WO2025229155A1

WO2025229155A1 - Process to treat a cellulose-containing textile feedstock

Info

Publication number: WO2025229155A1
Application number: PCT/EP2025/062022
Authority: WO
Inventors: Adam Walker; Naomi LABROM; Alba RACERO EIZAGUIRRE; Jack MARRON; Emma RODGERS
Original assignee: Worn Again Technologies Ltd
Current assignee: Worn Again Technologies Ltd
Priority date: 2024-05-03
Filing date: 2025-05-01
Publication date: 2025-11-06
Anticipated expiration: 2026-11-03
Also published as: GB202406229D0; GB2641208A; GB202506694D0

Abstract

The present invention provides a process for the treatment of a cellulose-containing textile feedstock, comprising the step of: contacting the cellulose-containing feedstock with a mixture of an acid and an oxidising agent.

Description

PROCESS TO TREAT A CELLULOSE-CONTAINING TEXTILE FEEDSTOCK

TECHNICAL FIELD

The present invention concerns a process for the treatment of textiles, in particular end- of-life textiles, for example as part of a textile recycling process. The process may be a pre-treatment step which occurs prior to further processing of the textile.

BACKGROUND

The global demand for textiles continues to rise, due to not only the increase in global population, but also an increasing demand for fabrics to make apparel, with growing trends such as “fast fashion”, which refers to the mass production of low-cost apparel designed to have a limited lifespan.

Additionally, textile production is one of the world’s most polluting industries, accounting for approximately 1.2 billion tonnes of greenhouse gas emissions each year. Some predictions even anticipate that by 2050, the fashion industry will use up to 25% of the world’s carbon budget. As an example, according to the United States Environmental Protection Agency (EPA), the United States produces 25 billion pounds per year of textile waste. Of this waste, only 15% is currently reused, and of this reused waste, about 14% is downcycled (e.g., for use in mattresses, seat cushion stuffing, insulation, and the like), and about 1% is chemically recycled. The remaining 85% goes to landfill.

Currently, there are limited options available for effectively recycling textiles and therefore, a vast majority of textiles end up being discarded in landfill or incinerated, for example textile waste is estimated to occupy about 8% of total landfill mass. The clothing production system in regard to manufacturing, distribution, and usage operates in an almost entirely linear way, with over 68% of current fibres being extracted from nonrenewable resources. These non-renewable resources, such as fossil fuels, are used to make clothes which are used for a very short time. Efforts are being made to increase the recycling rate of textiles, for example through policies such as the EU Waste Directive which will impose an obligation for EU Member States to collect waste textiles separately by 2025. Textile recycling currently requires collection and transporting of post-consumer and postindustrial textiles to a specialized facility that can recycle these materials for re-use into new fibres and textiles. Collecting, sorting, and transporting post-consumer and postindustrial textiles to the appropriate centralized recycling facility introduces significant cost into the recycling process, both financial and environmental, reducing the incentive for businesses and consumers to recycle textiles and thus creating textile waste.

A key challenge in textile recycling is the presence of contaminating trace metals, other polymers, and reactive dyes.

Another challenge that limits effective textile recycling is the use of fibre blends; that is textiles which are formed from two or more types of fibres spun together. These can include blends of both synthetic and natural fibres, such as polyester and cotton. Polyester and cotton blends represent a large proportion of textiles on the market. Polyesters are used extensively in many garments and these articles are regularly replaced, creating waste that would ideally be recycled. Polyester fabrics often include additives which complicate the recycling process as these must be separated from the polyester. In particular, polyesters are often modified to include dyes that add colour to the fabrics.

The majority of cellulose contained in end-of-life textiles is present in the form of cotton. Cotton is composed primarily of high average molecular weight cellulose in the form of hollow core wound fibres. The solubility of cellulose decreases with increasing molecular weight as a result of the increased interactions between large cellulose chains compared to smaller ones. As a result, cotton-derived cellulose is typically of too high an average molecular weight to be soluble in a solvent mixture containing an ionic liquid or in the Viscose or Lyocell processes meaning a molecular weight reduction step is required prior to dissolution being possible. Cellulose molecular weight reduction techniques are well known in the art and include both acid- and base-catalysed hydrolysis, enzymolysis and various other methods.

Solvent-based processes, such as those utilising a solvent mixture containing an ionic liquid, or the Viscose or Lyocell processes rely on the solvent dissolving cellulose from textiles. The presence of low levels of residual metal salts and metal oxides present in the textiles as contaminants may cause decomposition of the solvent used in the process, for example NMMO in the Lyocell process is particularly susceptible to decomposition. In processes which involve successive extraction of a polyester e.g., PET, and cellulose from a mixed textile feedstock, the presence of low levels of residual metal salts and metal oxides can contribute to the decomposition of the PET, which can render the products of such processes unusable.

Dyes are commonly used in blended textiles and present an acute challenge in recycling processes. For PET-based textiles, where dyestuffs are simply mixed into the molten polymer in order to achieve a desired colour, the dyes can be subsequently leached out easily with a hot solvent. However, for cotton-based textiles, the dyestuffs used are reactive dyes, where the dyeing process involves the formation of a covalent chemical bond between the chromophore and the polymer backbone, which makes their removal far more challenging. Chemical techniques, such as bleaching, are often required but these processes are not desirable as they can leave organic debris still covalently bound to the cellulose, which has detrimental effects on the quality and subsequent dyeability of the product.

Whilst it is well known that textiles such as cotton may be downcycled into lower grade products, there remains a need for effective methods to enable textiles to be recycled as to provide a textile of substantially equivalent quality. Effective recycling of textiles would facilitate the regeneration of fibres from textile waste that could be used to meet future textile production demands and reduce overall textile wastage, thereby enabling a circular textile economy. Examples of current textile recycling processes provided in the art are given below:

EP3088505 describes a method of treating a textile in which a textile is contacted with an aqueous solution comprising a nuclease enzyme, preferably a deoxyribonuclease or ribonuclease enzyme and low levels of alkyl benzene sulphonate surfactant.

WO20 14045062 describes a process of extracting polymers, such as polyesters from textile articles, using a solvent system including an ionic liquid. WO2016012755 describes a process for extracting polyester from packaging containing one or more dyes, by contacting the packaging with two solvent systems, including an ionic liquid.

