of decomposing microorganisms.

[0004] To solve these problems, various research projects are being conducted to minimize the accumulation of plastics and reduce their environmental impact, ranging from the development of new plastic substances with short decomposition cycles in natural conditions, to the chemical decomposition of existing petroleum-based plastics, to the physical recycling and reprocessing of plastics.

[0005] Polymers containing ester functional groups can be converted to monomers by depolymerization, and various chemical reaction pathways have been developed. Theoretically, the monomers produced by decomposition can have the same properties as the raw materials used in the initial polymer synthesis. Depolymerization pathways applied industrially to recycle polyester include hydrolysis, glycolysis, methanolysis, and ammonolysis, and various chemical depolymerization methods are widely used, including composite processes that combine these processes to utilize the advantages of each process.

[0006] More specifically, the above-listed depolymerization methods for polymers containing ester functional groups are known to be capable of decomposition through various reaction pathways in the presence of acid, base, or metal salt catalysts. In the case of reactions using acids as catalysts, a high concentration of sulfuric acid solution is always required to obtain a high reaction yield, and economic problems associated with process design, operation, and post-treatment have been pointed out as drawbacks. In the case of reaction systems using base and metal salt catalysts, the decomposition reaction rate is very slow, the product purity is low, and catalyst recovery is difficult, making them inefficient.

[0007] Glycolysis is a depolymerization reaction in which glycol is added as a reactant. The most common example of glycolysis is the process of producing bis(2-hydroxyethyl)terephthalate (BHET) by adding an excess of ethylene glycol, one of the monomer raw materials. Since ethylene glycol, one of the raw materials for the synthesis of polyethylene terephthalate (PET), is used as a reactant, the product produced by the depolymerization reaction has a chemical structure in which ethylene glycol is already bonded to both ends of the terephthalate. Therefore, even if it only partially replaces the raw materials of the existing condensation polymerization process that uses terephthalic acid, it can produce very favorable results in terms of reaction dynamics.

[0008] In addition, the product obtained by the glycolysis reaction can be directly used as a raw material for synthesizing PET, so it is advantageous that it can be applied to the production of polymer materials by only modifying a part of an existing PET production line without making an excessive investment in equipment. Glycolysis is generally performed under reflux conditions of the reactant glycol, and the rate of decomposition from oligomers to monomers is slow, and even if the reaction time is delayed, the equilibrium state between the compounds is reached, so the purity of the product may be low, and it is difficult to separate the final product, the monomer, from the reactants with high purity or high yield. Generally, metal salts such as zinc acetate or lithium acetate are used as reaction catalysts. Metal ions that constitute such catalysts may not be completely removed during the refining process and may remain in the product, and even a small amount of metals that are harmful to the human body may be contained in the recycled monomer, making it difficult to use them in products that are produced by re-injecting them, especially in the reprocessing of materials for food, medical use, and other daily necessities. In addition, glycolysis is a high-temperature reaction, and the product recovery and purification process generally involves a low-temperature recrystallization method, which results in high energy consumption and low costs and efficiency due to the heat source supply method for the production process.

[0009] The methanolysis process is one of the processes that has been widely applied in actual commercial processes not only by global chemical companies but also by small and medium-sized plastics companies. Theoretically, dimethyl terephthalate (DMT) is obtained as the final monomer product through this process, and as the transesterification reaction takes place, ethylene glycol equivalent to the molar number of the decomposed terephthalate may be liberated. In actual reactions, hydroxyethyl methyl terephthalate (1-(2-hydroxyethyl)4-methyl terephthalate (HEMT), monomethyl terephthalate (MMT), etc. may be by-produced in the reaction product due to side reactions such as partial methanolysis, reaction equilibrium with free ethylene glycol, and hydrolysis. DMT, the target compound of the methanolysis reaction, can be used as an intermediate material for a process to produce other monomers with higher additivity or a complex hybrid depolymerization process (e.g., methanolysis-glycolysis). In addition, it has a relatively low boiling point compared to other monomers, and the selectivity of hydrogenation reaction is easy to control, so it can be used as a gas phase reactant for producing highly-added diol monomers (e.g., 1,4-cyclohexanedimethanol). It is also easy to purify by recrystallization or distillation, so it can be used as a raw material for PET polymerization, which requires high purity and high quality. However, since methanol is used as a reaction solvent, harsh reaction conditions of high temperature and pressure are required, and the initial cost may be excessive in order to prepare a reactor that can meet such an operating environment and related durable auxiliary equipment, and since an additional unit process is required for recovery of reactants and purification of products, high investment costs may be required. The catalyst used is typically a transesterification reaction catalyst containing heavy metals such as magnesium acetate, cobalt acetate, lead dioxide, etc., including zinc acetate, which is a depolymerization catalyst commonly used in glycolysis reactions, but there is a risk of inducing human toxicity and environmental problems due to the amount of metal residues in the product.

[0010] Methanolysis has been widely used as a depolymerization reaction process for polymers containing ester functional groups, along with hydrolysis or alkaline decomposition, but both reactions are high-temperature, energy-intensive processes, and depolymerization at low temperatures can take a long time, limiting the quality and quantity of the product. When methanolysis is selected as a reaction route for producing depolymerized monomer, the yield and purity of the monomer product DMT are greatly affected by the reactivity of the catalyst and reaction impurities, and therefore an effective method for suppressing side reactions and high reactivity are simultaneously required to reduce the burden of the purification process on the product.

[0011] As a conventional technique, Japanese Patent Laid-Open Publication No. 1998-287741 (Patent Document 1) describes a method for recovering dimethyl terephthalate and alkylene glycol with high efficiency by treating waste PET with methanol, in which when recovering dimethyl terephthalate from a polyalkylene terephthalate polymer, methanol is continuously introduced into the polymer, at least a portion of which is in a molten state, and DMT is produced by a depolymerization reaction of the polyalkylene terephthalate, using potassium carbonate or the like as a catalyst at a depolymerization reaction temperature of 200 to 300° C. The above patent has the disadvantage that the depolymerization temperature is too high, resulting in excessive investment costs for equipment and excessive energy used in the reaction process.

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

[0013] As an example of the above reaction, in the transesterification reaction using DMT and ethylene glycol as starting materials and producing the highly-additive monomer BHET as the final product, HEMT, in which the methyl end groups bound to terephthalate are partially replaced, is produced as a reaction intermediate, and a compound in which a carboxylic acid functional group is bound to terephthalate is produced as a by-product by hydrolysis. It is expected that an efficient BHET production process can be designed by designing a reaction route that can promote step-by-step transesterification reactions so that all of the two molar equivalents of methanol bound to DMT can be replaced by ethylene glycol while minimizing such side reaction routes, and by clarifying the optimal operating conditions under which BHET production is predominant and applying them to the process.

[0014] The non-patent document "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) reports that when performing an ester exchange reaction using DMT and ethylene glycol, zinc and titanium are introduced into hydrotalcite, and then a composite metal planar structure produced by modification is used as a catalyst. An example is reported in which the selectivity of BHET, a highly added monomer, can be improved to 96.1%.

[0015] However, in the case of the above-mentioned prior art, even though the transesterification reaction was carried out 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 refining BHET from the obtained reaction mixture, the catalyst production process is complicated and there may be problems with reproducibility, and metals introduced into the catalyst may also be leached out, so that there may be limitations in the efficiency and economy of the process when applied to a commercial process.

[0016] Therefore, when producing highly-added terephthalate derivatives by transesterification of DMT, it is important to use environmentally friendly materials that are less harmful without using excessive energy, and to ensure economic efficiency by using low-value catalysts and simplifying the process. In addition, it is necessary to develop an integrated reaction and purification process technology that improves both process efficiency and economic efficiency, which enables not only the conversion rate of DMT but also the production of a high yield of terephthalate derivatives. The produced derivatives can be used as various upcycling raw materials with high industrial value, such as recycled monomers for recycling waste plastic resources, additives such as plasticizers, and polymerization raw materials for synthesizing materials in which glycols are partially or completely transformed to improve physical properties. Summary of the Invention [Problem to be solved by the invention]

[0017] In order to solve the above problems, the present invention provides a transesterification method capable of producing a high yield of a high addition monomer while simplifying the process, that is, a method for producing other types of terephthalate derivatives from dimethyl terephthalate (DMT).

[0018] In addition, the present invention provides a method for producing a high yield of a terephthalate derivative as a product at room temperature (25° C.) or a temperature below the boiling point of the applied alcohol by applying a reaction product generated from the depolymerization of a polymer containing an ester functional group and a monohydric and / or polyhydric alcohol as reactants, by expanding and applying the method for converting DMT into other forms of terephthalate derivatives. In other words, the present invention provides an efficient and economical depolymerization method for producing a highly-added terephthalate derivative by multiple transesterification using a polymer raw material containing an ester functional group as an initial material. [Means for solving the problem]

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

[0020] In one embodiment of the present invention, the transesterification reaction in step (a) may be carried out at a temperature ranging from room temperature to the boiling point of the monohydric and / or polyhydric alcohol solvent as the reactant, and the transesterification catalyst 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] The present invention also provides a method for producing a terephthalate derivative by depolymerizing a polymer having an ester functional group, the method comprising: (A) introducing an alcohol, a polar aprotic solvent, and potassium carbonate (K2CO3) into a polymer having an ester functional group to depolymerize the polymer; (B) introducing a carrier gas flow to the depolymerized product obtained in (A) to perform an ester exchange reaction; and (C) separating and obtaining the terephthalate derivative produced by the reaction.

