Method for producing bis - (2-hydroxyethyl) terephthalate and bis - (2-hydroxyethyl) terephthalate obtained therefrom, and method for producing polyester and polyester obtained therefrom

Abstract

To provide a method for producing bis - (2-hydroxyethyl) terephthalate by chemical recycling capable of reducing an environmental load, especially reducing the discharge amount of carbon dioxide.SOLUTION: A method for producing bis - (2-hydroxyethyl) terephthalate by depolymerizing polyethylene terephthalate in ethylene glycol, wherein the ethylene glycol comprises ethylene glycol derived from biomass resources.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing bis-(2-hydroxyethyl) terephthalate by depolymerizing a polyester, and the resulting bis-(2-hydroxyethyl) terephthalate, as well as a method for producing a polyester using the thus-obtained bis-(2-hydroxyethyl) terephthalate, and the resulting polyester. [Background technology]

[0002] Polyesters, typified by polyethylene terephthalate, are widely used in a variety of fields, such as fibers, molding materials, films, and beverage containers, because they have excellent mechanical strength, chemical stability, heat resistance, moisture resistance, low moisture absorption, and can also be made highly transparent, and they are available at low cost and with stable supply.Thus, while polyesters are produced in large quantities, they are also discarded in large quantities.

[0003] To reduce the environmental impact, discarded polyester products, such as PET beverage bottles, are washed, crushed, and, if necessary, re-pelletized to be reused as recycled polyester resin. In recent years, chemical recycling has also come into practical use, in which polyester is decomposed to the monomer level of bis-(2-hydroxyethyl) terephthalate, which is then reused as a raw material for polycondensation (for example, Patent Document 1).

[0004] Chemical recycling has made it possible to reuse polyester containing colorants and fillers, which has made progress in reducing the environmental impact, but it is still not sufficient. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-175912 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a method for producing bis-(2-hydroxyethyl) terephthalate by chemical recycling, which can further reduce the environmental load, particularly the amount of carbon dioxide emissions. Furthermore, the present invention provides a method for producing bis-(2-hydroxyethyl) terephthalate with a high biomass content in a sustainable and stable manner, while reducing the amount of waste material in the chemical recycling process. [Means for solving the problem]

[0007] The present invention comprises the following configurations. [Section 1] A method for producing bis-(2-hydroxyethyl) terephthalate by depolymerizing polyethylene terephthalate in ethylene glycol, wherein the ethylene glycol includes ethylene glycol derived from a biomass resource. [Section 2] Item 2. The method for producing bis-(2-hydroxyethyl) terephthalate according to Item 1, wherein the ethylene glycol contains 50 mol % or more of ethylene glycol derived from a biomass resource. [Section 3] Item 3. The method for producing bis-(2-hydroxyethyl) terephthalate according to Item 1 or 2, wherein the ethylene glycol contains 99 mol % or less of ethylene glycol derived from a biomass resource. [Section 4] Item 4. The method for producing bis-(2-hydroxyethyl) terephthalate according to any one of Items 1 to 3, wherein the amount of ethylene glycol is 4 to 12 times by mass relative to the amount of polyethylene terephthalate. [Section 5] 5. The method for producing bis-(2-hydroxyethyl) terephthalate according to claim 1, wherein the ethylene glycol comprises ethylene glycol recovered from the production method according to claim 1. [Section 6] Item 6. The method for producing bis-(2-hydroxyethyl) terephthalate according to Item 5, wherein the ethylene glycol contains 50% by mass or more of the recovered ethylene glycol. [Section 7] Item 7. The method for producing bis-(2-hydroxyethyl) terephthalate according to Item 5 or 6, wherein the ethylene glycol is obtained by adding ethylene glycol derived from a biomass resource to the recovered ethylene glycol. [Section 8] Item 8. A method for producing bis-(2-hydroxyethyl) terephthalate according to any one of Items 1 to 7, wherein the polyethylene terephthalate contains an ethylene glycol component derived from a biomass resource as a constituent unit. [Section 9] A method for producing a polyester using bis-(2-hydroxyethyl) terephthalate obtained by the method according to any one of items 1 to 8. [Section 10] Bis-(2-hydroxyethyl) terephthalate obtained by depolymerizing polyester, with a biomass ratio based on the number of carbon elements of 17% or more but less than 33.3%. [Section 11] Chemically recycled polyester with a biomass content of 10% or more but less than 20% based on the number of carbon elements. [Effects of the Invention]

