Chemical recycle method

Abstract

To provide a chemical recycle method capable of obtaining a benzene-based aromatic ester, and a heterocycle aromatic ester which can be applied when using a mixed raw material composed of one or more raw materials.SOLUTION: A chemical recycle method is applied to a case where a raw material polyester includes one or a plurality of raw materials capable of obtaining two kinds of monomers of a benzene-based aromatic ester, and a heterocycle aromatic ester. More specifically, a chemical recycle method includes: a depolymerization process of adding a solvent and performing depolymerization to generate a depolymerization liquid containing two kinds of monomers of BHET and BHEF when, for example, a raw material polyester of a recycling object includes two raw materials of a PET flake and a PEF flake; and a crystallization process of cooling the generated depolymerization liquid to recrystallize BHET of two kinds of monomers.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a chemical recycling method in which raw material polyester is depolymerized and decomposed into monomers, and the monomers are reused as materials. [Background technology]

[0002] There is a chemical recycling method in which raw polyester is depolymerized and decomposed into monomers, and the monomers are reused as materials. For example, a chemical recycling method is known in which polyethylene terephthalate (PET), one of the raw polyester materials, is depolymerized and decomposed into bis(2-hydroxyethyl) terephthalate (BHET), which is reused (see, for example, Patent Document 1). In addition, Patent Documents 2 and 3 are prior art documents related to the present invention. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-169623 A [Patent Document 2] JP 2012-72400 A [Patent Document 3] European Patent Application Publication No. 0723951 Summary of the Invention [Problem to be solved by the invention]

[0004] In the chemical recycling method of Patent Document 1, used PET is converted into the intermediate raw material BHET to produce high-purity PET products again. In addition, Patent Document 2 discloses a chemical recycling method applied to various polyesters. On the other hand, the need for biomass-derived chemical products is increasing from the viewpoint of various environmental problems such as marine littering and global warming. In recent years, PEF resin has been attracting attention as a plastic that can be 100% biomass-derived. It is expected that products using PEF will replace PET products in the future. For example, a typical PET product is a PET bottle, but there is a possibility that PET bottles will also be replaced by bottles using PEF resin (e.g., PEF bottles).

[0005] At present, PEF products are limited to certain fields and are distributed in small quantities, so the need for recycling is not great. On the other hand, if the need for PEF products increases and, for example, PEF bottles begin to circulate in the market, it is expected that both PET bottles and PEF bottles will be mixed as recycling targets. Naturally, neither of the chemical recycling methods in Patent Documents 1 and 2 assumes that these will be mixed. For this reason, in order to apply the chemical recycling method in Patent Document 1, for example, it becomes necessary to properly separate PET bottles and PEF bottles in advance. The same type of separation is also required in the case of the chemical recycling method in Patent Document 2.

[0006] In addition, general chemical recycling methods often include a process of depolymerizing raw materials into monomers. For example, the chemical recycling method of Patent Document 1 also includes a similar process, in which BHET is obtained as a monomer for PET. On the other hand, if a similar depolymerization were to occur in PEF, BHEF (methyl 3-methyl-2-furancarboxylate) would be obtained as a monomer. BHET and BHEF have similar chemical structures and molecular weights, and when both are present in a solution, it is expected that it would be difficult to distinguish between the two from the solution using general methods such as distillation.

[0007] Patent Document 3 discloses a method of lowering the temperature of an aqueous solution when crystallizing BHET from a depolymerization liquid. However, since BHEF is a type of furan compound that is generally insoluble (poorly water-soluble) in water, it is expected that both BHET and BHEF will crystallize and precipitate when a crystallization operation is performed by lowering the temperature in a solvent whose main component is water (including various types of water such as heavy water and semi-heavy water), and it is difficult to predict how to separate each substance from the depolymerization liquid in which both are mixed.

[0008] In any case, when the raw material to be recycled contains both PET and PEF, it is not considered that a process of simultaneously depolymerizing both in the same solvent can be applied without resistance, considering the properties of the resulting monomer. As a result, it is generally considered necessary to separate PET and PEF in advance, also in terms of the properties of the resulting monomer. However, thorough separation in advance is often difficult. Furthermore, it is possible to add PEF in a multi-layer or blend form to PET bottles for the purpose of improving gas barrier properties, etc., and in such a case, PET and PEF become an inseparable unit, making separation virtually impossible.

[0009] A similar tendency is expected for the benzenic aromatic esters and heterocyclic aromatic esters to which BHET and BHEF belong, respectively, and therefore the same can be said when one or more raw materials from which benzenic aromatic esters and heterocyclic aromatic esters are obtained are the subject of recycling.

[0010] Therefore, an object of the present invention is to provide a chemical recycling method that can be applied when one or more raw materials from which a benzene-based aromatic ester and a heterocyclic aromatic ester can be obtained are mixed. [Means for solving the problem]

