KR102452871B1 - Method for producing bis-(2-hydroxyethyl) terephthalate from dimethyl terephthalate and efficient depolymerization method of polymer containing ester functional group thereby - Google Patents

Abstract

The present invention relates to a method for producing bis-(2-hydroxyethyl) terephthalate from dimethyl terephthalate, and specifically, to a method for producing bis-(2-hydroxyethyl) terephthalate with improved process efficiency and economic feasibility capable of producing bis-(2-hydroxyethyl) terephthalate through a simple process by optimizing reaction conditions and a catalyst for a transesterification reaction.

Description

Method for producing bis-(2-hydroxyethyl) terephthalate from dimethyl terephthalate and efficient depolymerization method by using the method for producing bis-(2-hydroxyethyl) terephthalate from dimethyl terephthalate of polymer containing ester functional group thereby}

The present invention relates to a transesterification reaction for preparing bis-(2-hydroxyethyl) terephthalate (BHET) from dimethyl terephthalate (DMT) and a polymer including an ester functional group by the transesterification reaction In the transesterification reaction using DMT and ethylene glycol as a raw material, at least one selected from alkali metal carbonate, alkali hydroxide, alkali metal alkoxide, alkaline earth metal oxide and guanidine-based organic compound is catalyzed. An efficient conversion method that can produce BHET in high yield by performing a transesterification reaction at room temperature (25° C.) to a temperature below the boiling point of the applied alcohol using a It relates to a depolymerization reaction process of a polymer containing an ester functional group that can improve the process efficiency and economic feasibility of the transesterification reaction at the same time as obtained by

Plastic is an inexpensive and durable material, and has the advantage of being convenient for molding and processing, so it is used in the production of various products. Due to these advantages, the consumption of plastics in industry and life has increased dramatically over the decades. However, as plastic waste that is not properly managed is left in the environment, it causes environmental pollution, or microplastics decomposed into small pieces float around the ecosystem, accumulate in living things, and eventually enter the human body again through fine dust, drinking water, and food. is being caused Moreover, more than 50% of these plastics are used for single-use single-use applications such as packaging, agricultural films, disposable consumer products, etc., or as short-term products that are discarded within one year of manufacture.

Most of the discarded plastics are randomly discharged to designated landfills or natural habitats, which are difficult to purify naturally, so the seriousness of the environmental pollution problem is increasing day by day. Even biodegradable or biodegradable plastics can persist for decades, depending on local environmental factors such as level of UV exposure, temperature, and the presence of degrading microorganisms.

In order to solve these problems, from the chemical degradation of existing petroleum-based plastics to the physical regeneration and reprocessing of plastics, including the development of new plastic materials with a short decomposition cycle in the natural state, to minimize the accumulation of plastics or reduce the environmental impact. Several studies are in progress.

Polymers containing ester functional groups can be monomerized through depolymerization, and various chemical reaction pathways have been developed. The monomers generated through decomposition can theoretically have properties equivalent to those of raw materials used for initial polymer synthesis. Depolymerization routes that are industrially applied to recycle polyester include Hydrolysis, Glycolysis, Methanolysis, Ammonolysis, and the like. Various chemical depolymerization methods are widely used, ranging from complex processes that take advantage of specific advantages.

More specifically, the method for preparing depolymerization of a polymer containing the ester functional groups listed above is known. In the case of hydrolysis, it is known that decomposition can proceed through various reaction pathways in the presence of an acid, base, or metal salt catalyst. In the case of a reaction using an acid as a catalyst, a very high concentration of sulfuric acid solution is required to obtain a high reaction yield, so economical problems due to design, operation, and post-treatment of the process are pointed out as disadvantages. In the case of a reaction system using a base and metal salt catalyst, the decomposition reaction rate is very slow, the product purity is low, and the catalyst recovery is difficult, so it is inefficient.

Glycolysis is a depolymerization reaction in which glycol is added as a reactant. The most common example of glycolysis is a process for 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 of polyethylene terephthalate (PET) polymer synthesis, is used as a reactant, products manufactured by depolymerization have a chemical structure in which ethylene glycol is already bonded to both ends of terephthalate. Therefore, even if only a part of the raw material of the polycondensation process using terephthalic acid is replaced, very advantageous results can be obtained in terms of reaction kinetics. In addition, since the product obtained from the glycolysis reaction can be used directly as a synthetic raw material for PET, it has the advantage that it can be applied to the manufacture of polymer materials by modifying only a part of the existing PET production line without additional investment in excessive equipment. Glycolysis is generally carried out under reflux conditions of glycol as a reactant, and the product purity may be low because the rate of decomposition from oligomers to monomers is slow and the equilibrium state between compounds is reached even if the reaction time is delayed. There is a problem in that it is not easy to separate the product monomer from the reactant with high purity or high yield. In general, metal salts such as zinc acetate or lithium acetate are used as the reaction catalyst. Metal ions constituting these catalysts may remain in the product without being completely removed during the refining process, and even a small amount of metal toxic to the human body may be included in the regenerated monomer. And there is an aspect that is difficult to use in the reprocessing of materials for other household goods. In addition, although glycolysis proceeds at a high temperature, the recovery and purification process of the product generally follows a low-temperature recrystallization method, so the energy consumption is high and the cost and efficiency of the heat source supply method of the production process are low. There is a problem with losing.

The methanolysis process is one of the processes widely applied to actual commercial processes not only in the past global chemical companies but also in small and medium-sized plastics industries. By the above process, dimethyl terephthalate (DMT) is theoretically obtained as a final monomer product, and as the transesterification reaction proceeds, ethylene glycol equivalent to the number of moles of decomposed terephthalate can be liberated. In the actual reaction, hydroxyethylmethyl terephthalate (1-(2-Hydroxyethyl) 4-methyl terephthalate, HEMT), monomethyl terephthalate (monomethyl terephthalate, MMT) and the like may be by-produced in the reaction product. DMT, the target compound of the methanolysis reaction, can be used as an intermediate raw material for a process for producing a higher value-added other monomer or a complex hybrid depolymerization process (eg, methanolysis-glycolysis). In addition, it has a relatively low boiling point compared to other monomers and is easy to control the selectivity for the hydrogenation reaction, so it can be used as a gas phase reactant for the production of a high added diol monomer (eg 1,4-cyclohexanedimethanol), and recrystallization Alternatively, it can be used as a raw material for PET polymerization that requires high purity and high quality because it is easily purified by a distillation process. However, since methanol is used as a reaction solvent, severe reaction conditions of high temperature and high pressure are required, and the initial cost may be excessive to equip a reactor that can meet these operating environments and related equipment with durability, and recovery of reactants and product purification Since additional unit processes are essential, high investment cost may be required. As the catalyst used, a transesterification reaction catalyst containing heavy metals such as magnesium acetate, cobalt acetate, and lead dioxide, including zinc acetate, which is a depolymerization catalyst generally used for glycolysis reactions, can be typically used. It may cause harm to human body and environmental problems.

In the depolymerization reaction process of polymers containing ester functional groups, methanolysis was widely used along with hydrolysis or alkali decomposition processes, but both reactions are high-temperature and energy-consuming processes. Product quality and quantity may be limited. When methanolysis is selected as the reaction route for the production of the depolymerization monomer, the yield and purity of the monomer product, DMT, are greatly affected by the reactivity of the catalyst and the reaction impurities. Method and high reactivity are required at the same time.

As a prior art, Japanese Patent Application Laid-Open No. 1998-287741 (Patent Document 1) discloses a method of recovering dimethyl terephthalate and alkylene glycol with high efficiency by treating waste PET with methanol, respectively, from polyalkylene terephthalate polymer to dimethyl terephthalate. When recovering phthalate, in producing DMT by the depolymerization reaction of the polyalkylene terephthalate while continuously introducing methanol into the polymer in which at least a part is in a molten state, the depolymerization reaction temperature is 200 ~ 300 ℃ potassium carbonate and the like as catalysts are described. In the above patent, there are disadvantages in that the depolymerization temperature is too high, so the investment cost for equipment and the energy used in the reaction process are excessive.

Therefore, in depolymerizing a polymer including an ester functional group by methanolysis, it is possible to increase the depolymerization reaction rate without using excessive energy, and to improve the selectivity of the reaction to prepare a high-yield DMT. This may be advantageous, and if a continuous transesterification reaction can be formed by using it as an intermediate, it can be expected that energy consumption will be reduced while implementing an efficient and economical process capable of producing BHET in high yield.

The monomer product (DMT) that can be prepared from methanolysis is put into the reactor in a molten state at 150°C, and then ethylene glycol is added to the PET through a high-temperature reaction process at 160-220°C where transesterification and polycondensation are performed. can be manufactured. This manufacturing method was used until the 1960s, when a high-purity purification method of terephthalic acid was developed and popularized. In the modern PET manufacturing process, a method of synthesizing BHET initially by direct esterification of terephthalic acid (TPA) and ethylene glycol is generally used. In this direct esterification process, since it is a reaction between solid TPA and liquid ethylene glycol, it is difficult to control the initial reaction due to the low solubility of TPA. Transesterification of ethylene glycol, Korean Chem. Eng. Res., 51(1), 144-150 (2013)). In addition, water generated in the polycondensation process may be disadvantageous in terms of energy because it has a high latent heat of evaporation and requires continuous removal. On the other hand, the TPA method by the direct esterification reaction does not require the recovery process of the initially generated methanol, it is easy to connect the continuous polymerization and production process, and it has the advantages of low influence of impurities in the product by the catalyst. In both polymerization processes for PET synthesis, BHET generated through the initial esterification reaction undergoes a step in which BHET is generated as an intermediate product before chain polymerization. However, in terms of energy management, it may be advantageous for the polymerization process. Therefore, in carrying out the depolymerization of a polymer containing an ester functional group, rather than obtaining DMT or TPA by methanolysis or hydrolysis, BHET, a high value-added monomer, is produced by glycolysis or a hybrid reaction process. It may be more advantageous industrially to lead to the final product.

