How to recycle polyester blend fabrics

Abstract

The present invention relates to the recycling of textiles, and further to a method for recycling polyester blended fabrics. After the raw material containing polyester is treated, the polyester is decomposed by a catalyst at 40°C to 120°C for 0.5 to 8 hours to achieve complete depolymerization, and then separated and recycled, and the separated polyester component and other blended components are reused. The method of the present invention realizes 100% depolymerization of polyester under low temperature conditions, and the depolymerized polyester component can be easily separated from other components, so that the polyester and other temperature-sensitive fiber components in the blended fabric can be completely separated. The polyester depolymerized monomer obtained by recycling can also be used to synthesize new polyester, realizing the closed-loop recycling of different fiber components in polyester blended waste, which is of great importance for protecting the ecological environment and reducing the cost of regenerated fibers.

Description

[Technical field]

[0001] The present invention relates to textile recycling, and more particularly to a method for recycling polyester blend fabrics. [Background technology]

[0002] Polyester is one of the most popular textile materials in the world, and since 2010, polyester fiber has become the most consumed fiber in the world. In 2020, the world's annual polyester production reached 57 million tons. Polyester as a textile fiber is not only used alone, but is also often blended with other fibers. After blending, polyester fabric not only has the excellent mechanical properties of polyester fabric, but also obviously retains the excellent properties of other fiber fabrics. Therefore, various blended fabrics of polyester are becoming increasingly popular in the apparel industry. For example, polyester and cotton blended fabric is one of the most common fabrics in casual clothing. It is a fabric that not only has the comfort of cotton, but also the cheapness of polyester fabric. In sportswear, polyester and spandex blended fabric is the most important fabric. Such blended fabrics not only maintain the appearance and texture of polyester fiber, but also have excellent elasticity and wearability. However, clothes made of blended fabrics are discarded in large quantities after use. This is because existing technology lacks the technology to completely separate polyester from other fiber components. As a result, millions of tons of polyester blended fabrics are simply incinerated and landfilled every year. This disposal method not only wastes a lot of resources but also has serious negative effects on our living environment. If polyester blended fiber waste could be recycled into high-value textile fibers using sustainable processes, it would not only reduce the negative impact on the environment from waste disposal, but also make the most of limited resources.

[0003] Among the currently disclosed recycling technologies for polyester blended fabrics, chemical depolymerization of polyester is the most common method. However, the depolymerization temperature during the depolymerization process of polyester fibers is usually 200°C or higher (Patent Document 1, Patent Document 2), and at this temperature, temperature-sensitive components decompose before polyester, making it difficult to recycle other components of the blended fabric. Patent Document 3 discloses a low-temperature depolymerization method for polyester, which can depolymerize polyester at temperatures of 120°C or higher, but temperature-sensitive components such as spandex begin to become sticky under reaction conditions of 120°C, and the separated spandex component loses elasticity, making recycling difficult. Patent Document 4 discloses a method for depolymerizing polyester under temperature conditions of 100°C to 180°C, but this disclosed method does not allow 100% depolymerization of polyester under low-temperature reaction conditions (100°C to 140°C). This makes it impossible to completely separate polyester from the blended fabric, making it difficult to recycle other fabric components. In addition, this method has a low yield of polyester monomers under low temperature conditions, which makes the economic cost of the recycling process high. Therefore, the key to realizing the recycling of polyester blended fabrics is how to depolymerize 100% of the polyester component under low temperature conditions without damaging the other components. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] CN106113319A [Patent Document 2] CN102250379B [Patent Document 3] US8,541,477B2 [Patent Document 4] WO2021126661A1 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a method for recycling polyester blend fabrics. [Means for solving the problem]

[0006] To achieve the above objectives, the present invention adopts the following technical solutions:

[0007] This is a method for recycling polyester blended fabrics, in which raw materials containing polyester are treated, and then the polyester is decomposed by a catalyst at 40-120°C for 0.5-8 hours to achieve complete depolymerization, and then separated and recycled. The separated polyester component and other blended components can be reused.

[0008] The catalyst is an organic base main catalyst and a co-catalyst, where the catalyst addition amount is 0.1-20wt% of the mass of the blended fabric, and the mass ratio of the organic base main catalyst and the co-catalyst is 1:0.01-100.

[0009] The main catalyst of the organic base is one or more of nitrogen-containing amidine or guanidine compounds and derivatives, and the co-catalyst is a nitrile compound.

