Method for preparing biogas from a residue of a polymer blend comprising a cellulose based polymer

Abstract

In a first aspect, the invention relates to a method for preparing biogas comprising providing a polymer blend, which comprises (i) a polyester and (ii) optionally one or more component(s) selected from the group consisting of a second polymer, a colorant, and a filler; (iii) a cellulose based third polymer; wherein the optional second polymer (ii) and the cellulose based third polymer (iii) are different from each other and different from the polyester of (i); the method comprising: a step (e), related to preparing biogas from the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in a preceding step (c).

Description

[0001] Method for preparing biogas from a residue of a polymer blend comprising a cellulose based polymer

[0002] In a first aspect, the invention relates to a method for preparing biogas comprising providing a polymer blend, which comprises (i) a polyester and (ii) optionally one or more component(s) selected from the group consisting of a second polymer, a colorant, and a filler; (iii) a cellulose based third polymer; wherein the optional second polymer (ii) and the cellulose based third polymer (iii) are different from each other and different from the polyester of (i); the method comprising: (a) providing the polymer blend and providing a solvent system comprising gamma valerolactone (GVL) or dimethyl sulfoxide (DMSO) or a mixture of GVL and DMSO, which comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the solvent system being 100 weight-%; (b) optionally contacting the polymer blend with the solvent system at a temperature T1 of < 170 °C, thereby obtaining a solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and a residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler; (c) contacting the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) with a solvent system at a temperature T2 of > 170 °C, thereby obtaining a solvent system, which is enriched in dissolved polyester compared to the solvent system provided in (a) and comprises optionally the filler or a part of the filler, and a residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler; (d) optionally precipitating the polyester from solvent system, which is enriched in dissolved polyester, obtained in (c), thereby obtaining a precipitated polyester and a solvent system, which is depleted in dissolved polyester and which optionally comprises the filler or a part of the filler; (e) preparing biogas from the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c); wherein neither before (b) nor in-between steps (b) and (c) nor before step (c) the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) is contacted with an acidic component and / or a basic component. A second aspect of the invention relates to a method for preparing biogas from cellulose based polymer separated from a polymer blend comprising (i) separation of cellulose based polymer from a polymer blend comprising cellulose based polymer and at least one further polymer different from the cellulose based polymer, thereby obtaining a separated cellulose based polymer fraction; (ii) treating the cellulose based polymer fraction obtained in (i) with a solvent system comprising gamma valerolactone (GVL), which comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the solvent system being 100 weight-%, thereby obtaining a treated cellulose based polymer fraction; (iii) preparing biogas from the treated cellulose based polymer fraction obtained in (ii); wherein neither before step (i) nor during step (i) nor in-between steps (i) and (ii) the polymer blend or the separated cellulose based polymer fraction is contacted with an acidic component and / or a basic component. In a third aspect, the invention is directed to biogas, preferably biogas comprising methane, obtained or obtainable from the method of the first or the second aspect. A fourth aspect of the invention relates to the use of biogas according to the third aspect as carbon and / or hydrogen source; and / or the use of biogas according to the third aspect as source of energy, preferably as source of thermal energy, for one or more of the steps (b) to (d). A fifth aspect of the invention is related to a polyester obtained or obtainable from the method of the first or the second aspect. A sixth aspect of the invention relates to the use of the polyester of the fifth aspect for textile applications, fiber applications, packaging applications, plastic applications, automotive applications, and / or electronic applications. In a seventh aspect, the invention is related to a method for preparing a product comprising (I) providing polyester of the fifth aspect; and (II) preparing a textile, a fiber, a packaging, a plastic, an automotive part, an electronic part from the polyester provided in (I). An eight aspect of the invention relates to a method focused on obtaining a separated fraction comprising the second polymer; and a ninth aspect of the invention relates to a method focused on converting the second polymer and / or the re-ob- tained polyester to obtain one or more monomer, polymer or polymer product.

[0003] State of the art

[0004] The demand for polymeric materials has drastically increased over the last decades. However, the poor biodegradability has led to large amounts of plastic waste which is in Europe usually incinerated thereby losing valuable materials and generating huge CO2 emissions. Even worse is landfill due to the poor biodegradability. Polymeric materials based on polyesters have been used extensively in the packaging sector, for example, in beverage packaging or food packaging. The vast majority of food and drink today is packaged within plastic bottles and containers, made from, for example, polyester materials comprising polyethylene terephthalate (PET). PET is also a main component of clothing nowadays. As these materials typically have poor biodegradability and are also still valuable products, it is desirable for these plastics to be recovered and recycled. Furthermore, especially many textiles comprise, aside from polyester, also large amounts of natural polymers such as cotton, which, due to being mixed-up with synthetic polymers, is almost lost for further use. Several attempts have been made to put such natural polymers such as cotton to further use, or at least, to improve, for example, its digestibility: Anacleto et al. (2022) have summarized various pretreatment methods to improve anaerobic digestion of textile waste and textile dying sludges, such as enzymatic, (thermo)chemical, biological and physical pretreatment methods, including also commonly used treatments such as with NaOH and 4-methylmorpholine 4-oxide (NMMO) (Anacleto, T.M.; Kozlowsky-Suzuki, B.; Wilson, A.E.; Enrich-Prast, A. Comprehensive Meta-Analysis of Pathways to Increase Biogas Production in the Textile Industry. Energies 2022, 15, 5574. https: / / doi.org / 10.3390 / en15155574). Hasanzadeh et al. (2018) have applied Na2CC>3 treatment for hydrolysis of the polyester and the cotton part of mixed textiles. It was found that Na2COs treatment did improve biogas yield in subsequent anaerobic digestion (Elnaz Hasanzadeh, Safoora Mirmohamadsadeghi, Keikhosro Karimi, Enhancing energy production from waste textile by hydrolysis of synthetic parts, Fuel, Volume 218, 2018, Pages 41-48, ISSN 0016-2361 , https: / / doi.Org / 10.1016 / j.fuel.2018.01.035). Kumar et. al (2020) have shown a codigestion of textile aerobic sludge with cow dung and food waste in lab scale BMP tests (0.5L). Here, the textile aerobic sludge used for the BMP test was collected from an effluent treatment plant of a textile facility and was already faced with microbial degradation during the aerobic treatment (Kumar, P., Samuchiwal, S. & Malik, A. Anaerobic digestion of textile industries wastes for biogas production. Biomass Conv. Bioref. 10, 715-724 (2020). https: / / doi.org / 10.1007 / s13399-020-00601-8). Xiang et al (2016) have tested different pretreatment methods for anaerobic digestion of organic compounds in textile dyeing sludges during textile manufacturing. (Xinyi Xiang, Xiaoguang Chen, Ruobin Dai, Ying Luo, Puyue Ma, Shengsheng Ni, Chengyu Ma, Anaerobic digestion of recalcitrant textile dyeing sludge with alternative pretreatment strategies, Bioresource Technology, Volume 222, 2016, Pages 252-260, ISSN 0960-8524, https: / / doi.Org / 10.1016 / j.biortech.2016.09.098).

[0005] Among other drawbacks, most of the commonly used methods have to rely on abrasive chemicals such as NaOH and / or have to use solvents, which are at least irritant, such as NMMO. Furthermore, it was so far not possible to use mixed materials such as polymer blends for microbial fermentation. Thus, there is still a need to further simplify the separation of natural polymers such as cotton and / or to improve its digestibility for increasing, for example, biogas yield in a microbial fermentation, while avoiding or at least minimizing the use of toxic solvents etc.

[0006] The technical problem underlying the present invention was thus the provision of a method for separating natural cellulose-based polymers from a polymeric material, which overcomes these disadvantages, and which especially enables obtaining a digestible cellulose-based polymer.

[0007] In a first aspect, the invention relates to a method for preparing biogas comprising providing a polymer blend, which comprises

[0008] (i) a polyester and

[0009] (ii) optionally one or more component(s) selected from the group consisting of a second polymer, a colorant, and a filler;

[0010] (iii) a cellulose based third polymer; wherein the optional second polymer (ii) and the cellulose based third polymer (iii) are different from each other and different from the polyester of (i); the method comprising:

[0011] (a) providing the polymer blend and providing a solvent system;

[0012] (b) optionally contacting the polymer blend with the solvent system at a temperature T1 of < 170 °C, thereby obtaining a solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and a residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler;

[0013] (c) contacting the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) with a solvent system at a temperature T2 of > 170 °C, thereby obtaining a solvent system, which is enriched in dissolved polyester compared to the solvent system provided in (a) and comprises optionally the filler or a part of the filler, and a residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler;

[0014] (d) optionally precipitating the polyester from solvent system, which is enriched in dissolved polyester, obtained in (c), thereby obtaining a precipitated polyester and a solvent system, which is depleted in dissolved polyester and which optionally comprises the filler or a part of the filler;

[0015] (e) preparing biogas from the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c).

[0016] It was surprisingly found that the inventive method not only enables to separate a cellulose base polymer from a polymer blend comprising also a polyester, but furthermore that the separated, cellulose based polymer comprising residue is usable in biogas preparation with an efficiency comparable to other, commonly used, pre-treatments.

[0017] In some embodiments, the method for preparing biogas comprises providing a polymer blend, which comprises

[0018] (i) a polyester and (ii) optionally one or more component(s) selected from the group consisting of a second polymer, a colorant, and a filler;

[0019] (iii) a cellulose based third polymer; wherein the optional second polymer (ii) and the cellulose based third polymer (iii) are different from each other and different from the polyester of (i); the method comprising:

[0020] (a) providing the polymer blend and providing a solvent system comprising gamma valerolactone (GVL) or dimethyl sulfoxide (DMSO) or a mixture of GVL and DMSO, which comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the solvent system being 100 weight-%;

[0021] (b) optionally contacting the polymer blend with the solvent system at a temperature T1 of < 170 °C, thereby obtaining a solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and a residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler;

[0022] (c) contacting the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) with the solvent system at a temperature T2 of > 170 °C, thereby obtaining a solvent system, which is enriched in dissolved polyester compared to the solvent system provided in (a) and comprises optionally the filler or a part of the filler, and a residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler;

[0023] (d) optionally precipitating the polyester from the solvent system, which is enriched in dissolved polyester, obtained in (c), thereby obtaining a precipitated polyester and a solvent system, which is depleted in dissolved polyester and which optionally comprises the filler or a part of the filler;

[0024] (e) preparing biogas from the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c); wherein neither before (b) nor in-between steps (b) and (c) nor before step (c) the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) is contacted with an acidic component and / or a basic component. The expression “contacted with an acidic component and / or a basic component” with respect to beforehand steps and / or in-between steps means that the respective material is not brought into contact with a medium, which comprises > 1 weight-%, preferably > 2 weight-%, more preferably > 4 weight-%, more preferably > 4 weight-%, more preferably > 5 weight-%, more preferably > 6 weight-%, more preferably > 8 weight-%, more preferably > 10 weight-% of acidic and / or basic component(s) based on the total weight of the medium being 100 weight-%

[0025] Conducting no step of contacting with an acidic component and / or a basic component, neither before (b) nor in-between steps (b) and (c) nor before step (c) offers the advantage that a process with a reduced number of steps is achieved, this making the process economically advantageous.