[0011] The chemical recycling method of the present invention is a chemical recycling method in which a raw material polyester is depolymerized and decomposed into monomers, and the monomers are reused as materials. When the raw material polyester contains one or more raw materials from which two types of monomers, a benzene-based aromatic ester and a heterocyclic aromatic ester, are obtained as the monomers, the method includes the following steps: a depolymerization step of adding a solvent to the one or more raw materials to depolymerize the one or more raw materials, thereby producing a depolymerized liquid containing the two types of monomers; and a crystallization step of cooling the depolymerized liquid to crystallize the benzene-based aromatic ester of the two types of monomers. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is an explanatory diagram for explaining a procedure of a chemical recycling method according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a line graph plotting the amount of BHET monomer dissolved in water at different temperatures. [Diagram 3] FIG. 1 is a line graph plotting the amount of BHEF monomer dissolved in water at different temperatures. [Figure 4] FIG. 1 is an explanatory diagram for explaining a test procedure. [Diagram 5] FIG. 5 is a line graph plotting test results of the procedure of FIG. 4 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, one embodiment of the chemical recycling method of the present invention will be described. The chemical recycling method of this embodiment is a chemical recycling method in which raw material polyester (raw material to be recycled) is depolymerized and decomposed into monomers, and the monomers are reused as materials, but is a method that is applied when the raw material polyester contains one or more raw materials from which two types of monomers, benzene-based aromatic esters and heterocyclic aromatic esters, can be obtained.

[0014] The raw material polyester may contain an appropriate number of various raw materials that can obtain a benzene-based aromatic ester and a heterocyclic aromatic ester as one or more raw materials. For example, as one or more raw materials, two or more raw materials that separately contain a raw material that can obtain a benzene-based aromatic ester (hereinafter, sometimes referred to as a benzene-based raw material) and a raw material that can obtain a heterocyclic aromatic ester (hereinafter, sometimes referred to as a heterocyclic raw material), a raw material that is formed by mixing a benzene-based raw material and a heterocyclic raw material (hereinafter, sometimes referred to as a mixed raw material), and a raw material that includes a copolymer of a benzene-based aromatic ester and a heterocyclic aromatic ester and functions as both a benzene-based raw material and a heterocyclic raw material (hereinafter, sometimes referred to as a copolymer raw material) may be used. Below, as an example, a case where the raw material polyester contains a benzene-based raw material and a heterocyclic raw material separately as one or more raw materials will be described.

[0015] The benzene-based raw material may be any suitable raw material from which a benzene-based aromatic ester can be obtained, and includes raw materials such as PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PEN (polyethylene naphthalate), and PTT (polytrimethylene terephthalate). Similarly, the heterocyclic raw material may be any suitable raw material from which a heterocyclic aromatic ester can be obtained, and includes raw materials such as PEF (polyethylene furanoate), PBF (polybutylene furanoate), and PTF (polytrimethylene furanoate). These various raw materials can be appropriately used as the benzene-based raw material and the heterocyclic raw material, and the following will explain the case where PET (polyethylene terephthalate) and PEF (polyethylene furanoate) are used, respectively, as examples.

[0016] PET can be used in various products and distributed in the market, but a representative PET product is a PET bottle (a bottle made of polyethylene terephthalate). PEF is a type of biopolyester, and is a polyester that can be 100% derived from biomass, and is expected to be used in various products in today's world where environmental issues are attracting attention. For example, PEF may be used as a PEF bottle (a bottle made of polyethylene furanoate) to replace PET products. PET products and PEF products may correspond to benzene-based raw materials and heterocyclic raw materials, respectively. Alternatively, PEF may be mixed with PET and manufactured into a product. And a mixed product in which PET and PEF are mixed may correspond to a mixed raw material. As described above, the chemical recycling method of the present invention can also be applied to the recycling of mixed raw materials (mixed products), but the following will explain the case where PET bottles and PEF bottles are recycled as examples of PET products and PEF products, respectively.

[0017] FIG. 1 is an explanatory diagram for explaining the procedure of a chemical recycling method according to one embodiment of the present invention. As shown in FIG. 1, raw material polyester (plastic material) to be recycled contains PEF flakes and PET flakes. Various raw materials such as PET bottles are often crushed in a crusher and reused as flakes (small pieces) or bales (small grains). PEF flakes and PET flakes are flakes corresponding to PEF and PET, respectively. The raw materials can be recycled in any suitable state, but in the example of FIG. 1, they contain PET flakes in a crushed state of PET bottles and PEF flakes in a crushed state of PEF bottles.

[0018] The PEF flakes and PET flakes may be formed by crushing the mixed product. Alternatively, when a product of copolymerization raw materials is recycled, the raw polyester may contain flakes of the copolymerization raw materials (raw materials that are neither PEF flakes nor PET flakes, but from which similar monomers can be obtained). Similarly, the raw materials (products) to be recycled are not limited to the flake state as described above, and may be in an appropriate state, for example, in the state of products such as PET bottles, or in the state of bales in which PET bottles are compressed under reduced pressure. In addition, the chemical recycling method may appropriately include various steps that can be realized by well-known procedures (techniques), such as a step of removing foreign matter such as metals (which may include plastic materials other than PEF and PET), a step of flaking (crushing) the plastic material, or a step of washing the plastic material, but the description of these steps will be omitted below.

[0019] On the other hand, the procedure of the chemical recycling method according to one embodiment of the present invention includes a depolymerization step (S1), a crystallization step (S2), and a recovery step (S3) in that order. Although the explanation of the procedure generally performed in each step will be omitted as appropriate, for example, each step is performed as follows. First, the depolymerization step (S1) is a step of depolymerizing the raw material polyester, and includes the steps of adding a solvent, adding a catalyst, and heating, and is configured to depolymerize the raw material polyester in the solvent. In other words, the depolymerization step is configured to depolymerize the raw material to be recycled through the solvent, thereby generating a depolymerized liquid as a solution (mixture) containing the depolymerized monomer and the solvent.

