Process for recovering chemicals in process for recycling hybrid textiles

Abstract

The invention relates to a process for recovering NaOH, polyester monomers, dyes and byproducts in an alkaline depolymerization liquid agent generated by a depolymerization reaction of polyester in a mixed textile. The process comprises: concentrating a liquor solution into a mixture comprising water, solid NaOH, dye and other liquid products; extracting ethylene glycol from the mixture; solid NaOH is dissolved; recovering the solid dye; and recovering terephthalic acid.

Description

Technical Field

[0001] The present invention relates to a process for recovering chemical substances (i.e., chemical products containing dyes obtained in the process of recycling mixed textiles), and more particularly to a process for recovering and separating NaOH, polyester monomers and dyes, which can be obtained in the process of recycling polyester blended fabrics by alkaline depolymerization of polyester. The process of the present invention is particularly applicable to those recycling processes for recovering and recycling cellulose staple fibers from fabrics containing polyester filaments or fibers and cellulose staple fibers (especially cotton staple fibers). The present invention also relates to a process for recovering vat dyes from textiles. Background Art

[0002] Due to the extensive use of petrochemical and natural resources, and due to the trend of increasing consumption of current clothing and its shortened lifespan, the textile industry has had a huge impact on the environment. Recycling waste textiles from fabrics, old clothing and the like has become an important issue in the fashion field. The cost of recycling waste textiles not only includes retrieving the waste textiles, but also includes defining appropriate methods for treating waste textiles that can be financially sustainable on a large scale. Polyester such as polyethylene terephthalate (PET) fibers and cotton are the most widely used man-made and natural fibers. Known methods for treating waste textiles include the step of removing polyester from waste textiles by depolymerization, and the step of recovering the depolymerization products for further processing, such as the step of obtaining reusable polyester again.

[0003] WO2022195433A1 describes a method for recycling poly-cotton waste textiles (i.e., textiles comprising a cotton component and a polyester component), wherein the textiles are subjected to a depolymerization reaction of the polyester component by alkaline hydrolysis, such as in a sodium hydroxide solution. The recovery of terephthalic acid is carried out through the steps of terephthalic acid precipitation, terephthalic acid separation, terephthalic acid washing, crystallization and terephthalic acid drying.

[0004] The patent application EP23156251, filed on February 13, 2023 in the name of the present applicant and incorporated herein by reference, discloses a process for recycling poly-cotton textiles, especially fabrics and clothing, which contain polyester filaments or fibers and cellulose staple fibers, especially cotton staple fibers.

[0005] The process of EP'251 includes a step of depolymerization of polyester using an alkaline depolymerization solution, which results in the degradation of polyester into monomers and forms a structure of cellulose fibers, which is substantially corresponding to the structure of the original poly-cotton fabric minus its polyester part. A step of bleaching the treated textiles with a bleaching solution after polyester depolymerization and a step of washing the treated textiles with a washing solution after bleaching the treated textiles are also provided.

[0006] In particular, the invention of EP’251 relates to a process for recycling waste mixed textiles comprising polyester and cellulose fibers (preferably cotton fibers), the process comprising the depolymerization of polyester in an alkaline aqueous solution, comprising the following steps: a) Providing a quantity of said textiles in a reaction chamber; b) Providing an amount of said alkaline depolymerization solution at a liquor ratio in the range of 1 / 2 to 1 / 20 based on the weight of the textiles to the weight of the solution; c) Circulating said amount of depolymerization solution through said textiles to depolymerize said polyester into corresponding monomers and removing said polyester monomers from said textiles; d) Removing said depolymerization solution from said reaction chamber; wherein the temperature of said depolymerization solution in step c) is in the range between 101 °C and 160 °C, preferably between 120 °C and 160 °C, more preferably between 130 °C and 140 °C. And wherein e) The textiles are all in a stationary state, and the solution is circulated through them to provide a treated textile substantially free of polyester material comprising cellulose staple fibers (preferably cotton staple fibers). The reaction proceeds for 100 minutes to 150 minutes, more preferably 120 minutes. The depolymerization solution is pumped through the textiles in the reactor, and the textiles remain in a stationary (i.e., stable) state.

[0007] In other words, in the process of EP’251, under reaction conditions that allow the ester bonds of the polyester to break into its monomers, terephthalic acid and ethylene glycol (EG) in the form of disodium salt (Na2TP), a depolymerization solution is added to the chamber to depolymerize the polyester fibers of the waste mixed textiles kept in a stationary state in the reaction chamber, resulting in a significant detachment or removal of dyes, especially indigo and other vat dyes, from the fabric, and greatly reducing the depolymerization of the cellulose staple fibers of the fabric.

