JP6960709B1 - Method for producing high-purity bis- (2-hydroxyethyl) terephthalate, method for purifying regenerated polyethylene terephthalate, decolorizing solvent and bis- (2-hydroxyethyl) terephthalate. - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing high-purity BHET capable of easily producing high-purity bis- (2-hydroxyethyl) terephthalate (BHET) from colored polyester waste. SOLUTION: The method for producing a high-purity BHET of the present invention includes a depolymerization step of depolymerizing a colored polyester waste to obtain a depolymerized product containing a colored crude BHET, and a low content contained in the depolymerized product. A concentration step of removing the boiling point component to concentrate the BHET, a recovery step of recovering the BHET from the crude BHET to obtain a medium-purity BHET, and a recovery step of crystallizing the medium-purity BHET in a decolorizing solvent and containing crystals and a dye. It has a crystallization separation step of solid-liquid separation of the solvent component to obtain purified BHET, and a desolvation step of removing the solvent remaining in the crystal of the purified BHET to obtain high-purity BHET. [Selection diagram] Fig. 1

Description

The present invention relates to a method for producing high-purity bis- (2-hydroxyethyl) terephthalate from colored polyester waste (particularly colored polyester clothing waste), and such high-purity bis- (2-hydroxy). Regarding recycled polyethylene terephthalate using ethyl) terephthalate.
Further, the present invention comprises a decolorizing solvent used for easily removing a dye from colored bis- (2-hydroxyethyl) terephthalate to decolorize, and a bis- (2-hydroxyethyl) using such a decolorizing solvent. ) Regarding the purification method of terephthalate.

Polyester (for example, polyethylene terephthalate) is widely used as clothing, films, resin molded products, etc. due to its excellent properties. However, effective utilization of polyester waste (manufacturing process loss) such as thread fibers, film pieces, resin pieces, etc. generated in the manufacturing process of these products and waste of used molded products such as used PET bottles is costly. It has become a big issue not only from the aspect of the above, but also from the environmental problem. Material recycling, thermal recycling, chemical recycling, etc. have been studied and proposed as these treatment methods.

Of these, in material recycling, waste of polyester molded products such as used PET bottles is collected mainly by local governments and actively reused. Further, with respect to yarn fiber scraps, materials are recycled by a method such as processing into large pellets called popcorn and then remelting and regenerating into yarn fibers. However, it is extremely difficult to apply the material recycling method for clothing, and there are no examples of reuse.

Further, thermal recycling, which converts polyester waste containing clothing and yarn fiber waste into fuel, has an advantage that the combustion heat of polyester waste can be reused. However, since the calorific value of polyester is relatively low, a large amount of polyester waste must be burned in order to utilize the heat of combustion. Therefore, there is a problem of loss of polyester raw material and generation of carbon dioxide, which is not preferable from the viewpoint of resource saving and environmental protection.

On the other hand, in chemical recycling, polyester waste is described as a raw material monomer, bis- (2-hydroxyethyl) terephthalate (hereinafter, also referred to as "BHET") or dimethyl terephthalate (hereinafter, also referred to as "DMT"). The regenerated BHET or DMT is polycondensed again to produce a new polyester (see, for example, Patent Documents 1 to 3). Therefore, there is little deterioration in the quality of polyester due to regeneration, and it is excellent for closed-loop recycling. However, even in chemical recycling, most of the recycled raw materials are non-colored and low-impurity used PET bottles, resin scraps, and film scraps.

It is an essential condition to remove coloring pigments such as dyes and pigments in order to recycle polyester from the polyester clothing waste through the raw material monomer using the colored polyester clothing waste as a recycling raw material. It is known that when a large amount of coloring pigment is mixed in the regenerated raw material monomer, the regenerated polyester is colored (particularly yellowed).
In addition, polyester clothing waste includes various stabilizers, antistatic agents, easy-to-dye agents, flame-retardant agents, hygroscopic agents, gas barrier agents, etc., which are used for the purpose of satisfying the required characteristics according to the application of clothing. Compounds, dissimilar materials such as nylon, urethane, cotton, and olefins that are partially used in clothing, additives such as titanium oxide used as matting agents, and impurities such as zippers, buttons, metals, glass, and sand. Etc. are included. Therefore, it is also important to efficiently remove these in order to regenerate polyester clothing waste.

A chemical recycling method has been proposed in which a colorant such as a dye or a pigment is removed from a colored fibrous polyester, and then a recycled polyester is obtained again via a DMT as a raw material monomer (for example, Patent Documents 4 and 5). reference).
However, the methods described in Patent Documents 4 and 5 are methods for recovering DMT from colored fibrous polyester, which requires a long recycling process and requires a large amount of energy, and therefore has many cost problems. Further, the purified recycled DMT has a big demerit that it cannot be directly used in the polymerization process (terephthalic acid process) using terephthalic acid as a raw material, which is currently widely used worldwide.

Patent No. 3715812 Patent No. 5189266 Patent No. 4067306 Patent No. 4537288 Patent No. 5134563

An object of the present invention is to efficiently remove pigments such as dyes and pigments from colored polyester waste (particularly polyester clothing waste) to easily obtain high-purity bis- (2-hydroxyethyl) terephthalate. It is an object of the present invention to provide a method for producing a high-purity bis- (2-hydroxyethyl) terephthalate which can be produced, and a regenerated polyethylene terephthalate produced from such a high-purity bis- (2-hydroxyethyl) terephthalate as a raw material.
Further, a decolorizing solvent used for smoothly removing the dye from the colored bis- (2-hydroxyethyl) terephthalate to decolorize, and a bis- (2-hydroxyethyl) terephthalate using such a decolorizing solvent. To provide a purification method.

Such an object is achieved by the present invention of the following (1) to (16).
(1) A solution containing a colored crude bis- (2-hydroxyethyl) terephthalate by mixing a dye-colored polyester waste with monoethylene glycol and a depolymerization catalyst and depolymerizing the polyester waste. Depolymerization process to obtain a polymer and
A concentration step of removing the low boiling point component containing the monoethylene glycol from the depolymerization product and concentrating the crude bis- (2-hydroxyethyl) terephthalate.
The bis- (2-hydroxyethyl) terephthalate is recovered from the concentrated crude bis- (2-hydroxyethyl) terephthalate, and the medium-purity bis- is higher in purity than the crude bis- (2-hydroxyethyl) terephthalate. Recovery step to obtain (2-hydroxyethyl) terephthalate,
By cooling the solution prepared by dissolving the medium-purity bis- (2-hydroxyethyl) terephthalate in a decolorizing solvent, the crystals of the bis- (2-hydroxyethyl) terephthalate are precipitated, and the crystals and the dye are contained. A crystallization separation step of solid-liquid separating the solvent component to obtain purified bis- (2-hydroxyethyl) terephthalate having a higher purity than the medium-purity bis- (2-hydroxyethyl) terephthalate.
Having a solvent removing step of removing the solvent component remaining in the crystal to obtain a high-purity bis- (2-hydroxyethyl) terephthalate having a higher purity than the purified bis- (2-hydroxyethyl) terephthalate. A method for producing a high-purity bis- (2-hydroxyethyl) terephthalate.

