JP2022022286A - Method for producing bis-(2-hydroxyethyl)terephthalate and method for producing recycled polyethylene terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing bis-(2-hydroxyethyl)terephthalate (BHET), the method allowing simple production of a BHET with high purity from a colored polyester waste.

SOLUTION: A method for producing a BHET according to the present invention comprises: a depolymerization step for mixing a polyester waste colored by a pigment, with a monoethylene glycol and a depolymerization catalyst, and depolymerizing the polyester waste to obtain a depolymerization product containing a crude colored BHET; a pigment decomposition and removal step for adding a pigment decomposition agent to the depolymerization product and cooling and centrifuging the resultant mixture, thereby separating extracted solids and a decomposition product of the pigment and removing at least a portion of the decomposition product from the depolymerization product; a concentration step for removing a low boiling-point component containing monoethylene glycol from the depolymerization product from which at least a portion of the decomposition product has been removed, and concentrating the crude BHET; and a collection step for collecting, by distillation, BHET from the concentrated crude BHET to obtain a BHET having higher purity than the crude BHET.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

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 colored PET bottle waste), and a method for producing high-purity bis- (2-hydroxyethyl) terephthalate. The present invention relates to a method for producing a regenerated polyethylene terephthalate using such bis- (2-hydroxyethyl) terephthalate.

Polyester (for example, polyethylene terephthalate) is widely used as clothing, films, PET bottles, resin molded products and the like 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 is a big issue not only from the aspect of the above, but also from the environmental problem. As these treatment methods, material recycling, thermal recycling, chemical recycling and the like have been studied and proposed.

Of these, in material recycling, waste of polyester molded products such as used transparent PET bottles is collected mainly by local governments and actively reused. Further, regarding the yarn fiber waste, the material is recycled by a method such as processing into a large pellet-like material called popcorn, then remelting and regenerating into the yarn fiber. However, it is extremely difficult to apply the material recycling method for clothing and colored PET bottles, 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 subjected to polycondensation 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 used transparent PET bottles, resin scraps, and film scraps that are not colored and have few impurities.

It is an essential condition to remove coloring dyes such as dyes and pigments in order to recycle polyester using polyester waste colored with a dye as a recycled raw material, and then to regenerate the polyester again through a raw material monomer. 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 yellowing).
In addition, polyester clothing waste includes various stabilizers, antistatic agents, easy dyeing agents, flame retardant agents, hygroscopic agents, gas barrier agents, etc., which are used for the purpose of satisfying the required characteristics according to the clothing application. 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, 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 the colored fibrous polyester, and then the recycled polyester is obtained again via DMT, which is 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 have a long recycling process and require a large amount of energy, and thus have 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 colored polyester clothing waste and colored PET bottle waste), and to remove bis- (2). Provided are a method for producing bis- (2-hydroxyethyl) terephthalate capable of easily producing -hydroxyethyl) terephthalate, and a method for producing regenerated polyethylene terephthalate produced from such bis- (2-hydroxyethyl) terephthalate as a raw material. To do.

Such an object is achieved by the present invention of the following (1) to (14).
(1) A solution containing a colored crude bis- (2-hydroxyethyl) terephthalate by mixing polyester waste colored with a dye, monoethylene glycol and a depolymerization catalyst, and depolymerizing the polyester waste. The depolymerization process to obtain the polymer and
By adding a dye-decomposing agent to the depolymerization, cooling the mixture, and centrifuging, the precipitated solid content and the decomposition product of the dye are separated, and at least a part of the decomposition product is separated from the depolymerization product. The dye decomposition removal process to remove and
A concentration step of removing the low boiling point component containing monoethylene glycol from the depolymerized product from which at least a part of the decomposition product has been removed to concentrate the crude bis- (2-hydroxyethyl) terephthalate.
The bis- (2-hydroxyethyl) terephthalate is recovered from the concentrated crude bis- (2-hydroxyethyl) terephthalate by distillation, and the bis- has a higher purity than the crude bis- (2-hydroxyethyl) terephthalate. A method for producing a bis- (2-hydroxyethyl) terephthalate, which comprises a recovery step for obtaining (2-hydroxyethyl) terephthalate.

(2) The bis- (2-hydroxyethyl) according to (1) above, wherein the dye-decomposing agent contains at least one of ozone, hydrogen peroxide, concentrated sulfuric acid, an oxygen-based oxidizing agent and a chlorine-based oxidizing agent. ) How to manufacture terephthalate.
(3) The method for producing a bis- (2-hydroxyethyl) terephthalate according to (1) or (2) above, wherein the dye-decomposing agent is added until the depolymerized product is centrifuged.
(4) The amount of the ester component other than the bis- (2-hydroxyethyl) terephthalate remaining in the bis- (2-hydroxyethyl) terephthalate is 2.5% by mass or less, and the bis- (2-hydroxyethyl) terephthalate. The method for producing a bis- (2-hydroxyethyl) terephthalate according to any one of (1) to (3) above, wherein the color b value of the hydroxyethyl) terephthalate is 0 or less.