[0008] According to the present invention, in a method for producing bis-(2-hydroxyethyl) terephthalate by chemical recycling, it is possible to reduce the environmental load, in particular the amount of carbon dioxide emissions, and further, it is possible to provide a method for producing bis-(2-hydroxyethyl) terephthalate with a high biomass content in a sustainable and stable manner by reducing the amount of waste in the chemical recycling process. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention relates to a method for producing bis-(2-hydroxyethyl) terephthalate by depolymerizing polyethylene terephthalate in ethylene glycol, where the ethylene glycol used for depolymerization includes ethylene glycol derived from a biomass resource. Hereinafter, ethylene glycol may be abbreviated as EG, and ethylene glycol derived from a biomass resource may be abbreviated as bioEG or bio-EG. Bis-(2-hydroxyethyl) terephthalate may be abbreviated as BHET. Polyethylene terephthalate may be abbreviated as PET.

[0010] Examples of ethylene glycol derived from biomass resources include ethylene glycol produced by producing ethanol from raw materials such as sugarcane, bagasse, and carbohydrate crops by a biological treatment method, and then producing ethylene oxide.

[0011] The amount of bioEG in the ethylene glycol used for depolymerization may be 100 mol %, but is not necessarily required to be 100 mol % when cost and industrial productivity are taken into consideration.

[0012] For example, when fossil-derived polyethylene terephthalate (PET) is depolymerized with 100% biomass ethylene glycol (EG), bioEG attacks the ester bonds of PET, resulting in a transesterification reaction that breaks the PEG molecular chain. This reaction converts -TPA-ptEG-TPA- to -TPA-ptEG+bioEG-TPA- (TPA is the terephthalic acid residue, ptEG is the EG residue derived from the fossil materials (oil, natural gas, etc.) contained in the polyethylene, and bioEG is the bioEG residue). However, not all PET becomes ptEG-TPA-bioEG. The ptEG-TPA in the resulting tpEG-TPA-bioEG exchanges with bioEG to form bioEG-TPA-bioEG+EG, resulting in the inclusion of EG derived from fossil materials in the PET reaction system.

[0013] In industrial production, it is preferable to recover excess EG used in depolymerization and reuse it for depolymerization. Therefore, even if bioEG is added to replace the EG consumed in depolymerization, the amount of bioEG in the EG used for depolymerization gradually decreases, and the biomass content in the resulting BHET decreases. Therefore, the preferred range of the amount of bioEG in the EG used for depolymerization can be determined depending on the biomass content in the resulting BHET and the number of times EG is reused.

[0014] The lower limit of the amount of bioEG in the EG used for depolymerization may preferably be 50 mol%, 60 mol%, 70 mol%, 75 mol%, 70 mol%, 73 mol%, 75 mol%, 78 mol%, or 80 mol%. A higher value within the above lower limit is preferred to increase the biomass content of the bis-(2-hydroxyethyl) terephthalate obtained by using the above or higher amount and to increase the biomass content of the polyester resin produced using the same.

[0015] The upper limit of the amount of bioEG in the EG used for depolymerization may be 100 mol%, 99 mol%, 97 mol%, 95 mol%, 92 mol%, 90 mol%, 88 mol%, or 85 mol%. When repeated reuse is performed, the initial amount may be 100 mol%, but from the viewpoint of stability of quality (biomass content), the upper limit range may be used from the beginning. Any combination of upper and lower limits can be selected from the above.