(2) The decolorizing solvent used in the crystallization separation step is selected from the group consisting of glycol monoethers or glycol diethers having 4 to 12 carbon atoms and glycols having 2 to 6 carbon atoms. The method for producing a high-purity bis- (2-hydroxyethyl) terephthalate according to (1) above, which contains at least one glycol-based compound.
(3) The high-purity bis- (2-hydroxyethyl) terephthalate according to (2) above, wherein the content of the glycol-based compound in the decolorizing solvent used in the crystallization separation step is 85% by mass or more. Production method.

(4) The dye has a chromophore containing a nitrogen atom and has a chromophore.
The high-purity bis- (2-hydroxyethyl) according to any one of (1) to (3) above, wherein the amount of the nitrogen atom remaining in the high-purity bis- (2-hydroxyethyl) terephthalate is 20 ppm or less. Hydroxyethyl) A method for producing terephthalate.
(5) The method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to any one of (1) to (4) above, wherein the polyester waste contains 65% by mass or more of polyethylene terephthalate.
(6) The method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to any one of (1) to (5) above, wherein the polyester waste is polyester clothing waste.

(7) The method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to (6) above, wherein in the depolymerization step, the polyester clothing waste is depolymerized in the form of clothing.
(8) The above (6) or (7), further comprising a solid matter removing step of removing the solid content contained in the polyester clothing waste and insoluble in polyester from the depolymerized product after the depolymerization step. The method for producing a high-purity bis- (2-hydroxyethyl) terephthalate according to the above method.
(9) The high-purity screw according to any one of (1) to (8) above, which has a dye pre-removal step of removing a part of the dye from the depolymerized product after the depolymerization step. -(2-Hydroxyethyl) terephthalate production method.

(10) The dye has a chromophore containing a nitrogen atom and has a chromophore.
The method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to (9) above, wherein the dye pre-removal step is carried out until the amount of the nitrogen atoms remaining in the depolymerization becomes 900 ppm or less.
(11) Weight of high-purity bis- (2-hydroxyethyl) terephthalate obtained by the method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to any one of (1) to (10) above. A regenerated polyethylene terephthalate characterized by being a condensate.
(12) The regenerated polyethylene terephthalate according to (11) above, wherein the regenerated polyethylene terephthalate contains 50% by mass or more of a structure derived from the high-purity bis- (2-hydroxyethyl) terephthalate.

(13) A decolorizing solvent used for removing the dye from bis- (2-hydroxyethyl) terephthalate colored with the dye to decolorize the dye.
It is characterized by containing at least one glycol-based compound selected from the group consisting of glycol monoethers or glycol diethers having 4 to 12 carbon atoms and glycols having 2 to 6 carbon atoms. Decolorizing solvent.
(14) The decolorizing solvent according to (13) above, wherein the content of the glycol-based compound in the decolorizing solvent is 85% by mass or more.

(15) By cooling a solution prepared by dissolving bis- (2-hydroxyethyl) terephthalate colored with a dye in a decolorizing solvent, crystals of the bis- (2-hydroxyethyl) terephthalate are precipitated and the crystals are formed. A method for purifying the bis- (2-hydroxyethyl) terephthalate by solid-liquid separation of the dye and the solvent component containing the dye.
The decolorizing solvent contains at least one glycol-based compound selected from the group consisting of glycol monoethers or glycol diethers having 4 to 12 carbon atoms and glycols having 2 to 6 carbon atoms. A method for purifying bis- (2-hydroxyethyl) terephthalate.
(16) The method for purifying bis- (2-hydroxyethyl) terephthalate according to (15) above, wherein the content of the glycol-based compound in the decolorizing solvent is 85% by mass or more.

According to the present invention, dyes, pigments and other pigments are efficiently removed from colored polyester waste (particularly polyester clothing waste) to obtain high-purity bis- (2-hydroxyethyl) terephthalate (BHET). It can be easily manufactured. In particular, since high-purity BHET can be easily produced from colored polyester clothing waste, polyester clothing waste, which has been mostly incinerated or landfilled, is passed through a raw material monomer and then polyester again. Can be played. As a result, it becomes possible to recycle a sustainable closed loop using recycled polyester as polyester clothing waste, which can greatly contribute to the construction of a sound material-cycle society.
Further, the recycled BHET purified by the present invention has a great merit that it can be directly used in a polymerization process (terephthalic acid process) using terephthalic acid as a raw material, which is currently widely used worldwide.

FIG. 1 is a flowchart showing a preferred embodiment of the method for producing a high-purity bis- (2-hydroxyethyl) terephthalate of the present invention.

Hereinafter, the method for producing high-purity bis- (2-hydroxyethyl) terephthalate, the regenerated polyethylene terephthalate, the decolorizing solvent, and the method for purifying bis- (2-hydroxyethyl) terephthalate of the present invention will be described based on the preferred embodiments shown in the drawings. This will be described in detail.
The following description illustrates the present invention and does not limit the scope of the present invention. It goes without saying that other embodiments may also belong to the scope of the present invention as long as they are consistent with the gist of the present invention.
For example, in the present invention, the "process" does not mean only a process that can be distinguished from others, but is combined with other operations, is dispersed in a plurality of practical processes, and is this "process". As long as other process elements are included in the "invention" and those in which the operations of a plurality of processes can be combined in one process are consistent with the gist of the invention, they can belong to the category of the present invention.

FIG. 1 is a flowchart showing a preferred embodiment of the method for producing a high-purity bis- (2-hydroxyethyl) terephthalate of the present invention.
The method for producing high-purity bis- (2-hydroxyethyl) terephthalate (BHET) of the present invention is a method for producing various colored polyester wastes such as clothing, films, resin molded products (for example, bottles) (hereinafter, "colored"). It can also be applied to "polyester waste". In the following description, a case where the colored polyester waste is applied to colored polyester clothing waste (colored polyester clothing waste) will be described.

