Colour removal for pet recycling

Abstract

The invention is directed to methods of producing a decolourised polymeric material, a decolourised polymeric material obtainable by such methods, and to a method of producing a purified supercritical stream. The methods of producing a decolourised polymeric material of the invention comprise contacting a polymeric material with a supercritical stream under specific conditions. The supercritical stream comprises supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol. The method of producing a purified supercritical stream comprises contacting a contaminated supercritical stream comprising a contaminant and a supercritical stream comprising one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical alcohol, supercritical dimethyl sulphoxide, supercritical dimethylformamide, supercritical acetone, supercritical ozone with a non-volatile liquid stream.

Description

[0001]P135910PC00 Title: COLOUR REMOVAL FOR PET RECYCLING The invention is directed to methods of producing a decolourised polymeric material, a decolourised polymeric material obtainable by such methods, and to a method of producing a purified supercritical stream. The recycling of polymeric materials is more important than ever before due to environmental concerns. However, colourants typically present in polymeric materials may affect the recycling process possibly leading to dark, grey or black recycled polymeric material, unless removed during the recycling process. Therefore, it is advantageous to remove the colourants from polymeric materials during their recycling to obtain high-value colourless recycled polymeric materials. Several attempts have been made to remove the colour from the coloured polymeric materials. For instance, EP-A-3770208 describes a process comprising dissolving a colourant in a polar solvent and separating a synthetic material form the colourant solution. US-B-11802370 discloses a process for decolourising textiles comprising a synthetic fibre and a dye by contacting the dyed textile with a supercritical fluid. DE-A-4333 221 discloses a process for decolouring synthetic fibres in a treatment comprising contacting with a fluid under supercritical conditions in the presence of an absorbent. CN-A-115198509 discloses a process for decolouring textiles using a mixture comprising a decolourising agent as a major component and supercritical carbon dioxide. US-A-2024 / 0052130 describes a method for decolourising a polyester including adding a decolourising agent to the polyester and then contacting the polyester with superheated steam. The above-mentioned processes can lead to degradation of the polymeric material, e.g. due to hydrolysis, leading in turn to partially depolymerised material, formation of volatile organic components such as acetaldehyde and benzene in case of polyesters, and / or incomplete decolourisation of the material. Moreover, some of these processes use harmful chemicals and / or generate complex waste stream mixtures which are difficult to recycle. US-A-2022 / 0204720 discloses a method for decolourisation of polyester fabrics, wherein polyester fabrics are put into an extraction cell, a supercritical fluid and a co-solvent flow are made into the extraction cell, a temperature in the extraction cell is adjusted to be greater than or equal to a glass transition temperature of the polyester fabrics, and the supercritical fluid and the co-solvent are made to flow out of the extraction cell. Garrigos et al. (J. Chromat. A 2002, 963(1-2), 427-433) discloses a study for the optimization of the extraction of some azo colorants used in toys wherein several extraction methods were evaluated and compared, i.e. supercritical fluid extraction, microwave-assisted extraction, and Soxhlet extraction. WO-A-2022 / 178704 discloses a method for decolorizing a dyed textile comprising a synthetic fibre and a disperse dye, the method including contacting the dyed textile with a supercritical fluid thereby extracting at least a portion of the disperse dye from the textile into the supercritical fluid and forming an at least partially decolorized textile. DE-A-19839147 discloses a process for the processing of used thermoplastic material, which is coloured with a particular organic dye, for the purpose of reusing the plastic material, characterised in that the plastic material is at least partially decolorised by exposure to a treatment gas in a supercritical state and at an exposure temperature lying between the glass transition temperature and the melting temperature of the plastic material. There is a need for improved methods of obtaining decolourised polymeric materials. Furthermore, there is a need to reduce or avoid degradation of polymeric material during its decolourisation. There is also a need to provide a method suitable for decolourisation of polymeric material with relatively large dimensions, e.g. polymeric material in form of chips, flakes, shreds, crumbs and / or granules. Furthermore, there is a need for improved method of producing a purified supercritical stream, e.g. in the process of obtaining decolourised polymeric materials. Objective of the invention is to address these needs in the art and to overcome one or more of disadvantages faced in the prior art. Yet a further objective of the invention is to provide a method of producing a decolourised polymeric material that at least maintains the molecular weight of the polymeric material. Yet a further objective of the invention is to provide a method of producing a decolourised polymeric material that has substantially the same colour as a virgin polymeric material. The inventors found that one or more of these objectives can, at least in part, be met by contacting a polymeric material with a supercritical stream under specific conditions. The invention is broadly based on the insight that a coloured polymeric material, e.g. a coloured solid polymeric material, in particular comprising polyester, can be at least partially decolourised by contacting a polymeric material with a supercritical stream comprising supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol under specific conditions as defined herein. These specific conditions advantageously allow for maintaining or even increasing intrinsic viscosity of the polymeric material. Furthermore, the at least partially decolourised polymeric material may advantageously exhibit very low content of volatile organic compounds, such as acetaldehyde, limonene, 2-methyl-1,3-dioxolane, benzene, toluene and benzaldehyde, and semi- or non-volatile organic compounds, such as bisphenol A. Moreover, the at least partially decolourised polymeric material may advantageously exhibit visually uniform and strong discolouration, so that the colour of the decolourised polymeric material is substantially the same as a corresponding virgin polymeric material. In one aspect the invention is directed to a method of producing a decolourised polymeric material the method comprising contacting a coloured polymeric material, such as a solid coloured polymeric material, comprising a polymeric material and a contaminant, preferably a colourant, with a supercritical stream to form the decolourised polymeric material, and a contaminated supercritical stream comprising the colourant and the supercritical stream, and optionally a contaminant, wherein the supercritical stream comprises 90 mol% or more, relative to total supercritical stream, of one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, and wherein the contacting is performed at a temperature of 150 °C or more and below the melting temperature of the polymeric material or below the Tei,m of the polymeric material as determined in accordance with ISO 11357-1 / 3:2023. Typically, the colourant comprises one or more pigments and / or one or more dyes. Preferably, the colourant comprises one or more solvent dyes and / or one or more disperse dyes. Suitable colourants may be selected from the group consisting of Solvent Yellow 43 (CAS number 19125-99-6 / 1226-96-9), Solvent Yellow 72 (CAS number 61813-98-7), Solvent Yellow 93 (CAS number 4702-90-3 / 61969-52-6), Solvent Yellow 114 (CAS number 75216-45-4), Disperse Yellow 64 (CAS number 10319-14-9), Disperse Yellow 184 (CAS number 71838-87-4), Disperse Yellow 201 (CAS number 80748-21-6), Disperse Yellow 211 (CAS number 70528-90-4), Disperse Yellow 241 (CAS number 83249-52-9), Solvent Violet 36 (CAS number 61951-89-1), Solvent Red 23 (CAS number 85-86-9), Solvent Red 26 (CAS number 477-79-6), Solvent Red 111 (CAS number 82-38-2), Solvent Red 135 (CAS number 71902-17-5), Solvent Red 149 (CAS number 71902-18-6 / 21295-57-8), Solvent Red 179 (CAS number 89106-94-5), Solvent Red 195 (CAS number 164251-88-1), Solvent Red 207 (CAS number 15958-68-6), Disperse Red 60 (CAS