[0016] Furthermore, when the polyethylene terephthalate used for depolymerization contains bioEG, the amount of bioEG in the EG used for depolymerization may be determined according to the bioEG content in the polyethylene terephthalate. If the amount of bioEG components in all EG components in the polyethylene terephthalate to be depolymerized is X mol%, the amount of bioEG in the EG used for depolymerization is preferably X mol% or more, more preferably X+20 mol% or more, and even more preferably X+30 mol% or more, with the upper limit being 100 mol%. When the polyethylene terephthalate to be depolymerized is 100% bioEG, the amount of bioEG in the ethylene glycol used for depolymerization is preferably 100%.

[0017] The polyethylene terephthalate used for depolymerization may have a bio-EG content of 10 mol% or more (2% or more of the total carbon in the PET derived from biomass resources) of the total ethylene glycol content, 30 mol% or more (6% or more), 50 mol% or more (10% or more), 70 mol% or more (14% or more), 90 mol% or more (18% or more), or even 100 mol% (20% or more). Note that the above values ​​are based on the amount of carbon element, but if the amount of bio-EG components in the total EG content were 100%, the biomass content calculated based on the weight of the entire PET would be 31% (molecular weight of the ethylene glycol component: 60 / molecular weight of the structural unit of ethylene terephthalate: 192).

[0018] EG used in depolymerization but not consumed as BHET is preferably recovered and purified by distillation (rectification) or the like, and then reused for depolymerization. The recovery rate (amount of EG after purification / (amount of EG input into the depolymerization step - amount of EG consumed as BHET (theoretical amount)) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, particularly preferably 75% by mass or more, and most preferably 78% by mass or more. It may be 80% by mass or more, 82% by mass or more, or even 90% by mass. By achieving a recovery rate above the above range, the amount of waste can be reduced. The upper limit of the recovery rate is preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less. By achieving a recovery rate below the above range, the amount of impurities in the recovered EG can be easily reduced.

[0019] When the recovered EG is reused, it is preferable to add bioEG to make up for the deficiency. However, within the above range, lowering the recovery rate has the advantages of making it easier to maintain a high level of bioEG in the recovered EG when it is recovered and reused repeatedly, reducing the impurities in the recovered EG, and enabling the production of high-purity BHET with a high yield even when it is reused for depolymerization. However, it also tends to produce a large amount of waste and impose a heavy environmental burden. On the other hand, higher recovery rates can reduce the amount of waste, but make it more difficult to maintain a high level of bioEG in the recovered EG when it is reused repeatedly, and also tend to increase the amount of impurities in the recovered EG. The appropriate recovery rate can be determined taking these factors into consideration.

[0020] The recovered EG is preferably reused for depolymerization. The lower limit of the amount of recovered EG in the EG used for depolymerization is preferably 50% by mass, more preferably 60% by mass, even more preferably 70% by mass, still more preferably 80% by mass, particularly preferably 85% by mass, and most preferably 90% by mass. The upper limit of the amount of recovered EG in the amount of EG used for depolymerization is preferably 99% by mass, more preferably 97% by mass, and even more preferably 95% by mass. By setting the amount within the above range, it is possible to achieve cost advantages, reduce the amount of EG to be discarded, and perform depolymerization under stable conditions. The above applies when a fixed amount of PET is repeatedly depolymerized under fixed conditions, but the above ranges are not restrictive when the amount varies. For example, when the amount of PET to be depolymerized is small, only recovered EG may be used, and when the amount of PET to be depolymerized increases, recovered EG may be less than 50% by mass, or only bio-EG may be used in the first depolymerization without using recovered EG.

[0021] It is preferable that the EG used for depolymerization other than recovered EG be bio-EG. In other words, it is preferable to use a mixture of recovered EG and bio-EG for the EG used for depolymerization. Thus, when recovering EG, it is preferable to add bio-EG to compensate for losses. However, lowering the recovery rate results in a larger amount of bio-EG being added, which makes it easier to maintain a high level of bio-EG in EG when recovered and reused repeatedly. This has the advantage of reducing impurities in the recovered EG, allowing for the efficient production of high-purity BHET even when reused for depolymerization. However, this also increases the amount of waste and tends to place a heavy burden on the environment. On the other hand, increasing the recovery rate reduces the amount of waste, but makes it more difficult to maintain a high level of bio-EG in EG when recovered and reused repeatedly. Furthermore, the amount of impurities in the recovered EG also tends to increase. The appropriate recovery rate and the amount of recovered EG in the EG used for depolymerization are preferably selected taking into consideration the desired purity of BHET, the amount of waste, the quality and amount of substances other than polyester in the polyester used for depolymerization, and other factors.