The method for producing high-purity BHET of the present embodiment is (1) depolymerization step, (2) solid matter removal step, (3) dye pre-removal step, (4) concentration step, and (5) recovery step. It also has (6) a crystallization separation step and (7) a desolvation step.
Hereinafter, each step will be described in order.

(1) Depolymerization Step First, a polyester clothing waste colored with a dye (coloring dye) such as a dye or a pigment is reacted with monoethylene glycol (hereinafter, also referred to as “MEG”) and a depolymerization catalyst. It is charged in a tank and mixed to depolymerize the colored polyester clothing waste to obtain a depolymerization liquid (liquid depolymerization) containing colored crude BHET. Hereinafter, the depolymerization liquid containing the colored crude BHET is also referred to as “colored depolymerization liquid”.
Examples of polyesters constituting polyester clothing include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBN). And so on.

The polyester garment targeted in the present invention is preferably a garment mainly composed of polyethylene terephthalate (PET) fiber.
Such polyester garments may contain different materials such as nylon, urethane, cotton, and olefins, and are used as stabilizers, antistatic agents, easy-to-dye agents, etc. for the purpose of satisfying the required characteristics according to the garment application. It may contain various compounds such as a flame retardant, a hygroscopic agent and a gas barrier agent, additives such as titanium oxide used as a matting agent, and solids such as zippers, buttons, metals, glass and sand.

The amount of PET (for example, PET fiber) contained in the polyester clothing is not particularly limited, but is preferably 65% by mass or more, more preferably 75% by mass or more, and preferably 85% by mass or more. It is more preferably 95% by mass or more, and particularly preferably 95% by mass or more. The upper limit value may be 100% by mass.

Dyes used for coloring (dyeing) polyester clothing are roughly classified into dyes and pigments.
Examples of the dye include a disperse dye, a naphthol dye, a mordant dye, a virgin dye, and the like, and a disperse dye is preferable. This disperse dye binds to polyester by intermolecular force and is therefore most suitable for coloring polyester. Further, according to the study of the present inventor, it has been found that the use of the present invention for removing the disperse dye is highly effective.

Examples of such disperse dyes include C.I. I. Compounds classified as Disperse Black, C.I. I. Compounds classified as Disperse Blue, C.I. I. Compounds classified as Disperse Red, C.I. I. Compounds classified as Disperse Orange, C.I. I. Compounds classified as Disperse Yellow, C.I. I. Compounds classified as Disperse Green, C.I. I. Compounds classified as Disperse Violet, C.I. I. Examples thereof include compounds classified into Disperse Brown.

On the other hand, as the pigment, for example, C.I. I. Compounds classified as Pigment Black, C.I. I. Compounds classified as Pigment Blue, C.I. I. Compounds classified as Pigment Red, C.I. I. Compounds classified as Pigment Orange, C.I. I. Compounds classified as Pigment Yellow, C.I. I. Compounds classified as Pigment Green, C.I. I. Compounds classified as Pigment Violet, C.I. I. Examples thereof include compounds classified as Pigment Brown.

The form of polyester clothing waste to be depolymerized is a granular form that has been granulated by some method, whether it is in the form of clothing without cutting or in the form of cut flakes. Although it may be used, it is preferably in the form of clothing having a high bulk density.
In the form of the cut flakes, the handling process is complicated, and at the same time, the bulk density becomes small, which may be disadvantageous in depolymerization.
In terms of ease of handling and large bulk density, the granulated granular form is advantageous, but the cost increases depending on the method adopted to form the polyester garment waste into the granular form. There is.

Further, when the polyester clothing waste and the MEG in a predetermined amount ratio are charged into the reaction tank and the polyester clothing waste is depolymerized, the depolymerization reaction is carried out with the polyester clothing waste completely immersed in the MEG. Is preferable.
The bulk density of the polyester fiber, 0.10~0.14g / cm ³ (without compression) in garment form a 0.08~0.10g / cm ³ (without compression) in the form of flakes. That is, the polyester fiber can maintain a large bulk density in the form of clothing.
Therefore, in order to efficiently carry out the depolymerization reaction, the amount of MEG used can be reduced even when the polyester clothing waste is completely immersed in MEG. When the polyester clothing waste in the form of clothing is completely immersed in MEG to carry out the depolymerization reaction, the amount of MEG used should be about 4.5 to 7.0 times the mass of the polyester clothing waste. Is preferable, and more preferably about 5.0 to 6.5 times.

If the amount of MEG used is too small, depending on the shape of the polyester clothing waste, the polyester clothing waste cannot be sufficiently immersed in the MEG, the time required for the depolymerization reaction becomes long, or the polyester due to the depolymerization reaction ( For example, the conversion rate from PET) to BHET may be low. In this case, a large amount of polyester oligomer is likely to be present in the depolymerization liquid, and the viscosity of the depolymerization liquid tends to increase. On the other hand, if the amount of MEG used is too large, purification of MEG becomes economically disadvantageous, and depending on the reaction conditions and the like, diethylene glycol (hereinafter, also referred to as “DEG”), 1,4- A large amount of impurities such as dioxane may be produced as a by-product. When such BHET is used, the physical properties (particularly, softening point) of the obtained recycled PET may be significantly lowered depending on the production conditions.

Examples of the depolymerization catalyst include alkali metal hydroxides, alkali metal carbonates, alkali metal fatty acid salts, alkali metal alkoxides, alkaline earth metal hydroxides, alkaline earth metal carbonates, and alkalis. Examples thereof include fatty acid salts of earth metals, alkoxides of alkaline earth metals, oxides of alkaline earth metals, hydroxides of transition metals, carbonates of transition metals, fatty acid salts of transition metals, and alkoxides of transition metals. One or a combination of two or more of these can be used. By using these depolymerization catalysts, BHET can be efficiently produced.
Examples of the alkali metal include Li, Na, K and the like, examples of the alkaline earth metal include, for example, Mg and Ca, and examples of the transition metal include Ti, Zn, Mn and the like.

The temperature at the time of depolymerization is preferably about 180 to 210 ° C, more preferably about 185 to 200 ° C.
When the temperature is in the above range, the time for depolymerization is preferably about 1 to 10 hours, more preferably about 1.5 to 7 hours.
The atmospheric pressure at the time of depolymerization is preferably about 60 kPa to 160 kPa.

