TWI869670B - Method for recycling polyethylene terephthalate - Google Patents

Abstract

The present invention provides a method for recycling polyethylene terephthalate, which includes the following steps. Forming a first mixture, wherein the first mixture includes polyester blended fabric, ethylene glycol, and pre-added bis-hydroxyethyl terephthalate. The polyester blended fabric includes polyethylene terephthalate and fabric. Heating the first mixture, and depolymerizing the polyethylene terephthalate in the first mixture to form a second mixture. Filtering the second mixture to obtain a first solution. Purifying the first solution.

Description

Method for recycling polyethylene terephthalate

The present invention relates to a method for recycling polyester, and in particular to a method for recycling polyethylene terephthalate.

Polyethylene terephthalate (PET) and cotton blends are common textile materials. With the rise of environmental awareness, many factories are committed to developing recycling technologies for PET and cotton blends. Generally speaking, the cotton in the blend must be separated before the PET and cotton in the blend can be recycled separately.

However, in the general separation process, the polyethylene terephthalate needs to be depolymerized and then separated from the cotton by filtering. In the existing technology, the blended fabric needs to be heated to a high temperature to make the polyethylene terephthalate in the blended fabric have a sufficient depolymerization rate. However, cotton is easily dissolved in a high temperature environment, making the subsequent product purification process difficult and increasing the recycling cost.

The present invention provides a method for recovering polyethylene terephthalate. By adding pre-added diethylene glycol terephthalate, polyethylene terephthalate can be efficiently depolymerized at a lower temperature, thereby reducing the recovery cost.

The polyethylene terephthalate recovery method of the present invention comprises the following steps: forming a first mixture, wherein the first mixture comprises a polyester blended fabric, ethylene glycol and pre-added diethylene terephthalate, and the polyester blended fabric comprises polyethylene terephthalate and fiber; heating the first mixture, and depolymerizing the polyethylene terephthalate in the first mixture to form a second mixture; filtering the second mixture to obtain a first solution; and purifying the first solution.

In one embodiment of the invention, the fibers comprise cotton fibers.

In one embodiment of the present invention, the first mixture further includes a catalyst, and the catalyst includes at least one of an organic metal and an ionic liquid, wherein the organic metal includes at least one of zinc acetate, cobalt acetate, an organic titanium compound, an organic antimony compound, and an organic aluminum compound. The ionic liquid includes 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6), 1-butyl-3-methylimidazolium tetrachlorozincate (BMI ₂ ZnCl ₄ ), 1-butyl-3-methylimidazolium tetrachloroironate (BMI ₂ FeCl ₄ ), 1-butyl-3-methylimidazolium tetrachlorocobaltate (BMI ₂ CoCl ₄ ) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMI 2 tetrafluoroborate, abbreviated as BMI-BF4).

In one embodiment of the present invention, in the first mixture, the total weight of polyethylene terephthalate and ethylene glycol is 100 parts by weight, and the catalyst is 0.3 parts by weight to 8 parts by weight.

In one embodiment of the present invention, polyethylene terephthalate accounts for 30 wt % to 95 wt % in the polyester blended fabric.

In one embodiment of the present invention, in the first mixture, the total weight of polyethylene terephthalate and ethylene glycol is 100 parts by weight, and the ethylene glycol is 30 parts by weight to 80 parts by weight.

In one embodiment of the present invention, in the first mixture, the total weight of polyethylene terephthalate and ethylene glycol is 100 parts by weight, and the pre-added diethylene terephthalate is 5 parts by weight to 20 parts by weight.

In one embodiment of the present invention, the first mixture is heated to 180°C to 240°C and maintained for 1 hour to 6 hours.

In one embodiment of the present invention, the method of filtering the second mixture includes filtering at a temperature ranging from 90° C. to 180° C. using a filter having a pore size ranging from 0.1 mm to 10 mm to separate the fibers in the second mixture.

