METHOD FOR PRODUCING DECOLORED POLYESTER, DECOLORED POLYESTER, AND DECOLORING AGENT

Abstract

A method for producing a decolorized polyester according to the present invention includes: a step of preparing a polyester colored with a colorant, and a decolorizing agent containing a glycol ether-type compound having a boiling point at atmospheric pressure of 160° C. or higher; and a step of removing the colorant, by bringing the decolorizing agent into contact at least once with the colored polyester while heating the decolorizing agent to a temperature equal to or lower than a melting point of the polyester, to thereby obtain the decolorized polyester.

Claims

1-15. (canceled)

16. A method for producing a decolorized polyester, comprising: a step of preparing a polyester colored with a colorant, and a decolorizing agent containing a glycol ether-type compound having a boiling point at atmospheric pressure of 160° C. or higher; and a step of removing the colorant, by bringing the decolorizing agent into contact at least once with the colored polyester while heating the decolorizing agent to a temperature equal to or lower than a melting point of the polyester, to thereby obtain the decolorized polyester.

17. The method for producing a decolorized polyester as claimed in claim 16, wherein the glycol ether-type compound contains a glycol monoether.

18. The method for producing a decolorized polyester as claimed in claim 16, wherein the number of carbon atoms of the glycol ether-type compound is in the range of 5 to 15.

19. The method for producing a decolorized polyester as claimed in claim 16, wherein an amount of the glycol ether-type compound contained in the decolorizing agent is 80 mass % or more.

20. The method for producing a decolorized polyester as claimed in claim 16, wherein a heating temperature of the decolorizing agent is in the range of 160 to 210° C.

21. The method for producing a decolorized polyester as claimed in claim 16, wherein a contact time per once of the heated decolorizing agent with the colored polyester is in the range of 5 to 30 minutes.

22. The method for producing a decolorized polyester as claimed in claim 16, wherein the number of contacts of the heated decolorizing agent with the colored polyester is in the range of 1 to 7 times.

23. The method for producing a decolorized polyester as claimed in claim 16, wherein in each contact of the heated decolorizing agent with the colored polyester, an amount of the heated decolorizing agent brought into contact with 1 part by mass of the colored polyester is in the range of 1 to 10 parts by mass.

24. The method for producing a decolorized polyester as claimed in claim 16, wherein the colorant has a chromophore containing nitrogen atoms, and an amount of the nitrogen atoms contained in the decolorized polyester is 30 ppm or less.

25. The method for producing a decolorized polyester as claimed in claim 16, wherein the polyester contains 65 mass % or more of polyethylene terephthalate.

26. The method for producing a decolorized polyester as claimed in claim 16, wherein the colorant contains a disperse dye.

27. The method for producing a decolorized polyester as claimed in claim 16, wherein the polyester is fibrous or flaky.

28. The method for producing a decolorized polyester as claimed in claim 16, wherein the colored polyester which is fibrous is in the form of clothing.

29. A decolorized polyester obtained by removing a colorant having a chromophore containing nitrogen atoms from a polyester colored with the colorant, wherein an amount of the nitrogen atoms contained in the decolorized polyester is 30 ppm or less.

30. A decolorizing agent used for decolorizing a polyester colored with a colorant by removing the colorant therefrom, wherein the decolorizing agent contains a glycol ether-type compound having a boiling point at atmospheric pressure of 160° C. or higher.

Description

EXAMPLES

[0073] Hereinafter, more detailed description will be made on the present invention with reference to examples thereof. It is to be noted that the present invention is not limited to these examples.

1. Decolorization of Clothing Made of Colored PET Fibers (Polyester Fibers) and Manufacture of Recycled PET

Example 1

[0074] First, 450 g in total of two articles of clothing made of PET fibers colored with a black disperse dye and a blue disperse dye (hereinafter, also referred to as “colored clothing”) was put into a 5 L flask. In this regard, the colored clothing was uncut, a bulk density thereof was 0.12 g/cm.sup.3, and an amount of nitrogen atoms contained therein was 850 ppm. 2,970 g of a heated decolorizing agent obtained by heating diethylene glycol monohexyl ether (number of carbon atoms: 10) to a temperature of 180° C. as a decolorizing agent was added thereinto, and then a first decolorization operation was performed for 10 minutes without stirring. Thereafter, a solid-liquid separation operation, in which the clothing (clothing after first decolorization operation) was separated from the decolorizing agent containing the dyes through a wire mesh, was performed.

