Method for preparing dihydroxyethyl terephthalate from waste textiles and its products

Abstract

This application provides a method for preparing dihydroxyethyl terephthalate (BHET) and its product from waste textiles. The method includes: S1: placing the waste textiles in extraction solvent I for a first extraction; obtaining waste textiles after the first extraction; S2: placing the waste textiles after the first extraction in extraction solvent II for a second extraction; obtaining waste textiles after the second extraction; S3: placing the waste textiles after the second extraction in extraction solvent III for a third extraction; obtaining an extract; S4: subjecting the extract to a depolymerization reaction with ethylene glycol to obtain an alcoholysis solution; crystallizing to obtain crude dihydroxyethyl terephthalate; S5: dissolving the crude dihydroxyethyl terephthalate in a solvent to obtain a crude product solution, passing the crude product solution through a fixed-bed adsorption, and crystallizing to obtain dihydroxyethyl terephthalate. The method of this application can improve the purity of BHET crystals.

Description

Technical Field

[0001] This application relates to the field of chemical fiber technology, and in particular to a method for preparing dihydroxyethyl terephthalate from waste textiles and the product thereof. Background Technology

[0002] Waste textiles are chemically inert and extremely difficult to degrade under natural conditions. Currently, they are mainly disposed of through incineration or landfill, with a recycling rate of less than 15%. This not only causes serious environmental pollution but also represents a huge waste of resources. Therefore, the recycling of waste textiles is of paramount importance.

[0003] Currently, the main recycling methods for waste textiles include physical recycling, mechanical recycling, chemical recycling, and energy recovery. Chemical recycling involves processing waste polyester into monomer compounds using chemical methods, and then manufacturing new polyester products. This mainly includes hydrolysis, alcoholysis, and ammonolysis. Alcoholysis is further divided into methanol alcoholysis and ethylene glycol alcoholysis. Methanol alcoholysis often requires supercritical conditions (250-280℃, 8-15 MPa), placing extremely high demands on equipment for industrialization. Catalyst recovery is also difficult, and the yield of DMT monomer, a product of methanol alcoholysis, is at most only 95%, limiting its industrialization. Ethylene glycol alcoholysis is currently the most promising method for industrialization. Unlike methanol alcoholysis, ethylene glycol alcoholysis typically occurs at 190-230℃ under normal pressure. The product of ethylene glycol alcoholysis is diethyl terephthalate (BHET). BHET has a high boiling point (317℃), making it difficult to purify, and it readily polymerizes at high temperatures, producing dimers and oligomers.

[0004] Waste mixed textiles have complex compositions, typically containing a mixture of polyester, cotton, cellulose, wool, silk, spandex, nylon, acrylic, oils, matting agents, and polyester catalysts. Due to the complexity of the composition, the separation of each component is difficult, which poses a great challenge to the purification and refining process of BHET.

[0005] Therefore, there is an urgent need to develop a method for preparing high-purity dihydroxyethyl terephthalate from waste textiles. Summary of the Invention

[0006] This application provides a method for preparing dihydroxyethyl terephthalate (BHET) from waste textiles and the product thereof. The method of this application can obtain high-purity BHET.

[0007] In a first aspect, this application provides a method for preparing dihydroxyethyl terephthalate from waste textiles, the method comprising:

[0008] S1: The waste textiles are placed in extraction solvent I for the first extraction; after removing the extract, the waste textiles after the first extraction are obtained.

[0009] S2: The waste textiles after the first extraction are placed in extraction solvent II for a second extraction; after removing the extract, the waste textiles after the second extraction are obtained.

[0010] S3: Place the waste textiles after the second extraction in extraction solvent III for a third extraction; remove the waste textiles after the third extraction to obtain the extract;

[0011] S4: The extract is subjected to a depolymerization reaction with ethylene glycol to obtain an alcoholysis solution; the alcoholysis solution is crystallized to obtain crude dihydroxyethyl terephthalate;

[0012] S5: Dissolve crude dihydroxyethyl terephthalate in a solvent to obtain a crude product solution, pass the crude product solution through a fixed bed adsorption to obtain a dihydroxyethyl terephthalate solution, and crystallize the dihydroxyethyl terephthalate solution to obtain the dihydroxyethyl terephthalate.

[0013] Among them, one of extraction solvent I and extraction solvent II includes at least one of DMF, DMAC, and DMSO, and the other of extraction solvent I and extraction solvent II includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether; extraction solvent III includes ethylene glycol.

[0014] In one possible implementation, the waste textiles comprise: 50-70 wt% polyester, 15-35 wt% cotton, 5-15 wt% nylon, 3-8 wt% spandex, 0.02-1.5 wt% dyes, and 1-3 wt% other components.