[0022] The polyester to be depolymerized is preferably polyethylene terephthalate, and of the dicarboxylic acid components constituting the polyester, the terephthalic acid component is preferably 80 mol% or more, more preferably 85 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. Furthermore, of the glycol components constituting the polyester, the EG component is preferably 80 mol% or more, more preferably 85 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. By adjusting the content within the above range, impurities are reduced and BHET productivity can be increased.

[0023] It is preferable that each polyester article to be depolymerized satisfies the above range, but it may be difficult to identify and separate each recovered and collected article and then feed it to the depolymerization step. Therefore, the above range may be the total polyester fed to the depolymerization step. Furthermore, when depolymerization is performed using a continuous method rather than a batch method, the total polyester fed every 15 or 30 minutes may be within the above range, for example.

[0024] The polyester products to be depolymerized are preferably those that have been used in some form. Examples include PET bottles, containers such as trays, housings, films, sheets, and fibers collected from the streets, as well as products, discarded products before being finished in manufacturing, B-grade products not shipped to the market, edge portions held during film stretching, slit offcuts, and molded products returned due to complaints. The original PET may be derived from petroleum-derived terephthalic acid or ethylene glycol (EG) or from biomass. It may also be a mechanically recycled molded product. It may also be a mixture of these PETs. ​​Examples of fibers include clothing fabrics, bedding and cushions, clothing batting, ropes, fishing nets, etc. Polyester products may also contain other fibers such as cotton, linen, wool, polyurethane, nylon, and acrylic; pigments; dyes; glass fibers; steel fibers; talc; kaolin; mica; calcium carbonate; whisker reinforcing materials; lightweight materials such as shirasu balloons and glass balloons; flame retardants; and the like. It may also include zippers, buttons, fasteners, decorative elements, etc.

[0025] These polyester products are depolymerized in EG (depolymerization step) to produce BHET. The depolymerized product contains substances other than BHET, such as excess EG, polyester oligomers, the above-mentioned non-polyester impurities, and side reaction components, and these must be removed. For example, when solid matter is present, physical solid-liquid separation methods such as filtration and centrifugation are preferably used.

[0026] The depolymerized product from which the solids have been removed is cooled to precipitate BHET (crude crystallization), which is then filtered to obtain crude BHET. The crude BHET may be further dissolved by adding EG, heated, and cooled, and then crude crystallized multiple times to remove impurities.

[0027] Although most of the EG is removed by crude crystallization, the crude crystallized BHET still contains substances with lower boiling points than BHET, such as EG. These low boiling substances can be removed by reheating the crude crystallized BHET to make it liquid and volatilizing the low boiling substances (concentration process).

[0028] The resulting BHET may be further purified to obtain a higher purity BHET. Purification methods include distillation under reduced pressure (distillation purification), particularly thin-film distillation, and dissolving the BHET in an appropriate solvent by heating, followed by cooling and recrystallization (crystallization purification). These BHET purification methods can be selected individually or in combination depending on the purity of the depolymerized product and the desired purity of the resulting BHET. For example, if the polyester product used for depolymerization contains almost no impurities other than the polyester, only distillation of low-boiling materials may be performed, or crude crystallization may be performed in addition. On the other hand, if the polyester product used for depolymerization contains impurities other than the polyester, it is preferable to remove solids by the physical method described above before distillation of low-boiling materials and crude crystallization. Furthermore, it is preferable to purify the crudely crystallized BHET by crystallization and / or distillation. In particular, if the polyester contains a large amount of nitrogen as an impurity, the polyester polymerized using the resulting BHET is likely to be colored yellow, so the above purification is preferred.

