Process for the recovery of raw materials from mixed textile waste

technical field

The present invention relates to a method for recovering raw materials from mixed textile waste.

State of the art

The recovery or recycling of raw materials from textile waste has become increasingly important for the textile industry in recent years, not least in order to reduce the burden of this textile waste on the environment.

The purely mechanical recycling of textile waste has been well known for a long time, with the textile waste being crushed and directly recycled end products such as cleaning cloths, filling materials or insulating materials being produced from it. Spinning yarns from such recycled textile fibers usually results in low-quality yarns that are only conditionally suitable for the production of new textiles.

To overcome the above problems offer chemical

recycling process. For example, cellulosic fibers can be spun into regenerated cellulosic fibers after chemical pretreatment. However, such processes for the production of regenerated cellulosic shaped bodies are very sensitive to impurities in the cellulose raw material, which means that such recycled cellulose raw material is generally unsuitable for spinning fibers from it.

[0005] WO 2015/077807 A1 shows a method for the pretreatment of recycled cotton fibers from textile waste, in which metals are first removed from the recycled cotton fibers and these are then subjected to oxidative bleaching. The cotton fibers recycled in this way can then be used to produce regenerated cellulosic molded articles.

WO 2018/115428 A1 discloses a method for treating a raw material based on cotton under alkaline conditions in conjunction with gaseous oxidizing agents.

WO 2018/073177 A1 in turn describes a method for recycling a cellulose raw material from cellulose textile waste. The textile waste is treated under alkaline conditions in the presence of a reducing agent in order to swell the cellulosic fibers in the textile waste and thus better remove foreign matter. After the alkaline treatment, the cellulose raw material is bleached with either oxygen and/or ozone.

Such methods usually use pure cellulosic textile waste as the starting material. In practice, however, the textile waste from clothing and fabrics is mixed textile waste, i.e. mixtures of cellulosic and synthetic fibers. The predominant fraction is mixed textile waste, which contains polyester and cellulosic fibers. Textile waste from cotton textiles is also usually contaminated with polyester from sewing threads, labels or the like. However, methods of the aforementioned type cannot usually process mixed textile waste, since significant contamination with synthetic polymer fibers can no longer be removed.

WO 2014/045062 A1 in turn describes a method for extracting polyester from textiles using extraction solvents. This enables the polyester component to be recovered; the cellulose component, on the other hand, is heavily contaminated by residues of extraction solvent, significant degradation of the molecular chain or by residues of remaining polyester and is not suitable for use in a process for the production of regenerated cellulosic shaped bodies. In addition, the polyester component is contaminated with foreign substances, dyes, matting agents, etc., and its molecular chain length and properties have changed significantly as a result of the dissolving process, which makes additional processing of the polyester component unavoidable.

Disclosure of Invention

It is therefore an object of the invention to provide a method for the recovery of raw materials from mixed textile waste of the type mentioned, which allows the recovery of raw materials in a higher purity.

The stated object is achieved according to the invention by a method according to claim 1.

By providing a mixed textile waste containing at least one cellulosic component and at least one polyester component, treating the mixed textile waste in an aqueous treatment solution to depolymerize and dissolve the polyester component in the treatment solution, separating the cellulosic component from the treatment solution, and recovering a cellulosic raw material a cellulosic raw material can be recovered in high quality from mixed textile waste in a technically simple manner and can thus be reused as a cellulosic starting material. Further, by filtering the processing solution to remove foreign matter from the processing solution n, and precipitating terephthalic acid from the treatment solution, separating the precipitated terephthalic acid and recovering a polyester raw material containing terephthalic acid, a particularly advantageous utilization and recovery of the polyester component can be achieved, with the polyester raw material obtained being able to be used again as a starting material for the production of polyester.

For the purposes of the present invention, “polyester” is mainly understood to mean polyethylene terephthalate (PET), which consists of the monomers terephthalic acid and ethylene glycol. However, the invention also works very well with other widespread polyesters such as polypropylene terephthalate (PPT), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT) and the like, or also mixtures of these polyesters. It is important in each case that the alcoholic component, i.e. ethylene glycol, butanediol, propylenediol, trimethylene glycol, etc., is readily soluble in the treatment solution and is not co-precipitated when the terephthalic acid is precipitated.

