Method for treating a textile fiber blend in a fiber fixed-bed reactor

Abstract

The invention relates to a method for treating, in particular for purifying, a textile fiber blend, wherein a treatment agent flows through the textile fiber blend, and to a device for carrying out the method according to the invention.

Description

[0001] Method for treating a textile fiber mixture in a fiber fixed bed reactor

[0002] The present invention relates to a method for treating, in particular for purifying, a textile fiber mixture, in which the textile fiber mixture is permeated by a treatment agent, and to a device for carrying out the method according to the invention.

[0003] Rapidly changing fashion trends are driving increased clothing production. Given the associated resource consumption and growing amounts of waste, the demand for sustainable solutions for dealing with used textiles is rising.

[0004] Currently, recycled textiles are difficult to process. Only a small percentage are resold as secondhand goods or reused for other purposes. In shredding plants, the textiles can be processed into fibers, which, depending on their quality, can be used as raw materials for painter's fleece, car interior trim, or as filler, or as an additive in yarn production. While this extends the lifespan of the fibers, the fibers obtained in this way are generally too short to be processed into new textiles on a satisfactory scale and reused in their original form.

[0005] Textile recycling generally presents the problem that many different, sometimes contaminated, materials are often disposed of together, and textiles themselves are made of mixed materials. Therefore, one aspect of a sustainable recycling process is the cleaning of the textile fibers or fiber blends, with a particular focus on separating synthetic and non-synthetic fibers. This is achieved, for example, through the depolymerization of the plastics used, allowing them to be recovered in the form of their monomers.

[0006] WO 2019 / 140245 describes a process for producing cellulose and terephthalic acid from textile waste, in which the textile waste is treated with subcritical water at a temperature of 105 to 190 °C and a pressure of 40 to 300 psi for up to 90 minutes, yielding cellulose with a degree of polymerization of 150 to 2500 and dissolved terephthalic acid and ethylene glycol. WO 2010 / 104458 relates to a process for producing formed cellulose material from lignocellulose by a sequence of separation, dissolution, and cellulose forming steps, in which the lignin is removed by boiling the material at a temperature between 110 and 200 °C for a period of 1 to 6 hours in an aqueous solution comprising soluble alkali, alkaline earth, or phosphorus compounds.

[0007] US 2023 / 0124761 discloses a process for treating a starting material comprising cellulose-containing and non-cellulose-containing material, in which various treatment methods are intended to lead to a change in the viscosity and average molecular weight of the cellulose material.

[0008] US 2024 / 270926 describes a process for recycling mixed textile waste comprising polyester and cellulose staple fibers, including cotton staple fibers, wherein the process includes depolymerization of the polyester in a basic aqueous solution.The process involves placing the textiles in a reaction chamber; providing a basic depolymerization solution in a bath ratio between V2 and 1 / 20 of the weight of the textiles to the weight of the solution; circulating the depolymerization solution through the textiles to depolymerize the polyester into the appropriate monomers and to remove the polyester monomers from the textiles; removing the depolymerization solution from the reaction chamber, wherein the temperature of the depolymerization solution is in the range between 101 °C and 160 °C, and circulating the depolymerization solution through the textiles to provide treated textiles that comprise the cellulose staple fibers, preferably including the cotton staple fibers, and are substantially free of polyester material.

[0009] DK 181 912 relates to a device for treating textile fibers in a solvent suspension, comprising a reactor, wherein the reactor includes a lower end and an upper end, an inlet for solvent, an outlet for solvent, an inlet for fiber material and an outlet for suspended or wetted fiber material, wherein the device is designed to push solvent from the solvent inlet to the solvent outlet through the reactor and to move the fiber material from the fiber material inlet to the outlet for suspended filter material.The claimed device shall be characterized in that the reactor further comprises a first filter arranged near the lower end and a second filter arranged near the upper end, wherein the distance between the first filter and the second filter defines a reaction volume for treating the textile fibers, wherein the inlet for solvent is arranged below the first filter, wherein the outlet for solvent is arranged above the second filter, wherein the inlet for fiber material is arranged below and usually near the second filter, and wherein the outlet for suspended or moistened fiber material is arranged above and usually near the first filter.