W02018150028 describes a method for recovering natural fibres and/or additional synthetic fibres from a polyester textile comprising polyester and natural fibres and/or additional synthetic fibres, wherein said method comprises the steps of providing said polyester textile soaked in a mixture comprising a solvent and a catalyst.

WO2018073177 describes a method for recycling textiles comprising cellulose with the following steps of: optionally disintegrating the textile, swelling the cellulose, under reducing conditions, wherein at least one reducing agent is present at least during a part of the swelling, and then performing at least one bleaching steps.

W02023030747 describes a method of recycling cellulose for use as a textile fibre feedstock, comprising: (i) providing a waste textile feedstock comprising greater than 50 wt% cellulose by weight of the waste textile feedstock; (ii) shredding the waste textile feedstock to provide a shredded waste textile feedstock comprising fibres which have a fibre length of less than 5 mm; (iii) mixing the shredded waste textile feedstock with an aqueous alkali solution having a pH of greater than 11 to produce a first mixture; (iv) filtering the first mixture to obtain an alkali treated shredded waste textile feedstock; (v) mixing the alkali treated shredded waste textile feedstock with an aqueous acid solution having a pH of less than 5 to produce a second mixture; and (vi) filtering the second mixture to obtain cellulose.

It is also known in the art to use oxidising agents, reducing agents and/or acids for various steps in the production of fibres (rather than in a textile recycling process).

EP1264846 describes a method of making a heat and light stable carboxylated cellulose fibre whose fibre strength and degree of polymerization is not significantly sacrificed. The method involves the use of a catalytic amount of a hindered cyclic oxammonium salt as a primary oxidant and a peracid and halide salt as a secondary oxidant in an aqueous environment. W003016614 describes a method of dyeing textile fibres using a vat acid dyeing method and, more particularly, to a vat acid dyeing method which utilizes additional reducing agent(s) to dye a variety of fibres to obtain deep shades and wash fastness.

W02013007358 describes the manufacture of a group of sulphur dyes in which are used, as raw materials, different types of natural “biomass”, and transforming them into soluble dyestuffs capable of dyeing textile fibres, particularly cellulose fibres and derivatives thereof.

However, there remains a need for suitable methods which enable the recycling of waste textiles into new textile products of equal quality, where such methods can be carried out in a sustainable way without excessive burden on the environment. The present invention was developed at least with the aim of addressing this problem, particularly in an improved process for pre-treating cellulose-containing textiles, in particular cottoncontaining textiles, for recycling processes, in which all three of the above noted challenges are addressed; the molecular weight of the cellulose is reduced, contaminants are removed, and dyes are removed.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a process for the treatment of a cellulose-containing textile feedstock, comprising the step of: contacting the cellulose-containing textile feedstock with a mixture of an acid and an oxidising agent.

The process according to the first aspect may constitute a step in a process for recycling a cellulose-containing textile feedstock.

Preferably, the acid is non-oxidisable i.e., the acid does not undergo a chemical reaction with oxygen, or only reacts with oxygen to a limited extent. This is preferred as it means the acid does not react with the oxidising agent.

The acid may comprise hydrochloric acid or hydrobromic acid. In preferred embodiments, the acid comprises hydrochloric acid. Hydrochloric acid is particularly advantageous as it is comparatively inexpensive, it is sufficiently strongly acidic to hydrolyse cellulose, it is non-oxidizing in its own right and it yields water-soluble salts with a wide variety of metals.

Particularly, hydrochloric acid is a preferred acid due to its ability to remove transition metals (which may be present as an inorganic contaminant) from the cellulose-containing textile feedstock as water-soluble salts. For example, oxides of barium may be removed from the textile feedstock by forming the water-soluble salt, barium chloride. Removing such transition metal contaminants from the textile feedstock is especially important where the textile feedstock also comprises polyester which is to be separated at a later stage in the process. The presence of transition metals can catalyse thermolysis of polyester causing significant degradation of the polyester and rendering it non-reusable.

The acid may comprise an aqueous acid solution.

The acid may comprise a dilute acid.

Preferably, the acid comprises aqueous hydrochloric acid. More preferably, the acid comprises dilute aqueous hydrochloric acid.

The oxidising agent may comprise potassium or sodium peroxymonosulfate. The oxidising agent may comprise a salt containing potassium peroxymonosulfate. Preferably, the oxidising agent comprises a triple salt having the chemical formula 2KHSO₅-KHSO4-K₂SO4, commonly referred to by the tradename Oxone™. Advantageously, potassium or sodium peroxymonosulfates do not interfere with the cellulose molecular weight reduction or negatively affect the metal extraction process.

Advantageously, dilute aqueous hydrochloric acid and Oxone™ are mild, easily obtainable and low-cost reagents, making the process more environmentally sustainable.

The inventors of the present invention have surprisingly found that treatment of a cellulose-containing textile feedstock with a mixture of an acid and an oxidising agent, particularly dilute aqueous hydrochloric acid and Oxone™, offers several key advantages. Firstly, the average molecular weight of the cellulose is reduced. Secondly, the amount of any inorganic contaminants present in the feedstock is significantly reduced or entirely removed. Thirdly, bonds between any reactive dye and cellulose present in the feedstock are cleaved to allow effective removal of the reactive dye.

The average molecular weight (M_w) of the cellulose in the textile feedstock may be reduced by at least about 1%, at least about 2%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55% or at least about 60% following treatment. For example, the M_w of the cellulose in the textile feedstock may be reduced by about 1% to about 90%, about 5% to about 80%, about 10% to about 70%, or about 20% to about 60% following treatment according to the present invention.

The extent of average molecular weight reduction is proportional to the residence time, temperature and HCI concentration. Advantageously, by controlling these variables, any desired % M_w reduction may be achieved.

The target value for the end molecular weight (M_w) post-treatment may depend on the intended final product; for example, if producing a pulp suitable for Lyocell production, an end point degree of polymerisation (DP_W) value in the range of 400-600 would be targeted. T o achieve this, and assuming that the acid concentration and temperature were constant, the residence time in the reactor may be controlled to achieve the desired end point from the starting M_w value. The M_w of the starting feedstock can range considerably depending on the origin, composition and history of the feedstock materials.