(2) Solid matter removal step As described above, polyester clothing waste often contains foreign substances other than polyester fibers (solid content insoluble in polyester), so these foreign substances are removed as necessary. It is preferable to remove it from the polymer solution.
Examples of such foreign substances include dissimilar materials such as cotton and olefins, solids such as zippers, buttons and metals, and coarse solids such as glass and sand mixed during waste collection.
These foreign substances can be collectively removed from the depolymerization solution by filtering with a coarse filter having a mesh size of about 20 to 40 meshes.

Further, titanium oxide, which is insoluble in polyester, may be added to polyester clothing as a matting agent in an amount of about 0.3 to 0.5% by mass. Further, various polyester-insoluble additives are often used for the purpose of satisfying the required characteristics according to the garment application.
Naturally, it is not preferable that these fine solids are mixed in the recycled PET, and depending on the size of these fine solids, they settle or accumulate inside the container or piping in the process to block the flow of liquid. There is a possibility, and it is preferable to remove these fine solids from the viewpoint of process passability.
Specifically, these fine solids can be removed by filtration or hot filtration using a long fiber filter having a size of several μm to several tens of μm.

(3) Dye pre-removal step Further, the colored polyester clothing waste is colored with a dye such as a dye or a pigment. When the degree of coloring of the polyester clothing waste is large, it is preferable to carry out a dye pre-removal step in order to further increase the purity of the finally obtained BHET.
In the following, as the dye, a disperse dye that is most suitable for coloring polyester will be described as a representative.

It is known that when a disperse dye contained in polyester clothing waste is mixed in the recycled polyester, the recycled polyester is colored and the yellowness is particularly increased. Therefore, when producing high-purity BHET from polyester clothing waste, while confirming the degree to which the disperse dye contained in the polyester clothing waste is removed (residual amount of disperse dye), a part of the disperse dye (dye) is used. It is preferable to perform the removal operation.
Here, since most of the disperse dyes (many dyes) are compounds having a chromophore containing nitrogen atoms, a depolymerization solution (solution) is used as one of the methods for confirming the degree to which the disperse dye is removed. A method of measuring the amount of nitrogen atoms remaining in the polymer) or BHET (residual amount) can be used.

As a result of diligent studies on a method for effectively removing the dye, the present inventors remove the dye in advance when the amount of nitrogen atoms derived from the dye contained in the colored polyester clothing waste exceeds 900 ppm (as a result). It was found that a higher purity BHET can be obtained by reducing the amount of nitrogen atoms remaining in the crude BHET after (pre-removal) to 900 ppm or less and performing the treatments in each step described later.

Such a dye pre-removal step can be performed, for example, as follows. That is, first, the depolymerization liquid that has undergone the above-mentioned depolymerization step and solid matter removing step is cooled to 20 to 25 ° C., and fine crystals of BHET and the polyester oligomer are precipitated as solid content. Then, using a centrifugal sedimentation type centrifuge (separation plate type, screw decanter type, etc.), the centrifugal force is set to 2,000 G or more, and the depolymerization liquid is centrifuged. As a result, the precipitated solid content and the MEG in the depolymerization liquid and the dye dissolved in the MEG can be solid-liquid separated. By the above operation, a solid content (solid depolymerization) of BHET or polyester oligomer having a residual nitrogen atom amount of 900 ppm or less can be obtained.

If the amount of nitrogen atoms remaining in one centrifugal sedimentation separation operation does not become 900 ppm or less, MEG can be further added to the obtained solid content, and the centrifugal sedimentation separation operation can be performed again.
Further, if the amount of nitrogen atoms derived from the dye contained in the polyester clothing waste is 900 ppm or less, this step (dye pre-removal step) may be omitted.

The operation of cooling the depolymerization liquid to precipitate BHET and polyester oligomer as solid content is the crystallization operation itself, and the above-mentioned Patent Document 1 also describes a similar method. However, a wide variety of impurities that hinder the crystallization operation are present in the depolymerization solution in this step, and since crystallization occurs in MEG, the solid content crystals obtained by the crystallization operation are present. It becomes a fine crystal with an extremely poor shape and a very small crystal size.
Therefore, it has been difficult to separate solid and liquid crystals and liquid components with a generally known crystal filtration separator or centrifugal filtration type crystal separator. On the other hand, if a centrifugal sedimentation type centrifuge is used, it becomes easy to perform solid-liquid separation between small fine crystals and liquid components.

It is preferable that the MEG separated by the centrifugal sedimentation type centrifuge and the dyes dissolved in the MEG are purified (recovered) by an evaporation operation, a distillation operation, or the like and reused.
On the other hand, the dye component (dye or chromophore) is preferably concentrated as an evaporation residue and a distillation can residue and treated as industrial waste.

(4) Concentration Step Next, the solid matter is melted by heating to obtain a liquid depolymerized product (depolymerized liquid) in a molten state. Then, a low boiling point component having a boiling point lower than that of BHET is removed from this depolymerization liquid to obtain a crude BHET containing BHET and a polyester oligomer as main components. Since the obtained crude BHET is a viscous liquid in a molten state, it is also referred to as a crude BHET concentrated liquid. Here, examples of the low boiling point component mainly include MEG and DEG. Further, in this crude BHET concentrate, impurities such as a pigment component for coloring, a polyamide component, a polyurethane component, a polyester copolymer component, and ultrafine titanium oxide of less than 5 μm that could not be removed in the solid matter removing step (2). May remain.

The removal (evaporation / distillation) of the low boiling point component performed in this step (4) can be performed using, for example, various evaporators.
In particular, in order to prevent the polymerization of BHET and the polyester oligomer during the evaporation operation, it is preferable to set the temperature of the crude BHET concentrate to 130 ° C. or lower under reduced pressure.
Further, it is preferable to select an evaporator having a structure (model) such that the residence time of the crude BHET concentrate in the evaporator is 10 minutes or less.
Specific examples of the evaporator include a flow-down membrane type evaporator and a thin film type evaporator.

(5) Recovery Step Next, a crude product containing BHET and a polyester oligomer as main components and, in some cases, impurities such as a residual coloring dye component, a residual polyamide component, a residual polyurethane component, a residual polyester copolymerization component, and a residual titanium oxide. BHET is recovered from the BHET concentrate to obtain a medium-purity BHET having a higher BHET purity than the crude BHET concentrate.
The recovery of BHET can be preferably performed by evaporation under vacuum (vacuum) (hereinafter, also referred to as "vacuum evaporation"). In this case, BHET is overwhelmingly the component that evaporates in vacuum, but an organic compound having a boiling point such as a trace amount of coloring dye component, polyester oligomer component, polyamide component, polyurethane component, polyester copolymer component, etc. together with BHET (hereinafter, , "Organic compounds having a boiling point") may also be distilled off.

