Recycled diethylene glycol terephthalate and preparation method thereof

Abstract

The preparation method comprises the following steps: firstly, carrying out high-temperature decoloration on waste colored polyester fibers in acid-containing ethylene glycol steam, then carrying out a depolymerization reaction on the decolorized recycled polyester fibers in ethylene glycol, after depolymerization is finished, pouring a depolymerization solution into water, and carrying out heat preservation for 1-2 hours, so as to obtain the recycled diethylene glycol terephthalate. Crude diethylene glycol terephthalate is obtained through precipitation and filtration, finally, the crude diethylene glycol terephthalate is dissolved in hot water to be filtered to remove impurities, then activated carbon is used for adsorbing dye in the crude diethylene glycol terephthalate, and then crystallization, filtration and drying are conducted to obtain purified diethylene glycol terephthalate. The dye concentration in the purified diethylene glycol terephthalate is lower than 500 ppm, the application range is wide, and the performance of a polymer obtained through repolymerization is also excellent.

Description

Technical Field

[0001] The present invention relates to diethylene glycol terephthalate, and specifically, to a recycled diethylene glycol terephthalate with low dye content and a preparation method thereof. Background Art

[0002] While the polyester fiber industry is developing rapidly, the treatment of waste polyester fibers has received increasing attention. The existence of waste polyester fibers not only causes environmental pressure but also results in the waste of petrochemical resources. The recycling of waste polyester, especially the recycling of waste colored polyester fibers, has gained more favor among researchers. If the waste colored polyester fibers are not decolorized during recycling, the recycled products are difficult to be widely used. Currently, there are mainly two methods for decolorizing waste colored polyester fibers. One is to heat an alcohol solvent to its boiling point and let it penetrate into the fiber interior to make the disperse dye molecules lose or weaken the interaction with polyester molecules. Chinese Patent CN107587362A discloses this method, but the removal effect of this method on ionic dyes will be greatly reduced. The other is to depolymerize the colored polyester fibers and add a decolorizing agent such as activated carbon to the depolymerization solution for decolorization. Chinese Patent CN107266664A discloses the use of activated carbon for decolorization. Although this method is effective for any type of dye, a large amount of decolorizing agent will not only increase the recycling cost but also reduce the recovery rate of ethylene glycol terephthalate.

[0003] Therefore, how to achieve efficient decolorization and recycling of colored polyester fibers is the breakthrough point and focus in the research field of colored polyester fiber regeneration. Summary of the Invention

[0004] The purpose of the present invention is to provide a recycled diethylene glycol terephthalate obtained after comprehensive and efficient decolorization treatment and a preparation method thereof.

[0005] The technical solution of the present invention:

[0006] The recycled diethylene glycol terephthalate has a dye content of less than 500 ppm, and preferably a diglycol content of less than 0.10 wt%.

[0007] The recycled diethylene glycol terephthalate is prepared by the following method,

[0008] Step 1: High-temperature decolorize waste colored polyester fibers in ethylene glycol vapor containing an acid, and obtain decolorized recycled polyester fibers. The acid is an organic acid and / or inorganic acid with a boiling point of 40.0 - 200.0 °C;

[0009] Step 2: Subject the decolorized recycled polyester fiber to a depolymerization reaction in ethylene glycol. After the depolymerization is completed, pour the depolymerized solution into water, and obtain crude diethylene glycol terephthalate through precipitation and filtration. The molar ratio of the decolorized recycled polyester fiber to ethylene glycol is 1:2 - 40;

[0010] Step 3: Dissolve the crude diethylene glycol terephthalate in hot water to filter out impurities, then use activated carbon to adsorb the dyes therein, and then perform crystallization, filtration, and drying to obtain purified diethylene glycol terephthalate.

[0011] The acid is preferably one or more of hydrochloric acid, nitric acid, formic acid, and acetic acid.

[0012] The temperature of the ethylene glycol vapor is preferably 190 - 230 °C.

[0013] The concentration of the acid in the ethylene glycol vapor is preferably 0.010 - 20.000 wt%, more preferably 0.050 - 5.000 wt%.