[0010] SE 2250 912 discloses a process for recycling at least a part of a textile material comprising polyester fibers, wherein the process includes a mixing step in which the textile material comprising polyester fibers and at least one other type of fiber is brought into contact with a suspension comprising a catalyst and methanol in a rotatable drum of a reactor unit, the rotatable drum being arranged to rotate about an axis having an angle to the horizontal plane of less than 45°; a depolymerization step in which a temperature of at least 80 °C is provided in the reactor unit, wherein the textile is exposed to the catalyst and methanol to carry out a methanolysis-depolymerization reaction of the polyester portion of the textile material, the other type of fiber remaining in a fiber state;wherein the drum is rotated during at least one of the steps, namely the mixing step and the depolymerization step, in order to mix the textile material with the catalyst and the methanol, and comprises the removal of a liquid solution containing depolymerized polyester from the reactor unit and the removal of a fiber material containing the fibers of the other type from the reactor unit.

[0011] US 2024 / 092991 relates to a process comprising: a) providing a starting material consisting of a mixed textile material or a mixture of textile materials comprising at least one target polymer together with an undesired polymer and an organic solvent having a boiling point below the melting point of the at least one target polymer; b) heating the organic solvent to a target temperature in the range of about 60°C to about 200°C; c) contacting the organic solvent with the mixed textile material or the mixture of textile materials for a period not exceeding 90 minutes to dissolve the undesired polymer in the organic solvent without dissolving the at least one target polymer, thereby providing 1) a solvent solution comprising the dissolved undesired polymer and 2) a purified textile material that is substantially free of the undesired polymer;and d) separating the solvent solution containing the dissolved unwanted polymer from the purified textile material.

[0012] Separating natural and synthetic fibers from waste textiles presents a challenge: chemical treatment can degrade the cellulose polymer chain, potentially rendering the fibers unsuitable for textile production and preventing fiber-to-fiber reuse. Furthermore, the monomers recovered from the synthetic fibers must be of high purity to be reused within the existing value chain as part of a sustainable recycling concept.

[0013] Against this background, the present invention aims to provide a method for the treatment, in particular the purification, of textile fibers, which improves the recycling of used textiles and allows the resources used to be utilized sustainably.

[0014] Within the scope of the present invention, it has surprisingly been found that this problem can be solved by a method as defined in claim 1. Advantageous embodiments of the method according to the invention are set out in the dependent claims.

[0015] Accordingly, a first object of the present invention is a method for treating, in particular for purifying, a textile fiber mixture, in which the textile fiber mixture is introduced into a reactor (fiber fixed bed reactor) and is permeated by a treatment agent, the treatment agent is subjected to purification after permeation, and the purified treatment agent is returned to the method.

[0016] The method according to the invention thus comprises the following steps: a) introducing a textile fiber mixture into a fiber fixed bed reactor; b) passing a treatment agent through the textile fiber mixture in the reactor; c) purifying the treatment agent after passing through the textile fiber mixture; and d) returning the purified treatment agent to the process.

[0017] Fixed-bed reactors are generally known to those skilled in the art as reactors in which fluids flow through a solid bed or packing, the fixed bed serving, for example, to fix heterogeneous catalysts or microorganisms. Within the scope of the present invention, it was surprisingly found that this type of reactor can also be advantageously used in the purification of textile fiber mixtures.