The degree of polymerisation (DP_W) of the cellulose in the textile feedstock may be reduced by at least about 1%, at least about 2%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55% or at least about 60% following treatment. For example, the DP_W of the cellulose in the textile feedstock may be reduced by about 1% to about 90%, from about 5% to about 80%, from about 10% to about 70%, or from about 20% to about 60% following treatment according to the present invention. The extent of degree of polymerisation reduction is proportional to the residence time, temperature and HCI concentration. Advantageously, by controlling these variables, any desired % DP_W reduction may be achieved. As with Mw, the target value for the end DP_W post-treatment may depend on the intended final product. The DP_W of the starting feedstock can range considerably depending on the origin, composition and history of the feedstock materials.

The inorganic contaminants may comprise metal salts and/or oxides. The metal may be a transition metal. For example, the inorganic contaminants may comprise salts and/or oxides of Ba, Ca, Cu, Fe, K, Mg, Na and/or Zn.

The amount of any particular inorganic contaminant or the amount of all inorganic contaminants present in the cellulose-containing textile feedstock may be reduced by at least about 50% w/w, at least about 55% w/w, at least about 60% w/w, at least about 65% w/w, at least about 70% w/w, at least about 75% w/w, at least about 80% w/w, at least about 85% w/w, at least about 90% w/w, at least about 95% w/w, at least about 98% w/w or at least about 99% w/w following treatment according to the present invention. For example, the amount of any particular inorganic contaminant or the amount of all inorganic contaminants present in the cellulose-containing textile feedstock may be reduced by about 50% w/w to about 100% w/w, or from about 60% w/w/ to about 100% w/w, or from about 70% w/w to about 100% w/w, or from about 80% w/w to about 100% w/w, or from about 90% w/w to about 100% w/w following treatment according to the present invention.

The amount of any particular inorganic contaminant or the amount of all inorganic contaminants present in the cellulose-containing textile feedstock following treatment according to the present invention may be less than about 500 ppm w/w, less than about 200 ppm w/w, less than about 150 ppm w/w, less than about 100 ppm w/w, less than about 50 ppm w/w, less than about 20 ppm w/w, less than about 10 ppm w/w or less than about 5 ppm w/w. For example, the amount of any particular inorganic contaminant or the amount of all inorganic contaminants present in the cellulose-containing textile feedstock following treatment according to the present invention may be from about 0 ppm w/w to about 200 ppm w/w, or from about 0 ppm w/w to about 100 ppm w/w, or from about 0 ppm w/w to about 50 ppm w/w. These values may particularly apply to inorganic contaminants comprising Ca, Mg and/or Na metals e.g., as salts and/or oxides.

It is particularly important to remove inorganic contaminants comprising the metals Ca, Mg and/or Na. The amount of inorganic contaminants comprising these metals varies between different textile feedstocks, for example as a result of the diverse nature of recycled feedstocks and as a result of inorganic contaminants being potentially introduced from a wide range of sources such as textile treatments, additives, hardwater, laundry detergents and deodorant products, amongst others.

Visual inspection of the cellulose-containing textile feedstock following treatment with the acid/oxidising agent mixture shows the effectiveness of reactive dye removal, for example, a deep blue-coloured textile may be white or off-white following treatment.

The combination of the acid and oxidising agent in the treatment step has been found to allow the three actions listed above to be carried out simultaneously in a single process step i.e., the reduction in cellulose average molecular weight, inorganic contaminant removal and cleavage of reactive dye bonds from the cellulose polymer, can all be achieved in a single process step under the same process conditions e.g., temperature and pressure, and in the same time period. This offers further economic, environmental and reduced complexity benefits. For example, the reduced footprint and capital requirements of a plant, the reduction in the number of chemical waste streams and more efficient material handling.

Conversely, the prior art teaches towards separate treatment steps to achieve the same results. Whilst it is known to use acid-catalysed hydrolysis to reduce the cellulose average molecular weight and that acids are capable of reacting with metal oxides and carbonates (both inorganic contaminants), the prior art focuses on techniques carried out at highly pH alkaline conditions for reactive dye removal. Inevitably, therefore, multiple separate treatment steps (acid and alkaline) were previously deemed necessary to achieve reduction in cellulose average molecular weight, inorganic contaminant removal and reactive dye removal. Without wishing to be bound by any such theory, the inventors of the present invention believe that the presence of the acid in the treatment step e.g., dilute aqueous hydrochloric acid, facilitates the reduction in cellulose average molecular weight whilst simultaneously removing inorganic contaminants from the feedstock. Dilute aqueous hydrochloric acid, in particular, has been found capable of reacting with poorly soluble metal oxides and carbonates (e.g., transition metal oxides and carbonates) to convert them into water- soluble chloride salts for easy removal from the feedstock.

It is believed that the presence of the oxidising agent in the treatment step e.g., Oxone™, facilitates the necessary cleavage of the covalent bonds attaching the reactive dye molecules to the cellulose polymer. This is preferable to certain bleaching processes which simply oxidize the chromophore itself, destroying its colour but leaving organic debris still covalently bound to the cellulose, which can affect the quality and subsequent dyeability of the product.

The selection of an oxidising agent comprising potassium or sodium peroxymonosulfate, more specifically Oxone™, has been found to be particularly beneficial as it is capable of cleaving the ether/ester covalent bonds that attach the reactive dye molecules to the cellulose polymer whilst also exhibiting a degree of selectivity against cleaving the 1,4- glycosidic (i.e., ether) bonds which hold the glucose monomers to each other. This is important as cleavage of the 1,4-glycosidic bonds would result in degradation of the polymer.

Thus, according to a second aspect of the present invention there is provided the use of a triple salt having the chemical formula 2KHSO5-KHSO4-K₂SO₄ (i.e., Oxone™) to remove a reactive dye from a cellulose-containing textile feedstock.

According to a third aspect of the present invention there is provided a process for the removal of a reactive dye from a cellulose-containing textile feedstock, comprising the step of: contacting the cellulose-containing textile feedstock with a triple salt having the chemical formula 2KHSO₅-KHSO4-K₂SO4 (i.e., Oxone™). According to a fourth aspect of the present invention there is provided the use of an acid and a triple salt having the chemical formula 2KHSO₅-KHSO4-K₂SO4 (i.e., Oxone™) to treat a cellulose-containing textile feedstock.

According to a fifth aspect of the present invention there is provided a cellulose-containing product obtainable or obtained from the process of the first aspect of the invention or the third aspect of the invention.

For the avoidance of doubt, all features relating to the first aspect of the present invention may apply, where appropriate, to any of the other aspects of the present invention and vice versa.