The amount of the organic compound having a boiling point distilled out is determined by the temperature, pressure (vacuum degree) in the operation of vacuum evaporation and the residual molar concentration of the organic compound having a boiling point in the crude BHET concentrate. Therefore, it is preferable to remove the organic compound having a boiling point as much as possible in the step prior to this step (5) from the viewpoint of producing a higher purity BHET.
Among the organic compounds having a boiling point, the coloring dye component (dispersion dye, etc.) has a property of sublimating at a temperature lower than the boiling point, and therefore remains in the crude BHET concentrate supplied in the present step (5). If the dye is removed until the amount of the nitrogen atom becomes 900 ppm or less, the problem that a large amount of the dye is mixed in the medium-purity BHET obtained in the present step (5) can be avoided.

The vacuum evaporation of BHET performed in this step (5) can be performed according to the conditions such as the temperature, pressure, and residence time of the thin film evaporator described in Patent Document 1. However, in order to reduce the sublimation amount of the coloring dye component as much as possible, it is preferable that the temperature and pressure of the thin film evaporator are lower.
The amount of nitrogen atoms remaining in the medium-purity BHET obtained in this step (5) is preferably 300 ppm or less, more preferably 200 ppm or less.

From the crude BHET (crude BHET concentrate), for example, the BHET is recovered by vacuum evaporation to obtain a medium-purity BHET. Organic compounds having a boiling point that cannot be completely evaporated and solid substances such as titanium oxide that do not have a boiling point are discharged to the outside of the system as residues of the evaporator. It is preferable that the discharged residue is effectively utilized by a separate treatment.
That is, it can be said that this step (5) also plays a role as a final separation step of a solid substance having no boiling point.

(6) Crystallization Separation Step Next, the dye is removed from the medium-purity BHET to obtain a purified BHET having a BHET purity higher than that of the medium-purity BHET.
Here, it is preferable that the color b value (yellowness) of the regenerated polyethylene terephthalate produced by polycondensation (melt polycondensation) using the finally obtained high-purity BHET as a raw material is 8 or less. For that purpose, the amount of nitrogen atoms remaining in the high-purity BHET is preferably 20 ppm or less, and more preferably 10 ppm or less.
In order to adjust the amount of nitrogen atoms remaining in the high-purity BHET to the above range, the present inventors also have the same amount of nitrogen atoms remaining in the purified BHET obtained in this step (6) of 20 ppm. We know that it is effective to do the following.

From the viewpoint of lowering the degree of coloring of the regenerated polyethylene terephthalate, it is preferable that the amount of nitrogen atoms remaining in the high-purity BHET is as small as possible. However, since a small amount of nitrogen atoms remain in the regenerated polyethylene terephthalate, for example, it can be used as a footprint mark indicating that the polyethylene terephthalate is regenerated from colored polyester clothing waste.

The present inventors have diligently studied a method for efficiently removing impurities such as dyes remaining in the medium-purity BHET obtained in the recovery step (5) and other organic compounds having a trace boiling point. As a result, it was found that the following method is suitable.
That is, by cooling the solution in which medium-purity BHET is dissolved in the decolorizing solvent, a solvent having a large ability (solubility) to dissolve dyes, chromophores, organic compounds having a boiling point, etc. (the decolorizing solvent of the present invention) is used. , BHET crystals are precipitated, and an operation of solid-liquid separation between the crystals and the solvent component containing the dye (hereinafter, also referred to as “combination crystallization operation”) is preferably performed.
Further, at the time of crystallization, the above impurities can be removed more efficiently by adjusting the mixing ratio of the medium-purity BHET and the decolorizing solvent according to the type of the decolorizing solvent.

From the results of the solubility tests on dyes, chromophores, organic compounds having a boiling point and the like carried out by the present inventors, it was found that a glycol-based compound is suitable as the decolorizing solvent.
Examples of the glycol-based compound include glycol monoether, glycol diether, and glycol, and one or a combination of two or more of these can be used.

Specific examples of glycol monoether include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, and triethylene glycol mono. Butyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monopropyl ether, dipropylene glycol Examples thereof include monopropyl ether, propylene glycol monobutyl ether, and dipropylene glycol monobutyl ether.

Specific examples of glycol diether include ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, and triethylene glycol. Examples thereof include dibutyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether and dipropylene glycol diethyl ether.

Specific examples of glycol include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, and neopentyl glycol. Examples thereof include 1,5-pentanediol, 1,6-hexanediol, and cyclohexanediol.

Further, the glycol monoether and the glycol diether each preferably have 4 to 12 carbon atoms, more preferably 4 to 10 carbon atoms, and further preferably 4 to 8 carbon atoms. On the other hand, the number of carbon atoms of glycol is preferably 2 to 6.
That is, the decolorizing solvent (the decolorizing solvent of the present invention) is at least selected from the group consisting of glycol monoethers or glycol diethers having 4 to 12 carbon atoms and glycols having 2 to 6 carbon atoms. It is preferable to contain one kind of glycol-based compound. By using it as a decolorizing solvent containing such a glycol-based compound, the effect of removing impurities such as dyes, chromophores, and organic compounds having a boiling point remaining in medium-purity BHET can be further enhanced.
Among these, glycol monoether is more preferable from the viewpoint of exhibiting an excellent decolorizing effect regardless of the degree of coloring of the colored polyester clothing waste (medium purity BHET).

In addition to the glycol-based compound, an organic solvent such as water, benzene, toluene, xylene, diethyl ether, ethyl acetate, or acetone may be mixed as the decolorizing solvent.
The content of the glycol-based compound in the decolorizing solvent is preferably 85% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. The upper limit of the content is 100% by mass. A decolorizing solvent containing a glycol-based compound in such an amount exhibits an extremely good dye removing ability (decolorizing effect).
Regarding the cooling temperature of the dissolution liquid, it is preferable that the cooling temperature is low from the viewpoint of reducing the amount of BHET dissolved in the decolorizing solvent and increasing the yield of BHET. However, considering the amount of energy required for cooling, the operability of solid-liquid separation due to the increase in viscosity of the decolorizing solvent due to the lowering of the temperature, and the like, the cooling temperature is preferably about 20 to 25 ° C.
The solution may be rapidly cooled, but slow cooling (including natural cooling) is preferable from the viewpoint of obtaining BHET crystals having a sufficient size.