In one embodiment of the present invention, purifying the first solution includes adding activated carbon to the first solution to adsorb impurities and performing a recrystallization step.

In one embodiment of the present invention, the recycling method further comprises synthesizing recycled polyethylene terephthalate from the purified diethylene terephthalate in the first solution, wherein the recycled polyethylene terephthalate is 80 to 100 parts by weight based on 100 parts by weight of the polyethylene terephthalate in the polyester blended fabric.

In one embodiment of the present invention, the method of forming the first mixture includes mixing together a polyester blend, ethylene glycol, and pre-added dihydroxyethyl terephthalate at room temperature.

In order to make the above features and advantages of the present invention more clearly understood, embodiments are specifically cited below and described in detail with reference to the accompanying drawings.

Hereinafter, embodiments of the present invention will be described in detail. However, these embodiments are exemplary, and the present invention is not limited thereto.

In this article, the range expressed by "a value to another value" is a summary expression method to avoid listing all the values in the range one by one in the specification. Therefore, the description of a specific numerical range covers any numerical value in the numerical range and the smaller numerical range defined by any numerical value in the numerical range, just as the arbitrary numerical value and the smaller numerical range are written in the description text in the specification.

FIG. 1 is a schematic flow diagram of a method for recovering polyethylene terephthalate according to an embodiment of the present invention.

Referring to FIG. 1 , in step S1, a first mixture is formed, the first mixture comprising a polyester blend, ethylene glycol, and pre-added bis(2-hydroxyethyl) terephthalate (BHET), and the polyester blend comprises polyethylene terephthalate and fiber. In some embodiments, the polyester blend, ethylene glycol, and pre-added bis(2-hydroxyethyl) terephthalate are mixed together at a temperature of 80° C. to 180° C.

In some embodiments, the fiber is, for example, cotton fiber.

In some embodiments, the first mixture may further include a catalyst, and the catalyst may be, for example, an organic metal, an ionic liquid or other suitable catalysts. The organic metal may be, for example, zinc acetate, cobalt acetate, an organic titanium compound, an organic antimony compound, an organic aluminum compound or a combination thereof or other suitable materials. The ionic liquid includes 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6), 1-butyl-3-methylimidazolium tetrachlorozincate (BMI ₂ ZnCl ₄ ), 1-butyl-3-methylimidazolium tetrachloroironate (BMI ₂ FeCl ₄ ), 1-butyl-3-methylimidazolium tetrachlorocobaltate (BMI ₂ CoCl ₄ ) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMI 2 tetrafluoroborate, abbreviated as BMI-BF4).

In some embodiments, in the polyester blended fabric, polyethylene terephthalate accounts for 30 wt% to 95 wt%, and cotton fiber accounts for 70 wt% to 5 wt%. In some embodiments, the polyester blended fabric also includes other small amounts of ingredients, such as dyes, nylon, acrylic, polyurethane fibers, surface treatment agents or other dopants.

In some embodiments, in the first mixture, the total weight of polyethylene terephthalate and ethylene glycol is 100 parts by weight, and the amount of ethylene glycol is, for example, 30 parts by weight to 80 parts by weight, and preferably, 40 parts by weight to 70 parts by weight.

In some embodiments, in the first mixture, the total weight of polyethylene terephthalate and ethylene glycol is 100 parts by weight, and the catalyst is, for example, 0.3 parts by weight to 8 parts by weight, preferably, 1 part by weight to 5 parts by weight.

In some embodiments, in the first mixture, the total weight of polyethylene terephthalate and ethylene glycol is 100 parts by weight, and the pre-added dihydroxyethylene terephthalate is, for example, 5 parts by weight to 20 parts by weight, preferably, 10 parts by weight to 15 parts by weight. When the pre-added dihydroxyethylene terephthalate is less than 5 parts by weight, the effect of increasing the rate of the subsequent depolymerization reaction of polyethylene terephthalate is limited. When the pre-added dihydroxyethylene terephthalate is greater than 20 parts by weight, the pre-added terephthalic acid occupies too much volume of the reaction tank, affecting the recovery efficiency of polyethylene terephthalate.

