Method for obtaining cellulose pulp from textile products

Abstract

This invention relates to a method for recovering pulp from textile products, pulp recovered by the method according to the present invention, and further processing and use thereof.

Description

Technical Field

[0001] The present invention relates to a method for recovering pulp from textile products, the pulp recovered by the method of the present invention, and its further processing and use.

Background Art

[0002] The reuse of valuable raw materials such as textile products has a long tradition, the origin of which dates back to the so-called rag pickers who collected old textile products to make a living. The recycling of textile products is generally industrialized and is classified into material recycling, chemical recycling and thermal recycling. The raw materials recovered from textile products are used for a wide range of applications including raw materials for the textile industry and the paper industry.

[0003] Despite the high recyclable ratio, most of the obtained old textile products are still discarded or incinerated. Here, there is a problem that it is difficult and costly to recycle textile fibers with high quality. That is, any recycling process first starts with sorting. The subsequent actual treatment depends on whether the material is reused in the textile industry ("closed-loop recycling") or utilized in other industries ("open-loop recycling"). The main problem is to increase the ratio of closed-loop recycling, that is, to process textile products so that they can be used again in the textile industry.

[0004] Textile products usually contain a high content of cotton, that is, cellulose, but in many cases, they are dyed and mixed with heterogeneous synthetic fibers. Therefore, complicated purification is required in advance to obtain cellulose of a quality that can be further processed. Furthermore, the chain length of cellulose becomes shorter with each reprocessing cycle, so that after several recycling cycles, the fibers become unsuitable for further processing, which is also a problem.

[0005] As conventional technology, several methods for processing textile products are known, mainly focusing on open-loop recycling, which involves processing fibers for reuse in the papermaking industry. Against this backdrop, International Publication No. 2020 / 245053 proposes a method for producing cellulosic pulp, in which used textile products are provided as starting materials, the used textile products contain cellulose and non-cellulose heterogeneous substances, particularly synthetic resins and / or metal oxides, and the cellulose is at least partially reduced from the non-cellulose heterogeneous substances to provide a reduced-weight starting material, from which a cellulosic pulp is formed.

[0006] International Publication No. 2020 / 245058 describes a method for continuously preparing pulverized cellulose-containing starting materials, particularly starting materials for producing cellulosic molded articles, the method comprising supplying cellulose-containing starting materials having a predetermined composition to a reactor, continuously preparing the cellulose-containing starting materials in the reactor to obtain treated cellulose-containing starting materials, and discharging the treated cellulose-containing starting materials from the reactor.

[0007] International Publication No. 2019 / 140245 discloses a method for producing cellulose and / or terephthalic acid from textile waste materials containing cotton and / or mixtures of cotton and polyester materials. The textile waste materials are treated with subcritical water at a temperature of 105°C to 190°C and a pressure of 40 psi to 300 psi for 0 to 90 minutes. The produced cellulose has a degree of polymerization of 150 to 2500. In addition to cellulose, dissolved terephthalic acid and ethylene glycol are obtained.

[0008] International Publication No. 2010 / 104458 relates to a method for producing a cellulose material molded from lignocellulose by a series of cellulose separation steps, a cellulose dissolution step, and a cellulose molding step.

[0009] U.S. Patent Application Publication No. 2023 / 0124761 describes a method for processing raw materials comprising cellulose and non-cellulose materials, the method comprising, in particular, a pretreatment of the starting materials intended to alter the viscosity and average molecular weight of the cellulose material. The pretreatment may be, for example, non-alkaline washing, enzymatic treatment, amorphous phase water treatment, swelling agent treatment, supercritical carbon dioxide (CO2) treatment, bleaching agent treatment, or organic solvent treatment.

[0010] Cellulose derived from textile products is typically recovered in the form of pulp and then further processed, for example, into filament fibers or yarn. Despite existing proposals in the prior art, there remains a demand for efficient and sustainable textile recycling methods, particularly in closed-loop recycling, where recovered pulp can be primarily processed back into textile products. In particular, there is a need for a comprehensive approach that not only recovers the material but also enables this through resource and environmentally protective processing. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] International Publication No. 2020 / 245053 [Patent Document 2] International Publication No. 2020 / 245058 [Patent Document 3] International Publication No. 2019 / 140245 [Patent Document 4] International Publication No. 2010 / 104458 [Patent Document 5] U.S. Patent Application Publication No. 2023 / 0124761 [Overview of the project] [Problems that the invention aims to solve]