[0008] The depolymerization solution or reaction liquor, as well as the bleaching solution and the washing solution, contain chemical substances such as NaOH, TPA, Na2TP, EG, dyes such as indigo dyes, reactive dyes, sulfur dyes, etc.

[0009] Said solutions (depolymerization solution, bleaching solution, washing solution) can be reused several times in the process, whereby the concentration of chemical substances (i.e., Na2TPA, EG, and dyes) increases after each cycle. The applicant has realized that an increase in the number of cycles has a positive effect on the processability of the solution for recovering the above chemical substances (including dyes).

[0010] In addition, the applicant has realized that if the chemical substance recovery process is carried out with the mentioned solutions (depolymerization solution, bleaching solution, washing solution) after multiple cycles, the efficiency of recovering chemical substances will increase due to the presence of more compounds to be processed in the solution. The efficiency can be in terms of reducing process costs, labor costs, and energy consumption.

[0011] Common problems in recycling PET fibers from polycotton textiles, especially clothing and fabrics, are the presence of further products, and especially a certain amount of dyes, as well as monomers TPA and EG, in the depolymerization reaction mixture.

[0012] Another problem is to recover NaOH from the reaction mixture or reaction liquid agent for reuse in further processes, especially in the same recovery cycle.

[0013] Therefore, the object of the present invention is to solve the above-mentioned disadvantages of the known process for recycling polyester-cotton textiles and to provide a method to improve the purity of polyester monomers recovered from the depolymerization solution and other solutions and mixtures produced by the known recycling depolymerization textile process.

[0014] Another object of the present invention is to recover NaOH, polyester monomers, and indigo or indigo-type dyes present in the depolymerization solution (as well as in the bleaching solution and in the washing solution) obtainable by the process of EP23156251. The recovery process can be carried out separately for different solutions or after the depolymerization solution, bleaching solution, and washing solution are collected in a single solution to be processed. Summary of the Invention

[0015] The above object is achieved by the process according to claim 1 of the present specification. Preferred embodiments are described in the dependent claims. According to claim 12, a further object of the present invention is a process for recovering vat dyes from textiles.

[0016] The starting material of the process of the present invention is the mixture produced in the process of depolymerizing the polyester part of textiles using a depolymerization solution containing NaOH. After the depolymerization process, monomer terephthalic acid (TPA) and monomer ethylene glycol (EG) are formed. In addition, the solution also contains dyes, especially vat dyes, namely indigo and indigo-like dyes or indigo-type dyes, which are present on the cotton or cellulose part of the textiles and have been removed from the textile surface and remain in the depolymerization solution. In some cases, other widely used polyesters may be present, such as poly(trimethylene terephthalate) (PTT), poly(propylene terephthalate) (PPT), poly(butylene terephthalate) (PBT), and the like, or mixtures of these polyesters; in such cases, the polyesters will be hydrolyzed by this process into the corresponding monomers, namely Na2TPA and butanediol, propanediol, trimethylene glycol.

[0017] The term "textiles" as used herein refers to fabrics, garments, yarns, and fibers. Fabrics can be woven fabrics, knitted fabrics, or non-woven fabrics. Garments include any article of clothing, such as T-shirts, trousers, jeans, jackets, shirts, sportswear, etc. An exemplary polyester-cotton yarn is a core-spun yarn having a polyester core and a cotton sheath containing cotton staple fibers. Blended non-woven textiles may contain non-woven polyester filaments on a cotton or cellulose substrate.

[0018] The term "cellulose fiber" as used herein defines cotton fibers, cotton derivative fibers, modified cotton fibers, and other fibers commonly used in yarns, such as linen fibers, fiber flax, jute fibers, hemp fibers, ramie fibers, kenaf fibers, sisal fibers, henequen fibers, and the like. Cotton and cellulose fibers are typically in the form of staple fibers in the yarn. Viscose and other regenerated cellulose-based fibers and filaments fall within the definition of cellulose fibers in this application. In both cases, the cotton fibers or cellulose fibers are recycled as-is (e.g., in the original form of staple fibers of the yarn), rather than being recycled as a pulp.