(5) The method for producing 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 bis- (2-hydroxyethyl) terephthalate according to any one of (1) to (5) above, wherein the polyester waste is polyester clothing waste or PET bottle waste.
(7) The method for producing 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 solids contained in the polyester clothing waste and insoluble in polyester from the depolymerized product after the depolymerization step. The method for producing a bis- (2-hydroxyethyl) terephthalate according to the above method.

(9) The dye has a chromophore containing a nitrogen atom and has a chromophore.
The bis- (2-hydroxy) according to any one of (1) to (8) above, wherein the dye decomposition removal step is carried out until the amount of the nitrogen atom remaining in the depolymerization becomes 900 ppm or less. Ethyl) A method for producing terephthalate.
(10) After the recovery step, the solution of the bis- (2-hydroxyethyl) terephthalate dissolved in a solvent is cooled to precipitate crystals of the bis- (2-hydroxyethyl) terephthalate. It has a crystallization purification step of solid-liquid separating the crystal and a solvent component containing an ester component other than the bis- (2-hydroxyethyl) terephthalate to increase the purity of the bis- (2-hydroxyethyl) terephthalate. The method for producing a bis- (2-hydroxyethyl) terephthalate according to any one of (1) to (9) above.

(11) The solvent contains water and / or a glycol-based compound.
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 above). 10) The method for producing a bis- (2-hydroxyethyl) terephthalate according to 10).
(12) The amount of the ester component remaining in the bis- (2-hydroxyethyl) terephthalate after the crystallization purification step is 1% by mass or less, and the purified bis- (12) after the crystallization purification step. The method for producing a bis- (2-hydroxyethyl) terephthalate according to (10) or (11) above, wherein the color b value of 2-hydroxyethyl) terephthalate is -1 or less.

(13) The step of obtaining the bis- (2-hydroxyethyl) terephthalate by the method for producing bis- (2-hydroxyethyl) terephthalate according to any one of (1) to (12) above.
A method for producing regenerated polyethylene terephthalate, which comprises a step of obtaining regenerated polyethylene terephthalate by polycondensing the bis- (2-hydroxyethyl) terephthalate.
(14) The method for producing regenerated polyethylene terephthalate according to (13) above, wherein the regenerated polyethylene terephthalate contains 50% by mass or more of a structure derived from the bis- (2-hydroxyethyl) terephthalate.

According to the present invention, dyes, pigments and other pigments are efficiently decomposed and removed from colored polyester waste (particularly, colored polyester clothing waste and colored PET bottle waste) to achieve high purity. Bis- (2-hydroxyethyl) terephthalate (BHET) can be easily produced. 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 sustainable closed loops using recycled polyester as polyester clothing waste, which can greatly contribute to the construction of a sound material-cycle society.
Further, the highly pure recycled BHET produced 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 bis- (2-hydroxyethyl) terephthalate of the present invention.

Hereinafter, the method for producing bis- (2-hydroxyethyl) terephthalate and the method for producing regenerated polyethylene terephthalate of the present invention will be described in detail based on the preferred embodiments shown in the illustration.
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 recognized separately from others, but a process that is combined with other operations, a process that is dispersed in a plurality of practical processes, and 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 performed in combination in one process are in line with the gist of the invention, they may belong to the category of the present invention.

FIG. 1 is a flowchart showing a preferred embodiment of the method for producing a bis- (2-hydroxyethyl) terephthalate of the present invention.
The method for producing bis- (2-hydroxyethyl) terephthalate (BHET) of the present invention comprises various colored polyester wastes such as clothing, PET bottles, films, and resin molded products (hereinafter, "colored polyester wastes"). It can also be applied to). 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 BHET of the present embodiment includes (1) depolymerization step, (2) solid matter removal step, (3) dye decomposition removal step, (4) concentration step, and (5) recovery step. (6) It has a crystallization purification 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 the polyester constituting the polyester clothing include polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), and polybutylene naphthalate (PBN). And so on.

As the polyester garment targeted in the present invention, garments mainly composed of polyethylene terephthalate (PET) fibers are suitable.
Such polyester garments may contain different materials such as nylon, urethane, cotton and olefins, and are used as stabilizers, antistatic agents, easy dyeing 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 solid substances 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 more 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 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 vat dye, and the like, and a disperse dye is preferable. This disperse dye is most suitable for coloring polyester because it binds to polyester by intermolecular force. Further, according to the study of the present inventor, it has been found that the use of the present invention for decomposing and 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 as 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 large 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 clothing 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 performed with the polyester clothing waste completely immersed in the MEG. Is preferable.
The bulk density of the polyester fiber is 0.10 to 0.14 g / cm ³ (without compression) in the form of clothing and 0.08 to 0.10 g / cm ³ (without compression) in the form of flakes. That is, the polyester fiber can maintain a larger 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 perform 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 points) 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, alkoxides of transition metals, etc. One of these or two or more of them can be used in combination. 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), and therefore, 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 solids such as sand mixed during waste collection.
These foreign substances can be collectively removed from the depolymerization solution by filtering with a coarse filter having an opening of about 20 to 40 mesh.