[0014] In the present invention, by using ethylene glycol vapor containing an acid to decolorize the colored polyester fiber, the contents of dyes and diethylene glycol in the obtained recycled diethylene glycol terephthalate are greatly reduced, the quality of the recycled diethylene glycol terephthalate is improved, and its application fields are expanded. Detailed implementation mode

[0015] The content of dyes in the diethylene glycol terephthalate obtained by depolymerizing waste colored polyester fiber is one of the important indicators to measure its service performance. The more dyes contained in the recycled diethylene glycol terephthalate, the worse the hue of the recycled polyester prepared therefrom, and the narrower the applicable range of the recycled polyester. At the same time, the dyes in the recycled diethylene glycol terephthalate will also affect the polymerization reaction during the preparation of the recycled polyester. The content of dyes in the recycled diethylene glycol terephthalate of the present invention is below 500 ppm, the hue of the recycled polyester prepared therefrom is good, and the recycled polyester has a wide range of applications.

[0016] In addition, the content of diethylene glycol in the recycled diethylene glycol terephthalate is also one of the important indicators to measure its service performance. If the content of diethylene glycol in the recycled diethylene glycol terephthalate is too high, the content of diethylene glycol in the recycled polyester prepared therefrom will also be on the high side, resulting in a low melting point and poor dyeability of the recycled polyester. The present invention preferably has the content of diethylene glycol in the recycled diethylene glycol terephthalate below 0.10 wt%.

[0017] The present invention also discloses a preparation method of the recycled diethylene glycol terephthalate, which mainly includes the following steps:

[0018] Step 1: High-temperature decolorization of waste colored polyester fiber in ethylene glycol vapor containing an acid to obtain decolorized recycled polyester fiber, where the acid is an organic acid and / or inorganic acid with a boiling point of 40.0 - 200.0 °C;

[0019] Step 2: Depolymerize the decolorized recycled polyester fiber in ethylene glycol. After the depolymerization ends, pour the depolymerized solution into water, and obtain crude diethylene glycol terephthalate through precipitation and filtration. The molar ratio of the decolorized recycled polyester fiber to ethylene glycol is 1:2 - 40;

[0020] Step 3: Dissolve the crude diethylene glycol terephthalate in hot water, filter to remove impurities, then adsorb the dyes therein with activated carbon, and then perform crystallization, filtration, and drying to obtain purified diethylene glycol terephthalate.

[0021] Step 1 is mainly a process of decolorizing waste colored polyester fiber. In the present invention, by placing the waste colored polyester fiber in ethylene glycol vapor containing an acid, ethylene glycol penetrates into the interior of the waste colored polyester fiber, causing the physical bond between the dye molecules and the polyester fiber to be lost or weakened; the acid in the ethylene glycol vapor can dissociate hydrogen ions, and the hydrogen ions enter the interior of the waste colored polyester fiber along with the ethylene glycol vapor, destroying the chemical bond between the dye molecules and the polyester molecules. Through the dual destruction of the physical and chemical bonds between the dye molecules and the polyester, the dyes in the waste colored polyester fiber can be removed faster and more thoroughly.

[0022] The temperature of the ethylene glycol vapor cannot be too low, otherwise ethylene glycol cannot cause the waste colored polyester fiber to swell sufficiently, and ethylene glycol cannot penetrate into the interior of the polyester fiber, resulting in the loss or weakening of the binding effect between the dye molecules and the polyester; the hydrogen ions ionized by the acid cannot further destroy the chemical bond between the dye molecules and the polyester; the temperature of the ethylene glycol vapor cannot be too high, otherwise the waste colored polyester fiber will depolymerize under the action of ethylene glycol, reducing the recovery rate of the waste colored polyester fiber. In the present invention, the temperature of the ethylene glycol vapor is preferably 190 - 230 °C.

[0023] The acid refers to an organic acid and / or inorganic acid with a boiling point between 40.0 - 200.0 °C, which can ionize hydrogen ions and can evaporate with ethylene glycol during heating. Since the acid in the present invention needs to form vapor with ethylene glycol, if its boiling point is lower than 40 °C, it is extremely easy to volatilize during heating; if the boiling point is higher than 200 °C, the acid is not easy to enter the interior of the waste colored polyester fiber along with the ethylene glycol vapor. Both of these situations will lead to a reduction in the decolorization effect. Therefore, in order to ensure that the acid can fully exert its decolorization effect, the boiling point of the acid is preferably 40.0 - 150.0 °C in the present invention.

[0024] Specifically, the acid is more preferably one or more of hydrochloric acid, nitric acid, formic acid, and acetic acid. When hydrochloric acid is selected, it is generally a commercially available aqueous hydrochloric acid solution. For example, when the concentration of the aqueous hydrochloric acid solution is 38%, the boiling point is 48.0 °C. When other acids are selected, these acids are generally used directly without further preparation into a solution. The boiling point of nitric acid is 83.0 °C, the boiling point of formic acid is 100.6 °C, and the boiling point of acetic acid is 117.9 °C.

