Method for recovering polyester and method for producing recycled polyester

Abstract

A polyester having little discoloration is obtained by treating a fiber product containing a polyester fiber and a urethane fiber with an aromatic alcohol in a temperature range of not less than the glass transition temperature of the polyester and not more than 100 DEG C of the glass transition temperature of the polyester.

Description

Technical Field

[0001] The present invention relates to a method for recovering polyester from a fiber product containing polyester fiber and urethane fiber, and a method for manufacturing polyester in which the polyester is depolymerized and further repolymerized. Background Art

[0002] Polyester is widely used as a fiber product or the like due to its excellent properties, but the effective utilization of used polyester fiber products has become a major issue including environmental problems.

[0003] As main treatment methods, material recycling, thermal recycling, chemical recycling, etc. have been studied. Among them, from the viewpoint of less deterioration of quality caused by recycling, chemical recycling such as depolymerizing a polyester polymer into raw materials composed of dicarboxylic acid and diol and then repolymerizing is excellent as a closed-loop recycling. Among them, from the viewpoint of energy consumption, a method using an intermediate capable of directly performing a polycondensation reaction to manufacture recycled polyester is also an excellent method.

[0004] However, the recycled polyester polymer thus obtained has a problem of being difficult to whiten.

[0005] In particular, when a polyester fiber product contains different types of polymers such as polyurethane or is a dyed product, it is difficult to recover efficiently and suppress coloring.

[0006] For example, in Patent Document 1, as a step for removing a coloring causative substance, an adsorption treatment in which the coloring causative substance is brought into contact with an adsorbent after forming a depolymerized intermediate, a decomposition treatment in which the coloring causative substance is decomposed with a decomposing agent, a reduction treatment in which the coloring causative substance is reduced with a reducing agent, etc. have been tried. However, although coloring causative substances such as dyes significantly mixed into the polymer are removed to some extent, a method for manufacturing a polyester polymer that suppresses coloring and is equivalent to that obtained by a conventional manufacturing method without using recycled raw materials has not been obtained.

[0007] In addition, according to the research by the present inventors, fiber products mainly composed of fibers formed of polyester and containing polyurethane are particularly difficult to separate in the steps before and after depolymerization, and the hue of the chemically recycled polyester after repolymerization is mostly brown. Moreover, when used for recycling of fiber products or the like, the quality is poor.

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-88096 Summary of the Invention

[0009] An object of the present invention is to provide a method for recovering polyester with less coloring from a fiber product containing polyester fiber and polyurethane fiber.

[0010] The method for recycling polyester of the present invention is characterized in that a fiber product mainly composed of fibers formed of polyester and containing fibers formed of a polymer having a urethane group as a constituent is treated with a solution of an aromatic alcohol or its derivative in a temperature range of not less than the glass transition temperature of polyester and not more than the glass transition temperature of polyester + 100°C.

[0011] The present invention includes the following constitution as a preferred mode: the fiber product is a fiber product dyed with a disperse dye, the polyester is polyethylene terephthalate, the polymer having a urethane group as a constituent is a polyether-based polyurethane, and the aromatic alcohol is benzyl alcohol.

[0012] Another invention of the present invention relates to a method for manufacturing recycled polyester, in which the polyester obtained by the above recycling method is depolymerized into an aromatic dicarboxylic acid bis(hydroxyalkyl) ester, and then the aromatic dicarboxylic acid bis(hydroxyalkyl) ester is repolymerized to produce recycled polyester.

[0013] According to the present invention, a method for recycling polyester with less coloring from a fiber product containing polyester fibers and polyurethane fibers can be provided. Detailed Description

[0014] 〔Fiber Product〕

[0015] The method for recycling polyester of the present invention is a method for recycling polyester from a fiber product mainly composed of fibers formed of polyester and containing fibers formed of a polymer having a urethane group as a constituent. Here, "mainly composed of fibers formed of polyester" means that the fibers formed of polyester are the most numerous fibers among the fibers constituting the fiber product. The fibers formed of polyester preferably account for 50 wt% or more of the fiber product, and more preferably 80 wt% or more.