[0018] A fiber fixed-bed reactor within the meaning of the present invention is therefore understood to be a fixed-bed reactor in which the introduced textile mixture is analogous to the fixed bed and is permeated by the treatment agent. The fiber fixed-bed reactor used in the process according to the invention, hereinafter also referred to as the reactor unless otherwise specified, is designed such that the textile fibers contained therein are permeated by the treatment agent. For this purpose, the reactor preferably has an inlet and an outlet arranged such that the treatment agent flows through the reactor along its entire length, as well as sieve trays which retain the textile fibers in the reactor.By using such a flow-through reactor, the process according to the invention offers an advantage over conventional alternatives, such as stirred tank reactors or mixers, in that the fibers are fixed and do not need to be moved during the process. This avoids the challenges associated with handling fiber suspensions, such as pumping, conveying, mixing, or stirring. Fixing the fibers offers the advantage that the remaining process control is based exclusively on liquid media, and greater scaling factors can be achieved. Furthermore, the flow through the fixed fibers enables efficient heat and mass transfer within the reactor, allowing the process to be operated not only energy-efficiently but also gently.In this way, excessive degradation of the fibers to be cleaned, which are usually cotton-based fibers, can be avoided. Heat exchangers cannot be used efficiently with fiber suspensions, so the process according to the invention, using liquids, enables a high degree of heat integration.

[0019] Due to the recirculation of the process according to the invention, it is easily possible to repeat steps b) to d) until a desired degree of purity of the textile fibers is achieved.

[0020] The process according to the invention is specifically designed for the separation of natural fibers and synthetic fibers. The textile fibers of the textile fiber mixture used preferably originate from waste textiles, such as those obtained from used and no longer worn textiles from used clothing collections or from remnants in textile and clothing manufacturing. Within the framework of the process according to the invention, the textile fiber mixture can be provided in a wide variety of forms. The fibers can be provided as free fibers, but also in the form of shredded and / or unshredded textiles, thus initially eliminating the need for complex preparation of the textiles to be recycled.

[0021] The textile fiber mixture preferably comprises natural and synthetic fibers. The natural fibers are preferably selected from cotton, hemp, and linen fibers, as well as man-made cellulose fibers such as lyocell or viscose fibers, and mixtures thereof. The synthetic fibers are preferably selected from polyester, polyether, polyurethane, and polyamide fibers, and mixtures thereof. Polyethylene terephthalate fibers are particularly preferred.

[0022] Cotton remains a major component of textiles. However, its cultivation is criticized due to its high water requirements and the use of pesticides and fertilizers, making alternative sources of great importance. This is where the inventive process comes into play, which has proven particularly suitable for the further utilization of cellulose from cotton fibers as a valuable raw material. Therefore, the textile fiber mixture used preferably has a proportion of cellulose-based fibers of at least 20% by weight, particularly preferably at least 60% by weight, especially at least 80% by weight, and in particular at least 90% by weight, in each case based on the total weight of the textile fiber mixture used. Cellulose-based fibers are understood to include, in particular, cotton fibers as well as man-made cellulose fibers such as lyocell fibers and viscose fibers.

[0023] The process according to the invention can be operated as a batch process with respect to the textile fibers and thus offers the advantage that the process can be individually adjusted to the respective batch, while all further process steps run continuously. For example, different treatment agents can be used sequentially in the same reactor without the need to transport the textile fibers.

[0024] In the process according to the invention, the textile fiber mixture is permeated with, or exposed to, a treatment agent stream. The treatment agent primarily serves to remove plastic fibers from the textile fiber mixture. Therefore, an embodiment of the process according to the invention is preferred in which the treatment agent is selected from the group consisting of alcoholic solvents, in particular methanol and ethylene glycol, and aqueous sodium hydroxide solution, as well as mixtures thereof. The treatment agent can be gaseous or liquid.

[0025] Various additives can be added to the treatment agent. A preferred embodiment of the process according to the invention is carried out in the presence of a catalyst, the catalyst preferably being added to the treatment agent. For example, alkali metals, alkaline earth metals, transition metals, and their respective salts can be used as catalysts. The catalyst is preferably selected from the group consisting of alkali acetates, alkaline earth acetates, transition metal acetates, carbonates, hydrogen carbonates, and mixtures thereof. The catalyst is particularly preferred from the group consisting of zinc acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate, sodium carbonate, and sodium hydrogen carbonate. Mixtures of different catalysts can also be used.The use of catalysts has proven particularly advantageous in combination with methanol as a treatment agent, as this allows for faster degradation of the plastic fibers even at low temperatures. In cases where a catalyst is added, the amount of catalyst in the treatment agent is preferably 0.1 to 1.0 g / l, and particularly preferably 0.15 to 0.7 g / l.