Please continue to refer to FIG. 1 . In step S2, the first mixture is heated to depolymerize the polyethylene terephthalate in the first mixture to form a second mixture. In some embodiments, the first mixture is heated to a temperature between 180° C. and 240° C., preferably between 190° C. and 230° C. In some embodiments, the first mixture is heated and maintained within the expected temperature range for 1 to 6 hours, preferably for 2 to 4 hours.

In some embodiments, polyethylene terephthalate is depolymerized to form diethylene glycol terephthalate. In other words, the diethylene glycol terephthalate in the second mixture includes pre-added diethylene glycol terephthalate and diethylene glycol terephthalate formed after depolymerization of polyethylene terephthalate in the polyester blended fabric.

In this embodiment, the pre-added dihydroxyethylene terephthalate allows polyethylene terephthalate to dissolve at the initial stage of the depolymerization reaction, thereby accelerating the depolymerization rate of polyethylene terephthalate, so that polyethylene terephthalate can have a sufficient depolymerization rate between 180° C. and 240° C., so there is no need to heat the first mixture to a high temperature of 240° C. Based on the above, the fiber can be prevented from dissolving during the depolymerization reaction, thereby reducing the cost of the subsequent filtration process and purification process.

In step S3, after forming the second mixture, the second mixture is filtered to obtain a first solution.

In some embodiments, the second mixture is filtered, for example, at a temperature ranging from 90° C. to 180° C., using a filter having a pore size of 0.1 mm to 10 mm to separate the fibers in the second mixture. The cotton fibers in the polyester blended fabric before recycling are 100 parts by weight, and the cotton fibers obtained after filtering the second mixture are 90 parts by weight to 100 parts by weight. In other words, the recovery rate of the cotton fibers is greater than or equal to 90%.

Next, in step S4, the first solution is purified. In some embodiments, polyethylene terephthalate is depolymerized at a relatively low temperature (e.g., 180° C. to 240° C.), so that impurities generated by side reactions and products generated by cotton pyrolysis are not easily present in the first solution, thereby reducing the cost required for the purification process and improving the purification capacity.

In some embodiments, the method of purifying the first solution includes, for example, adding activated carbon to the first solution to adsorb impurities, and performing a recrystallization step to obtain a purified first solution.

In some embodiments, the recycling method may further include synthesizing recycled polyethylene terephthalate from the purified dihydroxyethylene terephthalate in the first solution. The recycled polyethylene terephthalate is 80 to 100 parts by weight based on 100 parts by weight of the polyethylene terephthalate in the polyester blend. In other words, the recovery rate of polyethylene terephthalate is greater than or equal to 80%.

The following examples are used to describe in detail the polyethylene terephthalate recovery method of the present invention. However, the following examples are not intended to limit the present invention.

Embodiment 1

The first mixture formed includes 100g of polyester blended fabric, 400g of ethylene glycol, 50g of pre-added dihydroxyethyl terephthalate and 5g of cobalt acetate, wherein the polyester blended fabric includes 75g of PET, 20g of cotton and 5g of dye surface treatment agent.

The first mixture was heated to 195° C. and maintained for 3 hours to depolymerize the PET fibers of the blended fabric to form a second mixture.

The second mixture was then cooled to 120°C and filtered with a filter having a pore size of 1 mm to separate solid cotton fibers. The cotton fibers were then washed with 40 g of water. The wet weight of the washed cotton fibers was 40 g. After drying, the cotton fibers weighed 18.8 g. The recovery rate of the cotton fibers was 94% and the purity was 99.8% (0.2% was PET fibers).