[0016] Here, polyester refers to a polycondensate synthesized by dehydration condensation of a polycarboxylic acid and a polyol to form an ester bond. Moreover, polyester is a polymer having an ester bond, and is generally an aliphatic polyester, a semi-aromatic polyester, or a wholly aromatic polyester.

[0017] The polycarboxylic acid constituting the polyester is preferably a dicarboxylic acid or its ester-forming derivative. As the dicarboxylic acid, aromatic dicarboxylic acids such as terephthalic acid and 2,6-naphthalenedicarboxylic acid are preferably used.

[0018] The polyol as another component constituting the polyester is preferably a diol or its ester-forming derivative. As the diol, aliphatic diols having 2 to 20 carbon atoms are preferably used. As the aliphatic diol, ethylene glycol (hereinafter sometimes abbreviated as EG), 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol can be exemplified. The aliphatic diol can be an alicyclic diol having 3 to 30 carbon atoms, and specifically, 1,4-cyclohexanedimethanol can be exemplified.

[0019] In the present invention, a polyester formed by combining the above-mentioned polycarboxylic acid and polyol is used as a starting material. As the polyester, a polyalkylene terephthalate is preferred, and among them, polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate are preferred.

[0020] The fiber product used in the present invention contains, in addition to the fibers mainly formed of polyester as described above, further contains fibers formed of a polymer having a urethane group as a constituent.

[0021] Here, as the fibers formed of a polymer having a urethane group as a constituent, polyurethane fibers and polyurethane-urea fibers can be exemplified. Most of these fibers have the properties of elastic fibers.

[0022] As the fibers formed of a polymer having a urethane group as a constituent, polyurethane fibers having a urethane bond (-NHCOO-) in the molecular chain are preferred. The polyurethane fiber is composed of a soft segment having a low melting point and a bendability and a hard segment having a high melting point, and has excellent elasticity. The polyurethane fiber is classified into polyether-based polyurethane fibers and polyester-based polyurethane fibers according to its soft segment.

[0023] In the present invention, the polyurethane fiber is preferably a polyether-based polyurethane fiber. Among them, polyether diols such as polybutylene glycol are particularly preferably used as the diol component, aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate are used as the diisocyanate component, and ethylenediamine is used as the diamine component to obtain polyether-based polyurethane fibers.

[0024] As the polyether-based polyurethane fiber, “ROICA” (registered trademark) manufactured by ASAHI KASEI FIBERS Corporation can be exemplified.

[0025] The polyurethane fiber is preferably a fiber having a high elongation elastic modulus.

[0026] The polyurethane fiber can be used as a yarn of a single component, or can be in the form of a blended fiber, blended yarn, core-spun yarn (the core is a urethane fiber), composite yarn, etc. with polyester fibers or the like.

[0027] The content of the polyurethane fiber in the fiber product is preferably 50 wt% or less, more preferably less than 50 wt%, further preferably 30 wt% or less, and particularly preferably 5 to 20 wt%.

[0028] The fiber product can be in the form of, for example, sportswear, uniforms, socks, etc.

[0029] In the present invention, preferably, the fiber product is a dyed fiber product. Dyeing with a disperse dye is also a preferred method. In addition, it is also a preferred method that the disperse dye is a dye containing a nitrogen atom.

[0030] The recovery method of the present invention is a method for recovering polyester by treating the above-mentioned fiber product with a solution of an aromatic alcohol or its derivative in a temperature range above the glass transition temperature of polyester and below the glass transition temperature of polyester + 100°C.

[0031] 〔Aromatic alcohol〕

[0032] Examples of the aromatic alcohol or its derivative include benzyl alcohol, benzaldehyde, and benzoic acid, and benzyl alcohol (hereinafter sometimes referred to as "BA") is preferably used.

[0033] 〔Treatment〕

[0034] The aromatic alcohol or its derivative is used in a heated solution state. The aromatic alcohol or its derivative can be used in admixture with other solvents. The boiling points are all preferably 100°C or higher, and more preferably 150 - 250°C.

[0035] The recovery method of the present invention is to treat the fiber product with a solution of such an aromatic alcohol or its derivative under the condition of a temperature range above the glass transition temperature of polyester and below the glass transition temperature of polyester + 100°C to recover polyester.