[0025] If the concentration of the acid in the ethylene glycol vapor is too low, the amount of hydrogen ions is too small to sufficiently break the chemical bond between the dye and the polyester, resulting in poor decolorization effect. If the concentration of the acid in the ethylene glycol vapor is too high, in the presence of ethylene glycol, the acid may cause the depolymerization of waste colored polyester fibers, resulting in a decrease in the yield of recycled polyethylene terephthalate glycol; at the same time, a large amount of acid will also corrode the equipment and accelerate the aging of the equipment. The concentration of the acid in the ethylene glycol vapor of the present invention is preferably 0.010 - 20.000 wt%, more preferably 0.050 - 5.000 wt%.

[0026] The decolorization treatment in the first step of the present invention can remove almost all types of dyes in the waste colored polyester fibers, and the decolorization effect is good.

[0027] After the decolorization treatment, the obtained recycled polyester fibers are depolymerized. During depolymerization, the recycled polyester fibers are placed in ethylene glycol and depolymerized at a certain depolymerization temperature. After the depolymerization is completed, the depolymerization solution is poured into water, and crude ethylene glycol terephthalate is obtained through precipitation and filtration. As the amount of ethylene glycol increases, the depolymerization rate and the depolymerization ratio increase accordingly. However, when the amount of ethylene glycol exceeds a certain value, the depolymerization rate and the depolymerization ratio hardly change, but it will cause waste of ethylene glycol and the formation of diethylene glycol. Therefore, in order to ensure the depolymerization rate, reduce the waste of ethylene glycol and the formation of diethylene glycol, the molar ratio of the recycled polyester fibers to the diol in the present invention is 1:2 - 40.

[0028] The present invention does not particularly limit the temperature of the depolymerization, which can be within the general range of the existing recycled polyester depolymerization technology. However, if the temperature is too low, the depolymerization rate is slow, the depolymerization ratio is low, and the recovery rate of recycled polyethylene terephthalate glycol is small; if the temperature is too high, not only the reaction energy consumption increases, but also ethylene glycol will undergo a side reaction of dehydration to form diethylene glycol. Therefore, the present invention preferably selects the depolymerization temperature to be 180 - 220 °C.

[0029] Finally, the crude ethylene terephthalate is dissolved in hot water to filter out impurities, and then the dye therein is adsorbed by activated carbon. The activated carbon can be directly added to the aqueous solution of crude ethylene terephthalate, or a filter column containing activated carbon and capable of changing pressure and time can be used. Then, it is recrystallized, filtered, and dried to obtain purified ethylene terephthalate. The dosage of the activated carbon in the present invention is not particularly limited and can be appropriately adjusted according to the concentration of the dye in the aqueous solution of crude ethylene terephthalate.

[0030] Through the decolorization treatment method defined in Step 1 of the present invention, the dye content in the recycled ethylene terephthalate obtained by depolymerizing and recycling waste colored polyester fibers is below 500 ppm, greatly improving the quality and reuse range of the recycled ethylene terephthalate.

[0031] The measurement methods and evaluation methods for various indexes of the present invention are described below.

[0032] (1) DEG content

[0033] Take 0.5 g of the sample, add 1.25 ml of the solvent (internal standard 1,6 - hexanediol / solvent B = 5 mg / 1.25 ml), heat to dissolve, then add 10 ml of methanol, cool in an ultrasonic bath until ammonium salts precipitate; then add 8 g of terephthalic acid for neutralization, and filter with filter paper to obtain a clear solution. Inject 2 μl of the filtrate into a GC for analysis and determination.

[0034] (2) Dye concentration

[0035] Take 0.1 g of ethylene terephthalate, add it to 10 g of absolute ethanol and dissolve for half an hour. Then, after the solution is clear and transparent, take a certain amount of the solution and measure the dye content in a UV - visible spectrophotometer.

[0036] (3) Recovery rate of ethylene terephthalate

[0037] Recovery rate = (M2 / M1) × 100%

[0038] Wherein, M1 is the weight of the waste colored polyester fiber, and M2 is the weight of the purified ethylene terephthalate.

[0039] The advantages of the present invention will be described in detail below with reference to the listed examples and comparative examples, but the present invention is not limited to the following examples.

[0040] Example 1

[0041] A certain amount of waste colored polyester fiber was placed in a reaction kettle containing ethylene glycol vapor (temperature 210°C, acetic acid concentration 1.000 wt%) for decolorization treatment for 60 minutes. After the decolorization was completed, the decolorized recycled polyester fiber was depolymerized in ethylene glycol. The molar ratio of the recycled polyester fiber to ethylene glycol was 1:18, the depolymerization temperature was 210°C, and the depolymerization time was 2 hours.