On the other hand, in the transesterification reaction using DMT and ethylene glycol as starting materials and using BHET, a high value-added monomer, as a final product, HEMT in which the methyl end group bonded to terephthalate is partially substituted is produced as a reaction intermediate product, Thus, a compound in which a carboxylic acid functional group is bonded to terephthalate may be produced as a side reactant. The design of a reaction pathway capable of inhibiting these side reaction pathways as much as possible, promoting the step-by-step transesterification reaction so that all 2 molar equivalents of methanol bound to DMT can be exchanged with ethylene glycol, and BHET production can be dominant It is expected that the design of an efficient BHET manufacturing process will be possible by identifying the optimal operating conditions and applying them to the process.

Non-patent literature “Zn- and Ti-Modified Hydrotalcites for Transesterification of Dimethyl Terephthalate with Ethylene Glycol: Effect of the Metal Oxide and Catalyst Synthesis Method” (Amarsinh L. Jadhav, Radhika S. Malkar, and Ganapati D. Ya, ACS Omega 2020 , 5, 2088-2096) use a composite metal planar structure prepared through reforming after introducing zinc and titanium into hydrotalcites as a catalyst in carrying out the transesterification reaction using DMT and ethylene glycol. Thus, an example has been reported in which the selectivity of BHET, a high value-added monomer, can be improved to 96.1%.

However, in the case of the prior literature, despite the transesterification reaction being carried out at a high temperature of 180 ° C, the conversion rate of dimethyl terephthalate remains at a level of less than 70%, and a lot of energy is consumed for the purification of BHET from the obtained reaction mixture. In addition, there may be problems in reproducibility due to the complicated manufacturing process of the catalyst, and the metal introduced into the catalyst may also be leached, so that there may be limitations in the efficiency and economic feasibility of the process to be applied to a commercial process.

Therefore, in manufacturing BHET from the transesterification reaction by the addition of ethylene glycol of DMT, it does not use excessive energy, applies eco-friendly materials with low harmfulness, and at the same time secures economical efficiency through the use of low-cost catalysts and process simplification. it is important In addition, it is required to develop a reaction and purification integrated process technology with improved process efficiency and economic feasibility, which enables the conversion of DMT as well as high yield of BHET.

Japanese Laid-Open Patent Publication No. 1998-287741 (published on Oct. 27, 1998)

Transesterification reaction between dimethyl terephthalate and ethylene glycol, Korean Chem. Eng. Res., 51(1), 144-150 (2013) “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. Yadav, ACS Omega 2020, 5, 2088-2096)

In order to solve the above problems, the present invention provides a transesterification reaction method capable of producing high-addition monomers in high yield while simplifying the process, that is, from dimethyl terephthalate (DMT) to bis-(2-hydroxyethyl) tere. It is intended to provide a method for preparing phthalate (BHET).

In addition, the present invention extends and applies the method for converting BHET from DMT to room temperature (25° C.) to below the boiling point of the applied alcohol by using a reaction product generated from depolymerization of a polymer containing an ester functional group and ethylene glycol as a reactant. A method capable of producing a high yield of BHET as a final product at a temperature, that is, bis-(2-hydroxyethyl) terephthalate can be prepared through multiple transesterification from a polymer raw material containing an ester functional group as a starting material. We aim to provide an efficient and economical depolymerization method.

In order to solve the above problems, the present invention is (a) dimethyl terephthalate by adding ethylene glycol as a solvent for transesterification, and from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides and guanidine-based organic compounds. In the presence of one or more selected catalysts for the transesterification reaction, while applying a flow of a carrier gas, performing the transesterification reaction; (b) separating and obtaining the bis-(2-hydroxyethyl) terephthalate prepared by the above reaction; A method of manufacturing is provided.

In one embodiment of the present invention, the transesterification reaction of step (a) may be carried out in a temperature range between room temperature and the boiling point of the diol solvent as the reactant, and the catalyst for transesterification per mole of dimethyl terephthalate is 0.00005 to 1.0 molar ratio can have

In addition, the present invention comprises the steps of (i) depolymerizing by adding alcohol, a polar aprotic solvent and potassium carbonate (K ₂ CO ₃ ) to a polymer containing an ester functional group; (ii) performing a transesterification reaction while adding a flow of a carrier gas to the depolymerization product obtained in step (i); and (iii) separating and obtaining BHET prepared by the above reaction; It provides a method for producing bis- (2-hydroxyethyl) terephthalate by depolymerization of a polymer containing an ester functional group, characterized in that it comprises a.

In an embodiment of the present invention, after step (i), the step of isolating some compounds from the depolymerization product to the outside may be further performed, wherein some of the compounds isolated to the outside include unreacted ester functional groups It may include one or more selected from a polymer, a part of an insoluble catalyst, a polar aprotic solvent, and a reaction by-product.

In addition, the polar aprotic solvent in step (i) is an inert solvent that does not participate in the depolymerization reaction of a polymer containing an ester functional group, and is a solvent capable of lowering the solubility of the catalyst in alcohol, and the skeleton structure of the organic compound is a chain A compound in the form and/or ring form, wherein at least one of a halogen element, oxygen and nitrogen is bonded to the organic compound, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propio Nitrile, aminopropionitrile, methylaminopropionitrile, iminodipropionitrile, butyronitrile, methylbutenenitrile, butanenitrile, methylethylether, diethylether, ethylphenylether, dimethoxybenzene, trimethoxy It may be at least one selected from benzene, methoxyphenol, tetrahydrofuran, methyltetrahydrofuran, dioxane, chloromethane, dichloromethane, chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, and trichlorobenzene.

In addition, in one embodiment of the present invention, in step (i), the number of moles of the alcohol and the number of moles of the polar aprotic solvent compared to the number of moles of the repeating unit of the polymer raw material containing the ester functional group, the number of moles of the ester functional group It may be in a ratio range of 0.1 to 5,000 times the number of moles of repeating units of the polymer raw material contained therein.

In addition, in one embodiment of the present invention, before carrying out the transesterification reaction in step (ii), ethylene glycol and/or as a solvent for transesterification in the depolymerization product in step (i); The number of moles in a predetermined range per mole of dimethyl terephthalate contained in the depolymerization product of one or more transesterification catalysts selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides and guanidine-based organic compounds and the methanol recovered in step (iii) may be reused as a raw material for depolymerization in step (i).

Further, in one embodiment of the present invention, the catalyst for the transesterification reaction controlled in step (ii) is characterized in that the number of moles per mole of dimethyl terephthalate is 0.00005 to 1.0 times the number of moles.

The present invention provides a method for obtaining BHET, a high value-added monomer, from DMT in high yield through a small amount of transesterification catalyst and a simple process configuration that does not consume much energy. In more detail, a method of changing the reaction equilibrium that can be reached in a closed system by methanol liberated by the transesterification reaction and ethylene glycol added with the monomer raw material is used. For example, by selectively discharging only methanol to the outside, methanolysis corresponding to a reverse reaction is suppressed and glycolysis corresponding to a forward reaction is promoted to provide a method of obtaining BHET in high yield. As the catalyst in the reactant that can be prepared according to an example of the present invention, a catalyst effective for transesterification can be used, and it is not necessary to distinguish reaction selectivity for methanolysis or glycolysis, and depolymerization of a polymer containing a general ester functional group It can be used to induce an effective and efficient transesterification reaction capable of maintaining selectivity and exhibiting sufficient reactivity with only a trace amount of 1/10 to 1/10 of the mass of the catalyst added to the reaction. Therefore, the transesterification reaction can be performed only with all or a part of the catalyst remaining in the reaction product discharged from the previously performed methanolysis reaction system. The vapor discharged to the outside is high-purity methanol equivalent to the equivalent of DMT, and most of it can be concentrated/recovered, and the recovered methanol can be 100% recycled as a reactant of methanolysis for depolymerization of polymers containing ester functional groups , when methanolysis and glycolysis are combined, theoretically, it corresponds to a technology that enables complete methanol recycling.

In addition, the present invention can provide a method for preparing BHET in high yield by using DMT and ethylene glycol obtained from depolymerization of a polymer containing an ester functional group as a reaction intermediate. For example, a high yield of DMT and ethylene glycol are produced 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 ethylene glycol is added to the produced DMT. can provide a method for producing BHET as an end product. When depolymerization of a polymer containing an ester functional group is performed according to an example of the present invention, high-yield production of BHET, a high value-added monomer, can be achieved in spite of not using the existing high-temperature reaction conditions (190 to 280° C.) of glycolysis. It is possible. For example, BHET in high yield can be selectively prepared only by a series of reaction processes maintained at a temperature close to room temperature below the boiling point of ethylene glycol or even lower than the boiling point of methanol, which is a low-temperature, low-energy glycolysis depolymerization technology. This means that implementation is possible.

In the method according to the present invention, the amount of dimer or oligomer production can be maintained lower than that of the conventional high-temperature glycolysis reaction, and a relatively high concentration of BHET can be obtained therefrom, while the temperature of the reactant is It can be maintained similar to the operating range of the purification process for removing dimers and oligomers), and energy loss is minimized because it can be directly applied to the purification process without going through the preheating or cooling process that accompanies energy consumption in transporting the reactants. At the same time, it is easy to implement a continuous reaction and post-treatment process.

1 is a schematic view of a method of supplying a carrier gas for discharging methanol generated from the transesterification reaction of DMT to the outside of the reactor according to an embodiment of the present invention.
2 is a schematic diagram of an example of a process combination that may be configured to obtain a BHET depolymerized monomer from a polymer raw material including an ester functional group according to an embodiment of the present invention.
Figure 3 is a schematic diagram of one configuration example of an experimental apparatus for performing the transesterification reaction of DMT according to an embodiment of the present invention.

Unless defined otherwise, 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. In general, the nomenclature used herein is those well known and commonly used in the art.