number 17418-58-5), Disperse Red 152 (CAS number 78564-86-0), Disperse Red 343 (CAS number 99035-78-6), Solvent Green 3 (CAS number 128-80-3), Solvent Green 28 (CAS number 71839-01-5), Solvent Blue 36 (CAS number 14233-37-5), Disperse Blue 60 (CAS number 12217-80-0), Solvent Blue 97 (CAS number 61969-44-6), Solvent Blue 101 (CAS number 6737-68-4), Solvent Blue 104 (CAS number 116-75-6), Solvent Orange 60 (CAS number 61969-47-9 / 6925-69-5), Disperse Orange 25 (CAS number 31482-56-1), Disperse Orange 47 (CAS number 12236-03-2), Solvent Black 7 (CAS number 8005-02-5), and any combination thereof. Suitable colourants are not limited to the dyes mentioned herein. This method is particularly suitable for the removal of solvent dyes and disperse dyes with high efficiency, e.g.80 % or more by total weight of the coloured polymeric material, or 90 % or more, or 95 % or more, or 99 % or more, or 99.5 % or more. Preferably, the coloured polymeric material comprises 5 % or less by total weight of the coloured polymeric material of the colourant, e.g.2 % or less, or 1 % or less, or 0.5 % or less, or 0.1 % or less. Preferably, the at least partially decolourised polymeric material obtainable by said method comprises 1 % or less by total weight of the at least partially decolourised coloured polymeric material of the colourant, e.g. 0.5 % or less, or 0.1 % or less, or 0.05 % or less, or 0.001 % or less. Thereby, the method advantageously allows for high degree of a colourant removal. The coloured polymeric material may further comprise one or more additives, e.g. (semi) volatile organic compounds, alkenes, stabilisers, plasticisers, lubricants, antioxidants, flame retardants. Said additive can have a molecular weight of 2000 g / mol or less, such as 1000 g / mol or less, 500 g / mol or less, or 200 g / mol or less. The coloured polymeric material may further comprise one or more fillers. The skilled person can identify typical additives and fillers used in polymeric materials. Advantageously, this method allows for at least partial removal of one or more additives. Preferably, 50 % or more by total weight of the coloured polymeric material of one or more additives is removed from the coloured polymeric material, such as 60 % or more, 70 % or more, 80 % or more, 90 % or more, 95 % or more, 99 % or more, or 99.5 % or more. Preferably, one or more additives is removed from one or more vinyl polymers. The term “supercritical stream” as used herein is meant to refer to a stream comprising one or more substances, wherein one or more substances are in a supercritical state. The supercritical stream may, for instance, be a binary or ternary mixture of substances. The supercritical stream is preferably a fluid. The supercritical stream can comprise 90 mol% or more, relative to total supercritical stream, of one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol. Preferably, the supercritical stream is a supercritical alkane selected from the group consisting of methane, ethane, propane, butane, methylpropane, pentane, 2-methylbutane, 2,2-dimethylpropane, hexane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2,2-dimethylbutane, and combination thereof. More preferably, the supercritical alkane is methane, ethane, propane or combination thereof. Preferably, the supercritical stream is a supercritical alkene selected from the group consisting of ethene, propene, but-1-ene, but-2-ene, 2-methylprop-1-ene, pent-1-ene, pent-2-ene, 2-methylbut-1-ene, 2-methylbut-2-ene, 3-methylbut-1-ene, hex-1-ene, hex-2-ene, hex-3-ene, 2-methylpent-1-ene, 3-methylpent-1-ene, 4-methylpent-1-ene, 2-methylpent-2-ene, 3-methylpent-2-ene, 4-methylpent-2-ene, 2,3-dimethylbut-1-ene, 3,3-dimethylbut-1-ene, 2-ethylbut-1-ene, 2,3-dimethylbut-2-ene, and combination thereof. More preferably, the supercritical alkene is ethene, propene or combination thereof. Preferably, the contaminant comprises a colourant, a volatile organic compound, a semi-volatile organic compound, and / or a non-volatile compound, preferably the contaminant comprises one or more colourants. Even more preferably, said contaminant has a molecular weight of 2000 g / mol or less, such as 1000 g / mol or less, 500 g / mol or less, or 200 g / mol or less. Preferably, one or more volatile organic compounds and / or a semi-volatile organic compounds are removed from one or more vinyl polymers and / or polyesters. For example, this method advantageously allows for extracting bisphenol A from polyesters. The term “volatile organic compound” as used herein is meant to refer to any organic molecule having a vapour pressure of 0.01 kPa or more at 20 °C, or having a corresponding volatility under the particular conditions of use. Preferably, the volatile organic compound is selected from the group consisting of acetaldehyde, benzaldehyde, limonene, benzene, toluene, xylene, ethylbenzene, ethylene glycol, formaldehyde, methylene chloride, tetrachloroethylene, styrene, and 1,3-butadiene. More preferably, the volatile organic compound is acetaldehyde, limonene or benzene. The term “semi-volatile organic compound” as used herein is meant to refer to any organic molecule having a vapour pressure between 10-8and 10-2kPa at 20 °C, or having a corresponding volatility under the particular conditions of use. The semi-volatile organic compound is e.g. bisphenol A. The term “non-volatile organic compound” as used herein is meant to refer to any organic molecule having a vapour pressure of less than 10-8kPa, at 20 °C or having a corresponding volatility under the particular conditions of use. The supercritical stream may comprise 90 mol% or more, relative to total supercritical stream, of one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, e.g.95 mol% or more, 97 mol% or more, 98 mol% or more, 99 mol% or more, or 99.5 mol% or more, up to 100 mol%. Most preferably, the supercritical stream comprises 90 mol% or more, relative to the total of the supercritical stream, of supercritical carbon dioxide, e.g.95 mol% or more, 97 mol% or more, 98 mol% or more, 99 mol% or more, or 99.5 mol% or more, up to 100 mol%. Preferably, the solid coloured polymeric material is contacted with the supercritical stream at a pressure above 70 bar, preferably at a pressure between 100 and 350 bar, or between 120 and 350 bar, or between 150 and 350 bar, or between 170 and 350 bar, or between 200 and 350 bar, or between 250 and 350 bar, or between 120 and 250 bar, or between 150 and 250 bar, or between 170 and 250 bar, or between 200 and 250 bar. The solid coloured polymeric material is contacted with said supercritical stream at a temperature of 150 °C or more and below the Tei,m of the polymeric material. Preferably, the solid coloured polymeric material is contacted with the supercritical stream at a temperature of 250 °C or less, e.g.150-250 °C, 160-250 °C, 180-250 °C, 200-250 °C, 220-250 °C, 160-220 °C, 180-220 °C, or 200-220 °C. The Tei,m refers to the interpolated onset melt temperature. It is defined in, and can be determined in accordance with ISO 11357-1 / 3:2023. Tei,m as used herein is the intercept of the tangent at the inflection point at the near side (i.e. lower temperature) of the highest melting peak and the tangent of the baseline, based on a differential scanning calorimetry (DSC) heating curve. These conditions are particularly suitable for producing decolourised polymeric materials, such as polyesters, with a high degree of colour removal, e.g.80 % or more by total weight of the colourant in the coloured polymeric material. In these conditions, the supercritical stream partly dissolves in the polymeric material and / or swells the polymeric material, acting as molecular lubricant or carrier, thereby accelerating diffusion of dyes in the polymer melt and promoting extraction of colourants. A supercritical stream comprising 90 mol% or more, relative to total supercritical stream, of one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, advantageously allows for a simplified process and easier recycling of the supercritical stream. Additionally, a supercritical stream comprising 90 mol% or more, relative to total supercritical stream, of supercritical carbon dioxide, leads to a safer and more stable process because of its lower toxicity and flammability than e.g. supercritical alkenes or supercritical alkanes. Advantageously, the decolourised polymeric materials, such as polyesters, are uniformly decolourised with a high removal of colourant, e.g. 90 % or more by total weight of the colourant in the coloured polymeric material, when the pressure is above 150 bar, such as 200 bar or more. Preferably, the removal of colourant is 95 % or more, such as 97 % or more, or 99 % or more. Advantageously, the decolourised polymeric material, such as decolourised polyester, has an increased intrinsic viscosity