If the filtering of the treatment solution in step d) includes at least one filtering through an adsorbing filter medium, in particular to remove dyes and metal ions from the treatment solution, it can be ensured that the precipitate of terephthalic acid obtained in step e) after precipitation from the treatment solution is of high purity. Otherwise, the metal ions or dyes have a high affinity for binding to the terephthalate molecules, which would contaminate the terephthalic acid precipitate during precipitation and would greatly impair the quality of the recovered starting material containing terephthalic acid. The filtering according to the invention using an adsorbing filter medium enables the main contaminants to be efficiently removed even before precipitation from the treatment solution, since these are preferentially bound to the particles of the adsorbing filter medium.

If the adsorbing filter medium also has activated charcoal and/or zeolite, the adsorbing and reductive properties of the activated charcoal allow impurities such as degradation products of dyes and textile auxiliaries to be adsorbed particularly reliably and in some cases selectively and removed from the treatment solution. This selectivity can be further increased by additional coating of the adsorbing filter medium.

[0016] Recycled cellulosic raw material in the context of this invention is generally understood as meaning recycled pulp, textile pulp, cotton pulp, rag pulp or the like or combinations thereof. This cellulose raw material can be particularly suitable as a starting material for the production of regenerated cellulose fibers such as lyocell, viscose, modal or cupro fibers. Alternatively, the recycled cellulosic raw material can be used as a starting material for the production of paper, paper-like materials or nonwovens from chemical pulp.

In general, it is mentioned that the mixed textile waste in the sense of the present invention can be a mixture containing any cellulosic fibers that form the cellulosic component of the mixed textile waste and any polyester fibers that form the polyester component. Suitable cellulosic fibers include, for example, natural cellulosic fibers such as cotton, flax, hemp, ramie, kapok, etc., or regenerated cellulosic fibers such as rayon, viscose, lyocell, cupro, or modal. The synthetic polymer component can, for example, comprise polyamide or polyester fibers or also other synthetic fibers which can be degraded by hydrolysis. The fibers specified above can vary in diameter and length and can be continuous fibers (filaments) or staple fibers or can also be in non-woven form. Such mixed textile waste has at least 1% by weight, preferably at least 2% by weight, particularly preferably at least 3% by weight, of the cellulose and polyester components.

Furthermore, a particularly economical and reliable recycling process can be provided if the mixed textile waste is pre- and/or post-consumer textile waste. Post-consumer textile waste refers to textiles that have already reached the end consumer and can therefore contain foreign substances, sometimes to a considerable extent, as a result of their use. Post-consumer textile waste may include one or more of the following items: worn-out garments such as shirts, jeans, skirts, dresses, suits, overalls, pants, underwear, sweaters, and the like; used home textiles such as bed linen, towels, curtains, cloths, tablecloths, seat covers, curtains, upholstery fabrics or the like; Non-woven articles such as towels, diapers, filters or the like. Pre-consumer textile waste refers to textile materials that have not yet reached the end user,but rather as waste in the course of production. This can be leftovers from cuttings or waste from the manufacture of clothing, home textiles, nonwovens, etc. or production waste from the manufacture of yarns, textiles or regenerated cellulose fibers.

[0019] The method can be further improved if the aqueous treatment medium contains at least one hydrolyzing agent. Furthermore, the amount of the at least one hydrolysis agent can be adjusted to the amount of the polyester component in the mixed textile waste, so that the polyester component is essentially completely depolymerized during the treatment in step b), i.e. the hydrolysis agent is added in at least such an amount that essentially all hydrolytically cleavable bonds in the polyester component are broken during the treatment in step b). The hydrolysis agent can accelerate the hydrolysis reaction during the cleavage of the hydrolytically cleavable bonds in the polyester component. The hydrolytically cleavable bonds in the polyester component are essentially the ester bonds formed between the monomers terephthalic acid and ethylene glycol. The amount of hydrolysis agent required in relation to the content of the polyester component in the mixed textile can be added to the treatment solution by appropriate dosing before and/or after the treatment in step b). The dosing can be done in particular in such a way that no excess hydrolysis agent remains in the treatment solution after the complete depolymerization of the polyester component

increased degradation of the cellulose component by the excess hydrolysis agent does not take place and thus an improvement in the quality of the cellulose raw material recovered in step c) can be achieved. However, metering can also be carried out in such a way that, after complete depolymerization of the polyester component, a specific amount of hydrolysis agent remains in the treatment solution, by which the chain length of the molecules in the cellulose component is broken down to a desired extent and the viscosity of the recovered cellulose raw material is thus adjusted can. A method with improved control over the behavior of the degradation reactions of the polyester component and the cellulose component can thus be provided.