[0019] The term "depolymerization solution" or "depolymerization liquor" (DL) as used herein defines an aqueous mixture (or aqueous liquor) that contains NaOH to achieve a pH of about 13 (with an average NaOH concentration of about 3 wt%) and monomers produced by the alkaline depolymerization reaction of the polyester fibers of the waste textiles. The DL contains disodium terephthalate (Na2TPA) and ethylene glycol (EG). Since the waste textiles are derived from dyed fabrics or garments, the DL may also contain indigo and indigo-like dyes detached from the textiles (e.g., by mechanical action on the depolymerization solution on the textiles), and may also contain cellulose fibers and other reaction products. Other dyes that may be present in the DL are hydrolyzed reactive dyes, sulfur dyes, etc.

[0020] In one aspect, the present invention provides a method for recovering Na2TPA by selectively changing the alkaline pH of the depolymerization liquor to change the pH of the solution, thereby changing the physical state of Na2TPA between the salt dissolved in the aqueous solution and the solid salt. Liquid impurities are removed from the solid salt, and solid impurities are removed from Na2TPA in the form of salts dissolved in the aqueous solution.

[0021] In another aspect, the present invention relates to a process for recovering NaOH from the depolymerization liquor for further depolymerization processes of mixed textiles by precipitating Na2TPA in the form of a solid salt from an aqueous solution containing NaOH and Na2TPA (in dissolved state).

[0022] The process of the present invention comprises the following steps: providing an aqueous alkaline depolymerization agent having a normal pH of about 13; concentrating the agent into a sludge-like product (i.e., a muddy mixture with a solid content in the range of 40% to 80% by weight), which sludge-like product is a mixture comprising water, solid NaOH, and solid and liquid products of the depolymerization reaction (including dyes); extracting EG or other diols from the sludge-like mixture with an organic solvent; changing the pH of the undissolved solid phase remaining after extracting EG so that Na2TPA dissolves first and then TPA precipitates in the form of a sodium salt or in the acid form. Recovering especially vat dyes such as indigo and indigo-like from the undissolved solid phase. Alternatively, sulfur dyes can be recovered with the process of the present invention. Disperse dyes present in the depolymerization agent can generally be dissolved in the liquid organic phase.

[0023] According to one aspect of the present invention, the process of the present invention comprises the following steps: a) Evaporating part of the water from the depolymerization agent to provide a concentrated mixture containing the depolymerized reaction products; b) Extracting the mixture with an organic solvent to obtain a liquid phase containing EG, water, and NaOH and a solid phase containing NaOH, Na2TPA, water, and optionally dyes; c) Dissolving at least Na2TPA of the solid part in an alkaline solution having a pH in the range of 9.5 to 11.0, whereby the solution includes a solid component containing dyes; d) Separating the solid component containing dyes from the alkaline solution to obtain a purified alkaline solution and solid dyes; e) Precipitating TPA from the purified alkaline solution; f) Recovering EG and NaOH from the liquid phase.

[0024] According to one aspect, the aqueous depolymerization agent is concentrated under vacuum at a temperature below 100 °C to obtain a sludge-like solid, i.e., a concentrated mixture having a slurry consistency, until the solid content of the resulting concentrated mixture is in the range of 40% to 80% by weight, for example, about 50% to 65% by weight. Advantageously, the water evaporated in this step can be reused in the process, for example, after the step of extraction with an organic solvent, it is added to the sludge-like concentrated mixture in order to dissolve NaOH and Na2TPA in an alkaline solution in which the dyes are still present in the form of solid particles that can be removed from the solution.

[0025] In an embodiment, NaOH is added to the purified alkaline solution to precipitate Na2TPA; preferably, the NaOH is added to the solution as a concentrated solution up to 20 wt% to provide a NaOH solution suitable for the depolymerization process for mixed fabrics and textiles. The NaOH solution suitable for the process according to EP’251 is a 48 Baumè NaOH solution.

[0026] Thus, the advantage of the step of alkaline precipitation of Na2TPA is that after removing the disodium terephthalate (Na2TPA) from the alkaline solution in a manner known per se (e.g., by filtration or centrifugation), the remaining alkaline solution is suitable for recycling in a general depolymerization process.

[0027] According to another embodiment, HCl is added to the purified alkaline solution to precipitate TPA in the form of an acid; in this case, the resulting solution contains water and NaCl.

[0028] Advantageously, the organic solvent for extracting the glycol monomer (e.g., ethylene glycol) from the sludge-like solid obtained after evaporation of water is selected from: methanol, ethanol, isopropanol, ethyl acetate. In other words, the organic solvent used in this step is suitable for removing the ethylene glycol monomer, some water, and some NaOH dissolved in water from the previously obtained concentrated mixture.

