METHOD FOR THE RECOVERY OF STARTING MATERIALS FROM BLENDED TEXTILE WASTES

Abstract

What is shown is a method for the recovery of raw materials from blended textile wastes, which includes the following steps in the given order: a) providing blended textile waste that includes at least a cellulose component and at least a polyester component, b) treating the blended 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 in order to remove foreign substances, particularly dyes and metal ions, from the treatment solution, and e) precipitating terephthalic acid from the treatment solution, separating the precipitated terephthalic acid, and recovering a terephthalic-acid-including polyester raw material. In order to, within the scope of the mentioned method, enable the recovery of raw materials with an increased level of purity, it is proposed that filtering the treatment solution in step d) should at least comprise a filtration by an adsorbent filter medium.

Claims

1. A method for the recovery of raw materials from blended textile wastes, including the steps in the given order: providing blended textile waste containing at least a cellulose component and at least a polyester component, treating the blended textile waste in an aqueous treatment solution in order to depolymerize the polyester component and dissolve it in the treatment solution, separating the cellulose component from the treatment solution and recovering a cellulose raw material, filtering the treatment solution in order to remove foreign substances, particularly dyes and metal ions, from the treatment solution, and precipitating terephthalic acid from the treatment solution, separating the precipitated terephthalic acid, and recovering a terephthalic-acid-including polyester raw material, wherein filtering the treatment solution in step d) comprises at least a filtration by an adsorbent filter medium, characterized in that the aqueous treatment solution is an aqueous alkaline treatment solution, includes a hydrolyzing agent and particularly a base, more preferably NaOH, as the hydrolyzing agent.

2. The method as claimed in claim 1, characterized in that the adsorbent filter medium includes active carbon and/or zeolite.

3. The method as claimed in claim 1, wherein the treatment solution, during the treatment of the blended textile waste in step b), has a temperature greater than 100° C., particularly greater than 110° C.

4. The method as claimed in claim 1, wherein the separating of the cellulose component in step c) includes at least screening, pressing, or centrifuging.

5. The method as claimed in claim 1, wherein the precipitating of the terephthalic acid in step e) includes at least acidifying of the treatment solution.

6. A cellulose raw material recovered according to the method as claimed in claim 1 for the production of regenerated cellulosic fibers, optionally according to a viscose, modal, cupro, or lyocell process.

Description

MODES FOR CARRYING OUT THE INVENTION

[0028] In the following, the invention is exemplified based on a first embodiment variant. Further embodiment variants follow from the modifications mentioned in the description which can be combined with one another in any given way.

[0029] According to a first embodiment variant, the method according to the invention for the recovery of raw materials from blended textile wastes, in a first step, provides blended textile waste including at least a cellulose component and at least a polyester component. In this case, such blended textile waste contains a blend of any given cellulose fibers that form the cellulose component and any given polyester fibers that form the polyester component. For example, in one embodiment variant the blended textile waste contains a blend of cotton and polyester fibers (more specifically, PET), wherein these can be blended at the yarn level in the blended textile.

[0030] In a further step, the blended 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, particularly diluted soda lye, which includes NaOH as the hydrolyizing agent. The treatment takes place at temperatures greater than 100° C., and preferably at temperatures greater than 110° C. During the depolymerization of the polyester component, the molecular weight and the molecular chain length of the polyester molecules are deliberately reduced by hydrolysis which takes place in the presence of the aqueous treatment solution. In this way, the degraded molecules of the polyester component are gradually reduced in their molecular chain length and ultimately split into their monomeric starting materials, i.e., terephthalic acid and the alcohol ethylene glycol (C.sub.2H.sub.6O.sub.2). In this process, the terephthalic acid consumes two Na ions and forms a terephthalate salt, namely, disodium terephthalate (C.sub.8H.sub.4O.sub.4Na.sub.2). As a result of the hydrolysis, the readily soluble disodium terephthalate and ethylene glycol are present in the aqueous treatment solution in a dissolved form. Subsequently, this enables a process-technically simple separation of the depolymerized polyester component from the cellulose component, whereby the cellulose raw material can be recovered with a high level of purity from the blended textile waste. In fact, due to the generally mild process conditions, only a small, relatively insignificant degradation of the cellulose polymers in the cellulose component takes place, more specifically so small that substantially no or only minimal quantities of glucose monomers are separated from the cellulose polymers. At the same time, however, the cellulose component can advantageously be partially pulped by the treatment solution and be freed of impurities such as bonded dyes or cross-linking agents, which in turn benefits the quality and purity of the recovered cellulose raw material.

[0031] In another embodiment of the method, the blended textile waste contains other polyesters such as PTT, PBT, etc., as the polyester component, as a consequence whereof other alcohols are formed accordingly as monomeric starting materials in the depolymerization. In such cases, the above-described method can be applied analogously.