[0010] The main catalysts of the organic bases are (a) 1,8-diazabicycloundec-7-ene (DBU), polymer or compound supported DBU, and organic salts formed by DBU and imidazole and its derivatives, (b) 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), polymer or compound supported TBD, and organic salts formed by TBD and imidazole and its derivatives, and (c) 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), polymer or compound supported DBN, and organic salts formed by DBN and imidazole and its derivatives.

[0011] The polymer- or compound-supported catalyst (eg, polymer- or compound-supported DBU) is polystyrene-supported DBU (PS-DBU) or activated carbon-supported DBU.

[0012] Examples of organic salts formed (for example, organic salts formed by DBU and imidazole and its derivatives) include organic salts formed by DBU and imidazole ([HDBU][Im]), organic salts formed by DBU and 2-ethylimidazole ([HDBU][2-EtIm]), organic salts formed by DBU and benzimidazole ([HDBU][BIm]), organic salts formed by DBU and 2-methylimidazole ([HDBU][2-MeIm]), organic salts formed by DBU and 2-ethyl-4-methylimidazole ([HDBU][2-Et-4-MeIm]), and organic salts formed by DBU and 2-phenylimidazole ([HDBU][2-PhIm]).

[0013] The co-catalyst is one or more of acetonitrile, propanenitrile, benzonitrile, and adiponitrile.

[0014] Preferably, the method involves treating a raw material containing polyester, adding it to a methanol solution, then adding a catalyst and reacting at 60 to 110°C for 1 to 5 hours to decompose the polyester and achieve complete depolymerization, and then separating and recycling the separated polyester component for reuse.

[0015] More preferably, the method involves treating a raw material containing polyester, adding it to a methanol solution, then adding a catalyst and reacting at 80 to 110°C for 1 to 2 hours to decompose the polyester and achieve complete depolymerization, and then separating and recycling the separated polyester component for reuse.

[0016] The polyester-containing raw material to be treated is a polyester blended fabric or a blended fabric of polyester and other fabrics, in which the polyester content in the blended fabric is 5% to 100%, and the polyester blended fabric is a fabric in which polyester is blended with one or more of spandex, cotton, viscose fiber, regenerated cellulose fiber, nylon, wool, cashmere, and pure silk.

[0017] In the above blended fabric, the polyester content is at least 5%, or at least 25%, or at least 50%, or at least 75%, or at least 95%.

[0018] The raw material to be treated containing the polyester is washed in alcohol or a mixed system containing alcohol at 40 to 130°C for 0.3 to 2 hours, where the mixed system containing alcohol is a mixture of alcohol and an alkaline compound, and the alkaline compound is soda ash (Na 2 CO 3 ), sodium acetate, sodium methoxide, sodium ethoxide, potassium carbonate, potassium acetate, potassium methoxide, calcium oxide, calcium hydroxide.

[0019] Furthermore, the raw material is washed in alcohol or a mixed system containing alcohol at 50 to 110°C, 80 to 100°C, or 90 to 100°C for 0.3 to 2 hours to remove dirt, oily dirt, and other impurities contained in the raw material.

[0020] After the polyester is decomposed, the polyester is separated into solid and liquid, the solid is collected, and the polyester component is separated from other fiber components by Soxhlet extraction. The liquid is recycled by atmospheric distillation to recover the alcohol and co-catalyst. Then, the diol and dibasic acid monomers of the polyester, as well as the organic base catalyst, are recycled by vacuum distillation or extraction. After the polyester is depolymerized, the recycled monomers, such as dimethyl terephthalate (DMT) and ethylene glycol, are purified by vacuum distillation and can be used as raw materials to synthesize new polyester.

[0021] The working principle of the present invention is as follows. In the process of catalyzing the decomposition of methanol into polyester by organic base main catalyst, the organic base main catalyst first activates methanol, which generates highly nucleophilic methanol anion, as shown in the figure below: [ka] The formed methanol anion is more likely to attack the ester bond by a nucleophilic reaction, and the cleavage of the ester bond is achieved. However, the reaction of activating methanol by the organic base main catalyst is reversible. When a nitrile (RC≡N:) is added to the reaction system, the strong polarity of -C≡N: and the lone electron on the nitrogen atom make the organic base main catalyst cation generated by the reaction stable in the system, shifting the reaction equilibrium toward the production of more methanol anions, thereby improving the catalytic activity of the organic base main catalyst. Effect of the Invention

[0022] The advantages of the present invention are as follows:

[0023] The method of the present invention achieves 100% depolymerization of polyester under low temperature conditions. The depolymerized polyester components can be easily separated from other components, so that polyester and other temperature-sensitive fiber components in the blended fabric can be completely separated. In addition, the reaction separation process in the present invention is gentle and efficient, and the other fibers can be obtained with 100% purity components, with little damage to the fibers, which can be directly respun into silk yarn or used as raw material for regenerated fibers. The depolymerized monomer of polyester obtained by recycling can also be used to synthesize new polyester, realizing closed-loop recycling of different fiber components in polyester blend waste, which is of great importance for protecting the ecological environment and reducing the cost of regenerated fibers.