[0036] The treatment temperature of the fiber product is preferably in the range of +10°C or higher and +80°C or lower, and more preferably in the range of +15°C or higher and +60°C or lower, of the glass transition temperature of polyester.

[0037] Based on the weight of the fiber product to be treated, the amount of the solution during treatment is preferably 3 - 1000 times, more preferably 5 - 500 times, and particularly preferably 8 - 50 times.

[0038] The treatment is carried out by immersing the fiber product in the solution. This treatment can be carried out by standing in the solution in which the fiber product is immersed, but it is preferably carried out by stirring the solution in which the fiber product is immersed by liquid flow circulation or a rotating blade, etc.

[0039] After impregnation, the fiber product is dewatered. As the treatment for dewatering after impregnation, methods such as pressing treatment, dewatering treatment based on centrifugal separation, and Soxhlet extraction can be adopted.

[0040] It is preferred to carry out impregnation and dewatering repeatedly. It is preferred to carry out impregnation and dewatering 5 times or more, and particularly preferably 6 - 10 times.

[0041] The de-liquefaction treatment is carried out under the condition that, based on the dry weight of the fibrous product, the weight of the fibrous product containing the solution after de-liquefaction is preferably 300 wt% or less, more preferably 150 - 250 wt%, and particularly preferably 180 - 220 wt%.

[0042] 〔Method for manufacturing recycled polyester〕

[0043] Then, another method for manufacturing recycled polyester of the present invention is a method for manufacturing recycled polyester in which the polyester obtained by the above-mentioned polyester recycling method is depolymerized into aromatic dicarboxylic acid bis(hydroxyalkyl) ester, and then the aromatic dicarboxylic acid bis(hydroxyalkyl) ester is repolymerized.

[0044] According to this method, a polyester with a small yellowness and a high whiteness can be obtained.

[0045] 〔Depolymerization〕

[0046] A catalyst is preferably used during depolymerization. As the catalyst, a first transition metal-based catalyst is preferably used. Specifically, oxides, fatty acid salts, carbonates, sulfates, phosphates, oxides, hydroxides, halides, and alcoholates of the first transition metal series can be exemplified.

[0047] As the first transition metal, manganese and zinc are preferably used. As the catalyst, manganese oxide, manganese acetate, zinc oxide, and zinc acetate are preferably used, and manganese acetate is particularly preferably used. One kind of catalyst can be used, or two or more kinds can be combined.

[0048] The catalyst is preferably used in the form of a solution pre-dissolved in alkylene glycol. As the alkylene glycol (hereinafter sometimes abbreviated as AG), the same alkylene glycol as the diol component forming the backbone structure of the polyester used in the fibrous product is preferably used.

[0049] As the alkylene glycol, the alkylene glycol constituting the polyester obtained as the final product by repolymerizing the intermediate aromatic dicarboxylic acid bis(hydroxyalkyl) ester can be used.

[0050] When the polyester is polyethylene terephthalate (PET), the alkylene glycol same as the diol component forming the backbone structure of the polyester is ethylene glycol (EG); when the polyester is polytrimethylene terephthalate, it is 1,3-propanediol (trimethylene glycol, C3G); when the polyester is polybutylene terephthalate, it is 1,4-butanediol (C4G). The diol can be a mixture.

[0051] Generally, the degree of discoloration of the depolymerized product of polyester gradually increases after long-term storage, etc., but the discoloration of the products obtained by the recycling method and manufacturing method of the present invention is significantly less. Especially when a manganese-based catalyst is used during depolymerization, the discoloration is less.

[0052] When depolymerizing polyester, the amount of catalyst used is preferably 20 to 500 mmol%, more preferably 30 to 300 mmol%, and particularly preferably 50 to 150 mmol%. Here, "mol%" represents the ratio of the number of catalyst molecules to the constitutional units of the polyester. "mmol%" is 1 / 1000 times of it. If the amount of catalyst used is less than the above range, the catalyst activity is insufficient. If it is more, the effect of suppressing discoloration decreases, so it is not preferred. If a manganese-based catalyst is used as the catalyst, depolymerization can be carried out with a small amount of usage.