[0029] These steps will be explained in order. [Depolymerization process] In the depolymerization step, the polyester article and EG are placed in a reaction vessel, and a catalyst is added and the mixture is heated. The polyester material is preferably pulverized and charged into the reaction vessel so that it can be sufficiently stirred.

[0030] The lower limit of the amount of EG used for depolymerization is preferably 4 times by mass, more preferably 4.5 times by mass, and even more preferably 5 times by mass relative to the polyester used for depolymerization. By using an amount greater than the above, the depolymerization reaction can be accelerated and the amount of BHET produced can be increased. Furthermore, the proportion of EG derived from fossil raw materials after depolymerization can be reduced, allowing the number of times EG can be reused to be increased.

[0031] The upper limit of the amount of EG used for depolymerization relative to the polyester used for depolymerization is preferably 12 times by mass, more preferably 10 times by mass, even more preferably 9 times by mass, particularly preferably 8 times by mass, and most preferably 7 times by mass. By setting the amount to the above or less, the amounts of by-produced impurities such as diethylene glycol and dioxane can be reduced, and recovery and purification of EG after depolymerization becomes easy.

[0032] Examples of depolymerization catalysts used in polyester production include esterification catalysts, transesterification catalysts, and polycondensation catalysts, such as metal hydroxides, carbonates, organic acid salts, organic phosphates, oxides, hydroxides, and alcoholates. Metals include Li, Na, K, Mg, Ca, Ti, Zn, Mn, Co, Al, Ge, and Sb. Among these, preferred examples include sodium hydroxide, potassium hydroxide, sodium acetate, potassium acetate, magnesium acetate, magnesium hydroxide, zinc acetate, calcium acetate, cobalt acetate, and manganese acetate. These depolymerization catalysts may be used in combination.

[0033] The depolymerization temperature is preferably 170° C. or higher, more preferably 180° C. or higher, and even more preferably 185° C. or higher. The depolymerization temperature is preferably 220° C. or lower, more preferably 210° C. or lower, and even more preferably 200° C. or lower. The depolymerization time is preferably 1 hour or more, more preferably 2 hours or more, and is preferably 10 hours or less, more preferably 8 hours or less. The boiling point of ethylene glycol is 197°C at atmospheric pressure, and if heating to above this temperature during depolymerization is desired, pressure may be applied. In this case, the depolymerization pressure is preferably 200 kPa or less, more preferably 180 kPa or less, and even more preferably 160 kPa or less. The depolymerization pressure is preferably 60 kPa or more, more preferably 70 kPa or more, and even more preferably 80 kPa or more. If the pressure is low, the temperature may not rise above the above range.

[0034] [Filtration process] The diameter of the filter material in the filtration process can be appropriately selected depending on the size of the solid impurities. For coarse solids of 1 mm or more, a metal or fiber mesh filter large enough to remove them, such as a metal mesh with an opening of about 0.5 to 0.9 mm, can be used. For particles of about 10 μm or larger, a cartridge filter or leaf filter made of metal mesh, filter cloth, nonwoven fabric laminate, thread wound, or resin sintered material can be used.

[0035] [Centrifugal separation process] The centrifuge is preferably a gravity separation type, and a stretch filtration type can be included in the category of the filtration step. The centrifuge may be a batch type or a continuous type. Examples of continuous centrifuges include a separation disk type and a screw decanter type. The centrifugal force of the stretch separator is preferably 50 G or more, more preferably 100 G or more, even more preferably 200 G or more, and particularly preferably 500 G or more. By setting it to the above or higher, the efficiency of centrifugation can be increased. The centrifugal force of the centrifuge is preferably 50,000 G or less, more preferably 20,000 G or less, and even more preferably 10,000 G or less. Although it may be higher than the above, in the case of ultrafine solids that require high centrifugal forces for separation, other methods such as distillation are often more efficient and the equipment may be expensive. The centrifugal force can be selected appropriately depending on the size and specific gravity of the solids to be removed.