[0029] According to an embodiment, the solvent in the organic phase containing the solvent, EG, water, and NaOH obtained above is evaporated to provide a liquid phase and NaOH. The advantage of the process of the present invention is that the NaOH can be recycled by use in a further depolymerization reaction of mixed textiles. Generally, the purity of the NaOH is 60 - 70%.

[0030] According to an embodiment, the liquid phase disclosed above is distilled to separate the solvent from the mixture of EG (or other glycol monomers) and water; advantageously, the solvent is reused in a further extraction according to step b). BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further aspects and advantages according to the present invention will be discussed in more detail with reference to the accompanying drawings, which are given by way of non-limiting example, wherein: Figure 1 is a flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0032] As in Figure 1As can be seen in the flowchart, the process for recovering NaOH and polyester monomers produced by the alkaline depolymerization reaction of polyester in mixed textiles includes the following steps: providing an aqueous alkaline depolymerization agent 1 containing polyester monomers, NaOH, and optionally dyes; evaporating water from the agent to obtain a sludge-like, muddy concentrated mixture 2, which includes water, solid NaOH, dyes, and solid and liquid products of the depolymerization reaction; extracting EG from the sludge-like mixture with an organic solvent; changing the pH of the residual solid phase after extracting EG so that TPA first dissolves and then precipitates as a sodium salt or in acid form.

[0033] Initially, the depolymerization agent 1 obtained from the alkaline depolymerization process of mixed textiles is provided; in addition to the cellulose and non-polyester fibers of the textiles, this agent also contains all the products and reagents used in this process. The agent 1 is heated under vacuum (step b), that is, at a temperature below 100 °C under reduced pressure conditions, preferably in the range of 50 °C to 95 °C, most preferably 75 °C to 85 °C. In the examples, typical pressure values are in the range of 100 mmHg to 700 mmHg, preferably 250 mmHg to 700 mmHg. Water is evaporated from the agent 1 until the agent becomes a concentrated sludge-like mixture with a solid content of about 50 wt% to 80 wt% and a slurry consistency. The evaporated water 0 is collected for further use in this process.

[0034] The concentrated mixture 2 is extracted with an organic solvent (step b) to obtain a liquid organic phase 3 and a solid phase 4. The liquid phase contains the organic solvent and the extracted ethylene glycol (EG), water, and NaOH; the solid phase 4 contains NaOH, Na2TPA, and vat dyes such as indigo and indigo dyes (if they are present in the textiles). The organic solvent is a polar solvent, preferably selected from methanol, ethanol, isopropyl alcohol, ethyl acetate, and mixtures thereof. The preferred solvent is isopropyl alcohol.

[0035] The extraction is preferably carried out at room temperature. After extraction, the solid part is preferably separated from the liquid phase by centrifugation (e.g., at 4500 - 5000 rpm) to provide an undissolved solid part 4 and a liquid organic phase part 3. In the examples, the undissolved solid part 4 is dried in an oven at, for example, 60 - 70 °C to remove any organic solvent that may be present.

[0036] Collect the liquid organic phase containing solvent, EG, water and NaOH, and evaporate the liquid organic phase under vacuum (preferably in the range of 250 mmHg to 700 mmHg) at a temperature of 50 °C to 80 °C, preferably 65 °C to 75 °C, to remove EG, solvent and water. The remaining solid includes NaOH 6 with a purity of at least 60% by weight, usually at least 70% by weight. By weight, the remaining part usually includes impurities such as polyester fragments or cellulose fragments that are not fully depolymerized. Thus, the obtained NaOH can be purified. The solid NaOH can be used without purification to increase the NaOH content in the initial depolymerization agent 1; in addition, as disclosed in the previous EP23156251, for example, the unpurified NaOH can also be used in the depolymerization reaction of mixed textiles. Any impurities from this step will not affect the depolymerization process.

[0037] Then, distill the liquid organic phase 5 containing solvent 7, EG and water 8 to separate the solvent 7 from EG and water; advantageously, the recovered solvent 7 is used in extraction step b), that is, it is used again to extract the sludge-like solid 2 obtained from step a) of this process. Preferably, distill the liquid phase 5 in the temperature range of 65 °C to 75 °C (preferably 82.5 °C) to obtain the solvent 7 and the EG / water mixture 8. Recover ethylene glycol from the mixture 8 in a manner known per se in the art (for example, separating EG 15 from water 14 by fractional distillation). Water 14 is advantageously reused in the process of the present invention.