[0012] The object of the present invention is to provide a method for recovering pulp from textile products that meets this demand and protects resources and the environment. [Means for solving the problem]

[0013] Therefore, the present invention first, a) Provide a starting mixture of textile fibers containing cellulose fibers and heterogeneous fibers, b) Separate cellulose fibers from heterogeneous fibers by treatment with a methanol-based solvent, and c) A method for recovering pulp from a textile product, which includes hydrothermal treatment of cellulose fibers to obtain pulp. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 shows a schematic step representing an example of the method of the present invention. [Modes for carrying out the invention]

[0015] Within the scope of this invention, the terms "pulp" and "dissolved pulp" are used synonymously and refer to cellulose in the form of short fibers or particles. Those skilled in the art will generally understand these terms to refer to cellulose used as a starting material for the production of cellulose regenerated materials capable of producing fibers or sheets such as viscose.

[0016] Within the scope of the present invention, the term "cellulose" means a polysaccharide composed of β-D-glucose moieties linked to one another by β-1,4-glycosidic bonds.

[0017] Within the scope of the present invention, it has been surprisingly discovered that the method according to the present invention yields high-quality pulp that can be further processed into new products for a variety of applications.

[0018] Possible sources of the starting mixture of textile fibers in the present invention include both used and unused textile products obtained from, for example, vintage recycling and residues during the manufacture of fibers and clothing. Therefore, the method of the present invention is not limited with respect to the starting mixture of textile fibers. In a preferred embodiment, the starting mixture of textile fibers has a proportion of at least 10% by weight of natural fibers, particularly cotton fibers, based on the total weight of the starting mixture of textile fibers.

[0019] Textile products are further composed of a significant proportion of cellulose fibers, but the proportion of heterogeneous fibers continues to increase. In a preferred embodiment, such heterogeneous fibers are selected from the group consisting of polyester fibers, particularly polyethylene terephthalate (PET) fibers, polyether fibers, polyurethane fibers, polyamide fibers, and mixtures thereof.

[0020] The method of the present invention includes, as a first step, separating the starting mixture of textile fibers in order to reduce the proportion of heterogeneous fibers. For this purpose, the starting mixture of textile fibers is treated with a methanol-based solvent. In the scope of the present invention, a methanol-containing solvent refers to a solvent or solvent mixture whose main component is methanol. Preferably, the proportion of methanol in the methanol-containing solvent is at least 50% by volume, more preferably at least 60% by volume, particularly at least 80% by volume, based on the total volume of the solvent.

[0021] This treatment is preferably carried out at a temperature of 160°C to 240°C and / or a pressure of 1.8 MPa to 8 MPa, more preferably at a temperature of 170°C to 220°C and / or a pressure of 2.2 MPa to 5.8 MPa, particularly at a temperature of 180°C to 200°C and / or a pressure of 2.7 MPa to 4 MPa. Preferably, the treatment time has been found to be 1 minute to 120 minutes, preferably 1 minute to 60 minutes or 15 minutes to 120 minutes, more preferably 10 minutes to 90 minutes.

[0022] Treatment with methanol-based solvents can particularly separate polyester fibers contained in the starting mixture of textile fibers, the most common of which is PET fiber. Treating the starting mixture of textile fibers under the above conditions mildly converts PET back into monomers, which can then be used in the production of new PET. Within the scope of the present invention, treatment with methanol-based solvents favorably converts PET to dimethyl terephthalate as a monomer, which may then be repolymerized or used for other purposes.

[0023] Step b) of the method of the present invention can be carried out in or without a catalyst. For example, zinc acetate (Zn(OAc)2) or sodium methanolate may be used as a catalyst. In another preferred embodiment, step b) of the method of the present invention may be carried out in a basic solvent, for example, by adding NaOH or KOH.

[0024] Preferably, step b) of the method of the present invention is carried out in the absence of a catalyst, and in particular, there is no active addition of a catalyst. By not using a catalyst, on the one hand, contamination of the fibers by the catalyst is avoided, and on the other hand, further salt load formed when the catalyst is separated is not generated.

[0025] In the treatment of the starting mixture of textile fibers with a methanol-based solvent, the solvent may be in liquid or vapor form. Treatment of the starting mixture of textile fibers with a vaporized methanol-based solvent has the advantage of allowing more fibers to come into contact with the solvent, resulting in better mixing even with long-fiber materials. Therefore, embodiments of the method of the present invention preferably involve treatment with a vaporized methanol-based solvent. Alternatively, the starting mixture of textile fibers can be suspended in the solvent to thoroughly wet the fibers. In a particularly preferred embodiment, the methanol-based solvent is in equilibrium between the vapor phase and the liquid phase.