When the aqueous treatment solution is an aqueous alkaline treatment solution, the controllability of the process can be further improved. The hydrolysis of the polyester component in the treatment solution can take place primarily as alkaline hydrolysis or saponification and can have a faster reaction rate than aqueous hydrolysis. If the hydrolysis agent is a base, a particularly simple and cost-effective process can also be created. The base can act as an effective accelerator in the alkaline hydrolysis reaction to cleave the ester bonds. During this alkaline hydrolysis reaction, the base is consumed in the reaction - for example through the formation of salts with the monomer components of the cleaved polyester component. The salt of terephthalic acid formed (disodium terephthalate) also advantageously has high solubility in the aqueous solution. Thus, after the synthetic polymer component has been completely degraded, only a slight excess of free base remains in the aqueous alkaline treatment solution, and the degradation of the cellulose component can be effectively reduced. Furthermore, by treating the cellulose component in the aqueous alkaline treatment solution, the dyes, foreign substances, impurities or textile auxiliaries (for example crosslinking agents) bound to the cellulose component can be removed. A purified, recycled cellulosic raw material of higher quality can thus be obtained.

When the base used as the hydrolyzing agent is sodium hydroxide (NaOH), which is widely used for the treatment of pulp and cellulose raw material, a reliable and cost-effective process can be provided. The total content of NaOH in the aqueous alkaline

Treatment medium can be in the range of 10 to 300 g, such as 20 to 250 g, per kg of mixed textile waste, depending on the proportion of the polyester component in the mixed textile waste.

If the treatment solution has a temperature of greater than 100° C., in particular greater than 110° C., during the treatment of the mixed textile waste in step b), a very reliable depolymerization of the polyester component into its monomer components can take place. If the treatment solution also has a temperature of less than 200° C., sufficiently mild process conditions can be ensured so that excessive degradation of the cellulose component is avoided that can become. In further configurations of the invention, the temperature can be in particular between 110° C. and 190° C., preferably between 120° C. and 180° C., particularly preferably between 125° C. and 175° C., more preferably between 130° C. and 170° C .

Furthermore, if the separation of the cellulose component in step c) involves at least sieving, squeezing or centrifuging the treatment solution, the recovered cellulose raw material can be obtained from the treatment solution in a technically simple manner. In this way, the essentially undegraded or essentially undissolved cellulose component can be easily separated from the treatment solution. Part of the cellulose component can be dissolved in the treatment solution as a result of the degradation processes described and thus remains—like the dissolved monomer constituents of the polyester component and foreign substances—in the treatment solution during the separation in step c).

The precipitation of the terephthalic acid in step e) can be facilitated if step e) comprises at least acidification of the treatment solution. Such acidification can in particular include adding an acid to the treatment solution, wherein the acid can be added, for example, until the terephthalic acid has completely precipitated out or alternatively until the pH falls below a certain value. Sulfuric acid (H2SO4), which is regularly used in cellulose pulping processes, can advantageously be used as the acid.

The reliability of the method can be further improved if the mixed textile waste is comminuted and/or isolated before the treatment in step b).

The shredding and/or separation of the mixed textile waste can be used to mechanically separate the cellulose particles from the polyester particles and thus enable the polyester component to be broken down (dissolved) more reliably in the aqueous treatment medium.

The reliability of the process can be further improved if non-fibrous solids are at least partially removed from the mixed textile waste prior to the treatment in step b). Non-fibrous solids may contain, for example, buttons, zippers, decorative elements, prints, labels and/or dirt or parts thereof.

The cellulose raw material recovered according to the method described above can also be suitable according to the invention for the production of regenerated cellulosic fibers, in particular by a viscose, modal, cupro or lyocell process.

Ways to carry out the invention

[0028] In the following, the invention is presented as an example using a first variant. Further design variants result from the modifications mentioned in the description, which can be combined with one another in any desired way.