[0075] Next, the clothing with the decolorizing agent used for the first time still maintained on a surface thereof was put into the 5 L flask again. 2,970 g of a new heated decolorizing agent (diethylene glycol monohexyl ether) having a temperature of 180° C. was added thereinto, and then a second decolorization operation was performed for 10 minutes without stirring. Thereafter, a solid-liquid separation operation, in which the clothing (clothing after second decolorization operation) was separated from the decolorizing agent containing the dyes through the wire mesh, was performed.

[0076] Next, a third decolorization operation was performed under the same method and conditions as above. Thereafter, a solid-liquid separation operation, in which the clothing (clothing after third decolorization operation) was separated from the decolorizing agent containing the dyes through the wire mesh, was performed. In this way, the clothing with the decolorizing agent used for the third time still maintained on the surface thereof was collected.

[0077] Next, the decolorized white clothing (hereinafter, also referred to as “decolorized clothing”) was centrifuged to separate the decolorizing agent used for the third time maintained on the surface thereof, to thereby obtain a dry decolorized clothing. It is to be noted that weight loss (mass reduction ratio) of the dry decolorized clothing was 4.8%.

[0078] Further, the residual amount of the nitrogen atoms contained in the dry decolorized clothing was 20 ppm.

[0079] Thereafter, 400 g of the dry decolorized clothing was treated according to a chemical recycling process described below, to obtain bis-2-hydroxyethyl terephthalate (hereinafter, also referred to as “BHET”) which is a PET monomer, and then recycled PET was manufactured.

Depolymerization Reaction Step

[0080] First, 400 g of the dry decolorized clothing was mixed with a mixture of 2,245 g of ethylene glycol (EG) preheated to 195° C. and 1 g of sodium hydroxide as a depolymerization catalyst, and reacted with each other for 5.5 hours at normal pressure without stirring. As a result, a depolymerization solution containing BHET was obtained.

Solid Matter Filtration Step

[0081] Next, the depolymerization solution was hot-filtered through a wire mesh strainer having a mesh opening of 30 mesh, to thereby obtain a solid matter filtration depolymerization solution. In this solid matter filtration step, matters other than PET (fasteners used in clothing, cotton components, plastic components other than PET and the like) were mainly removed.

Depolymerization Solution Concentration Step

[0082] Next, the solid matter filtration depolymerization solution was sent to a thin film evaporator so that excess EG was distilled off under the conditions in which a jacket heat medium temperature was 140° C. and an evaporator internal pressure was 400 Pa (3.0 mmHg). In this way, a concentrated depolymerization solution, in which solid components containing BHET were concentrated, was obtained.

BHET Evaporation Purification Step

[0083] Next, the concentrated depolymerization solution was sent to a short-stroke thin film evaporator (manufactured by VTA, Germany), and BHET was evaporated and distilled off under the conditions in which a jacket heat medium temperature was 190° C. and an evaporator internal pressure was 13 Pa (0.1 mmHg). In this way, BHET was collected from the concentrated depolymerization solution. The residual amount of the nitrogen atoms contained in the collected BHET was 16 ppm.

BHET Crystallization Step

[0084] Next, 1 part by weight of BHET and 4 parts by weight of distilled water were put into a 5 L flask, heated until a temperature of the inside liquid had reached 80° C., to thereby dissolve BHET in distilled water. Thereafter, the inside liquid was naturally cooled so that the temperature thereof was lowered to 20° C. In this way, crystals of BHET were precipitated.

Solid-Liquid Separation Step

[0085] Next, a solid-liquid separation operation, in which the precipitated crystals of BHET was separated from the distilled water by a Nutche-type solid-liquid separator was performed, to obtain wet crystallized BHET containing the distilled water. Next, the distilled water was removed from the wet crystallized BHET at a low temperature of 40° C. to dry it. In this way, dry crystallized BHET was obtained. The residual amount of the nitrogen atoms contained in the finally obtained dry crystallized BHET was 6.5 ppm.

[0086] Next, the obtained dry crystallized BHET was subjected to a polycondensation reaction according to a conventional method, to thereby obtain PET (recycled PET).

Example 2

[0087] Dry crystallized BHET and recycled 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 agent.

Example 3

[0088] Dry crystallized BHET and recycled 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 agent.

Example 4

[0089] Dry crystallized BHET and recycled 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 agent.

Example 5

[0090] Dry crystallized BHET and recycled 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 agent, and the heating temperature of the decolorizing agent was changed to 170° C.

Example 6

[0091] Dry crystallized BHET and recycled PET were obtained in the same manner as in Example 1 except that diethylene glycol monomethyl ether (number of carbon atoms: 5) was used instead of diethylene glycol monohexyl ether as the decolorizing agent.

