Manufacturing method of bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt

Abstract

To provide a technique for manufacturing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt using used polyesters copolymerized with 5-sulfoisophthalic acid residues, more specifically, using waste clothing copolymerized with 5-sulfoisophthalic acid residues as feedstock.SOLUTION: The problem is solved by a method of manufacturing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt, where polyesters copolymerized with 5-sulfoisophthalic acid residues are depolymerized in an ethylene glycol solution. After removing unreacted ethylene glycol, water is added to the depolymerized solution in an amount ranging from 100 wt.% to 4000 wt.%. The solution is then adjusted to a temperature of 2°C or more and 30°C or less, and solids are removed to yield an aqueous solution containing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt. The water is subsequently evaporated to produce bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt using polyester as a raw material.

Background Art

[0002] Modern economic society has been maintained by a mass production, mass consumption, and mass disposal type of social system. However, various adverse effects on the environment have been confirmed, such as the depletion of natural resources, natural destruction associated with resource extraction, global warming caused by greenhouse gas emissions, and sea-level rise. Therefore, in order to efficiently utilize limited resources and continue sustainable growth, it is essential to construct a recycling-based social system that minimizes the generation of waste and reuses or recycles the generated waste so as not to impose a burden on the environment.

[0003] As a technology for realizing a recycling-based social system, attention has been focused on chemical recycling technology that decomposes and purifies waste plastics down to raw material monomer units and regenerates plastic materials of the same quality as before disposal from the obtained monomers. For polyesters that are inexpensive and exhibit suitable physical properties for clothing, regeneration by chemical recycling is also expected, and technologies for obtaining terephthalic acid or bis(2-hydroxyethyl) terephthalate, which are raw material monomer units, from polyesters by hydrolysis or glycolysis have been studied.

[0004] However, sufficient research has not been conducted on the technology for recycling copolymer components other than polyethylene terephthalate contained in polyester, such as isophthalic acid residues and 5-sulfoisophthalic acid residues, into monomer units. In particular, there is a need for a technology to recycle 5-sulfoisophthalic acid residues, which impart water solubility, easy hydrolyzability, and vivid dyeing with quaternary ammonium type cationic dyes when copolymerized with polyester, into monomer units and purify them to a quality that can be used again as a copolymer monomer. At present, there is no effective technology for producing 5-sulfoisophthalic acid monomers with good color tone, especially 5-sulfoisophthalic acid bis(2-hydroxyethyl) and its metal salts, which have excellent copolymerizability with polyester, from waste polyester as a raw material. They are only produced by petrochemical methods using naphtha as a raw material (Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the methods of Patent Documents 1 to 3 described above, m-xylene obtained by pyrolyzing naphtha is oxidized with chromic acid to form isophthalic acid, and then contacted with fuming sulfuric acid to obtain 5-sulfoisophthalic acid. Since 5-sulfoisophthalic acid has poor copolymerizability with polyethylene terephthalate, 5-sulfoisophthalic acid is further neutralized with a metal hydroxide, and then reacted under high temperature and high pressure conditions in methanol to obtain a dimethyl metal salt of 5-sulfoisophthalic acid. Further, it is reacted under high temperature and normal pressure conditions in ethylene glycol to obtain a bis(2-hydroxyethyl) metal salt of 5-sulfoisophthalic acid with a purity of 50% or more and less than 70%. Since the above method has a large number of reaction processes and strict reaction conditions, it not only consumes petroleum raw materials but also consumes a large amount of energy in the manufacturing process, which is not preferable in terms of environmental load.

[0007] An object of the present invention is to provide a technique for producing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or a metal salt thereof using a used polyester copolymerized with a 5-sulfoisophthalic acid residue, more specifically, waste fibers, cloth pieces, fabrics, and clothing copolymerized with a 5-sulfoisophthalic acid residue as raw materials, as a method capable of solving the problems of the above prior art.

Means for Solving the Problems

[0008] The above problems are solved by the method of the present invention, which depolymerizes a polyester copolymerized with a 5-sulfoisophthalic acid residue in an ethylene glycol solution, removes unreacted ethylene glycol, then adds water in an amount of 100% by weight or more and 4000% by weight or less to the depolymerization solution, adjusts the temperature to 2°C or more and 30°C or less, removes solids, obtains an aqueous solution containing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or a metal salt thereof, and then evaporates the water to produce bis(2-hydroxyethyl) 5-sulfoisophthalate and / or a metal salt thereof.