After filtering the second mixture, a first solution was obtained. The first solution weighed 555 g. After adding activated carbon for heating and decolorization, purified dihydroxyethyl terephthalate was obtained by recrystallization. Then, 102 g of PET (referred to as r-PET) was obtained by polymerization, of which 38 g was contributed by 50 g of pre-added dihydroxyethyl terephthalate. Therefore, 64 g of PET was recovered from the polyester blended fabric, and the recovery rate was 64 g/75 g = 85.3%.

The measurement method of the analytical separation method (purity by weight ratio) of polyester blended fabrics is as follows: take a 1000 ml triangular flask, pour 600 ml of a 75% by weight sulfuric acid aqueous solution, take 3g of the separated PET fabric sample and put it into the flask, heat the flask to 50℃±5℃ for 1 hour, and shake it once every 10 minutes. After completion, use a funnel with a 3 mm pore size screen to evacuate and drain the liquid, pour 200 ml of a 75% by weight sulfuric acid aqueous solution into the funnel to wash the fabric and evacuate and drain the liquid, then pour 200 ml of clean water into the funnel to wash the fabric twice, evacuate and drain the liquid each time, place the PET fabric in an oven at 105℃ for 2 hours and weigh it to confirm the PET weight; the cotton weight is the sample weight minus the PET weight. This method is adopted in the following other embodiments and comparative examples, so it will not be described in detail.

Embodiment 2

The first mixture formed includes 100g of polyester blended fabric, 400g of ethylene glycol, 40g of pre-added dihydroxyethyl terephthalate and 5g of cobalt acetate, wherein the polyester blended fabric includes 75g of PET, 20g of cotton and 5g of dye surface treatment agent.

The first mixture was heated to 195° C. and maintained for 3 hours to depolymerize the PET fibers of the blended fabric to form a second mixture.

The second mixture was then cooled to 120°C and filtered with a filter having a pore size of 1 mm to separate solid cotton fibers. The cotton fibers were then washed with 40 g of water. The wet weight of the washed cotton fibers was 40 g. After drying, the cotton fibers weighed 19.0 g. The recovery rate of the cotton fibers was 95% and the purity was 97.4% (2.4% was PET fibers).

After filtering the second mixture, a first solution was obtained, and the obtained first solution weighed 545 g. After adding activated carbon for heating and decolorization, purified dihydroxyethyl terephthalate was obtained by recrystallization, and then polymerized to obtain PET weighing 91 g (abbreviated as r-PET), of which 30 g was contributed by 40 g of pre-added dihydroxyethyl terephthalate. Therefore, 61 g of PET was recovered from the polyester blended fabric, and the recovery rate was 61 g/75 g = 81.3%.

Embodiment 3

The first mixture formed includes 100g of polyester blended fabric, 400g of ethylene glycol, 80g of pre-added dihydroxyethyl terephthalate and 5g of cobalt acetate, wherein the polyester blended fabric includes 75g of PET, 20g of cotton and 5g of dye surface treatment agent.

The first mixture was heated to 195° C. and maintained for 3 hours to depolymerize the PET fibers of the blended fabric to form a second mixture.

The second mixture was then cooled to 120°C and filtered with a filter having a pore size of 1 mm to separate solid cotton fibers. The cotton fibers were then washed with 40 g of water. The wet weight of the washed cotton fibers was 40 g. After drying, the cotton fibers weighed 19.2 g. The recovery rate of the cotton fibers was 96% and the purity was 99.9% (0.1% was PET fibers).

The second mixture was filtered to obtain a first solution, which weighed 585 g. The first solution was decolorized by heating with activated carbon and recrystallized to obtain purified dihydroxyethyl terephthalate. The solution was then polymerized to obtain 126 g of PET (referred to as r-PET), of which 60 g was contributed by 80 g of pre-added dihydroxyethyl terephthalate. Therefore, 66 g of PET was recovered from the polyester blended fabric, and the recovery rate was 66 g/75 g = 86.6%.