Further, titanium oxide, which is insoluble in polyester, may be added to the 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 deposit inside the container or the inside of the pipe in the process to block the flow of the 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) Pigment decomposition removal step Further, the colored polyester clothing waste is colored with a dye such as a dye or a pigment. The dye decomposition removal step is performed in order to further increase the purity of the finally obtained BHET when the degree of coloring of the colored polyester clothing waste is large.
In the following, as the dye, the most suitable disperse dye for coloring polyester will be described as a representative.
Colored Polyester It is known that when a disperse dye contained in clothing waste is mixed with a recycled polyester, the recycled polyester is colored and the yellowness is particularly liable to increase. Therefore, when producing BHET from colored polyester clothing waste, it is preferable to pre-decompose and remove the disperse dye contained in the colored polyester clothing waste with a dye-decomposing agent.

As a result of diligent studies on a method for effectively removing the dye, the present inventors added a dye decomposition agent to the colored depolymerization solution obtained in the above (1) depolymerization step, and colored polyester clothing waste. It was found that BHET with higher purity can be obtained by decomposing and removing the disperse dye contained in the above and performing the treatments in each step described later.
The dye decomposition is performed, for example, by containing at least one of ozone, hydrogen peroxide, concentrated sulfuric acid, an oxygen-based oxidizing agent and a chlorine-based oxidizing agent in the colored depolymerization solution after the above-mentioned depolymerization step. It can be preferably carried out by oxidative decomposition to which an agent is added. Among them, a dye-decomposing agent containing a chlorine-based oxidizing agent is preferable because the dye has excellent resolution, is inexpensive, and is easily available.

Examples of the oxygen-based oxidizing agent include hydrogen persulfate, persulfate, percarbonate, perborate, tetraacetylethylenediamine and the like.
Specific examples of the hydrogen persulfate include alkali metal salts such as lithium salt, sodium salt and potassium salt, alkaline earth metal salts such as barium salt, ammonium salts and hydrates thereof. The hydrogen persulfate may be a hydrogen sulfate or a double salt with a sulfate.
Specific examples of the persulfate include alkali metal salts such as sodium salts and potassium salts, ammonium salts, hydrates thereof and the like.
Specific examples of the percarbonate include sodium salts, alkali metal salts such as potassium salts, ammonium salts, hydrates thereof and the like.
Specific examples of perboric acid include sodium salts, alkali metal salts such as potassium salts, ammonium salts, hydrates thereof and the like.

Examples of the chlorine-based oxidizing agent include chloroamine compounds, chlorates, chlorinated isocyanuric acids, trisodium chloride phosphate, chlorine dioxide and the like.
Specific examples of the chloroamine compounds include chloramine B (N-chlorobenzenesulfonamide sodium), dichloramine B (N, N'-dichlorobenzenesulfonamide), chloramine T (N-chloro-P-toluenesulfonamide sodium), and dichloramine. Examples thereof include T (N, N'-dichloro-P-toluenesulfonamide).
Specific examples of chlorates include sodium chlorate, potassium chlorate, lithium chlorate, ammonium chlorate, calcium chlorate, sodium hypochlorite, potassium hypochlorate, calcium hypochlorate, and chloric acid. Sodium, disodium chlorate, potassium perchlorate, rubidium perchlorate, cesium perchlorate, tetraalkylammonium, ammonium perchlorate, potassium perchlorate, calcium perchlorate, silver perchlorate, perchloric acid Examples thereof include sodium and magnesium perchlorate.
Specific examples of chlorinated isocyanuric acids include chlorinated isocyanuric acid, chlorinated sodium isocyanuric acid, chlorinated potassium isocyanuric acid, dichloroisocyanuric acid, dichloroisocyanuric acid sodium, dichloroisocyanuric acid potassium, trichloroisocyanuric acid, trichloroisocyanuric acid, and so on. Examples thereof include potassium trichloroisocyanurate.

It is preferable to add the dye-decomposing agent before centrifuging the colored depolymerization solution described later. For example, the addition of the dye-decomposing agent can be performed before, after, or both of cooling the colored depolymerization solution to precipitate the solid content.
The amount of the dye-decomposing agent added is preferably 10 parts by mass or less with respect to 100 parts by mass of BHET contained in the colored depolymerization solution, and may be 5 parts by mass or less or 2 parts by mass or less. On the other hand, the lower limit of the amount of the dye-degrading agent added is appropriately set according to the type of the dye and the dye-decomposing agent, and is not particularly limited, but is usually preferably 0.5 parts by mass or more.
The amount of BHET contained in the colored depolymerization liquid is calculated by the mass of the colored polyester clothing waste × 254/192 × 100.
By adding the dye-decomposing agent in the above range, the amount of the dispersed dye generally contained in the colored polyester clothing waste becomes an appropriate amount for oxidative decomposition, which is advantageous in terms of cost.