[0042] The depolymerized solution was poured into water, precipitated and filtered to obtain crude diethylene glycol terephthalate. The crude dimethyl terephthalate was further dissolved in hot water, the impurities were filtered off, and then filtered through a filter column containing activated carbon. Finally, the filtrate was crystallized, filtered and dried to obtain purified ethylene glycol terephthalate. The dye concentration and diethylene glycol content in the final ethylene glycol terephthalate were measured, and the specific data are shown in Table 1.

[0043] Examples 2 - 18

[0044] The conditions of the decolorization treatment or depolymerization were changed, and the others were the same as in Example 1. The specific data are shown in Table 1.

[0045] Comparative Example 1

[0046] A certain amount of waste colored polyester fiber was placed in a reaction kettle containing ethylene glycol vapor (temperature 210°C, without acid) for decolorization treatment for 60 minutes. After the decolorization was completed, the decolorized recycled polyester fiber was depolymerized in ethylene glycol. The molar ratio of the recycled polyester fiber to ethylene glycol was 1:18, the depolymerization temperature was 210°C, and the depolymerization time was 2 hours.

[0047] The depolymerized solution was poured into water, precipitated and filtered to obtain crude diethylene glycol terephthalate. The crude dimethyl terephthalate was further dissolved in hot water, the impurities were filtered off, and then filtered through a filter column containing activated carbon. Finally, the filtrate was crystallized, filtered and dried to obtain purified ethylene glycol terephthalate. The dye concentration and diethylene glycol content in the final ethylene glycol terephthalate were measured, and the specific data are shown in Table 2.

[0048] Since no acid was added to the ethylene glycol vapor, the dye removal was not complete, and the dye concentration in the final ethylene glycol terephthalate was relatively high.

[0049] Comparative Example 2

[0050] A certain amount of waste colored polyester fiber was placed in a reaction kettle containing ethylene glycol vapor (temperature 210°C, cerotic acid concentration 1.000 wt%) for decolorization treatment for 60 minutes. After the decolorization was completed, the decolorized recycled polyester fiber was depolymerized in ethylene glycol. The molar ratio of the recycled polyester fiber to ethylene glycol was 1:18, the depolymerization temperature was 210°C, and the depolymerization time was 2 hours.

[0051] The depolymerization solution is poured into water, followed by precipitation and filtration to obtain crude diethylene glycol terephthalate. The crude dimethyl terephthalate is further dissolved in hot water, and impurities are removed by filtration. Then, it is filtered through a filter column containing activated carbon. Finally, the filtrate is crystallized, filtered, and dried to obtain purified ethylene glycol terephthalate. The dye concentration and diethylene glycol content in the final ethylene glycol terephthalate are measured, and the specific data are shown in Table 2.

[0052] Since adding an acid with a boiling point higher than 200 °C to ethylene glycol vapor is not easily volatilized with the ethylene glycol vapor, the dye removal is incomplete, resulting in a relatively high dye concentration in the final ethylene glycol terephthalate.

[0053] Comparative Example 3

[0054] A certain amount of waste colored polyester fiber is placed in a reaction kettle containing ethylene glycol vapor (temperature 210 °C, hydrofluoric acid concentration 1.000 wt%) for decolorization treatment for 60 min. After the decolorization is completed, the decolorized recycled polyester fiber is depolymerized in ethylene glycol. The molar ratio of the recycled polyester fiber to ethylene glycol is 1:18, the depolymerization temperature is 210 °C, and the depolymerization time is 2 hours.

[0055] The depolymerization solution is poured into water, followed by precipitation and filtration to obtain crude diethylene glycol terephthalate. The crude dimethyl terephthalate is further dissolved in hot water, and impurities are removed by filtration. Then, it is filtered through a filter column containing activated carbon. Finally, the filtrate is crystallized, filtered, and dried to obtain purified ethylene glycol terephthalate. The dye concentration and diethylene glycol content in the final ethylene glycol terephthalate are measured, and the specific data are shown in Table 2.

[0056] Since adding an acid with a boiling point lower than 40 °C to ethylene glycol vapor is extremely volatile, it cannot act on the colored polyester, resulting in incomplete dye removal and a relatively high dye concentration in the final ethylene glycol terephthalate.