In the present specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

The present invention provides an optimal catalyst for obtaining BHET, a high-addition monomer, in high yield in performing a transesterification reaction that can proceed by using DMT as a raw material and adding ethylene glycol.

In one aspect, the present invention is a catalyst for converting DMT into BHET in high yield through transesterification, and is selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides and guanidine-based organic compounds. It provides a method of the transesterification reaction in which one or more can be selected.

In addition, the present invention provides a DMT-derived BHET monomer capable of obtaining BHET in high yield by setting optimal reaction conditions in addition to the optimal transesterification reaction catalyst in converting DMT to BHET by glycolysis. A process for transesterification that can be prepared is provided.

The method of the present invention comprises (a) adding ethylene glycol to DMT as a reactant for transesterification, and any one selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides and guanidine-based organic compounds. performing the transesterification reaction in the presence of one or more transesterification catalysts while applying a flow of a carrier gas; (b) separating and obtaining BHET prepared by the above reaction;

In the present invention, the input of the catalyst in step (a) and the flow of the carrier gas may be supplied to the reactants without limitation before or after the reactants reach the target temperature, and may be performed under batch reaction conditions or conditions with continuous flow. can The catalyst and ethylene glycol as an addition reactant may be added in a mixed form with DMT before preparing the reaction.

The flow of the carrier gas is used as a means for discharging methanol to the outside, and a flow by forced circulation of the gas phase with a pressure difference may be used. In addition, after condensing methanol vapor from the outside of the reactor, a continuous flow of gas that is recirculated in a state where the vapor phase concentration is almost dilute is used (FIG. 2 a), or an inert gas is continuously supplied from the outside to discharge methanol to the outside. The method (Fig. 2b) may also be used.

In carrying out the transesterification reaction according to step (a), dimethyl terephthalate, ethylene glycol, and a catalyst for transesterification are added to the reactor, and the carrier gas is in direct gas-liquid contact with the reactants in the reactor can be induced. The transfer tube may be placed below the water level of the reactant to allow air bubbles to be sprayed. In 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. Methanol vapor diffusing into the carrier gas may be advantageous for the reactivity if mass transfer occurs above the saturation concentration, but when a sufficient rate of carrier gas is supplied, the methanol emission can be controlled by the rate of the transesterification reaction.

The temperature of the transesterification reaction is a range in which the evaporation rate of methanol occurring from the reaction or present in the reactant occurs from the reaction in the gas-liquid contact process, that is, the temperature between room temperature and the boiling point of the diol applied as the reactant, and 0.1 torr based on absolute pressure. A pressure of 5 atm may be maintained, but it may be changed within the above range in consideration of the range of temperature and pressure for the transesterification reaction and the rate of methanol removal by the carrier gas.

The temperature range may be changed depending on the catalyst for the transesterification reaction to be introduced, and is preferably a temperature between room temperature and the boiling point of the diol applied as a reactant, and the pressure is stable and continuous process operation to proceed at a pressure near atmospheric pressure can be beneficial to In addition, the reaction time in step (a) may vary depending on the type of catalyst used in the reaction and the amount of DMT and ethylene glycol supplied in addition to the input amount.

First, in step (a), the catalyst for transesterification per unit mole of DMT as a raw material may be added to have a molar ratio of 0.00005 to 1.0, preferably 0.0001 to 0.2. When the catalyst for the transesterification reaction is included in a molar ratio of less than 0.00005 per unit mole of DMT, which is a raw material, the transesterification reaction of DMT by ethylene glycol may proceed slowly, thereby reducing process efficiency, and exceeding a molar ratio of 1.0 may be included. When the amount of the improvement effect is not large compared to the content of the increased catalyst, it is uneconomical, rather, by-products may increase, and the excess catalyst remains as an impurity during BHET separation, which may affect separation and purification efficiency.

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 K ₂ CO ₃ , KHCO ₃ , Na ₂ With at least one selected from CO ₃ , NaHCO ₃ , NaOH, KOH, MgO, CaO, CH ₃ OK, CH ₃ ONa and TBD, the amount and combination of the catalyst significantly improves the conversion rate of DMT, and the yield for BHET is also significantly improved. It should be something that can be improved.

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 may occur most efficiently.

In the step (a) of the transesterification reaction by adding ethylene glycol to DMT under the catalyst for the transesterification reaction, BHET and methanol are generated, and the flow of carrier gas is maintained so that the forward reaction to BHET can continue beyond the equilibrium concentration. It is carried out under the condition that methanol vapor is continuously discharged to the outside of the reaction system by placing it inside the reactor. As a method of supplying the carrier gas, as shown in FIG. 2, a method by a unidirectional flow (b in FIG. 2) discharged to the outside after separating methanol vapor by a condenser or a method in which methanol vapor is removed and then recycled (FIG. 2) a) of can be used.

As for the carrier gas injected into the reactor, the reaction conditions to keep the concentration of methanol in the reactant lean to prevent or suppress the recombination of methanol by-product from the transesterification reaction by the reverse reaction is advantageous for improving the DMT conversion rate and the yield of BHET products. can In this case, the carrier gas may be used without limitation as long as it does not have a chemical action on the ethylene glycol addition transesterification reaction of DMT or the catalyst, and preferably air, nitrogen, argon, helium, etc. may be used, preferably moisture. An inert gas that is substantially free of

In the present invention, step (b) is a step to obtain by separating the BHET formed by the reaction, specifically, the BHET formed in the step (a) including unreacted residual DMT, ethylene glycol, residual catalyst, etc. Separation from the reaction mixture to obtain high purity, may be carried out by a generally known purification method, and the method is not limited, but physical methods such as filtration, crystallization, centrifugation, evaporation, distillation, or adsorption, neutralization, Chemical methods such as salting out can be carried out in parallel.

In the present invention, in preparing BHET, which is a high addition monomer, through a transesterification reaction in which ethylene glycol can be added using DMT as a starting material, the DMT can be obtained from depolymerization of a polymer containing an ester functional group, and the depolymerization result is pretreated. BHET can be prepared by transesterification with ethylene glycol with or without the process.

The transesterification reaction by the addition of ethylene glycol of DMT is a two-step serial reaction in which a reaction product prepared through a methanolysis reaction from a polymer raw material containing an ester functional group is directly used as a reaction raw material for glycolysis. It can also be applied to a reaction process for producing a yield of BHET.

That is, the present invention includes a method of producing BHET as a final product by initiating depolymerization of a polymer containing an ester functional group, (i) alcohol, a polar aprotic solvent and potassium carbonate (K ₂ ) in a polymer containing an ester functional group CO ₃ ) by inputting depolymerization; (ii) performing a transesterification reaction while adding a flow of carrier gas to the depolymerization product obtained in step (i); and (iii) separating and obtaining BHET prepared by the above reaction; It provides a method for producing bis-(2-hydroxyethyl) terephthalate by depolymerization of a polymer containing an ester functional group, characterized in that it comprises a.

1 is a conceptual diagram illustrating a process for preparing BHET through transesterification from a polymer raw material containing the ester functional group. First, the (i) step (100) to the polymer (1) containing an ester functional group; In a step of depolymerizing alcohol, a polar aprotic solvent, and potassium carbonate (K ₂ CO ₃ ) as a catalyst (2), the polymer including the ester functional group is an alcohol, a polar aprotic solvent and potassium carbonate (K ₂ CO ₃ ) ), an alcohol addition monomer can be prepared through a transesterification reaction, and low-temperature depolymerization of the polymer proceeds effectively. The process is very simple, can obtain DMT in a high yield of 90% or more, and is very economical because energy consumption is low.

Here, the polymer containing the 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 in which the polymer containing the ester functional group is mixed with the polymer. Other polymers to be mixed with the polymer containing the ester functional group listed as examples above are merely examples and are not limited to those listed above.

In addition, the polymer including the ester functional group may be a polymer formed by condensation polymerization of dicarboxylic acid and dialcohol, wherein the dicarboxylic acid is terephthalic acid, naphthalene dicarboxylic acid, diphenyldicarboxylic acid, diphenyl ether dicarboxyl. Acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, trimellitic acid, pyro selected from the group consisting of mellitic acid and combinations thereof, and the dialcohol is ethylene glycol, trimethylene glycol, 1,2-propanediol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, decamethylene 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(tetra methylene) glycol, polytetramethylene glycol, pentaerythritol, 2,2-bis(4-β-hydroxyethoxyphenyl)propane, and combinations thereof.

For example, the polymer containing the ester functional group is 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.

The most common example of the polymer including the ester functional group is polyethylene terephthalate (PET), wherein the starting materials for preparing the polymer are terephthalic acid or its derivative monomer and ethylene glycol.

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

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

The alcohol may be used in a ratio of 0.1 to 5,000, preferably 1 to 500, in a ratio of 0.1 to 5,000 per mole of repeating units of the polymer raw material including the ester functional group.

Potassium carbonate is used as the catalyst. Potassium carbonate is represented by the formula K ₂ CO ₃ , and is a white crystal that dissolves in water. It is preferable to use the anhydrous form of the potassium carbonate rather than the hydrate form, and it is more preferable to dry it before use. The amount of potassium carbonate used may be 0.01 times or more of the moles of the polymer repeating unit including an ester functional group, preferably 0.01 to 100 times, more preferably 0.1 to 10 times.

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

The skeletal structure of the organic compound in the polar aprotic solvent may be a chain or ring compound, a halogen element directly bonded to the organic compound, or the organic compounds themselves or connected to each other by oxygen or nitrogen, specific examples Examples include toluene, acetone, methyl ethyl ketone, methyl iso-butyl ketone, acetonitrile, tetrahydrofuran, dichloromethane, chloroform Any one or more selected from (chloroform), chlorobenzene, methyl phenyl ether, and ethyl phenyl ether may be used.

