How to recycle polyester fabric

Abstract

To provide an efficient method for recycling a polyester fabric.SOLUTION: There is provided a polyester fabric including polyethylene terephthalate and dyes. An extraction process including using ethylene glycol as an extraction solvent, immersing the polyester fabric in the extraction solvent, and extracting under a temperature of 80°C to 180°C is performed to remove the dyes from the polyester fabric. A depolymerization process including using a chemical depolymerization solution to depolymerize the polyester fabric treated with the extraction process to obtain a product including BHET (bis(2-hydroxyethyl) terephthalate) is performed. The chemical depolymerization solution is ethylene glycol. A purification process is performed to remove impurities of the product obtained by the depolymerization process and to obtain a purified BHET. A solvent recycling process is performed. The solvent recycling process includes collecting waste solutions of the extraction process and the depolymerization process, and recycling ethylene glycol in the waste solutions by a distillation separating system.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recycling fabrics, in particular polyester fabrics. [Background technology]

[0002] Recycling of waste polyester fabric (PET fabric) typically involves depolymerizing the polyester fabric using a chemical depolymerization solution to obtain a product containing bis(2-hydroxyethyl) terephthalate (BHET), which is then repolymerized to obtain recycled polyester fabric (r-PET). The waste polyester fabric is typically further processed, for example, by dyeing, and used as clothing. To obtain high-quality recycled polyester fabric (r-PET) from these dyed waste polyester fabrics, it is necessary to remove impurities (such as dyes) from the polyester fabric before and / or after the depolymerization reaction to produce purer bis(2-hydroxyethyl) terephthalate, which can then be polymerized and recycled. For example, Patent Document 1 discloses a recycling process in which xylene is used as a solvent to first extract impurities such as dyes from polyethylene terephthalate (PET) fabric, and then the PET fabric is depolymerized with ethylene glycol (EG) to produce BHET. However, the solvent on the PET fabric must be dried during the processing process, which results in solvent loss and requires the installation of an additional solvent recovery system, making it economically unprofitable. For example, Patent Document 2 discloses a recycling process in which PET fabric is directly depolymerized with EG to obtain BHET. Because the crude BHET contains a large amount of impurities, such as dyes, multiple purification steps are required. For example, the crude BHET is crystallized in an EG solvent, purified by distillation, dissolved in hot water to adsorb the impurities with activated carbon, and then cooled to crystallize the BHET. The purified BHET is then filtered and dried to obtain purified BHET. However, the complex purification process results in a low BHET yield. The purified BHET is finally polymerized to produce recycled polyester (r-PET), but this increases the overall production cost. [Prior art document] [Patent documents] [Patent Document 1] International Publication No. 2007 / 018161 [Patent Document 2] Chinese Patent Application Publication No. 110590551 Summary of the Invention [Problem to be solved by the invention]

[0003] Therefore, the current challenge for improvement is how to efficiently recycle polyester fabric. [Means for solving the problem]

[0004] The present invention provides a method for recycling polyester fabrics with a simplified process that can reduce production costs.

[0005] The method for recycling polyester fabric of the present invention includes the following steps. A polyester fabric is provided. The polyester fabric contains polyethylene terephthalate and a dye. An extraction process is performed to remove the dye from the polyester fabric. The extraction process involves immersing the polyester fabric in an extraction solvent using ethylene glycol and extracting at a temperature of 80°C to 180°C. A depolymerization process is performed. The depolymerization process involves depolymerizing the polyester fabric treated in the extraction process using a chemical depolymerization solution to obtain a product containing BHET (bis(2-hydroxyethyl terephthalate)). The chemical depolymerization solution is ethylene glycol. A purification process is performed to remove impurities from the product obtained by the depolymerization process and obtain purified BHET. A solvent recycling process is performed. The solvent recycling process involves recovering waste liquid from the extraction and depolymerization processes and recycling the ethylene glycol in the waste liquid using a distillation separation device.