DETAILED DESCRIPTION

Textiles may denote textile raw materials, textile structures manufactured therefrom, and finished articles and products e.g., fabrics and clothing. Textile raw materials may in particular be natural fibres, such as cellulose, and/or chemical fibres, such as PET. In textile material, also non-textile raw materials may be additionally contained, which may be processed to line-shaped, planar, and spatial structures by different methods. Thus, from the raw materials, in particular line-shaped textile structures (for example yarns or twines), planar textile structures (for example tissue, meshes, fleece textiles and felts), and spatial textile structures (for example textile tubes, socks or textile semifinished products) may be manufactured.

The cellulose-containing textile feedstock may comprise any article which comprises cellulose, for example an article to be recycled, such as fabrics e.g., in the form of clothing.

In the process according to the invention, the textile feedstock comprises cellulose.

Cellulose is an organic compound which is a constituent of plant cell walls or can be manufactured synthetically. Cellulose is a polysaccharide (i.e., a multiple sugar). Cellulose is unbranched and typically comprises multiple hundred up to tens of thousands 0-D- glucose molecules (0-1,4-glycosidic linkage) and cellobiose-units, respectively. From cellulose molecules, cellulose fibres are built by plants in a controlled manner. By means of a technical process, cellulose molecules may be agglomerated under formation of regenerated fibres, for example as tearproof fibres.

The cellulose may be provided in the form of cotton, i.e., the cellulose-containing textile feedstock may comprise cotton. The majority of cellulose contained in end-of-life textiles is present as cotton, which is primarily composed of high average molecular weight cellulose in the form of hollow core wound fibres.

As outlined above, high average molecular weight cellulose e.g., in the form of cotton, is typically insoluble in known solvents for cellulose extraction/dissolution, such as ionic liquids or those used in the Viscose or Lyocell processes. However, it has surprisingly been found that the process of the present invention is capable of reducing the average molecular weight of the cellulose to a suitable level such that it can be further processed using known extraction/dissolution techniques.

The average molecular weight of the cellulose in the textile feedstock may be reduced by at least about 1%, at least about 2%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55% or at least about 60% following treatment. For example, the M_w of the cellulose in the textile feedstock may be reduced by about 1% to about 90%, about 5% to about 80%, about 10% to about 70%, or about 20% to about 60% following treatment according to the present invention.

The degree of polymerisation (DP_W) of the cellulose in the textile feedstock may be reduced by at least about 1%, at least about 2%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55% or at least about 60% following treatment. For example, the DP_W of the cellulose in the textile feedstock may be reduced by about 1% to about 90%, from about 5% to about 80%, from about 10% to about 70%, or from about 20% to about 60% following treatment according to the present invention.

Gel permeation chromatography (GPC) may be used to measure cellulose molecular weight (M_w). The GPC column provides values for molecular weight distribution (M_w). The degree of polymerisation (DP_W) and polydispersity index (PDI) may be extrapolated from the M_w measurement using an appropriate algorithm, for example:

Mw (Da)

DPw =

162 As an example, GPC analysis may be carried out using a PSS SECcurity² GPC system (Agilent™ 1260 Infinity II). The GPC system may have the following apparatus and parameter details:

The sample for GPC analysis may be prepared by the following method. Activating the sample with dimethylsulfoxide (DMSO), followed by solvent exchange with DMAc. Dissolving the sample in DMAc/LiCI (8.7 wt.%) at 35°C for 3 - 72 hours. Diluting the sample with DMAc to DMAc/LiCI (2.5 wt.%) and subsequently centrifuging at 4000 RPM for 10 minutes followed by filtering using a 0.45 pm syringe filter. The sample is then ready for analysis.

It will be appreciated, that sample preparation and GPC analysis can be carried out using any known method. The above description provides one example of how the GPC analysis can be carried out and is the method that was used in the specific examples.

The cellulose-containing textile feedstock may comprise one or more natural or synthetic polymers in addition to cellulose. For example, the cellulose-containing textile feedstock may comprise a polyolefin e.g., polypropylene, a polyester e.g., polyethylene terephthalate (PET) and/or a polyamide e.g., nylon.

Polyesters are frequently used in the textile industry and are often paired with cellulose- fibres to form blended textiles.

The polyester may comprise: polyglycolic acid (PGA), polylactic acid (PLA), polycaprolactone (PCL), polyethylene adipate (PEA), polyhydroxyalkanoate (PHA), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN) and/or combinations of two or more thereof.

In certain embodiments, the polyester comprises polyethylene terephthalate (PET).

The cellulose-containing textile feedstock may comprise one or more contaminants.

The contaminants may comprise inorganic contaminants. The inorganic contaminants may comprise metal salts and/or oxides. The metal may be a transition metal. For example, the inorganic contaminants may comprise salts and/or oxides of Ba, Ca, Cu, Fe, K, Mg, Na and/or Zn.

The sources of these contaminants may be varied and include manufacturing ingredients, environmental contamination e.g., from domestic water, and in-use contamination e.g., antiperspirant residues or laundry detergents. Levels of contaminants in the feedstock may vary widely depending on the composition and origin of the feedstock. Additionally, in a blended textile, certain contaminants, for example Ca, tend to be more associated with the cellulose-containing fraction of the feedstock e.g., cotton.

As a specific example, it has been found that cellulose-containing textile feedstocks often comprise Ca contamination in the form of CaCO₃, likely caused from hard water residues, and Ca₃(PO₄)2, likely from detergent residues. The total Ca content of the cellulose- containing feedstock (prior to treatment) may be relatively high, for example in excess of 2500 ppm.

Where the cellulose-containing textile feedstock is a blended textile also comprising a polyester such as PET, this level of inorganic contaminant becomes particularly problematic as has been found to cause significant degradation of PET in any subsequent PET high-temperature extraction step.

One advantage of the process of the present invention is that the amount of inorganic contaminants present in the cellulose-containing textile feedstock is reduced.

Following treatment according to the present invention, the amount of any particular inorganic contaminant or the amount of all inorganic contaminants present in the cellulose-containing textile feedstock may be reduced by at least about 70% w/w, at least about 75% w/w, at least about 80% w/w, at least about 85% w/w, at least about 90% w/w, at least about 95% w/w, at least about 98% w/w or at least about 99% w/w. For example, the amount of any particular inorganic contaminant or the amount of all inorganic contaminants present in the cellulose-containing textile feedstock may be reduced by about 50% w/w to about 100% w/w, or from about 60% w/w/ to about 100% w/w, or from about 70% w/w to about 100% w/w, or from about 80% w/w to about 100% w/w, or from about 90% w/w to about 100% w/w following treatment according to the present invention.

