Method of recycling 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] The recycling method of waste polyester fabric (PET fabric) is usually to depolymerize polyester fabric using a chemical depolymerization solution to obtain a product containing bis(2-hydroxyethyl) terephthalate (Bis(2-HydroxyEthyl Terephthalate, BHET), and then repolymerize the bishydroxyethyl terephthalate to obtain recycled polyester fabric (r-PET). Usually, the waste polyester fabric is further processed, for example dyed, 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) in the polyester fabric before and / or after the depolymerization reaction to produce purer bishydroxyethyl terephthalate, which can then be polymerized and recycled. 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 step is performed to remove the dye from the polyester fabric. The extraction step includes immersing the polyester fabric in an extraction solvent using ethylene glycol as an extraction solvent and extracting at a temperature of 80°C to 180°C. A depolymerization step is performed. The depolymerization step 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)). The chemical depolymerization solution is ethylene glycol. A purification step is performed to remove impurities from the product obtained by the depolymerization step and obtain purified BHET. A solvent recycling step is performed. The solvent recycling step includes recovering waste liquid from the extraction step and the depolymerization step, and recycling the ethylene glycol in the waste liquid by a distillation separation device.

[0006] In one embodiment of the present invention, in the extraction process, the polyester fabric undergoes 1 to 10 extraction steps, each extraction step immersing the polyester fabric in fresh 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 between 190°C and 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 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% to 8% by weight of the total weight of the polyester fabric treated in 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. Effect of the Invention

[0015] Based on the above, the polyester fabric recycling method of the present invention can simplify the process and obtain r-PET with good color quality and yield by using ethylene glycol as the extraction solvent and chemical depolymerization solution. 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, thus not only reducing the loss of solvent, but also reducing equipment and operation costs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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] In this specification, the ranges expressed as "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 this 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 explaining 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 in this specification. 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 this specification based on different perspectives and applications without departing from the concept of the present invention. The following embodiments further describe 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. In this specification, the term "or" can include any one or more combinations of the relevant enumerated items according to 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% by weight or more of the polyester fabric, but the invention is not limited thereto. In some embodiments, the dye accounts for 0.1% by weight or more 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. The extraction process includes, for example, using ethylene glycol as an extraction solvent, immersing the polyester fabric in the extraction solvent, and extracting 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 account energy consumption and operation costs, but the present invention is not limited thereto.

[0025] Next, a depolymerization step is carried out. The depolymerization step includes a step of 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. Since the extraction solvent is the same as the chemical depolymerization solution, both of which are ethylene glycol, the polyester fabric after the extraction step in this embodiment may be directly subjected to the depolymerization step without a drying step for removing the extraction solvent before carrying out the depolymerization step. The process steps are simplified, and the loss of the extraction solvent due to the drying step can be avoided.

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

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

[0028] In some embodiments, the depolymerization step is carried out in an environment that includes a catalyst 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 the ionic liquid 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, abbreviated as 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 substrate.

[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, but 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 clays, and the like to adsorb impurities remaining in the product resulting 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 subjected to a polymerization process to form recycled polyethylene terephthalate. The recycled polyethylene terephthalate produced by the recycling method of this embodiment has good hue quality, for example, the L value is 55 to 65, the a value is -1 to +1, and the b value is -5 to 5, but the present invention is not limited thereto. The L value, the a value, and the b value 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, recycled polyester granules can be formed by granulating polymerized recycled polyethylene terephthalate through a single screw granulator or a twin screw granulator.

[0036] Furthermore, a solvent recycling step may be performed after the extraction step and the depolymerization step. The solvent recycling step involves concentrating the waste liquid generated in the extraction step and the depolymerization step and recycling the ethylene glycol in the waste liquid by a distillation separation device. Since both the extraction solvent and the chemical depolymerization solution use ethylene glycol, the ethylene glycol can be separated and recycled in a single distillation separation device without separately distilling the extraction solvent and the chemical depolymerization solution. In this way, the equipment cost and the operation procedure of the solvent recycling can be reduced.

[0037] In some embodiments, in the solvent recycling step, the recycling rate of ethylene glycol is more than 98% by weight, and the ethylene glycol can be effectively recycled and the loss rate of ethylene glycol can be reduced (i.e., the loss rate of ethylene glycol is less than 2% by weight).

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

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

[0040] Example 1

[0041] 106 grams of PET fabric (containing about 100.2 grams of PET and about 5.8 grams of impurities such as dyes) 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, and the wet PET fabric contained about 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, and this process was repeated twice. In other words, the PET fabric went through a total of four extraction steps.