Here, the disperse dye (many dyes) is overwhelmingly a compound having a chromophore containing a nitrogen atom, and when the disperse dye contained in the colored polyester clothing waste is mixed in the regenerated polyester, the regenerated polyester is colored. However, it is known that the yellowness is particularly likely to increase.
As described above, even after the dye (dispersion dye) is oxidatively decomposed, nitrogen atoms derived from the disperse dye remain in the decomposition product of the dye (hereinafter, also referred to as “dye decomposition product”).
As one of the methods for confirming the degree of removal of nitrogen atoms derived from the disperse dye, a method for measuring the amount of nitrogen atoms remaining in the depolymerization solution (depolymerization) or BHET (N residual amount) is used. be able to.

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

The removal of the dye decomposition product can be carried out, 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. to precipitate fine crystals of BHET or the polyester oligomer 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-decomposed product dissolved in the MEG can be solid-liquid separated. By the above operation, a solid content (solid depolymerization) of BHET or a 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.
If the amount of nitrogen atoms derived from the dye contained in the polyester clothing waste is 900 ppm or less, this step (dye decomposition removal step) may be omitted, but this step is to remove the dye decomposition product. It is preferable to carry out.

The operation of cooling the depolymerization liquid to precipitate BHET and the 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, solid content crystals obtained by the crystallization operation are present. The shape is extremely poor, and the crystal size becomes a very small fine crystal.
Therefore, in a generally known crystal filtration separator or centrifugal filtration type crystal separator, solid-liquid separation between a crystal and a liquid component tends to be complicated, but if a centrifugal sedimentation type centrifuge is used, small fine crystals are used. The solid-liquid separation between the liquid component and the liquid component can also be easily performed.

It is preferable that the MEG separated by the centrifugal sedimentation type centrifuge is purified (recovered) by an evaporation operation, a distillation operation, or the like and reused.
On the other hand, it is preferable that the dye component for coloring (dye, its decomposition product or chromophore) is concentrated as an evaporation residue and a distillation can residue and treated as industrial waste.
Further, in this step, only a part of the dye decomposition product may be removed, or all of the dye decomposition product may be removed (that is, the residual amount of N may be below the detection limit).

(4) Concentration Step Next, the solid substance 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 solution 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 concentrate. Here, examples of the low boiling point component mainly include MEG and DEG. In addition, impurities such as dye component, polyamide component, polyurethane component, polyester copolymer component, and ultrafine titanium oxide of less than 5 μm that could not be removed in the solid matter removing step (2) remain in this crude BHET concentrate. May be.

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 (type) 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 BHET concentration containing BHET and a polyester oligomer as main components and, in some cases, impurities such as a residual 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 liquid to obtain BHET having a higher purity than the crude BHET concentrate.
The recovery of BHET can be preferably carried out by distillation, preferably distillation under vacuum (vacuum) (hereinafter, also referred to as “vacuum distillation”). In this case, BHET is overwhelmingly the component to be distilled, but an organic compound having a boiling point such as a trace amount of dye component, polyester oligomer component, polyamide component, polyurethane component, polyester copolymer component, etc. together with BHET (hereinafter, "" Also referred to as "organic compound having a boiling point") may also be distilled off.

The amount of distillate of the organic compound having a boiling point is determined by the temperature, pressure (vacuum degree) in the operation of distillation 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 organic compounds having a boiling point, dye components (dispersed dyes, etc.) have the property of sublimating at a temperature lower than the boiling point, so nitrogen atoms remaining in the crude BHET concentrate supplied in this step (5). If the dye component is removed until the amount of the dye is 900 ppm or less, the problem that a large amount of the dye component is mixed in the BHET obtained in the present step (5) can be avoided.

When the distillation of BHET performed in this step (5) is performed by simple distillation, this simple distillation 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 the case of simple distillation, in order to reduce the sublimation amount of the dye component as much as possible and ensure the required quality of BHET, it is necessary to lower the temperature and pressure of the thin film evaporator, which is inevitable. The production amount (recovery amount) tends to decrease due to the decrease in the evaporation amount.
In order to improve this, it is preferable to employ distillation with recirculation (rectification) for distillation. Distillation with recirculation can easily satisfy the required quality of BHET by selecting an appropriate reflux ratio.

As for the quality of BHET obtained in this step (5), the amount of ester components other than BHET remaining in BHET (hereinafter, also referred to as “other ester components”) is 2.5% by mass or less (preferably). 2% by mass or less), and the color b value of BHET is preferably 0 or less (preferably −0.5 or less).
Here, examples of other ester components include mono- (2-hydroxyethyl) terephthalate (MHET), diethylene glycol ester, polyester dimer, polyester oligomer and the like. It should be noted that these components are incorporated into the obtained recycled polyethylene terephthalate when the recycled polyethylene terephthalate is produced.