[0024] In the separation process of the present invention, an organic alkali catalyst is used to catalyze the cleavage of the ester bond of polyester, and an auxiliary catalyst is added during the system process to improve the catalytic activity and efficiency of the organic base under low temperature conditions. When the organic base is used in combination with the auxiliary catalyst, 100% depolymerization of polyester can be achieved under low temperature conditions. In addition, after the addition of the auxiliary catalyst, the recycling rate of polyester monomer is greatly improved. [Brief description of the drawings]

[0025] [Figure 1] 1 is an infrared spectrum (FTIR) of dimethyl terephthalate (DMT), a recycled polyester monomer after depolymerization provided by an embodiment of the present invention; [Diagram 2] 1 is an infrared spectrum (FTIR) of furan-2,5-dicarboxylic acid dimethyl ester, a polyester monomer recycled after depolymerization provided by an embodiment of the present invention; [Diagram 3] The separated and recycled polyester and cotton blended fabric provided by the embodiment of the present invention, where A is the blended fabric before the separation reaction, and B is the pure cotton fabric after the separation reaction. [Figure 4] The separated recycled polyester and spandex blended printed fabric provided by the embodiment of the present invention, where A is the blended fabric before separation reaction, B is the pure spandex fabric after separation reaction, and C shows that the spandex yarn is not damaged under optical microscope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The specific embodiments of the present invention will be further described below in conjunction with examples. It should be noted that the specific embodiments described herein are only for the purpose of explaining and interpreting the present invention, and are not intended to be limited by the present invention.

[0027] The method of the present invention achieves 100% depolymerization of polyester fiber components under lower temperature conditions, and the recycling rate of polyester monomers is as high as 95%, enabling more efficient recycling and regeneration of polyester. Lower reaction temperatures make the process more environmentally friendly and reduce the energy required for the reaction, resulting in lower recycling process costs.

[0028] The present invention aims at recycling and reusing waste materials of temperature sensitive fibers and polyester blends, such as blends of spandex and polyester, blends of cotton and polyester, blends of viscose fibers and polyester, blends of regenerated cellulose fibers and polyester, blends of nylon and polyester, blends of wool and polyester, blends of cashmere and polyester, blends of pure silk and polyester, and blends of these fibers and polyester, where the regenerated cellulose fibers can be modal and lyocell fibers.

[0029] The above-mentioned polyester depolymerization refers to decomposing polyester into monomers and low molecular weight oligomers such as dimers, trimers, tetramers, pentamers, hexamers, and heptamers, which are then dropped and separated from the blended fabric, and the polyester components are separated and recycled. The polyester in this technology refers to polymers containing ester bonds, such as polyethylene terephthalate (PET), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT), polyethylene 2,5-furandicarboxylate (PEF), polytrimethylene 2,5-furandicarboxylate (PTF), polybutylene 2,5-furandicarboxylate (PBF), polylactic acid (PLA), polyhydroxyalkanoate (PHA), polybutylene glycol succinate (PBS), and low melting point polyester copolymers.

[0030] The depolymerization efficiency (E) can be calculated from the amount of solid remaining after the reaction. The formula is: Depolymerization efficiency (E) = (polyester fiber content in woven fabric - amount of undepolymerized polyester) / polyester fiber content in woven fabric.

[0031] Preparation of organic salt catalysts in the following examples: Preparation of organic salt catalysts formed by DBU and imidazole and its derivatives: The organic salt catalyst formed by DBU and imidazole and its derivatives is prepared by neutralizing equimolar amounts of DBU and imidazole and its derivatives at room temperature. For example, the organic salt formed by DBU and 2-ethylimidazole ([HDBU][2-EtIm]) used in the examples was prepared by neutralizing 0.025 mol of DBU and 0.025 mol of 2-ethylimidazole at room temperature for 5 hours.