Effects of the Invention

[0009] According to the present invention, bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt can be obtained with a purity of 65% by weight or more and 100% by weight or less from a polyester copolymerized with 5-sulfoisophthalic acid residue without using petrochemical industry methods. By copolymerizing the recovered bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt obtained by the method of the present invention into polyethylene terephthalate, water solubility, easy hydrolysis, dyeability with quaternary ammonium type cationic dyes, etc. can be imparted to the polyester without newly consuming petroleum resources.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail.

[0011] In this specification, "A and / or B" means having either A, B, or both A and B.

[0012] The present invention relates to a method for producing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt, which comprises depolymerizing a polyester copolymerized with 5-sulfoisophthalic acid residue in an ethylene glycol solution, removing unreacted ethylene glycol, adding water in an amount of 100% by weight or more and 4000% by weight or less to the depolymerization solution, adjusting the temperature to 2°C or more and 30°C or less, removing solids, obtaining an aqueous solution containing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt, and then evaporating the water.

[0013] In the present invention, the polyester copolymerized with 5-sulfoisophthalic acid residue means a polyester in which a part of the dicarboxylic acid residues in the polyester molecular chain is derived from 5-sulfoisophthalic acid, a metal salt of 5-sulfoisophthalic acid, or a quaternary ammonium compound salt of 5-sulfoisophthalic acid.

[0014] The form of the polyester copolymerized with 5-sulfoisophthalic acid residues is not limited, but it is preferably used waste fibers, scraps of cloth, fabrics, and clothing for ease of recovery and depolymerization. Generally, it is more preferably waste copolymerized polyethylene terephthalate fibers, scraps of cloth, fabrics, and clothing dyed with a quaternary ammonium type cationic dye that shows absorbance at 400 to 800 nm because a large amount of 5-sulfoisophthalic acid residues is contained and 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt can be produced in good yield.

[0015] The amount of 5-sulfoisophthalic acid residues contained in the polyester copolymerized with 5-sulfoisophthalic acid residues is preferably 1.0 mol% or more, more preferably 2.0 mol% or more, based on the total amount of dicarboxylic acid residues, from the viewpoint that 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt can be produced in good yield. Further, since the polyester becomes brittle and it becomes difficult to produce fiber products as the amount of 5-sulfoisophthalic acid residues increases, the amount of 5-sulfoisophthalic acid residues contained in waste copolymerized polyethylene terephthalate clothing dyed with a quaternary ammonium type cationic dye is generally 10.0 mol% or less.

[0016] The composition of the polyester copolymerized with 5-sulfoisophthalic acid residues is not particularly limited. As the dicarboxylic acid residues, in addition to 5-sulfoisophthalic acid residues, aromatic carboxylic acid residues such as terephthalic acid and isophthalic acid, and aliphatic carboxylic acid residues such as adipic acid, sebacic acid, and cyclohexanedicarboxylic acid may be included. From the viewpoint of excellent fiber strength and generally large throughput, it is preferably composed of two components, 5-sulfoisophthalic acid residues and terephthalic acid residues. As the diol residues, alkylene glycol residues such as ethylene glycol, diethylene glycol, and 1,4-butanediol, and polyalkylene glycol residues such as polyethylene glycol and polytetramethylene glycol may be included. From the viewpoint of excellent fiber strength and generally large throughput, it is preferably composed of two components, ethylene glycol residues and polyethylene glycol residues. From the viewpoint of improving the purity of the obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt, it is more preferably composed only of ethylene glycol.

[0017] In the present invention, it is essential to go through the step of depolymerizing the polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution. By depolymerizing the polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution, the 5-sulfoisophthalic acid residues are converted into 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt, or a quaternary ammonium compound salt.

[0018] When depolymerizing the polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution, the depolymerization temperature is preferably 160°C or higher, more preferably 180°C or higher, and even more preferably 195°C or higher, which is near the boiling point of ethylene glycol, in order to promote the depolymerization reaction. Further, in order to further promote the reaction, it may be set at 200°C or higher under sealing. In order to prevent the modification of the bis(2-hydroxyethyl) structure of the obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt, or the quaternary ammonium compound salt, the depolymerization temperature is preferably 220°C or lower, and more preferably 210°C or lower. When depolymerizing a polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution, in order to accelerate the depolymerization reaction, the addition amount of ethylene glycol is preferably 2 equivalents or more, more preferably 3 equivalents or more, still more preferably 4 equivalents or more, and most preferably 5 equivalents or more of the molar amount of all dicarboxylic acid residues contained in the polyester. In order to improve the removal efficiency of unreacted ethylene glycol carried out in a later step, the addition amount of ethylene glycol is preferably 17 equivalents or less, more preferably 15 equivalents or less, still more preferably 13 equivalents or less, and most preferably 11 equivalents or less of the molar amount of all dicarboxylic acid residues contained in the polyester.

