Method for decolorizing waste PET textile in regeneration process by using hydrophobic deep-eutectic solvent

Abstract

The invention provides a method for decolorizing a waste PET textile in a regeneration process by using a hydrophobic deep-eutectic solvent. The method comprises the following steps: degrading a PET textile through a chemical method, blending the PET textile into a low-molecular solution, and extracting dye in the low-molecular solution through a hydrophobic deep-eutectic solvent, so as to obtain a decolorized polyester degradation product, namely bis (2-hydroxyethyl) terephthalate (BHET). The eutectic solvent used in the method can also be regenerated in a reverse extraction mode for recycling. Extraction decolorization is simple to operate and convenient to operate, and has certain advantages compared with other decolorization technologies.

Description

Technical Field

[0001] The invention relates to a method for decolorizing a waste PET textile alcoholysis monomer, in particular to an extraction method for separating BHET and a dye from a PET alcoholysis solution by using a hydrophobic low eutectic solvent as an extractant. Background Art

[0002] At present, the chemical recycling of polyester textiles mainly includes methanolysis, glycolysis and hydrolysis, etc., which depolymerize PET into monomers and oligomers, and synthesize recycled PET (r-PET) after purification. However, due to the complexity of textile products, which usually contain many additives such as pigments, dyes, dispersants, etc., it is a huge challenge to chemically recycle PET fibers, especially the residual dyes reduce the product quality, which greatly limits the application of recycled PET (r-PET).

[0003] In recent years, various methods have been developed to solve this problem. The ion-modified activated carbon prepared by the invention of patent CN109574835A decolorizes PET alcoholysis liquid, and the ion-modified activated carbon can be regenerated after use, and the decolorization rate of BHET by the ion-modified activated carbon after 5 repeated adsorptions can still reach 71.11%. However, the adsorption capacity of the activated carbon will be partially lost after each use, until it loses its function and becomes hazardous waste; and the adsorption of activated carbon is not selective, and while adsorbing the dye, it will also adsorb the product BHET, causing great material loss. Patent CN116082158A provides a decolorization and purification method for BHET, including the first addition of activated carbon to preliminarily treat the BHET material, followed by crystallization and use of an oxidant to destroy the dye molecules on the BHET, and then adding a second dose of activated carbon for treatment to adsorb the oxide after the chemical reaction, and finally cooling and crystallizing for the second time to obtain the BHET finished product. This can obtain clean BHET, but multiple crystallizations and activated carbon adsorption will cause great BHET losses. Patent CN116715581A uses electrochemical technology to remove dyes from colored waste PET fibers during alcoholysis to recover monomer BHET. After the glycol alcoholysis of PET fibers, BHET is not separated, and the dyes in BHET and EG are removed simultaneously, and the deep decolorization of BHET and the preliminary decolorization of EG are achieved at the same time. The obtained BHET meets the standard of being reused as non-food grade PET for bottles. However, the oxidation reaction at H2O2 and the anode is not selective, and the hydroxyl group in BHET may also be oxidized when the structure of the dye molecule is destroyed by oxidation. CN115894223A uses the phase change properties of BHET crystals to realize a chemical recovery method for waste PET products. The method includes mixing waste PET products with catalysts in ethylene glycol, performing alcoholysis reaction to obtain alcoholysis solution, cooling and crystallizing the alcoholysis solution to obtain crystals containing BHET; decompressing and sublimating the crystals; condensing and collecting BHET. However, the huge energy demand limits its industrial application, and the heavy components remaining after sublimation become more difficult to handle.

[0004] In summary, there are certain defects in obtaining pure and high purity BHET. Extraction method, as a traditional means of material separation, is used in many aspects. Dyes, as impurities in alcoholysis, can be selectively extracted into the oil phase by selecting a suitable extractant, and BHET can be retained in the water phase, thereby achieving the separation of the two and completing the decolorization goal. Summary of the invention

[0005] The purpose of the present invention is to address the shortcomings of the existing methods for obtaining white BHET and propose a method for removing dyes from BHET alcoholysis solution, which can solve the problem of recycling colored PET textiles. Extraction decolorization is simple to operate and easy to run, and has certain advantages over other decolorization technologies.