[0023] In an embodiment of the present invention, after step (A), a step of separating a portion of compounds from the depolymerization resultant may be further performed. The portion of compounds separated to the outside may include at least one selected from a polymer having an unreacted ester functional group, an insoluble catalyst, a polar aprotic solvent, a reaction by-product, and the like.

[0024] In addition, the polar aprotic solvent in step (A) is an inert solvent that does not participate in the depolymerization reaction of the polymer containing an ester functional group and can reduce the solubility of the catalyst in alcohol. The organic compound has a backbone structure that is a chain and / or cyclic compound, and at least one of a halogen element, oxygen, and nitrogen is bonded to the organic compound. The backbone structure may be 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.

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

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

[0027] In addition, in one embodiment of the present invention, the transesterification catalyst adjusted in step (B) is 0.00005 to 1.0 times the number of moles per mole of dimethyl terephthalate contained in the depolymerization resultant. Effect of the Invention

[0028] The present invention provides a method for producing a highly-added terephthalate derivative from DMT in high yield using a simple process configuration with a small amount of transesterification catalyst and low energy consumption. More specifically, a method is used in which a monomer raw material, an added monohydric and / or polyhydric alcohol, and methanol liberated by the transesterification reaction can reach a reaction equilibrium in a closed system. For example, the present invention provides a method for producing a terephthalate derivative in high yield by selectively discharging only methanol to the outside, thereby suppressing methanolysis, which corresponds to a reverse reaction, and promoting transesterification, which corresponds to a forward reaction.

[0029] The catalyst in the reactant prepared according to an embodiment of the present invention can be an effective catalyst for transesterification, and does not require a distinction between reaction selectivity for methanolysis and transesterification to produce derivatives. Even a small amount of catalyst, 1 / 1000 to 1 / 10 of the mass of catalyst introduced into the depolymerization reaction of a polymer containing an ester functional group, can exhibit sufficient reactivity and can be used to induce an effective and efficient transesterification reaction that can maintain selectivity. Therefore, transesterification can be performed with only all or a part of the catalyst remaining in the reaction product discharged from the first methanolysis reaction system. The vapor discharged to the outside is high-purity methanol equivalent to DMT, and almost all of it can be concentrated and recovered. The recovered methanol can be 100% recycled as a reactant for methanolysis for depolymerization of a polymer containing an ester functional group, so that if methanolysis and transesterification to produce derivatives are both configured, it corresponds to a technology that theoretically allows perfect methanol recycling.

[0030] In addition, the present invention can provide a method for producing a terephthalate derivative in high yield 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 in which DMT and ethylene glycol are produced in high yield from a low-temperature methanolysis reaction that can be carried out in the presence of methanol, a polar solvent, and a transesterification catalyst, and then BHET is produced as a final product through a transesterification reaction in which ethylene glycol is added to the produced DMT. When a polymer containing an ester functional group is depolymerized according to one embodiment of the present invention, it is possible to produce BHET, which is a highly added monomer, in high yield without using the high-temperature reaction conditions (190 to 280°C) of conventional glycolysis. For example, BHET can be selectively produced in high yield only through a series of reaction steps maintained at a temperature close to room temperature, which is lower than the boiling point of the applied diol reactant (e.g., ethylene glycol) and thus lower than the boiling point of methanol. This means that a low-temperature, low-energy glycolysis depolymerization technology can be realized.

[0031] The method according to the present invention can maintain the amount of dimer or oligomer produced at a lower level than the existing high-temperature glycolysis reaction, and thus can obtain a relatively high concentration of BHET. At the same time, the temperature of the reactants can be maintained within the operating range of the purification process for removing impurities (including dimers and oligomers). Since the method can be directly applied to the purification process without preheating or cooling processes that consume energy when transporting the reactants, the amount of energy loss can be minimized and continuous reaction and post-treatment processes can be easily realized.

[0032] The transesterification reaction that can be performed according to the present invention can be applied to the production of recycled monomers or terephthalate derivatives that can be applied to the synthesis of various types of materials other than BHET that can be used for the repolymerization of PET. As an example, the monomer produced has geometrical characteristics different from the structure of estrogen hormones, so it can be used as a material to replace phthalate-based plasticizers, which are known to cause hormone disruption in the human body. In addition, it can be used to produce raw materials for improving the physical properties of various types of plastics. PET has excellent thermal and mechanical properties, but it is known that it is difficult to perform injection molding within a short cycle due to its low final crystallization temperature and slow crystallization rate, and these characteristics limit its uses. Therefore, the market demand for various forms of polymer resins with improved physical properties according to purpose and use is steadily increasing. For example, a method of improving the physical properties of the final product by modifying a part of the diol, which is used when introducing a new monomer into the diol unit of PET to copolymerize or condense polymerize, has already been universally used in industry. As an example, when ethylene glycol is replaced with butylene glycol during the condensation polymerization process, a polybutylene terephthalate (PBT) material with a polymeric form that is excellent for injection molding can be produced due to the characteristics of a more flexible chain structure. In addition, when different types of diols are introduced, it can be applied to the synthesis of polymeric materials of various forms. That is, when performing the transesterification reaction of DMT according to one example of the present invention, by modifying the reactants of monohydric and / or polyhydric alcohols and adding similar reaction conditions, various forms of terephthalate derivatives can be easily produced. In particular, when the reaction product produced from the methanolysis of waste PET is directly used as a raw material, a recycled monomer can be economically produced by a very simple and easy reaction process, and a wide range of upcycling processes can be configured to flexibly produce various highly-added terephthalate derivatives by different injection of raw materials. [Brief description of the drawings]

[0033] [Figure 1]1 is a schematic diagram of a method for supplying a carrier gas to discharge methanol produced from the transesterification reaction of DMT to the outside of a reactor according to one embodiment of the present invention. [Diagram 2] 1 is a schematic diagram of an example of a process combination that can be configured to obtain a terephthalate derivative as a product in high yield by depolymerization from a polymer raw material containing an ester functional group according to an embodiment of the present invention. [Diagram 3] 1 is a schematic diagram of an example of an experimental setup for carrying out a transesterification reaction of DMT according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] 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 belongs. Generally, the nomenclature used herein is one that is well known and commonly used in the art.

[0035] Throughout this specification, when a part is described as "comprising" a certain element, this means that it may further include other elements, rather than excluding other elements, unless specifically stated to the contrary.

[0036] The present invention provides an optimal catalyst for obtaining a highly-added terephthalate derivative in high yield when a transesterification reaction that can proceed by adding monohydric and / or polyhydric alcohols using DMT as a raw material is carried out.

[0037] In one aspect, the present invention provides a method for transesterification, in which at least one selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds can be used as a catalyst for converting DMT into a terephthalate derivative in high yield by transesterification.

[0038] The present invention also provides a transesterification method for producing a DMT-derived terephthalate derivative in high yield by setting optimal reaction conditions in addition to the optimal transesterification catalyst when converting DMT into a terephthalate derivative by a glycolysis reaction.

[0039] The method of the present invention includes the steps of: (a) adding a monohydric and / or polyhydric alcohol to DMT as a reactant for transesterification, and carrying out a transesterification reaction in the presence of at least one transesterification catalyst selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds while adding a carrier gas flow; and (b) isolating and obtaining a terephthalate derivative produced by the reaction.

[0040] 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 restriction before or after the reactants reach a target temperature, and can be carried out under batch reaction conditions or under continuous flow conditions. The catalyst and the monohydric and / or polyhydric alcohols, which are the additional reactants, can be introduced in a form mixed with DMT before preparing the reaction.

[0041] The flow of the carrier gas is used as a means for discharging the methanol to the outside, and can be a flow by forced circulation of the gas phase with a pressure gradient.Also, after condensing the methanol vapor outside the reactor, a continuous flow of gas is used in which the vapor phase is recirculated in a nearly dilute state (Figure 2a), or a method of continuously supplying an inert gas from the outside to discharge the methanol to the outside (Figure 2b) can also be used.

[0042] When carrying out the transesterification reaction according to step (a), dimethyl terephthalate, monohydric and / or polyhydric alcohol, and a catalyst for transesterification reaction are introduced into a reactor, and a transfer pipe is placed below the water level of the reactants so that the carrier gas can directly come into gas-liquid contact with the reactants in the reactor, allowing air bubbles to be injected. During this process, the concentration of methanol vapor in the gas phase is formed, and it can be continuously discharged to the outside through the flow to the outside by the carrier gas. The methanol vapor diffused by the carrier gas may be advantageous in terms of reactivity if mass transfer occurs at a saturation concentration or higher, and if the carrier gas is supplied at a sufficient rate, the amount of methanol discharged can be adjusted according to the speed of the transesterification reaction.