In addition, the polar aprotic solvent may be used in a mole number range of 0.1 to 5,000 times the mole number of the repeating unit of the polymer raw material including the ester group, preferably in a mole number ratio range of 1 to 500 times.

In the step (i), alcohol addition depolymerizes a polymer containing an ester functional group in the range of 0 to 80 ° C., preferably 10 to 60 ° C. According to some examples according to (i), the polymer at ambient pressure and near room temperature Because it can induce complete decomposition of the reaction system and implement a reaction system through a simple structure and configuration, the investment cost can be much lower than that of existing technologies or existing processes, and efficient and stable energy management is also possible.

On the other hand, in the depolymerization of step (i), because a low-cost, heterogeneous catalyst that is basically water-soluble is used, the catalyst can be easily recovered and reused after the reaction, and the monomer prepared by lowering the temperature of the reactant itself to room temperature or less is used in a high ratio. It can be recovered, and the used solvent can be reintroduced as a raw material for depolymerization of a new polymer raw material, so that the economic feasibility of the recycling process can be further improved.

In addition, in the depolymerization of the polymer in step (i), sufficient energy for depolymerization may be obtained only by heat of mixing and heat of dissolution generated in the process of preparing a mixed solution for the depolymerization reaction without input of an additional heat source. In this case, the depolymerization may be carried out in an insulated reactor. In addition, as in some embodiments according to the present invention, depolymerization may be performed while supplying an external heat source.

In addition, depolymerization of the polymer may be performed at atmospheric pressure or higher. Specifically, it may be carried out at a pressure of about 1 atm to 6.5 atm.

In addition, the depolymerization of the polymer may be performed in a form exposed to the atmosphere or a closed system, or may be performed by refluxing the solvent by placing a condenser.

In addition, the depolymerization reaction time of step (i) may vary depending on the amount of polymer used, but in the case of room temperature where no energy is applied, the monomer can be obtained in a sufficiently high yield within 24 hours, and materials other than the reactants are Since no significant chemical changes occur, most can be recovered and reintroduced into the process.

After step (i), the step 200 of isolating some compounds from the depolymerization product obtained through depolymerization to the outside may be further performed. Specifically, the step of separating some of the compounds from the depolymerization product may include unreacted substances, methanol, polar aprotic solvents, catalysts, or monomethyl terephthalate remaining together with DMT and ethylene glycol obtained after completion of the depolymerization reaction of step (i) Mono-methyl terephthalate, MMT), terephthalic acid (terephthalic acid, TPA) from the reaction mixture (10) containing by-products such as derivatives, the polymer, insoluble catalyst, polar aprotic solvent, a flow containing at least one selected from reaction by-products, etc. The step of separating to the outside may be performed by a generally known method, and the method is not limited thereto.

As an example of separation, if the insoluble catalyst and unreacted polymer are separated from the depolymerization product through filtration, the depolymerization product may have a uniform liquid form, and the concentration of the polar aprotic solvent or methanol by applying a temperature or reducing the pressure thereto When some or all of the evaporation or distillation occurs, crystallization of DMT in the depolymerization product may occur. Here, a washing solution is additionally added as a method to remove foreign substances and increase the concentration of DMT, and methods such as recrystallization, physical filtration, distillation, evaporation, and drying are additionally used to prepare as a raw material for ethylene glycol addition transesterification reaction. can The solvent and catalyst separated from the depolymerization product may be reintroduced 20 as a raw material for the methanolysis depolymerization 100, which is the step (i) above.

On the other hand, the step 200 of isolating some of the compounds may be a step carried out to prepare the transesterification step 300 performed by adding ethylene glycol to the generated DMT, but it does not mean that it must be performed. . That is, it may be directly used as a raw material in step (ii) without going through the step 200 of separating the depolymerization product obtained from the depolymerization step of the polymer containing the ester functional group in step (i).

In the present invention, step (ii) (300) is a step of performing a transesterification reaction while adding a flow (3) of a carrier gas to the depolymerization product obtained in step (i). The method for performing the transesterification reaction in step (ii) is carried out by the same method as the method for preparing BHET from DMT described above, and thus detailed description thereof will be omitted. The DMT in step (ii) is obtained by depolymerization of a polymer containing an ester functional group (30), and the depolymerization can be carried out by a simple process at room temperature and pressure, and the product of depolymerization has a high yield of DMT. and a diol, and by using the method for preparing BHET from DMT of the present application, BHET can be obtained as a final product directly from a polymer containing an ester functional group.

Before carrying out the transesterification reaction in step (ii), ethylene glycol and/or as a solvent for the transesterification reaction in the depolymerization product in step (i); The number of moles in a predetermined range per mole of dimethyl terephthalate contained in the depolymerization product of one or more transesterification catalysts selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides and guanidine-based organic compounds After adjusting as much as possible, the transesterification reaction may be carried out.

Control of the number of moles of the ethylene glycol and/or the transesterification catalyst is performed by adding ethylene glycol and/or the transesterification catalyst to the depolymerization product or partially removing it from the depolymerization product. In this case, the removal process and the addition process may be performed in the step 200 of isolating some of the compounds described above.

The number of moles of ethylene glycol after the adjustment may range from 0.1 to 100 moles, preferably from 1 to 50 moles, per mole of dimethyl terephthalate contained in the depolymerization product.

In addition, the number of moles of the catalyst for the transesterification reaction 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 product.

In the transesterification reaction 300, methanol may be discharged to the outside of the reactor 40 by the flow 3 of the carrier gas in order to suppress the reverse reaction by methanol and to continue the addition reaction of ethylene glycol at the same time, and is maintained at a low temperature. The methanol recovered through the condenser 400 may be reused (60) as a raw material for the depolymerization of step (i). Compared with the conventional glycolysis method using high-temperature reaction conditions (usually in the range of 200 to 280°C), the reaction proceeds quickly even at a low temperature much lower than the boiling point of ethylene glycol, effectively reducing BHET. products (dimers or oligomers) that are generated by less decomposition (or depolymerization) in the product because the reaction temperature range and the reaction path to the product are different, while the products (dimers or oligomers) are generated or not generated at a relatively low concentration. , BHET can be obtained in high yield.

According to the method of the present invention, as the reactivity of the low-temperature region and the efficiency of the purification process are improved, the energy consumption can be greatly reduced compared to the existing process, and as a result, a means for economically manufacturing BHET, a high value-added monomer, can be provided. have.

In the present invention, step (iii) is a step 500 of isolating and obtaining BHET prepared by the above reaction, and can be performed in the same manner as the method for preparing BHET from DMT described above, so detailed description is omitted.

Hereinafter, the details of the process of the present invention will be described through comparative examples and examples. These are representative examples for describing the present invention, and the scope of application of the present invention is not limited by the following examples.

Raw material 1 (dimethyl terephthalate raw material)

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

Raw material 2 (polymer raw material containing ester functional groups)

As a polymer material containing an ester functional group, the bottle of waste polyethylene terephthalate discharged after consumption is washed and dried so that there is no residual foreign matter, and then pulverized using a continuous grinding mill (manufacturer and model: IKA MF10.1) Only plastic chips having a width and length of 1 to 3 mm and a thickness of 0.5 mm or less on the wide side were collected and prepared as raw material 2 using

<Example 1>

About 14.5 g of DMT raw material prepared according to the process of raw material 1 and about 55.6 g of ethylene glycol (Sigma-Aldrich; purity > 99.8%), which is a dihydric alcohol polar solvent (corresponding to 12 times the number of moles compared to raw material 1) were mixed with 3- It was put into a neck flask, and a cooling device was installed, and then stirring was started at a speed of 1,200 rpm using a magnetic stirrer.

In order to effectively remove the reaction product, methanol, high-purity nitrogen (Central Industrial Gas; 99.9992%) was used as an inert carrier gas, and the gas flow rate in contact with the liquid in the reactor was 200 sccm, or the volume of the initial reaction mixture under standard conditions. When normalized to and converted to gas space velocity (Gas Hourly Space Velocity, GHSV(hr ^-1 )), the set value was adjusted using a mass flow controller so that the set value could be kept constant at 240.

After that, when the flask containing the reactant is heated and the final temperature of the reaction solution reaches 80℃, about 0.05 g of potassium carbonate (K ₂ CO ₃ , potassium carbonate; Sigma-Aldrich, ACS reagent) as a catalyst (input raw material 1) (corresponding to 0.005 times the number of moles relative to the number of moles) was added to initiate the reaction, and then the transesterification reaction was performed for a total of 8 hours to obtain BHET, a high value added depolymerization monomer.

As the reaction proceeded, methanol produced was degassed from the reactants by the flow of carrier gas, discharged to the outside of the reactor, and collected by an external trap maintained at 0° C. or lower.

After collecting a trace amount (50 mg or less) of a liquid reactant for each time period during the reaction, high-performance liquid chromatography (HPLC with Optimapak C ₁₈ Column (250 mm, 5micron), UV detector (λ=254 nm)) calibrated in advance as a standard sample was used. Through quantification, the distribution and concentration of the product were estimated from this, and the conversion rate and the yield of the product were respectively calculated through this. For HPLC analysis, a mixed solution having a volume ratio of methanol:water of 70:30 was used as the mobile phase, and the total flow rate was maintained at 0.7 ml/min.

The conversion rate of DMT by the transesterification reaction, bishydroxyethyl terephthalate (BHET), hydroxyethylmethyl terephthalate (HEMT), and potassium monomethyl terephthalate (K-MMT) and dipotassium terephthalate ( The yield of K ₂ -TPA) was calculated by the following formula.

DMT conversion rate = (N ₀ - N) / N ₀ (Equation 1)

BHET yield = (N _BHET / N ₀ ) × 100% (Equation 2)

HEMT yield = (N _HEMT / N ₀ ) × 100% (Equation 3)

MMT yield = (N _MMT / N ₀ ) × 100% (Equation 4)

TPA yield = (N _TPA / N ₀ ) × 100% (Equation 5)

BHET dimer yield = (N _dimer / N ₀ ) × 100% (Equation 6)

In the above formula, N ₀ is the number of moles of DMT as the initial input raw material, and N _BHET , N _HEMT , N _MMT , N _TPA , and N _dimer are the number of moles of terephthalate in the produced BHET, HEMT, MMT, TPA and dimer. to be.