At these levels, the inorganic contaminants do not significantly degrade any other polymers present in the feedstock e.g., PET, in any subsequent high-temperature extraction process.

The amount of inorganic contaminants present in the cellulose-containing textile feedstock may be determined using inductively coupled plasma - optical emission spectroscopy (ICP-OES) techniques.

The cellulose-containing textile feedstock may comprise other impurities, for example other polymers, dirt, dye stuffs and/or water. These may be removed from the feedstock using techniques known in the art, for example, dye stuffs in PET or other synthetic polymers (where present) can be leached out using hot solvent.

Cellulosic fibres are primarily dyed using reactive dyes, which contain a chromophore that is covalently bonded to the fibres during the dying process. More specifically, reactive dyes typically contain a chromophore having appended functional groups which are capable of forming covalent bonds with nucleophilic oxygen sites in, or on, cellulose. Thus, the cellulose-containing textile feedstock may comprise one or more reactive dyes. The reactive dye may be selected from triazines, for example mono-chloro triazine reactive dyes such as ITOFIX CT (supplied by MagnaColours™); vinylsulfones, for example vinyl sulphone reactive dyes such as ITOFIX VS and ITOFIX VSRR (supplied by MagnaColours™); and bi-functional reactive dyes such as ITOFIX VM (supplied by MagnaColours™). Although specific examples have been provided, it will be appreciated that the type of reactive dye is not limited and may be any known reactive dye.

When it is desirable to produce a non-coloured cellulose pulp in a textile recycling process, the reactive dyes must be removed from the cellulose-containing textile feedstock. It has been found that simply washing the feedstock is not sufficient to cleave the covalent bonds between the reactive dye and the cellulose. Bleaching is also not optimal in this regard as rather than decoupling the chromophore from the cellulose, the chromophore may be simply oxidised to remove the colour but leave organic debris covalently bound to the cellulose. However, as outlined above, it has surprisingly been found that the process of the invention cleaves the covalent bonds between the reactive dyes and the cellulose to allow effective removal of the dye.

The process according to the first aspect of the invention involves the step of contacting the cellulose-containing feedstock with a mixture of an acid and an oxidising agent.

Preferably, the acid is non-oxidisable.

The acid may comprise hydrochloric acid or hydrobromic acid.

Hydrochloric acid is a particularly preferred acid.

The acid may comprise an aqueous acid solution.

The acid may comprise a dilute acid.

Preferably, the acid comprises aqueous hydrochloric acid. More preferably, the acid comprises dilute aqueous hydrochloric acid. The dilute aqueous hydrochloric acid may comprise less than about 40% hydrochloric acid, less than about 35% hydrochloric acid, less than about 30% hydrochloric acid, less than about 25% hydrochloric acid, less than about 20% hydrochloric acid, less than about 15% hydrochloric acid or less than about 10% hydrochloric acid by volume of the solution.

The oxidising agent may comprise potassium or sodium peroxymonosulfate. The oxidising agent may comprise a salt containing potassium peroxymonosulfate. Preferably, the oxidising agent comprises a triple salt having the chemical formula 2KHSO₅-KHSO4-K₂SO4, commonly referred to by the tradename Oxone™.

Oxone™ is regarded as non-toxic with an acute oral toxicity LD₅o of 2000 mgkg ¹ in rats compared to comparable oxidation agents such as TEMPO (2,2,6,6-tetramethylpiperidine- 1-oxyl) which has a toxicity of 1050 mgkg ¹. Furthermore, Oxone™ is readily soluble in water, widely commercially available, inexpensive and has a good bench-stability profile.

Surprisingly, the inventors of the present invention have found that Oxone™ is capable of the effective removal of reactive dyes from cellulose-containing textile feedstocks under acidic conditions, for example with dilute aqueous hydrochloric acid. This combination of reagents has also been found capable of the controlled hydrolysis of cellulose at a rate only slightly greater than dilute aqueous hydrochloric acid alone. Importantly, the presence of Oxone™ does not inhibit the removal inorganic contaminants from the feedstock.

Preferably, the oxidising agent is dissolved in the acid to form the mixture.

The oxidising agent may be present in an amount of from about 0.01% to about 10%, or from about 0.1% to about 5%, or from about 0.5% to about 2% by weight of the acid.

Preferably, the liquid to solid ratio of the acid/oxidising agent mixture (liquid) to the cellulose-containing textile feedstock (solid) in the treatment step is from about 5:1 to about 100:1, or from about 10:1 to about 80:1, or from about 20:1 to about 50:1. For example, the liquid to solid ratio may be about 25:1.

The treatment step may be carried out at an elevated temperature. The temperature may be at least about 50°C, at least about 60°C, at least about 70°C, or at least about 80°C. The temperature (at atmospheric pressure) may be in the range of from about 25°C to about 95°C. For example, the temperature (at atmospheric pressure) may be in the range of from about 30°C to about 90°C, from about 40°C to about 90°C, from about 50°C to about 90°C, or from about 50°C to about 85°C.

It may be possible to use higher temperatures where a higher pressure is used. For example, the temperature may be up to about 150°C, up to about 140°C, up to about 130°C, up to about 120°C, up to about 110°C, or up to about 100°C.

The cellulose-containing textile feedstock may be held at the elevated treatment temperature for a prolonged period of time. For example, the treatment time may be at least about 30 seconds, at least about 1 minute, at least about 5 minutes, at least about 10 minutes, at least about 20 minutes, at least about 30 minutes, at least about 40 minutes, at least about 50 minutes, or at least about 60 minutes.

The treatment time may be from about 30 seconds to about 120 minutes, or from about 10 minutes to about 60 minutes, or from about 15 minutes to about 40 minutes. However, it should be noted that the treatment time will be dependent on the amount and type of feedstock used and the amount and type of contaminant and/or reactive dye present in the feedstock. It will be appreciated that the treatment time can be varied to ensure effective removal of contaminant and/or reactive dye, for example by visual inspection.

Preferably, the mixture of cellulose-containing textile feedstock, acid and oxidising agent is agitated during the treatment step, for example by stirring.