[0043] The temperature of the transesterification reaction may 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, i.e., a temperature between room temperature and the boiling point of the monohydric and / or polyhydric alcohol applied to the reactants, and a pressure of 0.1 torr to 5 atm based on absolute pressure, but may be changed within the above ranges in consideration of the temperature and pressure ranges for carrying out the transesterification reaction and the methanol removal rate by the carrier gas.

[0044] The above temperature range can be changed depending on the transesterification catalyst to be added, and is preferably a temperature between room temperature and the boiling point of the alcohol applied to the reactant, and the pressure is preferably around atmospheric pressure, which is advantageous for stable and continuous process operation. Also, the reaction time in step (a) can be changed depending on the amount of DMT and alcohol supplied as well as the type and amount of catalyst used in the reaction.

[0045] First, in step (a), the transesterification catalyst may be added in a molar ratio of 0.00005 to 1.0, preferably 0.0001 to 0.2, per unit mole of DMT as raw material. If the transesterification catalyst is included in a molar ratio of less than 0.00005 per unit mole of DMT as raw material, the transesterification reaction of DMT with monohydric and / or polyhydric alcohols may proceed slowly, resulting in a decrease in process efficiency. If the transesterification catalyst is included in a molar ratio of more than 1.0, the degree of improvement in effect is not significant compared to the increased catalyst content, making it uneconomical and possibly increasing by-products. In addition, the excess catalyst remains as an impurity during separation of the terephthalate derivative, which may affect the efficiency of separation and purification.

[0046] The catalyst for the transesterification 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 catalyst should be such that the conversion rate of DMT can be significantly improved and the yield of the terephthalate derivative can be significantly improved.

[0047] The amount of ethylene glycol in step (a) may be in the range of 1 to 50 moles per mole of DMT. When the amount of ethylene glycol is in the above range, the esterification reaction can occur most efficiently.

[0048] The monohydric and polyhydric alcohols may be linear, branched, cyclic or a mixture thereof having 1 to 20 carbon atoms, and the polyhydric alcohol has two or more OH functional groups. Examples of the alcohol 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.

[0049] In the step (a) of carrying out the transesterification reaction by adding monohydric and / or polyhydric alcohol to DMT in the presence of the transesterification catalyst, a carrier gas flow is provided inside the reactor and methanol vapor is continuously discharged outside the reaction system so that the forward reaction to produce a terephthalate derivative product continues to proceed at an equilibrium concentration or higher. As a method for supplying the carrier gas, as shown in Figure 2, a unidirectional flow method (b in Figure 2) in which methanol vapor is separated by a condenser and then discharged to the outside, or a method (a in Figure 2) in which methanol vapor is removed and then recycled, can be used.

[0050] The carrier gas injected into the reactor may be advantageous in improving the DMT conversion rate and the yield of the terephthalate derivative product under reaction conditions that maintain a low concentration of methanol in the reactants so as to prevent or suppress the recombination of methanol produced as a by-product from the transesterification reaction by a reverse reaction. In this case, the carrier gas may be any gas that does not have a chemical effect on the alcohol addition transesterification reaction of DMT or the catalyst, and may be preferably air, nitrogen, argon, helium, etc., and may be preferably an inert gas that is substantially free of moisture.

[0051] In the present invention, step (b) is a step of separating and obtaining the terephthalate derivative formed in the reaction. Specifically, the step of separating and obtaining the terephthalate derivative formed in step (a) from a reaction mixture containing unreacted residual DMT, ethylene glycol, residual catalyst, etc., to obtain a high-purity terephthalate derivative. This can be carried out by a generally known purification method, and the method is not limited thereto. For example, physical methods such as filtration, crystallization, centrifugation, evaporation, and distillation, or chemical methods such as adsorption, neutralization, and salting out can be carried out in parallel.

[0052] In the present invention, a highly-added terephthalate derivative is produced by a transesterification reaction in which a monohydric and / or polyhydric alcohol can be added to DMT as an starting material. The DMT is obtained by depolymerization of a polymer containing an ester functional group, and the depolymerization result can be transesterified with a monohydric and / or polyhydric alcohol with or without a pretreatment process to produce a terephthalate derivative.

[0053] The transesterification reaction by addition of monohydric and / or polyhydric alcohols to DMT can also be applied to a reaction process for producing terephthalate derivatives in high yields by a two-step tandem reaction in which a reaction product produced by a methanolysis reaction of a polymeric raw material containing an ester functional group is directly used as a raw material for a second transesterification reaction.

[0054] That is, the present invention includes a method for producing a terephthalate derivative as a final product by initiating depolymerization of a polymer having an ester functional group, and provides a method for producing a highly-added terephthalate derivative by depolymerizing a polymer having an ester functional group, the method comprising: (A) introducing an alcohol, a polar aprotic solvent, and potassium carbonate (K2CO3) into a polymer having an ester functional group to depolymerize the polymer; (B) introducing a carrier gas flow to the depolymerized product obtained in the step (A) to perform an ester exchange reaction; and (C) separating and obtaining a terephthalate derivative product produced by the reaction.

[0055] 1 is a conceptual diagram of a process for producing a terephthalate derivative from a polymer raw material containing an ester functional group by transesterification. First, in step (A) (100), a polymer containing an ester functional group, an alcohol, a polar aprotic solvent, and potassium carbonate (K2CO3) are introduced into a depolymerization reactor to depolymerize the polymer, and the polymer containing an ester functional group can be contacted with the alcohol, the polar aprotic solvent, and potassium carbonate (K2CO3) to produce an alcohol addition monomer by transesterification, and low-temperature depolymerization of the polymer is effectively performed. This process is very simple, can produce DMT in a high yield of 90% or more, and is very economical due to low energy consumption.

[0056] Here, the polymer containing an ester functional group may be in the form of a single or mixed waste plastic, for example, polyethylene, high density polyethylene, low density polyethylene, polypropylene, or a combination thereof, mixed with the polymer containing an ester functional group. The other polymers to be mixed with the polymer containing an ester functional group listed above as examples are merely examples and are not limited to those listed above.

[0057] The polymer containing an ester functional group may be a polymer formed by condensation polymerization of a dicarboxylic acid and a dialcohol, wherein the dicarboxylic acid is selected from the group consisting of terephthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenyletherdicarboxylic 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, tetramethylol ... In some embodiments, the glycerol is selected from the group consisting of ethanol, neopentyl glycol, hexamethylene glycol, decanemethylene glycol, dodecamethylene glycol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, di(tetramethylene) glycol, tri(tetramethylene) glycol, polytetramethylene glycol, pentaerythritol, 2,2-bis(4-β-hydroxyethoxyphenyl)propane, and combinations thereof.

[0058] By way of example, the polymer containing ester functional groups 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.

[0059] One of the most common examples of polymers containing such ester functional groups is polyethylene terephthalate (PET), where the starting materials for the preparation of the polymer are terephthalic acid or its derived monomers and ethylene glycol.

[0060] The polymer containing ester functional groups used in the present invention may not be in a pure state, but may contain various impurities. For example, in addition to the polymer containing ester functional groups, a mixture of debris, including but not limited to bottle caps, adhesives, paper, residual liquids, dust, or combinations thereof, may be used as the raw material for depolymerization.

[0061] The alcohol is a reactant and is preferably a straight chain primary alcohol, such as methanol, ethanol, propanol, butanol, or combinations thereof.

[0062] The alcohol can be used in a ratio of 0.1 to 5,000 moles, preferably 1 to 500 moles, per mole of the repeating unit of the polymer raw material containing the ester functional group.

[0063] Potassium carbonate is used as the catalyst. Potassium carbonate is represented by the chemical formula K2CO3 and is a white crystal that dissolves in water. The potassium carbonate is preferably used in anhydrous form rather than in hydrate form, and more preferably dried before use. The amount of potassium carbonate used may be 0.01 times or more, preferably 0.01 to 100 times, and more preferably 0.1 to 10 times the number of moles of the repeating unit of the polymer containing an ester functional group.

[0064] The polar aprotic solvent is used as an organic liquid compound that can be applied to reduce the activation energy of the decomposition reaction or transesterification reaction of the ester functional group, and is a non-reactive, inert solvent that does not directly participate in the reaction, and is thermodynamically favorable in that it can reduce the solubility of the catalyst (potassium carbonate) in the reactant (alcohol) to induce a heterogeneous catalytic reaction and dissolve the produced monomer.

[0065] The backbone structure of the organic compound in the polar aprotic solvent may be a chain or cyclic compound, a halogen element may be directly bonded to the organic compound, or the organic compounds may be linked to each other or to each other via oxygen or nitrogen. Specific examples thereof include at least one selected from toluene, acetone, methyl ethyl ketone, methyl iso-butyl ketone, acetonitrile, tetrahydrofuran, dichloromethane, chloroform, chlorobenzene, methyl phenyl ether, and methyl phenyl ether.