[0032] At the same time, the above method also allows the formation of an organic salt ([HDBU][BIm]) from DBU and benzimidazole, the formation of a catalyst ([HDBU][2-MeIm]) from DBU and 2-methylimidazole, the formation of a catalyst ([HDBU][2-Et-4-MeIm]) from DBU and 2-ethyl-4-methylimidazole, and the formation of a catalyst ([HDBU][2-PhIm]) from DBU and 2-phenylimidazole.

[0033] Example 1 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, the fiber, 20g of methanol, 20g of acetonitrile and 2g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 65℃. After reacting for 8 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol using a Soxhlet extractor to obtain 8.94g of dimethyl terephthalate (DMT), which is a polyester depolymerization monomer (see Figure 1), and no solid remained in the Soxhlet extractor. That is, the polyester fiber was completely depolymerized. The separated liquid part was recycled to methanol and acetonitrile by distillation, and then ethylene glycol and DBU were recycled by vacuum distillation (see Table 2).

[0034] Example 2 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, the fiber, 28g of methanol, 12g of different cocatalysts and 0.54g of DBU were added to the reaction kettle, and then the reaction kettle was heated to 85℃. After reacting for 2.5 hours, the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction to obtain DMT, which is the polyester depolymerization monomer, and the remaining solid in the Soxhlet extractor is the non-depolymerized polyester fiber (see Table 1).

[0035] After depolymerization using acetonitrile as a cocatalyst, the solid and liquid parts in the reaction system were separated by filtration, and the solid part was extracted with methanol by Soxhlet extraction to obtain 9.35g of DMT, the polyester depolymerization monomer, and no solid remained in the Soxhlet extractor. In other words, the polyester fiber was completely depolymerized. The separated liquid part was distilled to recycle methanol and acetonitrile, and then vacuum distilled to recycle ethylene glycol and DBU (see Table 2).

[0036] Table 1. Comparison of the activity of various cocatalysts in the catalytic degradation of polyester with DBU under low-temperature reaction conditions. [Table 1]

[0037] Example 3 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, the fiber, 28g of methanol, 12g of benzonitrile and 0.54g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 85℃. After reacting for 2.5 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction and separated to obtain 8.67g of DMT, which is the polyester depolymerization monomer. The polyester fiber was completely depolymerized, and no solid remained in the Soxhlet extractor. That is, the polyester fiber was completely depolymerized. The separated liquid part was recycled by distillation to recycle methanol, and then vacuum distillation to recycle benzonitrile, ethylene glycol and DBU (see Table 2).

[0038] Example 4 2g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.1g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, 6.4g of methanol, 1.6g of acetonitrile and 0.14g of [HDBU][2-EtIm] were added to the reaction vessel, and then the reaction vessel was heated to 90℃. After reacting for 2 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction to obtain 1.74g of DMT, which is the polyester depolymerization monomer, and no solid remained in the Soxhlet extractor. In other words, the polyester fiber was completely depolymerized. The separated liquid part was distilled to recycle methanol, acetonitrile and ethylene glycol to extract and recycle [HDBU][2-EtIm] (see Table 2).

[0039] Example 5 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, 36g of methanol, 4g of acetonitrile and 0.3g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 95℃ and reacted for 2.5 hours, after which the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction to obtain 9.60g of DMT, which is the polyester depolymerization monomer, and no solid remained in the Soxhlet extractor. That is, the polyester fiber was completely depolymerized. The separated liquid part was recycled to methanol and acetonitrile by distillation, and then ethylene glycol and DBU were recycled by vacuum distillation (see Table 2).

[0040] Example 6 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, the fiber, 36g of methanol, 4g of adiponitrile and 0.3g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 95℃ and reacted for 2.5 hours, after which the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was subjected to Soxhlet extraction with methanol to obtain 8.55g of DMT, which is the polyester depolymerization monomer, and no solid remained in the Soxhlet extractor. That is, the polyester fiber was completely depolymerized. The separated liquid part was recycled by distillation to recycle methanol, and then vacuum distillation to recycle ethylene glycol, adiponitrile and DBU (see Table 2).

[0041] Example 7 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, 28g of methanol, 12g of acetonitrile and 0.18g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 115℃ and reacted for 2 hours, after which the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction to obtain 8.61g of DMT, which is the polyester depolymerization monomer, and no solid remained in the Soxhlet extractor. That is, the polyester fiber was completely depolymerized. The separated liquid part was recycled to methanol and acetonitrile by distillation, and then ethylene glycol and DBU were recycled by vacuum distillation (see Table 2).