[0006] The technical solution provided by the present invention is as follows:

[0007] The method uses a hydrophobic eutectic system as an extractant and does not contain any diluent. The method comprises the following steps:

[0008] (1) Preparation of ethylene glycol alcoholysis solution of PET textiles; (2) Synthesis of low eutectic solvent; (3) Extraction and decolorization; (4) Evaluation of decolorization effect; (5) Dye stripping; (6) Regeneration of stripping agent. All experimental conditions of the present invention are first carried out in a 1wt% BHET content alcoholysis solution simulated by single dye dyeing BHET, and then decolorization is carried out on 9 real colored PET ethylene glycol alcoholysis solutions, 5 of which are single color solid color fabrics and 4 are fancy color fabrics. The dye described in this method is an organic dye, and its molecular structure may include the following structural units:

[0009]

[0010] 1) Preparation of PET ethylene glycol alcoholysis solution: Using zinc acetate with a mass of 1% of the mass of waste PET as a catalyst, PET textiles and ethylene glycol are added to the reactor at a ratio of 1:4 (mass ratio), and reacted at 190°C for alcoholysis. Subsequently, water 8 times the mass of PET is added and heated at 90°C for 30 minutes, followed by filtration to remove oligomers. According to the BHET yield of 70%, the filtrate is prepared into a solution with a BHET content of 0.1wt% to 5%. In addition, BHET dyed with a single dye, ethylene glycol and water are configured into a simulated alcoholysis solution of a known dye structure, in which the mass of ethylene glycol is 4 times that of BHET and the BHET content is 0.1wt% to 5wt%.

[0011] 2) Preparation of organic phase: directly use a single organic solvent as the organic phase without any purification or addition of diluent; heat and stir the corresponding mass of hydrogen bond donor and hydrogen bond acceptor at a certain molar ratio at a certain temperature until they become a clear liquid, and use the obtained clear liquid as the extraction organic phase.

[0012] 3) Extraction: the aqueous extraction phase prepared in step 1 and the organic extraction phase prepared in step 2 are mixed and then extracted, the temperature is controlled at 50-90° C., the aqueous extraction phase and the organic phase (mass ratio) are 5:1-30:1, and the single extraction time is 1-30 min;

[0013] 4) Evaluation of decolorization effect: After the extraction, the oil phase was tested for BHET loss rate by liquid chromatography, and the aqueous phase was allowed to stand at 4°C for 24 h for crystallization. The obtained BHET crystals were used to calculate the decolorization rate by a desktop spectrophotometer.

[0014] 5) Stripping: The low eutectic solvent uses analytical pure formic acid as the stripping agent to strip the extracted organic phase to obtain a darker stripping phase and a lighter raffinate phase. The ratio of the stripping phase to the organic phase is controlled at 1:2-3:1. The single stripping time is 1-10 min and the temperature is 30-60°C.

[0015] 6) Regeneration of stripping agent: The formic acid after stripping is regenerated by reduced pressure rotary evaporation.

[0016] The present invention uses a low eutectic solvent as a decolorizing extractant for the alcoholysis solution of PET textiles. The reasons for its good decolorizing effect include the following two points:

[0017] 1) Hydrophobic low eutectic solvents have a certain degree of fat solubility and can dissolve many organic substances. Most of the dyes on textiles are organic dyes, and they contain a large number of carbon atoms and have large molecules. Therefore, the solubility of dyes in low eutectic solvents is greater than in water, resulting in a good decolorization effect.

[0018] 2) There are usually some electronegative groups in the dye molecules, such as Cl, Br and O, and the low eutectic solvents with good decolorization effect all have some carboxyl groups or hydroxyl groups. These functional groups can combine with the electronegative groups in the dye due to electrostatic and van der Waals forces, thereby extracting the dye molecules from the aqueous phase into the organic phase.

[0019] Advantages of the present invention:

[0020] 1. The present invention is the first to use an extraction method to remove dyes from ethylene glycol alcoholysis solution of PET fibers. The color of the BHET simulated alcoholysis solution dyed with a single disperse dye and the alcoholysis solution of some PET textiles is removed in a very short decolorization time.

[0021] 2. The BHET obtained after decolorization of the present invention was subjected to HPLC, nuclear magnetic hydrogen spectrum and differential thermal analysis. The results showed that the obtained BHET had high purity, no side reaction occurred, and the extractant did not remain on the BHET.

[0022] 3. The used low eutectic solvent can be regenerated by stripping with formic acid, and the extracted formic acid can be regenerated by vacuum rotary evaporation.

[0023] 4. The decolorization method proposed in the present invention is consistent with the existing PET glycol alcoholysis process, and there is no need to make major changes to the existing process. The extraction method is simple to operate and easy to implement in terms of process. At the same time, the extraction and decolorization consumes less energy, which greatly saves the cost of dye removal and is expected to achieve closed-loop recycling of PET fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0025] Embodiment 1:

[0026] Process flow chart Figure 1 shown.

[0027] 1) Preparation of PET alcoholysis solution simulating 1 wt% BHET content: 1 g DB56-dyed BHET and 4 g ethylene glycol were added to 95 g water, and heated and stirred at 60° C. to dissolve to prepare a solution.

[0028] 2) Prepare the extraction organic phase: add lauric acid and tetrabutylammonium chloride in a molar ratio of 1:1 into a sample bottle and stir at 80° C. until a clear liquid is formed.