[0066] The polar aprotic solvent can be used in a molar ratio of 0.1 to 5,000 times, and preferably 1 to 500 times, the molar ratio of the repeating unit of the polymer raw material containing the ester group.

[0067] In the step (A), a polymer containing an ester functional group is subjected to alcohol addition depolymerization at a temperature in the range of 0 to 80°C, preferably 10 to 60°C. Therefore, in some examples of the step (A), complete decomposition of the polymer can be induced at about room temperature and atmospheric pressure. Since the reaction system can be realized with a simple structure and configuration, the investment cost may be lower than that of existing technologies or processes, and efficient and stable energy management is also possible.

[0068] Meanwhile, in the depolymerization of step (A), a water-soluble heterogeneous low-cost catalyst is basically used, so that the catalyst can be easily recovered and reused after the reaction, and the temperature of the reactants themselves can be lowered below room temperature to recover a high percentage of the produced monomers. The used solvent can be reintroduced as a depolymerization raw material for new polymer raw material, so that the economic efficiency of the recycling process can be further improved.

[0069] In addition, the depolymerization of the polymer in step (A) can be performed by obtaining sufficient energy required for the depolymerization only from heat of mixing, heat of dissolution, etc., generated during the preparation of a mixed solution for the depolymerization reaction without the input of an additional heat source. In this case, the depolymerization can be performed in an insulated reactor. Also, as in some embodiments according to the present invention, the depolymerization can be performed while supplying an external heat source.

[0070] The depolymerization of the polymer can be carried out at atmospheric pressure or higher, specifically, at a pressure of about 1 atm to 6.5 atm.

[0071] In addition, the depolymerization of the polymer may be carried out in a system exposed to the atmosphere or in a closed system, and may be carried out by refluxing the solvent using a condenser.

[0072] In addition, the depolymerization reaction time in step (A) varies depending on the amount of polymer used, but in the case of room temperature without adding any energy, monomers can be obtained in a sufficiently high yield within 24 hours, and most of the materials other than the reactants can be recovered and reintroduced into the process because they do not undergo any significant chemical changes.

[0073] 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 stream containing at least one selected from the polymer, the insoluble catalyst, the polar aprotic solvent, the reaction by-products, etc., from the reaction mixture 10 containing unreacted materials remaining together with DMT and ethylene glycol obtained after the completion of the depolymerization reaction of the step (A), methanol, a polar aprotic solvent, a catalyst, or by-products such as mono-methyl terephthalate (MMT) and terephthalic acid (TPA) derived compounds, to the outside, and the method is not limited thereto since it can be performed by a commonly known method.

[0074] As an example of separation, when the insoluble catalyst and unreacted polymer are separated from the depolymerization product by filtration, the depolymerization product can take the form of a uniform liquid, and when the polar aprotic solvent or methanol is partially or completely evaporated or distilled by heating or reducing the pressure, crystallization of DMT in the depolymerization product can occur. In order to remove foreign matter and increase the concentration of DMT, a washing solution can be further added, and methods such as recrystallization, physical filtration, distillation, evaporation, and drying can be further used to prepare the raw material for ethylene glycol addition transesterification. The solvent and catalyst separated from the depolymerization product can be reintroduced (20) as raw materials for the methanolysis depolymerization 100, which is the previous step (A).

[0075] Meanwhile, the step of separating some of the compounds (200) may be performed to prepare for the transesterification step (300) in which monohydric and / or polyhydric alcohols are added to the produced DMT, but this does not necessarily mean that it must be performed. That is, the depolymerization result obtained from the depolymerization step of the polymer containing ester functional groups in the step (A) may be directly used as a raw material in the step (B) without going through the step of separating the depolymerization result (200).

[0076] In the present invention, step (B) (300) is a step of carrying out an ester exchange reaction while adding a carrier gas flow 3 to the depolymerization result obtained in step (A). The method of carrying out the ester exchange reaction in step (B) is the same as the method of preparing a terephthalate derivative from DMT described above, and therefore a detailed description will be omitted. The DMT in step (B) is obtained by depolymerizing a polymer containing an ester functional group (30), and the depolymerization can be carried out by a simple process at room temperature and pressure. The depolymerization product contains DMT and polyhydric alcohol in high yield, and by using this again in the method of preparing a terephthalate derivative from DMT described herein, a terephthalate derivative can be obtained as a final product directly from a polymer containing an ester functional group.

[0077] Before carrying out the transesterification in step (B), the depolymerization result in step (A) may be treated with a monohydric and / or polyhydric alcohol as a solvent for the transesterification, and / or at least one transesterification catalyst selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds in an amount adjusted to a predetermined range of moles per mole of dimethyl terephthalate contained in the depolymerization result, and then the transesterification may be carried out.

[0078] The mole number of the alcohol and / or the transesterification catalyst is adjusted by adding the alcohol and / or the transesterification catalyst to the depolymerization product, partially removing the alcohol and / or the transesterification catalyst from the depolymerization product, or adding new monohydric and / or polyhydric alcohol after the partial removal. In this case, the removing and adding processes may be performed in the step (200) of separating the part of the compound.

[0079] The newly added monohydric and / or polyhydric alcohol may be a linear, branched, cyclic or mixture thereof alcohol having 1 to 20 carbon atoms, and the polyhydric alcohol has two or more OH functional groups.

[0080] The number of moles of ethylene glycol after the adjustment may be in the range of 0.1 to 100 moles, preferably 1 to 50 moles, per mole of dimethyl terephthalate contained in the depolymerization resultant.

[0081] In addition, the number of moles of the transesterification catalyst after adjustment may be in the range of 0.00005 to 1.0 mole, preferably 0.0001 to 0.2 mole, per mole of dimethyl terephthalate contained in the depolymerization resultant.

[0082] In the transesterification reaction 300, in order to suppress the reverse reaction caused by methanol and to maintain the addition reaction of monohydric and / or polyhydric alcohols in the direction in which the product is produced, methanol can be discharged (40) to the outside of the reactor by the flow of carrier gas 3, and methanol recovered through the condenser 400 maintained at a low temperature can be reused (60) as a raw material for the depolymerization reaction in step (A). This is because, compared to the existing glycolysis method for producing BHET using high-temperature reaction conditions (usually in the range of 200 to 280°C), the reaction proceeds quickly and a terephthalate derivative product can be effectively obtained even at a low temperature that is much lower than the boiling point of the monohydric and / or polyhydric alcohols, and because the reaction temperature range and the reaction path leading to the product are different, decomposition (or depolymerization) in the product proceeds less, and the generated product (dimer or oligomer) is generated at a relatively low concentration or not generated at all, whereas the terephthalate derivative is obtained in a high yield.

[0083] According to the method of the present invention, the reactivity in the low temperature region and the efficiency of the purification process are improved, so that the amount of energy used can be significantly reduced compared to the existing processes. As a result, a method capable of economically producing a highly-added terephthalate derivative can be provided.

[0084] In the present invention, step (C) is a step (500) of separating the terephthalate derivative produced in high yield from the reaction, and since it can be performed in the same manner as the above-mentioned method for producing a terephthalate derivative from DMT, detailed description thereof will be omitted.

[0085] The process of the present invention will be described in detail below with reference to comparative examples and examples, which are merely representative examples for explaining the present invention, and the scope of the present invention is not limited to the following examples.

[0086] Raw material 1 (dimethyl terephthalate raw material) Dimethyl terephthalate (Sigma-Aldrich, catal. #185124, purity >99.0%) supplied by a reagent manufacturer was uniformly ground using a pestle and mortar to prepare a fine powder as raw material 1.

[0087] Raw material 2 (polymer raw material containing ester functional groups) Bottles made of waste polyethylene terephthalate material, which is a polymeric substance containing ester functional groups and was discarded after consumption, were washed to remove any residual foreign matter, dried, and then crushed using a continuous crushing mill (manufacturer and model: IKA MF10.1). After that, using a standard sieve, only plastic chips having a width and length of the widest surface of 1 to 3 mm and a thickness of 0.5 mm or less were collected and prepared as raw material 2.

[0088] <Example 1> Approximately 14.5 g of DMT raw material prepared according to the process for raw material 1 and approximately 55.6 g (corresponding to 12 times the number of moles of raw material 1) of ethylene glycol (Sigma-Aldrich; purity ≧99.8%) as a dihydric alcohol polar solvent were placed in a three-neck flask, and after attaching a distillation apparatus with a condenser, stirring was started at a speed of 1,200 rpm using a magnetic stirrer.

[0089] In order to effectively remove the reaction product methanol, high purity nitrogen (manufactured by 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 200sccm, or when this was normalized to the volume of the initial reaction mixture under standard conditions and converted to Gas Hourly Space Velocity (GHSV(hr-1)), the set value was adjusted using a mass flow controller so that it could be kept constant at 240.

