Textile fiber recovery method

Abstract

The invention relates to a method for recycling textile fibers. According to the method, active addition of a catalyst is not needed.

Description

[0001] This invention relates to a method for treating textile fibers without the need for the active addition of a catalyst.

[0002] Although textiles are used in many fields, the largest branch of textile processing remains the garment industry. In particular, frequently changing fashion trends, inexpensive products, and high demand lead to enormous production volumes, often with little consideration for human health and the environment. Furthermore, high garment consumption generates a corresponding amount of waste, which is mostly disposed of or incinerated. Given stricter legal requirements and within the ongoing discussion of sustainability, recycling methods for handling textile waste are increasingly becoming a focus of industry and research. Sustainable recycling needs to conserve resources and reduce environmental impact. However, due to the complexity of the materials, textile processing involves a considerable amount of work, so the production of new products is generally less expensive than the processing and reprocessing of waste textiles.

[0003] For example, US 5,236,959 describes a method for converting polyester / cotton blends, wherein polyester fibers are depolymerized to diterephthalate in the presence of a catalyst, and cotton fibers are separated and processed into cellulose acetate via cellulose and acetylation processes.

[0004] CN 112646135 discloses a method for continuously preparing polyester from colored waste polyester textiles to obtain a spinnable and colorless polyester. Within the scope of the method, the textile waste is pulverized and melted, and the melt is subjected to methanol hydrolysis in the presence of a catalyst. The resulting monomer is purified, recrystallized, and processed into a spinnable and colorless polyester through transesterification, prepolymerization, and subsequent polycondensation.

[0005] US 10,167,374 describes a method for recovering organic fibers from a composite material comprising a polymer matrix and organic fibers, wherein a solution comprising a mixture of water and alcohol is provided, the composite material is placed in a reactor, and the mixture is brought into contact with the composite material to carry out a solvent decomposition reaction of the polymer matrix of the composite material and recover the organic fibers. The pressure and temperature within the reactor are controlled to be within the homogeneous subcritical range, supercritical range, or near the critical point of the phase diagram, and wherein the temperature is below the decomposition temperature of the organic fibers.

[0006] Methods for reprocessing textiles are well known in the art. For example, US 10,501,599 discloses a method for producing cellulose and / or terephthalic acid from textile waste containing cotton and / or mixtures of cotton and polyester materials. The textile waste is treated with subcritical water for 0 to 90 minutes at a temperature of 105 to 190°C and a pressure of 40 to 300 psi. The cellulose produced thereby has a degree of polymerization of 150-2500. In addition to cellulose, dissolved terephthalic acid and ethylene glycol are also obtained.

[0007] However, a drawback of known methods is that they are mostly carried out in the presence of catalysts and under harsh conditions, leading to a deterioration in the quality of the recycled fibers. Therefore, a method for processing textiles, particularly those containing cellulose fibers, to produce high-quality fibers remains needed. A standard for evaluating the quality of cellulose fibers is, in particular, their average degree of polymerization (DP), an important characteristic of the processing and use properties of the fiber-forming polymer, and is typically described by intrinsic viscosity parameters. Especially for cellulose fibers, the average degree of polymerization allows for qualitative characterization of chemical damage that the fibers may undergo, for example, during processing.

[0008] Against this backdrop, the object of the present invention is to provide a method for processing textile fibers that overcomes the shortcomings of conventional methods and produces fibers that can be used to produce novel cellulose fibers, such as Lyocell or viscose fibers, particularly cellulose fibers.

[0009] According to the invention, this objective is achieved by the method defined in claim 1. Preferred embodiments of the method according to the invention are set forth in the dependent claims.

[0010] Therefore, the present invention relates first to a method for treating textile fibers, wherein the textile fibers are treated with a methanol-containing solvent at a temperature of 160 to 240°C and a pressure of 2 to 8.2 MPa, wherein the treatment is carried out without the active addition of a catalyst.

[0011] The method according to the invention is characterized by a catalyst-free reaction process, wherein no catalyst is actively added. Surprisingly, contrary to general teachings, the treatment of textile fibers can also be carried out without the active addition of a catalyst, under mild conditions and reaction kinetics that enable an economically viable process. Since no catalyst is used, the complex purification and treatment steps typically necessary for catalyst removal and fiber purification can be omitted. Therefore, the method of the invention allows for mild treatment of textile fibers, where the additional purification required by adding a catalyst can be avoided. Another advantage of the method of the invention is that the salt loading and disposal typically required during catalyst separation can be omitted.