when the pressure is below 250 bar, such as 200 bar or less, as compared to the colourised polymeric material, such as colourised polyester. In an optional further step, which may be performed prior to or after the solid coloured polymeric material has been contacted with a supercritical stream comprising 90 mol% or more of supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, the solid coloured polymeric material may further be contacted with a supercritical stream comprising one or more selected from supercritical carbon dioxide supercritical alkane, supercritical alkene, and 50 mol% or less, relative to total supercritical stream, of one or more co-solvents selected from alcohol, dimethyl sulphoxide, dimethylformamide, acetone, ozone, alkane, alkene, SO2, and NOx. The supercritical stream may comprise 45 mol% or less, relative to total supercritical stream, of the one or more co-solvents, such as 40 mol% or less, 35 mol% or less, 30 mol% or less, 25 mol% or less, 20 mol% or less, 15 mol% or less, and preferably 10 mol% or more, or 20 mol% or more. In this further step, the supercritical stream preferably comprises 90 mol% or less, relative to total supercritical stream, of one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, such as 80 mol% or less, 70 mol% or less, or 60 mol% or less. Preferably, the amount of one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol in this further step is 50 mol% or more, relative to total supercritical stream. Preferably, in the optional further step the solid coloured polymeric material is contacted with the supercritical stream at a pressure of 70-280 bar, such as 100-200 bar, 120-200 bar, 150-200 bar, or 170-200 bar. Preferably, in the optional further step the solid coloured polymeric material is contacted with said supercritical stream at a temperature of 70-250 °C, more preferably 100-200 °C, 80-150 °C, or 100-220 °C. The addition of co-solvent may advantageously increase the solubility of the colourant in the supercritical stream, as well as increase the diffusion rate of the colourant from the coloured polymeric material, which enhances colourant removal. The method may comprise gradual change of composition of the supercritical stream in time between the first supercritical stream and the second supercritical stream. The temperature of the supercritical stream may be subjected to change during the contacting, e.g. from a temperature of 70-250 °C to a temperature of 150 °C or more and lower than the Tei,m of the polymeric material, preferably in combination with a change of a composition of the supercritical stream. The pressure of the supercritical stream may be subjected to change during the contacting, e.g. from above 70 bar, preferably a pressure of 100-350 bar, 70-280 bar, or 100-200 bar, preferably in combination with a change of a composition and / or a temperature of the supercritical stream. Preferably, the method further comprises separating at least part of the contaminated supercritical stream to obtain a purified supercritical stream and colourant, and recycling at least part of the purified supercritical stream to contacting with coloured polymeric material. Changing the composition of the supercritical stream, as well as the temperature and pressure during the contacting of the coloured polymeric material with the supercritical stream advantageously allows for an efficient colour removal, e.g. by 80 % or more by total weight of the colourant in the coloured polymeric material, 90 % or more, 95 % or more, or 99 % or more, optionally combined with an increased intrinsic viscosity of the polymeric material and overall reduced time of the process. Preferably, contacting the solid coloured polymeric material with the supercritical stream is carried out for 24 hours or less, such as 8 hours or less, 6 hours or less, 5 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, 1 hour or less, 30 minutes or less, or 15 minutes or less. Preferably, the contacting is carried out for 5 minutes or more. Preferably, contacting the solid coloured polymeric material with the supercritical stream is carried out with a linear flow rate of the supercritical stream of 0.1 cm / s or more, such as 0.25 cm / s or more, 0.5 cm / s or more, 0.75 cm / s or more, 1.0 cm / s or more, preferably 0.1-1.0 cm / s or 0.2-0.8 cm / s. Suitably, contacting the solid coloured polymeric material with the supercritical stream is carried out in a separation vessel, e.g. an extractor, comprising an inlet for a supercritical stream and an outlet for a contaminated supercritical stream, wherein the solid coloured polymeric material is contained in the volume of the vessel and wherein the supercritical stream is passed though the vessel thereby allowing for contacting of the solid coloured polymeric material with the supercritical steam. The vessel may comprise a distribution device such as a perforate plate or perforated tube, to distribute the supercritical stream evenly through the coloured polymeric material, so as to ensure that all polymer is contacted with the same flow of the supercritical stream. Thereby, the at least partially decolourised polymeric material is obtained in the vessel after the contacting step. Even distribution of the supercritical stream advantageously allows for uniform discolouration of coloured polymeric material. The contaminated supercritical stream may be supplied to a downstream separation system for purifying the contaminated supercritical stream. Preferably, the co-solvent comprises an alcohol selected from the group consisting of methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, 2-methylpropan-1-ol, 2-methylpropan-2-ol, pentan-1-ol, pentan-2-ol, pentan-3-ol, 2-methylbutan-1-ol, 2-ethylbutan-2-ol, 2,2-dimethylpropan-1-ol, 3-methylbutan-1-ol, 3-methylbutan-2-ol, hexan-1-ol, hexan-2-ol, hexan-3-ol, 2-methylpentan-1-ol, 3-methylpentan-1-ol, 4-methylpentan-1-ol, 2-methylpentan-2-ol, 3-methylpentan-2-ol, 4-methylpentan-2-ol, 2-methylpentan-3-ol, 3-methylpentan-3-ol, 2,2-dimethylbutan-1-ol, 2,3-dimethylbutan-1-ol, 3,3-dimethylbutan-1-ol, 2,3-dimethylbutan-2-ol, 3,3-dimethylbutan-2-ol, 2-ethylbutan-1-ol. Alcoholic solvents as described herein advantageously allow for improved colourant removal in terms of removal efficiency and speed due to an increased polarity of a supercritical stream comprising an alcoholic solvent as compared to a supercritical stream not comprising an alcoholic solvent. Addition of an alcoholic co-solvent may advantageously increase the solubility of the colourant in the supercritical stream, as well as increase the diffusion rate of the colourant from the coloured polymeric material, which in turn enhances the colourant removal. Preferably, the supercritical stream comprises supercritical carbon dioxide and 30 mol% or less, relative to total supercritical stream, of alcohol solvent, such as 25 mol% or less, 20 mol% or less, 15 mol% or less, and preferably 10 mol% or more. NOx, as describes herein refers to one or more substances selected from the group consisting of N2O, NO, NO2, NO3, N2O3, N2O5. Preferably, x is greater than zero and 3 or less, more preferably x is 0.5-2. Preferably, NOxcomprises 90 % or more by total weight of NOxof N2O. Preferably, the co-solvent comprises an alkane selected from the group consisting of methane, ethane, propane, butane, methylpropane, pentane, 2-methylbutane, 2,2-dimethylpropane, hexane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2,2-dimethylbutane, and combination thereof. Preferably, the co-solvent comprises an alkene selected from the group consisting of ethene, propene, but-1-ene, but-2-ene, 2-methylprop-1-ene, pent-1-ene, pent-2-ene, 2-methylbut-1-ene, 2-methylbut-2-ene, 3-methylbut-1-ene, hex-1-ene, hex-2-ene, hex-3-ene, 2-methylpent-1-ene, 3-methylpent-1-ene, 4-methylpent-1-ene, 2-methylpent-2-ene, 3-methylpent-2-ene, 4-methylpent-2-ene, 2,3-dimethylbut-1-ene, 3,3-dimethylbut-1-ene, 2-ethylbut-1-ene, 2,3-dimethylbut-2-ene, and combination thereof. An alkene co-solvent may be advantageous over alcohol co-solvent in that it does not depolymerises polyester. The addition of an alkane or alkene co-solvent advantageously increases solubility of the colourant in the supercritical stream, which enhances the colourant removal. The addition of an alkane or alkene co-solvent may advantageously decrease an operational pressure of the process. Suitably, the solid coloured polymeric material is fibre-based, e.g. a textile fibre, or woven, knitted, or nonwoven fabric. Preferably, 80 % or more of individual fibres in the fibre-based material have a length to diameter ratio of 100 : 1 or more, more preferably 1000 : 1 or more. More preferably, 90 % or more of individual fibres in the fibre-based material have such a length to diameter ratio, even more preferably 95 % or