[0006] In one embodiment of the present invention, during the extraction process, the polyester fabric undergoes 1 to 10 extraction steps, with each extraction step immersing the polyester fabric in a new extraction solvent.

[0007] In one embodiment of the present invention, the duration of each extraction step is between 20 minutes and 1 hour.

[0008] In one embodiment of the present invention, the weight ratio of the extraction solvent to the polyester fabric is 5:10 in each extraction step.

[0009] In one embodiment of the present invention, the depolymerization step is carried out at a temperature of 190°C to 240°C.

[0010] In one embodiment of the present invention, the weight of the chemical depolymerization solution accounts for 30% by weight to 80% by weight of the total weight of the polyester fabric treated with the chemical depolymerization solution and the extraction process.

[0011] In one embodiment of the present invention, the depolymerization step is carried out in an environment that includes a catalyst, the catalyst including an organometallic or an ionic liquid.

[0012] In one embodiment of the present invention, the weight of the catalyst accounts for 0.3 wt% to 8 wt% of the total weight of the polyester fabric treated with the chemical depolymerization solution and extraction process.

[0013] In one embodiment of the present invention, the duration of the depolymerization step is between 1 hour and 6 hours.

[0014] In one embodiment of the present invention, the recycling rate of ethylene glycol in the solvent recycling step is greater than 98% by weight. [Effects of the Invention]

[0015] Based on the above, the polyester fabric recycling method of the present invention simplifies the process by using ethylene glycol as the extraction solvent and chemical depolymerization solution, enabling the production of r-PET with good color quality and yield. Furthermore, the polyester fabric recycling method of the present invention can effectively utilize a single distillation separation device to recycle the extraction solvent and chemical depolymerization solution, thereby reducing not only solvent loss but also equipment and operating costs. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described in detail. However, these embodiments are merely examples, and the disclosure of the present invention is not limited thereto.

[0017] It should be noted that, in this specification, ranges expressed as "from one value to another value" are general expressions to avoid listing all values ​​within the range. Thus, the recitation of a particular numerical range covers any numerical value within that numerical range and any smaller numerical range bounded by any numerical value within that numerical range, as if such any numerical value and such smaller numerical range were expressly set forth in the specification.

[0018] The following are specific examples for illustrating the implementation of the present invention. Those skilled in the art should be able to understand the advantages and effects of the present invention from the contents disclosed herein. The present invention can be implemented or applied through other different specific embodiments, and various modifications and changes can be made to the details of the present specification based on different perspectives and applications without departing from the concept of the present invention. The following embodiments further explain the technical contents related to the present invention in detail, but the disclosed contents are not intended to limit the scope of the present invention. It should be noted that the term "or" in this specification may include any one or more combinations of the relevant listed items depending on the actual situation.

[0019] The method for recycling polyester fabric of the present invention will be described in detail below.

[0020] First, a polyester fabric is provided. The polyester fabric includes polyethylene terephthalate (PET) and a dye. In some embodiments, the polyethylene terephthalate accounts for 80% or more by weight of the polyester fabric, but the invention is not limited thereto. In some embodiments, the dye accounts for 0.1% or more by weight of the polyester fabric, but the invention is not limited thereto.

[0021] Next, an extraction process is carried out to remove the dye from the polyester fabric, which involves immersing the polyester fabric in an extraction solvent, such as ethylene glycol, at a temperature of 80°C to 180°C.

[0022] In some embodiments, during the extraction process, the polyester fabric may be subjected to multiple extraction steps (e.g., 1-10, 3-6, or other suitable number of times) by immersing the polyester fabric in fresh extraction solvent for each extraction step.

[0023] In some embodiments, the duration of each extraction step is between 20 minutes and 1 hour, although the invention is not so limited.

[0024] In some embodiments, the weight ratio of the extraction solvent to the polyester fabric in each extraction step is 5 to 10. In this way, efficient extraction can be achieved while taking into consideration energy consumption and operating costs, but the present invention is not limited thereto.