[0026] The reaction conditions under which the process according to the invention is carried out can be adapted depending on the textile fiber mixture to be treated. Preferably, the treatment of the textile fiber mixture is carried out at a temperature of 140 to 240 °C, particularly preferably 150 to 210 °C. The process according to the invention can be carried out at various pressures, which can be adapted depending on the type of treatment agent and the reaction temperature, with pressures of 1 to 80 bar being preferred.

[0027] The cleaned textile fibers can be subjected to further treatments within the framework of the inventive process, the advantage being that the textile fibers can remain in the reactor. A preferred embodiment involves subjecting the textile fibers, after achieving the desired degree of purity, to a further washing step, preferably with water, to remove, for example, any remaining treatment agent. For this purpose, the flow of the treatment agent can advantageously be replaced by water, eliminating the need to transport or relocate the fibers. Drying of the fibers can also be carried out in the reactor, for which it is preferably perfused with a drying gas such as air or nitrogen. The drying gas can be heated to accelerate the drying process.

[0028] In a preferred embodiment of the process according to the invention, the textile fiber mixture or the cleaned textile fibers are subjected to a decolorization step, which is advantageously also carried out in the reactor. For this purpose, the textile fibers can, for example, be treated with sodium hydroxide, ozone, or other bleaching agents, or the treatment agent stream can be mixed with these agents. The conditions of the decolorization step can be adapted depending on the dye used. In a preferred embodiment, the textile fiber mixture or the cleaned textiles can, for example, be subjected to alkaline hydrolysis followed by washing and then an oxidative post-treatment. This has proven particularly advantageous for fibers dyed with reactive or direct dyes. For the alkaline hydrolysis, for example, sodium hydroxide, potassium hydroxide, sodium carbonate, or sodium bicarbonate can be used.To protect the textile fibers and improve the decolorization result, further additives can be used, with carbon disulfide, urea, carboxymethyl cellulose and polyethylene glycol proving particularly advantageous.

[0029] The decolorization step preferably includes a washing step following alkaline hydrolysis. Water is the preferred washing solution, but other reactants may be added. These are preferably selected from the group consisting of polyvinylpyrrolidone (PVP), acetic acid, citric acid, hydrochloric acid, and sulfuric acid. Complexing agents, such as ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and ethylene glycol bis(aminoethyl ether)-N,N, / V', may also be added to the washing solution to complex unwanted metals. / / V'- tetraacetic acid (EGTA) or ethylenediamine succinic acid (EDDS).

[0030] As a further step in the decolorization process, the washing step is preferably followed by an oxidative post-treatment, such as ozonolysis or hydrogen peroxide treatment. Alternatively or in combination, other oxidizing agents such as potassium permanganate or sodium hypochlorite can be used.

[0031] Alternatively or additionally, decolorization can be achieved with a reductive treatment, which has proven particularly advantageous for vat and sulfur dyes. In reductive decolorization, the textile fiber mixture or the textile fibers can, for example, be subjected to sodium dithionite reduction, whereby other compounds such as glucose, sodium disulfite, amino(imono)methylsulfinates, or sodium borohydride can also be used as reducing agents. The reduction is preferably carried out under a protective gas atmosphere. The fibers treated in this way can then be washed again and subjected to an oxidative post-treatment as described.

[0032] Another method of decolorization involves subjecting the textile fiber blend or the textile fibers themselves to a washing process with supercritical CO2 (Sc-CO2). This treatment has proven particularly advantageous for removing disperse dyes and other finishing chemicals.