Prior to contacting the cellulose-containing textile feedstock with the mixture of acid and oxidising agent, the feedstock may be comminuted, for example by mechanically shredding, grinding, grating or milling the feedstock.

Following the treatment step, the cellulose-containing textile feedstock may be referred to as an acid-treated cellulose-containing textile feedstock. Any excess acid/oxidising agent mixture may be removed from the acid-treated cellulose- containing textile feedstock. For example, the excess acid/oxidising agent mixture may be removed by vacuum filtration or using a separator.

The acid-treated cellulose-containing textile feedstock may be subjected to a neutralisation step.

The neutralisation step may comprise contacting the acid-treated cellulose-containing textile feedstock with an alkaline solution. The alkaline solution may be an aqueous alkaline solution. The alkaline solution may comprise sodium hydroxide and/or potassium hydroxide.

The neutralisation step may additionally comprise contacting the acid-treated cellulose- containing textile feedstock with a reducing agent. The reducing agent may comprise ascorbic acid and/or sodium thiosulfate.

Contacting the feedstock with alkaline solution and reducing agent may occur simultaneously i.e., in a single process step, or may occur successively.

The neutralisation step may be carried out under agitation, for example stirring.

The neutralisation step may be carried out at ambient conditions i.e., ambient temperature and pressure. The alkaline solution may be at ambient temperature i.e., unheated.

Following the neutralisation step, the alkaline solution may be removed from the neutralised cellulose-containing textile feedstock. For example, the alkaline solution may be removed by vacuum filtration or using a separator.

The neutralised cellulose-containing textile feedstock may be washed with water in one or more wash steps. Preferably, the neutralised cellulose-containing textile feedstock is washed with water until the pH is neutral. The water may be clean water and/or may be water recovered from other upstream or downstream process steps (where the treatment step of the invention is part of a larger textile recycling process). The process of the present invention may form a “pre-treatment” step as part of a larger textile recycling process. The cellulose-containing textile feedstock following pretreatment may be referred to as the “pre-treated cellulose-containing textile feedstock”.

The pre-treated cellulose-containing textile feedstock may be suitable for further processing and/or recycling. The pre-treated cellulose-containing textile feedstock may be used as the feedstock for any known cellulose separation processes or textile recycling processes, for example as described in WO2020221932 (in the name of the Applicant), the contents of which are incorporated herein by reference.

WO2020221932 describes a process for separating polyester and cellulose from a textile feedstock, comprising the steps of: i. dissolving and extracting polyester; and ii. separating cellulose using an ionic liquid.

Thus, according to a further aspect of the present invention, there is provided a process for separating polyester and cellulose from a textile feedstock, comprising the steps of: i. contacting the textile feedstock with a mixture of an acid and an oxidising agent to form an acid-treated textile feedstock; ii. optionally neutralising the acid-treated feedstock with an alkaline solution to form a neutralised textile feedstock; iii. optionally washing the neutralised textile feedstock with water; iv. dissolving and extracting polyester from the textile feedstock; and v. separating cellulose from the textile feedstock using an ionic liquid.

Further processes for dissolving and extracting polyester from a feedstock are described in W02014045062 and WO2016012755 (in the name of the Applicant), the contents of which are incorporated herein by reference. The pre-treated cellulose-containing textile feedstock may be used as the feedstock in such processes where it also comprises polyester, such as PET. Downstream recycling processes may be mixed-input, dual-output, solvent-based operations that successively extract polyester e.g., polyethylene terephthalate) (PET), and cellulose from end-of-life textiles. The PET extraction may take place prior to the cellulose extraction, meaning that the cellulose would be present in the process whilst the PET is extracted. PET extraction requires the use of solvent at high temperature (>200°C). During development of downstream processes for treating the textile feedstock, it was unexpectedly found that low levels of certain residual metal salts and metal oxides present in the textile feedstock as contamination, when exposed to high temperature, had the undesirable effect of rapidly decomposing the PET, to an extent that it was rendered unusable. However, it was surprisingly found that the pre-treatment process of the present invention was effective at reducing the inorganic contaminants in the cellulose- containing textile feedstock to a level below that at which PET degradation became significant. Thus, the pre-treated cellulose-containing textile feedstock can advantageously be used in such downstream recycling processes.

The pre-treated cellulose-containing textile feedstock may also be suitable for other known cellulose processing methods. For example, in downstream processes where cellulosic fibres are generated through the Viscose process, in which carbon disulfide is used to form cellulose xanthate, which is soluble in aqueous sodium hydroxide. A further example is in a downstream process where cellulosic fibres are generated through the Lyocell process, in which N-methylmorpholine N-oxide (NMMO) is used to directly dissolve up to 14 wt.% of cellulose. In this process, stabilising additives have to be used to prevent side reactions.

The invention will now be more particularly described with reference to the following, nonlimiting figures and examples, in which;

Figure 1 is a simplified process flow diagram, illustrating the process of textile treatment to generate a neutralised textile feedstock for further processing.

Figure 2 shows the results of the treatment process on reactive dye removal from cotton samples. Figure 3 shows the results of the treatment process on reactive dye removal from cotton samples compared to L*A*B* colour charts.

Figure 4 shows the progression of reactive dye removal over time.

In Figure 1 there is shown a process flow diagram which illustrates the process according to one embodiment of the present invention. Raw cellulose-containing textile feedstock (1), which is preferably end-of-life textiles e.g., clothing, is provided to a shredder (101), in which it is shredded into smaller pieces (2). Shredded textile (2) is provided to a screw reactor (102), where the shredded textile is mixed with aqueous filtrate (3), which is recovered from downstream mixing reactor (104). The process of mixing the shredded textile (2) and the aqueous filtrate (3) generates a textile stream (4) and off-gas (5).

The textile stream (4) is passed to a separator (103), which comes in the form of a screw press. In the separator (103), acid-treated textile pulp in suspension (6) is separated from the untreated textile (7), and off-gas (5). The untreated textile (7) flows to a mixing reactor (104) in which the textile is mixed with recovered water (8), acid (9) e.g., dilute hydrochloric acid, and oxidising agent (10) e.g., Oxone™. Liquid condensate (11), obtained from a catalytic reactor, is also added to the mixing reactor (104). The textile mixture mixed with aqueous filtrate (3) is returned to the screw reactor (102), subsequently passing into the separator (103). The acid-treated textile pulp (6) is separated and transferred to a further mixing reactor (105).

