Method for recycling textile fibers

Abstract

The present invention relates to a method for recycling textile fibers, which dispenses with the active addition of a catalyst.

Description

[0001] Process for processing textile fibers

[0002] The present invention relates to a process for processing textile fibers which does not require the active addition of a catalyst.

[0003] Although textiles are used in many areas, the clothing industry remains the largest textile-processing sector. Frequently changing fashion trends, inexpensive goods, and high demand, in particular, result in large production volumes that are usually manufactured with little consideration for people and the environment. Furthermore, the high consumption of clothing generates corresponding amounts of waste, which in most cases ends up in landfills or incinerated. In light of stricter legal requirements and the ongoing sustainability debate, recycling processes for processing textile waste are increasingly becoming the focus of industry and research. A sustainable recycling system is intended to conserve resources and reduce environmental impact.However, due to the complexity of the material, the processing of textiles involves considerable effort, so that new production is often more cost-effective than the processing and reprocessing of old textiles.

[0004] For example, US 5,236,959 describes a process for converting polyester and cotton blends in which the polyester fibers are depolymerized in the presence of a catalyst to a diester of terephthalic acid, the cotton fibers are separated and processed into cellulose acetate by pulping and acetylation processes.

[0005] CN 112646135 provides a process for the continuous production of polyester from dyed polyester textile waste, yielding spinnable and colorless polyester. In the claimed process, the textile waste is comminuted and melted, and the melt is subjected to methanolic alcoholysis in the presence of a catalyst. The resulting monomer is purified, recrystallized, and processed into a spinnable and colorless polyester by means of an ester exchange reaction, prepolymerization, and subsequent polycondensation.

[0006] US 10,167,374 describes a process for recovering organic fibers from a composite material comprising a polymer matrix and organic fibers. A solution comprising a mixture of water and alcohol is provided, the composite material is placed inside a reactor, and the mixture and the composite material are brought into contact to conduct a solvolysis reaction of the polymer matrix of the composite material and recover the organic fibers. The pressure and temperature in the reactor are controlled to position them in the homogeneous subcritical region of the phase diagram, in the supercritical region, or near the critical point, and the temperature is below the decomposition temperature of the organic fibers.

[0007] Processes for processing textiles are generally known in the art. For example, US Pat. No. 10,501,599 discloses a process for producing cellulose and / or terephthalic acid from a textile waste material containing cotton and / or a blend of cotton and polyester. The textile waste material is treated with subcritical water at a temperature of 105 to 190 °C and a pressure of 40 to 300 psi for 0 to 90 minutes. The cellulose thus produced has a degree of polymerization of 150-2500. In addition to the cellulose, dissolved terephthalic acid and ethylene glycol are obtained.

[0008] However, known processes have the disadvantage that they are usually carried out in the presence of catalysts and under aggressive conditions, which compromises the quality of the recovered fibers. Therefore, there is still a need for a process for processing textiles, particularly the cellulose fibers processed in textiles, that produces high-quality fibers. One criterion for assessing the quality of cellulose fibers is their average degree of polymerization (DP), which is an important parameter for the processing and performance properties of fiber-forming polymers and is often described using the parameter of intrinsic viscosity. Especially with cellulose fibers, the average degree of polymerization allows a numerical characterization of chemical damage to the fibers, which the fibers may suffer, for example, during processing.

[0009] Against this background, the present invention seeks to provide a process for processing textile fibers which overcomes the disadvantages of conventional processes and provides fibers, in particular cellulose fibers, which allow the production of new cellulose fibers such as lyocell or viscose fibers.

[0010] This object is achieved according to the invention by a method as defined in claim 1. Preferred embodiments of the method according to the invention are set out in the subclaims.

[0011] A first object of the present invention is therefore a process for the processing of textile fibers, in which 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, the treatment being carried out without the active addition of a catalyst.

[0012] The process according to the invention is characterized by the catalyst-free reaction process, in which no active addition of a catalyst is required. It has surprisingly been shown that, contrary to current teaching, the processing of textile fibers can be carried out even without the active addition of a catalyst under gentle conditions with reaction kinetics that enable an economically viable process. By omitting the catalyst, complex purification and processing steps that would normally be necessary to remove the catalyst and purify the fibers are eliminated. The process according to the invention thus allows for gentle processing of the textile fibers, avoiding additional contamination, for example, through the addition of a catalyst. A further advantage of the process according to the invention is that the salt load and its disposal, which would otherwise arise when the catalyst is separated, are eliminated.