[0033] Furthermore, the inventive method offers the possibility of adjusting the degree of polymerization of the purified textile fibers. The corresponding treatment can also be carried out in the reactor, thus eliminating the need for conveying and mixing the textile fibers. To adjust the degree of polymerization, the fibers are preferably subjected to a hydrothermal treatment, whereby, for example, the fibers are permeated with water or steam at a temperature of 130 to 200 °C, preferably 160 to 190 °C, and / or a pressure of 0.3 to 1.6 MPa, preferably 0.6 to 1.3 MPa, in the reactor. The duration of the treatment depends on the desired degree of polymerization and is preferably 1 to 120 minutes.

[0034] After passing through the textile fiber mixture, the treatment agent stream undergoes purification. Without being bound to any specific theory, it is assumed that any plastic fibers present in the textile fiber mixture are degraded by reaction with the treatment agent, and the degradation products are carried away with the treatment agent. To separate these degradation products from the unused treatment agent, the agent is purified accordingly before being returned to the process. Various methods are available to those skilled in the art for this purification, with crystallization, rectification, and distillation, as well as combinations of these processes, being preferred within the framework of the process according to the invention. The treatment agent recovered during purification is returned to the process. Depending on their type and purity, the separated degradation products can be subjected to further use or purification.The inventive method thus allows for resource-saving process operation, since only the treatment agent consumed by the reaction needs to be replenished, while the unused treatment agent is generally operated in a closed-loop system.

[0035] The process according to the invention is carried out in a fiber fixed-bed reactor, which is designed such that the textile fiber mixture is not present as a moving suspension, as would be the case in a stirred tank or conventional mixer, but rather the treatment agent circulates through the textile fiber mixture. Suitable reactors are, for example, the solid-state extractors already established for plant extraction, used to hold the material to be extracted (in this case, the textile fiber mixture), which have inlets and outlets for the treatment agent, preferably arranged opposite each other such that the treatment agent flows through the reactor lengthwise. A suitable reactor preferably also has openings through which the textile fiber mixture can be introduced into and removed from the reactor.In a particular embodiment, the reactor is provided with an upper opening through which the textile mixture, for example in a cartridge, can be introduced. Using such a cartridge facilitates the handling of the textile fiber mixture to be cleaned and its fixation within the reactor; therefore, the textile fiber mixture is preferably introduced into the reactor in a cartridge through which the treatment agent flows. Additionally or alternatively, the reactor is provided with a resealable bottom opening through which the textile fiber mixture can be easily removed from the reactor. In this way, the reactor can be loaded and unloaded efficiently and quickly, ensuring an uninterrupted process flow.

[0036] Conventional fixed-bed reactors are typically sealed with flange connections, making opening the reactor a complex process. Since the reactor must be opened frequently in the process according to the invention, the fiber-reinforced fixed-bed reactor according to the invention is preferably equipped with one or more bayonet fittings, which allow for easy opening of the reactor and thus an efficient process flow.

[0037] In a conventional fixed-bed reactor, the fixed bed is typically a highly porous bed of material that serves not as a reactant but as a catalyst and is ideally not degraded. In contrast, the fiber fixed-bed reactor of the present invention is used to treat textile fiber mixtures in order to degrade specific fiber types within the textile fiber bed.

[0038] The textile fibers can be introduced into the reactor in either a dry or moist state. To achieve high reactor utilization, it is also preferable to compact the textile fibers before introducing them into the reactor.

[0039] The textile fiber mixture can undergo various pretreatments before being passed through it with the treatment agent. For example, the fibers can be pre-washed to remove coarse dirt and impurities. In this case, the pretreatment can take place directly in the reactor, or the pre-treated textile fiber mixture can be introduced directly into the reactor.

[0040] In a particularly preferred embodiment, the process according to the invention is carried out in an oxygen-deficient atmosphere, preferably under exclusion of oxygen. For this purpose, the reactor can, for example, be supplied with an inert gas such as nitrogen. Such a process has proven particularly advantageous when the textile fiber mixture contains cotton fibers, which can thus be treated gently.