Example 7

[0092] Dry crystallized BHET and recycled 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 agent.

Example 8

[0093] Dry crystallized BHET and recycled PET were obtained in the same manner as in Example 1 except that tetraethylene glycol monoheptyl ether (carbon atom number: 15) was used instead of diethylene glycol monohexyl ether as the decolorizing agent.

Example 9

[0094] Dry crystallized BHET and recycled PET were obtained in the same manner as in Example 1 except that a mixed solution containing 60 parts by mass of ethylene glycol monohexyl ether (number of carbon atoms: 8) and 40 parts by mass of dipropylene glycol monomethyl ether (number of carbon atoms: 8) instead of diethylene glycol monohexyl ether as the decolorizing agent.

Example 10

[0095] Dry crystallized BHET and recycled PET were obtained in the same manner as in Example 1 except that a mixed solution containing 90 parts by mass of diethylene glycol monomethyl ether (number of carbon atoms: 5) and 10 parts by mass of diethylene glycol diethyl ether (number of carbon atoms: 8) was used instead of diethylene glycol monohexyl ether as the decolorizing agent.

Example 11

[0096] Dry crystallized BHET and recycled PET were obtained in the same manner as in Example 1 except that a mixed solution containing 80 parts by mass of ethylene glycol monohexyl ether (number of carbon atoms: 8) and 20 parts by mass of monoethylene glycol (EG) was used instead of diethylene glycol monohexyl ether as the decolorizing agent.

Example 12

[0097] Dry crystallized BHET and recycled PET were obtained in the same manner as in Example 1 except that the heating temperature of the decolorizing agent was 165° C. and the contact time of the heated decolorizing agent with the colored clothing was 20 minutes.

Comparative Example 1

[0098] Dry crystallized BHET and recycled PET were obtained in the same manner as in Example 1 except that monoethylene glycol (number of carbon atoms: 2) was used instead of diethylene glycol monohexyl ether as the decolorizing agent.

Comparative Example 2

[0099] Dry crystallized BHET and recycled PET were obtained in the same manner as in Comparative Example except that the heating temperature of the decolorizing agent was 195° C. and the contact time of the heated decolorizing agent with the colored clothing was 30 minutes.

2. Measurement

2-1. Measurement of Amount of Nitrogen Atoms

[0100] An amount of nitrogen atoms contained in each of the colored clothing, the decolorized clothing and the dry crystallized BHET was measured using a trace total nitrogen analyzer (manufactured by Mitsubishi Chemical Analytech Co., Ltd., “TN-2100H”).

2-2. Measurement of Color b Value

[0101] A color b value of the recycled PET was measured using a color difference meter (manufactured by Nippon Denshoku Co., Ltd., “SE-7700”).

[0102] The above results are summarized in Table 1.

TABLE-US-00001 TABLE 1 Decolorization processing conditions Weight loss Decolorizing agent Teating of dry Residual amount of nitrogen Glycol ether-type compound Other: temp. (° C.) × decolorized atoms (ppm) Color b (number of carbon atoms): parts by Contact time clothing Dry decolorized Dry crystallized value of parts by mass mass (minutes) (%) clothing BHET recycled PET Ex. 1 Diethylene glycol monohexyl ether — 180 × 10 4.8 20 6.5 6.0 (10):100 Ex. 2 Triethylene glycol monobutyl ether — 180 × 10 6.1 18 6.0 5.4 (10):100 Ex. 3 Tripropylene glycol monomethyl ether — 180 × 10 5.4 24 10.5 7.2 (10):100 Ex. 4 Ethylene glycol monohexyl ether — 180 × 10 4.5 18 5.8 5.2 (8):100 Ex. 5 Ethylene glycol monobutyl ether — 170 × 10 3.0 48 30 13.2 (6):100 Ex. 6 Diethylene glycol monomethyl ether — 180 × 10 3.8 22 9.0 7.8 (5):100 Ex. 7 Triethylene glycol monohexyl ether — 180 × 10 6.5 15 5.7 5.2 (12):100 Ex. 8 Tetraethylene glycol monoheptyl ether — 180 × 10 7.6 17 5.3 5.0 (15):100 Ex. 9 Ethylene glycol monohexyl ether (8):60 — 180 × 10 4.4 20 5.8 5.3 Dipropylene glycol monomethyl ether (8):40 Ex. 10 Diethylene glycol monomethyl ether (5):90 — 180 × 10 4.9 28 10.8 8.3 Diethylene glycol diethyl ether (8):10 Ex. 11 Ethylene glycol monohexyl ether EG:20 180 × 10 7.4 30 12.1 8.4 (8):80 Ex. 12 Diethylene glycol monohexyl ether — 165 × 20 4.1 38 23.0 8.6 (10):100 Comp. Monoethylene glycol — 180 × 10 10.8 65 36.0 13.2 Ex. 1 (2):100 Comp. Monoethylene glycol — 195 × 30 14.8 42 18.0 10.2 Ex. 2 (2):100

[0103] In each example, it was possible to sufficiently decolorize the colored clothing while suppressing the weight loss of PET.