[0042] Example 8 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, the fiber, 28g of methanol, 12g of propanenitrile and 0.18g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 115℃ and reacted for 2 hours, after which the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction to obtain 7.79g of DMT, which is the polyester depolymerization monomer, and no solid remained in the Soxhlet extractor. That is, the polyester fiber was completely depolymerized. The separated liquid part was recycled to methanol and propanenitrile by distillation, and then ethylene glycol and DBU were recycled by vacuum distillation (see Table 2).

[0043] Example 9 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. After drying, the fiber, 28g of methanol, 12g of acetonitrile and 0.18g of TBD were added to the reaction vessel, and then the reaction vessel was heated to 115℃. After reacting for 2 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol using a Soxhlet extractor to obtain 8.36g of DMT, which is the polyester depolymerization monomer, and no solid remained in the Soxhlet extractor. That is, the polyester fiber was completely depolymerized. The separated liquid part was recycled to methanol and acetonitrile by distillation, and then ethylene glycol and TBD were recycled by vacuum distillation (see Table 2).

[0044] Comparative Example 1 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber, 40g of methanol and 2g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 65℃. After reacting for 8 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction, and 2.81g of DMT, the polyester depolymerization monomer, was obtained by separation. At the same time, 4.55g of polyester fiber that had not yet been depolymerized remained in the Soxhlet extractor. The separated liquid part was recycled to methanol, ethylene glycol and DBU by distillation (see Table 2).

[0045] Comparative Example 2 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber, 40g of methanol and 0.54g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 85℃. After reacting for 2.5 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol using a Soxhlet extractor to obtain 3.99g of DMT, which is the polyester depolymerization monomer. At the same time, 5.07g of polyester fiber that had not yet been depolymerized remained in the Soxhlet extractor. The separated liquid part was recycled by distillation to obtain methanol, ethylene glycol and DBU (see Table 2).

[0046] Comparative Example 3 2g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.1g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber, 8g of methanol and 0.14g of [HDBU][2-EtIm] were added to the reaction vessel, and then the reaction vessel was heated to 90℃. After reacting for 2 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction and separated to obtain 0.91g of DMT, the polyester depolymerization monomer. At the same time, 0.75g of polyester fiber that had not yet been depolymerized remained in the Soxhlet extractor. The separated liquid part was distilled to recycle methanol and ethylene glycol, and [HDBU][2-EtIm] was extracted and recycled (see Table 2).

[0047] Comparative Example 4 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber, 40g of methanol and 0.3g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 95℃. After reacting for 2.5 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction, and 5.41g of DMT, the polyester depolymerization monomer, was obtained by separation. At the same time, 3.48g of polyester fiber that had not yet been depolymerized remained in the Soxhlet extractor. The separated liquid part was recycled to methanol, ethylene glycol and DBU by distillation (see Table 2).

[0048] Comparative Example 5 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber, 40g of methanol and 0.18g of DBU were added to the reaction vessel, and then the reaction vessel was heated to 115℃. After reacting for 2 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction, and 4.94g of DMT, the polyester depolymerization monomer, was obtained by separation. At the same time, 3.25g of polyester fiber that had not yet been depolymerized remained in the Soxhlet extractor. The separated liquid part was recycled to methanol, ethylene glycol and DBU by distillation (see Table 2).

[0049] Comparative Example 6 10g of polyester fiber was washed with methanol at 50℃ for 30 minutes. During the washing process, 0.2g of soda ash was added for washing, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber, 40g of methanol and 0.18g of TBD were added to the reactor, and then the reactor was heated to 115℃. After reacting for 2 hours, the reactor was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction, and 4.69g of DMT, the polyester depolymerization monomer, was obtained by separation. At the same time, 3.61g of polyester fiber that had not yet been depolymerized remained in the Soxhlet extractor. The separated liquid part was recycled to methanol, ethylene glycol and TBD by distillation (see Table 2).

[0050] Table 2. Comparison of depolymerization efficiency and DMT monomer recycling rate between the examples under cocatalyst conditions and the comparative examples without cocatalyst. [Table 2]

[0051] Example 10 2g of polyester fiber was washed with methanol at 60℃ for 30 minutes. During the washing process, 0.1g of soda ash was added, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber, 6.4g of methanol, 1.6g of acetonitrile, and 0.21g of [HDBU][BIm] were added to the reaction vessel, and then the reaction vessel was heated to 95℃. After reacting for 2 hours, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. 1.82g of DMT, the polyester depolymerization monomer, was separated from the solid part by Soxhlet extraction, and no solid remained in the Soxhlet extractor. The separated liquid part was distilled to recycle methanol and ethylene glycol, and [HDBU][BIm] was extracted and recycled (see Table 3).