In the present specification, the value (area%) obtained as follows is adopted as the amount of other ester components remaining in BHET. That is, first, the obtained BHET is dissolved (diluted) in an appropriate solvent to prepare a sample for analysis. This analytical sample was analyzed using a high performance liquid chromatography device (for example, "LC-2010AHT" manufactured by Shimadzu Corporation), and the obtained chart was used to determine the peak area A derived from BHET and other ester components. Calculate the area B of the peak from which it is derived. Then, the ratio of the area B to the total of the area A and the area B is obtained as a 100% ratio (B / A + B × 100).
If BHET satisfying the above-mentioned quality is used as a raw material, the color b value (yellowness) of the regenerated polyethylene terephthalate produced by polycondensation (molten polycondensation) can be 8 or less, which is comparable to that of virgin polyethylene terephthalate. Regenerated polyethylene terephthalate having a color b value can be produced.

BHET is recovered from the crude BHET (crude BHET concentrate) by distillation to obtain BHET. Organic compounds having a boiling point that could not be completely evaporated and solids such as titanium oxide having no 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 and Purification Step If BHET as described above is used as a raw material, it is possible to produce regenerated polyethylene terephthalate having a color b value comparable to that of virgin polyethylene terephthalate. For example, BHET is used as a raw material for reagents and the like. In that case, it is preferable to increase the purity of BHET.
As a result of diligent studies on a method for increasing the purity of BHET obtained in the above recovery step (5), the present inventors have also found that the following method is suitable.

That is, a solvent having a high ability (solubility) to dissolve a dye, a decomposition product thereof, a chromophore, other ester components remaining in BHET, and other substances to be purified such as an organic compound having a boiling point (hereinafter, "crystallization"). By cooling the solution in which BHET is dissolved in the crystallization solvent, BHET crystals are precipitated, and the crystals and the chromophore solvent component containing the removed product to be purified are separated by using (also referred to as “solvent”). It is preferable to perform a solid-liquid separation operation (hereinafter, also referred to as “crystallization purification operation”). In other words, the method for producing BHET of the present invention preferably includes a crystallization purification step after the recovery step.
Further, in the case of crystallization purification, by adjusting the mixing ratio of BHET and the crystallization solvent according to the type of the crystallization solvent, the removed product to be purified can be removed more efficiently.

From the results of the solubility test on the removed product to be purified carried out by the present inventors, it was found that a solvent containing water and / or a glycol-based compound is suitable as the crystallization 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 the glycol monoether include, for example, 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, for example, 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 (monoethylene glycol), diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, and 1,4-butanediol. , Neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, cyclohexanediol and the like.

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 the glycol is preferably 2 to 6.
That is, the crystallization solvent is at least one glycol selected from the group consisting of water, glycol monoethers or glycol diethers having 4 to 12 carbon atoms, and glycols having 2 to 6 carbon atoms. It is preferable to contain a system compound. By using a solvent containing water and / or a glycol-based compound as the crystallization solvent, the effect of removing the removed product to be purified remaining in BHET can be further enhanced.
Among these, a crystallization solvent containing glycol monoether is more preferable from the viewpoint of high ability to remove the removed product to be purified.

When water is used, the content of water in the crystallization solvent is preferably 100% by mass. When a glycol-based compound is used, the content of the glycol-based compound in the crystallization solvent is preferably 85% by mass or more, more preferably 90% by mass or more, and 95% by mass or more. Is even more preferable. The upper limit of the content of the glycol-based compound in the crystallization solvent is 100% by mass. A crystallization solvent containing a glycol-based compound in such an amount exhibits an extremely good ability to remove a substance to be purified. Further, such a crystallization solvent is preferable because the dye component can also be dissolved.
Regarding the cooling temperature of the solution, it is preferable that the cooling temperature is low from the viewpoint of reducing the amount of BHET dissolved in the crystallization 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 crystallization 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.

As for the quality of the BHET (hereinafter, also referred to as “purified BHET”) obtained in this step (6), the amount of other ester components remaining in the BHET is 1% by mass or less (preferably 0.5% by mass). The color b value of the purified BET is -1 or less (preferably −1.5 or less).
The number of times the crystallization purification operation is performed is not particularly limited, but if the quality of the purified BHET obtained in the first operation does not reach the above quality, it is preferable to perform the crystallization purification operation again.
According to the present inventors, it has been confirmed that the quality of the purified BHET reaches the above-mentioned quality regardless of the degree of coloring if the crystallization purification operation is performed at least three times.

It is preferable that the crystallization solvent containing the removed product to be purified, which has been solid-liquid separated by the crystallization purification operation, is purified by an evaporation operation, a distillation operation, or the like and reused.
On the other hand, it is preferable that the removed product to be purified is recovered as an evaporation residue and a distillation can residue and treated as industrial waste.
In the present step (6) as described above, the method for purifying BHET of the present embodiment is carried out.