[0015] In one possible implementation, the extraction solvent I includes at least one of DMF, DMAC, and DMSO; the temperature of the first extraction is 80-130°C, and the extraction time is 20-50 min.

[0016] The extraction solvent II includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether; the temperature of the second extraction is 130-170℃, and the extraction time is 10-20 min.

[0017] In one possible implementation, the extraction solvent I includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether.

[0018] The temperature of the first extraction is 130-170℃, and the extraction time is 10-20 min;

[0019] The extraction solvent II includes at least one of DMF, DMAC, and DMSO; the temperature of the second extraction is 80-130℃, and the extraction time is 20-50 min.

[0020] In one possible implementation, the temperature of the third extraction is 190-230°C, and the time of the third extraction is 30-90 min.

[0021] In one possible implementation, the mass ratio of the extraction solvent I to the waste textiles is 3-20:1;

[0022] And / or; the mass ratio of the extraction solvent II to the waste textiles after the first extraction is 3-20:1;

[0023] And / or; the mass ratio of the extraction solvent III and the second extracted waste textile is 3-20:1.

[0024] In one possible implementation, in step S4, a catalyst is further added to the depolymerization reaction. The catalyst includes one or more of the following: AlSBA-15, β-type zeolite, γ-type zeolite, hydrotalcite, spinel, solid superacid, superparamagnetic γ-type iron oxide, imidazole hexafluorophosphate, imidazole trifluoromethanesulfonate, cobalt acetate, manganese acetate, zinc acetate, sodium carbonate, and potassium carbonate.

[0025] In one possible implementation, in step S4, the mass ratio of the extract to ethylene glycol is 1:(0.5-2).

[0026] In one possible implementation, the temperature of the depolymerization reaction is 190-250°C; the time of the depolymerization reaction is 60-180 min.

[0027] Secondly, this application provides a dihydroxyethyl terephthalate prepared according to the above method.

[0028] This application provides a method for preparing dihydroxyethyl terephthalate (BHET) from waste textiles and the product thereof. The method involves a first extraction of the waste textiles to extract spandex or nylon, followed by separation of the extract. Then, a second extraction is performed on the waste textiles after the first extraction to extract nylon or spandex. A third extraction is then performed on the waste textiles after the second extraction to extract polyester. The extract is then subjected to alcoholysis, crystallization, fixed-bed adsorption, and crystallization in sequence to obtain the final BHET crystals. The process involves two extraction steps: first and second extractions to extract spandex and nylon from solid-phase waste textiles. The extracted spandex and nylon dissolve in the extract, while a large amount of polyester and cotton remain in the solid phase (i.e., the waste textiles after the second extraction). The extract containing spandex or nylon is removed through solid-liquid separation. A third extraction is then performed on the waste textiles after the second extraction. After the third extraction, an extract containing polyester is obtained, while the cotton component remains in the solid phase. Solid-liquid separation continues, and the polyester-containing extract is sequentially subjected to alcoholysis, crystallization, fixed-bed adsorption, and crystallization to obtain the final BHET crystals. Because spandex and nylon are separated from the waste textiles in the first and second extractions, the purity of polyester in the third extraction extract is improved, thus increasing the purity of the final BHET crystals. Furthermore, the third extraction simultaneously separates the cotton component from the waste textiles, further increasing the polyester purity in the third extraction extract and thus improving the purity of the BHET crystals. Finally, the spandex, nylon, and cotton separated in this extraction process can be further recycled. Attached Figure Description

[0029] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0030] Figure 1 A schematic diagram of the preparation process of BHET in Example 1 provided in this application;

[0031] Figure 2 Product diagram of the BHET crystal of Embodiment 1 provided in this application;

[0032] Figure 3 A high-performance liquid chromatogram of BHET crystals from Example 1 provided in this application.

[0033] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present invention, this application will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the invention and are not intended to limit its scope. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. When the following description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0035] In a first aspect, this application provides a method for preparing dihydroxyethyl terephthalate from waste textiles, comprising:

[0036] S1: The waste textiles are placed in extraction solvent I for the first extraction; after removing the extract, the waste textiles after the first extraction are obtained.

[0037] S2: The waste textiles after the first extraction are placed in extraction solvent II for a second extraction; after removing the extract, the waste textiles after the second extraction are obtained.

[0038] S3: Place the waste textiles after the second extraction in extraction solvent III for a third extraction; remove the waste textiles after the third extraction to obtain the extract;

[0039] S4: The extract is subjected to a depolymerization reaction with ethylene glycol to obtain an alcoholysis solution; the alcoholysis solution is crystallized to obtain crude dihydroxyethyl terephthalate;

[0040] S5: Dissolve crude dihydroxyethyl terephthalate in a solvent to obtain a crude product solution. Pass the crude product solution through a fixed bed adsorption to obtain a dihydroxyethyl terephthalate solution. Crystallize the dihydroxyethyl terephthalate solution to obtain dihydroxyethyl terephthalate.