<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 in Example 1.

<Example 2>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that in Example 1, about 0.001 g of potassium carbonate (corresponding to 0.0001 times the mole of the raw material 1) was used.

<Example 3>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that in Example 1, about 0.01 g of potassium carbonate (corresponding to 0.001 times the mole of the raw material 1) was used.

<Example 4>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that in Example 1, about 0.1 g of potassium carbonate (corresponding to 0.01 times the mole of the raw material 1) was used.

<Example 5>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that in Example 1, about 0.5 g of potassium carbonate (corresponding to 0.05 times the mole of the raw material 1) was used.

<Example 6>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that in Example 1, about 2.1 g of potassium carbonate (corresponding to 0.2 times the mole of the raw material 1) was used.

<Comparative Example 2>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that an inert carrier gas was not used in Example 1.

<Example 7>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that in Example 1, high purity nitrogen was maintained at 50 sccm (GHSV=60h ⁻¹ ) as an inert carrier gas.

<Example 8>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that in Example 1, high purity nitrogen was maintained at 100 sccm (GHSV=120h ⁻¹ ) as an inert carrier gas.

<Example 9>

The transesterification reaction was carried out and evaluated in the same manner as in Example 1, except that in Example 1, high purity nitrogen was maintained at 500 sccm (GHSV=600h ⁻¹ ) as an inert carrier gas.

<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 solution in Example 1 was maintained at 50°C.

<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 solution in Example 1 was maintained at 65°C.

<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 solution in Example 1 was maintained at 100°C.

<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 solution in Example 1 was maintained at 110°C.

<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 solution in Example 1 was maintained at 120°C.

<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 solution was maintained at 130°C in Example 1.

<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 solution in Example 1 was maintained at 140°C.

<Example 17>

The same method as in Example 1, except that about 0.008 g of potassium bicarbonate (KHCO ₃ ) as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) was used and the reaction time was maintained at 3 hours The transesterification reaction was carried out and evaluated.

<Example 18>

The same as in Example 1, except that about 0.008 g of sodium carbonate (Na ₂ CO ₃ ) as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) was used and the reaction time was maintained at 3 hours The transesterification reaction was carried out and evaluated by the method.

<Example 19>

The same method as in Example 1, except that about 0.006 g of sodium bicarbonate (NaHCO ₃ ) was used as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) and the reaction time was maintained at 3 hours The transesterification reaction was carried out and evaluated.

<Comparative Example 3>

In Example 1, in the same method as in Example 1, except that about 0.007 g of potassium acetate (KOAc) as a catalyst (corresponding to 0.001 times the mole of raw material 1) was used and the reaction time was maintained at 3 hours. The transesterification reaction was carried out and evaluated.

<Comparative Example 4>

In the same method as in Example 1, except that about 0.006 g of sodium acetate (NaOAc) was used as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) and the reaction time was maintained at 3 hours. The transesterification reaction was carried out and evaluated.

<Comparative Example 5>

About 0.01 g of zinc acetate (Zn(OAc) ₂ .2H ₂ O) was used as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1), except that the reaction time was maintained at 3 hours carried out and evaluated the transesterification reaction in the same manner as in Example 1.

<Example 20>

In the same method as in Example 1, except that about 0.004 g of potassium hydroxide (KOH) as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) was used and the reaction time was maintained at 3 hours The transesterification reaction was carried out and evaluated.

<Example 21>

In the same method as in Example 1, except that about 0.003 g of sodium hydroxide (NaOH) as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) was used and the reaction time was maintained at 3 hours The transesterification reaction was carried out and evaluated.

<Example 22>

About 0.005 g of potassium methoxide (CH ₃ OK) as a catalyst in Example 1 (corresponding to 0.001 times the number of moles relative to the mole of raw material 1) was used and the reaction time was maintained at 3 hours. The transesterification reaction was carried out and evaluated by the same method.

<Example 23>

In Example 1, with the exception of using about 0.004 g of sodium methoxide (CH ₃ ONa) as a catalyst (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) and maintaining the reaction time at 3 hours, The transesterification reaction was carried out and evaluated by the same method.

<Example 24>

In the same method as in Example 1, except for using about 0.003 g of magnesium oxide (MgO) as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) and maintaining the reaction time for 3 hours The transesterification reaction was carried out and evaluated.

<Example 25>

In the same method as in Example 1, except that about 0.004 g of calcium oxide (CaO) as a catalyst in Example 1 (corresponding to 0.001 times the number of moles compared to the mole of raw material 1) was used and the reaction time was maintained at 3 hours The transesterification reaction was carried out and evaluated.

<Example 26>

In Example 1, about 0.01 g of triazabicyclodecene (TBD) as a catalyst (corresponding to 0.001 times the moles of raw material 1) was used and the reaction time was maintained at 3 hours. The transesterification reaction was carried out and evaluated by the same method as in 1.

<Comparative Example 6: PET depolymerization by high-temperature glycolysis reaction>

About 10 g of the PET raw material of raw material 2 was prepared as a raw material for the glycolysis reaction. About 38.75 g of ethylene glycol, a dihydric alcohol polar solvent, (12 moles per mole of polymer repeating unit) was put into a 3-neck flask, equipped with a reflux condenser at atmospheric pressure, and stirred using a heated magnetic stirrer. The temperature reached 177°C. When 10 g of the prepared polymer raw material was added, the temperature was continuously increased and the mixture was stirred simultaneously. When the reaction mixture reached 197°C or reflux temperature, about 0.571 g of zinc acetate catalyst (0.05 mol per mole of polymer repeating unit) was added to initiate a catalytic reaction, and stirring was continued for 2 hours, but the reaction temperature was within the range of ±0.5°C. The reaction was carried out using a condenser with one end exposed to atmospheric pressure while maintaining it constant. After the reaction, unreacted substances were separated and quantified through filtration, and the decomposed monomers, dimers, side reactants such as monohydroxyethyl terephthalate (MHET) and oligomers were quantified from the reactants of Example 1. Similar to the method used for

<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 and about 66.3 g of dichloromethane (Samjeon Pure Medicine; purity 99.5%) (corresponding to 50 times the moles of the repeating unit of the raw material 2 polymer), 24.96 g of methanol (Samjeon Pure Medicine; 99.9%) (corresponding to 50 times the number of moles of the repeating unit of the polymer of Raw Material 2) and about 0.43g of K ₂ CO ₃ (potassium carbonate; Sigma-Aldrich, ACS reagent) as a catalyst (0.2 times the number of moles of the repeating unit of the polymer of Raw Material 2) ) was put into a 3-neck flask, and secondary distilled water was added to adjust the initial water content of the reactant to have an initial number of moles of 0.4 compared to the moles of the repeating unit of the raw material polymer. The reaction was carried out while stirring at 500 rpm for 24 hours at 25° C. and atmospheric pressure using a magnetic stirrer.

After the reaction, the resultant is filtered and a filtrate containing DMT, HEMT, ethylene glycol and K-MMT, which is a potassium salt of MMT, an organic solvent, etc., and unreacted PET, K ₂ CO ₃ catalyst, K- It was separated into a solid (filter cake) containing MMT.

Trace amounts (50 mg or less) of potassium salts in the filtrate and solid content were each taken and diluted in a mobile phase aqueous solution to prepare a sample, and high-performance liquid chromatography (HPLC with Optimapak C ₁₈ Column (250mm, 5micron)), UV detector (λ=254nm) ))), the product distribution and concentration in each sample were estimated, and unreacted PET in the solid content was quantified by the gravimetric method. Through the quantified values, the conversion rate of PET according to depolymerization and DMT, HEMT, TPA, MMT The yield of was calculated. For HPLC analysis, a mixed solution having a volume ratio of methanol:water of 70:30 was used as the mobile phase, and the total flow rate was maintained at 0.7 ml/min. The conversion rate of PET and the yield of DMT by depolymerization were calculated by the following equations.

PET conversion = (M ₀ - M) / M ₀ × 100% (Equation 7)

DMT yield = (M _DMT / M ₀ ) × 100% (Equation 8)

In the above formula, M ₀ and M represent the number of moles of repeating units of the initially added raw polymer (PET) and unreacted polymer, respectively, and M _DMT represents the number of moles of the generated DMT.

The filtrate of the depolymerization product was applied to a transesterification reaction in which ethylene glycol was added using the filtrate as a raw material. In carrying out the transesterification reaction, it was carried out under the same conditions as the method of Example 1, except that the filtrate of the depolymerization product was used instead of the raw material 1 as a raw material, and the majority of methanol and the polar aprotic solvent were removed by a vacuum evaporator. Thereafter, the number of moles of DMT is adjusted to be the same as in Example 1, and the total amount of ethylene glycol is about 55.6 g (ratio of the number of moles 12 times the mole of DMT) by adding an additional amount of ethylene glycol generated from depolymerization. control, and the transesterification reaction was carried out and evaluated in the state that no additional catalyst was added.

The number of moles of catalyst and K-MMT in the solids recovered after filtration were quantified (measured at a molar ratio of 0.126 and 0.024 relative to the number of moles of the repeating unit of the raw material), respectively, using the gravimetric method and HPLC, and the number of moles of the catalyst initially added to the solid phase The number of moles excluding the recovered ones (based on the number of moles of potassium cations) was estimated as the number of moles of catalyst remaining in the filtrate of the depolymerization product. From this, it can be seen that the amount of catalyst (K ₂ CO ₃ ) in the raw material of the transesterification reaction to which ethylene glycol is added is present in a ratio of about 0.054 moles per unit mole of DMT.