[0019] When depolymerizing a polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution, in order to accelerate the depolymerization reaction, it is preferable to add a metal hydroxide. In particular, when the amount of 5-sulfoisophthalic acid residues in the polyester exceeds 2 mol%, the depolymerization does not proceed without the addition of a metal hydroxide. The metal species of the metal hydroxide to be added is not particularly limited, but from the viewpoint of suppressing gelation when the finally obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) metal salt is copolymerized with the polyester, it is preferably any one of lithium hydroxide, sodium hydroxide, and potassium hydroxide, and most preferably sodium hydroxide. The addition amount of the metal hydroxide is preferably 500 ppm or more, more preferably 5000 ppm or more, based on the weight of the polyester in order to accelerate the depolymerization reaction. From the viewpoint of improving the purity of the finally obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt, the addition amount of the metal hydroxide is preferably 50000 ppm or less, more preferably 5000 ppm or less.

[0020] In the present invention, after depolymerizing a polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution, it is essential to go through a step of removing unreacted ethylene glycol. After removing the unreacted ethylene glycol, proceeding to the next step, which is the water addition step, improves the yield of finally obtained bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt.

[0021] As a method for removing unreacted ethylene glycol, distillation under reduced pressure is preferable. To enhance the distillation efficiency under reduced pressure, the distillation temperature under reduced pressure is preferably 80°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher. On the other hand, to suppress the recondensation of bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt, or a quaternary ammonium compound salt, with other bis(2-hydroxyethyl) dicarboxylic acid compounds, the distillation temperature under reduced pressure is preferably 180°C or lower, more preferably 160°C or lower, and even more preferably 140°C or lower.

[0022] Also, to enhance the distillation efficiency under reduced pressure, the degree of reduced pressure is preferably 3000 Pa or lower, more preferably 2500 Pa or lower, even more preferably 1500 Pa or lower, further preferably 1000 Pa or lower, and most preferably 500 Pa or lower, with the internal pressure of the distillation apparatus being the absolute pressure. On the other hand, to suppress the recondensation of bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt, or a quaternary ammonium compound salt, with other bis(2-hydroxyethyl) dicarboxylic acid compounds, the degree of reduced pressure is preferably 50 Pa or higher, and more preferably 100 Pa or higher.

[0023] In the present invention, it is essential to depolymerize a polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution, remove unreacted ethylene glycol, and then add water to the depolymerization solution to remove solids. By adding water to the depolymerization solution and then removing solids, a poorly water-soluble dicarboxylic acid bis(2-hydroxyethyl) compound can be removed. On the other hand, 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt is water-soluble and can be recovered in an aqueous solution. Therefore, the purity and yield of the finally obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt are improved.

[0024] When adding water to the depolymerization solution, from the viewpoint of improving the purity of the finally obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt, it is essential that the amount of water added is 100% by weight or more based on the depolymerization solution, more preferably 300% by weight or more, still more preferably 500% by weight or more, very preferably 1000% by weight or more, particularly preferably 2000% by weight or more, and most preferably 3000% by weight or more. On the other hand, in order to improve the water removal efficiency in the subsequent process, it is essential that the amount of water added is 4000% by weight or less based on the depolymerization solution. In the present invention, a method of adding the depolymerization solution to water may also be employed.

[0025] After adding water to the depolymerization solution, from the viewpoint of improving the purity of finally obtained bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt, it is essential to adjust the liquid temperature to 30°C or lower before removing the solid matter, more preferably to 15°C or lower, and even more preferably to 5°C or lower. On the other hand, from the viewpoint of suppressing freezing of the liquid, the liquid temperature must be 2°C or higher. Further, after adding water, the liquid temperature may be adjusted to 80°C or higher and 98°C or lower to obtain an aqueous solution of the depolymerized product, and then cooled to 2°C or higher and 30°C or lower, and the generated solid matter may be removed. By adjusting to 80°C or higher and 98°C or lower once, the yield of finally obtained bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt can be improved.

[0026] When removing the solid matter after adding water to the depolymerization solution, the method for removing the solid matter is not particularly limited, but it is preferable to perform filter separation or centrifugal separation. When performing filter separation, from the viewpoint of removing pigments and hardly water-soluble bis(2-hydroxyethyl) dicarboxylate compounds contained in the polyester and improving the purity of bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt, the maximum pore size of the filter is preferably 50 μm or less, more preferably 20 μm or less, even more preferably 4 μm or less, and most preferably 1 μm or less.