[0057] Comparative Example 4

[0058] A certain amount of waste colored polyester fiber is placed in a reaction kettle containing ethylene glycol vapor (temperature 210 °C, acetic acid concentration 1.000 wt%) for decolorization treatment for 60 min. After the decolorization is completed, the decolorized recycled polyester fiber is depolymerized in ethylene glycol. The molar ratio of the recycled polyester fiber to ethylene glycol is 1:1, the depolymerization temperature is 210 °C, and the depolymerization time is 2 hours.

[0059] The depolymerization solution is poured into water, followed by precipitation and filtration to obtain crude bis(2-hydroxyethyl) terephthalate. The crude bis(2-hydroxyethyl) terephthalate is further dissolved in hot water, and impurities are removed by filtration. Then, it is filtered through a filtration column containing activated carbon. Finally, the filtrate is crystallized, filtered, and dried to obtain purified bis(2-hydroxyethyl) terephthalate. The dye concentration and diethylene glycol content in the final bis(2-hydroxyethyl) terephthalate are measured, and the specific data are shown in Table 2.

[0060] Since the molar ratio of recycled polyester fiber to ethylene glycol is 1:1, incomplete depolymerization of the recycled polyester fiber occurs, resulting in a significant reduction in the recovery rate of bis(2-hydroxyethyl) terephthalate.

[0061] Comparative Example 5

[0062] A certain amount of waste colored polyester fiber is placed in a reaction kettle containing ethylene glycol vapor (temperature 210 °C, acetic acid concentration 1.000 wt%) for decolorization treatment for 60 min. After the decolorization is completed, the decolorized recycled polyester fiber is depolymerized in ethylene glycol. The molar ratio of recycled polyester fiber to ethylene glycol is 1:40, the depolymerization temperature is 210 °C, and the depolymerization time is 2 hours.

[0063] The depolymerization solution is poured into water, followed by precipitation and filtration to obtain crude bis(2-hydroxyethyl) terephthalate. The crude bis(2-hydroxyethyl) terephthalate is further dissolved in hot water, and impurities are removed by filtration. Then, it is filtered through a filtration column containing activated carbon. Finally, the filtrate is crystallized, filtered, and dried to obtain purified bis(2-hydroxyethyl) terephthalate. The dye concentration and diethylene glycol content in the final bis(2-hydroxyethyl) terephthalate are measured, and the specific data are shown in Table 2.

[0064] Since the molar ratio of recycled polyester fiber to ethylene glycol is 1:50, a large amount of ethylene glycol needs to be added, resulting in a significant increase in the diethylene glycol content in bis(2-hydroxyethyl) terephthalate, which affects the product quality.

[0065]

[0066]

Claims

1. Recycled diethylene glycol terephthalate, characterized in that: The content of the dye in the diethylene glycol terephthalate is below 500 ppm.

2. The recycled diethylene glycol terephthalate according to claim 1, characterized in that: The content of the diethylene glycol in the diethylene glycol terephthalate is below 0.10 wt%.

3. The preparation method of the recycled polyethylene terephthalate diglycolate according to claim 1, characterized in that: The method comprises the following steps: Step 1, subjecting waste colored polyester fibers to high-temperature decolorization in ethylene glycol vapor containing an acid to obtain decolorized recycled polyester fibers, wherein the acid is an organic acid and / or an inorganic acid with a boiling point of 40.0 to 200.0 °C; Step 2, subjecting the decolorized recycled polyester fibers to a depolymerization reaction in ethylene glycol. After the depolymerization ends, pouring the depolymerization solution into water, and obtaining crude diethylene glycol terephthalate through precipitation and filtration. The molar ratio of the decolorized recycled polyester fibers to ethylene glycol is 1:2 to 40; Step 3, dissolving the crude ethylene glycol terephthalate in hot water, filtering to remove impurities, adsorbing the dye therein with activated carbon, and then performing crystallization, filtration, and drying to obtain purified diethylene glycol terephthalate.

4. The preparation method of recycled diethylene glycol terephthalate according to claim 3, characterized in that: The acid is one or more of hydrochloric acid, nitric acid, formic acid, and acetic acid.

5. The preparation method of recycled diethylene glycol terephthalate according to claim 3 or 4, characterized in that: The temperature of the ethylene glycol vapor is 190 to 230 °C.

6. The preparation method of recycled diethylene glycol terephthalate according to claim 3 or 4, characterized in that: The concentration of the acid in the ethylene glycol vapor is 0.010 to 20.000 wt%.

7. The preparation method of the recycled polyethylene terephthalate glycol according to claim 6, wherein: The concentration of the acid in the ethylene glycol vapor is 0.050 to 5.000 wt%.

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