The conversion rate of DMT, the yield of BHET, HEMT, and the BHET dimer by the transesterification reaction were calculated by Equations 1 to 4 described above, and the results are shown in Table 5.

[Comparison of transesterification reaction characteristics according to the amount of catalyst used]

[Table 1] shows the effect of the reaction by controlling the amount of potassium carbonate (K ₂ CO ₃ ) used as a catalyst according to the example of the present invention in carrying out the transesterification reaction in Examples 1 to 6 and Comparative Example 1. This is the observed result (reaction temperature 80℃, GHSV = 240h ^-1 ). Unlike the examples in which the catalyst was used, in the case of Comparative Example 1 in which no catalyst was added, the yield of BHET after 2 hours and 8 hours was about 0.0% and 2.4%, respectively, indicating that the rate of the transesterification reaction was very low. Able to know. This is a result explaining that the use of a catalyst is essential in order to promote the addition transesterification reaction of ethylene glycol of DMT under low temperature as exemplified in the present invention.

division reaction
hour
(h) moles of compound added per mole of DMT Conversion rate (%) transference number (%) EG K ₂ CO ₃ BHET HEMT BHET dimer K ₂ -TPA K-MMT oligomer Comparative Example 1 2 12 0.0 2.2 0.0 1.7 0.0 0.0 0.0 0.0 8 12 0.0 8.9 2.4 6.5 0.0 0.0 0.0 0.0 Example 2 2 12 0.0001 64.5 43.8 20.2 0.4 0.0 0.0 0.0 8 12 0.0001 100.0 81.9 16.6 1.5 0.0 0.0 0.0 Example 3 2 12 0.001 99.5 85.7 12.1 1.7 0.0 0.0 0.0 8 12 0.001 100.0 97.2 0.6 2.2 0.0 0.0 0.0 Example 1 2 12 0.005 99.8 86.3 8.6 1.7 0.7 0.0 0.0 8 12 0.005 100.0 97.0 0.0 2.1 0.9 0.0 0.0 Example 4 2 12 0.01 100.0 88.2 9.0 1.8 1.0 0.0 0.0 8 12 0.01 100.0 96.6 0.0 2.2 1.2 0.0 0.0 Example 5 2 12 0.05 99.5 80.9 11.6 1.4 5.6 0.0 0.0 8 12 0.05 99.8 84.0 8.2 1.6 6.0 0.0 0.0 Example 6 2 12 0.2 99.3 67.4 11.6 0.9 17.4 2.0 0.0 8 12 0.2 99.1 65.7 13.2 0.8 18.5 0.9 0.0 DMT: Dimethyl terephthalate, EG: Ethylene glycol,
BHET: Bis(2-hydroxyethyl) terephthalate;
HEMT: 1-(2-Hydroxyethyl) 4-methyl terephthalate
K ₂ -TPA: Dipotassium terephthalate
K-MMT: Potassium monomethyl terephthalate

Examples 1 to 4 are the results of the reaction using potassium carbonate corresponding to 0.0001 to 0.01 mol relative to 1 mol of DMT of raw material 1 as a catalyst, and as the amount of potassium carbonate increases, the production rate and yield of BHET are greatly improved showing that it is

On the other hand, Examples 5 and 6 used potassium carbonate corresponding to 0.05 and 0.2 mol, respectively, of the amount of catalyst relative to 1 mol of DMT, but rather showed a tendency to decrease the production rate and yield of BHET. On the other hand, the final yield of K ₂ -TPA, a by-product of the reaction, showed a tendency to increase to 6.0% and 18.5%, respectively. This is a result explaining that when an excessively excess catalyst is used relative to the number of moles of DMT input, not only catalyst consumption but also side reactions such as hydrolysis or alkali decomposition may be promoted. Therefore, proper control of the catalyst amount can help to improve the performance and economy of the transesterification reaction.

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

When the transesterification reaction of DMT is performed in the presence of an excess of ethylene glycol solvent, the production rate of the product, BHET, is observed to be very high at the beginning of the reaction. increases In a closed system, this transesterification reaction is not an irreversible reaction in which all of the initially input DMT is converted to BHET, and the reverse transesterification reaction involving by-product methanol and BHET may also have a rate. When the forward reaction and the reverse reaction reach equilibrium, the concentration of the compound no longer changes, and even if the conditions of the reaction are changed, there may be a limit to improving the yield of the product. However, if a part of the reaction product in the reaction product mixture is effectively removed 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 the concentration of the substance, that is, the mass transfer rate discharged to the outside. Methanol generated from the transesterification reaction carried out according to an example of the present invention is a material with the lowest boiling point among the raw materials and products (130 ° C or higher than ethylene glycol), If the incoming carrier gas is continuously flowed, methanol is selectively discharged to the outside and regeneration of DMT by reverse transesterification can be suppressed.

division reaction
hour
(h) moles of compound added per mole of DMT GHSV (h ^-1 ) conversion rate
(%) transference number (%) EG K ₂ CO ₃ BHET HEMT BHET dimer K ₂ -TPA K-MMT oligomer Comparative Example 2 3 12 0.005 0 88.9 58.4 29.5 0.8 0.3 0.0 0.0 8 12 0.005 0 90.0 59.3 29.5 0.8 0.4 0.0 0.0 Example 7 3 12 0.005 60 98.5 77.7 19.0 1.3 0.5 0.0 0.0 8 12 0.005 60 100.0 89.9 7.6 1.8 0.7 0.0 0.0 Example 8 3 12 0.005 120 98.9 79.7 17.3 1.3 0.7 0.0 0.0 8 12 0.005 120 100.0 94.6 2.4 1.9 1.1 0.0 0.0 Example 1 3 12 0.005 240 100.0 92.6 4.2 1.9 0.8 0.0 0.0 8 12 0.005 240 100.0 97.0 0.0 2.1 0.9 0.0 0.0 Example 9 3 12 0.005 600 100.0 97.0 0.3 2.1 0.6 0.0 0.0 8 12 0.005 600 100.0 83.7 0.0 1.7 0.6 0.0 13.9 DMT: Dimethyl terephthalate, EG: Ethylene glycol,
BHET: Bis(2-hydroxyethyl) terephthalate;
HEMT: 1-(2-Hydroxyethyl) 4-methyl terephthalate
K ₂ -TPA: Dipotassium terephthalate
K-MMT: Potassium monomethyl terephthalate

[Table 2] observes the characteristics of the transesterification reaction performed by varying the flow rate of the inert carrier gas (high purity nitrogen) introduced to cause gas-liquid contact with the reactants inside the reactor to remove methanol from the reaction product ( reaction temperature 80°C). When there was no carrier gas flow (Comparative Example 2), the transesterification reaction was performed at 80° C. for 3 hours. As a result, the yield of BHET was about 58.4%, and a relatively low value was observed. and a slight increase in the reaction yield of about 0.9% was observed. Although the reactor exists in the form of an open system and the internal temperature is maintained above the boiling point of methanol, the methanol produced as some transesterification reaction proceeds does not dominate the gas phase (headspace) filled with reactants or out of the reactor. and can be expected as a result of the presence of high concentrations in the reactants.

On the other hand, in the case of the transesterification reaction carried out under continuous flow conditions (Examples 1 and 7 to 9) in which the flow rate of nitrogen as a carrier gas is different, it can be seen that the conversion rate and the yield of BHET are greatly improved. In particular, in the reactions carried out according to Examples 1 and 9, in which the GHSV exceeds 200, it can be seen that when the reaction time exceeds 3 hours, a BHET yield of 92% or more is obtained.

On the other hand, it was found that the BHET yield was not improved as the yield of dimers and oligomers slightly increased when the flow rate of the carrier gas was maintained too high and exposed to reaction conditions for a long time. In the case of Example 1, no oligomer was observed in the reactant even if the reaction was carried out for 3 hours or longer. On the other hand, when the transesterification reaction was carried out according to Example 9, it was observed that the selectivity of BHET decreased as oligomers started to be generated after 6 hours. Even when only a small amount of less than 3% of the oligomer was generated, the viscosity of the reaction mixture was greatly increased, and a phenomenon in which a part of the product formed a non-uniform phase and the reactant was rapidly suspended was observed. Therefore, in order to maximize the yield of BHET, which is a polymer depolymerization monomer, a flow of carrier gas is applied, methanol generated from the transesterification reaction can be efficiently removed, and the addition reaction of ethylene glycol can also occur predominantly. Selection of flow conditions may be desirable to improve the final yield of BHET.

[Characteristics change of transesterification reaction according to reaction temperature]

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

When maintained at a temperature exceeding the boiling point of methanol (Example 1 and Examples 12 to 16), the BHET yield obtained from the transesterification reaction could be maintained high from the beginning of the reaction, and when the reaction time exceeds 4 hours, 95 It can be seen that a BHET yield of % or more is obtained. This yield improvement contributed to the increase in the mass transfer rate of methanol when the reaction temperature exceeds the boiling point of methanol, and the improvement of the sequential glycolysis catalytic reaction rate in which DMT is converted into HEMT and HEMT is converted to BHET. can be presumed to be

division Reaction time (h) moles of compound added per mole of DMT reaction temperature
(℃) Conversion rate (%) transference number (%) EG K ₂ CO ₃ BHET HEMT BHET dimer K ₂ -TPA K-MMT oligomer Example 10 2 12 0.005 50 58.4 45.4 12.5 0.4 0.0 0.0 0.0 4 12 0.005 50 88.1 68.1 19.1 0.9 0.0 0.0 0.0 Example 11 2 12 0.005 65 93.7 73.9 18.3 1.2 0.4 0.0 0.0 4 12 0.005 65 97.5 86.8 8.4 1.6 0.7 0.0 0.0 Example 1 2 12 0.005 80 99.8 86.3 8.6 1.7 0.7 0.0 0.0 4 12 0.005 80 100.0 95.6 1.7 2.1 0.6 0.0 0.0 Example 12 2 12 0.005 100 100.0 95.8 1.5 2.2 0.5 0.0 0.0 4 12 0.005 100 100.0 97.1 0.0 2.3 0.6 0.0 0.0 Example 13 2 12 0.005 110 100.0 95.4 0.6 2.2 0.9 0.0 0.0 4 12 0.005 110 100.0 96.6 0.3 2.2 0.9 0.0 0.0 Example 14 2 12 0.005 120 100.0 92.6 4.6 2.0 0.8 0.0 0.0 4 12 0.005 120 100.0 95.0 1.8 2.2 1.0 0.0 0.0 Example 15 2 12 0.005 130 100.0 96.5 0.3 2.4 0.8 0.0 0.0 4 12 0.005 130 100.0 96.6 0.0 2.4 1.0 0.0 0.0 Example 16 2 12 0.005 140 100.0 95.1 0.7 2.4 0.8 0.0 0.0 4 12 0.005 140 100.0 96.4 0.0 2.4 0.9 0.0 0.0 DMT: Dimethyl terephthalate, EG: Ethylene glycol,
BHET: Bis(2-hydroxyethyl) terephthalate;
HEMT: 1-(2-Hydroxyethyl) 4-methyl terephthalate
K ₂ -TPA: Dipotassium terephthalate
K-MMT: Potassium monomethyl terephthalate