[0053] When depolymerizing, relative to the weight of the recycled polyester, the amount of alkylene glycol used is preferably 2 to 20 times, more preferably 3 to 10 times. By using a large amount of alkylene glycol during depolymerization and then further performing crystallization and solid-liquid separation, the amount of depolymerization catalyst and other foreign substances mixed in can be reduced. In addition, especially when using manganese acetate as the catalyst, it has high solubility with alkylene glycol, and the amount of catalyst remaining in the subsequent process can be reduced more effectively.

[0054] 〔Crystallization〕

[0055] After depolymerization using a catalyst, it is preferably cooled in alkylene glycol for crystallization. As the temperature reduction conditions during crystallization, it is preferably cooled from a temperature of 60 °C or higher to 25 °C or lower, and more preferably cooled to 15 °C or lower.

[0056] It is further preferred to perform solid-liquid separation after crystallization. The alkylene glycol content in the filter cake after solid-liquid separation is preferably 100 wt% or less, more preferably 55 wt% or less, further preferably 1 to 30 wt%, and particularly preferably 5 to 25 wt%.

[0057] After crystallization of the depolymerized filter cake, it is preferably washed with water or alkylene glycol. The washing is preferably carried out by treating with a Nutsche filter while spraying the washing liquid. By performing these treatments, the depolymerization catalyst dissolved in the alkylene glycol, other coloring-causing substances, etc. can be washed away, and a higher-purity aromatic dicarboxylic acid bis(hydroxyalkyl) ester can be obtained.

[0058] As the solution used for washing, a solution with low viscosity is preferably used. From this perspective, water is preferably used. Based on the weight of the filter cake, the amount of the washing liquid is preferably 1 to 100 times, more preferably 1.5 to 10 times. The liquid temperature during washing is preferably 0 to 40 °C. If the liquid temperature is higher than this temperature, the filter cake itself is likely to dissolve and the yield decreases, so it is not preferred.

[0059] After washing, it can be dried using a vacuum dryer or the like to obtain an aromatic dicarboxylic acid bis(hydroxyalkyl) ester.

[0060] The obtained bis(hydroxyalkyl) aromatic dicarboxylate can be subjected to adsorption treatment of foreign matters and the like using an adsorbent such as activated carbon.

[0061] It should be noted that when the alkylene glycol used in the production method of the present invention is the same as the glycol component of the polyester after repolymerization, it can be directly used for repolymerization without drying. This is a preferred mode.

[0062] Bis(hydroxyalkyl) aromatic dicarboxylate

[0063] The bis(hydroxyalkyl) aromatic dicarboxylate thus obtained can be used for the production of recycled polyester.

[0064] The bis(hydroxyalkyl) aromatic dicarboxylate varies depending on the polyester of the fiber product used and the alkylene glycol used in depolymerization.

[0065] When the polyester of the fiber product is mainly made from a polyester (polyalkylene terephthalate) using terephthalic acid as the polycarboxylic acid, bis(hydroxyalkyl) terephthalate (hereinafter sometimes referred to as BHAT; bis(hydroxyalkyl) terephthalate) can be obtained.

[0066] In this case, if C3G (1,3-propanediol (trimethylene glycol)) is used as the alkylene glycol for depolymerization, BHPT (bis(hydroxypropyl) terephthalate) can be obtained. Additionally, if C4G (1,4-butanediol) is used as the alkylene glycol for depolymerization, BHBT (bis(hydroxybutyl) terephthalate) can be obtained. Further, when ethylene glycol is used as the alkylene glycol for depolymerization, BHET (bis(hydroxyethyl) terephthalate) can be obtained.

[0067] Repolymerization

[0068] The bis(hydroxyalkyl) aromatic dicarboxylate is repolymerized into polyester by a conventionally well-known method. This polyester is a recycled polyester with excellent hue that is not easily colored.

[0069] As the catalyst for repolymerization to obtain polyester, for example, a conventionally well-known catalyst such as an antimony-based, germanium-based, or titanium-based catalyst can be used, and antimony trioxide is preferably used.

[0070] During repolymerization, it is preferable to carry out the polycondensation reaction while flowing out the alkylene glycol generated during the reaction to the outside of the reactor. The usage amount of the catalyst is preferably in the range of 10 to 1000 ppm relative to the weight of the bis(hydroxyalkyl) aromatic dicarboxylate.