[0090] Then, the flask containing the reactants was heated, and when the final temperature of the reaction solution reached 80°C, about 0.05g (equivalent to 0.005 times the number of moles of the input raw material 1) of potassium carbonate (K2CO3, potassium carbonate; manufactured by Sigma-Aldrich, ACS reagent) was added as a catalyst to start the reaction, and the transesterification reaction was carried out for a total of 8 hours to obtain BHET as a highly added depolymerized monomer. Methanol produced as the reaction proceeded was degassed from the reactants by the flow of carrier gas and discharged to the outside of the reactor, and was collected by an external trap maintained at 0°C or lower.

[0091] During the reaction, a small amount (less than 50 mg) of 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, from which the distribution and concentration of the product were estimated. The conversion rate and product yield were calculated accordingly. During the 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.

[0092] The conversion rate of DMT in the transesterification reaction, and the yields of intermediate products resulting from partial transesterification of DMT with the alcohol reactant (e.g., HEMT in the case of ethylene glycol addition transesterification), monomer products resulting from complete transesterification (e.g., BHET in the case of ethylene glycol addition transesterification), dimers, and by-products, potassium monomethyl terephthalate (K-MMT) and dipotassium terephthalate (K2-TPA), were calculated using the following formulas.

[0093] DMT conversion rate = (N0-N) / N0 (Formula 1) Monomer yield = (N monomer / N0)×100% (Formula 2) Yield of intermediate = (N intermediate / N0)×100% (Formula 3) Yield of MMT = (N MMT / N0)×100% (Formula 4) Yield of TPA = (N TPA / N0)×100% (Formula 5) Dimer yield = (N dimer / N0)×100% (Formula 6)

[0094] In the above formula, N0 is the number of moles of DMT, which is the initial raw material, and N,N intermediate , N monomer , N MMT , N TPA and N dimer is the number of moles of terephthalate contained in unconverted DMT, intermediate products, monomeric products, MMT, TPA, and dimer.

[0095] <Comparative Example 1> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that potassium carbonate was not added.

[0096] <Example 2> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.001 g (corresponding to 0.0001 times the number of moles of the raw material 1) of potassium carbonate was used.

[0097] <Example 3> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.01 g (corresponding to 0.001 times the number of moles of the raw material 1) of potassium carbonate was used.

[0098] <Example 4> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.1 g (corresponding to 0.01 times the number of moles of the raw material 1) of potassium carbonate was used.

[0099] <Example 5> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.5 g (corresponding to 0.05 times the number of moles of the raw material 1) of potassium carbonate was used.

[0100] <Example 6> The ester exchange reaction was carried out and evaluated in the same manner as in Example 1, except that about 2.1 g (corresponding to 0.2 times the molar amount of the raw material 1) of potassium carbonate was used.

[0101] <Comparative Example 2> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the inert carrier gas was not used.

[0102] <Example 7> In the above-mentioned Example 1, high-purity nitrogen was used as the inert carrier gas at 50 sccm (GHSV=60 h -1 The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature was kept at 20° C.).

[0103] <Example 8> In the above-mentioned Example 1, high-purity nitrogen was used as the inert carrier gas at 100 sccm (GHSV=120 h -1 The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature was kept at 20° C.).

[0104] <Example 9> In the above-mentioned Example 1, high-purity nitrogen was used as the inert carrier gas at 500 sccm (GHSV=600 h -1 The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature was kept at 20° C.).

[0105] <Example 10> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature of the reaction liquid was maintained at 50°C.

[0106] <Example 11> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature of the reaction liquid was maintained at 65°C.

[0107] <Example 12> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature of the reaction liquid was maintained at 100°C.

[0108] <Example 13> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature of the reaction liquid was maintained at 110°C.

[0109] <Example 14> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature of the reaction liquid was maintained at 120°C.

[0110] <Example 15> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature of the reaction liquid was maintained at 130°C.

[0111] <Example 16> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that the temperature of the reaction liquid was maintained at 140°C.

[0112] <Example 17> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.008 g (corresponding to 0.001 times the number of moles of raw material 1) of potassium bicarbonate (KHCO3) was used as a catalyst and the reaction time was maintained for 3 hours.

[0113] <Example 18> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.008 g (corresponding to 0.001 times the number of moles of raw material 1) of sodium carbonate (Na2CO3) was used as a catalyst and the reaction time was maintained for 3 hours.

[0114] <Example 19> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.006 g (corresponding to 0.001 times the number of moles of raw material 1) of sodium bicarbonate (NaHCO3) was used as a catalyst and the reaction time was maintained for 3 hours.

[0115] <Comparative Example 3> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.007 g (corresponding to 0.001 times the number of moles of the raw material 1) of potassium acetate (KOAc) was used as a catalyst and the reaction time was maintained for 3 hours.

[0116] <Comparative Example 4> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.006 g (corresponding to 0.001 times the number of moles of raw material 1) of sodium acetate (NaOAc) was used as a catalyst and the reaction time was maintained for 3 hours.

[0117] <Comparative Example 5> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.01 g (corresponding to 0.001 times the number of moles of raw material 1) of zinc acetate (Zn(OAc)2·2H2O) was used as a catalyst and the reaction time was maintained for 3 hours.

[0118] <Example 20> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.004 g (corresponding to 0.001 times the number of moles of raw material 1) of potassium hydroxide (KOH) was used as a catalyst and the reaction time was maintained for 3 hours.

[0119] <Example 21> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.003 g (corresponding to 0.001 times the number of moles of raw material 1) of sodium hydroxide (NaOH) was used as a catalyst and the reaction time was maintained for 3 hours.

[0120] <Example 22> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.005 g (corresponding to 0.001 times the number of moles of raw material 1) of potassium methoxide (CHOK) was used as a catalyst in Example 1 and the reaction time was maintained for 3 hours.

[0121] <Example 23> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.004 g (corresponding to 0.001 times the molar amount of raw material 1) of sodium methoxide (CHONa) was used as a catalyst in Example 1 and the reaction time was maintained for 3 hours.

[0122] <Example 24> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.003 g (corresponding to 0.001 times the number of moles of raw material 1) of magnesium oxide (MgO) was used as a catalyst and the reaction time was maintained for 3 hours.

[0123] <Example 25> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.004 g (corresponding to 0.001 times the number of moles of raw material 1) of calcium oxide (CaO) was used as a catalyst and the reaction time was maintained for 3 hours.

[0124] <Example 26> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that about 0.01 g (corresponding to 0.001 times the number of moles of the raw material 1) of triazabicyclodecene (TBD) was used as a catalyst in Example 1 and the reaction time was maintained for 3 hours.

[0125] <Comparative Example 6: PET depolymerization by high-temperature glycolysis reaction> About 10g of PET raw material 2 was prepared as the raw material for the glycolysis reaction. About 38.75g of ethylene glycol (12 moles per mole of the repeating unit of the polymer), a dihydric alcohol polar solvent, was put into a three-neck flask, and a reflux condenser was attached at atmospheric pressure, followed by heating and stirring using a heated magnetic stirrer. When the temperature reached 177°C, 10g of the prepared polymer raw material was put in and the temperature was increased while stirring was continued. When the reaction mixture reached 197°C or the reflux temperature, about 0.571g of zinc acetate catalyst (0.05 moles per mole of the repeating unit of the polymer) was added to start the catalytic reaction. The mixture was stirred continuously for 2 hours, while the reaction temperature was kept constant within a range of ±0.5°C, and the reaction was carried out using a condenser with one end exposed to atmospheric pressure. After the reaction, the unreacted material in the resultant was separated and quantified by filtration. The decomposed monomers, dimers, mono(hydroxyethyl)terephthalate (MHET) which is a by-product, and oligomers were quantified using high performance liquid chromatography pre-calibrated with a standard sample in the same manner as used to quantify the reactants in Example 1, and the distribution and concentration of the products were then estimated.

[0126] <Example 27: PET depolymerization by room temperature methanolysis and low temperature glycolysis> About 3 g of PET raw material prepared according to raw material 2, about 66.3 g of dichloromethane (Samchun Pure Chemical Ind. Co. Ltd; purity 99.5%) (equivalent to 50 times the number of moles of the repeating unit of raw material 2 polymer), 24.96 g of methanol (Samchun Pure Chemical Ind. Co. Ltd; 99.9%) (equivalent to 50 times the number of moles of the repeating unit of raw material 2 polymer), and about 0.43 g of K2CO3 (potassium carbonate; Sigma-Aldrich, ACS reagent) as a catalyst (equivalent to 0.2 times the number of moles of the repeating unit of raw material 2 polymer) were placed in a three-neck flask, and secondary distilled water was added to adjust the initial water content of the reactants to have an initial number of moles of 0.4 relative to the moles of the repeating unit of the raw material polymer. The reaction was carried out at 25 ° C and atmospheric pressure for 24 hours while stirring at 500 rpm using a magnetic stirrer.