[0020] The steps of adding a catalyst and heating are optional and may be omitted, for example, when sufficient depolymerization can be achieved with only a solvent, but are performed in the example of FIG. 1. The heating in the heating step may be performed as appropriate, for example indirectly through a heated solvent, but as an example, is performed together with the solvent after the addition of the solvent. Thus, in the depolymerization step, a solvent and a catalyst are added to the raw material to be recycled and heated together with the raw material to be recycled. The steps of adding a catalyst and heating promote a depolymerization reaction, through which a depolymerization liquid containing monomers obtained by depolymerization of the raw material is generated.

[0021] The solvent, catalyst, and heating in the depolymerization step may be appropriately set according to the type of raw polyester. For example, when PEF flakes and PET flakes are to be recycled, the catalyst used in the catalyst addition step includes zinc acetate, zinc borate, fatty acid salts of zinc, magnesium, calcium, cobalt, antimony, and barium, carbonates of zinc, magnesium, calcium, cobalt, antimony, and barium, methylate of sodium and magnesium, metallic sodium, metallic magnesium, or oxides of zinc, antimony, lead, and germanium. Similarly, as the solvent, water (including heavy water and half-heavy water) or a liquid mainly composed of ethylene glycol (EG) is used. In this case, the solvent may be composed of only the main component, or may contain various subcomponents such as ethanol and methanol. In the following, as an example, the depolymerization step in which a solvent containing EG as the main component (hereinafter sometimes simply referred to as EG solvent) is used will be described.

[0022] Specifically, when the depolymerization process is performed on PEF flakes and PET flakes, EG solvent is added to the PEF flakes and PET flakes, and a procedure of adding a catalyst and heating to promote depolymerization is performed. Heating can be performed at an appropriate temperature and time, for example, at 160 to 200°C for several hours, generally about 1 to 6 hours. It is known that the depolymerization reaction of PEF flakes and PET flakes produces BHEF (3-methyl-2-methylfurancarboxylate) and BHET (bis(2-hydroxyethyl) terephthalate), respectively, as monomers. Therefore, in the depolymerization process, a depolymerization liquid containing BHEF, BHET, and EG solvent is generated.

[0023] The crystallization step (S2) is a step for obtaining a part of the monomer by crystallization from the depolymerization liquid obtained in the depolymerization step, and is configured to obtain a part of the monomer by utilizing the difference in the temperature at which the monomer precipitates. For example, the crystallization step includes the steps of cooling, applying an impact, and collecting. The cooling step is a step for cooling the depolymerization liquid. As described later in the Examples, when the depolymerization liquid contains two types of monomers, a benzene-based aromatic ester and a heterocyclic aromatic ester, the benzene-based aromatic ester can be crystallized first as the depolymerization liquid is cooled. For this reason, when the cooling step is performed on the depolymerization liquid containing BHEF, BHET, and an EG solvent, BHET crystallizes first among BHEF and BHET. The cooling step may be performed to an appropriate temperature, but when applied to the depolymerization liquid containing BHEF, BHET, and an EG solvent, for example, the cooling step is performed so that the temperature of the depolymerization liquid is lowered to about 0°C to 60°C, more preferably to 10°C to 40°C, and even more preferably to 15°C to 30°C. The cooling may be actively performed using a suitable cooling device or the like, but as an example, it is achieved by leaving it at room temperature until the temperature drops to a desired level.

[0024] The step of applying the impact is optional and may be omitted, but for any monomer, the solubility in the solvent tends to decrease due to the application (addition) of a physical impact from the outside. This tendency becomes more pronounced as the temperature decreases. Therefore, when the step of applying the impact is included, the tendency of BHET to crystallize is promoted. The physical impact in the step of applying the impact may be realized appropriately, and as an example, it is realized by stirring. In addition, various means may be used as a stirring means for realizing the stirring, for example, a manual stirring rod or various stirrers may be used, or ultrasonic waves in an ultrasonic treatment (apparatus) may be used. Therefore, in the crystallization step, the depolymerization liquid is left at room temperature to about 0°C to 60°C while being appropriately stirred by various physical means, and is cooled.

[0025] Through cooling in the crystallization step, BHET crystallizes, and the crystallized BHET is obtained. Collection is a procedure for collecting (removing) the crystallized BHET, and is performed to separate BHET from the depolymerization liquid. The depolymerization liquid after the crystallized BHET is removed in the collection step mainly contains BHEF and EG solvent as residual liquid components.

[0026] The recovery step (S3) is a step for recovering the remaining monomer from the residual liquid component after the crystallization step. The recovery step is optional and may be omitted if the remaining monomer is not required, but is performed in the example of FIG. 1. The recovery step may be configured appropriately depending on the properties of the remaining monomer, etc., but for example, if the remaining monomer is BHEF, it includes a distillation step. Specifically, when BHEF is recovered from the residual liquid component of BHEF and EG solvent, a distillation step is performed in the recovery step to distill the residual liquid component so as to extract (purify) BHEF. Then, BHEF purified through distillation is recovered.

[0027] As described above, according to this embodiment, when two raw materials, PET flakes and PEF flakes from which two types of monomers, BHET and BHEF, are obtained, respectively, are mixed in the raw polyester to be recycled, a depolymerized liquid containing two types of monomers, BHET and BHEF, is generated in the depolymerization step, and crystallization of BHET out of the two types of monomers is obtained in the crystallization step. Furthermore, crystallization of BHET is also recovered from the remaining liquid component after BHET is removed through a recovery step. Both crystallized BHET and BHEF can be reused as materials. Therefore, even when two raw materials, PET flakes and PEF flakes from which BHET and BHEF are obtained, respectively, are mixed, this method can be applied as a method for reusing both BHET and BHEF.