more. Preferably, 80 % or more of individual fibres in the fibre-based material have a diameter of 500 ^m or less, such as 200 ^m or less, 100 ^m or less, 70 ^m or less, 50 ^m or less, 70 ^m or less, 50 ^m or less, 30 ^m or less, 20 ^m or less, or 10 ^m or less, and preferably 1 ^m or more, or 5 ^m or more, such as 1-100 ^m or 5-30 ^m. More preferably, 90 % or more of individual fibres in the fibre-based material have such a diameter, even more preferably 95 % or more. Advantageously, fibre-based coloured polymeric materials have larger surface area / mass ratio compared with solid pieces of coloured polymeric materials having larger dimensions, in particular a diameter (or thickness). Higher surface area / mass ratio in turn allows for increased contacting surface and faster removal of the colourant from the polymeric material. Alternatively, the coloured polymeric material is in the form of chips, flakes, shreds, crumbs, and / or granules. Sizes of chips, flakes, shreds, crumbs, and granules typically are 50 mm or less in all dimensions (i.e. width, height, thickness), preferably 20 mm or less in all dimensions, and 1 mm or more in all dimensions. The present method is also suitable for coloured polymeric materials having larger dimensions because the conditions disclosed herein allow for extraction of colourant based on diffusion from the entire volume of the polymeric material due to the partial dissolution of the supercritical stream in the polymeric material. The solid coloured polymeric material comprises a polymeric material and a colourant. Preferably, the polymeric material comprises one or more materials selected from the group consisting of polyester, polyamide, polyolefins, vinyl polymers, polyurethane, polyethers, polycarbonates, and rubbers. Said polymeric materials may comprise copolymers of polyester, polyamide, polyolefins, vinyl polymers, polyurethane, polyethers, polycarbonates, and rubbers. Advantageously, the method as described herein is highly versatile and suitable for wide ranges of the polymeric materials. Preferably, the polymeric material comprises one or more polyesters selected from the group consisting of aliphatic homopolymer polyesters, aliphatic copolymer polyesters, semi aromatic copolymer polyesters, semi-aromatic homopolymer polyesters, aromatic copolymer polyesters, and aromatic homopolymer polyesters. More preferably, the polymeric material comprises one or more selected from polyethylene terephthalate (PET), poly(hexamethylene terephthalate) (PHT), polypropylene terephthalate (PPT), polyethylene naphthalate (PEN), polyethylene furanoate (PEF), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polybutylene succinate (PBS), polylactic acid (PLA), polyhydroxyalkanoates (PHAs), polybutylene adipate terephthalate (PBAT), poly(hydroxybutyrate-co-valerate) (PHBV). Advantageously, the method may allow for simultaneous removal of colourant and increase of intrinsic viscosity, particularly when polyesters are used as a polymeric material. This method is particularly suitable for producing at least partially decolourised polyesters without their degradation. This is particularly advantageous because polyesters are particularly susceptible to degradation during the decolourisation processes known in the art, as observed by, e.g. reduced molecular weight or intrinsic viscosity. Furthermore, the inventors observed that polyesters, such as PET, are advantageously swollen by the supercritical stream, such as the supercritical stream comprising supercritical carbon dioxide. Swelling of the polymeric materials, in particular polyesters, advantageously aids in extraction of the contaminants, e.g. colourants. Preferably, the polymeric material comprises one or more polyamides selected from the group consisting of aliphatic homopolymer polyamides, aliphatic copolymer polyamides, semi aromatic copolymer polyamides, semi-aromatic homopolymer polyamides, aromatic copolymer polyamides, and aromatic homopolymer polyamides. More preferably, the polymeric material comprises one or more selected from polyamide 4.6 (PA 4.6), polyamide 4.10 (PA 4.10), polyamide 4.12 (PA 4.12), polyamide 5.6 (PA 5.6), polyamide 6 (PA 6), polyamide 6.6 (PA 6.6), polyamide 6.10 (PA 6.10), polyamide 6.12 (PA 6.12), polyamide 10 (PA 10), polyamide 10.10 (PA 10.10), polyamide 10.12 (PA 10.12), polyamide 11 (PA 11), polyamide 12 (PA 12), polyphthalamide (PPA), aramid, e.g. poly-paraphenylene terephthalamide. Preferably, the polymeric material comprises one or more polyolefins, preferably selected from the group consisting of polyethylene (PE), high-density polyethylene (HDPE), polypropylene (PP), high-density polypropylene (HDPP). Preferably, the polymeric material comprises one or more vinyl polymers, preferably selected from the group consisting of polystyrene (PS), polyvinyl chloride (PVC), polyvinyl acetate (PVAc), polyacrylonitrile (PAN), polyvinyl alcohol (PVOH), styrene-acrylonitrile resin (SAN), acrylonitrile butadiene styrene (ABS), polycarbonate / acrylonitrile butadiene styrene (PC / ABS), poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA) and mixture thereof. Preferably, the polymeric material comprises one or more polyurethanes, preferably selected from the group consisting of a polyester-based thermoplastic polyurethane, a polyether-based thermoplastic polyurethane and mixture thereof. Preferably, the polyester-based thermoplastic polyurethane is based on adipic acid derivative. Preferably, the polyester-based thermoplastic polyurethane is based on tetrahydrofuran ethers. Preferably, the polymeric material comprises one or more polyethers, preferably selected from the group consisting of polyether, polyethylene glycol (PEG), polypropylene glycol (PPG), poly (butylene oxide) (PBO), polytetrahydrofuran (PTHF), polyether ether ketone (PEEK), polyether ketoneketone (PEKK), and mixture thereof. Preferably, the polymeric material comprises one or more polycarbonates, preferably selected from the group consisting of a bisphenol A-based polycarobante, poly(allyl diglycol carbonate) (PDAC), polycarbonate / acrylonitrile butadiene styrene (PC / ABS) and mixture thereof. Preferably, the polymeric material comprises one or more rubbers, preferably selected from the group consisting of styrene-butadiene rubbers (SBR) polyisoprene, neoprene, butadiene rubber (BR), nitrile rubber (NBR), ethylene propylene rubber (EPR), ethylene propylene diene monomer rubber (EPDM rubber), silicone rubber, and mixture thereof. In a further aspect, the invention is directed to a method of producing a decolourised polymeric material, the method comprising melt filtering a coloured polymeric feed comprising a polymeric material, a colourant, and a solid additive, e.g. one or more fillers and / or one or more pigments, thereby obtaining a flowable coloured polymeric material and solid additive, and contacting at least part of the flowable coloured polymeric material with a supercritical stream comprising supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, and optionally a co-solvent, to form decolourised polymeric material and a contaminated supercritical stream, wherein the flowable coloured polymeric material is contacted with the supercritical stream at a temperature at or above the melting temperature of the polymeric material or at a temperature at or above the Tef,m of the polymeric material as determined in accordance with ISO 11357-1 / 3:2023. The Tef,m refers to the interpolated end melt temperature. It is defined in, and can be determined in accordance with ISO 11357-1 / 3:2023. Tef,m as used herein is the intercept of the tangent drawn at the inflection point at the far side (i.e. higher temperature) of the highest melting peak and the tangent of the baseline, based on a differential scanning calorimetry (DSC) heating curve. Melt filtering is a process wherein a polymer melt passes a filter. This in contrast to a process wherein a solvent is first added to a polymer before filtration and a dissolved polymer passes a filter. Hence, the coloured polymeric feed that is melt filtered preferably has an amount of solvent of 5 % of less by total weight of the polymeric feed, preferably 4 % or less, such as 3 % or less, 2 % or less, 1 % or less, 0.5 % or less, or 0.1 % or less. Said method yields a decolourised polymeric material in a flowable state which may advantageously be used to obtain recycled polymeric material substantially free of colourants and additives, such as fillers. Furthermore, decolourising coloured polymeric material in a flowable state may be particularly advantageous for the feed comprising relatively thick pieces, such as chips and alike, as described herein. Such polymeric material may be subsequently converted into polymeric pellets or granules, which are typically easy to handle. Suitably, the