[0071] After polycondensation using a catalyst, it is preferable to add a phosphorus-based stabilizer known heretofore, such as orthophosphoric acid or phosphorous acid. The amount of the phosphorus-based stabilizer used is preferably in the range of 1 to 100 ppm relative to the weight of the aromatic dicarboxylic acid bis(hydroxyalkyl) ester.

[0072] The resulting recycled polyester has less discoloration such as yellowing. This effect is particularly significant in the case of depolymerization using a manganese-based catalyst at a low concentration. It is considered that this is because coloring by-products are not easily generated, and the catalyst is easily dissociated from the aromatic dicarboxylic acid bis(hydroxyalkyl) ester in subsequent processes such as crystallization and is not easily left as an impurity.

[0073] 〔Properties of recycled polyester〕

[0074] In the recycled polyester obtained by the polyester recovery method of the present invention, the polyurethane component is removed. In addition, when the fiber product is dyed, the dye is also removed.

[0075] The resulting recycled polyester preferably has the following properties.

[0076] For the resulting recycled polyester, using a colorimeter in the L * 、a * 、b * color space defined by the International Commission on Illumination (CIE), the b * value is 8 or less, preferably 1 to -20, and more preferably 0.5 to -15.

[0077] The yellowness index (YI) of the resulting recycled polyester is preferably 15 or less, more preferably 5 to -50, and further preferably 0 to -20.

[0078] The whiteness (W) of the resulting polyester is 75 or more, more preferably 80 to 100.

[0079] The nitrogen content derived from polyurethane or dye contained in the resulting recycled polyester is preferably 15 ppm or less, more preferably 10 ppm or less.

[0080] The IV of the polymer of the recycled polyester after repolymerization is preferably 0.30 to 1.50 dl / g, more preferably 0.40 to 1.30 dl / g, and particularly preferably 0.50 to 1.20 dl / g.

[0081] Examples

[0082] The present invention will be described in more detail below by way of examples. It should be noted that the values in the examples were determined by the following methods. "%owf" is an abbreviation for "percentage of fiber weight".

[0083] 1) Hue (L * a *b * )(Col(Lab))

[0084] The re-polymerized polymer (5 g) was pressed with two metal plates to form a plate, and then heated at 140 °C for 2 hours to crystallize the sample. The colorimetric values of L * , a * , b * were measured for this measurement sample using a measuring device (“ZE-6000” manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS Z8781-4:2013.

[0085] The yellowness index (YI) was calculated by the following formula (1), and the whiteness (W) was calculated by the following formula (2).

[0086] Yellowness index (YI): 0.34 − 71.7 × a / L + 178.78 × b / L (1)

[0087] Whiteness (W): 100 − √{(100 − L) 2 + a 2 + b 2} (2)

[0088] The higher the value of the yellowness index (YI), the stronger the yellow tone, and the higher the value of the whiteness (W), the higher the whiteness.

[0089] 2) Nitrogen (N) content

[0090] The nitrogen content contained in fiber products such as fabrics and fibers was measured using a total nitrogen analyzer (TN-110 manufactured by Mitsubishi Kasei Corporation).

[0091] 〔Example 1〕

[0092] (Polyester recovery process)

[0093] As a fiber product, a dyed fabric composed of 360 g of polyethylene terephthalate (hereinafter referred to as “PET”) fiber and 40 g of polyurethane (hereinafter sometimes referred to as “PU”) was prepared.

[0094] The PET fiber is a yarn with an IV of 0.60 dl / g, Tg = 70 °C, Tm = 255 °C, 24 dtex, a strength of 3.9 cN / dtex, and an elongation at break of 41%. It is a fiber containing 0.38 wt% of nitrogen (N) obtained by dyeing with nitrogen-containing orange dye at 0.87% owf, nitrogen-containing red dye at 0.4% owf, and nitrogen-containing black dye at 4.7% owf as disperse dyes. The PU fiber uses a polyether-based polyurethane fiber with high stretchability ("ROICA" manufactured by ASAHI KASEI FIBERS, 22 dtex per filament, strength 1.6 cN / dtex, elongation at break 345%, 300%, elongation elastic modulus 82%, containing 1.06 wt% of nitrogen (N)).