[0028] The present invention is not limited to the above-mentioned embodiment, and may be embodied in an appropriate modified or altered form. The present invention may also be embodied in an appropriate combination of various technical means included in the above-mentioned embodiment and the following modified embodiment. For example, in the above-mentioned embodiment, the chemical recycling method according to one embodiment of the present invention is applied to the recycling of PET flakes and PEF flakes from which BHET and BHEF are obtained as examples of benzene-based aromatic esters and heterocyclic aromatic esters, respectively. However, the present invention is not limited to such an embodiment. The chemical recycling method of the present invention is not limited to BHET and BHEF, and may be applied to an appropriate raw material polyester from which various benzene-based aromatic esters and heterocyclic aromatic esters are obtained. However, in consideration of the properties of the resulting monomer, it is considered to be more effective to apply the method to the recycling of one or more raw materials from which benzene-based aromatic esters having a benzene ring or a naphthalene ring and heterocyclic aromatic esters having a furan ring are obtained. EXAMPLES

[0029] Examples related to the chemical recycling method according to the above embodiment will be described below, however, the technical scope of the present invention is not limited to the following examples.

[0030] (Preparation of monomer) The BHET monomer and BHEF monomer for testing were prepared by the following procedure. Specifically, PET bottles and PEF bottles were crushed into flakes of about 20 mm to 30 mm each using a commercially available crusher, and 5.6 times the amount of EG and 1 / 400 of the amount of sodium hydroxide were added by weight. The resulting solution was heated to 180°C in a glass container while stirring for 1 hour, and then maintained with stirring for another 3 hours to depolymerize. The resulting depolymerized liquid was filtered and purified to obtain BHET monomer. BHEF monomer was obtained by filtering the depolymerized liquid and purifying it using liquid chromatography.

[0031] Example 1: Solubility Correlation of BHET Monomer in Water A test was conducted to investigate the correlation between the amount of BHET monomer dissolved in water (solvent) and temperature. The test was conducted under two conditions: without physical stimulation (application of impact), and with physical stimulation. The results are shown in Figure 2. Figure 2 shows a line graph in which the amount of BHET monomer dissolved in water is plotted against temperature. The horizontal axis of the graph in Figure 2 shows the temperature of the water (solution) containing the BHET monomer, and the vertical axis shows the amount of BHET monomer dissolved. Also, (A) in Figure 2 shows the case without physical stimulation, and (B) shows the case with physical stimulation.

[0032] The test conditions were as follows. In both cases, with and without physical stimulation, the purified BHET sample and the internal standard substance (DSS-D6) required for NMR measurement were dissolved in water and heated to 80°C in a warm bath. At the same time, the sample was quickly filtered using a heated filter syringe and measured by NMR (Nuclear Magnetic Resonance). After cooling to 40°C and 25°C, NMR measurements were performed in the same way. When physical stimulation was applied, pure water was placed in an ultrasonic cleaning tank and the NMR tube filled with the sample was immersed in it. Ultrasonic operation was performed after 40°C and 25°C.

[0033] As shown in Figure 2(A), in the absence of physical stimulation, the amount of dissolved BHET monomer was almost the same (slightly more than 14 mg / ml) at the temperatures of about 25°C, about 40°C, and about 80°C that were investigated. In other words, no significant change was observed between the temperature change and the amount dissolved.

[0034] On the other hand, as shown in FIG. 2(B), when a physical stimulus was applied, the amount of dissolved BHET monomer gradually increased at the investigated temperatures of about 25° C., about 40° C., and about 80° C. Specifically, the amount of dissolved BHET monomer was about 7 mg / ml at a temperature of about 25° C., but changed to about 10 mg / ml at a temperature of about 40° C. and to about 15 mg / ml at a temperature of about 80° C. In other words, it was confirmed that physical stimulus affects the amount of dissolved BHET monomer.

[0035] In addition, the amount of BHET monomer dissolved with physical stimulation was higher than that without physical stimulation at a temperature of about 80° C., but was far lower than that without physical stimulation at temperatures of about 25° C. and about 40° C. In other words, it was confirmed that at temperatures below about 80° C., the lower the temperature, the greater the effect of physical stimulation on crystallization of the BHET monomer (reducing the amount dissolved).

[0036] (Example 2: Correlation of Solubility of BHEF Monomer to Water) A test was conducted to investigate the correlation between the amount of BHEF monomer dissolved in water (solvent) and temperature. As with the BHET monomer, the test was conducted under two conditions: without physical stimulation (stirring) and with physical stimulation. The results are shown in Figure 3. Figure 3 shows a line graph in which the amount of BHEF monomer dissolved in water is plotted against temperature. The horizontal axis of the graph in Figure 3 shows the temperature of the water (solution) containing the BHEF monomer, and the vertical axis shows the amount of BHEF monomer dissolved. Also, (A) in Figure 3 shows the case without physical stimulation, and (B) shows the case with physical stimulation.

[0037] The test conditions were as follows. In both cases, with and without physical stimulation, the purified BHEF sample and the internal standard substance (DSS-D6) required for NMR measurement were dissolved in water and heated to 80°C in a warm bath. At the same time, the sample was quickly filtered using a heated filter syringe and subjected to NMR measurement. NMR measurement was also performed in the same way at 60°C, 40°C, and 25°C after cooling. When physical stimulation was applied, pure water was placed in an ultrasonic cleaning tank and the NMR tube filled with the sample was immersed in it. Ultrasonic operation was performed after 60°C, 40°C, and 25°C.