[0041] Among them, one of extraction solvent I and extraction solvent II includes at least one of DMF, DMAC, and DMSO, and the other of extraction solvent I and extraction solvent II includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether; extraction solvent III includes ethylene glycol.

[0042] This application involves a first extraction of waste textiles to extract spandex or nylon. After separating the extract, a second extraction is performed on the waste textiles after the first extraction to extract nylon or spandex. A third extraction is then performed on the waste textiles after the second extraction to extract polyester. The extract is then subjected to alcoholysis, crystallization, fixed-bed adsorption, and crystallization sequentially to obtain the final BHET crystals. Specifically, the first and second extraction processes extract spandex and nylon from the solid-phase waste textiles, with the extracted spandex and nylon dissolving in the extract. A large amount of polyester and cotton, the main components, remain in the solid phase (i.e., the waste textiles after the second extraction). The extract containing spandex or nylon is removed by solid-liquid separation. The waste textiles after the second extraction are then subjected to a third extraction, resulting in an extract containing polyester. The cotton component remains in the solid phase. Solid-liquid separation continues, and the extract containing polyester is subjected to alcoholysis, crystallization, fixed-bed adsorption, and crystallization sequentially to obtain the final BHET crystals. Since spandex and nylon are separated from waste textiles in the first and second extractions, this improves the purity of polyester in the extract of the third extraction, thus increasing the purity of the final BHET crystals. Furthermore, the third extraction simultaneously separates cotton components from the waste textiles, further improving the purity of polyester in the extract and consequently the purity of the BHET crystals. Finally, the spandex, nylon, and cotton separated in this extraction process can be further recycled.

[0043] Secondly, the raw materials used in this application have a wide range of applications. Existing technologies are limited to relatively pure PET products / bottle flakes, while the raw materials used in this application are unrestricted in terms of both color and type, and can include waste clothing, quilts, blankets, curtains, and other types of waste textiles provided by waste recycling companies. Compared with the DMT route, this scheme has a shorter process route, does not involve two-step transesterification reactions and high-temperature distillation, has lower energy consumption, and lower production costs. Compared with the existing BHET process, this scheme solves the problem of poor product quality, low purity, and difficulty in purification caused by the easy polymerization of BHET during molecular distillation through an adsorption-crystallization process. Compared with the existing BHET decolorization process that directly adds adsorbent to the alcoholysis solution, this scheme uses fixed-bed adsorption after crystallizing crude BHET, effectively solving the problem of large adsorbent consumption and significantly reducing the cost of the preparation process.

[0044] Furthermore, this solution achieves the tiered high-value utilization of waste textiles through a two-step forward solid-phase extraction process (first and second extraction) and a one-step reverse solid-phase extraction process (third extraction). This provides high-purity raw materials for downstream applications of polyester, nylon, spandex, and cotton cellulose, overcoming the difficulty of effectively separating the complex components of waste textiles. Addressing the issues of fluctuating raw material values ​​and high impurity content in waste textiles, which lead to poor product quality and instability, this solution is suitable for large-scale production processes. It truly realizes the high-value utilization of waste textiles.

[0045] In one possible implementation, the waste textiles include: 50-70 wt% polyester, 15-35 wt% cotton, 5-15 wt% nylon, 3-8 wt% spandex, 0.02-1.5 wt% dyes, and 1-3 wt% other components.

[0046] It is understood that waste textiles include 50-70 wt% polyester, such as 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, or any two of these values.

[0047] It is understood that waste textiles include 15-35 wt% cotton, such as 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or any two of these values.

[0048] It is understood that waste textiles include 5-15 wt% nylon, such as 5 wt%, 10 wt%, 15 wt%, or any two of these values.

[0049] It is understood that waste textiles include 3-8 wt% spandex, such as 3 wt%, 5 wt%, 8 wt%, or any two of these values.

[0050] It is understood that waste textiles include 0.02-1.5 wt% of dyes, such as 0.02 wt%, 0.05 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, or any two of these values.

[0051] It is understood that waste textiles include 1-3 wt% of other components, such as 1 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3 wt%, or any two of these values.

[0052] It is understood that this application does not limit the specific type of dye; it can be a natural dye or a synthetic dye.