According to a first embodiment variant, a mixed textile waste is provided in the inventive method for the recovery of raw materials from mixed textile waste in a first step, which has at least one cellulose component and at least one polyester component. Such mixed textile waste contains a mixture of any cellulose fibers that form the cellulose component and any polyester fibers that form the polyester component. In one embodiment variant, for example, the mixed textile waste contains a mixture of cotton and polyester fibers (in particular PET), which can be mixed in the mixed textile at the yarn level.

In a further step, the mixed textile waste is then treated in an aqueous treatment solution in order to depolymerize the polyester component and dissolve it in the treatment solution. In the first embodiment variant, the aqueous treatment solution is an aqueous alkaline treatment solution, in particular a diluted sodium hydroxide solution, which has NaOH as the hydrolysis agent. The treatment takes place at temperatures above 100.degree. C., or preferably at temperatures above 110.degree. During the depolymerization of the polyester component, the molecular weight and molecular chain length of the polyester molecules are purposefully reduced by hydrolysis that occurs in the presence of the aqueous treatment solution. In this way, the broken down molecules of the polyester component are continuously reduced in their molecular chain length and finally split into their monomeric starting materials terephthalic acid and the alcohol ethylene glycol (C2H6O2). The terephthalic acid thereby consumes two nations and forms a terephthalate salt, namely disodium terephthalate (CsH404Na2). As a result of the hydrolysis, the readily soluble disodium terephthalate and ethylene glycol are dissolved in the aqueous treatment solution. This subsequently enables a simple process-technical separation of the depolymerized polyester component from the cellulose component, whereby the cellulose raw material can be recovered from the mixed textile waste with high purity. Because of the generally mild process conditions, there is only a small, rather insignificant degradation of the cellulose polymers in the cellulose component, in particular so small that essentially no or only small amounts of glucose monomers are split off from the cellulose polymers. At the same time, however, the cellulose component can advantageously be partially broken down by the treatment solution and freed from impurities such as bound dyes or crosslinking agents, which in turn is beneficial to the quality or purity of the recovered cellulose raw material.

In a further embodiment of the process, the mixed textile waste contains other polyesters, such as PTT, PBT, etc., as the polyester component, as a result of which other alcohols are formed as monomeric starting materials during the depolymerization. The method described above can be used analogously.

In a further step, the cellulose component is then separated from the treatment solution and a cellulose raw material is recovered in the process. Since the depolymerized polyester component is dissolved in the aqueous treatment solution together with the dyes and foreign matter dissolved out of the cellulose component, the insoluble cellulose component can be separated from the liquid part, namely the treatment solution, are separated. A cleaned and processed cellulose component is thus obtained as a cellulose raw material. This cellulose raw material can subsequently be washed and/or dried in order to prepare it for further use. The aqueous alkaline treatment solution that remains as a liquid during the separation now still contains the depolymerized polyester components (disodium terephthalate and ethylene glycol) and any impurities from foreign substances.

The remaining treatment solution is then filtered in a next step in order to separate the undesired substances from the depolymerized polyester component. According to the invention, the treatment solution is filtered through an adsorbing filter medium. This filtration can take place in particular in the form of a fixed-bed filter, but it is also possible to disperse the filter medium in the treatment solution and then separate the filter medium loaded with the solids to be separated off again by means of a simple solid-liquid separation. In the first variant, the adsorbing filter medium contains activated carbon and/or zeolite. In further embodiment variants, however, the filter medium can also include other adsorbing filter media which are suitable for the adsorption of metal ions/dyes, etc. The activated charcoal enables a particularly reliable and even selective adsorption of dyes, metal ions or textile auxiliaries such as crosslinking agents, these substances being preferentially adsorbed due to the reductive effect of the activated charcoal. This selectivity can, for example, be further increased in a further embodiment by additional coating of the adsorbing filter medium, i.e. in particular the activated carbon or the zeolite, with suitable substances.