[0095] Put 400 g of this fiber product into a 5-liter separable flask, and additionally put 4000 g of benzyl alcohol (BA) heated to an internal temperature of 105 °C into another beaker. Stir for 30 minutes while adjusting the internal temperature to 105 °C.

[0096] Take out the cloth-like fiber product from the separable flask and press to remove the excess treatment liquid. Coloration was observed in the treatment liquid, and the weight of the gently decolorized fiber product after pressing was 970 g.

[0097] Put the fiber product after pressing back into the above separable flask again, and perform the operations of impregnating and pressing with the same solution as above a total of 6 times. It was visually observed that after the 3rd treatment, the fiber product became whitened. After the 4th time, there was still some coloration in the pressed treatment liquid, and finally the treatment liquid became transparent after the 6th treatment.

[0098] Dry the above-treated fiber product in a vacuum dryer at 80 °C for 8 hours to recover white polyester with high whiteness.

[0099] (Polyester regeneration process)

[0100] To 300 parts by weight of the polyester recovered by the above method, add 1500 parts by weight of ethylene glycol (EG) and 0.38 part by weight of manganese acetate as a depolymerization catalyst (100 mmol% relative to polyester) to a 2-L separable flask and seal the nitrogen. At this time, manganese acetate is pre-dissolved in EG and then added.

[0101] Thereafter, the separable flask containing the sample was heated to an internal temperature of 220 °C using an electric heating mantle, and depolymerization treatment was carried out at normal pressure for 4 hours under stirring. The depolymerized BHET (bis(2-hydroxyethyl) terephthalate) solution was colorless and transparent, and no coloring was observed. Further, the depolymerized solution was filtered through a 200-μm sieve to remove the solid components remaining inside, and after slowly cooling to 70 °C, it was cooled with stirring while decreasing the temperature from 70 °C to 40 °C over a period of 0 minutes to 10 minutes, from 40 °C to 30 °C over a period of 10 minutes to 60 minutes, and from 30 °C to 15 °C over a period of 60 minutes to 180 minutes. Thereafter, stirring was carried out for 60 minutes while maintaining the internal temperature at 15 °C, and the internal temperature was lowered to precipitate crystals of BHET (total 4 hours), obtaining a BHET / EG slurry.

[0102] The BHET / EG slurry was subjected to pressing treatment using a filter press manufactured by Nippon Filter K.K. to separate the solid and liquid of BHET and EG. The separated BHET contained 35 wt% of EG relative to the weight of the filter cake recovered after filter pressing. While spraying 2 weight times of pure water at 25 °C onto the filter cake after the EG separation, a water washing treatment was carried out using a Nutsche filter. For the BHET after the solid-liquid separation was completed, a drying treatment was then carried out at 50 °C for 8 hours using a vacuum dryer to obtain dried BHET. The obtained BHET was white, and no foreign matter was observed to be mixed in.

[0103] Thereafter, 254 parts by weight of the obtained dried BHET, 0.007 parts by weight of a phosphorus-based stabilizer, and 0.07 parts by weight of antimony trioxide as a repolymerization catalyst were put into a reaction vessel under normal pressure in a nitrogen atmosphere. Next, the temperature inside the reactor was set to 285 °C, and under normal pressure for 10 minutes, at a pressure of 4 kPa for 10 minutes, and further at a pressure of 0.4 kPa for 40 minutes, stepwise pressure reduction was carried out respectively, while distilling out ethylene glycol and the like generated during the reaction outside the reactor, and a polycondensation reaction was carried out to obtain a recycled polyester.

[0104] The Lab values and nitrogen content and other physical properties of the dried products before and after the recovery treatment and the recycled polyester after repolymerization are shown in Table 1.

[0105] 〔Example 2〕

[0106] The treatment temperature of benzyl alcohol (BA) was raised from 105 °C to 130 °C, and except for this, the recovery treatment and the regeneration treatment were carried out in the same manner as in Example 1. The color of the residual liquid after pressing in the recovery process was darker than that in Example 1, and a precipitate seemingly being a PET dissolved substance was confirmed in the residual liquid. The fiber product itself was a polyester fabric with high whiteness. However, the weight of the fiber product after being treated and dried became 302 g, and the yield was slightly poor.