The BHET obtained in the molten state may be polycondensed (molten polycondensed) as it is to produce regenerated polyethylene terephthalate (regenerated PET), or the BHET obtained in the molten state may be once granulated and then polycondensed (melted). Regenerated PET may be produced by polycondensation). That is, the method for producing recycled PET of the present invention includes a step of obtaining BHET by the above-mentioned manufacturing method of BHET and a step of obtaining recycled PET by polycondensing BHET. Therefore, the obtained regenerated PET is a polycondensate of BHET.
When producing recycled PET by polycondensation, recycled PET can be easily produced by mixing 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 or more of the structure derived from BHET in the recycled PET. It is more preferable to contain it.

Although the method for producing BHET and the method for producing recycled PET of the present invention have been described above, the present invention is not limited thereto.
For example, the method for producing BHET and the method for producing recycled PET of the present invention may be replaced with any step in which the same effect is exhibited, or any desired step 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, as the colored polyester waste applicable to the present invention, colored PET bottle waste is also preferable. In the case of colored PET bottle waste, for example, it is pulverized and then subjected to a depolymerization step. Further, the treatment conditions can be set in the same manner as in the case of colored polyester clothing waste.

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 Distilled BHET, Purified BHET and Recycled PET from Colored Polyester Clothing Waste (Example 1)
<(1) Depolymerization step>
First, a total of 400 g of PET clothing waste (hereinafter, also referred to as "colored clothing waste") 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 preheated 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.
The amount (g) of BHET in the depolymerization liquid was calculated by the mass of colored clothing waste (400 g) × 254/192 × 100.

<(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 solution was cooled to 95 ° C., and the mixture was 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 decomposition removal step>
Next, 176.4 g (hydrogen peroxide: 52.9 g) of hydrogen peroxide solution having a concentration of 30% by mass was added to the colored depolymerization solution at 95 ° C. as a dye-decomposing agent, and the mixture was stirred for 30 minutes.
Next, the colored depolymerization solution containing the dye decomposition product 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 solution. The dissolved dye decomposition product was separated into solid and liquid. 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 decomposition product separated by the centrifuge was 56% by mass with respect to the entire colored depolymerization solution, and the amount of nitrogen atoms remaining in the solid content was 425 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 concentrate. 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 simply distilled from the crude BHET concentrate to recover BHET (hereinafter, also referred to as "single-distilled BHET").
The amount of other ester components remaining in the obtained simple distillation BHET was 3.5% by mass, and the color b value of the simple distillation BHET was 0.9. The amount of nitrogen atoms remaining in the simple distillation BHET (N residual amount) was 40 ppm.

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

(Example 2)
It is also referred to as BHET (hereinafter, “rectified BHET”” in the same manner as in Example 1 except that the simple distillation in the recovery step is changed to distillation accompanied by reflux (reflux ratio: 2.0). ) And regenerated PET.

(Example 3)
The simple distillation BHET and the regenerated PET were prepared in the same manner as in Example 1 except that the temperature of the colored depolymerization solution in the dye decomposition removal step was changed to 25 ° C. and the dye decomposition agent was changed to 53 g of concentrated sulfuric acid having a concentration of 96%. Obtained.

(Example 4)
Distilled BHET and regenerated PET were obtained in the same manner as in Example 3 except that the simple distillation in the recovery step was changed to distillation accompanied by reflux (reflux ratio: 2.0).

(Example 5)
In the same manner as in Example 1, the dye-degrading agent in the dye-decomposing and removing step was simply changed to 441.0 g (sodium hypochlorite: 52.9 g) of a sodium hypochlorite aqueous solution having a concentration of 12% by mass. Distilled BHET and regenerated PET were obtained.

(Example 6)
Distilled BHET and regenerated PET were obtained in the same manner as in Example 5 except that the simple distillation in the recovery step was changed to distillation accompanied by reflux (reflux ratio: 2.0).

(Example 7)
In the same manner as in Example 1, the dye-degrading agent in the dye-decomposing and removing step was simply changed to 441.0 g (calcium hypochlorite: 52.9 g) of a calcium hypochlorite aqueous solution having a concentration of 12% by mass. Distilled BHET and regenerated PET were obtained.

(Example 8)
Distilled BHET and regenerated PET were obtained in the same manner as in Example 7 except that the simple distillation in the recovery step was changed to distillation accompanied by reflux (reflux ratio: 2.0).

(Example 9)
1 part by mass of the simple distillation BHET obtained in Example 1 and 4 parts by mass of diethylene glycol monohexyl ether (carbon atom number: 10) as a crystallization solvent were put into a 5 L flask, and the temperature inside the liquid was 80 ° C. It was heated until it became. As a result, simple distilled 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. to precipitate BHET crystals.