[0026] The methanol-based solvent may be mixed with other solvents. The other solvent is preferably selected from the group consisting of water, dichloromethane, chloroform, and mixtures thereof. When the methanol-based solvent contains other solvents, the proportion of the other solvent is preferably 20% by volume or less, more preferably 10% by volume or less, relative to the total volume of the solvent. In a particularly preferred embodiment, a methanol-water mixture is used, and the water content is preferably a maximum of 10% by volume relative to the total volume of the solvent.

[0027] In addition to separating heterogeneous fibers, the separation of cellulose fibers from the starting mixture of textile fibers in step b) of the method of the present invention may include a further purification step. In a preferred embodiment, an oxidizing agent and / or a metal complexing agent may be further added to the starting mixture of textile fibers. This can achieve a bleaching effect on the cellulose fibers or remove any metallic impurities that may be present in the starting mixture of textile fibers. The oxidizing agent is preferably selected from the group consisting of oxygen, ozone, and hydrogen peroxide (H2O2), while the metal complexing agent is preferably different from any catalyst. Examples of suitable metal complexing agents include EDTA, DTPA, MGDA, EDDS, NTA, and IDS.

[0028] In another embodiment, step b) is carried out under oxygen-free conditions. In this way, the risk of undesirable degradation of cellulose fibers in the textile can be minimized.

[0029] In a preferred embodiment, the method of the present invention includes a step of washing the starting mixture of textile fibers. This washing step preferably follows step b). The washing medium is preferably selected from the group consisting of methanol, ethanol, chloroform, dichloromethane, ethyl acetate, water, and mixtures thereof.

[0030] As a further step, the method of the present invention provides the implementation of hydrothermal treatment. In a preferred embodiment, the treatment is carried out at a temperature of 130°C to 200°C, preferably 160°C to 190°C, and / or at a pressure of 0.3 MPa to 1.6 MPa, preferably 0.6 MPa to 1.3 MPa. The preferred treatment time is 1 minute to 120 minutes. During the treatment, the water may be in liquid phase, steam, or a mixture thereof.

[0031] Similar to step b) of the method of the present invention, step c) may be carried out in or without a catalyst, with hydrothermal treatment in the absence of a catalyst being preferred. Conventional methods typically use water and a catalyst such as NaOH or KOH, but within the scope of the present invention, it has been surprisingly shown that the method is economically efficient even without a catalyst, and as a result has the advantage of avoiding the disadvantages associated with subsequent neutralization and the use of further salt loads or further chemicals.

[0032] In a preferred embodiment of the method of the present invention, steam explosion may be performed before and / or after step c). This increases the surface area of ​​the fibers, enabling more efficient processing.

[0033] Within the scope of the method of the present invention, it has been surprisingly found that a relatively large amount of cellulose fibers can be processed, and as a result, the energy used can be optimally utilized. In a preferred embodiment of the method of the present invention, the ratio of fibers to solvent in step b) is 1:1 to 1:20.

[0034] In a more preferred embodiment, the ratio of fiber to water in step c) of the method of the present invention is 1:1 to 1:20.

[0035] Since textile products are often dyed, a decolorization process is necessary during the recycling process to remove or decolorize the dyes bound to the cellulose fibers. There are two methods of decolorization: oxidative decolorization and reductive decolorization. Therefore, in a preferred embodiment of the method of the present invention, a reduction treatment and / or oxidation treatment of the cellulose fibers is further performed before step c) of the method of the present invention. Within the scope of the method of the present invention, decolorization under basic conditions with the addition of an oxidizing agent has been shown to be a milder and preferred method for cellulose. For example, decolorization under basic conditions using an oxidizing agent such as hydrogen peroxide or ozone has the advantage of reducing damage to the cellulose fibers while obtaining good decolorization results. The decolorization process is preferably carried out under a basic atmosphere at a temperature of 60°C to 180°C. In a preferred embodiment, suitable metal complexing agents such as EDTA, DTPA, MGDA, EDDS, NTA and / or IDS, and / or suitable stabilizers in the form of antioxidants such as propyl gallate or magnesium sulfate (MgSO4) may be added for further protection of cellulose and reduction of metal content.