[0053] In one possible implementation, extraction solvent I includes at least one of DMF, DMAC, and DMSO; the temperature of the first extraction is 80-130°C, and the extraction time is 20-50 min; extraction solvent II includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether; the temperature of the second extraction is 130-170°C, and the extraction time is 10-20 min.

[0054] It is understandable that in this embodiment, the extraction solvent I is mainly used to extract spandex. The first extraction time should not be too fast. Insufficient extraction time will prevent the spandex from being effectively extracted from waste textiles by solid-phase extraction, thereby affecting the purity of BHET products.

[0055] The temperature of the first extraction should not be too high. If the temperature of the spandex is too high, it will cause micro-depolymerization of the spandex to form substances such as polytetrahydrofuran, which will affect the purity of the BHET product.

[0056] Understandably, the temperature of the first extraction is 80-130°C, for example, 80°C, 100°C, 130°C, or any two of these values.

[0057] Understandably, the first extraction time is 20-50 min, such as 20 min, 30 min, 40 min, 50 min, or any two of these ranges.

[0058] Extraction solvent II is mainly used to extract nylon. The extraction time should not be too long, as prolonged nylon extraction will lead to micro-depolymerization of nylon, generating impurities that affect the purity of BHET products.

[0059] The second extraction temperature should not be too low. Nylon is limited by its solubility in the extractant, and low temperature cannot effectively extract nylon from waste textiles, thus affecting the purity of BHET.

[0060] Understandably, the temperature for the second extraction is 130-170°C, for example, 130°C, 150°C, 170°C, or any two of these values.

[0061] Understandably, the second extraction time is 10-20 min, such as 10 min, 15 min, 20 min, or any value between two of these.

[0062] In one possible implementation, extraction solvent I includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether; the temperature of the first extraction is 130-170°C, and the extraction time is 10-20 min; extraction solvent II includes at least one of DMF, DMAC, and DMSO; the temperature of the second extraction is 80-130°C, and the extraction time is 20-50 min.

[0063] It is understood that in this embodiment, extraction solvent I is mainly used to extract nylon, while extraction solvent II is mainly used to extract spandex.

[0064] In one possible implementation, the temperature of the third extraction is 190-230°C, and the extraction time is 30-90 min.

[0065] When the temperature of the third extraction is too low, the polyester cannot be effectively dissolved, and the separation of polyester and cotton fibers cannot be achieved, which in turn affects the purity of BHET products.

[0066] Understandably, the temperature for the third extraction is 190-230°C, for example, 190°C, 200°C, 210°C, 220°C, 230°C, or any two of these ranges.

[0067] Understandably, the third extraction time is 30-90 min, for example, 30 min, 50 min, 70 min, 90 min, or any two of these ranges.

[0068] In one possible implementation, the solvent of extraction solvent III can be recycled in the depolymerization reaction.

[0069] In one possible implementation, the mass ratio of extraction solvent I to waste textiles is 3-20:1.

[0070] It is understood that the mass ratio of extraction solvent I to waste textiles is 3-20:1, for example, 3:1, 4:1, 5:1, 6:1, 10:1, 15:1, 20:1 or any value between two of these.

[0071] In one possible implementation, the mass ratio of extraction solvent I to waste textiles is 4-6:1.

[0072] In one possible implementation, the mass ratio of extraction solvent II to the waste textiles after the first extraction is 3-20:1.

[0073] It is understood that the mass ratio of extraction solvent II to the waste textiles after the first extraction is 3-20:1, for example, 3:1, 4:1, 5:1, 6:1, 10:1, 15:1, 20:1 or any value between two of these.

[0074] In one possible implementation, the mass ratio of extraction solvent II to waste textiles is 4-6:1.

[0075] In one possible implementation, the mass ratio of extraction solvent III to the second extracted waste textile is 3-20:1.

[0076] It is understood that the mass ratio of extraction solvent III and the second extracted waste textiles is 3-20:1, for example, 3:1, 4:1, 5:1, 6:1, 10:1, 15:1, 20:1 or any value between two of these.

[0077] In one possible implementation, in step S4, a catalyst is also added to the depolymerization reaction. The catalyst includes one or more of the following: AlSBA-15, β-type zeolite, γ-type zeolite, hydrotalcite, spinel, solid superacid, superparamagnetic γ-type iron oxide, imidazole hexafluorophosphate, imidazole trifluoromethanesulfonate, cobalt acetate, manganese acetate, zinc acetate, sodium carbonate, and potassium carbonate.

[0078] This application incorporates a catalyst into the reaction process, which can accelerate the depolymerization reaction of polyester and increase the reaction rate.

[0079] In one possible implementation, in step S4, the mass ratio of the extract to ethylene glycol is 1:(0.5-2), for example, 1:0.5, 1:1, 1:1.5, 1:2 or any range between the two.