Next, the BHET crystals precipitated by the Nutche-type solid-liquid separator and the diethylene glycol monohexyl ether were solid-liquid separated. That is, a purified BHET was obtained by performing the crystallization purification operation once.
The amount of other ester components remaining in the purified BHET was 0.5% by mass, and the color b value of the purified BHET was −1.5. The amount of nitrogen atoms remaining in the purified BHET (N residual amount) was 9.8 ppm.

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

(Example 10)
Purified BHET and regenerated PET were obtained in the same manner as in Example 9 except that the crystallization solvent was changed to triethylene glycol monobutyl ether (number of carbon atoms: 10).

(Example 11)
Purified BHET and regenerated PET were obtained in the same manner as in Example 9 except that the crystallization solvent was changed to ethylene glycol monohexyl ether (number of carbon atoms: 8).

(Example 12)
Purified BHET and regenerated PET were obtained in the same manner as in Example 9 except that the crystallization solvent was changed to ethylene glycol monobutyl ether (number of carbon atoms: 6).

(Example 13)
Purified BHET and regenerated PET were obtained in the same manner as in Example 9 except that the crystallization solvent was changed to ethylene glycol (number of carbon atoms: 2).

(Example 14)
Purified BHET and regenerated PET were obtained in the same manner as in Example 9 except that the crystallization solvent was changed to diethylene glycol (number of carbon atoms: 4).

(Example 15)
Purified BHET and regeneration were carried out in the same manner as in Example 9 except that the simple distillation BHET obtained in Example 1 was changed to the simple distillation BHET obtained in Example 5 and the crystallization solvent was changed to water. Obtained PET.

(Example 16)
Purified BHET and regenerated PET were obtained in the same manner as in Example 15 except that the simple distillation BHET obtained in Example 5 was changed to the rectified BHET obtained in Example 6.

(Example 17)
Purified BHET and regenerated PET were obtained in the same manner as in Example 15 except that the crystallization solvent was changed to ethylene glycol (number of carbon atoms: 2).

(Example 18)
Purified BHET and regenerated PET were obtained in the same manner as in Example 17 except that the simple distillation BHET obtained in Example 5 was changed to the rectified BHET obtained in Example 6.

(Example 19)
Purified BHET and regenerated PET were obtained in the same manner as in Example 15 except that the crystallization solvent was changed to ethylene glycol monobutyl ether (number of carbon atoms: 6).

(Example 20)
Purified BHET and regenerated PET were obtained in the same manner as in Example 19 except that the simple distillation BHET obtained in Example 5 was changed to the rectified BHET obtained in Example 6.

(Example 21)
In the same manner as in Example 5, the dye-degrading agent in the dye-decomposing and removing step was simply changed to 220.5 g (sodium hypochlorite: 26.5 g) of a sodium hypochlorite aqueous solution having a concentration of 12% by mass. Distilled BHET and regenerated PET were obtained.

(Example 22)
In the dye decomposition removal step, first, the colored depolymerization liquid was cooled to 25 ° C. to precipitate solid content, and then a simple distillation BHET and regenerated PET were obtained in the same manner as in Example 5 except that a dye decomposition agent was added. Got

(Comparative Example 1)
Simple distillation BHET and regenerated PET were obtained in the same manner as in Example 1 except that the dye decomposition removal step was omitted.

(Comparative Example 2)
Purified BHET and regenerated PET were obtained in the same manner as in Example 12 except that the dye decomposition removal step was omitted.

(Comparative Example 3)
Purified BHET and regenerated PET were obtained in the same manner as in Comparative Example 2 except that the crystallization purification operation was performed three times.

2. 2. Measurement 2-1. Measurement of the amount of nitrogen atoms The amount of nitrogen atoms remaining in colored clothing waste, solid matter after dye decomposition and removal, distilled BHET, and purified BHET (N residual amount) is a trace total nitrogen analyzer (Mitsubishi Chemical Analytech). It was measured by "TN-2100H") manufactured by the company.
2-2. Measurement of color b value The color b value of distilled BHET, purified BHET, and recycled PET was measured with a color difference meter (manufactured by Nippon Denshoku Co., Ltd., "SE-7700").
2-3. Measurement of the amount of other ester components The amount of other ester components remaining in the distilled BHET and the purified BHET was measured by a high performance liquid chromatography device (manufactured by Shimadzu Corporation, "LC-2010AHT").

なお、表１および表２中の略語は、以下の通リである。
ＤＥＧＨＥ：ジエチレングリコールモノヘキシルエーテル
ＴＥＧＢＥ：トリエチレングリコールモノブチルエーテル
ＭＥＧＨＥ：エチレングリコールモノヘキシルエーテル
ＭＥＧＢＥ：エチレングリコールモノブチルエーテル
ＭＥＧ ：エチレングリコール
ＤＥＧ ：ジエチレングリコール The above results are summarized in Tables 1 and 2.