[0012] The textile fibers used within the scope of the method of this invention are preferably natural fibers and / or synthetic fibers, preferably selected from the group consisting of cellulose fibers, polyester fibers, polyether fibers, polyurethane fibers, and mixtures thereof. The cellulose fibers are preferably processed cellulose fibers. These fibers can be obtained, for example, as production waste in textile manufacturing. Another source of cellulose fibers can be old or new textiles, such as those obtained from worn or unworn garments.

[0013] In a preferred embodiment, the textile fibers comprise cellulose fibers and synthetic fibers, particularly PET and / or elastane fibers. In such cases, the mass ratio of cellulose fibers to synthetic fibers (particularly PET fibers) is preferably 100:0 to 0:100, preferably 99:1 to 1:99, more preferably 90:10 to 10:90, particularly 80:20 to 20:80, and especially from 60:40 to 40:60. In this way, the challenge of using a mixture of cellulose and synthetic fibers in most textiles can be taken into account within the scope of the method of the invention. The method of the invention was developed with a particular focus on enabling textile waste to be reused for meaningful purposes. Therefore, embodiments in which the textile fibers are derived from textile waste are particularly preferred. "Textile waste" refers to material remaining after the production of textiles, or, for example, material that would otherwise need to be disposed of at the end of its service life. Such textile waste can include any substance ranging from fabric residues to old clothes and household textiles. In a preferred embodiment, the proportion of natural fibers, particularly cotton fibers, in the textile fibers is at least 10% by weight, based on the total weight of the textile fibers.

[0014] Within the scope of the method of this invention, textile fibers are treated with a methanol-containing solvent. Within the scope of this invention, "methanol-containing solvent" refers to a solvent or solvent mixture whose main component is methanol. Preferably, based on the total volume of the solvent, the proportion of methanol in the methanol-containing solvent is at least 50% by volume, more preferably at least 60% by volume, and particularly at least 80% by volume. The solvent can be in liquid or vapor form. In an alternative embodiment, the solvent is a mixture of liquid and vapor states. The advantage of treatment with a vapor solvent is that the fiber length of the textile fibers is not limited, whereas it would be limited if the fibers were agitated. Furthermore, a larger quantity of textile fibers can be processed in this manner.

[0015] Furthermore, it was surprisingly found that under these conditions, the PET degradation products formed (which are produced during the reaction through full contact between the vapor and the textile fibers) dissolved in methanol and deposited at the bottom of the reaction vessel.

[0016] In a preferred embodiment of the method of the present invention, the textile fibers are suspended in a methanol-containing solvent, which allows the solvent to thoroughly wet the fibers. In such cases, the solid content in the suspension is preferably 1 to 20% by mass, more preferably 3 to 10% by mass.

[0017] Other solvents may be added to the methanol-containing solvent. The one or more solvents are preferably selected from the group consisting of water, chloroform, dichloromethane, and mixtures thereof. When the methanol-containing solvent contains other solvents, their proportion is preferably no more than 20% by volume, and more preferably no more than 10% by volume, based on the total volume of the solvent. When the solvent is in the form of a methanol-water mixture, the volume ratio of methanol to water is preferably from 100:0 to 90:10.

[0018] This method is characterized by its mild process conditions, where it has been surprisingly found that treatment can be carried out at relatively low temperatures without the addition of a catalyst. Therefore, the treatment of textile fibers is preferably carried out at temperatures of 170 to 220°C, particularly 180 to 200°C.

[0019] Within the scope of the method of the present invention, the treatment of textile fibers is carried out under increased pressure, wherein the pressure is preferably 2.5 to 5 MPa, more preferably 2.1 to 4 MPa.

[0020] To avoid placing unnecessary stress on the textile fibers during processing, it has been found advantageous to shorten the processing duration as much as possible within the temperature and pressure range of the present invention. Therefore, a preferred embodiment is one in which the processing duration is 1 to 60 minutes, preferably 1 to 30 minutes.

[0021] The method of this invention specifies the treatment of textile fibers with a methanol-containing solvent. Treatment with a methanol solvent specifically separates polyester fibers contained in the starting textile fiber mixture, the most common fiber type being PET fibers. Treatment of the starting textile fiber mixture under these conditions successfully and mildly converts PET back into its monomer, which can then be used to produce new PET. Within the scope of this invention, treatment with a methanol solvent advantageously converts PET into dimethyl terephthalate as a monomer, which can then be repolymerized or used for other applications.

[0022] In a preferred embodiment, the treatment is carried out in the absence of oxygen. This minimizes the risk of accidental decomposition of the cellulose fibers contained in the textile fibers.