[0038] As shown in Figure 3 (A), in the absence of physical stimulation, the amount of dissolved BHEF monomer increased slightly to about 1400 mg / ml at the investigated temperature of about 25°C, but was roughly the same (about 1350 mg / ml) at temperatures of about 40°C and about 80°C, and could be said to be roughly stable across the three temperature ranges. In other words, no significant change was observed between the temperature change and the amount of dissolved BHEF monomer.

[0039] On the other hand, as shown in FIG. 3B, when physical stimulation was applied, the amount of dissolved BHEF monomer gradually increased at the temperatures of about 25° C., about 40° C., and about 60° C., but at a temperature of about 80° C., the amount of BHEF monomer added fell below the saturated amount and became unsaturated. Specifically, the amount of dissolved BHEF monomer was about 300 mg / ml, about 850 mg / ml, about 1400 mg / ml, and about 1350 mg / ml at temperatures of about 25° C., about 40° C., about 60° C., and about 80° C., respectively. From these results, it was confirmed that physical stimulation at least affects the amount of dissolved BHEF monomer.

[0040] In addition, when comparing the amount of dissolved BHEF monomer with physical stimulation in the same temperature range, the solubility was almost the same as that without physical stimulation at a temperature of about 80° C., but was far lower than that without physical stimulation at temperatures of about 25° C. and about 40° C. In other words, it was confirmed that the lower the temperature, the greater the effect of physical stimulation on crystallization of the BHEF monomer (reducing the amount dissolved).

[0041] (Example 3: Change in dissolution amount in depolymerization solution with temperature) Based on the results of Examples 1 and 2, a test was conducted to investigate the temperature change in the dissolution amount of BHET monomer and BHEF monomer in a depolymerization liquid containing BHET monomer and BHEF monomer. A solvent containing water as a main component (hereinafter, sometimes referred to as water solvent) and an EG solvent were used as the solvent in the depolymerization liquid. FIG. 4 is an explanatory diagram for explaining the test procedure. As shown in FIG. 4, in the test, the procedures shown in F1 to F4 were carried out in order, and ultrasonic impact was applied appropriately in the procedures F3 and F4. The test conditions in each procedure are as follows.

[0042] When water solvent was used, in the procedure of F1 (preparation), the purified BHET sample (about 15.92 mg), BHEF monomer (about 1.80 mg), and the internal standard substance required for NMR measurement (DSS-D6: about 2.20 mg) were mixed in a vial, and water (heavy water: about 1000 μL) was added (F1). In the procedure of F2, the mixture produced in F1 was incubated at 80 ° C for 30 minutes, and the solution was filtered and the sample was measured by NMR. In the procedure of F3, the temperature was lowered to 40 ° C, and the solution was incubated for 30 minutes, and pure water was placed in an ultrasonic cleaning tank (oscillation frequency 38 Hz), and the NMR tube filled with the sample was immersed in it for about 10 minutes. Then, the solution was filtered and the sample was measured by NMR. In the procedure of F4, the work and measurement were carried out at 25 ° C in the same manner as in the procedure of F3.

[0043] On the other hand, when EG solvent was used, in the procedure of F1 (preparation), the purified BHET sample (about 16.40 mg), BHEF monomer (about 2.26 mg), and internal standard substance (DSS-D6: about 1.75 mg) were mixed in a vial, and ethylene glycol (EG: about 1000 μL) was added. In the procedure of F2, the mixture produced in F1 was incubated at 80°C for 30 minutes, and the solution was filtered and the sample was measured by NMR. In the procedure of F3, the temperature was lowered to 60°C, and the mixture was incubated for 30 minutes, and pure water was placed in an ultrasonic cleaning tank (oscillation frequency 38 Hz), and the NMR tube filled with the sample was immersed in it for about 10 minutes. Then, the solution was filtered and the sample was measured by NMR. In the procedure of F4, the same work and measurement as in the procedure of F3 were performed at 40°C and 25°C.

[0044] Figure 5 is a line graph plotting the test results of the procedure in Figure 4. Two types of line graphs are shown in Figure 5: (A) when a water solvent was used, and (B) when an EG solvent was used. In the graph in Figure 5, the horizontal axis indicates the temperature of the mixture (solution), and the vertical axis indicates the amount of each monomer dissolved.

[0045] As shown in Figure 5(A), when using water as a solvent, the amount of dissolved BHEF monomer remains almost constant over the entire temperature range measured because it is unsaturated, whereas the amount of dissolved BHET monomer changes linearly as the temperature decreases. In other words, it was revealed that there is a large difference in the nature of the change in the amount of dissolved BHET monomer with respect to temperature change between BHET monomer and BHEF monomer.

[0046] Specifically, when the mixture was prepared according to the procedure F1 in FIG. 4, the ratio of BHET monomer to BHEF monomer in the mixture was about 9:1. In this case, the amount of dissolved BHEF monomer was 1.75 mg / mL at about 80° C. (measurement performed according to the procedure F2) and about 25° C. (measurement performed according to the procedure F4), and was 1.74 mg / mL at about 40° C. (measurement performed according to the procedure F3). Although the amount of dissolved BHEF monomer at about 40° C. differs from the other temperature ranges by 0.01 mg / mL, this is considered to be within the range of error when the measurement result at about 80° C. is also taken into consideration. In addition, although the amount of BHEF monomer added in each of the procedures F1 was about 1.8 mg, it remained in an unsaturated state over the entire temperature range, and as a result, no precipitation of BHEF monomer was observed.