On the other hand, when the transesterification reaction was carried out while maintaining the reaction temperature below the boiling point of methanol (Example 10 and Example 11), the BHET yield according to the elapsed reaction time was 45.4% and 73.9%, respectively, when the reaction time elapsed 2 hours, 4 A rather slow rate of increase was observed over time to 68.1% and 86.8%.

In addition, although not shown in the table, oligomers started to be detected as they were exposed to reaction conditions for a long time (after reaction time of 7 hours), and about 11.2% and 3.3% of the DMT raw materials applied after 8 hours of reaction time were converted to oligomers. At this time, the viscosity of the reaction solution was greatly increased, and it was also observed that the reaction solution was changed to a non-uniform suspension.

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

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

The existing glycolysis reaction for preparing BHET from a polymer containing an ester functional group is performed at a high temperature, so a large amount of energy consumption is pointed out as a problem. In order to overcome this problem, a novel reaction route capable of producing high-yield BHET in the low-temperature region can be considered. As an example of such a reaction route, the methanolysis reaction for preparing DMT from a polymer raw material containing an ester functional group can be carried out at room temperature, and it can provide a low-temperature reaction condition in which ethylene glycol addition can predominantly occur continuously. If there is, it can be expected to be able to manufacture high yield of BHET.

If a separate separation process is not performed after the first reaction, methanolysis, some of the catalyst may remain in the resulting reaction mixture. can

Catalysts commonly used in transesterification may include acidic, basic, and metal salt catalysts. However, acidic catalysts tend to react more slowly than basic catalysts, so it is common to carry out the reaction at high temperatures (100° C. or higher) to prevent corrosion. In order to do this, an acid-resistant design of the reactor and auxiliary equipment is required, which may result in excessive initial investment cost.

Therefore, in the present invention, evaluation of the reaction performance and usefulness of basic catalysts and metal salt catalysts expected to have reactivity and selectivity for the ethylene glycol addition transesterification reaction of DMT was made.

To compare the relative performance of the catalyst, the same reaction conditions except for the type of catalyst, that is, the amount of the ester reaction catalyst added is 0.001 moles per mole of DMT, the carrier gas flow is GHSV 240h ^-1 , and the reaction temperature is maintained at 80℃ 3 A time reaction was performed.

As catalysts for performance evaluation, metal acetate salts (eg zinc acetate), alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides, and guanidine-based organic compounds, which are expected to show the best performance in the transesterification reaction, were used. They were selected and used, and their reaction performance and acid dissociation equilibrium constant (pK _a ) are shown in Table 4 (reaction temperature 80° C., reaction time 3 h, GHSV=240 h ^-1 ).

division catalyst
type moles of compound added per mole of DMT conversion rate
(%) transference number (%) pKa EG catalyst BHET HEMT BHET dimer K ₂ -TPA K-MMT oligomer Comparative Example 3 KOAc 12 0.001 9.8 3.1 6.7 0.0 0.0 0.0 0.0 4.8 Comparative Example 4 NaOAc 12 0.001 10.7 3.6 7.1 0.0 0.0 0.0 0.0 4.8 Comparative Example 5 Zn(OAc) ₂ 12 0.001 4.0 0.7 3.3 0.0 0.0 0.0 0.0 4.5 Example 3 K ₂ CO ₃ 12 0.001 100.0 92.0 6.0 2.0 0.0 0.0 0.0 10.3 Example 17 KHCO ₃ 12 0.001 98.5 76.8 20.4 1.3 0.0 0.0 0.0 6.4 Example 18 Na ₂ CO ₃ 12 0.001 100.0 92.3 5.7 2.0 0.0 0.0 0.0 10.3 Example 19 NaHCO ₃ 12 0.001 98.4 78.9 18.2 1.4 0.0 0.0 0.0 6.4 Example 20 KOH 12 0.001 100.0 91.4 6.7 1.9 0.0 0.0 0.0 15.7 Example 21 NaOH 12 0.001 100.0 91.9 6.2 1.9 0.0 0.0 0.0 15.7 Example 22 CH ₃ OK 12 0.001 100.0 90.6 7.5 1.9 0.0 0.0 0.0 22.1 Example 23 CH ₃ ONa 12 0.001 100.0 83.6 14.7 1.7 0.0 0.0 0.0 22.1 Example 24 MgO 12 0.001 96.0 77.4 17.3 1.3 0.0 0.0 0.0 15.7 Example 25 CaO 12 0.001 100.0 90.6 7.5 1.9 0.0 0.0 0.0 12.8 Example 26 TBD 12 0.001 100.0 90.5 7.6 1.9 0.0 0.0 0.0 15.2 DMT: Dimethyl terephthalate, EG: Ethylene glycol,
BHET: Bis(2-hydroxyethyl) terephthalate;
HEMT: 1- (2-Hydroxyethyl) 4-methyl terephthalate,
KOAc : CH ₃ COOK, NaOAc : CH ₃ COONa, Zn(OAc) ₂ : Zn(CH ₃ COO) 2H ₂ O,
TBD: Triazabicyclodecene
K ₂ -TPA: Dipotassium terephthalate
K-MMT: Potassium monomethyl terephthalate

In a general high-temperature reaction process for preparing BHET through depolymerization of a polymer containing an ester functional group, acetic acid metal salts are used as catalysts. In particular, zinc acetate (Zn(CH ₃ COO) ₂ ·2H ₂ O) has high polymer depolymerization reactivity and excellent selectivity to BHET, so it is most commonly used in commercial processes. In order to confirm the catalyst effectiveness of the metal acetate salt for the transesterification reaction according to the present invention, potassium acetate, sodium acetate, zinc acetate, and the like were replaced with catalysts and then a reaction experiment was performed.

In Comparative Examples 3 and 4, in which the reaction was performed after replacing potassium acetate and sodium acetate with catalysts under the same conditions, the BHET yield was 4% or less after 3 hours, and very low reaction performance was observed. Also, in Comparative Example 5 using zinc acetate as a catalyst, the yield of BHET was 0.7%, and almost no BHET was produced as in Comparative Example 1, which was carried out without a catalyst. Therefore, it was confirmed that the metal acetate salt, which can be usefully used in the existing high-temperature (≥190°C) glycolysis reaction, cannot be used as an efficient catalyst for the transesterification reaction performed according to the present invention.

Comparing the reaction results of Examples 3 and 17 to 19 using a metal salt catalyst composed of anions of carbonic acid and bicarbonate, potassium carbonate (K ₂ CO ₃ ) and sodium carbonate (Na ₂ CO ₃ ) were applied as catalysts to react was carried out for 3 hours, the yield of BHET was 92.0% and 92.3%, respectively, compared to the case of using potassium bicarbonate (KHCO ₃ ) and sodium bicarbonate (NaHCO ₃ ) as catalysts. A BHET yield higher than 13% was obtained.

Alkali hydroxide (or alkali metal hydroxide) is used as a representative raw material for alkali decomposition during depolymerization of polymers containing ester functional groups. In the alkali decomposition reaction, since alkali hydroxide directly participates as a reactant in the decomposition of ester bonds, it is supplied in excess of the number of moles of ester bond groups possessed by the polymer, water or alcohol is used as a medium for the reaction, and ethylene glycol is used as the reaction product. is emitted

In the present application, the function of alkali hydroxide as a catalyst rather than a reactant for alkali decomposition was observed. When the reaction conditions according to the present application, that is, ethylene glycol is supplied in excess, and a trace amount of alkali hydroxide is added in the temperature range between room temperature (25° C.) and the boiling point of ethylene glycol, the function as a catalyst for the transesterification reaction can be expressed. have.

Potassium hydroxide and sodium hydroxide (Example 20 and Example 21) were added in trace amounts in an amount of 0.001 mol per 1 mol of DMT, and as a result of transesterification, all of the DMT was converted, and the BHET yield after 3 hours of reaction was 91% or more. reached

Next, when an alkoxide metal salt was used as an alternative catalyst, the performance for the transesterification reaction was confirmed. When potassium methoxide (CH ₃ OK) or sodium methoxide (CH ₃ ONa) was replaced with a catalyst (Examples 22 and 23), the BHET yield after 3 hours of reaction with high reactivity was 90.6%, respectively, and A relatively high value of 83.6% was observed. These catalysts are effective in increasing the rate of the first ethylene glycol addition reaction (HEMT production) from DMT compared to the case where the alkali metal-based carbonate catalyst was previously applied (Example 3 and Example 18), whereas in the second addition (BHET production) It exhibited rather low reaction rate characteristics.