The number of times the combination crystallization operation is performed is not particularly limited, but if the amount of nitrogen atoms remaining in the purified BHET obtained in the first operation exceeds 20 ppm, the combination crystallization operation may be performed again. preferable.
According to the present inventors, it has been confirmed that if the combination crystallization operation is performed at least three times, the amount of nitrogen atoms remaining in the purified BHET becomes 20 ppm or less regardless of the degree of coloring.

The decolorizing solvent containing impurities such as dyes, chromophores, and organic compounds having a boiling point separated by solid-liquid crystallization operation is preferably purified by evaporation operation, distillation operation, or the like and reused.
On the other hand, impurities such as dyes, chromophores, and organic compounds having a boiling point are preferably recovered as evaporation residues and distillation can residues and treated as industrial waste.
In the present step (6) as described above, the method for purifying BHET of the present invention is carried out.

A method of decolorizing the colored polyester clothing waste before depolymerizing using the decolorizing solvent of the present invention is also conceivable. However, in this case, the decolorizing solvent remains in the polyester clothing (polyester fiber). Specifically, a decolorizing solvent of about 3.5 to 4.0 times the mass of the clothing remains in the polyester clothing. When polyester clothing is depolymerized in this state, depending on the type of decolorizing solvent (for example, ether-based compound), it reacts with the benzene ring terminal of polyester instead of MEG, and a side reaction product is produced instead of BHET. The amount will increase. The present inventors have confirmed that when a reaction occurs, a side reaction product is produced by about 10 to 12%, and the yield of BHET is reduced by about 10 to 12%.

In order to avoid a decrease in the yield of BHET, a method is also conceivable in which the decolorized polyester garment is washed with a detergent (for example, MEG) having a mass of about 20 to 25 times the mass of the polyester garment and then depolymerized. However, in this case, the production cost of high-purity BHET becomes too high due to the use of a large amount of cleaning agent. In addition, when the amount and frequency of the cleaning agent used for cleaning are reduced, the present inventors improve the yield of BHET as compared with the case where no cleaning agent is used, but the regenerated product produced from the obtained BHET. It has also been confirmed that the color b value of polyethylene terephthalate becomes 13 or more, and the degree of yellowing is significantly deteriorated.

On the other hand, as in the present invention, after depolymerizing the colored polyester clothing waste with MEG, BHET is recovered (molecular distillation) to obtain a medium-purity BHET (recovery step), and then remains in the medium-purity BHET. In the method of extracting and removing the dye with a decolorizing solvent (crystallization separation step), the production of by-products does not occur or is highly suppressed, so that the yield of BHET can be increased.
Further, according to the present invention, since the crystallization of BHET and the separation of BHET and the dye are performed in one crystallization separation step (6), the dye or chromophore is less likely to be mixed in the BHET crystal, and more. It is easy to produce high-purity crystals (BHET).

(7) Desolvent Step Next, the solvent component remaining in the BHET crystal obtained in the crystallization separation step is removed to obtain a high-purity BHET having a higher BHET purity than the purified BHET.
The removal (evaporation / distillation) of the solvent component performed in this step (7) can be performed using, for example, various evaporators.
In particular, in order to prevent the polymerization of high-purity BHET during the evaporation operation, it is preferable that the temperature and pressure of the evaporator are low.

The high-purity BHET obtained in the molten state may be polycondensed (molten polycondensation) as it is to produce regenerated polyethylene terephthalate, or the high-purity BHET obtained in the molten state may be once granulated and then polycondensed (melted). Regenerated polyethylene terephthalate may be produced by polycondensation). That is, the regenerated polyethylene terephthalate of the present invention is a polycondensate of high-purity BHET.
When producing regenerated polyethylene terephthalate by polycondensation, regenerated polyethylene terephthalate can be easily produced by mixing high-purity BHET and terephthalic acid in an arbitrary ratio. In this case, in order to contribute to the recycling construction of the sustainable closed loop, it is preferable to contain 50% by mass or more, preferably 65% by mass or more, and 80% by mass of the structure derived from high-purity BHET in the regenerated polyethylene terephthalate. It is more preferable to contain it in an amount of mass% or more.

The method for producing high-purity BHET, the method for producing recycled PET, the decolorizing solvent, and the method for purifying BHET of the present invention have been described above, but the present invention is not limited thereto.
For example, the method for producing high-purity BHET and the method for purifying BHET of the present invention may be replaced with any step in which the same effect is exhibited, or a step of arbitrary purpose may be added. .. Further, the process of the present invention may be a batch type (batch type), a continuous type, or a combination thereof.
Further, the regenerated PET and the decolorizing solvent of the present invention may be replaced with arbitrary configurations that exhibit the same effect, respectively, and arbitrary configurations may be added.

Hereinafter, the contents of the present invention will be described in more detail with reference to Examples. The present invention is not limited to these examples.

1. 1. Production of high-purity BHET and recycled PET from colored polyester clothing waste (Example 1)
<(1) Depolymerization step>
First, a total of 400 g (hereinafter, also referred to as "colored clothing waste") of PET clothing colored with uncut black disperse dye, blue disperse dye, red disperse dye and yellow disperse dye (hereinafter, also referred to as "colored clothing waste"). Bulk density: 0.12 g / cm ³ , total amount of nitrogen atoms contained in colored clothing waste: 1,150 ppm) was prepared.
Next, after putting the colored clothing waste in the form of these clothing into a 5 L flask, 2,245 g of MEG previously heated to 195 ° C. and 1 g of sodium hydroxide as a depolymerization catalyst are placed in the flask. The reaction was carried out at 195 ° C. and normal pressure for 5.0 hours without stirring. As a result, a depolymerization liquid (colored depolymerization liquid) containing a colored crude BHET as a main component was obtained.

<(2) Solid matter removal process>
Next, the colored depolymerization liquid was hot-filtered with a wire mesh strainer having a mesh opening of 30 mesh to obtain a colored depolymerization liquid from which the coarse solid matter was removed. At this stage, coarse solids such as dissimilar materials (cotton, olefins) other than PET, zippers, buttons, metals, glass, and sand were mainly removed.
Next, the temperature of the colored depolymerization liquid was cooled to 95 ° C., and then hot-filtered with a 10 μm stainless steel long fiber filter (Naslon filter) to remove fine solids such as titanium oxide insoluble in polyester of 10 μm or more. Removed.