Comparison Example 1

The first mixture formed includes 100 g of polyester blended fabric, 400 g of ethylene glycol and 5 g of cobalt acetate, wherein the polyester blended fabric includes 75 g of PET, 20 g of cotton and 5 g of dye surface treatment agent.

The first mixture was heated to 195° C. and maintained for 3 hours to depolymerize the PET fibers of the blended fabric to form a second mixture.

The second mixture was then cooled to 120°C and filtered with a filter having a pore size of 1 mm to separate solid fibers, including cotton fibers and a large amount of PET fibers. The fibers were washed with 40 g of water, and the wet weight of the washed fibers was 65 g. After drying, the fiber weight was 45 g, of which the cotton fibers were 19.2 g and the PET fibers were 25.8 g, showing a mixed state.

After filtering the second mixture, a first solution was obtained, and the obtained first solution weighed 440 g. After adding activated carbon and heating to decolorize, purified diethyl terephthalate was obtained by recrystallization, and then polymerized to obtain PET weighing 47 g (abbreviated as r-PET). Therefore, the PET recovered from the polyester blended fabric was 47 g, and the recovery rate was 47 g/75 g = 62.6%.

Comparison Example 2

The first mixture formed includes 100 g of polyester blended fabric, 400 g of ethylene glycol and 5 g of cobalt acetate, wherein the polyester blended fabric includes 75 g of PET, 20 g of cotton and 5 g of dye surface treatment agent.

The first mixture was heated to 215° C. and maintained for 3 hours to depolymerize the PET fibers of the blended fabric to form a second mixture.

The second mixture was then cooled to 120°C and filtered with a filter having a pore size of 1 mm to separate the solid cotton fiber. The cotton fiber was then washed with 40 g of water. The wet weight of the washed cotton fiber was 30 g. After drying, the cotton fiber weighed 9.4 g. The recovery rate of the cotton fiber was 47% and the purity was 99.9% (0.1% was impurities).

After filtering the second mixture, a first solution was obtained. The first solution weighed 515 g. After adding activated carbon for heating and decolorization, and purification procedures such as recrystallization, 1 to 3 activated carbon adsorption and recrystallization purification procedures were added because of the presence of cotton pyrolysis products to reduce the residual cotton pyrolysis products. The purified dihydroxyethyl terephthalate was polymerized to obtain PET (abbreviated as r-PET) weighing 43 g. Therefore, the PET recovered from the polyester blended fabric was 43 g, and the recovery rate was 43 g/75 g = 57.3%.

Comparison Example 3

The first mixture formed includes 100 g of polyester blended fabric, 400 g of ethylene glycol and 5 g of cobalt acetate, wherein the polyester blended fabric includes 75 g of PET, 20 g of cotton and 5 g of dye surface treatment agent.

The first mixture was heated to 195° C. and maintained for 9 hours to depolymerize the PET fibers of the blended fabric to form a second mixture.

The second mixture was then cooled to 120°C and filtered with a filter having a pore size of 1 mm to separate solid cotton fibers. The cotton fibers were then washed with 40 g of water. The wet weight of the washed cotton fibers was 32 g. After drying, the cotton fibers weighed 10.4 g. The recovery rate of the cotton fibers was 52% and the purity was 99.8%.

After filtering the second mixture, a first solution was obtained. The first solution weighed 513 g and was subjected to purification procedures such as heating with activated carbon for decolorization and recrystallization. Due to the presence of cotton pyrolysis products, 1 to 3 activated carbon adsorption and recrystallization purification procedures were added to reduce the residual cotton pyrolysis products. The purified dihydroxyethyl terephthalate was polymerized to obtain PET (abbreviated as r-PET) weighing 47 g. Therefore, 47 g of PET was recovered from the polyester blended fabric, and the recovery rate was 47 g/75 g = 62.6%.