[0127] After the reaction, the resultant was filtered and separated into a filtrate containing DMT, HEMT, ethylene glycol, and a portion of K-MMT (the potassium salt of MMT), as well as an organic solvent, and a filter cake containing unreacted PET, K2CO3 catalyst, and K-MMT.

[0128] A small amount (less than 50mg) of potassium salt from the filtrate and solids was taken and diluted with an aqueous mobile phase to prepare samples. The product distribution and concentration in each sample was estimated by quantitative analysis using high performance liquid chromatography (HPLC with Optimapak C18 Column (250nm, 5micron), UV detector (λ=254nm)), and unreacted PET in the solids was quantified by gravimetry. From the quantified values, the conversion rate of PET due to the depolymerization reaction and the yields of DMT, HEMT, TPA, and MMT were calculated. During the 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 0.7ml / min.

[0129] The PET conversion rate and DMT yield in the depolymerization reaction were calculated using the following formulas.

[0130] PET conversion rate = (M0-M) / M0 x 100% (Formula 7) Yield of DMT = (M DMT / M0)×100% (Formula 8)

[0131] In the above formula, M0 and M respectively represent the moles of the repeating units of the raw polymer (PET) and the unreacted polymer initially charged, and M DMT indicates the number of moles of DMT produced.

[0132] The filtrate of the depolymerization product was used as a raw material for a transesterification reaction in which ethylene glycol was added. The transesterification reaction was carried out under the same conditions as in Example 1, but the filtrate of the depolymerization product 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 molar amount of DMT was adjusted to be the same as in Example 1, and ethylene glycol was adjusted to a total amount of about 55.6 g (12 times the molar amount of DMT) by adding ethylene glycol produced by depolymerization and ethylene glycol added further. The transesterification reaction was carried out and evaluated without adding additional catalyst.

[0133] The number of moles of catalyst and K-MMT in the solids recovered after filtration was quantified using gravimetry and HPLC, respectively (measured in a molar ratio of 0.126 and 0.024 relative to the number of moles of the repeating unit of the raw material), and the number of moles (based on the number of moles of potassium cations) obtained by subtracting the number of moles recovered as a solid phase from the number of moles of catalyst initially added was estimated as the number of moles of catalyst remaining in the filtrate of the depolymerization product. From this, it was found that the amount of catalyst (K2CO3) in the raw material for the transesterification reaction in which ethylene glycol is added is present at a ratio of about 0.054 moles per unit mole of DMT.

[0134] The conversion rate of DMT by the transesterification 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.

[0135] <Example 28> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that, instead of using ethylene glycol as a reactant in Example 1, the same molar amount (12 times the molar amount of DMT unit) of 1,3-propanediol (Sigma-Aldrich, purity ≧98%) was used and the temperature of the reaction solution was maintained at 100° C.

[0136] <Example 29> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that, instead of using ethylene glycol as a reactant in Example 1, the same molar amount (12 times the molar amount of the DMT unit) of 1,4-butanediol (Sigma-Aldrich; ReagentPlus (registered trademark); purity ≧99%) was used, and the temperature of the reaction solution was maintained at 100° C.

[0137] <Example 30> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that, instead of using ethylene glycol as a reactant in Example 1, the same molar amount (12 times the molar amount of DMT unit) of 1,6-hexanediol (Sigma-Aldrich; purity ≧99%) was used and the temperature of the reaction solution was maintained at 100° C.

[0138] <Example 31> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that, instead of using ethylene glycol as a reactant in Example 1, the same molar amount (12 times the molar amount of DMT unit) of 1,2-propanediol (Sigma-Aldrich; RagentPlus (registered trademark); purity ≧99%) was used and the temperature of the reaction solution was maintained at 100° C.

[0139] <Example 32> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that, instead of using ethylene glycol as a reactant in Example 1, the same molar amount (12 times the molar amount of the DMT unit) of 1,3-butanediol (manufactured by Sigma-Aldrich; Anhyrous, purity ≧99%) was used, and the temperature of the reaction solution was maintained at 100° C.

[0140] <Example 33> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that, instead of using ethylene glycol as a reactant in Example 1, the same molar amount (12 times the molar amount of the DMT unit) of 1,4-cyclohexanedimethanol (Sigma-Aldrich; mixture of cis anthracene, purity ≧99%) was used, and the temperature of the reaction solution was maintained at 100° C.

[0141] <Example 34> The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that instead of using ethylene glycol as a reactant in Example 1, the same molar amount (12 times the molar amount of DMT unit) of 2-ethyl-1-hexanol (Sigma-Aldrich; purity ≧99.6%) was used and the temperature of the reaction solution was maintained at 100° C.

[0142] [Comparison of transesterification reaction characteristics depending on the amount of catalyst used] Table 1 shows the results of observing the reaction effect by adjusting the amount of potassium carbonate (K2CO3) used as a catalyst in the transesterification reaction in Examples 1 to 6 and Comparative Example 1 (reaction temperature 80°C, GHSV = 240 h). -1 ). In the case of Comparative Example 1, in which no catalyst was added, unlike the examples in which a catalyst was used, the yields of BHET after 2 hours and 8 hours were about 0.0% and 2.4%, respectively, indicating that the transesterification reaction rate was very low. This result explains that the use of a catalyst is essential to promote the addition transesterification reaction of DMT with ethylene glycol at low temperatures, as exemplified in the present invention.

[0143] [Table 1] DMT: dimethyl terephthalate, EG: ethylene glycol BHET: Bis(2-hydroxyethyl) terephthalate HEMT: 1-(2-hydroxyethyl)-4-methyl terephthalate K2-TPA: Dipotassium terephthalate K-MMT: Potassium monomethyl terephthalate

[0144] Examples 1 to 4 are the results of reactions carried out using, as a catalyst, potassium carbonate in an amount equivalent to 0.0001 to 0.01 moles per mole of DMT in the raw material 1, and show that the production rate and yield of BHET are significantly improved as the amount of potassium carbonate increases.

[0145] On the other hand, in Examples 5 and 6, potassium carbonate was used as a catalyst in an amount of 0.05 and 0.2 moles per mole of DMT, respectively, but the production rate and yield of BHET tended to decrease. In contrast, 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 when an excess of catalyst is used compared to the moles of DMT added, not only is the catalyst consumed, but side reactions such as hydrolysis and alkali decomposition can be promoted. Therefore, appropriately adjusting the amount of catalyst can help improve the performance and economy of the transesterification reaction.

[0146] [Comparison of transesterification reaction characteristics based on gas hourly space velocity (GHSV)] When transesterification of DMT is carried out in the presence of excess ethylene glycol solvent, the rate of production of the product BHET is observed very high at the beginning of the reaction, and the rate of production of methanol, which is a by-product of the transesterification reaction, also increases in proportion to the moles of BHET produced. In a closed system, such a transesterification reaction is not an irreversible reaction in which all of the DMT initially charged is converted to BHET, but the reverse transesterification reaction in which the by-product methanol and BHET participate can also have a rate. When the forward and reverse reactions reach equilibrium, there is no longer any change in the concentration of the compounds, and even if the reaction conditions are changed, there may be a limit to improving the product yield. However, if a portion of the reaction product is effectively removed from the reaction product mixture or discharged to the outside of the reaction system, the reverse reaction can be suppressed, and the characteristics of the reaction can be determined by the amount of change in concentration of the substance, i.e., the rate of transfer of the substance discharged to the outside.

[0147] Methanol produced from the transesterification reaction carried out according to one embodiment of the present invention can be selectively discharged to the outside by continuously flowing a carrier gas from the outside, in addition to increasing the temperature or reducing the pressure of the reaction system by using a substance having the lowest boiling point (130°C or higher than ethylene glycol) among the raw materials and products input, thereby suppressing the regeneration of DMT due to the reverse transesterification reaction.

[0148] [Table 2]

[0149] Table 2 shows the characteristics of the transesterification reaction carried out at different flow rates of the inert carrier gas (high purity nitrogen) introduced to the reactor to cause gas-liquid contact with the internal reactants in order to remove methanol from the reaction product (reaction temperature 80°C).

[0150] In the absence of carrier gas flow (Comparative Example 2), the transesterification reaction was carried out at 80°C for 3 hours, resulting in a relatively low yield of BHET of about 58.4%, and even though the reaction was carried out under long reaction conditions for about 8 hours, a slight increase of about 0.9% in the reaction yield was observed. This is expected to be due to the fact that even if the reactor is in the form of an open system and the internal temperature is maintained above the boiling point of methanol, methanol produced by the progress of some of the transesterification reaction does not diffuse predominantly into the head space where the reactants are not filled or outside the reactor, but is present in a high concentration in the reactants.

[0151] On the other hand, in the case of transesterification reactions carried out under continuous flow conditions with different flow rates of nitrogen as a carrier gas (Example 1 and Examples 7 to 9), the conversion rate and the yield of BHET are significantly improved. In particular, in the reactions carried out in Examples 1 and 9, where the GHSV exceeds 200, a BHET yield of 92% or more can be obtained when the reaction time exceeds 3 hours.