coloured polymeric feed comprises the polymeric material as described herein. Suitably, the flowable coloured polymeric material is a molten polymeric mass. Suitably, the flowable coloured polymeric material has an intrinsic viscosity at temperature of 20 °C of 0.1 dl / g or more, as determined by an Ubbelohde viscosity measurement in dichloroacetic acid according to the AP 337 internal standard of GETEC laboratory, Emmen (NL), e.g.0.2 dl / g or more, 0.3 dl / g or more, 0.4 dl / g or more, 0.5 dl / g or more, 0.6 dl / g or more, 0.7 dl / g or more, 0.8 dl / g or more, or 0.9 dl / g or more. The flowable coloured polymeric material can have an intrinsic viscosity at temperature of 20 °C of 1.0 dl / g or less. Preferably the flowable coloured polymeric material has an intrinsic viscosity at temperature of 20 °C of 0.1-1.0 dl / g, such as 0.2-0.8 dl / g, 0.3-0.7 dl / g, or 0.4-0.8 dl / g. Preferably, the supercritical stream comprises 10 mol% or more, relative to total supercritical stream, of one or more selected from the group consisting of supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, e.g.20 mol% or more, 30 mol% or more, 40 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, o 97 mol% or more, 98 mol% or more, 99 mol% or more, or 99.5 mol% or more, up to 100 mol%. Optionally, the supercritical stream can comprise a co-solvent. Suitably, the supercritical stream comprises 5 mol% or more, relative to total supercritical stream, of the co-solvent, e.g.10 mol% or more, 20 mol% or more, 30 mol% or more, 40 mol% or more, 50 mol% or more, 60 mol% or more, or 70 mol% or more, up to 90 mol%. Preferably, the supercritical stream is provided as a counter-current flow with respect to the flowable coloured polymeric material flow direction, which advantageously allows for higher efficiency of the method, e.g. reduced time needed to decolour the polymeric material and / or a higher colourant extraction efficiency, compared to a co-current flow. Preferably, melt filtering a coloured polymeric feed is performed in an extruder, e.g. a single screw extruder or a twin screw extruder to provide for a flowable molten stream mass, provided with a downstream filtration setup to give a flowable coloured polymeric material stream and a solid additive stream. Suitably, the flowable coloured polymeric material stream is supplied to a vessel wherein it is contacted with the supercritical stream. Preferably, the contacting is carried out in a vessel, which may comprise a perforate plate or perforated tube, to distribute the supercritical stream evenly through the coloured polymeric material, so as to ensure that all polymer is contacted with the same flow of the supercritical stream. Alternatively, the contacting is carried out in a vessel comprising a filter comprising sintered materials, wherein the supercritical stream is provided on the filtrate side and the flowable molten stream is provided on the retentate side. Preferably, the pore size of said filter is too small to allow for filtration of the flowable molten stream, and large enough to allow for the flow of the supercritical stream. Suitably, the vessel is configured to allow for (uniform) contacting of the supercritical stream and the flowable molten stream by passing the supercritical stream through the flowable molten stream. Uniform contacting advantageously allows for improved mass transfer between the streams and even colour removal. Preferably, the method further comprises separating at least part of the contaminated supercritical stream to obtain a purified supercritical stream and colourant, and recycling at least part of the purified supercritical stream to contacting with coloured polymeric material. Advantageously, this allows for more efficient resource management in the process of producing a decolourised polymeric material and reduce need of waste product management. Suitably, separating at least part of the contaminated supercritical stream is carried out by depressurising the contaminated supercritical stream, e.g. to a pressure of 60 bar or less, such as 50 bar or less, 40 bar or less, 30 bar or less, 20 bar or less, 10 bar or less, or 5 bar or less, and suitably 1 bar or more, to precipitate the colourant. Recycling at least part of the purified supercritical stream to contacting with coloured polymeric material may suitably be carried out by pressurising and heating the purified supercritical stream prior to supplying said supercritical stream to the contacting step. Alternatively, said separating may comprise contacting the contaminated supercritical stream with non-volatile liquid stream, wherein contacting the contaminated supercritical stream with non-volatile liquid stream is performed at substantially the same pressure, e.g. within ± 20 bar and / or ± 20 % pressure difference, as a preceding production step. The term “non-volatile liquid” as used herein is meant to refer to a chemical substance having a melting temperature lower than 25 °C and an equilibrium vapour pressure of 3.1690 kPa or less at 25 °C. Suitably, the non-volatile liquid has solubility in the supercritical stream of 10-3g / g or less, preferably 10-4or less, more preferably 10-5g / g or less. The non-volatile liquid is, e.g. an ionic liquid, a deep eutectic solvent (DES), one or more polymers, one or more oligomers, or a mixture thereof. Selection of a non-volatile liquid advantageously allows for recycling of the supercritical stream within the process without contaminating it with the non-volatile liquid, thereby leading to more streamline process without a need to further purify the supercritical stream prior to its contacting with the coloured polymeric material. Performing the above mentioned separation step at substantially the same pressure advantageously allows for more energy-efficient and streamlined separation process and recycling of the supercritical stream. Preferably, a decolourised polymeric material obtainable by methods as described herein comprises 50 ppb or less by total weight of the decolourised polymeric material of benzene, e.g.40 ppb or less, 30 ppb or less, 20 ppb or less, 10 ppb or less, 5 ppb or less, or 1 ppb or less. The benzene concentration can be determined by the AC 424 internal standard of GETEC laboratory, Emmen (NL). Preferably, the decolourised material obtainable by methods as described herein comprises 1000 ppb or less by total weight of the decolourised polymeric material of acetaldehyde, e.g.700 ppb or less, 500 ppb or less, 200 ppb or less, 100 ppb or less, 50 ppb or less, 10 ppb or less, 5 ppb or less, or 1 ppb or less. The acetaldehyde concentration can be determined according to ASTM F-2013. Suitably, a decolourised polymeric material, obtained according to the methods as described herein, has a higher intrinsic viscosity at temperature of 20 °C than the coloured polymeric material, such as a solid coloured polymeric material, preferably higher by 0.05 dl / g or more, e.g.0.10 dl / g or more, 0.20 dl / g or more, 0.30 dl / g or more, 0.40 dl / g or more, or 0.50 dl / g or more, or 0.60 dl / g or more, or 0.70 dl / g or more, or 0.80 dl / g or more, or 0.90 dl / g or more, or 1.00 dl / g or more. The intrinsic viscosity at 20 °C can be determined by an Ubbelohde viscosity measurement in dichloroacetic acid according to the AP 337 internal standard of GETEC laboratory, Emmen (NL). Suitably, the increased intrinsic viscosity is observed when contacting with the supercritical stream is performed at a temperature of 200 °C or more, e.g.220 °C or more, or 240 °C or more, and preferably lower than the melting temperature of the polymeric material or below the Tei,m of the polymeric material, and preferably wherein the contacting is performed at a pressure of 250 bar or less, e.g.200 bar or less, or 150 bar or less, or 100 bar or less, and preferably 70 bar or more. Preferably, the polymeric material with an increased intrinsic viscosity is a polyester. Advantageously, the material having a higher intrinsic viscosity has higher molecular weight compared to the coloured polymeric material which indicates that said decolourised polymeric material did not depolymerise during the process. Advantageously, the mechanical performance of said decolourised polymeric material are at least maintained, which is beneficial for the recycling of such material. Preferably, a decolourised polymeric material, obtained according to the methods as described above, has a higher L colour value than the solid coloured polymeric material, preferably wherein L value is 80 or more, e.g.85 or more, or 90 or more, or 92 or more, or 95 or more, or 97 or more. The L colour value can be determined by a colour measurement according to an internal standard of GETEC laboratory, Emmen (NL). Preferably, the decolourised polymeric material has a