[0027] In the present invention, when using waste copolymerized polyethylene terephthalate clothing dyed with a quaternary ammonium type cationic dye as a raw material, after adding water to the depolymerization solution and removing solids, the obtained aqueous solution contains a quaternary ammonium type cationic dye and a quaternary ammonium compound salt of 5-sulfoisophthalic acid bis(2-hydroxyethyl) in which the quaternary ammonium type cationic dye is ionically bonded to 5-sulfoisophthalic acid bis(2-hydroxyethyl). In order to improve the color tone of the finally obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt, a step may be carried out to dissociate the quaternary ammonium type cationic dye ionically bonded to 5-sulfoisophthalic acid bis(2-hydroxyethyl) and further remove the quaternary ammonium type cationic dye from the aqueous solution. As the step of removing the quaternary ammonium type cationic dye from the aqueous solution, it is preferable to carry out a cation exchange treatment.

[0028] The aqueous solution after the cation exchange treatment has 5-sulfoisophthalic acid bis(2-hydroxyethyl) as the main solute and shows strong acidity. In addition to the purpose of improving the handleability of the aqueous solution, for the purpose of finally obtaining 5-sulfoisophthalic acid bis(2-hydroxyethyl) in the structure of a metal salt and improving the copolymerizability with polyester, a neutralization treatment of adding a metal hydroxide to the aqueous solution may be carried out. The metal species of the metal hydroxide to be added is not particularly limited, but from the viewpoint of being able to suppress gelation when the finally obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) metal salt is copolymerized with polyester, it is preferably any one of lithium hydroxide, sodium hydroxide, and potassium hydroxide, and most preferably sodium hydroxide. The metal hydroxide is preferably added so that the pH of the aqueous solution is 6 or more and 7 or less in order to prevent modification of the bis(2-hydroxyethyl) structure of the obtained 5-sulfoisophthalic acid bis(2-hydroxyethyl) metal salt.

[0029] In the present invention, after obtaining an aqueous solution containing bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt, it is essential to carry out a step of evaporating and removing water. When copolymerizing bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt for the purpose of modifying polyester, adding it in the form of an aqueous solution generates foreign substances in the polyester and significantly deteriorates the fiber formability.

[0030] The recovered bis(2-hydroxyethyl) 5-sulfophthalate metal salt obtained in the present invention is not limited in its metal species as long as it is a metal salt. However, from the viewpoint of suppressing gelation when copolymerizing the bis(2-hydroxyethyl) 5-sulfophthalate metal salt into polyester, it is preferably any one of lithium bis(2-hydroxyethyl) 5-sulfophthalate, sodium bis(2-hydroxyethyl) 5-sulfophthalate, and potassium bis(2-hydroxyethyl) 5-sulfophthalate, and most preferably sodium bis(2-hydroxyethyl) 5-sulfophthalate.

[0031] The recovered bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt obtained in the present invention preferably has a color tone L* value of 90 or more, more preferably 91 or more, still more preferably 92 or more, and most preferably 93 or more, from the viewpoint of achieving a good color tone of the copolymerized polyester when copolymerizing bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt for the purpose of modifying polyester. Note that the color tone L* value of bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt with a purity of 100% does not exceed 95. Also, the recovered bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salt preferably has a color tone b* value of -5 or more and 5 or less, more preferably 0 or more and 5 or less, still more preferably 0 or more and 3 or less, particularly preferably 0 or more and 2 or less, and most preferably 0 or more and 1 or less, from the viewpoint of achieving a good color tone of the copolymerized polyester when copolymerizing it for the purpose of modifying polyester.

[0032] The 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt described in the present invention means those with a purity of 65% or more and 100% or less. When copolymerizing 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt for the purpose of modifying polyester, in order not to impair the fiber formability of the copolyester, the purity is preferably 70% or more, more preferably 80% or more, still more preferably 90% or more, and most preferably 95% or more.

[0033] The recovered 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt obtained in the present invention may contain 5-sulfoisophthalic acid and / or its metal salt by-produced as impurities due to the dehydration reaction of 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt. When copolymerizing 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt for the purpose of modifying polyester, in order not to significantly impair the fiber formability of the copolyester, the total content of 5-sulfoisophthalic acid and / or its metal salt is preferably 10% by weight or less, more preferably 2% by weight or less, still more preferably 1% by weight or less, and most preferably 0% by weight.

[0034] The recovered 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt obtained in the present invention may contain alkylene glycol and / or its condensate mixed in during the depolymerization process of polyester as impurities. From the viewpoint of maintaining a good color tone of the copolyester when copolymerizing 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or its metal salt for the purpose of modifying polyester, the total content of alkylene glycol and / or its condensate is preferably 10% by weight or less, more preferably 8% by weight or less, still more preferably 1% by weight or less, and most preferably 0%.