[0013] The textile fibers used in the process according to the invention are preferably natural and / or synthetic fibers, which are preferably selected from the group consisting of cellulose fibers, polyester fibers, polyether fibers, polyurethane fibers, and mixtures thereof. Processed cellulose fibers are preferably used as cellulose fibers. These can arise, for example, as production waste during textile production. Another possible source for the cellulose fibers are used textiles, such as those obtained from worn and unworn clothing. In a preferred embodiment, the textile fibers comprise cellulose fibers and synthetic fibers, in particular PET and / or elastane fibers.The mass ratio of cellulose fibers to synthetic fibers, in particular PET fibers, is in such cases preferably 100:0 to 0:100, preferably 99:1 to 1:99, particularly preferably 90:10 to 10:90, in particular 80:20 to 20:80, especially 60:40 to 40:60. In this way, the process according to the invention can take into account the challenge that most textiles use mixtures of cellulose fibers with synthetic fibers. The process according to the invention was developed with the particular focus of being able to put textile waste to sensible use again. Therefore, an embodiment in which the textile fibers originate from textile waste is particularly preferred. Textile waste is understood to mean materials that remain during the production of textiles or are disposed of in other ways, for example at the end of their service life.Such textile waste can include anything from fabric scraps to old clothes and household textiles. In a preferred embodiment, the textile fibers contain at least 10% by weight of natural fibers, especially cotton fibers, based on the total weight of the textile fibers.

[0014] In the process according to the invention, the textile fibers are treated with a methanol-containing solvent. In the context of the present invention, a methanol-containing solvent is understood to mean a solvent or solvent mixture whose main constituent is methanol. The proportion of methanol in the methanol-containing solvent is preferably at least 50 vol.%, particularly preferably at least 60 vol.%, and in particular at least 80 vol.%, based on the total volume of the solvent. The solvent can be liquid or vaporous. In an alternative embodiment, the solvent is present as a mixture of liquid and vaporous. Treatment with vaporous solvent has the advantage that there is no restriction on the fiber length of the textile fibers, as occurs, for example, when the fibers are stirred. A larger quantity of textile fibers can also be treated in this way.

[0015] Furthermore, it has surprisingly been shown that under these conditions, the PET degradation products formed during the reaction due to sufficient contact of the vapor with the textile fibers dissolve in the methanol and precipitate at the bottom of the reaction vessel. In a preferred embodiment of the process according to the invention, the textile fibers are suspended in the methanol-containing solvent, which allows comprehensive wetting of the fibers with the solvent. In these cases, the solids content in the suspension is preferably 1 to 20% by mass, preferably 3 to 10% by mass.

[0016] Other solvents can be added to the methanol-containing solvent. This one or more solvents are preferably selected from the group consisting of water, chloroform, dichloromethane, and mixtures thereof. If the methanol-containing solvent contains other solvents, their proportion is preferably no more than 20 vol.%, more preferably no more than 10 vol.%, based on the total volume of the solvent. If the solvent is present as a methanol-water mixture, the volume ratio of methanol to water is preferably 100:0 to 90:10.

[0017] The process is characterized by its gentle handling, and it has surprisingly been shown that the processing can be carried out at low temperatures even without the addition of a catalyst. Therefore, the textile fibers are preferably treated at a temperature of 170 to 220 °C, especially 180 to 200 °C.

[0018] In the process according to the invention, the treatment of the textile fibers is carried out under elevated pressure, the pressure preferably being 2.5 to 5 MPa, particularly preferably 2.1 to 4 MPa.

[0019] To avoid unnecessary stress on the textile fibers during processing, it has proven advantageous to keep the treatment time as short as possible within the temperature and pressure range according to the invention. Therefore, an embodiment in which the treatment time is 1 to 60 minutes, preferably 1 to 30 minutes, is preferred.

[0020] The process according to the invention provides that the textile fibers are treated with a methanol-containing solvent. By treating the textile fibers with a methanolic solvent, polyester fibers contained in the starting textile fiber mixture can be separated, with PET fibers being the most common fiber type. By treating the starting textile fiber mixture under the conditions mentioned, the PET can be gently converted back into its monomers, which can then be used to produce new PET. Within the scope of the present invention, by treating the PET with a methanolic solvent, it is advantageously converted into dimethyl terephthalate as a monomer, which can then be polymerized again or used for other applications.

[0021] In a preferred embodiment, this treatment is carried out in the absence of oxygen. This minimizes the risk of undesirable degradation of the cellulose fibers contained in the textile fibers.

[0022] Dyed fibers can also be used in the process according to the invention. Thus, the presence of dyes commonly used in industry has been shown to have no effect on the quality of the final product. In a preferred embodiment, the textile fibers can therefore further comprise dyed and / or coloring components. The dyes used are preferably those selected from the group consisting of azo dyes, sulfur dyes, di- and triphenylmethane dyes, thiazole dyes, nitro dyes, anthraquinone dyes, quinone imine dyes,

[0023] Cyanine dyes, indigoid dyes, quinoline dyes, indigosol acridine dyes, nitroso dyes, phthalocyanine dyes, and mixtures thereof. While in conventional processes the dyes usually have to be separated before processing the fibers, this has proven unnecessary in the process according to the invention.