[0025] Next, a depolymerization step is carried out. The depolymerization step involves depolymerizing the polyester fabric treated in the extraction step using a chemical depolymerization solution to obtain a product containing BHET (bis(2-hydroxyethyl terephthalate)). The chemical depolymerization solution is ethylene glycol. The extraction solvent is the same as the chemical depolymerization solution, both of which are ethylene glycol. Therefore, the polyester fabric after the extraction step in this embodiment can be directly subjected to the depolymerization step without undergoing a drying step to remove the extraction solvent before carrying out the depolymerization step. This simplifies the process steps and avoids the loss of the extraction solvent due to the drying step.

[0026] In some embodiments, the product obtained by the depolymerization step further comprises oligomers.

[0027] In some embodiments, the chemical depolymerization solution accounts for 30 wt% to 80 wt%, preferably 40 wt% to 70 wt%, of the total weight of the polyester fabric treated with the chemical depolymerization solution and extraction process, although the invention is not limited thereto.

[0028] In some embodiments, the depolymerization step is carried out in a catalytic environment to enhance the reaction rate. The catalyst may include an organometallic or an ionic liquid. Examples of organometallics include zinc acetate, organotitanium, organoantimony, organoaluminum, or other suitable organometallics. Examples of ionic liquids include 1-butyl-3-methylimidazolium hexafluorophosphate (abbreviated as BMI-PF6), 1-butyl-3-methylimidazolium tetrachlorozincate (abbreviated as BMI2ZnCl4), 1-butyl-3-methylimidazolium tetrachloroironate (abbreviated as BMI2FeCl4), 1-butyl-3-methylimidazolium tetrachlorocobaltate (abbreviated as BMI2CoCl4), and 1-butyl-3-methylimidazolium tetrafluoroborate (abbreviated as BMI2FeCl4). The ionic liquid may be at least one selected from the group consisting of, but not limited to, tetrafluoroborate (BMI-BF4). In some embodiments, to facilitate recycling of the ionic liquid, the ionic liquid may be grafted onto a particulate substrate. The particulate substrate may include carbon, silicon, iron, nickel, cobalt, or other suitable substrates.

[0029] In some embodiments, the catalyst comprises 0.3 wt % to 8 wt %, preferably 1.0 wt % to 5.0 wt %, of the total weight of the polyester fabric treated with the chemical depolymerization solution and extraction process, although the invention is not limited thereto.

[0030] In some embodiments, the duration of the depolymerization step is between 1 hour and 6 hours, preferably between 2 hours and 4 hours, although the present invention is not limited thereto.

[0031] Next, a purification step is carried out to remove impurities in the product obtained by the depolymerization step and obtain purified BHET. For example, the purification step may include dissolving the product obtained by the depolymerization step in water, cooling the product to crystallize ethylene terephthalate, and filtering.

[0032] In some embodiments, the purification step may also include using diatomaceous earth, activated carbon, acidic clay, etc. to adsorb impurities remaining in the product obtained from the depolymerization step.

[0033] In some embodiments, the purification step may further include drying the filtered ethylene terephthalate through a process such as hot air, microwave, or infrared.

[0034] The purified polyethylene terephthalate can then be polymerized to form recycled polyethylene terephthalate. The recycled polyethylene terephthalate produced by the recycling method of this embodiment has good hue quality, with an L value of 55 to 65, an a value of -1 to +1, and a b value of -5 to 5, for example, but the present invention is not limited thereto. The L, a, and b values ​​refer to the CIELab color space commonly used in the industry. The L value represents brightness, the a value represents green and red values, and the b value represents blue and yellow values.

[0035] In some embodiments, polymerized recycled polyethylene terephthalate can be granulated through a single screw granulator or a twin screw granulator to form recycled polyester granules.