The acid-treated textile pulp (6) is treated with an aqueous alkaline solution (12) e.g., aqueous NaOH, in mixing reactor (105). The aqueous alkaline solution (12) is provided from a mixing chamber (106), in which recovered water (8) is combined with concentrated alkaline solution (13) to generate the aqueous alkaline solution. The alkaline-washed textile (14) is mixed with a reducing agent (15), such as sodium thiosulphate, to provide a neutralised textile solution (16).

Off-gas (5) is vented from the separators and reactors (102, 103, 104 and 105) and is transferred to a selective catalytic reactor (108), in which toxic gases such as NO_X are converted, in the presence of recovered water (8), to less toxic gases, which are vented (17). The liquid condensate (11) is removed from the reactor (108) and is passed back to mixing reactor (104).

The neutralised textile solution (16) is passed to a separator (107), in which the neutralised textile pulp (18) is separated from the reagent solution (19). The reagent solution (19) is passed to a further treatment reactor (109), prior to passing to a wastewater treatment facility (20). The neutralised textile pulp (18) is passed to a mixing reactor (110), in which it is first washed with a recycled filtrate solution (21), obtained from downstream in the process. The rough-washed textile solution (22) is passed to a separator (111) in which the rough-washed textile pulp (23) is separated from the filtrate solution (24).

The filtrate solution (24) is transferred to dilution chamber (112) in which it is mixed with clean water (26). The diluted stream (27) is subsequently separated into the recovered water stream (8), which is used in earlier stages of the process, with the rest of the stream passing to a wastewater treatment facility (20).

The rough-washed textile pulp (23) is passed to a further washing chamber (113), in which the pulp is washed with clean water (26), to produce a clean textile solution (25), which is transferred to a separator (114). In the separator, the solution (25) is separated to provide a filtrate (21), which is transferred to mixing reactor (110) for the first washing step, and a clean textile pulp (28) for further processing and separation steps, such as those described in WO2020221932.

EXAMPLES

EXAMPLE 1

51 different textile samples composed of 100% cotton and dyed with a specific reactive dye were collated. The samples were split up into six different batches each containing a different reactive dye type as shown in Table 1.

TABLE 1

An approximately 1 cm wide strip was cut from each sample swatch, and the strip was subsequently cut into roughly 1 cm x 1 cm squares. All strips from each batch group were mixed and each batch was weighed and photographed.

The acid treatment was carried out at a 25:1 liquid:solid ratio (as shown in Table 1). The appropriate volume of 0.137M HCI was heated to 85°C in a beaker with stirring. Once the HCI had come to temperature, Oxone™ was added at a concentration of 0.92 wt.%. After the Oxone™ had fully dissolved, the textile batch was added and mixed for 15 minutes. Excess HCI was then removed from the textile by vacuum filtration. The dried textile was added to a beaker containing 0.1M NaOH at ambient temperature. The beaker was vigorously stirred, and then all NaOH was removed from the textile by vacuum filtration. The textile was washed with deionised H₂O until the pH had returned to neutral. Washed textiles were laid out on foil to dry overnight before photographs were again taken.

Figure 2 shows the before and after photographs for each batch. Analysis of the before and after photographs shows that the samples were all initially bright or dark in colour, with various colours within each batch. Good removal of the reactive dye was observed across all batches after the treatment process, with samples being returned to an off-white colour.

Figure 3 shows the results of the treatment process on reactive dye removal from cotton samples compared to L*A*B* colour charts. L*A*B* colour space, as defined by the International Commission on Illumination (CIE) in 1976, is comprised of three axes; L represents darkness to lightness, with values ranging from 0 to 100; a represents greenness to redness with values of -128 to +127; and b represents blueness to yellowness also with values from -128 to +127.

Analysis of the photographs shows that for each batch, the closest colour match is found in the two highest lightness rows, L80 and L90, on the colour chart. This shows that the process of the invention is effective at removing the reactive dyes tested from the cotton samples.

A second experiment was carried out with black swatches from the ‘Deep Shades’ batch. The swatches were subjected to the same treatment process as detailed above, except the overall time of the acid treatment was increased to 60 minutes. Swatches were removed at timed intervals between 30 seconds and the full 60 minutes.

Figure 4 shows the progression of reactive dye removal over time in the second experiment.

The results show that reactive dye removal increases for the first 30 to 40 minutes, with the majority of the visible dye removal happening in the first 30 seconds.

EXAMPLE 2

Samples of 100% cotton were subjected to the same treatment process as detailed above in Example 1 except that the concentration of hydrochloric acid was varied. The samples were mixed for either 15 minutes at 80°C or 60 minutes at 80°C. The cotton samples had a starting Mw of 312813 Da and a DPw of 1454. The change in cellulose molecular weight (Mw) and degree of polymerisation (DPw) was determined using gel permeation chromatography (GPC) which involved the cotton sample being dissolved in a DMAc/lithium chloride mobile phase and then eluted onto a GPC column, which provides values for the sample molecular weight distribution and polydispersity index (PDI). The degree of polymerisation values were extrapolated from the M_w measurement using an algorithm. The results are shown in Table 2.

TABLE 2

Table 2 shows that the process of the present invention causes a reduction in the cellulose molecular weight (M_w) and degree of polymerisation (DP_W), even when short treatment times of 15 minutes are used. As the concentration of the acid is increased, the reduction in M_wand DP_W values also increases. Similarly, longer treatment times result in a significant reduction in the M_w and DP_W values of the sample.

EXAMPLE 3

A third experiment was carried out with black and blue swatches from the ‘Deep Shades’ batch. The swatches were subjected to the same treatment process as detailed above in Example 1, except the overall time of the acid treatment was increased to 60 minutes. Swatches were removed at timed intervals between 30 seconds and the full 60 minutes.

L*A*B* values in the tables below are an average of five measurements taken using a ColorMeter Max. Figure 5 shows the progression of reactive dye removal over time for the black 100% cotton swatch, with both white (Figure 5A) and black (Figure 5B) backgrounds for contrast The L*A*B* values are provided in Table 3.

TABLE 3

Figure 6 shows the progression of reactive dye removal over time for the blue 100% cotton swatch, with both white (Figure 6A) and black (Figure 6B) backgrounds for contrast. The L*A*B* values are provided in Table 4.