[0042] The total amount of about 149.9 grams of wet PET fabric after four extractions contained about 99.8 grams of PET fabric, about 50 grams of EG, and about 0.1 grams of impurities such as dyes. The wet PET fabric was added to a 1-liter reactor (containing a heating pack formed by stirring and condensation), 350 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.

[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 BHET, after which 5 grams of activated carbon was added and stirred for 1 hour. Impurities such as activated carbon were then filtered through 0.1 μm filter paper, and the filtrate was cooled from 90°C to 5°C to precipitate BHET crystals, and filtered through 1 μm filter paper to obtain BHET filter cake. It was then dried at 75°C and 100 torr to obtain about 120 grams of purified BHET.

[0044] 120 g of purified BHET was polymerized to obtain about 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 process and the depolymerization process was recovered through a distillation process. The EG recycling rate was 2,167 g / 2,200 g=98.5%, and the total loss of EG was about 33 g.

[0046] Examples 2 to 6

[0047] The treatment methods of Examples 2 to 6 are the same as those of Example 1. However, the treatment conditions (including extraction temperature, extraction time, depolymerization temperature, and depolymerization time) of Examples 2 to 6 are as shown in Table 1. The L, a, b, yield, extraction solvent, and total loss rate of chemical depolymerization solution of 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 (containing about 100.2 grams of PET and about 5.8 grams of impurities such as dyes) 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, and this process was repeated twice. This means that the PET fabric went through 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 into a 1 liter reactor (containing a heating pack formed by stirring and condensation), 400 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 to depolymerize the PET to produce crude BHET product.

[0053] The crude BHET product was cooled to 15°C to crystallize and precipitate BHET, and 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 BHET, after which 5 grams of activated carbon was added and stirred for 1 hour. Impurities such as activated carbon were then filtered through 0.1 μm filter paper, and the filtrate was cooled from 90°C to 5°C to precipitate BHET crystals, and filtered through 1 μm filter paper to obtain BHET filter cake. It was then dried at 75°C and 100 torr to obtain about 115.0 grams of purified BHET.

[0054] 115.0 g of purified BHET was polymerized to obtain 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, in addition to the 50 grams of extraction solvent collected in the drying step, for a total of 1,681 grams of xylene. Xylene yield = 1,681 / 1,850 = 90.9%, with 169 grams of xylene solvent leaking out for a loss rate of 9.1%.

[0056] Recovery of chemical depolymerization solution: 394 grams of EG in the waste liquid of the depolymerization process was recovered by distillation. The recycling rate of EG = 394 grams / 400 grams = 98.5%. 6 grams of EG solvent leaked, and the loss rate was 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 Example 2 to Comparative Example 6 are 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 Example 2 to Comparative Example 6 are as shown in Table 2. The L, a, b, yield, extraction solvent, and loss rate of chemical depolymerization solution of r-PET obtained in Comparative Example 2 to Comparative Example 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, so that r-PET with good color quality and yield can be obtained even if the drying step for removing the extraction solvent before the depolymerization step is omitted, as compared with Comparative Examples 1 to 6. It can be seen that Examples 1 to 6 simplify and are efficient in their processes, and can avoid 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] In addition, the extraction solvent and the chemical depolymerization solution in Examples 1 to 6 can be recovered in 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 can simplify the process and obtain r-PET with good color quality and yield by using ethylene glycol as the extraction solvent and chemical depolymerization solution. 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, thus not only reducing the loss of solvent, but also reducing the equipment and operation costs.

[0064] Although 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 is defined by the appended claims rather than by the above detailed description. [Industrial Applicability]

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

Claims

1. Providing a polyester fabric comprising polyethylene terephthalate and a dye; carrying out an extraction process to remove the dye from the polyester fabric, the extraction process comprising immersing the polyester fabric in an extraction solvent using ethylene glycol as an extraction solvent 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 BHET (bis(2-hydroxyethyl terephthalate)), wherein the chemical depolymerization solution is ethylene glycol; carrying out a purification step to remove the product impurities obtained by the depolymerization step and to obtain purified BHET; performing a solvent recycling step of recovering waste liquid from the extraction step and the depolymerization step, and recycling ethylene glycol in the waste liquid by a distillation separation device; How to recycle polyester fabric, including:

2. 2. The method for recycling polyester fabrics according to claim 1, wherein in the extraction process, the polyester fabrics are subjected to 1-10 extraction steps, and in each extraction step, the polyester fabrics are immersed in fresh 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 process 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 fabrics 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% to 8% by weight of the total weight of the polyester fabric 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 time is from 1 hour to 6 hours.

10. 2. The method for recycling polyester fabrics according to claim 1, wherein in the solvent recycling step, the recycling rate of the ethylene glycol is more than 98% by weight.

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