[0035] The recovered bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt obtained in the present invention may contain bis(2-hydroxyethyl) terephthalate mixed in during the depolymerization process of polyester as an impurity. From the viewpoint of suppressing fluctuations in the copolymerization amount when copolymerizing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt for the purpose of modifying polyester, the total content of bis(2-hydroxyethyl) terephthalate is preferably 10% by weight or less, more preferably 5% by weight or less, still more preferably 3% by weight or less, and most preferably 0% by weight.

[0036] The recovered bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt obtained in the present invention may contain a quaternary ammonium type cationic dye showing absorbance at 400 to 800 nm, which is derived from waste copolymerized polyethylene terephthalate clothing, as an impurity. However, since the color tone fluctuates greatly when a large amount of the quaternary ammonium type cationic dye is contained, the absorbance intensity area derived from the quaternary ammonium type cationic dye showing absorbance at 400 to 800 nm obtained when measuring the absorbance intensity of a 1.0% by weight solution of the recovered product is preferably 0.40 or less, more preferably 0.08 or less, and most preferably 0.

[0037] The recovered bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt obtained in the present invention can be suitably used as a copolymerization monomer for modifying polyester. The composition of the polyester to be copolymerized is not limited, but it is assumed that copolymerization is carried out with polyethylene terephthalate from the viewpoint of imparting quaternary ammonium type cationic dye dyeability without impairing fiber formability.

[0038] The polyester resin copolymerized with bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt can be synthesized by any method. For example, the same steps as the general method for synthesizing copolyethylene terephthalate shown below can be used. Polyethylene terephthalate is synthesized by a first-step reaction in which an esterification reaction between terephthalic acid and ethylene glycol produces a glycol ester of terephthalic acid and / or its low polymer, and then the reaction product of the first step is heated under reduced pressure in the presence of a polymerization catalyst to carry out a polycondensation reaction until the desired degree of polymerization is reached in a second-step reaction. Bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt can be copolymerized by adding it at any stage from the start of the first-step reaction to before the end of the second-step reaction.

[0039] Also, when producing polyethylene terephthalate by a method in which bis(2-hydroxyethyl) terephthalate is used as a raw material and heated under reduced pressure in the presence of a polymerization catalyst to carry out a polycondensation reaction until the desired degree of polymerization is reached, bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt may be copolymerized by adding it at any stage until the end of the reaction. In this case, since methanol is mixed as an impurity when recovering and reusing ethylene glycol by-produced when producing copolyethylene terephthalate if a dimethyl dicarboxylate compound is present in the additive, it is preferable that bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt substantially do not contain a dimethyl dicarboxylate compound.

[0040] In particular, by utilizing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt obtained in the present invention as a modifying monomer for recycled polyethylene terephthalate obtained from recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerizing polyethylene terephthalate, it becomes possible to produce 100% recycled copolyethylene terephthalate.

[0041] A polyester resin copolymerized with bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt, such as recycled copolyethylene terephthalate, can be melt-molded by heating, and by melt-molding it into fibers, it can be suitably used for general clothing applications, sports clothing applications, bedding applications, and interior applications.

Examples

[0042] A. Composition analysis of the raw material polyester The composition analysis of the raw material polyester (types and contents of dicarboxylic acid residues / diol residues) was measured and calculated using a nuclear magnetic resonance apparatus (NMR, "AL-400" manufactured by JEOL Ltd.) with 1,1,1,3,3,3-hexafluoro-2-propanol-d2 (deuterated HFIP) as the deuterated solvent, at a sample concentration of 50 mg of the measurement sample per 1 mL of the deuterated solvent, with 128 integration times.

[0043] B. Measurement of the absorbance intensity area derived from quaternary ammonium type cationic dyes in the raw material polyester A mixed solvent of water and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) (1:4) was prepared, and a solution with a polyester concentration of 1.0 wt% was prepared using this mixed solvent. When the polyester was difficult to dissolve, it was dissolved in HFIP before preparing the mixed solvent and then water was added.

[0044] After preparing the polyester solution, using a spectrophotometer U3010 manufactured by Hitachi High-Tech Science Corporation, the absorbance was measured in the wavelength scan mode from 400 to 800 nm, and the area value A of the absorbance intensity (the integrated value of the absorbance intensity per 1 nm wavelength) was calculated. When the absorbance intensity was too large to be measured, the solution was diluted so that the polyester concentration became 0.1 wt% and re-measured, and a value 10 times the integrated value of the absorbance intensity per 1 nm wavelength was taken as the area value A of the absorbance intensity.