[0080] In one possible implementation, the temperature of the depolymerization reaction is 190-250°C; the time of the depolymerization reaction is 60-180 min.

[0081] Understandably, the temperature for the depolymerization reaction is 190-250°C, for example, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, or any two of these ranges.

[0082] It is understood that the depolymerization reaction time is 60-180 min, for example, 60 min, 100 min, 120 min, 140 min, 160 min, 180 min or any two of these ranges.

[0083] In one possible implementation, the fixed bed includes an adsorbent.

[0084] In one possible implementation, the adsorbent includes at least one of granular activated carbon, kaolin, diatomaceous earth, and molecular sieve.

[0085] In one possible implementation, granular activated carbon includes at least one of coal-based activated carbon, petroleum coke activated carbon, fruit shell activated carbon, and wood-based activated carbon.

[0086] In one possible implementation, the crystallization in steps S4 and S5 independently includes vacuum crystallization or cooling crystallization, respectively.

[0087] The termination temperature for cooling crystallization is -5℃ to 30℃; the cooling rate for cooling crystallization is 1-25℃ / min, or 5-15℃ / min.

[0088] In one possible implementation, the termination temperature for cooling crystallization is -5°C to 30°C, for example -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, or any combination of two of the above values.

[0089] In one possible implementation, the cooling rate for cooling crystallization is 1-25°C / min, for example, 1°C / min, 5°C / min, 10°C / min, 15°C / min, 20°C / min, 25°C / min, or any combination of two of the above values.

[0090] In one possible implementation, the initial crystallization temperature for cooling crystallization is preferably 100°C.

[0091] In one possible implementation, the crystallization process in steps S4 and S5 may or may not involve the addition of seed crystals.

[0092] In one possible implementation, the alcoholysis solution is first cooled to 100°C before crystallization.

[0093] In one possible implementation, the mass concentration of crude dihydroxyethyl terephthalate in the crude product solution is 1-50%, for example, 1%, 10%, 20%, 30%, 40%, 50%, or any combination of two of the above values.

[0094] In one possible implementation, the crude dihydroxyethyl terephthalate crude product has a mass concentration of 5-20% in the crude product solution.

[0095] In one possible implementation, the solvent in the crude product solution includes one or more of acetone, ethanol, methanol, ethylene glycol, butyl acetate, ethyl acetate, n-heptane, petroleum ether, isopropanol, propylene glycol, and water.

[0096] In one possible implementation, the fixed-bed adsorption temperature is 60-120°C, and the adsorption residence time is 0.5-8h.

[0097] It is understandable that the temperature for fixed-bed adsorption is 60-120℃, such as 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃ or any combination of two of the above values.

[0098] It is understandable that the adsorption residence time of fixed bed adsorption is 0.5-8h, such as 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h or any range of two of the above values.

[0099] In one possible implementation, the temperature of the fixed bed adsorption is 80-100℃, and the adsorption residence time is 2-4h.

[0100] Secondly, this application provides a dihydroxyethyl terephthalate prepared according to the above method.

[0101] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will be described below with reference to the accompanying drawings.

[0102] Example 1

[0103] like Figure 1 As illustrated, the method for preparing dihydroxyethyl terephthalate using waste textiles in this embodiment is as follows:

[0104] S1: 5 kg of waste mixed textiles (containing approximately 70% polyester, 20% cotton, 5% nylon, 3% spandex, 1 wt% dyes (containing approximately 70 wt% azo dyes, 20 wt% anthraquinone dyes, and 10 wt% other dyes), and 1 wt% other substances) are added to the first extraction tower via a solid feeder. DMAC is selected as the extraction solvent I, with a mass ratio of waste textiles to solvent I of 1:6. The extraction temperature is 120℃, and the residence time is 30 min. The resulting extract and solid components are separated using a solid-liquid separation device, yielding the waste textiles and extract after the first extraction. The spandex component is precipitated from the extract by cooling (the precipitated spandex component can be recycled).

[0105] S2: The waste textiles obtained from the first extraction in S1 flow into the second extraction tower. Diethylene glycol is used as the extraction solvent II. The mass ratio of the waste textiles after the first extraction to the extraction solvent II is 1:5. The extraction temperature is 160℃, and the residence time is 10 min. The extract and solid components are separated by a solid-liquid separation device to obtain the waste textiles after the second extraction and the extract. The extract is cooled to precipitate the nylon component (the nylon component precipitated by cooling can be recycled).

[0106] S3: The waste textiles obtained from the second extraction in S2 flow into the third extraction tower. The extraction solvent III is ethylene glycol. The mass ratio of the waste textiles after the second extraction to the extraction solvent III is 1:4. The extraction temperature is 190℃, and the residence time is 90 min. The extracted solid cotton is then separated from the extract and the solid waste textiles (mainly cotton) using a solid-liquid separation device.