[0052] Examples 11 to 13 The specific implementation steps and reaction conditions are the same as those in Example 7, and the main catalyst of the reaction is replaced, and the co-catalysts in Examples 8 to 9 are [HDBU][2-MeIm], [HDBU][2-Et-4-MeIm], and [HDBU][2-PhIm], respectively, and the experimental results are shown in Table 3.

[0053] Table 3 Depolymerization rate of polyester and recycling rate of DMT monomer in Examples 11 to 13 [Table 3]

[0054] Example 14 2g of polyethylene 2,5-furandicarboxylate (PEF) fiber was washed with methanol at 60℃ for 30 minutes. During the washing process, 0.1g of soda ash was added, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber was added to the reaction vessel. At the same time, 7.2g of methanol, 0.8g of acetonitrile, and 0.06g of DBU were added to the reaction vessel. Then, the reaction vessel was heated to 110℃ and reacted for 2 hours. After the reaction was completed, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction to obtain 1.71g of furan-2,5-dicarboxylic acid dimethyl ester, which is a polyester depolymerization monomer (see Figure 2). The separated liquid part was distilled to recycle methanol and acetonitrile, and then vacuum distilled to recycle ethylene glycol and DBU.

[0055] Example 15 10g of polylactic acid (PLA) fiber was washed with methanol at 60℃ for 30 minutes. During the washing process, 0.2g of soda ash was added, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber was added to the reaction kettle. At the same time, 36g of methanol, 4g of acetonitrile, and 0.3g of DBU were added to the reaction kettle. Then, the reaction kettle was heated to 100℃ and reacted for 2 hours. After the reaction was completed, the reaction kettle was cooled to room temperature. The PLA fiber was completely depolymerized. After the reaction, the solution was distilled to recycle methanol and acetonitrile, and then vacuum distilled to recycle 11.31g of methyl lactate.

[0056] Example 16 2g of polyester fiber and 2g of cotton fiber were washed with methanol at 60°C for 30 minutes. During the washing process, 0.1g of soda ash was added, and after washing, the fiber was dried at 75°C for 1 hour. The dried fiber was added to the reaction kettle. At the same time, 9.2g of methanol, 0.8g of acetonitrile, and 0.45g of DBU were added to the reaction kettle. Then, the reaction kettle was heated to different temperatures (100-115°C) and reacted for 2 hours, respectively, and after the reaction was completed, the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The polyester fiber was completely depolymerized. The solid part was separated by Soxhlet extraction with methanol to obtain cotton fiber. The recycling rate of the cotton fiber was 98% (reaction temperature 100°C) and 94% (reaction temperature 115°C), respectively. The physical properties of the recycled cotton fiber are shown in Table 4.

[0057] Comparative Example 7 2g of polyester fiber and 2g of cotton fiber were washed with methanol at 60℃ for 30 minutes. During the washing process, 0.1g of soda ash was added, and after washing, the fiber was dried at 75℃ for 1 hour. The dried fiber was added to the reaction vessel. At the same time, 10g of methanol and 0.45g of DBU were added to the reaction vessel. Then, the reaction vessel was heated to different temperatures (190-240℃) and reacted for 2 hours, respectively, and after the reaction was completed, the reaction vessel was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The polyester fiber was completely depolymerized. The solid part was extracted with methanol by Soxhlet extraction, and the cotton fiber and DMT, the polyester depolymerization monomer, were separated. The separated liquid part was recycled into methanol and acetonitrile by distillation, and then ethylene glycol and DBU were recycled by vacuum distillation. The physical properties of the recycled cotton fiber are shown in Table 4.

[0058] Table 4. Physical properties of cotton fibers recycled at different reaction temperatures in the examples and comparative examples [Table 4]

[0059] Example 17 200 g of polyester-cotton blend fabric (cotton content 50%) was washed with methanol at 100 °C for 45 min. During the washing process, Na 2 CO 34g of acetonitrile was added, and the washed fabric was dried at 75°C for 1 hour. The dried blended fabric was added to the reaction kettle. At the same time, 752g of methanol, 48g of acetonitrile, and 5g of DBU were added to the reaction kettle. The reaction kettle was then heated to 110°C and reacted for 2 hours. After the reaction was completed, the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction and separated to obtain 98.6g of cotton component and 184.2g of DMT, a polyester depolymerization monomer. The separated liquid part was distilled to recycle methanol and acetonitrile, and then vacuum distilled to recycle ethylene glycol and DBU. The cotton component was detected by gas chromatography in accordance with GB / T2912.3-2009 and GB / T7717.12-94, and no acetonitrile remained in the cotton fiber. The recycled cotton component (see Figure 3) was opened by a fiber opener to obtain cotton fiber. These recycled cotton fibers were blended with virgin cotton fibers to produce regenerated yarns. The physical properties of some of the regenerated cotton yarns are shown in Table 5.