[0026] Preferably, the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the residue being 100 weight-%. Preferably, the precipitated polyester obtained in (d) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the precipitated polyester being 100 weight-%.

[0027] Using a solvent system comprising gamma valerolactone (GVL) , which is essentially free of acidic and / or basic component(s) and avoiding steps of contacting with an acidic component and / or a basic component before (b) and in-between steps (b) and (c) and before step (c) allows to obtain the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler in (c) with essentially no acidic and / or basic component(s) contained therein. This, in turn, allows obtaining the residue of the polymer blend with a pH value in the range of from 3.5 to 7 i.e. close to the pH value, preferably around 5.5 to 7, required by cellulolytic bacteria for optimal hydrolysis of cellulosic material and subsequent use microbial breakdown to biomethane, bio-CCh and bio-C2-C7 acids, which consequently, allows to omit or at least to reduce the amount of required washing solvent. This makes the process more economical and environmentally beneficial.

[0028] “Contacting” in optional step (b) and in step (c) preferably means that the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) is at least partially immersed in the solvent system. Preferably, polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) is at least partially immersed in the solvent system in that at least 60 %, more preferably at least 70 %, more preferably at least 80 %, more preferably at least 90 %, more preferably at least 95 %, more preferably at least 99 % of the surface of the polymer blend provided in (a) or of the residue of the polymer blend optionally obtained in (b) are in contact with the solvent system, based on the total surface of the f the polymer blend provided in (a) or of the residue of the polymer blend optionally obtained in (b) being 100%. Regarding optional step (b), “enriched in second polymer” means that at least 50 weight-%, preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, of the second polymer - if present - comprised in the material provided in (a), are dissolved in the solvent system based on 100 weight-% of the second polymer - if present- comprised in the material provided in (a). “Depleted of said second polymer and” regarding the residue (optionally) obtained in (b) means that < 50 weight-%, preferably < 40 weight-%, more preferably < 30 weight- %, more preferably < 20 weight-%, more preferably < 10 weight-%, more preferably < 5 weight- %, of the second polymer - if present - comprised in the material provided in (a), are still present in the residue, based on 100 weight-% of the second polymer - if present- comprised in the material provided in (a). Regarding optional step (b), “enriched in colorant” means that at least 50 weight-%, preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, of the colorant - if present comprised in the polyester of the material provided in (a) are dissolved in the solvent system, based on 100 weight-% of the colorant - if present - comprised in the polyester comprised in the material provided in (a). “Depleted of said colorant” regarding the residue (optionally) obtained in (b) means that < 50 weight-%, preferably < 40 weight-%, more preferably < 30 weight-%, more preferably < 20 weight-%, more preferably < 10 weight-%, more preferably < 5 weight-%, of the colorant - if present - comprised in the polyester comprised in the material provided in (a), are still present in the residue, based on 100 weight-% of the colorant - if present - comprised in the polyester comprised in the material provided in (a). This means that colorant, which is comprised in the polyester (i), is comparatively easy removed in step (b), i.e. is dissolved together with the polyester in the solvent system in step (c), whereas colorant being comprised in third polymer - if present- is not easily dissolved but rather remains to a large extend in the third polymer and thus also in the residue comprising said third polymer. Regarding step (c), “solvent system, which is enriched in dissolved polyester compared to the solvent system provided in (a)” means that at least 50 weight-%, preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, of the polyester comprised in the material provided in (a), are dissolved in the solvent system based on 100 weight-% of the polyester comprised in the material provided in (a). Regarding the optionally obtained residue of the polymer blend of step (c), “depleted of polyester and comprises optionally the third polymer” means that < 50 weight-%, preferably < 40 weight-%, more preferably < 30 weight-%, more preferably < 20 weight-%, more preferably < 10 weight-%, more preferably < 5 weight-%, of the polyester comprised in the material provided in (a), are still present in the residue, based on 100 weight-% of the polyester comprised in the material provided in (a), wherein still at least 50 weight-%, preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, of the third polymer -if present- comprised in the material provided in (a), are present in the residue, based on 100 weight-% of the third polymer - if present - comprised in the material provided in (a). Regarding optional step (d), “solvent system, which is depleted in dissolved polyester” means that compared to 100 weight-% of polyester comprised in the solvent system obtained in (c), at least 50 weight-%, preferably at least 60 weight- %, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, are precipitated and no longer dissolved in the solvent system. The expressions “enriched optionally in filler or a part of the filler” regarding the solvent system obtained in (b) and “depleted optionally of the filler or a part of the filler” regarding the residue obtained in (b) mean that, if a filler is present in the polymer blend provided in (a), which is soluble in a solvent system at a temperature T 1 , said soluble filler is also dissolved in the solvent system, which is obtained in (b), and, consequently, the residue is depleted thereof. In case that not (only) a filler soluble at T1 is present in the polymer blend provided in (a) but (also) a filler, which is not soluble in a solvent system at a temperature T1 , said insoluble filler remains in the residue of the polymer blend obtained in (b). If that insoluble filler is then soluble at T2 in a solvent system, said insoluble filler is then dissolved in the solvent system at T2 and, consequently, the solvent system obtained in (c) is enriched in said filler and the residue obtained in (c) is depleted thereof. In cases where the polymer blend provided in (a) comprises only filler(s) soluble in in a solvent system at a temperature T1 , no filler remains in the residue of the polymer blend obtained in (b), and consequently, also the residue obtained in (c) does not contain filler. In cases where only filler(s) insoluble in in a solvent system at a temperature T2 are contained in the polymer blend provided in (a), all filler(s) remain(s) in the residue of the polymer blend obtained in (b), but are, consequently, then all dissolved in the solvent system at T2 and thus, the residue obtained in (c) does not contain filler. In cases where the polymer blend provided in (a) comprises filler(s) insoluble in in a solvent system at a temperature T1 and filler(s) insoluble in in a solvent system at a temperature T2, these insoluble filler(s) is / are retained in the residue obtained in (c).

[0029] Cellulose based third polymer (Hi)

[0030] In some embodiments of the method, the cellulose based third polymer is selected from the group consisting of natural cellulose based polymer, synthetic cellulose based polymer and mixtures of one or more natural cellulose based polymer(s) and one or more synthetic cellulose based polymer(s), wherein a natural cellulose based polymer is preferably selected from the group consisting of cotton, cellulose, lignin, linen, viscose and mixtures of two or more thereof and wherein a synthetic cellulose based polymer is preferably viscose, wherein the cellulose based polymer preferably comprises at least cotton, more preferably at least 65 weight-%, more preferably at least 70 weight-%, more preferably at least 75 weight-%, more preferably at least 80 weight-%, more preferably at least 85 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-% of the cellulose based polymer are cotton, based on the total weight of the cellulose based polymer being 100 weight-%, more preferably the cellulose based polymer is cotton.

[0031] Biogas preparation in (e)

[0032] In some embodiments of the method, preparing biogas from the residue of the polymer blend according to (e) comprises microbial fermentation, more preferably anaerobically microbial fermentation.

[0033] In some embodiments of the method, the residue of the polymer blend is used in microbial fermentation, preferably in anaerobically microbial fermentation, as substrate or co-substrate for biogas generation.

[0034] Microbial fermentation is herein also called digestion. Biogas (methane) generation is done using state-of the art anaerobic digesters. Common reactor types and process regimes for anaerobic digestion are described in the literature (e.g. Banerjee S, Prasad N, Selvaraju S. Reactor Design for Biogas Production-A Short Review. Journal of Energy and Power Technology 2022; 4(1): 004; doi: 10.21926 / jept.22O1004.). Suitable reactor types for the anaerobic digestion of the polymer blend are, among others, anaerobic plug-flow reactors (APFR), biofilm reactor with moving or fixed bed, continuous flow stirred-tank reactors (CSTR), anaerobic contact reactor (ACR), batch reactors, anaerobic baffled reactor (ABR) or hybrid bioreactors. These reactor types can be applied as single-, two or multistage systems and in combinations with different reactor concepts.

[0035] In some embodiments of the method, microbial fermentation, preferably anaerobically microbial fermentation, is done at a pH value in the range of from 4 to 9, preferably in the range of from 4.5 to 8.5, more preferably in the range of from 4.5 to 8.

[0036] Preferably, the pH value varies, especially in multistage systems, in the first and the subsequent fermentation stages and vessels from pH 4 to pH 9, preferably in the range of from 4.5 to 8.5, more preferably in the range of from 4.5 to 8. The reactors are operated in continuous or discontinuous mode, with or without agitation or active gassing. The anaerobic digestion of the residue of the polymer blend is conducted at a temperature in the range of from 10 to 60 °C, preferably at psychrophilic temperatures (10 to 30 °C), mesophilic (30 to 40 °C) and / or thermophilic (up to 60 °C) conditions. The biogas resulting from the microbial fermentation comprises methane and has a composition which varies during the anaerobic digestion. Typical composition of the biogas are methane (CH4): in the range of from 40 to 70 volume-%, carbon dioxide (CO2): in the range of from 30 to 60 volume-% , other gases: in the range of from 1 to 5 volume-%, including hydrogen (H2): in the range of from 0 to 1 volume-% and hydrogen sulfide (H2S): in the range of from 0 to 3 volume-% based on the total volume of the obtained biogas being 100 vol- ume-%.