[0036] Furthermore, a solvent recycling step may be carried out after the extraction step and the depolymerization step. The solvent recycling step involves concentrating the waste liquid produced in the extraction step and the depolymerization step and recycling the ethylene glycol in the waste liquid using a distillation separation device. Because both the extraction solvent and the chemical depolymerization solution contain ethylene glycol, the ethylene glycol can be separated and recycled using a single distillation separation device without the need to separately distill the extraction solvent and the chemical depolymerization solution. In this way, equipment costs and the operating procedures for solvent recycling can be reduced.

[0037] In some embodiments, the recycling rate of ethylene glycol in the solvent recycling step is greater than 98% by weight, which allows for effective recycling of ethylene glycol and reduces the loss rate of ethylene glycol (i.e., the loss rate of ethylene glycol is less than 2% by weight).

[0038] In some embodiments, the distillation separation unit comprises a dehydration column and a glycol purification column.

[0039] The method for recycling polyester fabrics according to the present invention will be described in detail below with reference to experimental examples, although the present invention is not limited to these examples.

[0040] Example 1

[0041] 106 grams of PET fabric (containing approximately 100.2 grams of PET and approximately 5.8 grams of dyes and other impurities) was placed in a 1-liter beaker, 500 grams of ethylene glycol (EG) (extraction solvent) was added, and the mixture was heated to 135°C and maintained for 30 minutes. The liquid was then filtered through a 1-mm pore funnel, revealing that the wet PET fabric contained approximately 50 grams of EG. The wet PET fabric was then placed in a 1-liter beaker, 450 grams of EG (extraction solvent) was added, and the mixture was heated to 135°C and maintained for 30 minutes. This process was repeated twice. In other words, the PET fabric underwent a total of four extraction steps.

[0042] After four extractions, a total of approximately 149.9 grams of wet PET fabric contained approximately 99.8 grams of PET fabric, approximately 50 grams of EG, and approximately 0.1 grams of impurities such as dyes. The wet PET fabric was added to a 1-liter reactor (including a heating pack formed by stirring and condensation), and 350 grams of EG (chemical depolymerization solution) and 1 gram of zinc acetate (catalyst) were added. The temperature was increased to 198°C and maintained for 4 hours to carry out the depolymerization process, which depolymerized the PET to produce a crude BHET product.

[0043] The crude BHET product was cooled to 15°C to crystallize and precipitate BHET, then filtered to obtain 200 grams of BHET filter cake. 200 grams of BHET filter cake was placed in a 1-liter beaker, 200 grams of water was added, and the temperature was raised to 90°C to dissolve the BHET. 5 grams of activated carbon was then added and stirred for 1 hour. Impurities such as activated carbon were then filtered through 0.1 μm filter paper. The filtrate was cooled from 90°C to 5°C to precipitate BHET crystals, which were then filtered through 1 μm filter paper to obtain a BHET filter cake. The BHET filter cake was then dried at 75°C and 100 Torr to obtain approximately 120 grams of purified BHET.

[0044] Polymerization of 120 g of purified BHET yielded approximately 88.7 g of recycled PET (r-PET) and 31.3 g of by-products such as EG and oligomers. r-PET yield = 88.7 g / 100.2 g = 88.5%, color quality L = 60.4, a = 0.2, b = 1.2.

[0045] The waste liquid obtained in the extraction and depolymerization processes was recovered through a distillation process. The EG recycling rate was 2,167 g / 2,200 g, or 98.5%, and the total amount of EG lost was approximately 33 g.

[0046] Examples 2 to 6

[0047] The treatment methods for Examples 2 to 6 were the same as those for Example 1. However, the treatment conditions (including extraction temperature, extraction time, depolymerization temperature, and depolymerization time) for Examples 2 to 6 were as shown in Table 1. The L, a, b, yield, and total loss rate of the extraction solvent and chemical depolymerization solution for r-PET obtained in Examples 2 to 6 are shown in Table 1.