[0036] Used textile products are typically crushed, and their fibers have varying lengths. The method of the present invention has high tolerance for long fibers. Nevertheless, it may be preferable to limit the fibers to a predetermined length, for example, to avoid entanglement or knotting of fibers during mechanical stirring. Therefore, embodiments of the method of the present invention in which the starting mixture of textile fibers is crushed before processing in step b) are preferred.

[0037] A certain chain length of cellulose is required for the recovered pulp to be processed again into textile products. Intrinsic viscosity is commonly used as a measure of chain length, and the value of intrinsic viscosity decreases as the polymer chain decomposes, and intrinsic viscosity is expressed as an average value. The method of the present invention enables recovery without causing significant decomposition of the polymer chain, but adjusting the intrinsic viscosity may be useful for specific applications. Therefore, in preferred embodiments, the method of the present invention further includes the step of mixing the pulp with other cellulose fibers so that the resulting mixture has a target value of average intrinsic viscosity. For example, the pulp obtained by the method of the present invention can be mixed with cellulose fibers having a lower intrinsic viscosity to achieve a desired target value of average intrinsic viscosity.

[0038] The method of the present invention produces high-quality pulp that can be further processed for multiple applications. Therefore, embodiments in which the obtained pulp is processed into other products, such as textile products or paper, particularly woven fibers, are preferred. In the field of textile product manufacturing, recycled pulp is further processed into a spinning solution, which serves as a starting material for producing cellulose fibers and, consequently, textile products. In particular, it has been found to be advantageous to provide the pulp in sheet form from the viewpoint of storage and transportation. Therefore, embodiments in which the obtained pulp is compressed into a sheet are preferred.

[0039] The present invention further relates to the pulp obtained according to the present invention.

[0040] The pulp obtained by the method of the present invention is particularly suitable for processing into new fibrous products. Here, it is advantageous that the cellulose has a predetermined chain length. Therefore, in a preferred embodiment, the pulp has an intrinsic viscosity measured according to ISO 5351:2010 of at least 400 ml / g and / or up to 700 ml / g, preferably 450 ml / g to 650 ml / g, and more preferably 450 ml / g to 580 ml / g.

[0041] The pulp obtained by the method of the present invention is characterized by its high purity. Surprisingly, it has been found that a significant improvement in whiteness can be achieved without decolorizing the fibers. Therefore, in a preferred embodiment, the pulp has a whiteness of at least 90% according to ISO 11475.

[0042] In addition to its advantageous whiteness, the pulp of the present invention is further characterized by its low impurity content. Therefore, in preferred embodiments, the pulp has an iron (Fe) content of 10 mg / kg or less. Preferably, the pulp of the present invention has a silicon dioxide (SiO2) content of less than 80 mg / kg and / or a calcium (Ca) content of less than 80 mg / kg. The ash content, measured at 650°C ± 10°C, is preferably 0.2% or less.

[0043] The present invention relates to the use of pulp obtained by the method of the present invention, particularly for the manufacture of textile products and / or paper. For such use, cellulose can be further processed into, for example, fibers or pulp. In another preferred embodiment, the pulp can be used as a starting material for the manufacture of cellulose acetate, which can be further processed into, for example, a film.

[0044] This invention relates to cellulose fibers produced from the pulp of the present invention. [Examples]

[0045] The present invention will be described in more detail by the following embodiments and drawings, but these should not be interpreted as limiting the concept of the invention.

[0046] Example 1 An undyed starting mixture of woven fibers containing cellulose fibers and PET fibers in an 80:20 ratio was suspended in methanol (2.5 g solids per 100 ml of methanol). The suspension was heated to 170°C to 220°C to depolymerize the PET. The cellulose fibers were then filtered and dried. The resulting cellulose fibers were suspended in water and heated to 160°C to 190°C. The resulting pulp was then filtered, washed, and dried. Subsequently, FTIR spectroscopy showed that no PET was detected, indicating a residual content of less than 2%. This result was confirmed by gravimetric analysis, which showed complete decomposition of PET within the measurement accuracy. The resulting pulp had an average intrinsic viscosity of 415 ml / g, and in a subsequent step, it was mixed with additional cellulose having a higher intrinsic viscosity to obtain a final product with an average intrinsic viscosity of 550 ml / g.

[0047] The process was carried out without the active addition of a catalyst.