[0041] Monomers such as dimethyl terephthalate (DMT), terephthalic acid (PTA), and bis(2-hydroxyethyl) terephthalate (BHET) are important raw materials in the production of polyesters, especially polyethylene terephthalate (PET), which is also used as a fiber in textiles. These monomers are mostly obtained from petroleum products and thus represent a finite resource. The process according to the invention allows the monomers DMT, PTA, and BHET to be recovered from PET fibers, which can then be used in turn for the production of esters such as PET, thus closing the value chain. Therefore, a particular embodiment of the process according to the invention relates to the purification of a textile fiber mixture comprising cotton fibers and PET fibers. In this embodiment, the textile fiber mixture is introduced into the fiber fixed-bed reactor and percolated with a treatment agent.Depending on the treatment agent used, the corresponding monomers can be recovered from the PET fibers. For example, when methanol is used as the treatment agent, the PET is depolymerized and can be carried out as dimethyl terephthalate (DMT) and its oligomers along with the methanol. The DMT is separated from the methanol and used for further purposes, such as the production of new PET fibers. The methanol is then recycled back into the process. Ethylene glycol produced in this process can also be separated and further processed. In this way, not only can the natural cotton fibers be recovered, but also the valuable raw materials DMT and EG. Similarly, by using ethylene glycol as the treatment agent, PET can be depolymerized to BHET, or, when using aqueous sodium hydroxide, to PTA.A further object of the present invention is a device for carrying out the method according to the invention. The device according to the invention preferably comprises an extraction system with at least one fiber fixed-bed reactor for receiving a textile fiber mixture through which a treatment agent flows, and a unit for purifying the treatment agent after the flow. In a preferred embodiment, the reactor is equipped with a flowable cartridge for receiving the textile fiber mixture, the cartridge preferably having a sieve bottom. For cases in which the textile fiber mixture is provided in cartridges, the device according to the invention further preferably comprises at least one cartridge changer. The reactor of the device according to the invention is preferably further equipped with inlets and outlets for the treatment agent.Depending on the embodiment, the reactor may have a resealable bottom opening through which the textile fiber mixture can be removed. Such an embodiment is particularly preferred when the textile fiber mixture cannot be provided in a cartridge.

[0042] In a further preferred embodiment, the device according to the invention has a reservoir for receiving, storing, temperature-controlled and dispensing the treatment agent.

[0043] The device according to the invention preferably comprises several fiber fixed-bed reactors, which are preferably connected in parallel. In this way, the process according to the invention can be operated continuously despite batch operation of the reactors. The number of reactors can be, for example, six or more.

[0044] The process according to the invention is designed for the purification of textile fiber mixtures, in particular for the separation of natural fibers and plastic fibers, which are recovered in the form of their monomers and oligomers. Therefore, a further object of the present invention is a process for the production of polyethylene terephthalate precursors, wherein a textile fiber mixture comprising natural fibers and polyethylene terephthalate fibers is introduced into a reactor and through which a treatment agent flows, and the polyethylene terephthalate precursors are isolated from the treatment agent stream, wherein the polyethylene terephthalate precursors are dimethyl terephthalate (DMT), terephthalic acid (PTA) and / or bis(2-hydroxyethyl) terephthalate (BHET), and the treatment agent is selected from the group consisting of methanol, ethylene glycol, and aqueous sodium hydroxide solution.

[0045] Examples and figures:

[0046] The present invention is explained in more detail with reference to the following examples and figures, which are in no way to be understood as limiting the inventive concept.