[0024] The same applies to metal residues that may be contained in the textile fibers. Within the scope of the process according to the invention, it has surprisingly been found that the active addition of a catalyst can be dispensed with, which, among other things, means that fewer side reactions, such as those that can be caused by a catalyst, were observed. Nevertheless, the presence of small amounts of metals introduced with or through the textile fibers has proven to be unproblematic. In a preferred embodiment, however, the metal content in the processed textile fibers is limited to less than 100 ppm, preferably less than 50 ppm, in particular less than 10 ppm. A metal content in this range has proven to be uncritical for the further processing of the fibers, so that a cleaning step to remove the metals can be dispensed with.

[0025] The textile fibers used in the process according to the invention are not subject to any restrictions regarding their length. In contrast to mechanical processing methods, both long and short fibers can be processed with consistent product quality. In a preferred embodiment, the textile fibers used therefore have an average fiber length of 0.5 to 20 mm, preferably 1 to 8 mm. The fibers can be comminuted, for example, in the form of textile scraps in a cutting mill.

[0026] The fibers obtained in the process according to the invention can be subjected to further steps as required. For example, it may be preferable to follow the process with a washing step. In a preferred embodiment of the process, the fibers are filtered off and washed at the end of the process. The washing medium is preferably one selected from the group consisting of methanol, ethanol, chloroform, dichloromethane, ethyl acetate, and water, as well as mixtures thereof.

[0027] The methanol-containing solvent obtained when filtering off the processed fibers can preferably be reused in the processing of other textile fibers, thus achieving a sustainable circular system here as well.

[0028] Due to its gentle process, the process according to the invention is particularly suitable for the processing of cellulose-containing textile fibers and allows the processing of the cellulose fibers while largely preserving their original degree of polymerization. Therefore, an embodiment is preferred in which the average degree of polymerization of the cellulose fibers after processing deviates by less than 25%, preferably less than 15%, from the average degree of polymerization of the original cellulose fibers before processing. In a particularly preferred embodiment, the average degree of polymerization of the processed cellulose fibers corresponds to an intrinsic viscosity of preferably more than 600 miyg, determined according to ISO 5351.

[0029] It has surprisingly been found that the process according to the invention is particularly suitable for recovering cellulose fibers from textile fibers. Therefore, an embodiment is preferred in which the processed fibers have a cellulose fiber content of at least 80%, preferably at least 90%, and particularly preferably at least 95%, based on the total proportion of cellulose fibers in the originally used textile fibers.

[0030] The process according to the invention is explained in more detail using the following example, which should in no way be understood as a limitation of the inventive concept.

[0031] Examples:

[0032] Example 1)

[0033] A mixture of cellulose fibers and PET fibers in a composition of 80:20 was suspended in methanol and treated in a reactor at a temperature of 200 °C for 60 minutes. After the reaction, 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 that formed in the filtrate was filtered out from the liquid, which was the unreacted methanol. The methanolysis product was then recrystallized in methanol to remove residual impurities. The yield of cellulose fibers was over 95%. The resulting cellulose fibers had an intrinsic viscosity of 2036 ml / g (ISO 5351).

[0034] Example 2)

[0035] A mixture of cellulose fibers and PET fibers with a composition of 72:28 was suspended in methanol and treated in a reactor at a temperature of 200 °C for 60 minutes. After the reaction, 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 that formed in the filtrate was filtered out from the liquid, which was the unreacted methanol. The methanolysis product was then recrystallized in methanol to remove residual impurities. The yield of cellulose fibers was over 97%. The resulting cellulose fibers had an intrinsic viscosity of 1639 ml / g (ISO 5351).

Claims

Patent claims:

1. A process for the processing of textile fibers, in which 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 active addition of a catalyst takes place.

2. Process according to claim 1, characterized in that the textile fibers are natural and / or synthetic fibers, preferably selected from the group consisting of cellulose fibers, polyester fibers, polyether fibers, polyurethane fibers and mixtures thereof.

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

4. Process according to at least one of the preceding claims, characterized in that the textile fibers originate from textile waste.

5. Process 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 vol.%, particularly preferably at least 60 vol.%, and in particular at least 80 vol.%, based on the total volume of the solvent 6. Process according to at least one of the preceding claims, characterized in that the methanol-containing solvent is liquid or vaporous or is present as a mixture of liquid and vaporous.

7. Process according to at least one of the preceding claims, characterized in that the methanol-containing solvent is present as a mixture with one or more further solvents, these being preferably selected from the group consisting of water, chloroform, dichloromethane and mixtures thereof.

8. Process 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. Process 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. Method according to at least one of the preceding claims, characterized in that the treatment duration is 1 to 60 minutes, preferably 1 to 30 minutes.

11. Process 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. Process 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 according to claim 12, characterized in that the washing medium is selected from the group consisting of methanol, ethanol, chloroform, dichloromethane, ethyl acetate and water and mixtures thereof.

14. A process according to at least one of the preceding claims, characterized in that the processed fibers have a content of at least 80%, preferably at least 90% and particularly preferably at least 95% of cellulose fibers, based on the total proportion of cellulose fibers in the originally used textile fibers 15. Process according to at least one of the preceding claims, characterized in that the average degree of polymerization of the processed fibers corresponds to an intrinsic viscosity of more than 600 mb / g, determined according to ISO 5351.