b colour value in the range between -4 and 4, e.g. between -3 and 3, or between -2 and 2, or between -1 and 1, between -0.5 and 0.5. The b colour value can be determined by a colour measurement according to an internal standard of GETEC laboratory, Emmen (NL). Preferably, the decolourised polymeric material has an a colour value in the range between -3 and 3, e.g. between -2 and 2, or between -1 and 1, between -0.5 and 0.5. The a colour value can be determined by a colour measurement according to an internal standard of GETEC laboratory, Emmen (NL). Preferably, the decolourised polymeric material has the L colour value which differs between test points spaced from each other by at least 1 cm in each direction by 3 or less, e.g.2 or less, or 1 or less, or 0.5 or less, or 0.1 or less, and preferably the a and b colour values differ by 0.5 or less, e.g.0.2 or less, or 0.1 or less, or 0.05 or less, as determined by a colour measurement according to an internal standard of GETEC laboratory, Emmen (NL), in the decolourised polymeric material having an area of at least 4 cm2based on the measurement performed at least in triplex in different spots of the decolourised polymeric material. Such material is considered to be uniformly decolourised polymeric material. Advantageously, the decolourised polymeric material as described herein is reusable without a need of further decolourisation, e.g. bleaching. Furthermore, such decolourised polymeric material can be coloured again without interference of the existing colour of the material. Preferably, the decolourised polymeric material obtainable by the method as described herein. In yet a further aspect the invention is directed to a method of producing a purified supercritical stream, the method contacting a contaminated supercritical stream comprising a contaminant and a supercritical stream comprising one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical alcohol, e.g. supercritical methanol and / or supercritical ethanol, supercritical dimethyl sulphoxide, supercritical dimethylformamide, supercritical acetone, supercritical ozone, and optionally a co-solvent as described herein, with a non-volatile liquid stream, thereby yielding a purified supercritical stream and a contaminated non-volatile liquid stream, wherein the method is carried out in a separation system comprising a separation vessel, wherein the separation vessel comprises an inlet for the non-volatile liquid stream, an inlet for the contaminated supercritical stream, an outlet for the purified supercritical stream, and an outlet for the contaminated non-volatile liquid stream. This aspect of the invention is broadly based on the judicious insight that a contaminated supercritical stream can be purified upon contacting with a non-volatile liquid stream. This includes, but is not limited to producing a purified supercritical stream from the contaminated supercritical stream wherein the contaminant is a colourant, preferably as described herein. Suitably, the method is also suitable, for example, for extraction of chemical substances from a solid stream, e.g. from biomass, for extraction of chemical substances from a liquid stream, removal of excess dye from dyed textiles during dying process. Preferably, the non-volatile liquid is an ionic liquid. An ionic liquid is a chemical compound comprising a cation and an anion. Suitably, the ionic liquid is a hydrophobic ionic liquid, preferably comprising a hydrophobic moiety in either a cation or an anion. Preferably, the cation of the hydrophobic ionic liquid is selected from the group consisting of substituted or unsubstituted pyrrolidinium cation, substituted or unsubstituted pyrazolium cation, substituted or unsubstituted imidazolium cation, substituted or unsubstituted thiazolium cation, substituted or unsubstituted oxazolium cation, substituted or unsubstituted triazolium cation, substituted or unsubstituted pyridinium cation, substituted or unsubstituted pyridazinium cation, substituted or unsubstituted pyrimidinium cation, substituted or unsubstituted pyrazinium cation, substituted or unsubstituted quaternary ammonium cation, substituted or unsubstituted quaternary phosphonium cation, substituted or unsubstituted quaternary guanidinium cation, substituted or unsubstituted quaternary uronium cation, substituted or unsubstituted quaternary thiouronium cation. Each of the cations may be substituted in one or more positions with F, Cl, C1-C10 alkyl group, C2-C10 alkyne group, phenyl group, C1-C10 alkoxy group. Alkyl, alkylene, phenyl and alkoxy substituents may be further substituted with one or more of the following electron withdrawing groups, such as F, Cl, CF3, SF5, CF3S, (CF3)2CHS and (CF3)3CS. Preferably, the cation of the hydrophobic ionic liquid is selected from the group consisting of F−, Cl−, CF3−, SF5−, CF3S−, (CF3)2CHS−and (CF3)3CS−, substituted or unsubstituted borate anion, and substituted or unsubstituted phosphate anion, imide anion, bis(fluorosulphonyl)imide anion, bis(trifluoromethanesulphonyl)imide anion. Each of the imide, borate, and phosphate anions may be substituted in one or more positions with F, Cl, C1-C10alkyl group, C2-C10alkyne group, phenyl group, C1-C10alkoxy group. Alkyl, alkylene, phenyl, alkoxy substituents may be further substituted with one or more of the following electron withdrawing groups, such as F, Cl, CF3, SF5, CF3S, (CF3)2CHS and (CF3)3CS. Advantageously, certain contaminants, e.g. colourants, exhibit higher solubility in hydrophobic ionic liquids compared to the supercritical stream, allowing for efficient extraction of said contaminants from the supercritical stream. For example, the ionic liquid is selected from the group consisting of 1-methyl-1-(2-methoxyethyl)pyrrolidinium bis(fluorosulphonyl)imide, 1-methyl-1-(2-methoxyethyl)pyrrolidinium bis(trifluoromethanesulphonyl)imide, N-butyl-N-methylpiperidinium bis(trifluoromethanesulphonyl)imide, 1-butyl-1-methylpyrrolidinium bis(fluorosulphonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulphonyl)imide, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide, N-pentyl-N-methylpyrrolidinium bis(trifluoromethanesulphonyl)imide, N-(3-methoxypropyl)-N-methylpyrrolidinium bis(fluorosulphonyl)imide, N-(3-methoxypropyl)-N-methylpyrrolidinium bis(trifluoromethanesulphonyl)imide, N-ethyl-N,N-dimethyl-N-(3-methoxypropyl)ammonium bis(fluorosulphonyl)imide, N-ethyl-N,N-dimethyl-N-(3-methoxypropyl)ammonium bis(trifluoromethanesulphonyl)imide, N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(fluorosulphonyl)imide, N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulphonyl)imide, N,N-diethyl-N-methyl-N-propylammonium bis(fluorosulphonyl)imide, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulphonyl)imide, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulphonyl)imide, N,N-dimethyl-N-ethyl-N-benzylammonium bis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-ethyl-N-phenethylammonium bis(trifluoromethanesulphonyl)imide, N-tributyl-N-methylammonium bis(trifluoromethanesulphonyl)imide, 1-octyl-3-methylimidazolium bis(trifluoromethanesulphonyl)imide, 1-methyl-1-propylpiperidinium bis(fluorosulphonyl)imide, N-propyl-N-methylpyrrolidinium bis(fluorosulphonyl)imide, trihexyl(tetradecyl)phosphonium chloride, trihexyl(octyl)phosphonium chloride and mixtures thereof. Alternatively, the non-volatile liquid is a deep eutectic solvent, more preferably, a hydrophobic deep eutectic solvent. Typically, the deep eutectic solvent comprises two components, a hydrogen bond acceptor and a hydrogen bond donor. The hydrogen bond acceptor may be selected from the group consisting of methyltrioctylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, tetraheptylammonium chloride, methyltrioctylammonium bromide, tetraoctylammonium bromide, tetraoctylammonium chloride, menthol, thymol, betaine, coumarin, carvacrol, choline chloride, L-carnitine, and dodecanoic acid. The hydrogen bond donor may be selected from the group consisting of hexafluoroisopropanol, ethyl 4-hydroxybenzoate, 10-undecylenic acid, dodecanoic acid, nonanoic acid, octanoic acid, decanoic acid, lauric acid, palmitic acid, lactic acid, 4-phenylphenol, 4-cyanophenol, hydroquinone, levulinic acid, acetic acid, pyruvic acid, oleic acid, salol, lidocaine, coumarin, carvacrol, and menthol. The skilled person is capable of selecting appropriate combinations of hydrogen bond acceptor and hydrogen bond donor. For example, hydrophobic DES may be a mixture of thymol and menthol, choline chloride and a fatty acid, e.g. decanoic acid, menthol and a fatty acid, e.g. decanoic acid, lidocaine and a fatty acid, e.g. decanoic acid, thymol and a fatty acid, e.g. decanoic acid, tetrabutylammonium salts, e.g. chloride or bromide, and a fatty acid, e.g. decanoic acid. In particular, such method of producing a