[0038] After extraction, preferably treat the undissolved part (i.e., the mixture of Na2TPA, NaOH, and dye) with an aqueous alkaline solution having a pH low enough to dissolve NaOH and Na2TPA at room temperature; a suitable pH is in the range of 9.5 to 11.0, preferably about pH 10. In this case, insoluble vat dyes, especially indigo and indigo-like dyes, are separated and collected by filtration or centrifugation (step d). The separated dye 10 is washed with water several times and dried in an oven. The water used to wash the dye is collected and reused in the process.

[0039] Thus, the obtained vat dye has a purity of at least 95%. The purity of the dye is determined by spectroscopy (UV-Vis). The purified dye is suitable for being reduced to a soluble (e.g., leuco) form for use in the dyeing process.

[0040] In order to recover terephthalic acid TPA from the alkaline solution 11 containing the disodium salt of NaOH and TPA (Na2TPA), change the pH of the solution in step e. Two possible ways to recover TPA are provided.

[0041] In the first step (e2), after adding an acid such as HCl, acetic acid, H2SO4 until the pH reaches about 2, TPA precipitates in its acid form; for example, the precipitated TPA is separated by filtration or centrifugation and dried to obtain solid TPA 13'.

[0042] Alternatively, the process further includes step e1), in which NaOH is added to the purified alkaline solution 11 to precipitate Na2TPA. Advantageously, the Na2TPA precipitate is obtained by adding a concentrated NaOH solution with a NaOH concentration of up to 20 wt%.

[0043] Preferably, the solid Na2TPA 13 is separated from the alkaline solution 11 (e.g., by filtering or centrifuging it) and washed several times with water. The remaining alkaline solution 16 contains water and NaOH and can be used for the depolymerization reaction of mixed textiles.

[0044] The present invention will now be further disclosed with reference to the following examples, which are for illustrative and non-limiting purposes.

[0045] Example 1 2.5 L of a depolymerization solution with a pH of 13.29 and an initial NaOH content of 3.06 wt% (obtained by continuously recycling 25 times according to the depolymerization process of EP23156251) was subjected to vacuum evaporation at 90 °C. This process produced a slurry solid with a weight of 708 g and a solid content of 62%. A two-step extraction procedure using methanol and IPA was used to extract the desired components. The amount of solvent used was determined by the following calculation: Solvent volume (ml) = solid amount (g) * 2.5 After extraction, the liquid and solid phases were separated by centrifuging at about 5000 rpm for 15 minutes. The organic solvent collected was 94% of the initial solvent volume, while the dried solid accounted for 37% of the initial solid amount. Then the solvent was evaporated under vacuum at 70 °C to obtain 98 g (82% yield) of NaOH (65% purity). The organic solvent collected (with a collection yield of 95%) was distilled at 82.5 °C, which allowed the recovery of pure organic solvent for reuse in the extraction process. After distillation, the mixture of water and EG was further fractionally distilled to separate out 37.67 g of EG. The solid residue obtained after extraction was dissolved in water with a pH of 10, resulting in a precipitate, and 4 g of indigo dye was collected by centrifugation. The dye purity was determined by spectroscopy (UV-Vis). The pH of the dissolved portion was adjusted to pH 2 with HCl, resulting in a precipitate, and 100.87 g of TPA was collected by centrifugation.

[0046] Example 2

[0047] After 30 cycles of use in the process according to EP23156251, the depolymerization, bleaching, and washing solutions were collected and mixed. 2200 ml of the solution was taken from the mixture and concentrated into a slurry by evaporation under vacuum at 90 °C. After evaporation, 596 grams of a solid with a solids content of 50% was obtained. Then, the same procedure as described in Example 1 above was carried out. The amounts of TPA, EG, NaOH, and indigo recovered were 62.04 g of TPA, 22.7 g of EG, 58 g of NaOH (62% purity, 85% yield), and 2.4 g of indigo dye (in its solid, colored form, 96% purity). In summary, the present invention provides a process for recycling the liquid agent (i.e., the depolymerization solution) generated by the depolymerization of polyester filaments in a mixed fabric to separate and recover polyester monomers (TPA, Na2TPA, EG, and other diols), NaOH, and indigo or other reducing dyes.