[0037] The residue of the polymer blend can be used as sole substrate for anaerobic digestion. To improve microbial growth and biogas production, one or more enzyme(s) from the class of cellulases, proteases, amylases, pectinases, lipases and PETases as well as nutrient solutions can be added to the reactor. Also, trace elements such as iron, zinc, cobalt, nickel, molybdenum and / or tungsten can be added to the bioreactor to improve microbial growth. Typical trace elements for anaerobic digestion are listed in the literature (e.g. in Trace Elements in Anaerobic Biotechnologies Edited by: Fernando G. Fermoso, Eric van Hullebusch, Gavin Collins, Jimmy Roussel, Ana Paula Mucha, Giovanni Esposito, https: / / doi.org / 10.2166 / 9781789060225, ISBN (electronic): 9781789060225, Publisher: IWA Publishing, Published: 2019; also in

[0038] Zhang, Wenxiang Ouyang, Aimin Lia, Essential Role of Trace Elements in Continuous Anaerobic Digestion of Food Waste, Procedia Environmental Sciences, Volume 16, 2012, Pages 102- 111 , ISSN 1878-0296, https: / / doi.Org / 10.1016 / j.proenv.2012.10.014. Further trace elements are listed in Bardi, M.J., Aminirad, H. Synergistic effects of co-trace elements on anaerobic co-di- gestion of food waste and sewage sludge at high organic load. Environ Sci Pollut Res 27, 18129-18144 (2020). https: / / doi.org / 10.1007 / s11356-020-08252-y

[0039] The residue of the polymer blend can also be added as a co-substrate in anaerobic reactors. Share of the residue of the polymer blend varies from of 0.1 to 50 weight-% within the total amount of feedstocks applied being 100 weight-%. Suitable feedstocks for biogas generation and for combination with the polymer blend residue are all kinds of biodegradable biomasses and organic wastes, for example agricultural wastes, energy crops, manure and sludges from livestock farming, waste water treatment sludges, the organic fraction of municipal solid waste, food-processing waste, waste streams from the beverage industry, cellulosic residues from the wood processing and pulp- and paper industry, as well as chemical wastes.

[0040] Anaerobic digestion can take place for at least 2 days of hydraulic retention time, more preferably for a period of time in the range of from 20 to 100 days, or even longer and at an organic loading in the range of from 0.05 to 5 g VS / liter / day (VS = volatile solids). The biogas produced comprises methane as indicated above and is preferably purified and concentrated, e.g., to replace natural fossil gas. Suitable purification methods are, among others, water scrubbing, cryogenic separation, adsorption (physical and chemical), membrane technologies, biological upgrading and in-situ upgrading methods. Various technologies for purification of biogas are described in the literature, e.g. in Zabava, Bianca-Stefania & Voicu, Gheorghe & Ungureanu, Nicoleta & Dinca, Mirela & G., Paraschiv & Munteanu, Mariana & Ferdes, Mariana. (2019). Method of Biogas Purification - a review.

[0041] Biogas comprising at least 40 volume-% methane is in some embodiments used as source of energy, preferably as source of thermal energy for one or more of the steps (b) to (d). The biogas is used directly or indirectly as source of thermal energy, i.e. it is burned and the burning heat is used for preparation of water steam or is used for generating electricity, which may be by also used in the process according to the present invention in one or more of the steps (a) to (f).

[0042] In some embodiments, the method comprises after (e)

[0043] (f) separating methane from the biogas obtained in (e) by one or more purification and / or concentration step(s), thereby obtaining methane (CH4) with a purity of at least 85 volume- %, more preferably at least 90 volume-%, even more preferably at least 95 volume-%, based on the total volume of the gas phase containing CH4 being 100 volume-%.

[0044] Intermediate steps

[0045] In some embodiments, the method comprises, if (b) is conducted, after (b) and before (c) (u) separating the solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and the residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler, thereby obtaining a separated solvent system enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler and a separated residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler.

[0046] Separation in (u) is preferably done by methods and means known to the skilled person, especially solid-liquid separation methods such as filtration, for example, heated pressure filtration, sedimentation or centrifugation (see Handbuch der mechanischen Fest-Flussig-Tren- nung Taschenbuch - 29. April 2004 von Klaus Luckert (Herausgeber)).

[0047] In some embodiments, the method comprises, if (b) is conducted, after (b) and before (c):

[0048] (v) washing the residue of the polymer blend obtained in (b) with a washing solvent, thereby obtaining a washed residue, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the third polymer and optionally the filler or a part of the filler;

[0049] (w) optionally drying the washed residue obtained in (v).

[0050] In some embodiments, the method comprises, if (b) is conducted, after (b), preferably after (u), and before (c):

[0051] (v) washing the (separated) residue of the polymer blend obtained in (b) or in (u) with a washing solvent, thereby obtaining a washed residue, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the third polymer and optionally the filler or a part of the filler;

[0052] (w) optionally drying the washed residue obtained in (v).

[0053] Washing in optional step (v) is preferably done with a solvent system having features (s.1 ), (s.2) and (s.3) as defined herein, preferably with a solvent system comprising one or more of the solvents) of any one of the groups defined herein. Preferably, washing in optional step (v) is done with the same solvent system as used for (b). In some embodiments, washing is done with a solvent selected from the group consisting of methanol, ethanol, propanol, isopropanol, acetonitrile, ethyl acetate, acetone, water or a mixture of two or more of these solvents. In some embodiments, the washing in optional step (v) is done with a solvent selected from the group consisting of methanol, ethanol, propanol, isopropanol, acetonitrile, ethyl acetate, acetone, water, GVL, or a mixture of two or more of these solvents, preferably with a solvent comprising at least GVL, more preferably the washing in optional step (v) is done with GVL . Drying in optional step (w) is preferably done under one or more conditions selected from the group consisting of a pressure in the range of from 1 to 1013 mbar; a temperature in the range of from 50 to 210 °C, preferably in the range of from 60 to 180°C, more preferably in the range of from 80 to 160 °C; drying time in the range of from 30 minutes to 24 hours; drying in an atmosphere comprising nitrogen, preferably in an atmosphere having at least 90 volume-%, more preferably 95 volume- %, more preferably at least 98 volume-% nitrogen. Drying is done by one or more methods selected from the group consisting of contact drying, convection drying and radiation drying. Contacting in step (c) is then done based on the washed (and optionally dried) residue obtained in (b). In some preferred embodiments, the method comprises after (c) and before step (d), if conducted, or after (c) and before step (e), if (d) is not conducted:

[0054] (w.1) optionally washing the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c) with acetone;

[0055] (w.2) washing the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler obtained in (c) or obtained in optional step (w.1) with water; wherein washing in (w.2) is preferably done until the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, comprises less than 10 weight-%, preferably less than 5 weight-%, more preferably less than 2 weight-%, of organic solvent(s), based on the total weight of the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, being 100 weight-%.

[0056] In some embodiments, the method comprises after (c) and before step (d), if conducted, or before step (e)

[0057] (x.1) separating the solvent system, which is enriched in dissolved polyester and comprises optionally the filler or a part of the filler obtained in (c) from the residue of the polymer blend, wherein the separation is preferably done by heated filtration, more preferably by heated filtration at a temperature T3 in the range of from T2 minus 20 °C to T2 plus 20 °C (T3 = T2 ± 20°C), more preferably at a temperature T3 in the range of from T2 minus 10 °C to T2 plus 10 °C (T3 = T2 ± 10°C), thereby obtaining the solvent system, which is enriched in dissolved polyester and comprises optionally the filler or a part of the filler, separated;

[0058] (x.2) optionally contacting said residue of the polymer blend obtained in (x.1) with solvent system, preferably at a temperature T3 as defined above in (x.1), followed by filtration, preferably heated filtration at a temperature T3 as defined above in (x.1), thereby obtaining a residue of the polymer blend, which is further depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler; and a solvent system, which contains further amount of the polyester and comprises optionally the filler or a part of the filler;

[0059] (x.3) optionally combining the solvent system, which contains the further amount of the polyester and comprises optionally the filler or a part of the filler obtained in (x.2) with the solvent system, which is enriched in dissolved polyester and comprises optionally the filler or a part of the filler, separated in (x.1); wherein precipitation in (d) is done based on the separated solvent system obtained in (x.1) or based on the combined solvent system obtained in (x.3). In heated filtration, the solution, filter, and funnel are heated, preferably heated so that each has temperature T3. Other means and methods for the separation in (x.1) are known to the skilled person such as non-heated filtration. In some embodiments, it is preferred that the heated filtration is done under a pressure of >1 bar, more preferably at a pressure in the range of from 1 bar to 30 bar, preferably in the range of from 1 to 10 bar, more preferably in the range of from 1 to 6 bar (heated pressure filtration). Preferably, the filter used in heated filtration is stable, especially does not dissolve or degrade, at the respective conditions and in connection with the respective solvent system. For example, the filter may be made of polyetheretherketone.

[0060] Preferably, the contacting in (x.2) is done in that, especially in cases where heated filtration is used in (x.1), the residue of the polymer blend obtained in (x.1) remains on the filter and is there brought into contact with solvent system, wherein the solvent system, which contains the remaining amount of the polyester and comprises optionally the filler or a part of the filler obtained in (x.2), is separated thereof due to filtration. In some embodiments, the solvent system, which contains the remaining amount of the polyester and comprises optionally the filler or a part of the filler obtained in (x.2) is combined with the solvent system, which is enriched in dissolved polyester and comprises optionally the filler or a part of the filler, obtained in (x.1).

[0061] In some embodiments, the method comprises after (c) and before step (d), if conducted, or after (c) and before step (e), if (d) is not conducted, and after (x.1) to (x.3) if conducted:

[0062] (x.4) optionally washing the residue of the polymer blend, which is further depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler obtained in (x.2) with acetone, thereby obtaining an acetone-washed residue;

[0063] (x.5) washing the residue of the polymer blend, which is further depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler obtained in (x.2) or the acetone-washed residue obtained in optional step (x.4) with water; wherein washing in (x.5) is preferably done until the residue of the polymer blend, comprises less than 10 weight-%, preferably less than 5 weight-%, more preferably less than 2 weight-%, of organic solvent(s), based on the total weight of the residue of the polymer blend being 100 weight-%.

[0064] In some embodiments, the method comprises after (d) and before (e)

[0065] (y.1) separating the precipitated polyester obtained in (d) from the solvent system, which is depleted in dissolved polyester and comprises optionally the filler or a part of the filler, thereby obtaining a precipitated polyester and the solvent system, which is depleted in dissolved polyester and which optionally comprises the filler or a part of the filler;

[0066] (y.2) optionally washing the precipitated polyester obtained in (y.1); (y.3) drying the precipitated polyester obtained in (y.1) or the washed precipitated polyester obtained in (y.2), thereby obtaining a dried (washed) precipitated polyester.