[0107] The physical properties of the dried product before and after recycling treatment and the recycled polyester after repolymerization are shown in Table 1.

[0108] [Example 3]

[0109] The treatment temperature of benzyl alcohol (BA) was raised from 105 °C to 160 °C, and the recycling treatment was carried out in the same manner as in Example 1 except for this. The color of the residual liquid after pressing in the recycling process was darker than that in Examples 1 and 2, and precipitates seemingly of PET dissolved matter more than in Example 2 were confirmed in the residual liquid. The fiber product itself was a polyester fabric with high whiteness. However, the weight of the fiber product after treatment and drying became 178 g, the yield was poor, and the recycling process was not carried out.

[0110] The physical properties of the dried product before and after recycling treatment are shown together in Table 1.

[0111] [Example 4]

[0112] An undyed white fabric was used, and the recycling treatment and recycling process were carried out in the same manner as in Example 1 except for this.

[0113] The physical properties of the dried product before and after recycling treatment and the recycled polyester after repolymerization are shown together in Table 1.

[0114] [Table 1]

[0115]

[0116] [Comparative Example 1]

[0117] The treatment temperature of benzyl alcohol (BA) was lowered from 105 °C to 25 °C, and the recycling treatment was carried out in the same manner as in Example 1 except for this. No coloring was observed for the fiber product and the residual liquid after pressing in the recycling process. In addition, no dissolution of PU occurred, and it was still a stretchable fabric. Moreover, the weight of the fiber product after treatment and drying was also 400 g and did not change.

[0118] The physical properties of the dried product before and after recycling treatment are shown in Table 2.

[0119] [Comparative Example 2]

[0120] The treatment temperature of benzyl alcohol (BA) was raised from 105 °C to 205 °C, and the recycling treatment was carried out in the same manner as in Example 1 except for this. In the treatment process at 205 °C, all the fiber products containing PET were dissolved in BA, and the products after pressing treatment could not be recovered.

[0121] The physical properties before recycling treatment are shown together in Table 2.

[0122] [Comparative Example 3]

[0123] Except for using an undyed white fabric in the same manner as in Example 4, a fiber product containing PU fibers as in Example 1 was used. Benzyl alcohol (BA) in Example 1 was changed to ethylene glycol (EG), and the treatment temperature was raised from 105 °C to 160 °C for the recovery treatment.

[0124] It was confirmed that the PU changed to a brown color during the recovery process, and most of the PU solid components still remained at the end of the 6th treatment. The physical properties of the dried product before and after the recovery treatment and the recycled polyester after repolymerization are shown in Table 2.

[0125] [Comparative Example 4]

[0126] A fiber product using a dyed PET fiber the same as in Example 1 except that it does not contain PU fibers was used. Benzyl alcohol (BA) in Example 1 was changed to ethylene glycol (EG). As a result, the fiber product and the pressing liquid did not change. Therefore, the treatment temperature was raised from 105 °C to 160 °C for the recovery treatment.

[0127] The fiber product decreased slightly in weight, and the fabric decolorized, but there was still coloring remaining at the end of the 6th treatment. The physical properties of the dried product before and after the recovery treatment and the recycled polyester after repolymerization are shown in Table 2.

[0128] [Table 2]

[0129]

[0130] [Reference Example 1]

[0131] A fiber product using a dyed PET fiber the same as in Example 1 except that it does not contain PU fibers was used. The recovery treatment and the recycling treatment were carried out in the same manner as in Example 1. The physical properties of the obtained recycled polyester were the same as those in Example 1.

[0132] The physical properties of the dried product before and after the recovery treatment and the recycled polyester after repolymerization are shown in Table 3.

[0133] [Reference Example 2]

[0134] Except for using an undyed white fabric in the same manner as in Example 4, a fiber product containing PU fibers as in Example 1 was used, and the recovery process was omitted. Otherwise, the recycling treatment was carried out in the same manner as in Example 4.

[0135] The physical properties of the recycled polyester before and after repolymerization are shown in Table 3.

[0136] [Reference Example 3]

[0137] A fiber product using only undyed PET fibers without using PU fibers, and omitting the recycling process, and otherwise performing the same regeneration treatment as in Example 1. The physical properties of the resulting regenerated polyester are the same as those in Example 1.