[0152] On the other hand, it was found that if the flow rate of the carrier gas is maintained too high and the reaction conditions are exposed for a long time, the yield of dimers and oligomers increases slightly, and the yield of BHET does not improve. In the case of Example 1, no oligomers were observed in the reaction product even after the reaction was performed for more than 3 hours. In contrast, when the transesterification reaction was performed according to Example 9, it was observed that oligomers began to be produced after 6 hours, and the selectivity of BHET decreased. Even if only a small amount of oligomers less than 3% were produced, the viscosity of the reaction mixture increased significantly and a part of the product formed a heterogeneous phase, causing the reaction product to suddenly become suspended. Therefore, in order to maximize the yield of BHET, which is a polymer depolymerization monomer, a carrier gas flow is applied, and it is preferable to select the optimal flow condition of the carrier gas, which can efficiently remove methanol produced from the transesterification reaction, while also allowing the addition reaction of ethylene glycol to occur predominantly, in order to improve the final yield of BHET.

[0153] [Changes in transesterification reaction characteristics due to reaction temperature] Table 3 shows the results of the transesterification reaction of DMT with ethylene glycol by the method of the present invention, observed at different reaction temperatures (GHSV=240 h). -1 ).

[0154] It can be seen that when the temperature is maintained above the boiling point of methanol (Example 1 and Examples 12 to 16), the yield of BHET obtained from the transesterification reaction can be maintained high from the early stage of the reaction, and when the reaction time exceeds 4 hours, a BHET yield of 95% or more can be obtained. It can be presumed that this improvement in yield is due to the fact that when the reaction temperature exceeds the boiling point of methanol, the mass transfer rate of methanol increases and also contributes to an increase in the rate of the sequential glycolysis catalytic reaction in which DMT is converted to HEMT and HEMT is converted to BHET.

[0155] [Table 3]

[0156] On the other hand, when the transesterification reaction was carried out while maintaining the reaction temperature below the boiling point of methanol (Examples 10 and 11), the yield of BHET with reaction time increased 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.

[0157] Although not shown in the table, oligomers began to be detected after exposure to reaction conditions for a long time (after 7 hours of reaction time), and about 11.2% and 3.3% of the DMT raw material applied after 8 hours of reaction time were converted to oligomers. At this time, it was observed that the viscosity of the reaction solution increased significantly and changed into an inhomogeneous suspension.

[0158] In summary, it was found that in order to increase the conversion rate of DMT within a short reaction time or residence time and improve the yield of monomeric BHET without oligomer formation, it is more advantageous to control the reaction temperature to a temperature above the boiling point of methanol.

[0159] [Comparison of transesterification reaction characteristics by selecting reaction catalyst] The existing glycolysis reaction for producing BHET from polymers containing ester functional groups is performed at high temperatures, which is problematic as it consumes a large amount of energy. To overcome this problem, a new reaction route that can produce BHET in high yield at low temperatures is being considered.

[0160] 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 carried out at room temperature. If it were possible to provide low-temperature reaction conditions in which the ethylene glycol addition could occur predominantly in succession, it would be possible to produce BHET in high yield.

[0161] If a separate separation step is not performed after the first reaction, methanolysis, some of the catalyst may remain in the reaction mixture produced, but it may be necessary to design or consider a new catalyst system that can perform sufficiently for the subsequent transesterification reaction.

[0162] Catalysts commonly used in transesterification reactions include acidic, basic and metal salt catalysts. Since acidic catalysts cause the reaction to proceed more slowly than basic catalysts, the reaction is generally carried out at high temperatures (100°C or higher). In order to prevent corrosion, the reactor and associated equipment must be designed to be acid-resistant, which can result in excessive initial investment costs.

[0163] Therefore, in the present invention, the reaction performance and usefulness of basic catalysts and metal salt catalysts, which are expected to have reactivity and selectivity in the ethylene glycol addition transesterification reaction of DMT, were evaluated and examined.

[0164] In order to compare the relative performance of the catalysts, the reaction conditions were the same except for the type of catalyst, that is, the amount of esterification catalyst charged was 0.001 mole per mole of DMT, and the carrier gas flow was GHSV240h. -1 The reaction temperature was maintained at 80° C. and the reaction was carried out for 3 hours.

[0165] 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 were selected and used, which are expected to show the best performance in transesterification reactions. Their reaction performance and acid dissociation equilibrium constants (pKa) are shown in Table 4 (reaction temperature 80°C, reaction time 3 hours, GHSV = 240 hours). -1 )

[0166] [Table 4] DMT: dimethyl terephthalate, EG: ethylene glycol BHET: Bis(2-hydroxyethyl) terephthalate HEMT: 1-(2-hydroxyethyl)-4-methyl terephthalate KOAc: Potassium acetate, Sodium acetate, Zinc diacetate, Zinc acetate dihydrate TBD: Triazabicyclodecene K2-TPA: Dipotassium terephthalate K-MMT: Potassium monomethyl terephthalate

[0167] Metal acetates are commonly used as catalysts in high-temperature reaction processes for producing BHET by depolymerization of polymers containing ester functional groups. In particular, zinc acetate (Zn(CH3COO)2·2H2O) is the most commonly used catalyst in commercial processes due to its high reactivity in polymer depolymerization and excellent selectivity for BHET. In order to confirm the catalytic effectiveness of metal acetates in the transesterification reaction according to the present invention, potassium acetate, sodium acetate, zinc acetate, etc. were used as catalysts instead and reaction experiments were carried out.

[0168] In Comparative Examples 3 and 4, in which potassium acetate and sodium acetate were added as alternative catalysts under the same conditions and the reaction was carried out, the BHET yield was less than 4% after 3 hours, which was a very low reaction performance. In Comparative Example 5, in which zinc acetate was used as a catalyst, the BHET yield was 0.7%, and almost no BHET was produced, as in Comparative Example 1, in which no catalyst was added. Therefore, it was confirmed that metal acetates, which can be effectively used in existing high-temperature (≧190° C.) glycolysis reactions, cannot be used as efficient catalysts for the transesterification reaction carried out according to the present invention.

[0169] Comparing the reaction results of Example 3 and Examples 17 to 19, in which a metal salt catalyst in which carbonate and bicarbonate were anions was used, when potassium carbonate (K2CO3) and sodium carbonate (Na2CO3) were used as catalysts and the reaction was carried out for 3 hours, the yields of BHET were 92.0% and 92.3%, respectively, which was 13% or more higher than when potassium bicarbonate (KHCO3) and sodium bicarbonate (NaHCO3) were used as catalysts.

[0170] Alkali hydroxides (or alkali metal hydroxide salts) are used as a typical raw material for alkaline decomposition reactions during the depolymerization of polymers containing ester functional groups. In alkaline decomposition reactions, alkali hydroxides directly participate in the decomposition of ester bonds as a reactant, so they are supplied in excess of the number of moles of ester bond groups in the polymer, and water or alcohol is used as a reaction medium, with ethylene glycol being discharged as the reaction product.

[0171] In this specification, the alkali hydroxide was observed to function as a catalyst rather than a reactant for alkaline decomposition. Under the reaction conditions described in this specification, i.e., 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 of the alkali hydroxide as a catalyst for transesterification reaction can be expressed. As a result of the transesterification reaction carried out by adding small amounts of potassium hydroxide and sodium hydroxide (Examples 20 and 21) in an amount of 0.001 mol per 1 mol of DMT, all of the DMT was converted and the yield of BHET after 3 hours of reaction reached a value of 91% or more.

[0172] Next, the performance in transesterification was confirmed when an alkoxide metal salt was used as an alternative catalyst. When potassium methoxide (CH3OK) or sodium methoxide (CH3ONa) was used as an alternative catalyst (Examples 22 and 23), high reactivity was observed, as well as relatively high BHET yields of 90.6% and 83.6% after 3 hours of reaction. Compared to the previous application of an alkali metal carbonate catalyst (Examples 3 and 18), these catalysts are effective in promoting the rate of the first ethylene glycol addition reaction (HEMT production) from DMT, but showed slightly lower reaction rate characteristics in the second addition reaction (BHET production).

[0173] The transesterification reaction also showed high performance when alkaline earth metal oxide catalysts were used. When magnesium oxide and calcium oxide were used as alternative catalysts (Examples 24 and 25), the conversion was observed to be 96% or higher, and the BHET yield after 3 hours of reaction was 77.4% and 90.6%, respectively.

[0174] Finally, the reaction characteristics of metal-free organic catalysts were compared. In Example 26, triazabicyclodecene (TBD), a guanidine-based compound that has strong basic properties and is commonly used as an organic synthesis catalyst, was used as a catalyst for the transesterification reaction. As in Example 3, in which potassium carbonate (K2CO3) was used as a catalyst, almost all of the DMT added after 3 hours of reaction was involved in the glycolysis reaction, and a relatively high BHET yield of 90.5% was observed.