[0067] The separation in (y.1) is done by methods and means known to the skilled person, especially solid-liquid separation methods such as filtration, for example, heated pressure filtration, sedimentation or centrifugation (see Handbuch der mechanischen Fest-Flussig-Trennung Taschen- buch - 29. April 2004 von Klaus Luckert (Herausgeber)). Washing in optional step (y.1) is preferably done with a solvent system having features (s.1 ), (s.2) and (s.3) as defined herein, preferably with a solvent system comprising one or more of the solvent(s) of any one of the groups defined herein. In some embodiments, a subsequent washing of the washed residue is done with a solvent selected from the group consisting of methanol, ethanol, propanol, isopropanol, acetonitrile, ethyl acetate, acetone, water or a mixture of two or more of these solvents or with a solvent selected from the group consisting of methanol, ethanol, propanol, isopropanol, acetonitrile, ethyl acetate, acetone, water, GVL, or a mixture of two or more of these solvents. In some embodiments, washing in optional step (y.2) is preferably done with a solvent system having features (s.1 ), (s.2) and (s.3) as defined herein, preferably with a solvent system comprising one or more of the solvent(s) of any one of the groups defined herein. In some embodiments, a subsequent washing of the washed residue is done with a solvent selected from the group consisting of methanol, ethanol, propanol, isopropanol, acetonitrile, ethyl acetate, acetone, water or a mixture of two or more of these solvents or with a solvent selected from the group consisting of methanol, ethanol, propanol, isopropanol, acetonitrile, ethyl acetate, acetone, water, GVL, or a mixture of two or more of these solvents. Drying in step (y.3) is preferably done under one or more conditions selected from the group consisting of a pressure in the range of from 1 to 1013 mbar; a temperature in the range of from 50 to 210 °C, preferably in the range of from 60 to 180°C, more preferably in the range of from 80 to 150 °C; drying time in the range of from 30 minutes to 24 hours; drying in an atmosphere comprising nitrogen, preferably in an atmosphere having at least 90 volume-%, more preferably 95 volume-%, more preferably at least 98 vol- ume-% nitrogen. Drying is done by one or more methods selected from the group consisting of contact drying, convection drying and radiation drying.

[0068] In some embodiments, the method comprises

[0069] (y.4) pelletizing the dried (washed) precipitated polyester obtained in (y.3), thereby obtaining a pelletized polyester.

[0070] “Pelletizing” is the process of compressing or molding a material into the shape of a pellet. Pelletizing can be done as known in the art, for example, by extruding and subsequently pelletizing under water or by strand granulation. In some embodiments, the method comprises after (d) and before (e), preferably after (y.3) or after (y.4) and before (e)

[0071] (z) increasing the intrinsic viscosity of the precipitated polyester obtained in (d) or of the dried (washed) precipitated polyester obtained in (y.3) or of the pelletized polyester obtained in (y.4).

[0072] Increasing the intrinsic viscosity according to (z) c is done in solid state and / or in molten state, wherein increasing the intrinsic viscosity increases molecular weight of the polyester. Increasing the intrinsic viscosity is preferably done at a temperature in the range of from 200 to 230 °C, more preferably in the range of from 200 to 220 °C; and / or, preferably and, for a period of time in the range of from 1 to 80 hour(s), preferably 10 to 50 hours; and / or, preferably and, at a pressure in the range of from 5 to 1013 mbar.

[0073] Precipitation in (d) - cooling

[0074] In some embodiments of the method, precipitation in (d) comprises cooling the solvent system obtained in (c), which is enriched in dissolved polyester compared to the solvent system provided in (a), from T2 to a temperature below 140°C, wherein the cooling is done so that the temperature of the solvent system, which is enriched in dissolved polyester, is within the temperature range of from 160 to 145 °C for a period of time of at least 5 minutes, preferably at least 10 minutes, more preferably in the range from 5 to 120 minutes, more preferably in the range of from 10 to 100 minutes, more preferably in the range of from 15 to 100 minutes.

[0075] In some embodiments of the method, cooling in (d) is done so that the solvent system, which is enriched in dissolved polyester, has within the temperature range of from 160 to 145 °C a viscosity in the range of from 1 to 12 Pa s, preferably in the range of from 1 to 10 Pa s, determined according to ASTM D445.

[0076] In some embodiments of the method, cooling is done with a cooling rate of < 3.0 °C / min, preferably < 1.5 °C / min, more preferably in the range of from 0.05 to 3.0 °C / min, more preferably in the range of from 0.13 to 3.0 °C / min, more preferably in the range of from 0.15 to 1.5 °C / min, more preferably in the range of from 0.15 to 1.0 °C / min.

[0077] In some embodiments of the method, the cooling of the solvent system in (d) is done from T2 to a temperature below 100°C.

[0078] In some embodiments of the method, the cooling of the solvent system in (d) is done from T2 to a temperature below 100°C with a cooling rate of < 3.0 °C / min, preferably < 1.5 °C / min, more preferably in the range of from 0.05 to 3.0 °C / min, more preferably in the range of from 0.13 to 3.0 °C / min, more preferably in the range of from 0.15 to 1.5 °C / min, more preferably in the range of from 0.15 to 1.0 °C / min.

[0079] In some embodiments of the method, the cooling of the solvent system in (d) is done without addition of an anti-solvent. An “antisolvent” is a solvent having a solubility regarding the polyester < 1 g / kg at a temperature in the range of from 20 to 25 °C. In some embodiments, only a small amount of one or more antisolvent(s) is / are added to and / or is / are present in the solvent system in step (d), wherein a small amount means that less than 5 weight-%, preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of antisolvent(s) is / are added and / or is / are present based on the total weight of the solvent system including the antisolvent(s) being 100 weight-%.

[0080] Solvent system

[0081] In some embodiments of the method, the solvent system comprises one or more solvent(s), wherein

[0082] (s.1) the solvent system has Hansen solubility parameters with respect to energy from dispersion forces between molecules (bDss), energy from dipolar intermolecular force between molecules (bPss) and energy from hydrogen bonds between molecules (5HSs), which fullfill equitation 1

[0083] (8.8)2> 4(5Dss-20)2+ (SPss-11.8)2+ (5Hss-4.5)2

[0084] [equitation 1];

[0085] (s.2) each solvent of the solvent system has a boiling point at 1013 hPa of at least 160 °C; and (s.3) solvents having a functional group selected from the group consisting of hydroxyl (OH), amino (NH2), carboxyl (COOH), and thiol (SH) are excluded.

[0086] The boiling point of a solvent is understood as the boiling point of the solvent at the respective pressure. Any solvent system for which 4(bDss-20)2+ (bPss-11.8)2+ (5HSs-4.5)2is larger than (8.8)2(i.e. 77.44) is not suited to dissolve polyalkylene terephthalate based polymer properly and any solvent system for which 4(bDss-20)2+ (bPss-11.8)2+ (bHss-4.5)2is equal to or smaller than (8.8)2(i.e. 77.44) is suitable for dissolving polyalkylene terephthalate based polymer. In case of two or more solvents being part of the solvent system, i.e. n solvents with n being an integer with n>2 and i=1 ... n, the Hansen solubility parameters of the resulting mixture with respect to each of bDss, 6HSSand <5PSSare calculated, knowing the percentage part of each solvent in the solvent system, as the weighted arithmetic mean from 6DSi, 6HSiand 5PSi Of each of the n solvents S(i). The Hansen parameters of solvents are to be found in in BIOVIA COSMOquick 2022.

[0087] Considering the three-dimensional form given by equitation 1 in the three-dimensional Hansen space, a sphere is formed which has its center at 5DC= 20, 5PC= 11.8 and 5HC= 4.5 and a radius r of 8.8. The doubling of the dispersion parameter value is required, according to Charles Hansen, for achieving a spherical form. A Hansen sphere, since there are no negative values possible for 5H, can also be considered as a dome, i.e. a half-sphere. PET has Hansen parameters according to the 5thEdition 5.1.03 (2008) of the HANSEN Solubility Parameters in Practice (HSPiP) of 5D = 18.2, 5P = 6.4 and 5H = 6.6 and lies within the sphere but not at its center.

[0088] In some embodiments of the method, at least 90 weight-%, more preferably at least 95 weight- %, more preferably at least 98 weight-%, more preferably at least 99 weight-%, of the solvent system consist of one solvent system, which fulfills equitation 1 , wherein in cases where the solvent system consists of only one solvent system, the temperature T is a temperature at least 7K below the boiling temperature of said one solvent.

[0089] In some embodiments of the method, at least 90 weight-%, more preferably at least 95 weight- %, more preferably at least 98 weight-%, more preferably at least 99 weight-%, of the solvent system consist of two or more solvent(s), wherein the respective mixture fulfill(s) equitation 1.

[0090] In some embodiments of the method, the one or more solvent(s) is / are selected from the group consisting of N,N-dimethylbenzamide, N,N-dimethylphenylacetamide, 1 ,4-benzoquinone, acetophenone, dimethyl terephthalate, 1 ,3,5-trimethoxybenzene, 2-phenylacetophenone, N- methylcaprolactam, methylbenzoate, methyl-4-methoxybenzoate, butylene carbonate, N- ethylpyrrolidone, benzophenone, di-benzyl malonate, N-ethyl-caprolactam, methyl 2-(5-oxotet- rahydrofuran-3-yl)acetate (FAME), methyl 2-(5-oxotetrahydrofuran-2-yl)acetate, propiophenone, N-methoxypropyl-pyrrolidone, 1 ,4-cyclohexanedione, cyclohexane-carbonate, N-methoxyethyl- pyrrolidone, N,N-diethylphenylacetamide, phenyl acetate, 1-(2-hydroxyethyl)pyrrolidin-2-one acetate (HEPAc), N,N-diethylbenzamide, isopropyl-benzoate, cyclohexyl phenyl ketone, phenylacetic acid ethylester, phenylacetat.N-methyl-morpholine, benzyl-propionate, benzylacetate, Ne- opentyl-glycol-dibenzoate, tetrahydrofurfuryl acetate, N-methyl-imidazole, benzyl butyrate, 2- pyrrolidone, 2-phenoxyethanol propionate, 2-phenoxyethyl isobutyrate, N,N-dipropylbenzamide, N,N-dimethylacetamide, N,N-diethylacetamide, dihydrolevoglucosenon (Cyrene), propylenecarbonate, caprolactone, dimethylisosorbide, N-butylpyrrolidone, t-butylpyrrolidone, methyl-1-me- thyl-5-oxopyrrolidine-3-carboxylate (MMOC), gamma-valerolactone (GVL), delta-valerolactone, gamma butyrolactone, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodiasolv Polar- clean), caprolactam, phen ethyl acetate, methyl phenylacetate, benzyl benzoate, N,N-dimethyl- lactamide (Agnique AMD 3L), 1 ,3-dimethyl-2-imidazolidinone (DMI) and dimethyl sulfoxide (DMSO). In some embodiments of the method, the one or more solvent(s) is / are selected from the group consisting of dihydrolevoglucosenon (Gyrene), propylenecarbonate, caprolactone, dimethylisosorbide, N-butylpyrrolidone, t-butylpyrrolidone, methyl-1-methyl-5-oxopyrrolidine-3-car- boxylate (MMOC), gamma-valerolactone (GVL), Delta-valerolactone, gamma butyrolactone, dimethylsulfoxide, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (RhodiasolvOPolarclean), caprolactam, phen ethyl acetate, methyl phenylacetate, benzyl benzoate, phenyl benzoate, methyl benzoate, propyl benzoate, and dimethyl sulfoxide (DMSO). In some embodiments of the method, the one or more solvent(s) of the solvent system is / are selected from the group consisting of propylenecarbonate, N-butylpyrrolidone, t-butylpyrrolidone, methyl-1-methyl-5-oxopyrroli- dine-3-carboxylate (MMOC), Delta-valerolactone, gamma butyrolactone, methyl 5-(dimethyla- mino)-2-methyl-5-oxopentanoate (RhodiasolvOPolarclean), caprolactam, phenethyl acetate, methyl phenylacetate, benzyl benzoate, phenyl benzoate, methyl benzoate, propyl benzoate and GVL. In some embodiments of the method, the one or more solvent(s) is / are selected from the group consisting of propylenecarbonate, N-butylpyrrolidone, t-butylpyrrolidone, methyl-1- methyl-5-oxopyrrolidine-3-carboxylate (MMOC), Delta-valerolactone, gamma butyrolactone, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (RhodiasolvOPolarclean), caprolactam, phen ethyl acetate, methyl phenylacetate, benzyl benzoate, phenyl benzoate, methyl benzoate, and propyl benzoate. In some embodiments of the method, the one or more solvent(s) of the solvent system is / are selected from the group consisting of propylenecarbonate, N-butylpyrrolidone, t- butylpyrrolidone, methyl-1-methyl-5-oxopyrrolidine-3-carboxylate (MMOC), methyl 5-(dimethyla- mino)-2-methyl-5-oxopentanoate (RhodiasolvOPolarclean), phenethyl acetate, and GVL. In some embodiments of the method, the one or more solvent(s) is / are selected from the group consisting of propylenecarbonate, N-butylpyrrolidone, t-butylpyrrolidone, methyl- 1-methyl-5-ox- opyrrolidine-3-carboxylate (MMOC), methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (Rho- diasolvOPolarclean), and phen ethyl acetate.