[0032] In a further step, the cellulose component is then separated from the treatment solution, and, in this process, a cellulose raw material is recovered. Since the depolymerized polyester component is present in a dissolved state in the aqueous treatment solution, together with the dyes and foreign substances dissolved out from the cellulose component, the insoluble cellulose component can be separated from the liquid portion, i.e., the treatment solution, by means of a simple solid/liquid separation such as screening, pressing, or centrifuging. This way, a purified and conditioned cellulose component is obtained as cellulose raw material. Subsequently, this cellulose raw material can still be washed and/or dried in order to condition it for further use. The aqueous alkaline treatment solution remaining behind as a liquid in the separation now still contains the depolymerized polyester components (disodium terephthalate and ethylene glycol) and possible contamination with foreign substances.

[0033] The treatment solution remaining behind is now filtered in a next step in order to separate the undesired substances from the depolymerized polyester component. In this process, the treatment solution is, according to the invention, filtered through an adsorbent filter medium. This filtration can, in particular, be implemented in the form of a fixed bed filter, but it is also possible to disperse the filter medium in the treatment solution and to then again separate the filter medium loaded with the solids to be separated by means of a simple solid/liquid separation. In the first embodiment variant, the adsorbent filter medium contains active carbon and/or zeolite. In further embodiment variants, however, the filter medium can also include other adsorbent filter media that are suited for the adsorption of metal ions/dyes, etc. In fact, the active carbon enables a particularly reliable and even selective adsorption of dyes, metal ions, or textile auxiliaries such as cross-linking agents, these substances being preferably adsorbed due to the reductive action of active carbon. This selectivity can, for example, be enhanced further in another embodiment variant by additionally coating the adsorbent filter medium, i.e., especially the active carbon and the zeolite, respectively, with suitable substances.

[0034] In a last step, the terephthalic acid is precipitated as a precipitate from the treatment solution in order to recover a reusable and purified polyester raw material. With the preceding filtration, it can be ensured that, during the precipitation step, no foreign substances are incorporated into the terephthalic acid precipitate, which would eventually lead to in part substantial contamination such that the terephthalic acid could only be made available again for subsequent usability, e.g., for repolymerization, through complex and cost-intensive purification steps. For the precipitation, a suitable acid, e.g., sulfuric acid, is added to the treatment solution, or the treatment solution is acidified with it, until the terephthalic acid separates from the treatment solution in the form of a precipitate. Since the acid anions neutralize with the Na cations of the disodium terephthalate, terephthalic acid is formed during the acidification, which exhibits very low solubility and precipitates immediately from the solution. Following the complete precipitation of the terephthalic acid, it is again separated from the liquid through a simple solid/liquid separation by means of commonly known procedural steps, rewashed if necessary, and the terephthalic acid is finally obtained as a polyester starting material.

EXAMPLES

[0035] Example 1: Post-consumer waste textiles (mixture of cotton and polyester, 80 to 20 wt %) were cooked with soda lye (15 wt % of NaOH, based on the mass of waste textiles) at a liquor ratio of 1:7 (mass of waste textiles:lye). The temperature was 150° C. for a cooking duration of 120 min. Because of the depolymerization of the polyester fibers which took place under these conditions, the disodium terephthalate formed and water-soluble under these conditions got into the cooking liquor which was eventually separated from the remaining solid material (the cotton fibers) by means of a screen.

[0036] The separated lye was agitated with an excess of active carbon, whereby impurities such as metal ions and dyes and/or their degradation products were adsorbed selectively and thus removed from the lye. Approx. 100 g of active carbon per 2000 ml of lye were used, which were stirred for 1 hour at room temperature. Then, the active carbon was separated and sedimented by means of filtration and subsequent centrifuging, and the supernatant was suctioned off by using a paper filter. Then, the active-carbon-free filtrate was acidified to pH 2 using sulfuric acid. This caused the terephthalic acid to precipitate as a precipitate which was subsequently suctioned off using glass frits and dried in the drying chamber.

[0037] As a result of the preceding active carbon filtration, the terephthalic acid obtained was nearly free of contamination, which is demonstrated, by way of example, based on the analyzed metal contents (see Table 1), and could therefore be reused without complex further purification steps.

[0038] The metal contents were determined as follows: Approx. 20 g of the sample were ashed, the ash was subsequently subjected to melting digestion with sodium tetraborate, and the residue was dissolved using 1.6 M nitric acid. For the photometric determination of the iron content, potassium thiocyanate was added to the sample, and then the red coloration of the iron thiocyanate was measured by means of a calibration curve. For the photometric determination of the silicon content, ammonium molybdate was added to the sample, and then the blue coloration of the silicon molybdate was measured by means of a calibration curve. Phosphates were complexed by oxalic acid in order to mask them.

[0039] Example 2 (comparison example): The method according to Example 1 was repeated, however, without the active carbon purification stage.

TABLE-US-00001 TABLE 1 Example Fe [mg/kg] Si [mg/kg] 1 9.8 215 2 58.4 1304