When the alkaline earth metal-based oxide catalyst was applied, the transesterification reaction performance was also observed to be high. As a result of carrying out the reaction by replacing magnesium oxide and calcium oxide with a catalyst (Example 24 and Example 25), the conversion rate was observed to be 96% or more, and the yield of BHET after 3 hours of reaction was 77.4% and 90.6%, respectively. .

Finally, the reaction characteristics of the organic catalysts containing no metal were compared. In Example 26, triazabicyclodecene (TBD), a guanidine-based compound commonly used as a catalyst for organic synthesis due to its strong basic properties, was used as a catalyst for transesterification. Similar to the case of Example 3 using potassium carbonate (K ₂ CO ₃ ) as a catalyst, almost all of the DMT input after 3 hours of reaction time was involved in the glycolysis reaction, and the yield of BHET was observed to be relatively high as 90.5%. became

Comparing the reaction performance according to the acid dissociation equilibrium constant (pK _a ) of the catalyst used in Table 4, the pK _a value in order to obtain a high yield of BHET by performing the low-temperature (≤ 100 ° C) glycolysis reaction of the present invention It is confirmed that this 6 or more catalyst is suitable.

[Production of BHET by transesterification of a polymer containing an ester functional group]

The glycolysis reaction for directly producing BHET by depolymerizing a polymer containing an ester functional group of a raw material is generally carried out at a high temperature of 190 to 300°C. As reported by a number of prior literatures, the high-temperature glycolysis reaction is generally carried out at a temperature near or above the boiling point of ethylene glycol, an addition reactant, with a metal acetate applied as a catalyst. In the catalytic reaction, the monomer product (BHET) according to glycolysis is obtained in a higher ratio than other compounds by 80% or more, but by-products generated from side reactions such as hydrolysis (e.g. monohydroxyethyl terephthalate (MHET) ), terephthalic acid), it was observed that dimers or oligomers were produced in a certain ratio depending on the reaction equilibrium. On the other hand, when depolymerization is carried out by adopting a low-temperature methanolysis-glycolysis series reaction path in which the temperature region and the BHET generation mechanism are different according to an example of the present invention, a small amount of a reaction intermediate (eg HEMT) and a dimer High-purity BHET containing only (dimer) can be obtained in high yield.

[Table 5] compares the results of high-temperature (190°C) glycolysis and low-temperature transesterification (25°C methanolysis and 80°C ethylene glycol addition transesterification) reactions prepared using Raw Material 2 as the same raw material. it has been shown

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

division
(catalyst) reaction
temperature
(℃) reaction
hour
(h) Number of moles of compound added per mole of PET repeat unit or DMT conversion rate
(%) transference number (%) EG catalyst BHET MHET HEMT BHET
dimer K ₂ -TPA/
K-MMT oligomer Comparative Example 6
(Zn(OAc) ₂ ) 190 2 12 0.05 100.0 80.6 2.2 - 4.1 - 13.1 8 12 0.05 100.0 82.1 3.5 - 4.1 - 10.3 Example 27
(K ₂ CO ₃ ) 80 2 12 0.05 100.0 90.6 - 2.9 2.3 4.2/0.0 0.0 8 12 0.05 100.0 92.3 - 0.4 2.6 4.7/0.0 0.0 DMT: Dimethyl terephthalate, EG: Ethylene glycol,
BHET: Bis(2-hydroxyethyl) terephthalate;
HEMT: 1-(2-Hydroxyethyl) 4-methyl terephthalate
MHET: mono(hydroxyethyl) terephthalate
K ₂ -TPA: Dipotassium terephthalate
K-MMT: Potassium monomethyl terephthalate

When the depolymerization reaction was carried out at a high temperature using zinc acetate (Comparative Example 6), the polymer was rapidly decomposed from the initial stage of the reaction (within 2 hours), and the yield of BHET was 80.6%. However, when it was exposed to the reaction conditions for a long time for about 8 hours, the yield increase of BHET was not remarkable, and the concentration of undecomposed compounds was observed to be high with a yield of about 4.1% for dimers and 10 to 15% for oligomers. .

In Example 27, a portion of the catalyst was obtained by filtration from a liquid reaction mixture (DMT yield: 91%) obtained by methanolysis-based room temperature (25° C.) depolymerization using the same PET raw material (raw material 2) used above and applying a cosolvent. After removing the solvent by increasing the temperature, ethylene glycol was added to carry out the second reaction, glycolysis. In this reaction, reaction characteristics and product distribution very different from those of the high-temperature glycolysis of Comparative Example 6 were observed.

In Example 27, a very high DMT conversion was observed from the beginning of the reaction, and when left in the reaction conditions for a sufficient time (8 hours or more), a BHET yield exceeding 92% was observed. Looking at the distribution of reaction by-products, MHET was obtained as a reaction by-product in the high-temperature glycolysis of Comparative Example 6, but in Example 27, HEMT in which ethylene glycol was added on only one side was obtained as a reaction intermediate, and a relatively fast reaction proceeded. After 8 hours of reaction, it was observed that only a very low HEMT concentration of 0.5% or less remained.

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

As described above in detail specific parts of the present invention, it will be clear to those skilled in the art that these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby. . Accordingly, it is intended that the substantial scope of the present invention be defined by the appended claims and their equivalents.

Claims (11)

A method for preparing bis-(2-hydroxyethyl) terephthalate from dimethyl terephthalate, the method comprising:
(a) Addition of ethylene glycol to dimethyl terephthalate as a reactant for transesterification, and the presence of at least one catalyst for transesterification selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides and guanidine-based organic compounds A step of performing a transesterification reaction while applying a flow of a carrier gas;
(b) separating and obtaining the bis-(2-hydroxyethyl) terephthalate prepared by the above reaction; How to manufacture. The method of claim 1,
The method for producing bis-(2-hydroxyethyl) terephthalate from dimethyl terephthalate, characterized in that the number of moles of the catalyst for transesterification per mole of dimethyl terephthalate in step (a) is in the range of 0.00005 to 1.0 mole. A method for preparing bis-(2-hydroxyethyl) terephthalate by depolymerization of a polymer containing an ester functional group, the method comprising:
(i) depolymerizing by adding alcohol, a polar aprotic solvent, and potassium carbonate (K ₂ CO ₃ ) to a polymer containing an ester functional group;
(ii) performing a transesterification reaction while adding a flow of carrier gas to the depolymerization product obtained in step (i); and
(iii) separating and obtaining bis-(2-hydroxyethyl) terephthalate prepared by the above reaction; characterized in that it comprises,
Bis-(2-hydroxyethyl) terephthalate is prepared by depolymerization of a polymer containing an ester functional group in which the alcohol in step (i) is methanol, ethanol, propanol, butanol, or a combination thereof, which are straight-chain primary alcohols How to. 4. The method of claim 3,
Bis-(2-hydroxyethyl) terephthalate is prepared by depolymerization of a polymer containing an ester functional group, characterized in that after step (i), a step of isolating some compounds from the depolymerization product to the outside is further carried out How to. 5. The method of claim 4,
Some of the compounds separated to the outside are depolymerized by depolymerization of a polymer containing an ester functional group, characterized in that it contains at least one selected from a polymer containing an unreacted ester functional group, an insoluble catalyst, a polar aprotic solvent, and a reaction by-product. Method for preparing -(2-hydroxyethyl) terephthalate. 4. The method of claim 3,
The polar aprotic solvent of step (i) is an inert solvent that does not participate in the depolymerization reaction of a polymer containing an ester functional group, and can lower the solubility of the catalyst in alcohol, and the skeletal structure of the solvent is in the form of a chain or An organic compound having at least one structure selected from among cyclic forms, wherein at least one of a halogen element, oxygen, and nitrogen is bonded to the organic compound by depolymerization of a polymer containing an ester functional group A process for preparing oxyethyl) terephthalate. 4. The method of claim 3,
The polar aprotic solvent of step (i) is toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propionitrile, aminopropionitrile, methylaminopropionitrile, iminodipropionitrile , butyronitrile, methylbutenenitrile, butanenenitrile, methyl ethyl ether, diethyl ether, ethylphenyl ether, dimethoxybenzene, trimethoxybenzene, methoxyphenol, tetrahydrofuran, methyltetrahydrofuran, dioxane, chloro Bis-(2-hydroxyethyl) terephthalate is prepared by depolymerization of a polymer containing an ester functional group, characterized in that at least one selected from methane, dichloromethane, chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, and trichlorobenzene How to. 4. The method of claim 3,
In step (i), the number of moles of the alcohol and the number of moles of the polar aprotic solvent compared to the number of moles of the repeating unit of the polymer raw material containing the ester functional group is 0.1 compared to the number of moles of the repeating unit of the polymer raw material containing the ester functional group A method for producing bis-(2-hydroxyethyl) terephthalate by depolymerization of a polymer containing an ester functional group, characterized in that the range is ~ 5,000 times. 4. The method of claim 3,
Before carrying out the transesterification reaction in step (ii), ethylene glycol as a reactant for transesterification in the depolymerization product in step (i); or any one or more transesterification catalysts selected from the group consisting of alkali carbonates, alkali hydroxides, alkali alkoxides, alkaline earth metal oxides and guanidine-based organic compounds; Bis-(2-hydroxyethyl) terephthalate by depolymerization of a polymer containing an ester functional group, characterized in that the number of moles in a predetermined range per mole of dimethyl terephthalate contained in the depolymerization product is adjusted so that at least one selected from among How to manufacture. 4. The method of claim 3,
Method for producing bis-(2-hydroxyethyl) terephthalate by depolymerization of a polymer containing an ester functional group, characterized in that the methanol recovered in step (iii) is reused as a raw material for depolymerization in step (i). 10. The method of claim 9,
The number of moles of the catalyst for transesterification, which is controlled before carrying out the transesterification reaction in step (ii), is characterized in that it is adjusted to 0.00005 to 1.0 per mole of dimethyl terephthalate contained in the depolymerization product, including an ester functional group A method for producing bis-(2-hydroxyethyl) terephthalate by depolymerization of a polymer.

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