[0091] In some embodiments of the method, ethyl benzoate and butyl benzoate are excluded as solvents).

[0092] In some embodiments of the method,

[0093] (s.3a) solvents having a functional group selected from the group consisting of hydroxyl (OH), amino (NH2), secondary amine (-NH-), carboxyl (COOH), and thiol (SH) are excluded. In some embodiments of the method, the one or more solvent(s) is / are selected from the group consisting of dihydrolevoglucosenon (Cyrene), methyl phenylacetate, 1 ,3-Dimethyl-2-imidazoli- dinone (DMI), dimethyl sulfoxide (DMSO) and GVL. In some embodiments of the method, the solvent system comprises gamma-valerolactone (GVL), or dimethyl sulfoxide (DMSO) or a mixture of GVL and DMSO.

[0094] In some embodiments of the method, the solvent system comprises gamma-valerolactone, wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of gamma-valerolactone, based on the total weight of the solvent system being 100 weight-%.

[0095] In some embodiments of the method, the solvent system comprises dimethyl sulfoxide, wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of dimethyl sulfoxide, based on the total weight of the solvent system being 100 weight-%.

[0096] In some embodiments of the method, the solvent system comprises gamma-valerolactone and dimethyl sulfoxide, wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of gamma-valerolactone and dimethyl sulfoxide, based on the total weight of the solvent system being 100 weight-%.

[0097] Preferably, the solvent system is free of acidic and / or basic component(s), wherein preferably, the solvent system comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-%, of acidic and / or basic component(s) based on the total weight of the solvent system being 100 weight-%. An acidic component is preferably an acid, more preferably an acid selected from the group of organic and inorganic acids and mixtures thereof. For example, an acidic component is sulphuric acid, hydrochloric acid, nitric acid or a mixture thereof. A basic component is preferably a base, more a based selected from the group of organic and inorganic bases and mixtures thereof. For example, a basic component is NaOH. All weight-%-values indicated for acidic and / or basic component(s) are directed to the dry weight of the acidic and / or basic component(s).

[0098] In some embodiments of the method, in optional step (b) the same solvent system as in (c) is used.

[0099] Polyester

[0100] In some embodiments of the method, the polyester is based on 1,4-butanediol or 1,2-ethandiol, more preferably the polyester according to (i) is selected from the group consisting of a polymer based on 1,4-butanediol and terephthalic acid (polybutylene terephthalate, PBT), a polymer based on 1,2-ethanediol and terephthalic acid (polyethylene terephthalate, PET), a copolymer of 1 ,4-butanediol, adipic acid and terephthalic acid (polybutylenadipat-terephthalat, PBAT), a polymer of 1,2-ethanediol and 2,5-furandicarboxylic acid (polyethylene furanoate, PEF) and mixtures of two or more of these (co)polymers, more preferably, the polyester comprises at least PET and / or PBT, more preferably the polyester is PET or PBT or a mixture of PET and PBT.

[0101] Colorant

[0102] In some embodiments of the method, the colorant is selected from the group consisting of dye and optical brightener and mixtures of dye and optical brightener.

[0103] A “colorant” is a substance that cause the change of color impression of material. This comprises dyes, which absorb wavelength intervals of visible light (400 to 780 nm) and optical brighteners, which amplify the light emission of a material through UV light adsorption and emittance of visible light (through fluorescence), i.e. an optical brightener converts radiation that is not visible to the human eye (<400nm) into visible fluorescence radiation of the blue-red spectral range (400 to 600 nm). Colorants usable or used for changing the color impression of polymeric materials are known to the skilled person. In the context of the present invention, the term “dye” means any kind of dye such as dye, pigment, dispersion, wherein a dye is, for example, one or more selected from the group consisting of acid dye, basic dye, direct dye, disperse dye, azoic dye, food dye, solvent dye, organic dye, organic pigment, sulfur dye, mordant dye and vat dye. The term “optical brightener” comprises optical brightening agents, fluorescent brightening agents, and fluorescent whitening agents.

[0104] Overviews of colorants for polymeric materials can be found, for example, in “Dyes and Pigments” Metin Agikyildiz, Kubra Gunes, Ahmet Gurses Springer, 2016 (ISBN: 10 : 3319338900); Industrial Organic Pigments - Klaus Hunger, Thomas Heber, Martin II. Schmidt, Friedrich Reisinger, Stefan Wanne Wiley-VCH, 4thedition, 2018 (ISBN: 978-3-527-32608-2); Chemistry and Technology of Natural and Synthetic Dyes and Pigments - Ashis Kumar Samanta, Nasser Awwad, IntechOpen, 2020 (ISBN: 9781789859980, 9781789859973, 9781839687587); Encyclopedia of Color, Dyes, Pigments - Volume 1, Gerhard Pfaff, de Gruyter, 2021 (ISBN: 311058588X); Heinrich Zollinger: Color Chemistry: Syntheses, Properties, and Applications of Organic Dyes and Pigments. 3rdedition. WILEY-VCH Verlag, Weinheim 2003 (ISBN: 3-906390- 23-3); Klaus Hunger (Ed.): Industrial Dyes: Chemistry, Properties, Applications. WILEY-VCH Verlag, Weinheim 2003 (ISBN: 3-662-01950-7); Hermann Rath: Lehrbuch der Textilchemie. ein- schl. der textilchemischen Technologie. 2nd edition. Springer-Verlag, Berlin, Heidelberg 1963 (ISBN: 978-3-662-00065-6); Wilfried Kratzert, Rasmus Peichert: Farbstoffe. Quelle & Meyer, Heidelberg 1981 (ISBN: 3-494-01021-8); Ullmann’s Encyclopedia of industrial chemistry, Wiley- VCH, 2000, sections “dyes and pigments” and “dyes, general survey” (ISBN: 9783527303854).

[0105] Preferably, in step b) only colorant(s) is / are removed from the polymer blend and transferred into the solvent system, which is / are non-covalently bonded to the polyester.

[0106] Second polymer

[0107] In some embodiments of the method, the second polymer is selected from the group consisting of polyurethane (PU), polyethylene glycol (PEG), polytetrahydrofuran (pTHF), mixtures of these polymers and copolymers of these polymers, wherein the second polymer is more preferably PU or a copolymer of PU and PEG and / or pTHF, more preferably spandex (copolymer of PU and PEG or of PU and pTHF).

[0108] “Spandex” is preferably a copolymer of polyurethane and polyethylene glycol and / or polytetra- hydrofurane, more preferably Spandex is a copolymer of polyurethane and polyethylene glycol or a copolymer of polyurethane with polytetrahydrofurane.

[0109] Filler

[0110] In some embodiments of the method, the filler is selected from the group consisting of glass fiber, coal fiber, carbon black, inorganic salts (for example, talc, disodium carbonate), adhesive, thickener, antifoam agent, finishing agent (for example water / oil / stain repellent, flame retardant, anticrease agent, biocide), binder, surfactant (for example, softener, scouring agent, antistatic agent), desizing agent, bleaching agent, oxidant, UV filter, emulsionant, fixing agent, washing dispersant, profiling agent. In some embodiments of the method, wherein the polyester comprises, preferably is PBT and the filler is one or more selected from the group consisting of glass fiber, coal fiber, carbon black, inorganic salts (for example, talc, disodium carbonate), adhesive, thickener, antifoam agent, finishing agent (for example water / oil / stain repellent, flame retardant, anticrease agent, biocide), binder, surfactant (for example, softener, scouring agent, antistatic agent), desizing agent, bleaching agent, oxidant, UV filter, emulsionant, fixing agent, washing dispersant, profiling agent, preferably the filler is one or more selected from glass fiber, coal fiber, carbon black, inorganic salts (for example, talc, Na2CO3).

[0111] In some embodiments of the method, wherein the polyester comprises, preferably is PET and the filler is one or more selected from the group consisting of glass fiber, coal fiber, carbon black, inorganic salts (for example, talc, disodium carbonate), adhesive, thickener, antifoam agent, finishing agent (for example water / oil / stain repellent, flame retardant, anticrease agent, biocide), binder, surfactant (for example, softener, scouring agent, antistatic agent), desizing agent, bleaching agent, oxidant, UV filter, emulsionant, fixing agent, washing dispersant, profiling agent, preferably the filler one or more selected from adhesive, thickener, antifoam agent, finishing agent (for example water / oil / stain repellent, flame retardant, anticrease agent, biocide), binder, surfactant (for example, softener, scouring agent, antistatic agent), desizing agent, bleaching agent, oxidant, UV filter, emulsionant, fixing agent, washing dispersant, profiling agent.