[0036] If the temperature is too low, BHET may precipitate. In the filtration step and the centrifugation step, the temperature of the depolymerized product is preferably maintained at a temperature at which BHET precipitates or higher.

[0037] [Rough crystallization process] The depolymerized product is cooled to precipitate BHET. The precipitated BHET is isolated by solid-liquid separation such as filtration or centrifugation. Centrifugation is particularly preferred. The cooling temperature is preferably 40°C or lower, more preferably 35°C or lower, even more preferably 30°C or lower, and particularly preferably 25°C or lower. The cooling temperature is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher. By setting the cooling temperature within the above range, a sufficient amount of BHET can be precipitated, and ordinary industrial water or chilled water can be used for cooling. Furthermore, before crude crystallization, ozone, hydrogen peroxide, concentrated sulfuric acid, an oxygen-based oxidizing agent, a chlorine-based oxidizing agent or the like may be added to the depolymerized product to oxidatively decompose the dye and the like.

[0038] [Concentration process] During the concentration treatment, as EG is removed, BHET may react to increase the amount of oligomers or the amount of DEG produced. Therefore, the concentration treatment is preferably carried out under reduced pressure and at a low temperature. Specifically, the pressure is preferably 10,000 Pa or less, more preferably 5,000 Pa or less, even more preferably 3,000 Pa or less, and particularly preferably 1,000 Pa or less. The pressure is preferably 1 Pa or more, more preferably 10 Pa or more, and even more preferably 50 Pa or more. The temperature is preferably 150°C or less, more preferably 140°C or less, and even more preferably 130°C or less. In the concentration step, the crude crystallized product may be heated and stirred to remove low boiling point substances, but in order to efficiently remove low boiling point substances and suppress oligomerization, it is preferable to use a thin film distiller or the like.

[0039] [Crystallization purification process] The solvent used for crystallization purification is preferably water or a glycol-based solvent, or a mixed solvent of water and a glycol-based compound. Examples of glycol-based compounds include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, and the like, as well as monoalkyl ethers and dialkyl ethers of these glycols. Examples of alkyl groups include methyl, ethyl, propyl, butyl, heptyl, and hexyl. When ethylene glycol is used as the solvent, recovered EG may be used.

[0040] After crude crystallization or after concentration treatment, these solvents are added to BHET and heated to dissolve it, and then cooled to precipitate BHET, which can be isolated by filtration or centrifugation. The amount of the solvent is preferably 2 times or more, more preferably 3 times or more, by mass relative to the solid material containing BHET, and is preferably 10 times or less, more preferably 8 times or less, by mass relative to the solid material containing BHET. The dissolving temperature is preferably 60 to 100°C, more preferably 70 to 90°C. The cooling temperature is preferably 5 to 40°C, more preferably 10 to 30°C, and even more preferably 15 to 25°C.

[0041] [Distillation and purification process] In order to distill at a low temperature and suppress oligomerization of BHET, distillation purification is preferably carried out under reduced pressure. The pressure is preferably 100 Pa or less, more preferably 50 Pa or less, and even more preferably 30 Pa or less. The pressure is preferably 1 Pa or more. For distillation purification, it is preferable to use a thin film still or the like. The distillation temperature, in terms of the jacket temperature of the thin film still, is preferably 200°C or less, more preferably 190°C or less. The jacket temperature is preferably 150°C or more, more preferably 160°C or more. The distillation is preferably carried out by a distillation (rectification) method accompanied by reflux.

[0042] The steps subsequent to the concentration step are preferably appropriately selected and employed depending on the purity of the depolymerized product, etc. The crystallization purification step and the distillation purification step may each be carried out multiple times or may be carried out in combination. When carried out in combination, the order of the steps may be arbitrary.