[0048] [Table 1]

[0049] Comparative Example 1

[0050] 106 grams of PET fabric (approximately 100.2 grams of PET and approximately 5.8 grams of dyes and other impurities) was taken and added to a 1-liter beaker. 500 grams of xylene (extraction solvent) was added, and the mixture was heated to 135°C and maintained for 30 minutes. The liquid was then filtered through a 1-mm pore funnel, and the wet PET fabric contained 50 grams of xylene. The wet PET fabric was then added to a 1-liter beaker, 450 grams of xylene (extraction solvent) was added, and the mixture was heated to 135°C and maintained for 30 minutes. This process was repeated twice. This means that the PET fabric underwent a total of four extraction steps.

[0051] After four extractions, a total of about 149.5 grams of wet PET fabric (containing about 99.4 grams of PET fabric, about 50 grams of xylene, and about 0.1 grams of impurities such as dyes) had to be dried (100 torr, 120°C) to remove the xylene, obtaining about 99.5 grams of dry PET fabric (containing about 99.2 grams of PET, 0.2 grams of xylene, and 0.1 grams of impurities such as dyes), and about 50 grams of xylene was collected by condensation at 5°C.

[0052] The above 99.5 grams of dried PET dough was added to a 1 liter reactor (including a heating pack formed by stirring and condensation), 400 grams of EG (chemical depolymerization solution) and 1 gram of zinc acetate (catalyst) were added, and the temperature was increased to 198°C and maintained for 4 hours to carry out the depolymerization process to depolymerize the PET to produce a crude BHET product.

[0053] The crude BHET product was cooled to 15°C to crystallize and precipitate BHET, then filtered to obtain 200 grams of BHET filter cake. 200 grams of BHET filter cake was placed in a 1-liter beaker, 200 grams of water was added, and the temperature was raised to 90°C to dissolve the BHET. 5 grams of activated carbon was then added and stirred for 1 hour. Impurities such as activated carbon were then filtered through 0.1 μm filter paper. The filtrate was cooled from 90°C to 5°C to precipitate BHET crystals, which were then filtered through 1 μm filter paper to obtain a BHET filter cake. The BHET filter cake was then dried at 75°C and 100 Torr to obtain approximately 115.0 grams of purified BHET.

[0054] 115.0 g of purified BHET was polymerized to yield 86.3 g of recycled PET (r-PET) and 28.7 g of by-products such as EG and oligomers. r-PET yield = 86.3 g / 100.2 g = 86.1%, color quality L = 60.7, a = 0.1, b = 3.2.

[0055] Extraction solvent recovery: Approximately 1,631 grams of extraction solvent were recovered by distillation. This was added to the 50 grams of extraction solvent collected during the drying process, for a total of 1,681 grams of xylene. Xylene yield = 1,681 / 1,850 = 90.9%. 169 g of xylene solvent leaked, for a loss rate of 9.1%.

[0056] Recovery of chemical depolymerization solution: 394 grams of EG in the waste liquid from the depolymerization process was recovered by distillation. The EG recycling rate was 394 grams / 400 grams = 98.5%. 6 grams of EG solvent leaked, resulting in a loss rate of 1.5%.

[0057] The total loss of the extraction solvent and chemical depolymerization solution was 175 grams, and the total loss rate was 7.8%.

[0058] Comparative Examples 2 to 6

[0059] The processing methods of Comparative Examples 2 to 6 were the same as those of Comparative Example 1. However, the processing conditions (including extraction solvent, extraction temperature, extraction time, depolymerization temperature, and depolymerization time) of Comparative Examples 2 to 6 were as shown in Table 2. The L, a, b, yield, extraction solvent, and loss rate of the chemical depolymerization solution of the r-PET obtained in Comparative Examples 2 to 6 are shown in Table 2.