[0045] Next, 20% by weight of the washed cation exchange resin ("Amberlite" IR120B(H) manufactured by Organo Corporation) was added to the polyester solution. After standing for 24 hours, the cation exchange resin was removed. Again, using a spectrophotometer U3010 manufactured by Hitachi High-Technologies Corporation, the absorbance at 400 to 800 nm was measured in the wavelength scan mode, and the area value B of the absorbance intensity (the integrated value of the absorbance intensity per 1 nm wavelength) was calculated.

[0046] In the present invention, the value obtained by subtracting the absorbance intensity area B from the absorbance intensity area value A obtained as described above was defined as the absorbance intensity area derived from the quaternary ammonium type cation dye in the raw material polyester.

[0047] C. Purity and impurity analysis of recovered bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt The analysis of the purity and impurities (types and contents) of the recovered bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt was carried out using a nuclear magnetic resonance apparatus (NMR, "AL-400" manufactured by JEOL Ltd.). Using 1,1,1,3,3,3-hexafluoro-2-propanol-D2 (deuterated HFIP) as the heavy solvent, the measurement was carried out with a sample concentration of 50 mg of the measurement sample per 1 mL of the heavy solvent and the number of integrations was 128 times, and the calculation was made.

[0048] D. Measurement of the total yield of the recovered 5-sulfoisophthalic acid component The molar amount X of the 5-sulfoisophthalic acid residue in the polyester charged as the raw material was calculated from the measurement results of Example A. Specifically, by the measurement of Example A, in addition to the molar fraction of the 5-sulfoisophthalic acid residue with respect to all dicarboxylic acid residues, the molar amount x (mol / g) of the 5-sulfoisophthalic acid residue in the polyester weight per 1 g was calculated. By multiplying the molar amount x by the raw material input weight W1, the molar amount X of the 5-sulfoisophthalic acid residue contained in the charged polyester can be calculated.

[0049] The total molar amount Y of bis(2-hydroxyethyl) 5-sulfophthalate and its metal salts, and 5-sulfophthalic acid and its metal salts contained as impurities was calculated from the results of Example C. Specifically, by the measurement of Example C, the total molar amount y (mol / g) of bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salts, and 5-sulfophthalic acid and / or its metal salts in the recovered product per 1 g was calculated. By multiplying the molar amount y by the weight W2 of the recovered product, the molar amount Y of the 5-sulfophthalic acid component contained in the recovered product can be calculated.

[0050] The value obtained by dividing the molar amount Y by the molar amount X and multiplying by 100 was defined as the yield of the recovered 5-sulfophthalic acid component.

[0051] E. Measurement of the absorbance intensity area derived from a quaternary ammonium type cationic dye contained as an impurity in bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salts A mixed solvent (1:4) of water and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) was prepared, and a solution with a concentration of 1.0 wt% of bis(2-hydroxyethyl) 5-sulfophthalate and / or its metal salts was prepared using this mixed solvent.

[0052] Using a spectrophotometer U3010 manufactured by Hitachi High-Tech Science Corporation, the absorbance of the prepared solution was measured at wavelengths from 400 to 800 nm in wavelength scan mode, and the area value C of the absorbance intensity (the integrated value of the absorbance intensity per 1 nm wavelength) was calculated. When the absorbance intensity was too high to be measured, the solution was diluted so that the recovered product concentration became 0.1 wt% and re-measured, and a value 10 times the integrated value of the absorbance intensity per 1 nm wavelength was defined as the area value C of the absorbance intensity.

[0053] Next, 20% by weight of the washed cation exchange resin (Amberlite IR120B(H) manufactured by Organo Corporation) was added to the recovered solution, and after allowing it to stand for 24 hours, the cation exchange resin was removed. Again, using a spectrophotometer U3010 manufactured by Hitachi High-Technologies Corporation, the absorbance at 400 to 800 nm was measured in wavelength scan mode, and the area value D of the absorbance intensity (the integrated value of the absorbance intensity per 1 nm wavelength) was calculated.

[0054] In the present invention, the value obtained by subtracting the absorbance intensity area D from the absorbance intensity area C obtained as described above was defined as the absorbance intensity area derived from the quaternary ammonium type cationic dye contained as an impurity in bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt.

[0055] F. Measurement of the color tone of bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt recovered Using a spectrophotometer CM-3700d type manufactured by Minolta, the sample was placed with a black calibration plate as a background, and the color tone L* value, a* value, and b* value were measured.