purified supercritical stream can be advantageously performed at substantially the same pressure, e.g. within ± 20 bar, such as within ± 10 bar, or within ± 5 bar, or within ± 1 bar, and / or within ± 20 % pressure difference, such as within ± 10 % pressure difference, or within ± 5 % pressure difference, or within ± 1 % pressure difference, as a preceding production step, in particular a production of a decolourised polymeric material. Advantageously, such method can be simpler and more energy efficient compared with state-of-the-art methods based on depressurisation and precipitation of the contaminant, followed by condensation of the purified supercritical stream. Suitably, the separation system comprises the separation vessel, wherein the separation vessel comprises the inlet for the non-volatile liquid stream, the inlet for the contaminated supercritical stream, wherein these inlets are on the opposite side of the separation vessel in streams flow direction, e.g. in a counter current separation column, thereby allowing for a counter-current flow of the non-volatile liquid stream and the contaminated supercritical stream. Such configuration of the separation system advantageously allows for an improved stripping efficiency, i.e. an efficiency of contaminant removal. Alternatively, the separation system comprises a vessel for the non-volatile liquid allowing for passing the contaminated supercritical stream through the non-volatile liquid, e.g. contacting both streams in a counter current mass transfer column, thereby providing the non-volatile liquid stream as a stationary phase. The column may comprise one or more means of increasing contact surface between the non-volatile liquid stream and the contaminated supercritical stream, such as a spraying device for the non-volatile liquid into the contaminated supercritical stream, a bubbling device to bubble the contaminated supercritical stream through the non-volatile liquid , a packing, such as but not limited to Berl saddles, Raschig rings, structured packing, a combination of mixer and cyclone, and / or one or more baffles comprising sintered materials, so that the flow of the non-volatile liquid is distributed evenly into the contaminated supercritical stream. Preferably, the method further comprises purifying the contaminated non-volatile liquid stream carried out in an non-volatile liquid purification system, thereby yielding a purified non-volatile liquid stream, wherein the non-volatile liquid purification system comprises an inlet for the contaminated non-volatile liquid stream and an outlet for the purified non-volatile liquid stream, wherein the outlet for the contaminated non-volatile liquid stream in the separation vessel is in a fluid communication with the inlet for the contaminated non-volatile liquid stream in the non-volatile liquid purification system, and wherein the outlet for the purified non-volatile liquid stream in the non-volatile liquid purification system is in a fluid communication with the inlet for the non-volatile liquid stream in the separation vessel. Advantageously, such step allows for reusing the non-volatile liquid stream thereby allowing for improved waste management in the process. Suitably, the non-volatile liquid purification system is operated at substantially the same pressure, e.g. within ± 10 bar, such as within ± 5 bar, or within ± 2 bar, or within ± 1 bar, and / or within ± 10 % pressure difference, such as within ± 5 % pressure difference, or within ± 2 % pressure difference, or within ± 1 % pressure difference, as the separation system. Suitably, the non-volatile liquid purification system is suitable for removing the contaminant from the contaminated non-volatile liquid stream e.g. by absorption, adsorption, precipitation, or crystallisation, thereby yielding a purified non-volatile liquid stream, which may be directly recycled to the separation system. Preferably, the method of producing a decolourised polymeric material as described herein further comprises producing a purified supercritical stream and preferably purifying the contaminated non-volatile liquid stream. This advantageously provides a full recycle process with reduced amount of waste products, i.e. recycling of the supercritical stream and the non-volatile liquid stream. The invention has been described by reference to various embodiments, and methods. The skilled person understands that features of various embodiments and methods can be combined with each other. All references cited herein are hereby completely incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising”, “having”, “including” and “containing” are to be construed as open ended terms (i.e., meaning “including, but not limited to”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. For the purpose of the description and of the appended claims, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term “about”. Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein. As used herein, pressure is given in kPa or bar. This relates to kPa or bar absolute. Preferred and suitable embodiments of this invention are described herein. Variation of those preferred and suitable embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the herein described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. Hereinafter, the invention will be illustrated in more detail, according to specific examples. However, the invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these example embodiments are provided so that this description will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The invention will now be further illustrated by the following non-limiting example(s). These examples do not limit the invention and do not limit the claims. Examples Example 1 0.1 g of a knitted polyester fabric, dyed with a disperse blue dye, was placed in a pressure tube so that any fluid stream passing through the tube was forced through the fabric. The tube was placed in an oven at 150 °C and a supercritical stream substantially consisting of supercritical carbon dioxide at 250 bar was pumped through the fabric at a flow rate of 10 ml / min for 70 minutes. Afterwards, the flow of the supercritical stream was stopped and the discoloured fabric was retrieved. The discoloured fabric was visually white. Example 2 A polyester fabric dyed red, was placed in a pressure tube so that any fluid stream passing through the tube was forced through the fabric. Then, supercritical carbon dioxide was passed through the pressure tube. The contaminated supercritical stream comprising the supercritical carbon dioxide and a dye was subsequently supplied to a downstream separation column filled with an ionic liquid, trihexyl(octyl)phosphonium chloride. The contaminated supercritical stream contacted with the ionic liquid was then supplied to the pressure tube and circulated during the decolourisation process. After the decolourisation process was completed, the fabric was visually discoloured and the ionic liquid was coloured red, thereby indicating that the dye was absorbed in the ionic liquid. Example 3 An (original) polyester fabric dyed red was applied to detect the effect of supercritical carbon dioxide exposure to its intrinsic viscosity (IV), colour change and change in acetaldehyde (AA) and benzene content. In addition, the free carboxylic acid end groups were detected to assess whether enough free carboxylic acid end groups are present for a solid state polycondensation reaction. The original sample showed a free carboxylic acid end group content of 30 meq / kg, according to the AV 361 internal standard of GETEC laboratory, Emmen (NL). This value is an indication that the free carboxylic end group content in the sample is sufficiently high for solid state polycondensation. The original sample was not exposed to super- or subcritical carbon dioxide. A polyester fabric dyed red sample was placed in a pressure tube so that any fluid stream passing through the tube was forced through the fabric. Then, supercritical carbon dioxide was passed through the pressure tube. The contaminated supercritical stream comprising the supercritical carbon dioxide. After 7 hours supercritical carbon dioxide exposure with a molar ratio of 1 at 230 °C and at a constant flow of the supercritical carbon dioxide of 25 g / min. The colour of the textile samples was only measured when the colour change after exposure was homogeneous for the whole sample area. Sample p T IV AA Benzene L a b (bar) (°C) dg / l mg / kg mg / kg (-) (-) (-) Original 1 20 0.575 0.54 < 0.02 48.89 92.11 14.7 1 70 230 0.907 0.21 < 0.02 Discolouration not homogeneous 2 100 230 0.713 N.A. N.A. Discolouration not homogeneous 3 200 230 0.639 N.A. N.A. 82.58 2.45 4.69 4 300 230 0.449 0.36 < 0.02 82.20 2.41 5.21 5 0.01 220 0.657 0.61 < 0.02 No discolouration