TABLE 4

EXAMPLE 4

The amount of inorganic contaminants present in mixed PET/cellulose textile samples before and after treatment according to the present invention was investigated. The samples were subjected to the same treatment process as detailed above in Example 1. The amount of certain transition metal contaminants (Ca, Mg and Zn) was determined before and after treatment using ICP-OES analysis. Examples are shown in Table 5 (all values are ppm w/w).

TABLE 5

The data in Table 5 shows that the amount of different metal inorganic contaminants following treatment of the samples according to the present invention, is significantly reduced.

Claims

1. A process for the treatment of a cellulose-containing textile feedstock, comprising the step of: contacting the cellulose-containing textile feedstock with a mixture of an acid and an oxidising agent.

2. The process according to claim 1, wherein the acid comprises hydrochloric acid or hydrobromic acid, preferably hydrochloric acid.

3. The process according to claim 1 or claim 2, wherein the acid comprises dilute aqueous hydrochloric acid, optionally wherein the dilute aqueous hydrochloric acid comprises less than about 40%, or less than about 35%, or less than about 30%, or less than about 25%, or less than about 20%, or less than about 15% or less than about 10% hydrochloric acid by volume of the solution.

4. The process according to any one of claims 1 to 3, wherein the oxidising agent comprises a salt containing potassium or sodium peroxymonosulfate.

5. The process according to any one of claims 1 to 4, wherein the oxidising agent comprises a triple salt having the chemical formula 2KHSO₅-KHSO4-K₂SO4.

6. The process according to any one of claims 1 to 5, wherein the oxidising agent is dissolved in the acid to form the mixture.

7. The process according to claim 6, wherein the oxidising agent is present in an amount of from about 0.01% to about 10%, or from about 0.1% to about 5%, or from about 0.5% to about 2% by weight of the acid.

8. The process according to any one of claims 1 to 7, wherein the liquid to solid ratio of the acid/oxidising agent mixture to the cellulose-containing textile feedstock is from about 5:1 to about 100:1, or from about 10:1 to about 80:1, or from about 20:1 to about 50:1.

9. The process according to any one of claims 1 to 8, wherein the treatment step is carried out at a temperature of from about 25°C to about 95°C.

10. The process according to any one of claims 1 to 9, wherein excess acid and oxidising agent mixture is removed following the acid treatment step.

11. The process according to any one of claims 1 to 10, wherein the process further comprises a neutralisation step where the acid-treated cellulose-containing textile feedstock is contacted with an alkaline solution.

12. The process according to claim 11, wherein the alkaline solution comprises sodium hydroxide and/or potassium hydroxide.

13. The process according to claim 11 or claim 12, wherein the neutralisation step additionally comprises contacting the acid-treated cellulose-containing textile feedstock with a reducing agent.

14. The process according to claim 13, wherein the reducing agent comprises ascorbic acid and/or sodium thiosulfate.

15. The process according to any one of claims 11 to 14, wherein the alkaline solution is removed following the neutralisation step.

16. The process according to any one of claims 11 to 15, wherein following the neutralisation step, the cellulose-containing textile feedstock is washed with water in one or more wash steps, optionally the cellulose-containing textile feedstock is washed in water until the pH is neutral.

17. The process according to any one of claims 1 to 16, wherein the average molecular weight of the cellulose in the cellulose-containing textile feedstock is reduced by at least about 1%, at least about 2%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55% or at least about 60% following treatment, optionally wherein the average molecular weight of the cellulose in the cellulose-containing textile feedstock is reduced by about 1% to about 90%, about 5% to about 80%, about 10% to about 70%, or about 20% to about 60% following treatment.

18. The process according to any one of claims 1 to 17, wherein the cellulose- containing textile feedstock comprises one or more inorganic contaminants, optionally wherein the one or more inorganic contaminants comprise metal salts and/or oxides, optionally wherein the metal is a transition metal, further optionally wherein the one or more inorganic contaminants comprise salts and/or oxides of Ba, Ca, Cu, Fe, K, Mg, Na and/or Zn.

19. The process according to claim 18, wherein the amount of any inorganic contaminant or the amount of all inorganic contaminants present in the cellulose- containing textile feedstock is reduced by at least about 50% w/w, at least about 55% w/w, at least about 60% w/w, at least about 65% w/w, at least about 70% w/w, at least about 75% w/w, at least about 80% w/w, at least about 85% w/w, at least about 90% w/w, at least about 95% w/w, at least about 98% w/w or at least about 99% w/w following treatment, optionally wherein the amount of any inorganic contaminant or the amount of all inorganic contaminants present in the cellulose-containing textile feedstock is reduced by about 50% w/w to about 100% w/w, or from about 60% w/w/ to about 100% w/w, or from about 70% w/w to about 100% w/w, or from about 80% w/w to about 100% w/w, or from about 90% w/w to about 100% w/w following treatment.

20. The process according to claim 18 or claim 19, wherein the amount of any inorganic contaminant or the amount of all inorganic contaminants present in the cellulose- containing textile feedstock following treatment is less than about 500 ppm w/w, less than about 200 ppm w/w, less than about 150 ppm w/w, less than about 100 ppm w/w, less than about 50 ppm w/w, less than about 20 ppm w/w, less than about 10 ppm w/w or less than about 5 ppm w/w.

21. The process according to any one of claims 1 to 20, wherein the cellulose- containing textile feedstock comprises one or more reactive dyes.

22. A process for separating polyester and cellulose from a textile feedstock, comprising the steps of: i. contacting the textile feedstock with a mixture of an acid and an oxidising agent to form an acid-treated textile feedstock; ii. optionally neutralising the acid-treated feedstock with an alkaline solution to form a neutralised textile feedstock; iii. optionally washing the neutralised textile feedstock with water; iv. dissolving and extracting polyester from the textile feedstock; and v. separating cellulose from the textile feedstock using an ionic liquid.

23. Use of a triple salt having the chemical formula 2KHSO5-KHSO4-K₂SO₄ to remove a reactive dye from a cellulose-containing textile feedstock.

24. A process for the removal of a reactive dye from a cellulose-containing textile feedstock, comprising the step of: contacting the cellulose-containing textile feedstock with a triple salt having the chemical formula 2KHSO5-KHSO4-K₂SO₄.

25. Use of an acid and a triple salt having the chemical formula 2KHSO5-KHSO4-K₂SO₄ to treat a cellulose-containing textile feedstock.

26. A cellulose-containing product obtainable or obtained from the process of any one of claims 1 to 22 or 24.