[0112] In some embodiments, the article provided in (a) comprises titanium dioxide (TiCh). In these preferred embodiments, said TiC>2 is absent in the precipitated polyester obtained in (d) or is present in the precipitated polyester obtained in (d) in an amount in the range of from 0.001 to 1 .0 weight-%, based on the total precipitated polyester obtained in (d) being 100 weight-%. In these preferred embodiments, said TiC>2, if present, is also present in the fiber prepared in (e).

[0113] Fourth polymer (iv)

[0114] In some embodiments of the method, the polymer blend further comprises a fourth polymer (iv), wherein the fourth polymer is different from the polyester (ii), from the third cellulose based polymer of (iii) and from the second polymer of (ii), wherein the fourth polymer is selected from polypropylene (PP), polyethylene (PE), polyamide (PA), and mixtures of two or more thereof.

[0115] In some embodiments of the method, the fourth polymer, if present in the polymer blend, is part of the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c) and subjected to biogas preparation in (e). The presence of fourth polymer in the residue subjected to biogas preparation in (e) does not impair the microbial, preferably anerobic, fermentation. The remaining thereof is simply discharged undigested from any biogas reactor.

[0116] Process conditions

[0117] In some embodiments of the method, T1 is a temperature in the range of from 110 to < 170°C, preferably a temperature in the range of from 110 to 165 °C, more preferably a temperature in the range of from 120 to 160 °C, more preferably a temperature in the range of from 120 to 150 °C, more preferably in the range of from 151 to 160 °C.

[0118] In some embodiments of the method, T2 is a temperature in the range of from > 170°C to 200 °C, preferably a temperature in the range of from 175 to 190 °C, more preferably a temperature in the range of from 180 to 190 °C.

[0119] In some embodiments of the method, (a), optionally (b), (c) and optionally (d) are done at a pressure in the range of from 800 to 200,000 hPa.

[0120] In some embodiments of the method, the contacting in (b) is done for a period of time of at least 5 minutes, preferably in the range of from 5 minutes to 10 hours, more preferably in the range of from 5 minutes to 5 hours, more preferably in the range of from 5 minutes to 4 hours.

[0121] In some embodiments of the method, the contacting in (c) is done for a period of time of at least 0.1 hours, preferably in the range of from 1 minute to 10 hours, more preferably in the range of from 1 minute to 2 hours, more preferably in the range of from 5 minutes to 1 hour.

[0122] In some embodiments of the method, the contacting in (b) and / or (c) is done with a in mass based ratio solvent system : polymer blend provided in (a) or residue obtained in (b) in the range of 1 :1 to 100:1, preferably in the range of from 1 :1 to 20:1.

[0123] In some embodiments of the method, at least steps (b) and (c), preferably all steps, are done in an inert atmosphere, preferably in the presence of an inert gas, wherein the inert gas is preferably selected from the group consisting of argon, helium, neon, nitrogen and mixtures of two or more of these inert gases, preferably comprises at least nitrogen, more preferably the inert gas is nitrogen. In some embodiments of the method, at least steps (b) and (c), preferably all steps, are done batch-wise or continuous.

[0124] Optional work-up steps

[0125] In some embodiments, the method further comprises work-up of the cellulose based polymer obtained in (d) or (w.2) or in (x.5) before (e) by applying one or more treatment(s) selected from the group consisting of: mechanical treatment, preferably selected from the group consisting of milling, beating, shredding, tearing and mixtures of two or more of these treatments; thermal treatment, preferably selected from the group consisting of freezing, heating or boiling and mixtures of two or more of these treatments, preferably in combination with application of excess pressure (excess pressure = pressure > 1013 mbar); incubation in an aqueous alkaline solvent, which preferably comprises water and one or more alkali, preferably sodium, salt selected from the group consisting of sodium hydroxide, sodium carbonate, sodium monochloroacetate and a mixture of two or more thereof; incubation in an acidic solvent, preferably in one or more acid(s) selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid and formic acid; incubation in an ionic liquid, preferably in one or more ionic liquid(s) selected from the group consisting of 1-allyl-3-methylimidazolium chloride ([AMIM]CI), 1-butyl-3-methylimid- azolium chloride ([BMIM]CI), 1-butyl-3-methylimidazolium acetate ([BMIM][OAc]) and 1 ,5- diazabicyclonon-5-enium acetate ([DBNH][OAc]); incubation in N-methylmorpholine-N-oxide (NMMO); sonication; radiation; addition of an enzyme, preferably selected from the group consisting of cellulase, protease, pectinase, glucosidase, glucanotransferases, PET hydrolase (PETase) and lipase and mixtures of two or more of these enzymes, more preferably selected from the group consisting of p-1 ,4-exoglucanase, p-1 ,4-endoglucanase, p-1 ,4-cellobiohydrolase, p-gluco- sidase, pyrolase and mixtures of two or more of these enzymes; and microbial cultivation, preferably by adding a cellulolytic bacterial or fungal strain or mixed culture.

[0126] Preferably, neither before (b) nor in-between steps (b) and (c) nor before step (c) the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) is contacted with an acidic component and / or a basic component. An acidic component is preferably an acid, more preferably an acid selected from the group of organic and inorganic acids and mixtures thereof. For example, an acidic component is sulphuric acid, hydrochloric acid, nitric acid or a mixture thereof. A basic component is preferably a base, more a based selected from the group of organic and inorganic bases and mixtures thereof. For example, a basic component is NaOH. All weight-%-values indicated for acidic and / or basic component(s) are directed to the dry weight of the acidic and / or basic component(s). As indicated above, preferably, the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c) comprises less than 10 weight- %, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the residue being 100 weight-%. Preferably, the precipitated polyester obtained in (d) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the precipitated polyester being 100 weight-%.

[0127] 2ndaspect - Biogas from cellulose based polymer

[0128] A second aspect of the invention relates to a method for preparing biogas from cellulose based polymer separated from a polymer blend comprising

[0129] (i) separation of cellulose based polymer from a polymer blend comprising cellulose based polymer and at least one further polymer different from the cellulose based polymer, thereby obtaining a separated cellulose based polymer fraction;

[0130] (ii) treating the cellulose based polymer fraction obtained in (i) with a solvent system, thereby obtaining a treated cellulose based polymer fraction;

[0131] (iii) preparing biogas from the treated cellulose based polymer fraction obtained in (ii).

[0132] All details, embodiments and preferred embodiments described above with respect to the method of the first aspect comprising steps (a), (b), optional step (c), steps (d) and (e) equally apply to the method for preparing biogas from cotton separated from a polymer blend of the second aspect. The “at least one further polymer” is preferably a second polymer as defined above. Especially, neither before step (i) nor during step (i) nor in-between steps (i) and (ii) the polymer blend or the separated cellulose based polymer fraction is contacted with an acidic component and / or a basic component. Preferably, the solvent system used in (ii) is free of acidic and / or basic components, wherein preferably the solvent system comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic components, based on the total weight of the solvent system being 100 weight-%. In some embodiments, the method for preparing biogas from cellulose based polymer separated from a polymer blend comprises

[0133] (i) separation of cellulose based polymer from a polymer blend comprising cellulose based polymer and at least one further polymer different from the cellulose based polymer, thereby obtaining a separated cellulose based polymer fraction;

[0134] (ii) treating the cellulose based polymer fraction obtained in (i) with a solvent system comprising gamma valerolactone (GVL) or dimethyl sulfoxide (DMSO) or a mixture of GVL and DMSO, which comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the solvent system being 100 weight-%, thereby obtaining a treated cellulose based polymer fraction;

[0135] (iii) preparing biogas from the treated cellulose based polymer fraction obtained in (ii); wherein neither before step (i) nor during step (i) nor in-between steps (i) and (ii) the polymer blend or the separated cellulose based polymer fraction is contacted with an acidic component and / or a basic component.

[0136] An acidic component is preferably an acid, more preferably an acid selected from the group of organic and inorganic acids and mixtures thereof. For example, an acidic component is sulphuric acid, hydrochloric acid, nitric acid or a mixture thereof. A basic component is preferably a base, more a based selected from the group of organic and inorganic bases and mixtures thereof. For example, a basic component is NaOH.

[0137] Preferably, the treated cellulose based polymer fraction obtained in (ii) comprises less than 10 weight-%, preferably less than8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the treated cellulose based polymer fraction being 100 weight-%.

[0138] Preferably, the solvent system comprises gamma-valerolactone, wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of gamma-valerolactone, based on the total weight of the solvent system being 100 weight-%. 3rdaspect - Biogas

[0139] A third aspect of the invention relates to biogas, preferably biogas comprising methane, obtained or obtainable from the method of the first or the second aspect. All details, embodiments and preferred embodiments described above with respect to the method of the first aspect or the second aspect apply also for the third aspect.

[0140] 4thaspect - Use

[0141] A fourth aspect of the invention relates to the use of biogas according to the third aspect, preferably of methane comprised in the biogas, preferably after purification and / or concentration, as carbon and / or hydrogen source. Said fourth aspect also relates to the use of biogas according to the third aspect, preferably biogas comprising at least 40 volume-% methane, as source of energy, preferably as source of thermal energy, for one or more of the steps (b) to (d). The biogas may be used directly or indirectly as source of thermal energy, e.g. it is burned and the burning heat is used for preparation of water steam or is used for generating electricity, which may be used in the process according to the present invention.

[0142] All details, embodiments and preferred embodiments described above with respect to the method of the first aspect, the second aspect or the third aspect apply also for the fourth aspect.

[0143] 5thaspect - Polyester

[0144] A fifth aspect of the invention relates to a polyester obtained or obtainable from the method of the first or second aspect.

[0145] All details, embodiments and preferred embodiments described above with respect to the method of the first to fourth aspect apply also for the fifth aspect.

[0146] 6thaspect - Use

[0147] A sixth aspect of the invention is related to the use of polyester of the fifth aspect for textile applications, fiber applications, packaging applications, plastic applications, automotive applications, electronic applications, preferably for the production of food packaging, beverage packaging, clothing, foot wear, wire, cable, wherein preferably for textile applications, fiber applications, packaging applications, plastic applications, more preferably for the production of food packag- ing, beverage packaging, clothing and foot wear. All details, embodiments and preferred embodiments described above with respect to the method of the first to fifth aspect apply also for the sixth aspect.

[0148] 7thaspect - method for preparing a product

[0149] The seventh aspect of the invention is related to a method for preparing a product comprising

[0150] (I) providing polyester obtained or obtainable from the method of the first or second aspect;

[0151] (II) preparing a textile, a fiber, a packaging, a plastic, an automotive part, an electronic part from the polyester provided in (I).

[0152] All details, embodiments and preferred embodiments described above with respect to the method of the first to sixth aspect apply also for the seventh aspect.