<(3) Dye pre-removal process>
Next, the colored depolymerization liquid that had passed through the long fiber filter at 95 ° C. was cooled to 25 ° C. As a result, fine crystals of BHET and polyester oligomer are precipitated as solid content, and a separation plate type (disk type) centrifugal sedimentation type centrifuge is used to prepare the precipitated solid content and MEG and MEG in the depolymerization liquid. The dissolved dye was solid-liquid separated. The conditions of the centrifuge were a centrifugal force of 4,000 G and a centrifuge time of 30 minutes.
The ratio of MEG containing the dye separated by the centrifuge was 52% by mass with respect to the entire colored depolymerization liquid, and the amount of nitrogen atoms remaining in the solid content was 465 ppm.

<(4) Concentration step>
Next, the solid content was melted by heating to 125 ° C., and then the liquid was sent to a thin film evaporator. The conditions of the thin film evaporator were that the jacket heating heat medium temperature was 140 ° C. and the pressure inside the evaporator was 400 Pa (3.0 mmHg). As a result, a low boiling point component having a boiling point lower than that of BHET was evaporated and distilled off to obtain a crude BHET concentrated solution. The obtained crude BHET concentrate was a colored viscous liquid.

<(5) Recovery process>
Next, the crude BHET concentrate was sent to a short-stroke thin film evaporator. The conditions of the thin film evaporator were that the jacket heating heat medium temperature was 180 ° C. and the pressure inside the evaporator was 10 Pa (0.08 mmHg). As a result, BHET was evaporated and distilled off from the crude BHET concentrate to recover medium-purity BHET. The amount of nitrogen atoms remaining in the medium-purity BHET was 135 ppm.

<(6) Crystallization separation step>
Next, 1 part by mass of medium-purity BHET and 4 parts by mass of diethylene glycol monohexyl ether (number of carbon atoms: 10) as a decolorizing solvent were put into a 5 L flask and heated until the temperature inside the liquid reached 80 ° C. .. As a result, medium-purity BHET was dissolved in diethylene glycol monohexyl ether to obtain a solution. Then, the solution was allowed to cool naturally to lower the temperature to 20 ° C., and BHET crystals were precipitated.
Next, the BHET crystals precipitated by the Nutche-type solid-liquid separator and the diethylene glycol monohexyl ether were solid-liquid separated to obtain purified BHET-1 containing a residual decolorizing solvent. The amount of nitrogen atoms remaining in the purified BHET-1 was 52 ppm.

Further, purified BHET-1 containing 1 part by mass of the residual decolorizing solvent and 4 parts by mass of diethylene glycol monohexyl ether were put into a 5 L flask, and the same operation as above was carried out to obtain purified BHET-2. .. The amount of nitrogen atoms remaining in the purified BHET-2 was 22 ppm.
Further, in the same manner as described above, purified BHET-3 was obtained again. The amount of nitrogen atoms remaining in the purified BHET-3 was 9.8 ppm.

<(7) Solvent removal step>
Next, the purified BHET-3 containing the residual decolorizing solvent was melted by heating to 125 ° C., and then sent to a thin film evaporator. The conditions of the thin film evaporator were that the jacket heating heat medium temperature was 135 ° C. and the pressure inside the evaporator was 350 Pa (2.6 mmHg). As a result, diethylene glycol monohexyl ether was evaporated and distilled off to obtain high-purity BHET. The obtained high-purity BHET was a colorless and transparent viscous liquid. The amount of nitrogen atoms remaining in the high-purity BHET was 9.2 ppm.

Next, the obtained high-purity BHET was melt-polycondensed according to a conventional method to obtain PET (regenerated PET).

(Example 2)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 1 except that triethylene glycol monobutyl ether (number of carbon atoms: 10) was used instead of diethylene glycol monohexyl ether as the decolorizing solvent.

(Example 3)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 1 except that tripropylene glycol monomethyl ether (number of carbon atoms: 10) was used instead of diethylene glycol monohexyl ether as the decolorizing solvent.

(Example 4)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 1 except that ethylene glycol monohexyl ether (number of carbon atoms: 8) was used instead of diethylene glycol monohexyl ether as the decolorizing solvent.

(Example 5)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 1 except that ethylene glycol monobutyl ether (number of carbon atoms: 6) was used instead of diethylene glycol monohexyl ether as the decolorizing solvent.

(Example 6)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 1 except that triethylene glycol monohexyl ether (number of carbon atoms: 12) was used instead of diethylene glycol monohexyl ether as the decolorizing solvent.

(Example 7)
Except for using a mixed solution of 85 parts by mass of diethylene glycol monomethyl ether (number of carbon atoms: 5) and 15 parts by mass of MEG (number of carbon atoms: 2) instead of diethylene glycol monohexyl ether as the decolorizing solvent. High-purity BHET and regenerated PET were obtained in the same manner as in Example 1.

(Example 8)
As the decolorizing solvent, a mixed solution of 70 parts by mass of diethylene glycol monomethyl ether (number of carbon atoms: 5) and 30 parts by mass of MEG was used instead of diethylene glycol monohexyl ether in the same manner as in Example 1. High-purity BHET and regenerated PET were obtained.

(Example 9)
Instead of colored clothing waste with a total amount of nitrogen atoms of 1,150 ppm, using colored clothing waste with a total amount of nitrogen atoms of 850 ppm as a raw material, instead of 4 parts by mass of diethylene glycol monohexyl ether, 6.5 mass High-purity BHET and regenerated PET were obtained in the same manner as in Example 1 except that the dye pre-removal step (3) was omitted by using the MEG of the part as a decolorizing solvent.

(Example 10)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 9 except that diethylene glycol (number of carbon atoms: 4) was used instead of MEG as the decolorizing solvent.

(Example 11)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 9 except that triethylene glycol (number of carbon atoms: 6) was used as the decolorizing solvent instead of MEG.

(Example 12)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 1 except that ethylene glycol dimethyl ether (number of carbon atoms: 4) was used instead of diethylene glycol monohexyl ether as the decolorizing solvent.

(Example 13)
High-purity BHET and regenerated PET were obtained in the same manner as in Example 1 except that ethylene glycol monomethyl ether (number of carbon atoms: 3) was used instead of diethylene glycol monohexyl ether as the decolorizing solvent.

(Comparative Example 1)
First, before depolymerization, colored clothing waste in the form of clothing was decolorized using diethylene glycol monohexyl ether (carbon atoms: 10) as a decolorizing solvent. As a result, the decolorizing solvent remained in the decolorized clothing waste in a state of being infiltrated.
Next, when the clothing waste in the state where the decolorizing solvent remained was depolymerized using MEG, the residual ether was bonded to the benzene ring instead of MEG, and a side reaction product other than BHET was produced.
In the test results of the present inventors, it was confirmed that the yield of BHET was deteriorated by about 10 to 12% by mass due to the formation of by-products, as compared with the method of the example (decolorization after depolymerization). Further, in order to avoid a decrease in the yield of BHET, it is necessary to wash with MEG of about 20 to 25 times the mass of the colored clothing waste, and it has been found that it is not cost effective.
The yield (%) of BHET was calculated by the mass of the produced crude BHET ÷ (mass of colored clothing waste × (254/192)) × 100.