[0029] 3) Extraction: The solution prepared in step 1 is used as the aqueous phase, and the solvent prepared in step 2 is used as the organic phase. 100 g of the aqueous phase and 10 g of the organic phase are mixed at a mass ratio of 10:1, and then heated and stirred at 60°C for 30 min, and then centrifuged at 8000 r / min for 5 min to separate the two phases. The aqueous phase is allowed to stand at 4°C for 24 h to obtain BHET crystals.

[0030] It was tested that after the alcoholysis solution of BHET simulated by DB56 dyed was decolorized by lauric acid / tetrabutylammonium chloride low-deep eutectic solvent, the decolorization rate of BHET was 70.4% and the loss rate of BHET was 8.5%.

[0031] Embodiment 2:

[0032] Process flow chart Figure 1 shown.

[0033] 1) Preparation of PET alcoholysis solution simulating 1 wt% BHET content: 1 g DB56-dyed BHET and 4 g ethylene glycol were added to 95 g water, and heated and stirred at 60° C. to dissolve to prepare a solution.

[0034] 2) Prepare the extraction organic phase: add lidocaine and oleic acid into the sample bottle at a molar ratio of 1:1, and stir at 100° C. until a clear liquid is formed.

[0035] 3) Extraction: The solution prepared in step 1 is used as the aqueous phase, and the solvent prepared in step 2 is used as the organic phase. 100 g of the aqueous phase and 10 g of the organic phase are mixed at a mass ratio of 10:1, and then heated and stirred at 60°C for 30 min, and then centrifuged at 8000 r / min for 5 min to separate the two phases. The aqueous phase is allowed to stand at 4°C for 24 h to obtain BHET crystals.

[0036] It was tested that after the alcoholysis solution of BHET simulated by DB56 was decolorized by lidocaine / oleic acid low eutectic solvent, the decolorization rate of BHET was 95.2% and the loss rate of BHET was 11.38%.

[0037] Embodiment 3:

[0038] Process flow chart Figure 1 shown.

[0039] 1) Preparation of PET alcoholysis solution simulating 1 wt% BHET content: 1 g DR60-dyed BHET and 4 g ethylene glycol were added to 95 g water, and heated and stirred at 60° C. to dissolve to prepare a solution.

[0040] 2) Preparation of extraction organic phase: Add oleic acid and menthol into a sample bottle at a molar ratio of 1:2, and stir at 60° C. until a clear liquid is formed.

[0041] 3) Extraction: The solution prepared in step 1 is used as the aqueous phase, and the solvent prepared in step 2 is used as the organic phase. 100 g of the aqueous phase and 10 g of the organic phase are mixed at a mass ratio of 15:1, and then heated and stirred at 60°C for 30 min, and then centrifuged at 8000 r / min for 5 min to separate the two phases. The aqueous phase is allowed to stand at 4°C for 24 h to obtain BHET crystals.

[0042] 4) Stripping: Analytical grade formic acid was used as stripping agent without further purification. DES regeneration was carried out under the conditions of formic acid:DES mass ratio of 3:1, 30°C and stirring time of 10 min.

[0043] 5) Regeneration of stripping agent: The used formic acid is subjected to reduced pressure distillation at 60°C to recover the formic acid.

[0044] It was tested that after the DR60-dyed BHET-simulated alcoholysis solution was decolorized by the oleic acid / menthol low eutectic solvent, the decolorization rate of BHET was 89.1%, the BHET loss rate was 8.6%, and 76.8% of the dye was removed by the low eutectic solvent after regeneration.

[0045] Embodiment 4:

[0046] Process flow chart Figure 1 shown.

[0047] 1) Preparation of PET glycol alcoholysis solution: dark blue PET textile and ethylene glycol were added to a four-necked flask at a mass ratio of 1:4, and zinc acetate was added as a catalyst in an amount of 1% of the mass of PET. Then, alcoholysis was carried out at 190°C, and the reaction was filtered while hot. Subsequently, water 8 times the mass of PET was added and heated at 90°C for 30 minutes, and then filtered to remove oligomers. According to the BHET yield of 70%, the filtrate was prepared into a 1% solution of BHET.

[0048] 2) Preparation of extraction organic phase: Add oleic acid and menthol into a sample bottle at a molar ratio of 1:1, and stir at 60° C. until a clear liquid is formed.

[0049] 3) Extraction: The solution prepared in step 1 is used as the aqueous phase, and the solvent prepared in step 2 is used as the organic phase. 100 g of the aqueous phase and 10 g of the organic phase are mixed at a mass ratio of 15:1, and then heated and stirred at 60°C for 30 min, and then centrifuged at 8000 r / min for 5 min to separate the two phases. The aqueous phase is allowed to stand at 4°C for 24 h to obtain BHET crystals.