[0047] Figure 1 shows the schematic setup of an exemplary apparatus of the present invention. A cartridge (4a) containing a textile fiber mixture is placed in a fiber fixed-bed reactor (3a) and a treatment agent from a reservoir (1) flows through it. After passing through the textile fiber mixture, the treatment agent is fed to a purification unit (5), and the purified treatment agent (7) is returned to the process. A continuous flow of the treatment agent is maintained by means of the reservoir (1, 8) and the pump (2). The by-products (6) separated during purification, for example, dimethyl terephthalate in the separation of a fiber mixture of cotton and PET fibers, can be fed into further processing.The continuous flow of treatment medium allows several reactors to be operated in parallel, so that, for example, fibers can already be processed in a second reactor (3b) while the purified fibers from the first reactor (3a) can be taken and fed to further processing.

[0048] Figure 2 shows a further schematic representation of the present invention, in which several fiber fixed-bed reactors are arranged in parallel. The reactors in section B are connected in parallel and can be operated sequentially, so that the process in section A can be operated fully continuously and steadily with constant flow rates and concentrations of the treatment agent. In this way, stable product quality is guaranteed, while customized recipes for each textile batch enable efficient treatment with heterogeneous feedstock.

[0049] Example 1: A 50:50 mixture of cellulose and PET fibers was placed in a fiber fixed-bed reactor and continuously treated with methanol at 200 °C for 60 minutes. After the reaction was complete, the cellulose fibers were removed from the reactor and washed with fresh methanol and ethyl acetate for further purification. DMT was isolated from the methanol stream as a white solid and recrystallized to remove any remaining impurities. The methanol filtrate was then fed into the next process cycle.

[0050] Example 2

[0051] A 50:50 mixture of cellulose and PET fibers was placed in a fiber fixed-bed reactor and treated with ethylene glycol at 200 °C for 60 minutes. After the reaction, the cellulose fibers were removed and washed with fresh ethylene glycol and distilled water. The PET depolymerization product was isolated from the ethylene glycol, and the excess ethylene glycol was recycled back into the process cycle. The isolated depolymerization product was washed with water at 40–50 °C to dissolve the BHET from the oligomer. The BHET was then recrystallized in water to remove any remaining impurities.

[0052] Example 3

[0053] A textile fiber mixture of cellulose and PET fibers in an 80:20 ratio was placed in a fiber fixed-bed reactor and treated with methanol at 160 °C for 60 minutes, with zinc acetate added to the methanol stream. After the reaction was complete, the cellulose fibers were filtered off and washed with fresh methanol and ethyl acetate. DMT was isolated from the methanol stream as a white solid, with the excess methanol being returned to the process. The isolated DMT, as a methanolysis product, was recrystallized to remove any remaining impurities.

[0054] Example 4

[0055] A textile fiber blend of cellulose and PET fibers in an 80:20 ratio was treated with ethylene glycol containing zinc acetate in a fiber fixed-bed reactor at a temperature of 195 °C for 60 minutes. After the reaction was complete, the cellulose fibers were filtered off and washed with fresh ethylene glycol and water. The PET depolymerization product was isolated from the ethylene glycol stream, and any unreacted ethylene glycol was recycled. The isolated depolymerization product was recrystallized to remove residual impurities.

[0056] The separation of PET fibers from textile blends can be supported by suitable catalysts, which can also be implemented within the framework of the process according to the invention. In the test series, PET fibers were subjected to a treatment agent stream to which the catalyst had been added. As can be seen from the following tables, efficient degradation of the PET can be achieved in this way, with methanol being used as the treatment agent in the tests listed in Table 1 and ethylene glycol in those listed in Table 2.

[0057] Table 1:

[0058] Table 2:

[0059] Example 5:

[0060] A textile fiber mixture of cellulose fibers and PET fibers was introduced into a device according to the present invention and subjected to a methanol treatment solution at 175 °C for 2 hours. 10% water and 8% ethylene glycol, along with zinc acetate as a catalyst, were added to the methanol. After 2 hours, the PET was completely degraded, as confirmed by FTIR. The resulting DMT was isolated and showed no byproducts by NMR spectroscopy.