[0060] Table 5. Mechanical properties of yarns regenerated from recycled cotton after reactive separation of polyester component [Table 5]

[0061] Example 18 8g of polyester and spandex blended printed fabric (spandex content is 15%) was washed with methanol at 85℃ for 30 minutes. During the washing process, 0.08g sodium acetate and 0.08g calcium oxide were added, and the washed fabric was vacuum dried at 45℃ for 1 hour. The dried blended fabric (see FIG. 14A) was added to the reaction kettle. At the same time, 28.8g methanol, 3.2g acetonitrile, and 0.4g DBU were added to the reaction kettle. The reaction kettle was then heated to 90℃ and reacted for 2 hours. After the reaction was completed, the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was separated by Soxhlet extraction to obtain 1.16g spandex (see FIG. 4B and C) and 6.40g DMT, which is a polyester depolymerization monomer. The separated liquid part was recycled by distillation to recycle methanol and acetonitrile, and then by vacuum distillation to recycle ethylene glycol and DBU.

[0062] From Figure 4, it can be seen that the spandex recycled from printed blended fabric is pure white, the spandex yarn is not damaged, and can be directly used as raw material for producing regenerated spandex yarn.

[0063] Comparative Example 8 8g of polyester and spandex blended printed fabric (spandex content is 15%) was washed with methanol at 85℃ for 30 minutes. During the washing process, 0.08g sodium acetate and 0.08g calcium oxide were added, and the washed fabric was vacuum dried at 45℃ for 1 hour. The dried blended fabric (see Figure 14A) was added to the reaction kettle. At the same time, 32g methanol and 0.4g DBU were added to the reaction kettle. The reaction kettle was then heated to 125℃ and reacted for 2 hours. After the reaction was completed, the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with Soxhlet to obtain only 6.67g of DMT, a polyester depolymerization monomer, and no spandex component. The spandex was completely decomposed at this reaction temperature, so it could not be recycled.

[0064] Example 19 8g of polyester and spandex blended dyed fabric (black, spandex content 15%) was washed with methanol at 85℃ for 30 minutes. During the washing process, 0.08g sodium acetate and 0.08g calcium oxide were added, and the washed fabric was vacuum dried at 45℃ for 1 hour. The dried blended fabric was added to the reaction kettle. At the same time, 28.8g methanol, 3.2g acetonitrile and 0.4g DBU were added to the reaction kettle. Then the reaction kettle was heated to 90℃ and reacted for 2 hours. After the reaction was completed, the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was separated by Soxhlet extraction to obtain 1.16g spandex and 6.36g DMT, which is a polyester depolymerization monomer. The separated liquid part was recycled by distillation to obtain methanol and acetonitrile, and then vacuum distillation to obtain ethylene glycol and DBU. The spandex recycled from the black printed blended fabric was light brown in color. The spandex yarn is not damaged and can be used directly as a raw material for producing regenerated spandex yarn.

[0065] Example 20 8g of polyester and wool blended fabric (wool content 65%) was washed with methanol at 85℃ for 30 minutes. During the washing process, 0.08g of sodium acetate and 0.08g of calcium oxide were added, and the washed fabric was vacuum dried at 65℃ for 1 hour. The dried blended fabric was added to the reaction kettle. At the same time, 30g of methanol, 2g of acetonitrile and 0.61g of DBU were added to the reaction kettle. Then the reaction kettle was heated to 95℃ and reacted for 2 hours. After the reaction was completed, the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was separated by Soxhlet extraction to obtain 5.1g of wool and 2.64g of DMT, which is a polyester depolymerization monomer. The separated liquid part was distilled to recycle methanol and acetonitrile, and then vacuum distilled to recycle ethylene glycol and DBU. The wool separated by the reaction was recycled and could be used to manufacture regenerated wool.