(Comparative Example 2)
High-purity BHET and regeneration were carried out in the same manner as in Example 1 except that 6.5 parts by mass of MEG was used as a decolorizing solvent instead of 4 parts by mass of diethylene glycol monohexyl ether and the recovery step (5) was omitted. Obtained PET.

2. Measurement 2-1. Measurement of the amount of nitrogen atoms The amount of nitrogen atoms remaining in colored clothing waste, solid matter after color pre-removal, medium-purity BHET, purified BHET-1 to 3, and high-purity BHET is a trace total nitrogen analyzer (each). It was measured with "TN-2100H" manufactured by Mitsubishi Chemical Analytech Co., Ltd.).
2-2. Measurement of color b value The color b value of the reproduced PET was measured with a color difference meter (manufactured by Nippon Denshoku Co., Ltd., "SE-7700").

The above results are summarized in Table 1.

Claims (15)

A dye-colored polyester waste is mixed with monoethylene glycol and a depolymerization catalyst, and the polyester waste is depolymerized to obtain a depolymerized product containing colored crude bis- (2-hydroxyethyl) terephthalate. Depolymerization process to obtain and
After precipitating the solid content by cooling the depolymerized product, the solid content is centrifuged to separate the solid content from the dye, and the dye pre-removal removes a part of the dye from the depolymerized product. Process and
A concentration step of removing the low boiling point component containing monoethylene glycol from the depolymerized product from which a part of the dye has been removed to concentrate the crude bis- (2-hydroxyethyl) terephthalate.
It is recovered from the concentrated crude bis- (2-hydroxyethyl) terephthalate by evaporating the bis- (2-hydroxyethyl) terephthalate, and has a higher purity than the crude bis- (2-hydroxyethyl) terephthalate. Recovery step to obtain medium-purity bis- (2-hydroxyethyl) terephthalate,
By cooling the solution prepared by dissolving the medium-purity bis- (2-hydroxyethyl) terephthalate in a decolorizing solvent containing a glycol-based compound, the crystals of the bis- (2-hydroxyethyl) terephthalate are precipitated and the above-mentioned A crystallization separation step of solid-liquid separating the crystal and the solvent component containing the dye to obtain purified bis- (2-hydroxyethyl) terephthalate having a higher purity than the medium-purity bis- (2-hydroxyethyl) terephthalate. ,
The solvent removal step of removing the solvent component remaining in the crystal to obtain a high-purity bis- (2-hydroxyethyl) terephthalate having a higher purity than the purified bis- (2-hydroxyethyl) terephthalate, and so on. A method for producing a high-purity bis- (2-hydroxyethyl) terephthalate, which comprises having. The claim that the glycol-based compound contains at least one selected from the group consisting of glycol monoethers or glycol diethers having 4 to 12 carbon atoms and glycols having 2 to 6 carbon atoms. The method for producing a high-purity bis- (2-hydroxyethyl) terephthalate according to 1. The method for producing a high-purity bis- (2-hydroxyethyl) terephthalate according to claim 1 or 2, wherein the content of the glycol-based compound in the decolorizing solvent used in the crystallization separation step is 85% by mass or more. .. The dye has a chromophore containing a nitrogen atom and has a chromophore.
The high-purity bis- (2-hydroxyethyl) according to any one of claims 1 to 3, wherein the amount of the nitrogen atom remaining in the high-purity bis- (2-hydroxyethyl) terephthalate is 20 ppm or less. How to make terephthalate. The method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to any one of claims 1 to 4, wherein the polyester waste contains 65% by mass or more of polyethylene terephthalate. The method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to any one of claims 1 to 5, wherein the polyester waste is polyester clothing waste. The method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to claim 6, wherein in the depolymerization step, the polyester clothing waste is depolymerized in the form of clothing. The high-purity screw according to claim 6 or 7, further comprising a solid matter removing step of removing solids contained in the polyester clothing waste and insoluble in polyester from the depolymerized product after the depolymerization step. A method for producing (2-hydroxyethyl) terephthalate. The dye has a chromophore containing a nitrogen atom and has a chromophore.
The high-purity bis- (2-hydroxyethyl) according to any one of claims 1 to 8, wherein the dye pre-removal step is carried out until the amount of the nitrogen atoms remaining in the depolymerization becomes 900 ppm or less. ) Manufacturing method of terephthalate. A step of obtaining high-purity bis- (2-hydroxyethyl) terephthalate by the method for producing high-purity bis- (2-hydroxyethyl) terephthalate according to any one of claims 1 to 9.
A method for producing regenerated polyethylene terephthalate , which comprises a step of obtaining regenerated polyethylene terephthalate by polycondensing the high-purity bis- (2-hydroxyethyl) terephthalate . The method for producing regenerated polyethylene terephthalate according to claim 10, wherein the regenerated polyethylene terephthalate contains 50% by mass or more of a structure derived from the high-purity bis- (2-hydroxyethyl) terephthalate. A decolorizing solvent used to remove and decolorize the dye from bis- (2-hydroxyethyl) terephthalate colored with the dye.
It is characterized by containing at least one glycol-based compound selected from the group consisting of glycol monoethers or glycol diethers having 4 to 12 carbon atoms and glycols having 3 to 6 carbon atoms. Decolorizing solvent. The decolorizing solvent according to claim 12, wherein the content of the glycol-based compound in the decolorizing solvent is 85% by mass or more. By cooling a solution prepared by dissolving bis- (2-hydroxyethyl) terephthalate colored with a dye in a decolorizing solvent, crystals of the bis- (2-hydroxyethyl) terephthalate are precipitated, and the crystals and the dye are formed. This is a method for purifying the bis- (2-hydroxyethyl) terephthalate by solid-liquid separation from the solvent component containing the above.
The decolorizing solvent contains at least one glycol-based compound selected from the group consisting of glycol monoethers or glycol diethers having 4 to 12 carbon atoms and glycols having 3 to 6 carbon atoms. A method for purifying bis- (2-hydroxyethyl) terephthalate. The method for purifying bis- (2-hydroxyethyl) terephthalate according to claim 14, wherein the content of the glycol-based compound in the decolorizing solvent is 85% by mass or more.

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