[0107] S4: The extract obtained in S3 is fed into an alcoholysis reactor for depolymerization. The alcoholysis reactor contains ethylene glycol and 10g of zinc acetate as an alcoholysis catalyst. The depolymerization reaction is carried out at 235℃ for 2 hours. The mass ratio of ethylene glycol to the extract obtained in S3 is 1:1.

[0108] The liquid after the depolymerization reaction was cooled to 100°C for primary filtration, and then the temperature was lowered to 20°C by cooling crystallization at a rate of 5°C / min to obtain crude BHET.

[0109] S5: Crude BHET is dissolved in butyl acetate to obtain a crude product solution.

[0110] Crude BHET was dissolved in a solvent; in this example, butyl acetate was used, and the concentration of crude BHET was controlled at 15 wt%. The liquid was then passed into a fixed-bed adsorption device for adsorption, using coconut shell activated carbon as the adsorbent. The feed flow rate of the crude product solution was 30 ml / min, and the volumetric hourly space velocity (VHSV) was 1.8 h⁻¹. -1 The temperature was 100℃ and the adsorption residence time was 4 hours.

[0111] After fixed-bed adsorption is completed, the liquid flows into the crystallization reactor, where the temperature is reduced from 100℃ to 10℃ at a rate of 5℃ / min. BHET crystals are obtained through processes such as filtration, washing, and drying.

[0112] Figure 2 This is a product drawing of the BHET crystal from Embodiment 1 provided in this application. Figure 3 The high-performance liquid chromatogram of BHET crystals in Example 1 provided in this application is obtained by... Figure 3 It can be seen that the BHET crystal prepared in this embodiment has a relatively high purity.

[0113] Example 2

[0114] The only difference between this embodiment and Embodiment 1 is that the extraction solvent in the first extraction tower in Embodiment 1 is replaced with DMSO.

[0115] Example 3

[0116] The only difference between this embodiment and Embodiment 1 is that the extraction solvent in the first extraction tower in Embodiment 1 is replaced with DMF.

[0117] Example 4

[0118] The only difference between this embodiment and Embodiment 1 is that the extraction solvent in the second extraction tower in Embodiment 1 is replaced with methanol.

[0119] Example 5

[0120] The only difference between this embodiment and Embodiment 1 is that the extraction solvent in the second extraction tower in Embodiment 1 is replaced with ethanol.

[0121] Example 6

[0122] The only difference between this embodiment and Embodiment 1 is that the extraction solvent in the second extraction tower in Embodiment 1 is replaced with propylene glycol.

[0123] Examples 7-12

[0124] The only difference between Examples 7-12 and Example 1 is that the extraction times of the first and second extractions are adjusted, as shown in Table 2.

[0125] Examples 13-18

[0126] The only difference between Examples 13-18 and Example 1 is that the temperatures of the first and second extractions are adjusted, as detailed in Table 3.

[0127] Example 19

[0128] The only difference between Example 19 and Example 1 is that the temperature of the third extraction is adjusted, as shown in Table 4.

[0129] Example 20

[0130] The only difference between this embodiment and Embodiment 1 is that:

[0131] In S1, the composition of the waste mixed textiles is as follows: approximately 50% polyester, approximately 35% cotton, approximately 8% nylon, approximately 4% spandex, 0.02 wt% dyes (of which, approximately 70 wt% are azo dyes, approximately 20 wt% are anthraquinone dyes, and approximately 10 wt% are others), and 2.98 wt% other substances; the mass ratio of waste textiles to extraction solvent I is 1:20.

[0132] In S2: The mass ratio of waste textiles after the first extraction to extraction solvent II is 1:20;

[0133] In S3: the temperature of the third extraction is 230℃, and the time of the third extraction is 70 min; the mass ratio of waste textiles after the second extraction to extraction solvent III is 1:20.

[0134] In S4: the alcoholysis catalyst is cobalt acetate, the mass ratio of extract to ethylene glycol is 1:0.5, the depolymerization reaction temperature is 250℃, and the reaction time is 60 min.

[0135] Example 21

[0136] The only difference between this embodiment and Embodiment 1 is that:

[0137] In S1, the composition of the waste mixed textiles is as follows: approximately 60% polyester by mass, approximately 15% cotton by mass, approximately 14.5% nylon by mass, approximately 8% spandex by mass, 1.5 wt% dyes (of which, approximately 70 wt% are azo dyes, approximately 20 wt% are anthraquinone dyes, and approximately 10 wt% are others), and 1 wt% other substances); the mass ratio of waste textiles to extraction solvent I is 1:3.