[0153] 8thaspect - Method focused on obtaining a separated fraction comprising the second polymer

[0154] An eight aspect relates to a method of the first aspect, wherein (b) comprises:

[0155] (b.1) contacting the polymer blend with the solvent system at a temperature T1 of < 170 °C, thereby obtaining a solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and a residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler;

[0156] (b.2) separating the solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, obtained in (b.1) from the residue, preferably by a physical separation method, thereby obtaining a separated solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, compared to the solvent system provided in (a); and

[0157] (b.3) separating the second polymer from the solvent system, thereby obtaining a separated fraction comprising the second polymer.

[0158] All details, embodiments and preferred embodiments described above with respect to the method of the first to seventh aspect apply also for the eight aspect.

[0159] 9thaspect - Method focused on converting the second polymer and / or the re-obtained polyester

[0160] A ninth aspect of the invention relates to a method, preferably according to the first or second aspect, comprising the further step: converting the second polymer and / or the re-obtained polyester, to obtain one or more monomer, polymer or polymer product. All details, embodiments and preferred embodiments described above with respect to the method of the first to eight aspect apply also for the ninth aspect.

[0161] Preferably, the monomer is a di- or polyol; preferably butandiol; aldehyde; preferably formaldehyde; di- or polyisocyanate; preferably methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), toluene diisocyanate (TDI), hexamethylenediisocyanate (HDI) or isophoronediisocyanate (IPDI); amide; preferably caprolactam; alkene; preferably styrene, ethene and norbornene; alkyne, (di)ester; preferably methyl methacrylate; mono or diacid; preferably adipic acid or terephthalic acid; diamine; preferably hexamethylenediamine, nonanediamine; or sulfones; preferably 4,4'-dichlorodiphenyl sulfone.

[0162] Preferably, the polymer is and / or the polymer product comprises polyamide (PA); preferably PA 6 or PA 66; polyisocyanate polyaddition product; preferably polyurethane (Pll), thermoplastic polyurethane (TPU), polyurea or polyisocyanurate (PIR); low-density polyethylene (LDPE), high- density polyethylene (HDPE), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyvinyl acetate (PVA), polystyrene (PS), poly acrylonitrile butadiene styrene (ABS), poly styrene acrylonitrile (SAN), poly acrylate styrene acrylonitrile (ASA), polytetrafluoroethylene (PTFE), poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA), polybutadiene (BR, PBD), poly(cis-1 ,4-isoprene), poly(trans-1 ,4-isoprene), polyoxymethylene (POM), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene adipate coterephthalate (PBAT), polyester (PES), polyether sulfone (PESLI), polyhydroxyalkanoate (PHA), poly-3-hy- droxybutyrate (P3HB), poly-4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO), polylactic acid (PLA), polysulfone (PSU), polyphenylene sulfone (PPSLI), polycarbonate (PC), polyether ether ketone (PEEK), poly(p-phe- nylene oxide) (PPO), poly(p-phenylene ether) (PPE); or copolymer or mixture thereof.

[0163] Preferably, the polymer and / or the polymer product is / are or is / are a part of: a part of a car; preferably cylinder head cover, engine cover, housing for charge air cooler, charge air cooler flap, intake pipe, intake manifold, connector, gear wheel, fan wheel, cooling water box, housing, housing part for heat exchanger, coolant cooler, charge air cooler, thermostat, water pump, radiator, fastening part, part of battery system for electromobility, dashboard, steering column switch, seat, headrest, center console, transmission component, door module, cover for car A, B, C or D pillar, spoiler, door handle, exterior mirror, windscreen wiper, windscreen wiper protection housing, decorative grill, cover strip, roof rail, window frame, sunroof frame, antenna panel, headlight and taillight, engine cover, cylinder head cover, intake manifold, airbag, cushion, or coating; a cloth; preferably shirt, trousers, pullover, boot, shoe, shoe sole, tight or jacket; an electrical part; preferably electrical or electronic passive or active component, circuit board, printed circuit board, housing component, foil, line, switch, plug, socket, distributor, relay, resistor, capacitor, inductor, bobbin, lamp, diode, LED, transistor, connector, regulator, integrated circuit (IC), processor, controller, memory, sensor, microswitch, microbutton, semiconductor, reflector housing for light-emitting diodes (LED), fastener for electrical or electronic component, spacer, bolt, strip, slide-in guide, screw, nut, film hinge, snap hook (snap-in), or spring tongue; a consumer, agricultural product or pharmaceutical product; preferably tennis string, climbing rope, bristle, brush, artificial grass, 3D printing filament, grass trimmer, zipper, hook and loop fastener, paper machine clothing, extrusion coating, fishing line, fishing net, offshore line and rope, vial, syringe, ampoule, bottle, sliding element, spindle nut, chain conveyor, plain bearing, roller, wheel, gear, roller, ring gear, screw and spring dampers, hose, pipeline, cable sheathing, socket, switch, cable tie, fan wheel, carpet, box or bottle for cosmetics, mattress, cushion, insulation, detergent, dishwasher tabs or powder, shampoo, body wash, shower gel, soap, fertilizer, fungicide, or pesticide; a packaging for the food industry; preferably mono- or multi-layer blown film, cast film (mono- or multi-layer), biaxially stretched film, or laminating film; or a part of a construction; preferably a rotor blade, insulating material, frame, housing, wall, coating, or separating wall.

[0164] Preferably, the content of the second polymer and / or the polyester polymer in the monomer, polymer and / or polymer product is 1 weight-% or more, preferably 2 weight-% or more, more preferably 5 weight-% or more, more preferably 15 weight-% or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more; and / or wherein the content of the second polymer and / or the polyester in the monomer, polymer and / or polymer product is 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less; and preferably wherein the content is determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models, preferably based on mass balance, preferably the International Sustainability and Carbon Certification (ISCC) standard.

[0165] The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for exam- ple in the context of a term such as "The method of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The method of any one of embodiments 1 , 2, 3 and 4". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and, thus, suitably supports, but does not represent the claims of the present invention.

[0166] 1 . A method for preparing biogas comprising providing a polymer blend, which comprises

[0167] (i) a polyester and

[0168] (ii) optionally one or more component(s) selected from the group consisting of a second polymer, a colorant, and a filler;

[0169] (iii) a cellulose based third polymer; wherein the optional second polymer (ii) and the cellulose based third polymer (iii) are different from each other and different from the polyester of (i); the method comprising:

[0170] (a) providing the polymer blend and providing a solvent system;

[0171] (b) optionally contacting the polymer blend with the solvent system at a temperature T 1 of < 170 °C, thereby obtaining a solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and a residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler;

[0172] (c) contacting the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) with a solvent system at a temperature T2 of > 170 °C, thereby obtaining a solvent system, which is enriched in dissolved polyester compared to the solvent system provided in (a) and comprises optionally the filler or a part of the filler, and a residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler;

[0173] (d) optionally precipitating the polyester from solvent system, which is enriched in dissolved polyester, obtained in (c), thereby obtaining a precipitated polyester and a solvent system, which is depleted in dissolved polyester and which optionally comprises the filler or a part of the filler; (e) preparing biogas from the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c).

[0174] 2. The method of embodiment 1, wherein the cellulose based third polymer is selected from the group consisting of natural cellulose based polymer, synthetic cellulose based polymer and mixtures of one or more natural cellulose based polymer(s) and one or more synthetic cellulose based polymer(s), wherein a natural cellulose based polymer is preferably selected from the group consisting of cotton, cellulose, lignin, linen, viscose and mixtures of two or more thereof and wherein a synthetic cellulose based polymer is preferably viscose, wherein the cellulose based polymer preferably comprises at least cotton, more preferably at least 65 weight-%, more preferably at least 70 weight-%, more preferably at least 75 weight-%, more preferably at least 80 weight-%, more preferably at least 85 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-% of the cellulose based polymer are cotton, based on the total weight of the cellulose based polymer being 100 weight-%, more preferably the cellulose based polymer is cotton.

[0175] 3. The method of embodiment 1 or 2, wherein preparing biogas from the residue of the polymer blend according to (e) comprises microbial fermentation, more preferably anaerobically microbial fermentation.

[0176] 4. The method of embodiment 3, wherein the residue of the polymer blend is used in microbial fermentation, preferably in anaerobically microbial fermentation, as substrate or cosubstrate for biogas generation.

[0177] 5. The method of embodiment 3 or 4, wherein microbial fermentation, preferably anaerobically microbial fermentation, is done at a pH value in the range of from 4 to 9, preferably in the range of from 4.5 to 8.5, more preferably in the range of from 4.5 to 8.

[0178] 6. The method of any one of embodiments 1 to 5, comprising after (e)

[0179] (f) separating methane from the biogas obtained in (e) by one or more purification and / or concentration step(s), thereby obtaining methane (CH4) with a purity of at least 85 volume-%, more preferably at least 90 volume-%, even more preferably at least 95 volume-%, based on the total volume of the gas phase containing CH4 being 100 volume-%. 7. The method of any one of embodiments 1 to 6, comprising, if (b) is conducted, after (b) and before (c):

[0180] (v) washing the residue of the polymer blend obtained in (b) with a washing solvent, thereby obtaining a washed residue, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the third polymer and optionally the filler or a part of the filler;

[0181] (w) optionally drying the washed residue obtained in (v).

[0182] 8. The method of any one of embodiments 1 to 7, comprising after (c) and before step (d), if conducted, or after (c) and before step (e), if (d) is not conducted:

[0183] (w.1) optionally washing the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c) with acetone;

[0184] (w.2) washing the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler obtained in (c) or obtained in optional step (w.1) with water; wherein washing in (w.2) is preferably done until the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, comprises less than 10 weight-%, preferably less than 5 weight-%, more preferably less than 2 weight-%, of organic solvent(s), based on the total weight of the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, being 100 weight-%.