[0060] [Table 2]

[0061] As can be seen from Tables 1 and 2, the extraction solvent and chemical depolymerization solution in Examples 1 to 6 are both ethylene glycol. Therefore, compared to Comparative Examples 1 to 6, r-PET with good color quality and yield can be obtained even without the drying step to remove the extraction solvent before the depolymerization step. Examples 1 to 6 simplify and streamline the process, avoiding the loss of the extraction solvent during the drying step. Therefore, the total loss rate of the extraction solvent and chemical depolymerization solution in Examples 1 to 6 is significantly lower than that of Comparative Examples 1 to 6.

[0062] Furthermore, the extraction solvent and chemical depolymerization solution in Examples 1 to 6 can be recovered using a single distillation separation apparatus. Compared with Comparative Example 2, which requires the use of at least two sets of distillation separation apparatuses to recover the extraction solvent and the chemical depolymerization solution, respectively, Examples 1 to 6 can reduce equipment costs and operating costs and simplify the recycling procedure.

[0063] Based on the above, the polyester fabric recycling method of the present invention simplifies the process by using ethylene glycol as the extraction solvent and chemical depolymerization solution, enabling the production of r-PET with good color quality and yield. Furthermore, the polyester fabric recycling method of the present invention can effectively utilize a single distillation separation device to recover the extraction solvent and chemical depolymerization solution, thereby reducing not only solvent loss but also equipment and operating costs.

[0064] While the present invention has been described with reference to the above embodiments, it will be apparent to those skilled in the art that modifications can be made to the described embodiments without departing from the spirit of the invention. Accordingly, the scope of the present invention will be defined by the appended claims rather than by the above detailed description. [Industrial Applicability]

[0065] The method for recycling polyester fabrics of the present invention can be applied to any fabric recycling method.

Claims

1. providing a polyester fabric comprising polyethylene terephthalate and a dye; performing an extraction step of removing the dye from the polyester fabric, the extraction step comprising immersing the polyester fabric in an extraction solvent using ethylene glycol and extracting at a temperature of 80°C to 180°C; carrying out a depolymerization step, which includes depolymerizing the polyester fabric treated in the extraction step using a chemical depolymerization solution to obtain a product containing BHET (bis(2-hydroxyethyl terephthalate)), wherein the chemical depolymerization solution is ethylene glycol; carrying out a purification step to remove impurities in the product obtained by the depolymerization step and obtain purified BHET; a solvent recycling step of recovering waste liquids from the extraction step and the depolymerization step and recycling ethylene glycol in the waste liquids using a single distillation separation device; Including, In the solvent recycling step, the recycling rate of the ethylene glycol is more than 98% by weight.

2. 2. The method for recycling polyester fabrics according to claim 1, wherein in the extraction process, the polyester fabric is subjected to 1 to 10 extraction steps, and in each extraction step, the polyester fabric is immersed in a new extraction solvent.

3. 3. The method for recycling polyester fabrics according to claim 2, wherein the duration of each extraction step is between 20 minutes and 1 hour.

4. 3. The method for recycling polyester fabrics according to claim 2, wherein in each extraction step, the weight ratio of the extraction solvent to the polyester fabric is 5:

10.

5. The method for recycling polyester fabrics according to claim 1, wherein the depolymerization step is carried out at a temperature of 190°C to 240°C.

6. 2. The method for recycling polyester fabrics according to claim 1, wherein the weight of the chemical depolymerization solution accounts for 30% by weight to 80% by weight of the total weight of the polyester fabric treated with the chemical depolymerization solution and the extraction process.

7. 2. The method for recycling polyester fabrics according to claim 1, wherein the depolymerization process is carried out in an environment containing a catalyst, and the catalyst comprises an organometallic or an ionic liquid.

8. 8. The method for recycling polyester fabrics according to claim 7, wherein the weight of the catalyst accounts for 0.3% by weight to 8% by weight of the total weight of the polyester fabrics treated in the chemical depolymerization solution and extraction process.

9. 2. The method for recycling polyester fabrics according to claim 1, wherein the depolymerization process lasts for 1 to 6 hours.

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