[0104] Further, the color b value of the recycled PET obtained in each example was the same as or close to that of commercially available products. Furthermore, the recycled PET obtained in each example had values comparable to those of the commercially available products in inspection items such as an ultimate viscosity (IV), a DEG content, carboxyl terminal groups, and a melting point.

[0105] On the other hand, in each comparative example, the weight loss of PET was severe, and the decolorizing effect of the colored clothing was not sufficiently obtained.

[0106] Further, when the colored flakes are decolorized in the same manner as in the above example, the same result as described above is obtained.

[0107] Furthermore, when the colored clothing is decolorized using an ethylene glycol monoaromatic ether instead of the ethylene glycol monoaliphatic ether in the same manner as in the above example, the same result as described above is obtained.

3. Decolorization of Colored PET Bottle Flakes (Polyester Flakes) and Manufacture of Recycled PET

[0108] First, 450 g of PET bottle flakes colored with a pigment (hereinafter, also referred to as “colored flakes”) was put into a 5 L flask. In this regard, the colored flakes were obtained by crushing PET bottles into 8 to 10 mm squares, a bulk density thereof was 0.28 g/cm.sup.3, and an amount of nitrogen atoms contained therein was 420 ppm. 2,970 g of a heated decolorizing agent obtained by heating diethylene glycol monohexyl ether (number of carbon atoms: 10) to a temperature of 195° C. as a decolorizing agent was added thereinto, and then a first decolorization operation was performed for 15 minutes without stirring. Thereafter, a solid-liquid separation operation, in which the flakes (flakes after first decolorization operation) was separated from the decolorizing agent containing the pigment through a wire mesh, was performed.

[0109] Next, the flakes with the decolorizing agent used for the first time still maintained on a surface thereof was put into the 5 L flask again. 2,970 g of a new heated decolorizing agent (diethylene glycol monohexyl ether) having a temperature of 195° C. was added thereinto, and then a second decolorization operation was performed for 15 minutes without stirring. Thereafter, a solid-liquid separation operation, in which the flakes (flakes after second decolorization operation) was separated from the decolorizing agent containing the pigment through the wire mesh, was performed.

[0110] Next, a third decolorization operation was performed under the same method and conditions as above. Thereafter, a solid-liquid separation operation, in which the flakes (flakes after third decolorization operation) was separated from the decolorizing agent containing the pigment through the wire mesh, was performed. In this way, the flakes with the decolorizing agent used for the third time still maintained on the surface thereof was collected.

[0111] Next, the decolorized flakes (hereinafter, also referred to as “decolorized flakes”) was centrifuged to separate the decolorizing agent used for the third time maintained on the surface thereof, to thereby obtain dry decolorizing flakes. It is to be noted that weight loss (mass reduction ratio) of the decolorized flakes was 7.8%.

[0112] Further, a residual amount of nitrogen atoms contained in the dry decolorized flakes was 16 ppm.

[0113] Thereafter, 400 g of the dry decolorized flakes were treated according to the same chemical recycling process as in Example 1, to obtain BHET, and then recycled PET was produced.

[0114] An amount of nitrogen atoms contained in each of the colored flakes, the decolorized flakes and the dry crystallized BHET, and the color b value of the recycled PET were measured by the same method as shown in the above item “2. Measurement”. As a result, the residual amount of nitrogen atoms contained in the dry crystallized BHET was 5.1 ppm. The color b value of PET (recycled PET) obtained by polycondensation reaction of the dry crystallized BHET according to a conventional method was 4.5. And it had values comparable to those of the commercially available products in the inspection items such as the ultimate viscosity (IV), the DEG content, the carboxyl terminal group, and the melting point.

INDUSTRIAL APPLICABILITY

[0115] According to the present invention, it is possible to provide the decolorized polyester by removing the colorant or the chromophore from the colored polyester. Further, the combination of the present invention with the chemical recycling method makes it possible to recycle the colored polyester, which has been incinerated and landfilled, into polyester products having high quality again. This is very meaningful in terms of resource saving and environmental protection.