[0047] On the other hand, the amount of dissolved BHET monomer was 15.18 mg / mL, 8.71 mg / mL, and 6.41 mg / mL at about 80°C, about 40°C, and about 25°C, respectively. In other words, the amount of dissolved BHET monomer showed a tendency to decrease almost linearly with decreasing temperature. The amount of BHET monomer added in the procedure of F1 was about 15.9 mg, but it remained saturated in the entire temperature range below about 80°C, and crystals of BHET monomer were precipitated. As the temperature decreased to about 40°C and about 25°C, this tendency became more pronounced, and the amount of precipitated gradually increased. In particular, at about 25°C, the amount of dissolved BHET monomer was the lowest, and a large amount of crystals of BHET monomer precipitated.

[0048] In addition, as shown in Figure 5(B), when EG solvent was used, the amount of dissolved BHEF monomer remained almost constant because it was unsaturated over the entire temperature range measured, while the amount of dissolved BHET monomer also showed a tendency to gradually decrease as the temperature decreased, although not as significantly as in the case of water solvent. In other words, it was revealed that there is a large difference in the nature of the change in the amount of dissolved BHET monomer with respect to temperature, even when EG solvent was used.

[0049] Specifically, when the mixture was prepared according to the procedure F1 in FIG. 4, the ratio of BHET monomer to BHEF monomer in the mixture was about 7:1. In this case, the amount of dissolved BHEF monomer was 1.32 mg / mL, 1.35 mg / mL, 1.29 mg / mL, and 1.30 mg / mL at about 80°C (measurement performed according to the procedure F2), about 60°C (measurement performed according to the procedure F3), about 40°C (measurement performed according to the procedure F4), and about 25°C (measurement performed according to the procedure F4), respectively. Compared to the amount of dissolved BHEF monomer at about 80°C, there was a difference of up to about 0.03 mg / mL in other temperature ranges, but this amount was also considered to be within the range of error. In addition, although the amount of BHEF monomer added in each procedure F1 was about 2.2 mg, it remained in an unsaturated state in the entire temperature range, and as a result, no precipitation of BHEF monomer was observed.

[0050] On the other hand, the amount of dissolved BHET monomer was 15.40 mg / mL, 15.32 mg / mL, 14.02 mg / mL, and 11.83 mg / mL at about 80°C, about 60°C, about 40°C, and about 25°C, respectively. In other words, the amount of dissolved BHET monomer showed a tendency to gradually decrease as the temperature decreased, although this tendency was not as pronounced as in the case of the water solvent. Although the amount of BHET monomer added in each F1 procedure was about 16.4 mg, it remained saturated in the entire temperature range below about 60°C, and crystals of BHET monomer were precipitated. As the temperature decreased to about 40°C and about 25°C, this tendency became more pronounced, and the amount of precipitate gradually increased.

[0051] The chemical properties of furan are well known, including its insolubility in water (poor water solubility). Since BHEF is also a substance with a furan ring, it was expected to be similarly poorly water-soluble, but the results of the above examples show that it can be dissolved in water. Furthermore, it was revealed that the solubility of BHEF in water is BHET>BHET, and the difference is at least one order of magnitude (see, for example, Figures 2B and 3B).

[0052] BHET and BHEF have similar chemical structures and molecular weights, and it is assumed that it is difficult to classify them from a solution containing both of them by a general method such as distillation. However, based on the results of Examples 1 and 2, we hypothesized that the difference in solubility could be utilized to separate the two. Example 3 is a test to verify this hypothesis, and the above test results showed that it is possible to utilize it to separate BHET and BHEF. Specifically, when a solution in which BHET and BHEF are dissolved in an aqueous solvent is heated and appropriately impacted with ultrasound, only the crystals of the BHET monomer precipitated out of both at a temperature of at least 80°C or less. In particular, at a temperature of about 25°C, many crystals of the BHET monomer precipitated, while the BHEF monomer still did not precipitate. Since the amount of BHET monomer dissolved changes linearly with temperature, it is thought that similar results can be obtained at temperatures above 80°C and below 25°C, but it was found that if an aqueous solution containing both of them is cooled to at least about 80°C to 25°C, it is possible to separate the two by utilizing the difference in the temperature at which they precipitate.

[0053] When EG solvent is used, the two can be separated in the same way as with water solvent, but the test results suggest that the cooling temperature of the aqueous solution should preferably be between 25°C and 60°C. In the case of EG solvent, although the change in the amount of BHET monomer dissolved with respect to temperature is not linear, it is presumed that similar results can be obtained between 60°C and 80°C, such as 70°C. The same is true for temperatures below 25°C (where crystals of the BHEF monomer do not precipitate).

[0054] In the above examples, the tests were conducted on BHET and BHEF, but it is believed that the same tendency is observed in the benzene-based aromatic esters and heterocyclic aromatic esters to which they belong. Various monomers belong to the benzene-based aromatic esters and heterocyclic aromatic esters, respectively, and for example, the benzene-based aromatic esters include monomers such as BHBT (bis 2-hydroxybutyl terephthalate) obtained from PBT and BHEN (bis 2-hydroxyethyl naphthalate) obtained from PEN. Similarly, the heterocyclic aromatic esters include monomers such as BHBF (bis 2-hydroxybutyl furanoate) obtained from PBF and BHTF (bis 2-trimethylene furanoate) obtained from PTF.