Claims

Claims 1. Method of producing a decolourised polymeric material, the method comprising contacting a solid coloured polymeric material comprising a polymeric material and a colourant with a supercritical stream to form a decolourised polymeric material and a contaminated supercritical stream comprising a colourant, wherein the supercritical stream comprises 90 mol% or more, relative to total supercritical stream, of one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, and wherein the contacting is performed at a temperature of 150 °C or more and below the melting temperature of the polymeric material or below the Tei,m of the polymeric material as determined in accordance with ISO 11357-1 / 3:2023.

2. Method according to claim 1, wherein the solid coloured polymeric material is contacted with the supercritical stream comprising 90 mol% or more, relative to total supercritical stream, of one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, at a pressure above 70 bar, preferably 100-350 bar, and preferably at a temperature of 250 °C or less.

3. Method according to claim 1, wherein the solid coloured polymeric material is contacted with the supercritical stream comprising one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol, and supercritical ethanol, and 50 mol% or less, relative to total supercritical stream, of one or more co-solvents selected from alcohol, dimethyl sulphoxide, dimethylformamide, acetone, ozone, alkane, alkene, SO2, and NOx, at apressure of 70-280 bar, preferably 100-200 bar, and preferably at a temperature of 100-200 °C.

4. Method according to any one of claims 1-3, wherein the co-solvent comprises an alcohol selected from the group consisting of methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol, butan-2-ol, 2-methylpropan-1-ol, 2-methylpropan-2-ol, pentan-1-ol, pentan-2-ol, pentan-3-ol, 2-methylbutan-1-ol, 2-ethylbutan-2-ol, 2,2-dimethylpropan-1-ol, 3-methylbutan-1-ol, 3-methylbutan-2-ol, hexan-1-ol, hexan-2-ol, hexan-3-ol, 2-methylpentan-1-ol, 3-methylpentan-1-ol, 4-methylpentan-1-ol, 2-methylpentan-2-ol, 3-methylpentan-2-ol, 4-methylpentan-2-ol, 2-methylpentan-3-ol, 3-methylpentan-3-ol, 2,2-dimethylbutan-1-ol, 2,3-dimethylbutan-1-ol, 3,3-dimethylbutan-1-ol, 2,3-dimethylbutan-2-ol, 3,3-dimethylbutan-2-ol, 2-ethylbutan-1-ol.

5. Method according to any one of claims 1-4, wherein the supercritical stream comprises supercritical carbon dioxide and 30 mol% or less, relative to total supercritical stream, of an alcoholic solvent.

6. Method according to any one of claims 1-5, wherein the co-solvent comprises an alkane selected from the group consisting of methane, ethane, propane, butane, methylpropane, pentane, 2-methylbutane, 2,2-dimethylpropane, hexane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2,2-dimethylbutane, and any combination thereof.

7. Method according to any one of claims 1-6, wherein the co-solvent comprises an alkene selected from the group consisting of ethene, propene, but-1-ene, but-2-ene, 2-methylprop-1-ene, pent-1-ene, pent-2-ene, 2-methylbut-1-ene, 2-methylbut-2-ene, 3-methylbut-1-ene, hex-1-ene, hex-2-ene, hex-3-ene, 2-methylpent-1-ene, 3-methylpent-1-ene,4-methylpent-1-ene, 2-methylpent-2-ene, 3-methylpent-2-ene, 4-methylpent-2-ene, 2,3-dimethylbut-1-ene, 3,3-dimethylbut-1-ene, 2-ethylbut-1-ene, 2,3-dimethylbut-2-ene, and combination thereof.

8. Method according to any one of claims 1-7, wherein the coloured polymeric material is fibre-based.

9. Method according to any one of claims 1-8, wherein the coloured polymeric material is in the form of polymeric polymeric chips, flakes, shreds, crumbs, and / or granules.

10. Method according to any one of claims 1-9, wherein the polymeric material is a polyester 11. Method according to claim 10, wherein the polyester isone or more selected from polyethylene terephthalate, polybutylene terephthalate, polyhexamethylene terephthalate, polypropylene terephthalate, polyethylene naphthalate, polyethylene furanoate, polybutylene succinate, polylactic acid, polyhydroxyalkanoates, polybutylene adipate terephthalate, and poly(hydroxybutyrate-co-valerate).

12. Method of producing a decolourised polymeric material, the method comprising melt filtering a coloured polymeric feed comprising a polymeric material, a colourant, and a solid additive, thereby obtaining a flowable coloured polymeric material and solid additive, and contacting at least part of the flowable coloured polymeric material with a supercritical stream comprising supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical methanol,and supercritical ethanol, and optionally a co-solvent, to form decolourised polymeric material and a contaminated supercritical stream, wherein the flowable coloured polymeric material is contacted with the supercritical stream at or above the melting temperature or at a temperature at or above the Tef,m of the polymeric material as determined in accordance with ISO 11357-1 / 3:2023.

13. Method according to claim 12, wherein the supercritical stream is provided as a counter-current flow with respect to the flowable coloured polymeric material flow direction.

14. Method according to claims 12 or 13, wherein the coloured polymeric feed that is melt filtered has an amount of solvent of 5 % or less by total weight of the polymeric feed.

15. Method according to any one of claims 1-14, further comprising separating at least part of the contaminated supercritical stream to obtain a purified supercritical stream and colourant, and recycling at least part of the purified supercritical stream to the contacting with the coloured polymeric material.

16. Method according to claim 15, wherein said separating comprises contacting the contaminated supercritical stream with a non-volatile liquid stream.

17. Method according to any one of claims 1-16, wherein the decolourised polymeric material comprises less than 50 ppb of benzene and / or less than 1000 ppb of acetaldehyde.

18. Method according to any one of claims 1-17, wherein the contacting with the supercritical stream is performed at a temperature of 200 ºC or more and lower than the melting temperature of the polymeric material, wherein the decolourised polymeric material has a higher intrinsic viscosity at temperature of 20 °C than the solid coloured polymeric material.

19. The method according to claim 18, wherein the polymeric material is a polyester.

20. Method according to any one of claims 1-19, wherein the decolourised polymeric material has a higher L colour value than the solid coloured polymeric material, preferably wherein L value is 80 or more.

21. Method according to any one of claims 1-20, wherein the decolourised polymeric material has a b colour value in the range between -4 and 4.

22. Method according to any one of claims 1-21, wherein the decolourised polymeric material has an a colour value in the range between -3 and 3.

23. Method according to any one of claims 1-22, wherein the coloured polymeric material further comprises one or more additives and wherein 80 % or more by total weight of the coloured polymeric material of one or more additives is removed from the coloured polymeric material.

24. Decolourised polymeric material obtainable by a method according to any one of claims 1-23.

25. Method of producing a purified supercritical stream, the method comprising contacting a contaminated supercritical stream comprising a contaminant and a supercritical stream comprising one or more selected from supercritical carbon dioxide, supercritical alkane, supercritical alkene, supercritical nitrogen, supercritical alcohol, e.g. supercritical methanol and / or supercritical ethanol, supercritical dimethyl sulphoxide, supercritical acetone, supercritical ozone, with a non-volatile liquid stream, thereby yielding a purified supercritical stream and a contaminated non-volatile liquid stream, wherein the method is carried out in a separation system comprising a separation vessel, wherein the separation vessel comprises an inlet for the non-volatile liquid stream, an inlet for the contaminated supercritical stream, an outlet for the purified supercritical stream, and an outlet for the contaminated non-volatile liquid stream.

26. Method according to claim 25, wherein the method further comprises purifying the contaminated non-volatile liquid stream carried out in an non-volatile liquid purification system, thereby yielding a purified non-volatile liquid stream, wherein the non-volatile liquid purification system comprises an inlet for the contaminated non-volatile liquid stream and an outlet for the purified non-volatile liquid stream, wherein the outlet for the contaminated non-volatile liquid stream in the separation vessel is in a fluid communication with the inlet for the contaminated non-volatile liquid stream in the non-volatile liquid purification system, and wherein the outlet for the purified non-volatile liquid stream in the non-volatile liquid purification system is in a fluid communication with the inlet for the non-volatile liquid stream in the separation vessel.

27. Method according to claim 25 or 26, wherein the supercritical stream comprises supercritical carbon dioxide.

28. Method according to any one of claims 25-27, wherein the contaminant is a colourant.

29. Method according to any one of claims 1-23, wherein the method further comprises the method steps according to any one of claims 25-28.