[0048] The present invention also provides a process for recovering reducing dyes, especially indigo, from waste textiles. According to this embodiment, a textile, preferably a waste textile, is treated with the basic solution by flowing the basic solution through the textile, where the textile is kept in a stable state to remove the reducing dye from the textile, and the insoluble reducing dye is collected (i.e., separated) from the resulting solution.

[0049] Generally, the basic solution is pumped through a container containing the waste textile, and the basic solution is circulated through the textile several times. The basic solution suitable for the removal process of reducing dyes (preferably indigo and indigo dyes) is the basic solution disclosed above, especially the basic solution in paragraphs

[004] to

[006] . The pH of the suitable solution is between 10 and 14. The preferred concentration of NaOH in the solution is in the range of 33 g / L to 237 g / L of NaOH, preferably 36 g / L to 43 g / L of NaOH.

Claims

1. A process for recovering NaOH and dye polyester monomers generated by the alkaline depolymerization reaction of polyester in mixed textiles, comprising the following steps: Provide an aqueous alkaline depolymerization agent (1) containing polyester monomers, NaOH, and optionally dyes; concentrate the agent into a mixture (2) including water, solid NaOH, and solid and liquid products of the depolymerization reaction; extract EG from the mixture (2) using an organic solvent; change the pH of the solid phase (4) remaining after the EG extraction so that TPA first dissolves and then precipitates as a sodium salt or in acid form.

2. The process according to claim 1 comprises the following steps: a) Evaporate part of the water from the depolymerization agent (1) to provide the concentrated mixture (2) containing the depolymerized reaction products; b) Extract the mixture (2) with an organic solvent to obtain a liquid phase (3) containing EG, water, and NaOH, and a solid phase (4) containing NaOH, Na2TPA, and optionally dyes; c) Dissolve at least Na2TPA of the solid part (4) in an alkaline solution with a pH in the range of 9.5 to 11.0, whereby a solid component (10) containing dyes is present in the solution; d) Separate the solid component (10) containing dyes from the alkaline solution to provide a purified alkaline solution (11) and solid dyes; e) Precipitate TPA from the purified alkaline solution (11).

3. The process according to claim 2 further comprises step e1), wherein NaOH is added to the purified alkaline solution (11) to precipitate Na2TPA (12).

4. The process according to claim 2 further comprises step e2), wherein HCl is added to the purified alkaline solution (11) to precipitate TPA (13’).

5. The process according to claim 3, wherein the solid Na2TPA (13) is separated from the alkaline solution and the alkaline solution is used for the depolymerization reaction of mixed textiles.

6. The process according to any one of the preceding claims, wherein the organic solvent is selected from methanol, ethanol, isopropanol, ethyl acetate, and mixtures thereof.

7. The process according to any one of the preceding claims, wherein the organic phase (3) containing the solvent, EG, water, and NaOH is evaporated to provide a liquid phase (5) and NaOH (6), and wherein the NaOH is used for the depolymerization reaction of mixed textiles.

8. The process according to claim 7, wherein the liquid phase (5) is distilled to provide a solvent (7) and a mixture (8) of EG and water, and the solvent is reused in the extraction step b).

9. The process according to any one of the preceding claims, wherein the water evaporated from the depolymerization agent (1) is added to the solid part (4) to dissolve Na2TPA of the solid part (4).

10. The process according to any one of the preceding claims, wherein water is evaporated from the depolymerization agent (1) under vacuum at a temperature below 100 °C until the solid content of the resulting concentrated mixture (2) is in the range of 50 to 80 wt%.

11. The process according to any one of claims 2 to 10, wherein the dye is a vat dye, and the process further comprises the following steps: Reduce the dyes present in the solid component of step d) of claim 2 to a soluble form in a reaction solution and filter any residual solids from the solution to recover the dyes.

12. A process for recovering vat dyes, especially indigo, from textiles, comprising the following steps: Treat a textile with the alkaline solution by flowing the alkaline solution through the textile, the textile being maintained in a stable state, whereby the insoluble form of the vat dye is removed from the textile; And separate the insoluble vat dye from the resulting alkaline solution.

13. The recovery process of the vat dye according to claim 12, wherein the textile includes polyester filaments, and the process further includes the following steps: Depolymerize the polyester into the corresponding polyester monomers and separate the monomers from the insoluble dyes.

14. The process for recovering a vat dye according to claim 12 or 13, wherein the alkaline solution is pumped through a container containing the waste textile and the alkaline solution is circulated through the textile several times.

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