[0138] In S2: The mass ratio of waste textiles after the first extraction to extraction solvent II is 1:3;

[0139] In S3: the third extraction time is 30 min; the mass ratio of waste textiles after the second extraction to extraction solvent III is 1:3;

[0140] In S4: the alcoholysis catalyst is β-type zeolite, the mass ratio of extract to ethylene glycol is 1:2, the depolymerization reaction temperature is 190℃, and the reaction time is 180 min.

[0141] Example 22

[0142] The only difference between this embodiment and Embodiment 1 is that:

[0143] S1: 5 kg of waste mixed textiles (containing approximately 70% polyester, 20% cotton, 5% nylon, 3% spandex, 1 wt% dyes (containing approximately 70 wt% azo dyes, 20 wt% anthraquinone dyes, and 10 wt% other dyes), and 1 wt% other substances) are added to the second extraction tower via a solid feeder. Diethylene glycol is used as the extraction solvent II, with a mass ratio of waste textiles to solvent II of 1:5. The extraction temperature is 160℃, and the residence time is 10 min. The extract and solid components are separated using a solid-liquid separation device, yielding the waste textiles and extract after the first extraction. The extract is cooled to precipitate the nylon component (which can be recycled).

[0144] S2: The waste textiles obtained from the first extraction in S1 flow into the first extraction tower. DMAC is selected as the extraction solvent, and the mass ratio of waste textiles to extraction solvent I is 1:6. The extraction temperature is 120℃, and the residence time is 30 min. The obtained extract and solid components are separated by a solid-liquid separation device to obtain the waste textiles and extract after the second extraction. The extract is cooled to precipitate the spandex component (the spandex component precipitated by cooling can be recycled).

[0145] S3-S5 are completely identical to Example 1.

[0146] Comparative Example 1

[0147] The only difference between Comparative Example 1 and Example 1 is that the third extraction is not performed; instead, the waste textiles obtained after the second extraction in S2 are directly subjected to the depolymerization reaction in S4 and the treatment in S5.

[0148] Table 1

[0149]

[0150] As can be seen from Table 1, both extraction solvent I and extraction solvent II in Examples 1-6 can yield BHET products with good purity and color value.

[0151] Table 2

[0152]

[0153] As shown in Examples 1, 7-8, and 11, the extraction residence time for spandex should not be too fast. Insufficient extraction time will prevent spandex from being effectively extracted from waste textiles via solid-phase extraction, thus affecting the purity of the BHET product. As shown in Examples 1, 9-10, and 12, the extraction time for nylon should not be too long. Long nylon extraction time will lead to micro-depolymerization of nylon, generating impurities that affect the purity of the BHET product.

[0154] Table 3

[0155]

[0156] As shown in Examples 1, 13-14, and 17, the extraction temperature for spandex should not be too high. Excessive temperature can cause micro-depolymerization of spandex, generating substances such as polytetrahydrofuran, which affects the purity of the BHET product. As shown in Examples 1, 15-16, and 18, the extraction temperature for nylon should not be too low. Nylon's solubility in the extractant is limited, and low temperatures cannot effectively extract nylon from waste textiles, thus affecting the purity of BHET.

[0157] Table 4

[0158]

[0159] By comparing Examples 1 and 19 with Comparative Example 1, it can be seen that the reverse solid-phase extraction process (S3) has a significant impact on the purity of BHET. Without the S3 process, a large amount of cotton fibers are present in the depolymerization solution, which affects the crystallization process of crude BHET and results in a lower purity of crude BHET.

[0160] Comparative Example 2

[0161] The only difference between this comparative example and Example 1 is that the S1-S3 treatments are not performed; instead, the waste textiles from Example 1 are directly subjected to the S4 depolymerization reaction and the S5 treatment.

[0162] Comparative Example 3

[0163] The only difference between this comparative example and Example 1 is that the S1 treatment is omitted, and the waste textiles of Example 1 are directly treated with S2-S5.

[0164] Comparative Example 4

[0165] The only difference between this comparative example and Example 1 is that the S2 treatment is omitted, and the waste textiles obtained from the first extraction in Example 1 are directly subjected to the S3-S5 treatment.

[0166] Test example:

[0167] High-performance liquid chromatography (HPLC) testing: The BHET prepared in the examples and comparative examples was tested by HPLC. The selected chromatographic column was a ZORBAX Eclipse Plus C18 with a size of 4.6 (inner diameter) * 250 mm (length) and a column particle size of 5 micrometers. The mobile phase was methanol and phosphoric acid water (the volume percentage of phosphoric acid in the phosphoric acid water was 0.05%). The purity of BHET was obtained by HPLC testing.