[0023] Within the scope of the method of this invention, colored fibers can also be used. Therefore, it has been found that the presence of commonly used industrial dyes has no impact on the quality of the final product. Therefore, in a preferred embodiment, the textile fiber may further comprise colored and / or dyeing components. The dyeing agent used is preferably selected from the group consisting of azo dyes, sulfur dyes, diphenylmethane and triphenylmethane dyes, thiazole dyes, nitro dyes, anthraquinone dyes, quinone imine dyes, cyanine dyes, indigo dyes, indigo dyes, quinoline dyes, lysodium acridine dyes, nitroso dyes, phthalocyanine dyes, and mixtures thereof. Although dye separation is typically required before fiber processing in conventional methods, this has been shown to be unnecessary within the scope of the method of this invention.

[0024] This also applies to metal residues that may be present in textile fibers. Surprisingly, within the scope of the method of the present invention, it has been found that the active addition of a catalyst can be omitted, resulting in fewer problems such as side effects that might be caused by the catalyst. Nevertheless, the presence of low levels of metals carried along with or introduced through the textile fibers has been found not to be problematic. However, in a preferred embodiment, the metal content in the treated textile fibers is limited to less than 100 ppm, preferably less than 50 ppm, and particularly less than 10 ppm. Metal content within this range has proven to be non-critical for further processing of the fibers, and therefore purification steps for metal removal can be omitted.

[0025] The textile fibers used in the method of this invention are not limited in length. Compared with mechanical processing methods, both long and short fibers can be processed while maintaining constant product quality. Therefore, in a preferred embodiment, the textile fibers used have an average fiber length of 0.5 to 20 mm, preferably 1 to 8 mm. The fibers can be pulverized, for example, in the form of textile waste in a cutting mill.

[0026] As needed, the fibers obtained within the scope of the method of this invention may undergo further steps. Therefore, a washing step is preferably performed after the method. In a preferred embodiment of the method, the fibers are filtered out and washed at the end of the process. Preferably, the washing medium is selected from the group consisting of methanol, ethanol, chloroform, dichloromethane, ethyl acetate, water, and mixtures thereof.

[0027] The methanol-containing solvent obtained during the filtration of the treated fibers is preferably recyclable for treating other textile fibers, thus achieving sustainable recycling.

[0028] Due to its mild processing conditions, the method of the present invention is particularly suitable for processing cellulose-containing textile fibers and allows for the processing of cellulose fibers while preserving their original degree of polymerization to the maximum extent. Therefore, a preferred embodiment is one in which the average degree of polymerization of the treated cellulose fibers deviates from that of the original cellulose fibers by less than 25%, preferably less than 15%. In a particularly preferred embodiment, the average degree of polymerization of the treated cellulose fibers, as determined according to ISO 5351, corresponds to an intrinsic viscosity preferably greater than 600 ml / g.

[0029] Surprisingly, the method of the present invention has been found to be particularly suitable for recovering cellulose fibers from textile fibers. Therefore, a preferred embodiment is wherein the treated fiber contains at least 80% cellulose fibers, preferably at least 90%, and more preferably at least 95%, based on the total proportion of cellulose fibers in the initially used textile fibers.

[0030] The present invention is further illustrated by the following embodiments, but these embodiments should in no way be construed as limiting the concept of the present invention. Example

[0031] Example 1)

[0032] A mixture of cellulose fibers and PET fibers in a ratio of 80:20 was suspended in methanol and treated in a reactor at 200°C for 60 minutes. After the reaction was complete, the cellulose fibers were filtered off and washed with fresh methanol and ethyl acetate. The filtrate was stored at 5°C for 24 hours. The white solid formed in the filtrate was filtered off from the liquid (which was unreacted methanol). Subsequently, the methanolysis product was recrystallized in methanol to remove residual contaminants. The yield of cellulose fibers was higher than 95%. The intrinsic viscosity of the obtained cellulose fibers was 2036 ml / g (ISO 5351).

[0033] Example 2)

[0034] A mixture of cellulose fibers and PET fibers in a ratio of 72:28 was suspended in methanol and treated in a reactor at 200°C for 60 minutes. After the reaction was complete, the cellulose fibers were filtered off and washed with fresh methanol and ethyl acetate. The filtrate was stored at 5°C for 24 hours. The white solid formed in the filtrate was filtered off from the liquid (which was unreacted methanol). Subsequently, the methanolysis product was recrystallized in methanol to remove residual contaminants. The yield of cellulose fibers was higher than 97%. The intrinsic viscosity of the obtained cellulose fibers was 1639 ml / g (ISO 5351).