[0055] Various aspects of the present invention derived from the above-mentioned embodiments and modifications will be described below. In the following description, to facilitate understanding of each aspect of the present invention, corresponding components shown in the accompanying drawings are written in parentheses, but the present invention is not limited to the illustrated forms.

[0056] The chemical recycling method of the present invention is a chemical recycling method in which a raw material polyester is depolymerized and decomposed into monomers, and the monomers are reused as materials. When the raw material polyester contains one or more raw materials from which two types of monomers, a benzene-based aromatic ester and a heterocyclic aromatic ester, are obtained as the monomers, the method includes a depolymerization step (S1) of adding a solvent to the one or more raw materials to depolymerize the one or more raw materials, thereby producing a depolymerized liquid containing the two types of monomers, and a crystallization step (S2) of cooling the depolymerized liquid to crystallize the benzene-based aromatic ester of the two types of monomers.

[0057] According to the present invention, when one or more raw materials from which two types of monomers, benzene-based aromatic ester and heterocyclic aromatic ester, are obtained are mixed in the raw polyester to be recycled, a depolymerization liquid containing these two types of monomers is generated in the depolymerization step, and crystallization of the benzene-based aromatic ester out of the two types of monomers is obtained in the crystallization step. The crystallized benzene-based aromatic ester can be reused as a material. Therefore, the method can be applied as a method for reusing benzene-based aromatic esters even when one or more raw materials from which benzene-based aromatic ester and heterocyclic aromatic ester are obtained are mixed.

[0058] The raw material polyester may contain, as one or more raw materials, an appropriate raw material from which two types of monomers, a benzene-based aromatic ester and a heterocyclic aromatic ester, can be obtained. For example, the one or more raw materials may be two raw materials from which two types of monomers can be obtained, or one raw material from which two types of monomers can be obtained. The one raw material from which two types of monomers can be obtained may be a raw material that is a mixture of two types of polymers from which two types of monomers can be obtained, or a raw material that contains a copolymer of two types of monomers. For example, in one embodiment of the chemical recycling method of the present invention, as the one or more raw materials, at least one of two or more raw materials separately containing a benzene-based raw material as a raw material from which the benzene-based aromatic ester is obtained and a heterocyclic raw material as a raw material from which the heterocyclic aromatic ester is obtained, a mixed raw material as a raw material formed by mixing the benzene-based raw material and the heterocyclic raw material, and a raw material that contains a copolymer of the benzene-based aromatic ester and the heterocyclic aromatic ester and functions as both the benzene-based raw material and the heterocyclic raw material may be used.

[0059] The depolymerization step and the crystallization step may include various steps in addition to the steps described above. For example, the depolymerization of one or more raw materials in the depolymerization step may be performed as appropriate depending on the structure or properties of the target raw materials, and may be achieved only by adding a solvent, or may be performed so as to include various other steps as appropriate. In addition, the crystallization step may include, for example, an appropriate step that affects the dissolution of the monomer. For example, the crystallization step may include a step of applying a physical impact to the depolymerization liquid, such as stirring using an appropriate means such as ultrasound.

[0060] Specifically, for example, in one embodiment of the chemical recycling method of the present invention, the depolymerization step may include a step of adding a catalyst that promotes depolymerization to the one or more raw materials, and a step of heating the one or more raw materials in the solvent. Similarly, for example, in one embodiment of the chemical recycling method of the present invention, the crystallization step may include a step of applying a physical impact to the depolymerized liquid. Note that cooling in the crystallization step may be appropriately realized as long as it is performed from a temperature after depolymerization to an appropriate desired temperature. For example, when the depolymerization step does not include heating, it may be realized by cooling the depolymerized liquid generated at room temperature to a desired temperature.

[0061] The benzene-based aromatic ester and the heterocyclic aromatic ester to be recycled may have any suitable structure. However, the benzene-based aromatic ester preferably has a benzene ring or a naphthalene ring, and the heterocyclic aromatic ester preferably has a furan ring. Therefore, for example, in one embodiment of the chemical recycling method of the present invention, the benzene-based aromatic ester may have a benzene ring or a naphthalene ring. Also, the heterocyclic aromatic ester may have a furan ring.

[0062] The raw material from which the benzene-based aromatic ester is obtained and the raw material from which the heterocyclic aromatic ester is obtained may be any suitable raw material. For example, in one embodiment of the chemical recycling method of the present invention, the benzene-based raw material may include at least one of PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PEN (polyethylene naphthalate), and PTT (polytrimethylene terephthalate). Similarly, for example, in one embodiment of the chemical recycling method of the present invention, the heterocyclic raw material may include at least one of PEF (polyethylene furanoate), PBF (polybutylene furanoate), PTF (polytrimethylene furanoate), PPeF (poly(pentylene-2,5-furandicarboxylate)), PISF (poly(isosorbide-2,5-furandicarboxylate)), PIIF (poly(isoidide-2,5-furandicarboxylate)), PIMF (poly(isomannide-2,5-furandicarboxylate)), PNPGF (poly(neopentylene-2,5-furandicarboxylate), PEFPEN (poly(ethylene-2,5-furandicarboxylate) having 1,8-naphthalenedicarboxylate), PCHF (poly(1,4-phenylene-2,5-furandicarboxylate)), and PDMFF (poly(1,2-dimethylphenylene-2,5-furandicarboxylate)).