[0056] [Example 1] An unstained copolymerized polyethylene terephthalate fabric containing 10.0 mol% of sodium 5-sulfoisophthalate residues based on all dicarboxylic acid residues was cut into pieces of 2 to 5 cm square. 300 g of the cut copolymerized polyethylene terephthalate fabric was placed in a 2 L four-necked flask, and further 970 g of ethylene glycol and 1.5 g of sodium hydroxide were added, and depolymerization was carried out at 200 °C for 2 hours while stirring. The depolymerization solution was adjusted to 120 °C, and the pressure was reduced to 200 Pa, and unreacted ethylene glycol was distilled off over 2 hours.

[0057] The obtained 420 g of the depolymerized solution was transferred to a 2 L beaker, prepared at 80°C, 1250 mL of water adjusted to 5°C was added, and it was cooled over 2 hours so that the overall liquid temperature became 5°C. The obtained aqueous solution containing solids was filtered using a filter paper with a maximum pore size of 4 μm diameter to obtain an aqueous solution whose main solute component was bis(2-hydroxyethyl) sodium 5-sulfoisophthalate. The obtained aqueous solution was concentrated using an evaporator with a water bath temperature set at 60°C to remove water, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was recovered.

[0058] [Examples 2 to 7] The procedure was carried out in the same manner as in Example 1 except that the amount of water added was changed as shown in Table 1, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was recovered.

[0059] [Examples 8 to 11] The procedure was carried out in the same manner as in Example 1 except that the liquid temperature after adding water was changed as shown in Table 1, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was recovered.

[0060] For Example 11, water was added and the liquid temperature was temporarily set at 80°C, and then it was cooled to 5°C over 2 hours.

[0061]

Table 1

[0062] [Examples 12 to 14] The procedure was carried out in the same manner as in Example 1 except that the depolymerization conditions were changed as shown in Table 2, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was recovered.

[0063] [Examples 15 to 17] The procedure was carried out in the same manner as in Example 1 except that the amount of 5-sulfoisophthalic acid residues contained in the copolyethylene terephthalate used as the raw material was changed as shown in Table 2, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was recovered.

[0064] [Example 18] The procedure was the same as in Example 1, except that the absorbance intensity area value derived from the quaternary ammonium type cationic dye contained in the copolymerized polyethylene terephthalate used as the raw material was changed as shown in Table 2, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was obtained.

[0065] [Examples 19, 20] The absorbance intensity area value derived from the quaternary ammonium type cationic dye contained in the copolymerized polyethylene terephthalate used as the raw material was changed as shown in Table 2. Before concentrating the obtained aqueous solution with an evaporator, 10% by weight of a cation exchange resin (“Amberlite” IR120B(H) manufactured by Organo Corporation) was added based on the weight of the depolymerized solution before water addition, and after performing an adsorption treatment for 3 hours, the cation exchange resin was removed. The procedure was the same as in Example 1, except that sodium hydroxide was added so that the pH of the aqueous solution became 7, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was obtained.

[0066] [Example 21] The procedure was the same as in Example 18, except that the copolymerized polyethylene terephthalate used as the raw material was changed to a copolymerized polyethylene terephthalate containing 1% by weight of polyethylene glycol residues based on the polymer weight, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was obtained.

[0067]

Table 2

[0068] [Comparative Example 1] The procedure was the same as in Example 1, except that the amount of water added was changed as shown in Table 3, and bis(2-hydroxyethyl) sodium 5-sulfoisophthalate was obtained.

[0069] Since the amount of water input was insufficient, the amount of bis(2-hydroxyethyl) terephthalate mixed in increased, and the purity of bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt decreased.

[0070] [Comparative Examples 2 and 3] The same procedure as in Example 1 was carried out except that the liquid temperature after the water input was changed as described in Table 3, and bis(2-hydroxyethyl) 5-sulfoisophthalate sodium was recovered.

[0071] Since the cooling of the liquid temperature was insufficient, the amount of bis(2-hydroxyethyl) terephthalate mixed in increased, and the purity of bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt decreased.

[0072] [Comparative Example 4] The same procedure as in Example 1 was carried out except that the step of removing unreacted ethylene glycol was not carried out, water was concentrated and removed at 60 °C with an evaporator, and then ethylene glycol was concentrated and removed at 85 °C, and bis(2-hydroxyethyl) 5-sulfoisophthalate sodium was recovered.

[0073] Since the solvent in the solid removal step became a mixed solvent of water and ethylene glycol, the amount of bis(2-hydroxyethyl) terephthalate mixed in increased, and the purity of bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt decreased.