The abbreviations in Tables 1 and 2 are as follows.
DEGHE: Diethylene glycol monohexyl ether TEGBE: Triethylene glycol monobutyl ether MEGHE: Ethylene glycol monohexyl ether MEGBE: Ethylene glycol monobutyl ether MEG: Ethylene glycol DEG: Diethylene glycol

From the results in Tables 1 and 2, it can be seen that the examples in which the dye decomposition / removal step was performed can remove the dye more efficiently than the comparative examples in which the dye decomposition / removal step was omitted.
In particular, if a chlorine-based oxidizing agent is used as the dye-decomposing agent, the effect is remarkable. It can be seen that the dye can be removed efficiently.
Further, when ozone or an oxygen-based oxidizing agent is used as the dye-decomposing agent, the same result as described above can be obtained.

Claims (14)

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 a colored crude bis- (2-hydroxyethyl) terephthalate. Depolymerization process to obtain and
By adding a dye-decomposing agent to the depolymerization, cooling the mixture, and centrifuging, the precipitated solid content and the decomposition product of the dye are separated, and at least a part of the decomposition product is separated from the depolymerization product. The dye decomposition removal process to remove and
A concentration step of removing the low boiling point component containing monoethylene glycol from the depolymerized product from which at least a part of the decomposition product has been removed to concentrate the crude bis- (2-hydroxyethyl) terephthalate.
The bis- (2-hydroxyethyl) terephthalate is recovered from the concentrated crude bis- (2-hydroxyethyl) terephthalate by distillation, and the bis- has a higher purity than the crude bis- (2-hydroxyethyl) terephthalate. A method for producing a bis- (2-hydroxyethyl) terephthalate, which comprises a recovery step for obtaining (2-hydroxyethyl) terephthalate. The production of the bis- (2-hydroxyethyl) terephthalate according to claim 1, wherein the dye-decomposing agent contains at least one of ozone, hydrogen peroxide, concentrated sulfuric acid, an oxygen-based oxidizing agent and a chlorine-based oxidizing agent. Method. The method for producing a bis- (2-hydroxyethyl) terephthalate according to claim 1 or 2, wherein the dye-degrading agent is added until the depolymerized product is centrifuged. The amount of the ester component other than the bis- (2-hydroxyethyl) terephthalate remaining in the bis- (2-hydroxyethyl) terephthalate is 2.5% by mass or less, and the bis- (2-hydroxyethyl) The method for producing a bis- (2-hydroxyethyl) terephthalate according to any one of claims 1 to 3, wherein the color b value of the terephthalate is 0 or less. The method for producing 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 bis- (2-hydroxyethyl) terephthalate according to any one of claims 1 to 5, wherein the polyester waste is polyester clothing waste or PET bottle waste. The method for producing 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 screw (2) according to claim 6 or 7, further comprising a solid substance removing step of removing solids contained in the polyester clothing waste and insoluble in polyester from the depolymerized product after the depolymerization step. -Hydroxyethyl) A method for producing a terephthalate. The dye has a chromophore containing a nitrogen atom and has a chromophore.
The bis- (2-hydroxyethyl) terephthalate according to any one of claims 1 to 8, wherein the dye decomposition removal step is carried out until the amount of the nitrogen atom remaining in the depolymerization becomes 900 ppm or less. Manufacturing method. After the recovery step, the solution in which the bis- (2-hydroxyethyl) terephthalate is dissolved in a solvent is further cooled to precipitate the bis- (2-hydroxyethyl) terephthalate crystals and the crystals. Claim 1 having a crystallization purification step of solid-liquid separating the solvent component containing an ester component other than the bis- (2-hydroxyethyl) terephthalate to increase the purity of the bis- (2-hydroxyethyl) terephthalate. The method for producing a bis- (2-hydroxyethyl) terephthalate according to any one of 9 to 9. The solvent comprises water and / or a glycol-based compound.
The glycol-based compound is claimed to contain 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. 10. The method for producing a bis- (2-hydroxyethyl) terephthalate according to 10. The amount of the ester component remaining in the bis- (2-hydroxyethyl) terephthalate after the crystallization purification step is 1% by mass or less, and the purified bis- (2-hydroxy) after the crystallization purification step. The method for producing a bis- (2-hydroxyethyl) terephthalate according to claim 10 or 11, wherein the color b value of ethyl) terephthalate is -1 or less. The step of obtaining the bis- (2-hydroxyethyl) terephthalate by the method for producing bis- (2-hydroxyethyl) terephthalate according to any one of claims 1 to 12.
A method for producing regenerated polyethylene terephthalate, which comprises a step of obtaining regenerated polyethylene terephthalate by polycondensing the bis- (2-hydroxyethyl) terephthalate. The method for producing regenerated polyethylene terephthalate according to claim 13, wherein the regenerated polyethylene terephthalate contains 50% by mass or more of a structure derived from the bis- (2-hydroxyethyl) terephthalate.

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