[0066] Example 21 5g nylon fabric and 5g polyester fabric were washed with methanol at 95℃ for 45 minutes. During the washing process, 0.08g sodium carbonate and 0.08g calcium oxide were added, and the washed fabric was vacuum dried at 95℃ for 1 hour. The mixed fabric after drying was added to the reaction kettle. At the same time, 36g methanol, 4g acetonitrile and 0.3g DBU were added to the reaction kettle. Then the reaction kettle was heated to 100℃ and reacted for 2 hours. After the reaction was completed, the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was separated by Soxhlet extraction to obtain 4.91g nylon fabric and 4.71g DMT, which is a polyester depolymerization monomer. The separated liquid part was distilled to recycle methanol and acetonitrile, and then vacuum distilled to recycle ethylene glycol and DBU. The nylon separated by the reaction was analyzed by infrared spectroscopy and found to be 100% pure nylon, which could be recycled and used to manufacture regenerated nylon yarn.

[0067] Example 22 100g of polyester fiber was washed with methanol at 50°C for 30 minutes. During the washing process, 0.2g of soda ash was added, and after washing, the fiber was dried at 75°C for 1 hour. After drying, 360g of methanol, 40g of acetonitrile and 3g of DBU were added to the reaction kettle, and then the reaction kettle was heated to 95°C and reacted for 2 hours, after which the reaction kettle was cooled to room temperature. The solid and liquid parts in the reaction system were separated by filtration. The solid part was extracted with methanol by Soxhlet extraction to obtain DMT, a polyester depolymerization monomer. The obtained polyester monomer was polymerized under vacuum at 290°C for 3 hours using antimony trioxide as a catalyst to produce polyester. The obtained polyester was depolymerized and polymerized multiple times, and the parameters of each depolymerization and polycondensation are shown in Table 6.

[0068] Table 6. Parameters for repeating polymerization and depolymerization of polyester depolymerization monomers multiple times [Table 6]

Claims

1. A method for recycling polyester blended fabrics, characterized in that after processing raw materials containing polyester, the polyester is decomposed by a catalyst at 40°C to 120°C for 0.5 to 8 hours to achieve complete depolymerization, and then separated and recycled, and the separated polyester component and other blended components can be reused.

2. The method for recycling polyester blended fabrics according to claim 1, characterized in that the catalyst is a main catalyst and a co-catalyst of organic base, the catalyst loading amount is 0.1-20wt% of the mass of the blended fabric, and the mass ratio of the main catalyst and the co-catalyst of organic base is 1:0.01-100.

3. The method for recycling polyester blended fabrics according to claim 2, characterized in that the main catalyst of the organic base is one or more of nitrogen-containing amidine or guanidine compounds or derivatives, and the co-catalyst is a nitrile compound.

4. The method for recycling polyester blended fabrics according to claim 3, characterized in that the main catalyst of the organic base is (a) 1,8-diazabicycloundec-7-ene (DBU), polymer or compound-supported DBU, and organic salts formed by DBU and imidazole and its derivatives, (b) 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), polymer or compound-supported TBD, and organic salts formed by TBD and imidazole and its derivatives, and (c) 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), polymer or compound-supported DBN, and organic salts formed by DBN and imidazole and its derivatives.

5. 4. The method for recycling polyester blended fabrics according to claim 3, wherein the co-catalyst is one or more of acetonitrile, propanenitrile, benzonitrile, and adiponitrile.

6. The method for recycling polyester blended fabrics according to claim 1, characterized in that the raw material containing polyester is a polyester blended fabric or a blend of polyester and other fabrics, in which the content of polyester in the raw material is 5% to 100%, and the polyester blended fabric is a fabric in which polyester is blended with one or more of spandex, cotton, viscose fiber, regenerated cellulose fiber, nylon, wool, cashmere, and pure silk.

7. The polyester-containing raw material to be treated is washed in alcohol or a mixed system containing alcohol at 40 to 130° C. for 0.3 to 2 hours, where the mixed system containing alcohol is a mixture of alcohol and an alkaline compound, and the alkaline compound is soda ash (Na ２ CO ３ 2. The method for recycling polyester blend fabrics according to claim 1, characterized in that the active ingredient is one or more of the following: sodium acetate, sodium methoxide, sodium ethoxide, potassium carbonate, potassium acetate, potassium methoxide, calcium oxide, and calcium hydroxide.

8. The method for recycling polyester blended fabrics according to claim 1, characterized in that after the polyester is decomposed, it is subjected to solid-liquid separation, the solid is collected, the polyester component is separated from other fiber components by Soxhlet extraction, the liquid is recycled, the alcohol and the co-catalyst are recycled by atmospheric distillation, and then the diol and dibasic acid monomers of the polyester and the organic base catalyst are recycled by vacuum distillation or extraction.

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