[0050] 4) Stripping: Analytical grade formic acid was used as stripping agent without further purification. DES regeneration was carried out under the conditions of formic acid:DES mass ratio of 1:1, 60°C and stirring time of 10 min.

[0051] 5) Regeneration of stripping agent: The used formic acid is subjected to reduced pressure distillation at 60°C to recover the formic acid.

[0052] It was tested that after the alcoholysis solution made of dark blue PET textiles was decolorized by a low eutectic solvent, the decolorization rate of BHET was 83.1%, the BHET loss rate was 8.6%, the secondary extraction decolorization rate was 98.2%, and the formic acid recovery rate was 96.4%.

[0053] Embodiment 5:

[0054] Process flow chart Figure 1 shown.

[0055] 1) Preparation of PET alcoholysis solution simulating 1 wt% BHET content: 1 g DB56-dyed BHET and 4 g ethylene glycol were added to 95 g water, and heated and stirred at 60° C. to dissolve to prepare a solution.

[0056] 2) Prepare the extraction organic phase: add tetrabutylammonium chloride and capric acid in a molar ratio of 1:1 into a sample bottle and stir at 65° C. until a clear liquid is formed.

[0057] 3) Extraction: The solution prepared in step 1 is used as the aqueous phase, and the solvent prepared in step 2 is used as the organic phase. 100 g of the aqueous phase and 10 g of the organic phase are mixed at a mass ratio of 15:1, and then heated and stirred at 60°C for 30 min, and then centrifuged at 8000 r / min for 5 min to separate the two phases. The aqueous phase is allowed to stand at 4°C for 24 h to obtain BHET crystals.

[0058] 4) Stripping: Analytical grade formic acid was used as stripping agent without further purification. DES regeneration was carried out under the conditions of formic acid:DES mass ratio of 3:1, 60°C and stirring time of 10 min.

[0059] 5) Regeneration of stripping agent: The used formic acid is subjected to reduced pressure distillation at 60°C to recover the formic acid.

[0060] It was tested that after the alcoholysis solution of DR60-dyed BHET simulation was decolorized by the oleic acid / menthol low eutectic solvent, the decolorization rate of BHET was 79.6%, the loss rate of BHET was 17.1%, and the formic acid recovery rate was 96.4%.

Claims

1. A method for decolorizing waste PET textiles in a regeneration process using a hydrophobic deep eutectic solvent, characterized in that: 1) Preparation of alcoholysis solution: Using zinc acetate (1% by weight of waste PET textile) as a catalyst, adding PET textile and ethylene glycol into a reactor in a mass ratio of 1:4, and reacting alcoholysis at 190°C; then adding water (8 times by weight of the PET textile) and heating at 90°C for 30 minutes, followed by filtering; preparing the filtrate into a solution with a BHET content of 0.1wt% to 5%; Alternatively, a single dye-dyed BHET, ethylene glycol and water are used to prepare a simulated alcoholysis solution of a known dye structure, wherein the mass of ethylene glycol is 4 times that of BHET and the content of BHET is 0.1wt% to 5wt%; 2) Extraction: After preparation, the low eutectic solvent is directly used for extraction; wherein the single extraction temperature and time are respectively controlled between 50 and 90°C, and the extraction is carried out between 1 and 30 minutes, and the mass ratio of the aqueous phase to the oil phase is 5:1 to 30:1; wherein the hydrogen bond acceptor HBA of the low eutectic solvent includes tetrabutylammonium chloride, tetrabutyl sodium bromide, methyl trioctyl ammonium chloride, tetraoctyl ammonium bromide, lidocaine, capric acid, oleic acid, and trioctyl phosphine oxide; wherein the low eutectic solvent hydrogen bond donor HBD includes glacial acetic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, oleic acid, propanol, hexanol, menthol, and thymol; the molar ratio of HBA:HBD in the synthetic low eutectic solvent is controlled between 5:1 and 1:

5.

2. The method according to claim 1, characterized in that: Also includes 3) Stripping: using formic acid as stripping agent, stripping the dye in the low eutectic solvent; the mass ratio of stripping phase to organic phase is controlled at 1:2-3:1, the single time is controlled at 1-10 minutes, and the temperature is controlled at 30-60°C.

3. The method according to claim 1, characterized in that: 4) Product crystallization: The decolorized alcoholysis solution was allowed to stand at 4°C for 24 hours, and then decolorized needle-shaped BHET crystals were obtained.

4. The method according to claim 1, characterized in that: The step 5) formic acid regeneration is also included: formic acid with dye is regenerated by rotary evaporation under reduced pressure at 60°C.

5. The method according to claim 1, characterized in that: The low eutectic solvent regenerated by back extraction can be used again for decolorization of the alcoholysis solution after drying.

6. The method according to claim 1, characterized in that: The formic acid regenerated by vacuum rotary evaporation can also be used again to regenerate the low eutectic solvent after decolorization.

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