Claims

1. A method of treating a textile fiber, wherein, The textile fibers are treated with a methanol-containing solvent at a temperature of 160 to 240°C and a pressure of 2 to 8.2 MPa, characterized in that no catalyst is added actively.

2. The method of claim 1, wherein, The textile fibers are natural fibers and / or synthetic fibers, preferably selected from the group consisting of cellulose fibers, polyester fibers, polyether fibers, polyurethane fibers and mixtures thereof.

3. The method according to at least one of the preceding claims, characterized in that The proportion of natural fibers, in particular cotton fibers, in the textile fibers is at least 10% by weight, based on the total weight of the textile fibers.

4. The method according to at least one of the preceding claims, characterized in that The textile fibers are derived from textile waste.

5. The method according to at least one of the preceding claims, characterized in that The proportion of methanol in the methanol-containing solvent is at least 50% by volume, more preferably at least 60% by volume and in particular at least 80% by volume, based on the total volume of the solvent.

6. The method according to at least one of the preceding claims, characterized in that The methanol-containing solvent is in liquid or vapor state or in the form of a mixture of a liquid component and a vapor component.

7. The method according to at least one of the preceding claims, characterized in that The methanol-containing solvent is in the form of a mixture with one or more other solvents, which are preferably selected from the group consisting of water, chloroform, dichloromethane and mixtures thereof.

8. The method according to at least one of the preceding claims, characterized in that The treatment is carried out at a temperature of 170 to 220°C, preferably 180 to 200°C.

9. The method according to at least one of the preceding claims, characterized in that The treatment is carried out at a pressure of 2.5 to 5 MPa, preferably 2.1 to 4 MPa.

10. The method according to at least one of the preceding claims, characterized in that The duration of the treatment is 1 to 60 minutes, preferably 1 to 30 minutes.

11. The method according to at least one of the preceding claims, characterized in that The textile fibers have a fiber length of 0.5 to 20 mm, preferably 1 to 8 mm.

12. The method according to at least one of the preceding claims, characterized in that The fibers are filtered off and washed after the end of the reaction.

13. The method of claim 12, wherein, The washing medium is selected from the group consisting of methanol, ethanol, chloroform, dichloromethane, ethyl acetate, water and mixtures thereof.

14. The method according to at least one of the preceding claims, characterized in that The content of cellulose fibers in the treated fibers is at least 80%, preferably at least 90% and more preferably at least 95%, based on the total proportion of cellulose fibers in the initially employed textile fibers.

15. The method according to at least one of the preceding claims, characterized in that The average degree of polymerization of the treated fibers corresponds to a intrinsic viscosity of more than 600 ml / g, determined according to ISO 5351. The textile fibers are treated with a methanol-containing solvent at a temperature of 160 to 240°C and a pressure of 2 to 8.2 MPa, characterized in that no catalyst is added actively. The textile fibers are natural fibers and / or synthetic fibers, preferably selected from the group consisting of cellulose fibers, polyester fibers, polyether fibers, polyurethane fibers and mixtures thereof. The proportion of natural fibers, in particular cotton fibers, in the textile fibers is at least 10% by weight, based on the total weight of the textile fibers. The textile fibers are derived from textile waste. The proportion of methanol in the methanol-containing solvent is at least 50% by volume, more preferably at least 60% by volume and in particular at least 80% by volume, based on the total volume of the solvent. The methanol-containing solvent is in liquid or vapor state or in the form of a mixture of a liquid component and a vapor component. The methanol-containing solvent is in the form of a mixture with one or more other solvents, which are preferably selected from the group consisting of water, chloroform, dichloromethane and mixtures thereof. The treatment is carried out at a temperature of 170 to 220°C, preferably 180 to 200°C. The treatment is carried out at a pressure of 2.5 to 5 MPa, preferably 2.1 to 4 MPa. The duration of the treatment is 1 to 60 minutes, preferably 1 to 30 minutes. The textile fibers have a fiber length of 0.5 to 20 mm, preferably 1 to 8 mm. The fibers are filtered off and washed after the end of the reaction. The washing medium is selected from the group consisting of methanol, ethanol, chloroform, dichloromethane, ethyl acetate, water and mixtures thereof. The content of cellulose fibers in the treated fibers is at least 80%, preferably at least 90% and more preferably at least 95%, based on the total proportion of cellulose fibers in the initially employed textile fibers. The average degree of polymerization of the treated fibers corresponds to a intrinsic viscosity of more than 600 ml / g, determined according to ISO 5351.