[0043] [Ethylene glycol distillation process] The liquid remaining after BHET is extracted in the crude crystallization step and the low-boiling point materials discharged in the concentration step, etc., contain a large amount of EG, and it is preferable to recover EG from these. In addition, if recovered EG is used in the crystallization purification step, it is also preferable to recover EG from the liquid remaining after BHET is extracted in the crystallization purification step. The recovery is preferably by distillation, and for example, a distiller equipped with a rectification system can be used to recover highly pure EG. The distillation is preferably carried out at a low temperature under reduced pressure to prevent the generation of by-products such as diethylene glycol and dioxane. The preferred temperature and pressure are the same as those in the concentration step. The purified EG is used in the depolymerization process.

[0044] The resulting BHET contains a bioEG component as the EG component. The bioEG component in the EG component contained in the BHET is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and particularly preferably 75 mol% or more. The upper limit of the bioEG component is preferably 99 mol% or less, and preferably 98 mol% or less. However, if repeatedly recovered EG is used as the EG used for depolymerization, the proportion of bioEG gradually decreases until a steady state is reached, and accordingly, the proportion of bioEG component in the resulting BHET also decreases. Therefore, the upper limit of the bioEG component may be 95 mol%, 90 mol%, or 85 mol%. Note that when the polyester used for depolymerization is PET containing ethylene glycol derived from a biomass resource, the bioEG component in the EG component contained in the resulting BHET can be 99 mol% or more, and when PET containing 100% bioEG is used, it can be 100 mol%.

[0045] The resulting BHET can be used as a raw material for polyesters containing terephthalic acid and ethylene glycol. The polyesters may be PET or copolymer polyesters. It may also be used in combination with BHET newly produced from terephthalic acid and ethylene glycol.

[0046] The polyesters produced using the obtained BHET can be used in a variety of applications, just like ordinary polyesters. For example, PET can be used for containers such as bottles and trays, housings, fibers, films, and sheets, while copolymer polyesters can be used for paint binder resins, coating resins, adhesives, and the like. [Example]

[0047] Furthermore, specific examples of the present invention will be described in examples, but the present invention is not limited to these examples.

[0048] [Biomass ratio] This was done by radiocarbon (C14) measurement as specified in ASTM D6866-16 Method B (AMS). In the case of PET, the weight ratio was calculated as the ratio of the weight of (-OCH2CH2O-) based on the bio-EG component to the weight of PET, and in the case of BHET, the weight ratio was calculated as the ratio of the weight of (-OCH2CH2OH) based on the bio-EG component to the weight of BHET.

[0049] [Limiting viscosity] The polyester resin (or film) was dissolved in a mixed solvent of phenol (6 parts by mass) and 1,1,2,2-tetrachloroethane (4 parts by mass), and the viscosity was measured at 30°C using an Ostwald viscometer.

[0050] [PET waste used for depolymerization] A mixture of cut pieces of polyester batting taken from bedding and crushed pieces of non-food grade PET bottles was used.

[0051] 1 kg of PET waste was placed in a stainless steel reactor, and a solution of 6 g of zinc acetate dihydrate dissolved in 6 kg of Bio-EG was added. The mixture was depolymerized at 195°C for 8 hours under atmospheric pressure with gentle intermittent stirring.

[0052] The obtained depolymerized product was filtered through a 50-mesh stainless steel filter and a disk-type Naslon filter with a nominal filtration diameter of 20 μm.

[0053] The depolymerized product was then cooled to 23°C and the precipitated BHET was removed using a batch-type gravity separation centrifuge. The centrifuge was operated at a centrifugal force of 2000G.

[0054] The extracted crude crystallized BHET was heated to 125°C to melt it, and introduced into a thin film still with a wall temperature of 130°C and an internal pressure of 300 Pa, where low boiling point substances, mainly EG, were distilled off and removed. The crude crystallized BHET from which the low boiling point substances had been removed was then introduced into another thin film distillation apparatus, where the BHET was purified by distillation. The thin film distillation was carried out at a wall temperature of 180°C and a pressure of 13 Pa. The proportion of bio-EG components in the EG components of the obtained BHET was 90 mol %, and the biomass ratio was 43% on a weight basis (30% on a carbon atom number basis).