The preparation methods and results of Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1 below. [Table 1] Embodiment 1 Embodiment 2 Embodiment 3 Comparison Example 1 Comparison Example 2 Comparison Example 3 First mixture heating temperature (℃) 195 195 195 195 215 195 First mixture heating time (hr) 3 3 3 3 3 9 Pre-added dihydroxyethyl terephthalate (g) 50 40 80 0 0 0 Cotton fiber recovery rate 94% 95% 96% - 47% 52% PET recovery rate from polyester blends 85.3% 81.3% 86.6% 62.6% 57.3% 62.6%

As can be seen from Table 1, in Examples 1 to 3, by adding pre-added ethylene terephthalate, polyethylene terephthalate can be efficiently depolymerized at a lower temperature, thereby increasing the PET recovery rate from polyester blended fabrics and efficiently recovering cotton fibers.

In summary, the polyethylene terephthalate recovery method of the present invention can increase the dissolution rate of polyethylene terephthalate by adding pre-added dihydroxyethylene terephthalate, and maintain the temperature between 180°C and 240°C during the depolymerization process to maintain the fiber structure in the blended fabric, so that the impurities of the crude product will not be increased, and the fiber can be recovered at the same time, thereby reducing costs and simplifying the process. At the same time, the pre-added dihydroxyethylene terephthalate does not need to be separated and recovered because it is also a product of the depolymerization of polyethylene terephthalate, that is, it has process compatibility, which is conducive to simplifying the subsequent recovery steps.

S1, S2, S3, S4: Steps

FIG. 1 is a schematic flow diagram of a method for recovering polyethylene terephthalate according to an embodiment of the present invention.

S1, S2, S3, S4: Steps

Claims (6)

A method for recovering polyethylene terephthalate comprises: forming a first mixture, wherein the first mixture comprises a polyester blended fabric, ethylene glycol, pre-added bis(ethylene terephthalate) and a catalyst, and the polyester blended fabric comprises polyethylene terephthalate and cotton fiber, wherein the catalyst comprises at least one of an organic aluminum compound, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrachlorozincate, 1-butyl-3-methylimidazolium tetrachloroferrate, 1-butyl-3-methylimidazolium tetrachlorocobaltate and 1-butyl-3-methylimidazolium tetrafluoroborate, wherein in the first mixture, the total weight of polyethylene terephthalate and ethylene glycol is 100 parts by weight, and the catalyst comprises 10 parts by weight of the catalyst. The first mixture is heated to 180°C to 240°C and maintained for 1 to 6 hours to depolymerize the polyethylene terephthalate in the first mixture to form a second mixture; the second mixture is filtered to obtain a first solution and the cotton fibers are separated, wherein the method of filtering the second mixture includes filtering at a temperature range of 90°C to 180°C with a filter having a pore size of 0.1 mm to 10 mm to separate the cotton fibers in the second mixture; washing the cotton fibers with clean water; drying the washed cotton fibers; and purifying the first solution. The recycling method as described in claim 1, wherein in the polyester blended fabric, polyethylene terephthalate accounts for 30wt% to 95wt%. The recycling method as described in claim 1, wherein in the first mixture, the total weight of polyethylene terephthalate and ethylene glycol is 100 parts by weight, and the ethylene glycol is 30 to 80 parts by weight. The recovery method as described in claim 1, wherein purifying the first solution comprises: adding activated carbon to the first solution to adsorb impurities, and performing a recrystallization step. The recycling method as described in claim 1 further comprises: using the purified diethylene terephthalate in the first solution to synthesize recycled polyethylene terephthalate, wherein the recycled polyethylene terephthalate is 80 to 100 parts by weight based on 100 parts by weight of polyethylene terephthalate in the polyester blended fabric. The recycling method as described in claim 1, wherein the method for forming the first mixture comprises: mixing the polyester blended fabric, ethylene glycol and the pre-added dihydroxyethyl terephthalate together at room temperature.