[0063] In addition, various monomers belonging to the benzene aromatic ester and the heterocyclic aromatic ester may be appropriately obtained. For example, in one embodiment of the chemical recycling method of the present invention, the two or more raw materials or the mixed raw material are used as the one or more raw materials, the benzene aromatic raw material and the heterocyclic raw material are respectively used as the PET and the PEF, and the benzene aromatic ester and the heterocyclic aromatic ester may respectively function as BHET (bis(2-hydroxyethyl) terephthalate) and BHEF (methyl 3-methyl-2-furan carboxylate).

[0064] In the depolymerization step, various solvents may be used appropriately depending on the structure or properties of the target raw material. For example, in an embodiment in which the raw material to be recycled contains multiple or one raw material including PET and PEF, the solvent may be configured to contain water or ethylene glycol as a main component.

[0065] The heterocyclic aromatic ester may or may not be recovered. In addition, when it is recovered, the recovery may be appropriately realized according to the structure, properties, etc. of the heterocyclic aromatic ester. For example, when the heterocyclic aromatic ester contains BHEF, and the heterocyclic aromatic ester can be recovered by distillation of the residual liquid component after removing the crystallization of the benzene-based aromatic ester, the heterocyclic aromatic ester may be recovered by distillation. Specifically, for example, as one aspect of the chemical recycling method of the present invention, an aspect further including a recovery step (S3) of recovering the heterocyclic aromatic ester from the residual liquid component of the depolymerization liquid after removing the crystallization of the benzene-based aromatic ester may be adopted. In this aspect, the recovery step may include a procedure of distilling the residual liquid component. [Explanation of symbols]

[0066] S1 Depolymerization process S2 Crystallization process S3 Recovery process

Claims

1. A chemical recycling method for depolymerizing raw material polyester into monomers and reusing the monomers as materials, comprising the steps of: a depolymerization step of adding a solvent to one or more raw materials from which two types of monomers, a benzene-based aromatic ester and a heterocyclic aromatic ester, can be obtained as the monomers in the raw material polyester, thereby depolymerizing the one or more raw materials to produce a depolymerized liquid containing the two types of monomers; a crystallization step of cooling the depolymerized liquid to crystallize the benzene-based aromatic ester of the two types of monomers; A chemical recycling method comprising:

2. 2. The chemical recycling method according to claim 1, wherein at least one of the following is used as the one or more raw materials: two or more raw materials separately including a benzene-based raw material as a raw material from which the benzene-based aromatic ester is obtained and a heterocyclic raw material as a raw material from which the heterocyclic aromatic ester is obtained; a mixed raw material as a single raw material formed by mixing the benzene-based raw material and the heterocyclic raw material; and a raw material including a copolymer of the benzene-based aromatic ester and the heterocyclic aromatic ester and functioning as both the benzene-based raw material and the heterocyclic raw material.

3. 3. The chemical recycling method according to claim 2, wherein the depolymerization step includes the steps of adding a catalyst to the one or more raw materials to promote depolymerization, and heating the one or more raw materials in the solvent.

4. The chemical recycling method according to claim 3 , wherein the benzene-based aromatic ester has a benzene ring or a naphthalene ring.

5. 5. The chemical recycling method according to claim 4, wherein the benzene-based raw material includes at least one of PET (polyethylene terephthalate), PBT (polybutylene terephthalate), PEN (polyethylene naphthalate), and PTT (polytrimethylene terephthalate).

6. The chemical recycling method according to claim 5 , wherein the heterocyclic aromatic ester has a furan ring.

7. The heterocyclic raw material is PEF (polyethylene furanoate), PBF (polybutylene furanoate), PTF (polytrimethylene furanoate), PPeF (poly(pentylene-2,5-furandicarboxylate)), PISF (poly(isosorbide-2,5-furandicarboxylate)), PIIF (poly(isoidide-2,5-furandicarboxylate)), PIMF (poly(isomannide-2,5-furandicarboxylate)), PNPGF (poly(neopentylene-2,5-furandicarboxylate), PEFPEN (poly(ethylene-2,5-furandicarboxylate) having 1,8-naphthalenedicarboxylate), PCHF (poly(1,4-phenylene-2,5-furandicarboxylate)), and PDMFF (poly(1,2-dimethylphenylene-2,5-furandicarboxylate)). The chemical recycling method according to claim 6, comprising at least one of the following.

8. As the one or more raw materials, the two or more raw materials or the mixed raw material are used, The PET and the PEF are used as the benzene-based raw material and the heterocyclic raw material, respectively; The chemical recycling method according to claim 7, wherein the benzene-based aromatic ester and the heterocyclic aromatic ester function as BHET (bis(2-hydroxyethyl) terephthalate) and BHEF (methyl 3-methyl-2-furan carboxylate), respectively.

9. The chemical recycling method according to claim 8 , wherein the solvent contains water or ethylene glycol as a main component.

10. The chemical recycling method according to any one of claims 1 to 9, further comprising a recovery step of recovering the heterocyclic aromatic ester from a residual liquid component of the depolymerization liquid after removing the crystallized benzene-based aromatic ester.

11. The chemical recycling method according to claim 10, wherein the recovery step includes a procedure of distilling the residual liquid component.

12. The chemical recycling method according to any one of claims 1 to 9, wherein the crystallization step includes a procedure of applying a physical impact to the depolymerization liquid.

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