In a last step, the terephthalic acid is precipitated out of the treatment solution in order to recover a purified polyester raw material that can be used further. With the previous filtering, it can be ensured that no foreign substances are incorporated into the terephthalic acid precipitate during the precipitation step, which would ultimately lead to sometimes considerable impurities, so that the terephthalic acid for the subsequent application, e.g. for repolymerization, only with complex and cost-intensive Cleaning steps could be made accessible again. For precipitation, the treatment solution is mixed with a suitable acid, for example sulfuric acid, or acidified until the terephthalic acid separates from the treatment solution as a precipitate. Since the acid anions are neutralized with the Na+ cations of the disodium terephthalate, terephthalic acid is formed during acidification, which has a very low solubility and precipitates out of the solution immediately. After the terephthalic acid has completely precipitated, it is in turn separated from the liquid by simple solid-liquid separation using process steps known in principle, washed again if necessary and the terephthalic acid is finally obtained as the polyester starting material.

examples

Example 1: Post-consumer old textiles (mixture of cotton and polyester, 80 to 20% by weight) were treated with sodium hydroxide solution (15% by weight of NaOH, based on the mass of old textiles) in a liquorratio of 1:7 (mass old textile: lye). The temperature was 150°C, with a cooking time of 120 min. Due to the depolymerization of the polyester fibers taking place under these conditions, the disodium terephthalate formed and water-soluble under these conditions got into the boiling liquor and this was finally separated from the remaining solid (the cotton fibers) through a sieve.

The separated lye was stirred with an excess of activated carbon, whereby impurities such as metal ions and dyes or their degradation products were selectively adsorbed and thus removed from the lye. About 100 g of activated carbon were used on 2000 ml of lye, which was stirred at room temperature for 1 hour. The activated charcoal was then separated and sedimented by means of filtration and subsequent centrifugation, and the supernatant was suctioned off using a paper filter. The charcoal-free filtrate was then acidified to pH2 using sulfuric acid. As a result, the terephthalic acid precipitated out, which was then filtered off with suction using glass frits and dried in a drying cabinet.

[0037] As a result of the preceding activated carbon filtering, the terephthalic acid obtained was almost free of impurities, which is shown by way of example on the basis of the metal contents analyzed (see Table 1), and can therefore be reused without further complex purification steps.

The metal contents were determined as follows: About 20 g of the sample were incinerated, the ash was then melted with sodium tetraborate and the residue was dissolved with 1.6 M nitric acid. To determine the iron content photometrically, potassium thiocyanate was added to the sample and the red coloration of the iron thiocyanate was then measured using a calibration curve. To determine the silicon content photometrically, ammonium molybdate was added to the sample and the blue coloration of the silicon molybdate was then measured using a calibration curve. Phosphates were complexed by oxalic acid to mask them.

patent claims

1. A process for the recovery of raw materials from mixed textile waste, comprising the steps in the given order:

a) providing a mixed textile waste containing at least one cellulose component and at least one polyester component,

b) treating the mixed textile waste in an aqueous treatment solution in order to depolymerize the polyester component and dissolve it in the treatment solution,

c) separating the cellulose component from the treatment solution and recovering a cellulose raw material,

d) Filtering the treatment solution to remove foreign substances, especially dyes and

metal ions to remove from the treatment solution, and

e) precipitating terephthalic acid from the treatment solution, separating the precipitated terephthalic acid and recovering a polyester raw material containing terephthalic acid,

wherein the filtering of the treatment solution in step d) comprises at least one filtering through an adsorbing filter medium, characterized in that the aqueous treatment solution is an aqueous alkaline treatment solution, has a hydrolysis agent and, in particular, has a base, particularly preferably NaOH, as the hydrolysis agent.

2. The method according to claim 1, characterized in that the adsorbing filter medium has activated carbon and / or zeolite.

3. The method according to any one of claims 1 to 2, characterized in that the treatment solution has a temperature of greater than 100 °C, in particular greater than 110 °C, during the treatment of the mixed textile waste in step b).

4. The method according to any one of claims 1 to 3, characterized in that the separation of the cellulose component in step c) comprises at least one screening, squeezing or centrifuging.

5. The method according to any one of claims 1 to 4, characterized in that the precipitation of the terephthalic acid in step e) comprises at least one acidification of the treatment solution.

6. Use of the recovered by a method according to any one of claims 1 to 5 cellulose raw material for the production of regenerated cellulosic

Fibres, in particular after a viscose, modal, cupro or lyocell process.