[0074] [Comparative Example 5] The same procedure as in Example 1 was carried out except that the step of removing unreacted ethylene glycol and the step of removing water were not carried out, the solid was removed by cooling to 5 °C in the state of an ethylene glycol solution, and ethylene glycol was concentrated and removed at 85 °C with an evaporator, and bis(2-hydroxyethyl) 5-sulfoisophthalate sodium was recovered.

[0075] In the solid content removal step, the solvent being ethylene glycol increased the amount of bis(2-hydroxyethyl) terephthalate mixed in, and the purity of bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt decreased.

[0076]

Table 3

Industrial Applicability

[0077] According to the present invention, bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt excellent in color tone can be obtained from a polyester copolymerized with a 5-sulfoisophthalic acid residue, and it is useful in the production of recycled high-functional polyester fibers and fiber products.

Claims

1. A method for producing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt, which comprises depolymerizing a polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution, removing unreacted ethylene glycol, adding 100 wt% or more and 4000 wt% or less of water to the depolymerization solution, adjusting the temperature to 2°C or more and 30°C or less, removing solids, obtaining an aqueous solution containing bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt, and then evaporating the water.

2. The method according to Claim 1, wherein the polyester copolymerized with 5-sulfoisophthalic acid residues is a copolymerized polyethylene terephthalate fabric or clothing dyed with a quaternary ammonium type cationic dye showing absorbance at 400 to 800 nm.

3. The method according to Claim 1, wherein the polyester copolymerized with 5-sulfoisophthalic acid residues is a polyester containing 1.0 mol% or more and 10.0 mol% or less of 5-sulfoisophthalic acid residues based on all dicarboxylic acid residues.

4. The method according to Claim 1, wherein when depolymerizing the polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution, a metal hydroxide is added in the range of 500 ppm or more and 50000 ppm or less based on the weight of the polyester to conduct the depolymerization.

5. A method for obtaining bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt according to any one of Claims 1 to 4, which comprises the following steps (1) to (3). (1) A step of depolymerizing a polyester copolymerized with 5-sulfoisophthalic acid residues in an ethylene glycol solution at 180°C or more and 210°C or less. (2) A step of distilling off ethylene glycol from the depolymerization solution obtained in (1) under reduced pressure in the temperature range of 80°C or more and 120°C or less, and then obtaining an aqueous solution in which 70% or more and 100% or less of the solute is bis(2-hydroxyethyl) 5-sulfoisophthalate and / or its metal salt in the step of (a) or (b). (a) A step of adding 100 wt% or more and 4000 wt% or less of water to the depolymerization solution from which ethylene glycol has been distilled off, adjusting the liquid temperature to 2°C or more and 30°C or less, and then removing the formed solids. (b) To the depolymerized solution from which ethylene glycol has been distilled off, water in an amount of 100% by weight or more and 4000% by weight or less based on the depolymerized solution is added, and the liquid temperature is adjusted to 80°C or higher and 98°C or lower to obtain an aqueous solution of the depolymerized product. Then, it is cooled to 2°C or higher and 30°C or lower, and the formed solid matter is removed. (3) A step of distilling off water from the aqueous solution obtained in step (2) to obtain 5-sulfoisophthalic acid bis(2-hydroxyethyl) having a purity of 70% or more and 100%.

6. A method for obtaining 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or a metal salt thereof according to claim 5, which comprises performing a cation exchange treatment on the aqueous solution obtained in step (2) and then adding a metal hydroxide to perform a neutralization treatment.

7. Recycled 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or a metal salt thereof, having a purity in the range of 70% by weight or more and 100% by weight or less, a color tone L* value of 90 or more and 95 or less, and a b* value of -5 or more and 5 or less.

8. Recycled 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or a metal salt thereof, substantially free of a dicarboxylic acid dimethyl ester compound, having a purity of 70% by weight or more and 100% by weight or less, containing 5-sulfoisophthalic acid and / or a metal salt thereof as impurities in a total amount of 0% or more and 10% or less, alkylene glycol and / or a condensate thereof in a total amount of 0% or more and 10% or less, and bis(2-hydroxyethyl) terephthalate in a range of 0% or more and 10% or less. When measuring the absorbance intensity of a 1.0% by weight solution of the recycled 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or a metal salt thereof, the absorbance intensity area derived from a quaternary ammonium type cationic dye of impurities showing absorbance at 400 to 800 nm is in the range of 0 or more and 0.4 or less.

9. A recycled polyester composition or fiber containing a 5-sulfoisophthalic acid residue derived from the recycled 5-sulfoisophthalic acid bis(2-hydroxyethyl) and / or a metal salt thereof according to claim 7 or 8 as a copolymerization component.

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