[0061] Example 6:

[0062] A textile fiber mixture of cellulose fibers and PET fibers was treated for one hour at 170 °C in the apparatus according to the invention with methanol as the treatment agent. 5% water and 5% ethylene glycol, as well as zinc acetate as a catalyst, were added to the methanol. After the specified time, the PET was completely degraded. The resulting DMT contained small amounts of BHET as a byproduct (0.2%).

[0063] As the examples show, the inventive process enables an efficient separation of cellulose and PET fibers, whereby not only is the PET completely degraded so that pure cellulose fibers are obtained, but the products resulting from the degradation of the PET are also recovered in high purity and can thus be easily put to further use.

Claims

Patent claims:

1. A method for treating a textile fiber mixture, characterized in that the textile fiber mixture is introduced into a fiber fixed bed reactor and is passed through by a treatment agent, the treatment agent is subjected to purification after passing through and the purified treatment agent is returned to the method.

2. Method according to claim 1, characterized in that the textile fiber mixture comprises natural fibers and plastic fibers, wherein the natural fibers are preferably selected from cotton fibers, hemp fibers, linen fibers, artificial cellulose fibers such as lyocell fibers and viscose fibers and mixtures thereof and / or the plastic fibers are preferably selected from polyester fibers, polyether fibers, polyurethane fibers, polyamide fibers and mixtures thereof.

3. Method according to at least one of the preceding claims, characterized in that the textile fiber mixture has a proportion of fibers based on cellulose of at least 20 wt.%, particularly preferably of at least 60 wt.%, in particular at least 80 wt.% and in particular at least 90 wt.%, in each case based on the total weight of the textile fiber mixture used.

4. Method according to at least one of the preceding claims, characterized in that the treatment agent is selected from the group consisting of alcoholic solvents, in particular methanol and ethylene glycol, and aqueous sodium hydroxide solution and mixtures thereof.

5. A method according to at least one of the preceding claims, characterized in that the method is carried out in the presence of a catalyst, which is preferably added to the treatment agent, wherein the catalyst is preferably selected from the group consisting of alkali acetates, alkaline earth acetates, transition metal acetates, carbonates, hydrogen carbonates and mixtures thereof, wherein the catalyst is preferably selected from the group consisting of zinc acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate, sodium carbonate and sodium hydrogen carbonate.

6. Method according to at least one of the preceding claims, characterized in that the treatment of the textile fiber mixture is carried out at a temperature of 140 to 240 °C, particularly preferably 150 to 210 °C and / or a pressure of 1 to 80 bar.

7. Method according to at least one of the preceding claims, characterized in that the purified textile fibers are further subjected to a hydrothermal treatment, wherein the fibers are preferably brought into contact with water or steam at a temperature of 130 to 200 °C, preferably 160 to 190 °C and / or a pressure of 0.3 to 1.6 MPa, preferably 0.6 to 1.3 MPa in the fiber fixed bed reactor.

8. Method according to at least one of the preceding claims, characterized in that the purification of the treatment agent is carried out by a method selected from crystallization, rectification and distillation as well as combinations of these methods.

9. Method according to at least one of the preceding claims, characterized in that the textile fiber mixture is present in a cartridge through which the treatment agent can flow.

10. Method according to at least one of the preceding claims, characterized in that the textile fiber mixture comprises cotton fibers and PET fibers.

11. Device for carrying out a method according to at least one of claims 1 to 10, characterized in that the device comprises at least one fiber fixed bed reactor for receiving a textile fiber mixture through which a treatment agent flows, and a unit for cleaning the treatment agent after the flow through.

12. Device according to claim 11, characterized in that the reactor is equipped with a flowable cartridge for receiving the textile fiber mixture, wherein the cartridge preferably has at least one sieve bottom.

13. Device according to claim 12, characterized in that the device further comprises at least one cartridge changer.

14. Device according to at least one of claims 11 to 13, characterized in that the device has a reservoir for receiving, storing and dispensing the treatment agent.

15. Device according to at least one of claims 11 to 14, characterized in that the device comprises more than one fiber fixed bed reactor, these preferably being connected in parallel.

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