[0138] The physical properties of the regenerated polyester before treatment and after repolymerization are shown together in Table 3.

[0139] 〔Reference Example 4〕

[0140] A fiber product using the same dyed PET fibers as in Example 1 except for not containing PU fibers, and omitting the recycling process, and otherwise performing the same regeneration treatment as in Example 1. The residual nitrogen content is high and the color tone turns yellow.

[0141] The physical properties of the regenerated polyester before treatment and after repolymerization are shown together in Table 3.

[0142] [Table 3]

[0143]

[0144] 〔Example 5〕

[0145] 1.5 g of manganese acetate was added to 4000 g of benzyl alcohol (BA), and otherwise, the recycling treatment and the regeneration treatment were carried out in the same manner as in Example 1. The weight of the fiber product after the recycling treatment and further drying was 319 g. The yield was slightly poor.

[0146] The physical properties of the regenerated polyester before the recycling treatment, the dried product after the treatment, and after repolymerization are shown in Table 4.

[0147] 〔Example 6〕

[0148] BHET dried in the same manner as in Example 1 was obtained. Thereafter, the above BHET was dissolved in 20 times its weight of hot water (90 °C), and 0.25 times the weight of activated carbon relative to BHET was added thereto. It was stirred for 1 hour. Thereafter, the aqueous solution from which the activated carbon was removed by Nutsche filtration was cooled to precipitate BHET. Nutsche filtration was carried out again to recover BHET.

[0149] The recovered BHET was dried in a vacuum dryer under the conditions of 50 °C for 8 hours. The obtained dried BHET was whiter than the BHET obtained in Example 1, and no foreign matter was seen to be mixed in.

[0150] 254 parts by weight of the above dried BHET, 0.007 parts by weight of a phosphorus-based stabilizer, and 0.07 parts by weight of antimony trioxide as a repolymerization catalyst were put into a reaction vessel under normal pressure in a nitrogen atmosphere.

[0151] Next, the temperature inside the reactor is set to 285°C, and stepwise depressurization is carried out under the conditions of normal pressure for 10 minutes, a pressure of 4 kPa for 10 minutes, and further a pressure of 0.4 kPa for 40 minutes. While distilling out ethylene glycol and the like generated during the reaction outside the reactor, a polycondensation reaction is carried out to obtain recycled polyester.

[0152] The physical properties such as the Lab values and nitrogen content of the final dried products before and after the recovery treatment and the recycled polyester after repolymerization are shown in Table 4.

[0153] 〔Example 7〕

[0154] An undyed white fabric is used as the fiber product. In the polyester recovery process, 1.5 g of manganese acetate is added to 4000 g of benzyl alcohol, and the processes of solution impregnation and pressing are carried out a total of 1 time. Except for this, the treatment is carried out through the same processes as in Example 1.

[0155] The physical properties of the dried products before and after the recovery treatment and the recycled polyester after repolymerization are shown together in Table 4.

[0156] [Table 4]

[0157]

[0158] Industrial Applicability

[0159] The polyester recovered and the recycled polyester manufactured in the present invention can be applied to uses such as fibers, films, and resins.

Claims

1. A method for recycling polyester, characterized in that, A fiber product mainly composed of fibers formed from a polyester and containing fibers formed from a polymer containing a urethane group as a constituent is treated with a solution of an aromatic alcohol or its derivative in a temperature range above the glass transition temperature of the polyester and below the glass transition temperature of the polyester + 100 °C.

2. The method for recycling polyester according to claim 1, wherein The fiber product is a fiber product dyed with a disperse dye.

3. The method for recycling polyester according to claim 1, wherein, The polyester is polyethylene terephthalate.

4. The method for recycling polyester according to claim 1, wherein, The polymer containing a urethane group as a constituent is a polyether-based polyurethane.

5. The method for recycling polyester according to claim 1, wherein, The aromatic alcohol is benzyl alcohol.

6. A method for manufacturing a recycled polyester, wherein the polyester obtained by the recovery method according to any one of claims 1 to 5 is depolymerized into an aromatic dicarboxylic acid bis(hydroxyalkyl) ester, and then the aromatic dicarboxylic acid bis(hydroxyalkyl) ester is repolymerized.

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