[0055] Antimony trioxide was added as a catalyst to the obtained BHET so that the amount of antimony element after polymerization became 200 ppm, and condensation was carried out under reduced pressure at 260°C. The obtained PET had an intrinsic viscosity of 0.72 dl / g and a biomass content of 28% by weight (18% by carbon atom number).

[0056] The liquid from which BHET was extracted by centrifugation and the low boiling point material distilled off from the crude crystallized BHET were collected and rectified under reduced pressure in a distillation vessel equipped with a rectifying tube to recover EG. The recovery rate was 90%. The recovery rate is the amount of EG recovered / (the amount of EG used - the amount of EG consumed assuming that all PET has been converted into BHET). The biomass content of the recovered ethylene glycol was 95% based on the number of carbon atoms.

[0057] [Example 2] Depolymerization was carried out in the same manner as in Example 1, except that 6 kg of ethylene glycol was used, prepared by adding fresh bio-EG to the ethylene glycol recovered in Example 1 (the proportion of bio-EG in the EG used for depolymerization was 96%). EG was also recovered in the same manner as in Example 1.

[0058] [Example 3] Depolymerization was carried out in the same manner as in Example 2, and the recovered ethylene glycol was reused 10 times by repeatedly using it and adding fresh bio-EG to make up for any shortfall (the proportion of bio-EG in the EG used for depolymerization was 82%). The EG component of the BHET obtained in the 10th run contained 74 mol% bio-EG components, and the biomass ratio was 36% by weight (25% by carbon atom number). The biomass ratio of the EG recovered in the 10th run was 78% by carbon atom number. [Industrial Applicability]

[0059] According to the present invention, in a method for producing bis-(2-hydroxyethyl) terephthalate by chemical recycling, it is possible to reduce the environmental load, in particular the amount of carbon dioxide emissions, and further, it is possible to provide a method for producing bis-(2-hydroxyethyl) terephthalate with a high biomass content in a sustainable and stable manner by reducing the amount of waste in the chemical recycling process.

Claims

1. A method for producing bis-(2-hydroxyethyl) terephthalate by depolymerizing polyethylene terephthalate in ethylene glycol, wherein the ethylene glycol includes ethylene glycol derived from a biomass resource.

2. 2. The method for producing bis-(2-hydroxyethyl) terephthalate according to claim 1, wherein the ethylene glycol contains 50 mol% or more of ethylene glycol derived from a biomass resource.

3. 2. The method for producing bis-(2-hydroxyethyl) terephthalate according to claim 1, wherein the ethylene glycol contains 99 mol% or less of ethylene glycol derived from a biomass resource.

4. 2. The method for producing bis-(2-hydroxyethyl) terephthalate according to claim 1, wherein the amount of ethylene glycol is 4 to 12 times by mass relative to the amount of polyethylene terephthalate.

5. 2. The method for producing bis-(2-hydroxyethyl) terephthalate according to claim 1, wherein the ethylene glycol comprises ethylene glycol recovered from the production method according to claim 1.

6. The method for producing bis-(2-hydroxyethyl) terephthalate according to claim 5, wherein the ethylene glycol contains the recovered ethylene glycol in an amount of 50% by mass or more.

7. 6. The method for producing bis-(2-hydroxyethyl) terephthalate according to claim 5, wherein the ethylene glycol is obtained by adding ethylene glycol derived from a biomass resource to the recovered ethylene glycol.

8. 2. The method for producing bis-(2-hydroxyethyl) terephthalate according to claim 1, wherein the polyethylene terephthalate contains an ethylene glycol component derived from a biomass resource as a constituent unit.

9. A method for producing a polyester using bis-(2-hydroxyethyl) terephthalate obtained by the method of any one of claims 1 to 8.

10. The bis-(2-hydroxyethyl) terephthalate is obtained by depolymerizing polyester, and has a biomass ratio based on the number of carbon elements of 17% or more but less than 33.3%.

11. A chemically recycled polyester having a biomass ratio based on the number of carbon elements of 10% or more and less than 20%.