[0175] Comparing the reaction performance based on the acid dissociation equilibrium constant (pKa) of the catalysts used above in Table 4, it is confirmed that a catalyst with 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.

[0176] [Production of BHET by transesterification of polymers containing ester functional groups] The glycolysis reaction for directly producing BHET by depolymerization of a polymer raw material containing an ester functional group is generally carried out at a high temperature of 190 to 300°C. As reported in many prior art documents, the high-temperature glycolysis reaction is generally carried out at a temperature near or above the boiling point of the addition reactant ethylene glycol using a metal acetate as a catalyst. In the catalytic reaction, the monomer product (BHET) by glycolysis is obtained at a rate of 80% or more, which is higher than other compounds, but in addition to by-products (e.g., monohydroxyethyl terephthalate (MHET), terephthalic acid) generated from side reactions such as hydrolysis, it has been observed that dimers and oligomers are generated at a certain rate depending on the reaction equilibrium. In contrast, when depolymerization is carried out using a low-temperature methanolysis-glycolysis tandem reaction pathway with different temperature ranges and BHET generation mechanisms, high-purity BHET containing only a small amount of reaction intermediates (e.g., HEMT) and dimers can be obtained in high yield according to one example of the present invention.

[0177] Table 5 shows a comparison of the results of high temperature (190°C) and low temperature transesterification reactions (methanolysis at 25°C and ethylene glycol addition transesterification at 80°C) produced using the same raw material 2 as the raw material.

[0178] In the table below, the number of moles of EG and catalyst in Comparative Example 6 is based on the repeating unit of PET, and the number of moles of EG and catalyst in Example 27 is based on DMT.

[0179] [Table 5]

[0180] When the depolymerization reaction was carried out at high temperature using zinc acetate (Comparative Example 6), polymer decomposition occurred at a high rate from the early stage of the reaction (within 2 hours), and a BHET yield of 80.6% was obtained. However, when the reaction was continued for a long period of time, such as 8 hours, the increase in the BHET yield was not significant, and the yield of the dimer was about 4.1%, and that of the oligomer was 10-15%, and the concentration of undecomposed compounds was high.

[0181] In Example 27, the same PET raw material (raw material 2) as used above was used, and a liquid reaction mixture (DMT yield: 91%) was obtained by depolymerization at room temperature (25°C) based on methanolysis using a co-solvent, and a part of the catalyst was removed by filtration. The temperature was then raised to remove the solvent, and ethylene glycol was added to carry out the second reaction, glycolysis. In this reaction, reaction characteristics and product distributions very different from those of the high-temperature glycolysis in Comparative Example 6 were observed.

[0182] In Example 27, a very high DMT conversion rate was observed from the beginning of the reaction, and a BHET yield exceeding 92% was observed when the reaction was left under reaction conditions for a sufficient time (8 hours or more). 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, in which ethylene glycol addition had progressed in only one direction, was obtained as a reaction intermediate product, and it was observed that the reaction proceeded relatively quickly, with only a very low HEMT concentration of 0.5% or less remaining after 8 hours of reaction.

[0183] These results confirm that the same catalyst can be used sequentially for each reaction in the preparation of BHET from polymers containing ester functional groups via low-temperature methanolysis-glycolysis reactions.

[0184] [Comparison of transesterification reaction characteristics and monomer product yields by type of alcohol reactant] Table 6 shows the results of observing the characteristics of the transesterification reaction carried out by adding different types of monohydric or polyhydric alcohols instead of ethylene glycol, which is the raw material for the glycolysis reaction, in the production of polymer monomers containing ester functional groups (reaction temperature 100°C, GHSV = 240 h). -1 ).

[0185] [Table 6] DMT: Dimethyl terephthalate, K2-TPA: Dipotassium terephthalate K-MMT: Potassium monomethyl terephthalate EG: ethylene glycol, PDO: propanediol, BDO: butanediol, HDO: hexanediol, CHEM: 1,4-cyclohexanedimethanol, 2E1H: 2-ethyl-1-hexanol Monomer product: Both methyl groups of DMT are completely replaced by diol reactants Intermediate: Only one methyl group of DMT is replaced by transesterification

[0186] As a result of carrying out transesterification using chain diols (Examples 12 and 28-32) and cyclic diols (Example 33) as the addition reactants, it was observed that the initial conversion rate of DMT became slightly slower as the carbon number increased. This can be expected as a result of the possibility of steric hindrance occurring as the molecular size of the diol increases, and the reaction activity for transesterification becoming lower as the carbon number increases. When 1,3-propanediol was used as a reactant for transesterification (Example 28), the rate of the primary transesterification reaction in which DMT was converted to 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 transesterification (Example 29), but the rate of the secondary transesterification reaction in which the reaction intermediate was converted to the product bis-(3-hydroxypropyl) terephthalate (BHPT) was observed to be relatively slow. This illustrates that the structural characteristics of the diol compound substituted in the primary transesterification reaction influence the rate of the secondary transesterification reaction.

[0187] Meanwhile, when a structural isomer (1,2-propanediol) that is expected to have a direct effect on the transesterification reaction because the second alcohol functional group is adjacent to the reactant (Example 31) was used instead of 1,3-propanediol (Example 28) having diols (α,ω-diol) at both ends of the chain as a reactant for the transesterification reaction, it was observed that the primary and secondary transesterification reaction rates were both significantly restricted. Comparing the results of the transesterification reaction using a structural isomer of butanediol having a relatively long chain structure as a reactant (Example 29 and Example 32), it was observed that the rates of the primary and secondary transesterification reactions were not significantly restricted due to 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 primary transesterification reaction proceeded selectively at the beginning of the reaction. This result indicates that it is possible to design monomer structures having different ester bond pairs by using different types of monohydric or polyhydric alcohol reactants in the primary and secondary transesterification reactions.

[0188] When a transesterification reaction was carried out using 2-ethylhexanol, the main raw material of plasticizers, as an additional reactant (Example 34), the conversion rate of DMT progressed rapidly from the beginning of the reaction, and most of the DMT was converted within 2 hours. Even after exposure to high temperature reaction conditions maintained for 8 hours, dioctyl terephthalate (DOTP) as a monomer product remained stable without the generation of by-products.

[0189] In summary, by applying different types of added alcohols under transesterification conditions according to the examples of the present specification, it is possible to produce monomers in which functional groups of various structures are bonded to terephthalate through ester bonds.

[0190] Although the specific parts of the present invention have been described in detail above, it is clear to those skilled in the art that these specific techniques are merely preferred embodiments and do not limit the scope of the present invention. Therefore, the substantial scope of the present invention should be defined by the appended claims and their equivalents.

Claims

1. A method for producing a terephthalate derivative from dimethyl terephthalate, comprising the steps of: (a) adding a monohydric and / or polyhydric alcohol to dimethyl terephthalate as a reactant for transesterification, and carrying out a transesterification reaction in the presence of at least one transesterification catalyst selected from the group consisting of alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds, while supplying a carrier gas flow; (b) separating and obtaining the terephthalate derivative produced in the reaction.

2. The method for producing a terephthalate derivative from dimethyl terephthalate according to claim 1, wherein the gas hourly space velocity (GHSV) of the carrier gas is within a range of 240 to 600 hr −1 , and the reaction time is 6 hours or less.

3. The method for producing a terephthalate derivative from dimethyl terephthalate according to claim 1, wherein the catalyst for the ester exchange reaction is at least one selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), potassium methoxide (CH3OK), calcium oxide (CaO) and triazabicyclodecene (TBD).

4. The method for producing a terephthalate derivative from dimethyl terephthalate described in claim 2, wherein the catalyst for the ester exchange reaction is at least one selected from the group consisting of potassium hydroxide (KOH), sodium hydroxide (NaOH), potassium methoxide (CH3OK), calcium oxide (CaO) and triazabicyclodecene (TBD).

5. The method for preparing a terephthalate derivative from dimethyl terephthalate according to any one of claims 1 to 4, wherein the amount of the catalyst for transesterification is in the range of 0.00005 to 1.0 mol per 1 mol of dimethyl terephthalate in step (a).

6. The method for preparing a terephthalate derivative from dimethyl terephthalate according to any one of claims 1 to 4, wherein the alcohol in step (a) is ethylene glycol.

7. Before steps (a) and (b), (A) A polymer containing an ester functional group is reacted with an alcohol, a polar aprotic solvent, and potassium carbonate (K ２ CO ３ ) to depolymerize; (B) carrying out a transesterification reaction while supplying a carrier gas flow to the depolymerization product obtained in the step (A); (C) separating and obtaining the terephthalate derivative produced by the reaction.

8. 8. The method for preparing a terephthalate derivative by depolymerization of a polymer having an ester functional group according to claim 7, wherein the polar aprotic solvent in step (A) is at least one 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, ethyl phenyl ether, dimethoxybenzene, trimethoxybenzene, methoxyphenol, tetrahydrofuran, methyltetrahydrofuran, dioxane, chloromethane, dichloromethane, chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, and trichlorobenzene.

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