[0168] BHET crystal color value: 45 under the optical geometry conditions of the colorimeter. ° / 0 ° Specifically, the light source is positioned at a 45° angle to the normal of the sample surface. ° Illumination at an angle, detector at vertical (0) ° The reflected light is received in the direction of the light source, and the L value and b value of the BHET crystal are measured under the illumination of a light source with a spectral range of 400nm~700nm.

[0169] The results of the above tests are shown in Table 1-6.

[0170] Table 5

[0171]

[0172] Table 6

[0173]

[0174] Comparing Examples 1 and 22, the extraction order slightly affects the purity of BHET. However, the extraction temperature for spandex is lower, while that for nylon is higher. Prioritizing the extraction of spandex makes better use of heat, and since the spandex component has a lower content than the nylon component, prioritizing the extraction of lower-content substances is more advantageous. Comparing Examples 1 and Comparative Examples 2-4, without the extraction processes S1-S3, substances such as nylon, spandex, and cotton significantly affect the alcoholysis process of polyester, resulting in excessively low purity of the BHET product.

[0175] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for preparing bis-hydroxyethyl terephthalate from waste textiles, characterized by, The method comprises: S1: disposing the waste textiles in an extraction solvent I for first extraction; after removing the extraction liquid, first-extracted waste textiles are obtained; S2: disposing the first-extracted waste textiles in an extraction solvent II for second extraction; after removing the extraction liquid, second-extracted waste textiles are obtained; S3: disposing the second-extracted waste textiles in an extraction solvent III for third extraction; after removing the third-extracted waste textiles, an extraction liquid is obtained; S4: subjecting the extraction liquid to depolymerization reaction by ethylene glycol to obtain an alcoholysis liquid; subjecting the alcoholysis liquid to crystallization to obtain crude bis-hydroxyethyl terephthalate; S5: dissolving the crude bis-hydroxyethyl terephthalate in a solvent to obtain a crude product solution, subjecting the crude product solution to fixed bed adsorption to obtain a bis-hydroxyethyl terephthalate solution, and subjecting the bis-hydroxyethyl terephthalate solution to crystallization to obtain the bis-hydroxyethyl terephthalate. The extraction solvent I and the extraction solvent II each include at least one of DMF, DMAC, and DMSO, and the other of the extraction solvent I and the extraction solvent II includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether; the extraction solvent III includes ethylene glycol.

2. The method of claim 1, wherein, The waste textiles include 50-70 wt% of polyester, 15-35 wt% of cotton, 5-15 wt% of nylon, 3-8 wt% of spandex, 0.02-1.5 wt% of dyes, and 1-3 wt% of other components.

3. The method according to claim 1 or 2, characterized in that, The extraction solvent I includes at least one of DMF, DMAC, and DMSO; The first extraction is performed at a temperature of 80-130°C for 20-50 min. The extraction solvent II includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether; the second extraction is performed at a temperature of 130-170°C for 10-20 min.

4. The method according to claim 1 or 2, characterized in that, The extraction solvent I includes at least one of methanol, ethanol, diethylene glycol, propylene glycol, ethyl acetate, and petroleum ether; The first extraction is performed at a temperature of 130-170°C for 10-20 min. The extraction solvent II includes at least one of DMF, DMAC, and DMSO; the second extraction is performed at a temperature of 80-130°C for 20-50 min.

5. The method according to claim 1 or 2, characterized in that, The third extraction is performed at a temperature of 190-230°C for 30-90 min.

6. The method according to claim 1 or 2, characterized in that, The mass ratio of the extraction solvent I to the waste textiles is 3-20:1; The mass ratio of the extraction solvent II to the first-extracted waste textiles is 3-20:1; The mass ratio of the extraction solvent III to the second-extracted waste textiles is 3-20:

1.

7. The method according to claim 1 or 2, characterized in that, In step S4, a catalyst is added in the depolymerization reaction, and the catalyst comprises one or more of AlSBA-15, zeolite beta, zeolite gamma, hydrotalcite, spinel, solid superacid, superparamagnetic gamma iron oxide, imidazole hexafluorophosphate, imidazole triflate, cobalt acetate, manganese acetate, zinc acetate, sodium carbonate, and potassium carbonate.

8. The method of claim 1 or 2, wherein, In step S4, the mass ratio of the extraction liquid to ethylene glycol is 1: (0.5-2).

9. The method of claim 1 or 2, wherein, The temperature of the depolymerization reaction is 190-250°C, and the time of the depolymerization reaction is 60-180 min.

10. Bis-hydroxyethyl terephthalate prepared by the method according to claims 1-9.

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