[0048] Example 2 A starting mixture of dyed woven fibers containing cellulose fibers and PET fibers in a 50:50 ratio was treated with vaporized methanol at a temperature of 170°C to 220°C to depolymerize the PET. The dyed cellulose fibers were then separated and dried. The cellulose fibers were decolorized by alkaline hydrolysis in a 1M KOH aqueous solution at 90°C to 140°C, followed by washing and drying. FTIR spectroscopy revealed no detectable PET, indicating a residual content of less than 2%. This result was confirmed by gravimetric analysis, which showed complete decomposition of PET within the measurement accuracy. The decolorized cellulose fibers were suspended in water at a concentration of 2% fiber content and heated at a temperature of 160°C to 190°C. The resulting pulp was then filtered, washed, and dried. The resulting pulp had an average intrinsic viscosity of 418 mL / g.

[0049] The process was carried out without the active addition of a catalyst.

[0050] These examples demonstrate that the method of the present invention can be used to process textile waste into high-quality pulp in an economical and sustainable manner.

[0051] Figure 1 shows a schematic step representing an example of the method of the present invention. The textile waste to be processed may originate from collected and sorted used textile products obtained in used clothing collection. The textile waste is crushed or pulverized by other means to form a starting mixture of textile fibers. To separate heterogeneous fibers, the starting mixture of textile fibers is treated with a methanol-based solvent (S1). The separated cellulose fibers are optionally decolorized before being subjected to hydrothermal treatment (S2). The resulting pulp may be further processed, for example, into cellulose fibers.

Claims

1. a) A step of providing a starting mixture of textile fibers containing cellulose fibers and other fibers, b) A step of separating cellulose fibers from heterogeneous fibers by treatment with a methanol-containing solvent, and c) A process comprising hydrothermal treatment of cellulose fibers to obtain pulp, A method for recovering pulp from textile products.

2. The method according to claim 1, characterized in that the process in step b) is carried out at a temperature of 160°C to 240°C, preferably 170°C to 220°C, more preferably 180°C to 200°C, and / or at a pressure of 1.8 MPa to 8 MPa, preferably 2.2 MPa to 5.8 MPa, more preferably 2.7 MPa to 4 MPa, for a time of preferably 1 minute to 120 minutes, preferably 1 minute to 60 minutes or 15 minutes to 120 minutes, more preferably 10 minutes to 90 minutes.

3. The method according to 1 or 2, characterized in that the process in step b) is carried out in the presence or absence of a catalyst.

4. The method according to any one of claims 1 to 3, characterized in that the methanol-based solvent is a liquid, a vapor, or a mixture thereof.

5. The method according to any one of claims 1 to 4, characterized in that the starting mixture of textile fibers has a proportion of at least 10% by weight of natural fibers, particularly cotton fibers, relative to the total weight of the starting mixture of textile fibers.

6. The method according to any one of claims 1 to 5, characterized in that the textile fibers are derived from textile waste.

7. The method according to any one of claims 1 to 6, characterized in that the proportion of methanol in the methanol-containing solvent in step b) is at least 50% by volume, more preferably at least 60% by volume, and particularly at least 80% by volume, relative to the total volume of the solvent.

8. The method according to any one of claims 1 to 7, characterized in that the process in step c) is carried out at a temperature of 130°C to 200°C, preferably 160°C to 190°C, and / or at a pressure of 0.3 MPa to 1.6 MPa, preferably 0.6 MPa to 1.3 MPa, for a time of preferably 1 minute to 120 minutes.

9. The method according to any one of claims 1 to 8, characterized in that the process in step c) is carried out in the presence or absence of a catalyst.

10. The method according to any one of claims 1 to 9, characterized in that the process in step c) is carried out using liquid water, steam, or a mixture thereof.

11. The method according to any one of claims 1 to 10, characterized in that the ratio of fiber to solvent in step b) is 1:1 to 1:20, and / or the ratio of fiber to water in step c) is 1:1 to 1:

20.

12. The method according to any one of claims 1 to 11, characterized in that a reduction treatment and / or an oxidation treatment is further carried out before step c).

13. The method according to any one of claims 1 to 12, further comprising a further processing step for the obtained pulp.

14. Pulp obtained by the method according to any one of claims 1 to 13.

15. The pulp according to claim 14, characterized in that the pulp has an intrinsic viscosity measured according to ISO 5351:2010 of at least 400 ml / g and / or up to 700 ml / g, preferably 450 ml / g to 600 ml / g, and more preferably 450 ml / g to 580 ml / g.

16. The pulp according to claim 14 or 15, characterized in that the pulp has a whiteness of 90% as measured by ISO 11475.

17. Use of the pulp according to any one of claims 14 to 16 for the production of textile products and / or paper and / or cellulose acetate.

18. Cellulose fibers produced from pulp according to any one of claims 14 to 16.

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