[0185] 9. The method of any one of embodiments 1 to 8, comprising after (c) and before step (d), if conducted, or before step (e)

[0186] (x.1) separating the solvent system, which is enriched in dissolved polyester and comprises optionally the filler or a part of the filler obtained in (c) from the residue of the polymer blend, wherein the separation is preferably done by heated filtration, more preferably by heated filtration at a temperature T3 in the range of from T2 minus 20 °C to T2 plus 20 °C (T3 = T2 ± 20°C), more preferably at a temperature T3 in the range of from T2 minus 10 °C to T2 plus 10 °C (T3 = T2 ± 10°C), thereby obtaining the solvent system, which is enriched in dissolved polyester and comprises optionally the filler or a part of the filler, separated;

[0187] (x.2) optionally contacting said residue of the polymer blend obtained in (x.1) with solvent system, preferably at a temperature T3 as defined above in (x.1), followed by filtration, preferably heated filtration at a temperature T3 as defined above in (x.1), thereby obtaining a residue of the polymer blend, which is further depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler; and a solvent system, which contains further amount of the polyester and comprises optionally the filler or a part of the filler;

[0188] (x.3) optionally combining the solvent system, which contains the further amount of the polyester and comprises optionally the filler or a part of the filler obtained in (x.2) with the solvent system, which is enriched in dissolved polyester and comprises optionally the filler or a part of the filler, separated in (x.1); wherein precipitation in (d) is done based on the separated solvent system obtained in (x.1) or based on the combined solvent system obtained in (x.3). The method of any one of embodiments 1 to 9 comprising after (d) and before (e)

[0189] (y.1) separating the precipitated polyester obtained in (d) from the solvent system, which is depleted in dissolved polyester and comprises optionally the filler or a part of the filler, thereby obtaining a precipitated polyester and the solvent system, which is depleted in dissolved polyester and which optionally comprises the filler or a part of the filler;

[0190] (y.2) optionally washing the precipitated polyester obtained in (y.1);

[0191] (y.3) drying the precipitated polyester obtained in (y.1) or the washed precipitated polyester obtained in (y.2), thereby obtaining a dried (washed) precipitated polyester;

[0192] (y.4) optionally pelletizing the dried (washed) precipitated polyester obtained in (y.3), thereby obtaining a pelletized polyester. The method of any one of embodiments 1 to 10 comprising after (d) and before (e), preferably after (y.3) or after (y.4) and before (e)

[0193] (z) increasing the intrinsic viscosity of the precipitated polyester obtained in (d) or of the dried (washed) precipitated polyester obtained in (y.3) or of the pelletized polyester obtained in (y.4). The method of any one of embodiments 1 to 11 , wherein precipitation in (d) comprises cooling the solvent system obtained in (c), which is enriched in dissolved polyester compared to the solvent system provided in (a), from T2 to a temperature below 140°C, wherein the cooling is done so that the temperature of the solvent system, which is enriched in dissolved polyester, is within the temperature range of from 160 to 145 °C for a period of time of at least 5 minutes, preferably at least 10 minutes, more preferably in the range from 5 to 120 minutes, more preferably in the range of from 10 to 100 minutes, more preferably in the range of from 15 to 100 minutes. The method of embodiment 12, wherein cooling in (d) is done so that the solvent system, which is enriched in dissolved polyester, has within the temperature range of from 160 to 145 °C a viscosity in the range of from 1 to 12 Pa s, preferably in the range of from 1 to 10 Pa s, determined according to ASTM D445. The method of embodiment 12 or 13, wherein cooling is done with a cooling rate of < 3.0 °C / min, preferably < 1.5 °C / min, more preferably in the range of from 0.05 to

[0194] 3.0 °C / min, more preferably in the range of from 0.13 to 3.0 °C / min, more preferably in the range of from 0.15 to 1.5 °C / min, more preferably in the range of from 0.15 to 1.0 °C / min. The method of any one of embodiments 12 to 14, wherein the cooling of the solvent system in (d) is done from T2 to a temperature below 100°C. The method of any one of embodiments 12 to 15, wherein the cooling of the solvent system in (d) is done without addition of an anti-solvent. The method of any one of embodiments 1 to 16, wherein the solvent system comprises one or more solvent(s), wherein

[0195] (s.1) the solvent system has Hansen solubility parameters with respect to energy from dispersion forces between molecules (5DSS), energy from dipolar intermolecular force between molecules (5PSS) and energy from hydrogen bonds between molecules (5HSS), which fullfill equitation 1

[0196] (8.8)2> 4(6Dss-20)2+ (5PSS-11.8)2+ (5Hss-4.5)2

[0197] [equitation 1];

[0198] (s.2) each solvent of the solvent system has a boiling point at 1013 hPa of at least

[0199] 160 °C; and

[0200] (s.3) solvents having a functional group selected from the group consisting of hydroxyl (OH), amino (NH2), carboxyl (COOH), and thiol (SH) are excluded. The method of any one of embodiments 1 to 17, wherein at least 90 weight-%, preferably at least 95 weight-%, more preferably at least 98 weight-%, more preferably at least 99 weight-%, of the solvent system consist of two or more solvent(s), wherein the respective mixture fulfill(s) equitation 1. The method of any one of embodiments 1 to 18, wherein the one or more solvent(s) is / are selected from the group consisting of N,N-dimethylbenzamide, N,N-dimethylphenyla- cetamide, 1,4-benzoquinone, acetophenone, dimethyl terephthalate, 1,3,5-trimethoxyben- zene, 2-phenylacetophenone, N-methylcaprolactam, methylbenzoate, methyl-4-methox- ybenzoate, butylene carbonate, N-ethylpyrrolidone, benzophenone, di-benzyl malonate, N-ethyl-caprolactam, methyl 2-(5-oxotetrahydrofuran-3-yl)acetate (FAME), methyl 2-(5- oxotetrahydrofuran-2-yl)acetate, propiophenone, N-methoxypropyl-pyrrolidone, 1,4-cyclo- hexanedione, cyclohexane-carbonate, N-methoxyethyl-pyrrolidone, N,N-diethylphenyla- cetamide, phenyl acetate, 1-(2-hydroxyethyl)pyrrolidin-2-one acetate (HEPAc), N,N-dieth- ylbenzamide, isopropyl-benzoate, cyclohexyl phenyl ketone, phenylacetic acid ethylester, phenylacetat.N-methyl-morpholine, benzyl-propionate, benzylacetate, Neopentyl-glycol- dibenzoate, tetrahydrofurfuryl acetate, N-methyl-imidazole, benzyl butyrate, 2-pyrrolidone, 2-phenoxyethanol propionate, 2-phenoxyethyl isobutyrate, N,N-dipropylbenzamide, N,N- dimethylacetamide, N,N-diethylacetamide, dihydrolevoglucosenon (Cyrene), propylenecarbonate, caprolactone, dimethylisosorbide, N-butylpyrrolidone, t-butylpyrrolidone, me- thyl-1-methyl-5-oxopyrrolidine-3-carboxylate (MMOC), gamma-valerolactone (GVL), delta- valerolactone, gamma butyrolactone, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodiasolv Polarclean), caprolactam, phen ethyl acetate, methyl phenylacetate, benzyl benzoate, N,N-dimethyllactamide (Agnique AMD 3L), 1,3-dimethyl-2-imidazolidinone (DMI) and dimethyl sulfoxide (DMSO).

[0201] 20. The method of any one of embodiments 1 to 19, wherein the one or more solvent(s) is / are selected from the group consisting of dihydrolevoglucosenon (Cyrene), propylenecarbonate, caprolactone, dimethylisosorbide, N-butylpyrrolidone, t-butylpyrrolidone, methyl-1- methyl-5-oxopyrrolidine-3-carboxylate (MMOC), gamma-valerolactone (GVL), Delta- valerolactone, gamma butyrolactone, dimethylsulfoxide, methyl 5-(dimethylamino)-2-me- thyl-5-oxopentanoate (RhodiasolvOPolarclean), caprolactam, phen ethyl acetate, methyl phenylacetate, benzyl benzoate, phenyl benzoate, methyl benzoate, propyl benzoate, and dimethyl sulfoxide (DMSO).

[0202] 21. The method of any one of embodiments 1 to 20, wherein the one or more solvent(s) of the solvent system is / are selected from the group consisting of propylenecarbonate, N-bu- tylpyrrolidone, t-butylpyrrolidone, methyl-1-methyl-5-oxopyrrolidine-3-carboxylate (MMOC), Delta-valerolactone, gamma butyrolactone, methyl 5-(dimethylamino)-2-methyl- 5-oxopentanoate (RhodiasolvOPolarclean), caprolactam, phenethyl acetate, methyl phenylacetate, benzyl benzoate, phenyl benzoate, methyl benzoate, propyl benzoate and GVL. The method of any one of embodiments 1 to 21 , wherein the one or more solvent(s) is / are selected from the group consisting of propylenecarbonate, N-butylpyrrolidone, t-butylpyr- rolidone, methyl-1-methyl-5-oxopyrrolidine-3-carboxylate (MMOC), Delta-valerolactone, gamma butyrolactone, methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodi- asolvOPolarclean), caprolactam, phen ethyl acetate, methyl phenylacetate, benzyl benzoate, phenyl benzoate, methyl benzoate, and propyl benzoate. The method of any one of embodiments 1 to 22, wherein the one or more solvent(s) of the solvent system is / are selected from the group consisting of propylenecarbonate, N-bu- tylpyrrolidone, t-butylpyrrolidone, methyl-1-methyl-5-oxopyrrolidine-3-carboxylate (MMOC), methyl 5-(dimethylamino)-2-methyl-5-oxopentanoate (RhodiasolvOPolarclean), phenethyl acetate, and GVL. The method of any one of embodiments 1 to 23, wherein the one or more solvent(s) is / are selected from the group consisting of propylenecarbonate, N-butylpyrrolidone, t-butylpyr- rolidone, methyl-1-methyl-5-oxopyrrolidine-3-carboxylate (MMOC), methyl 5-(dimethyla- mino)-2-methyl-5-oxopentanoate (RhodiasolvOPolarclean), and phen ethyl acetate. The method of any one of embodiments 1 to 24, wherein ethyl benzoate and butyl benzoate are excluded as solvent(s). The method of any one of embodiments 1 to 25, wherein

[0203] (s.3a) solvents having a functional group selected from the group consisting of hydroxyl (OH), amino (NH2), secondary amine (-NH-), carboxyl (COOH), and thiol (SH) are excluded. The method of any one of embodiments 1 to 26, wherein the one or more solvent(s) is / are selected from the group consisting of dihydrolevoglucosenon (Cyrene), methyl phenylacetate, 1 ,3-Dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO) and GVL. The method of any one of embodiments 1 to 27, wherein the one or more solvent(s) is / are GVL or dimethyl sulfoxide (DMSO) or a mixture of GVL and DMSO. The method of any one of embodiments 1 to 28, wherein the solvent system comprises gamma-valerolactone, wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least

[0204] 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of gamma-valerolac- tone, based on the total weight of the solvent system being 100 weight-%. The method of any one of embodiments 1 to 29, wherein the solvent system comprises dimethyl sulfoxide (DMSO), wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of DMSO, based on the total weight of the solvent system being 100 weight-%. The method of any one of embodiments 1 to 30, wherein the solvent system comprises gamma valerolactone (GVL) and dimethyl sulfoxide (DMSO), wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least

[0205] 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of GVL and DMSO, based on the total weight of the solvent system being 100 weight-%. The method of any one of embodiments 1 to 31 , wherein the solvent system is free of acidic and / or basic component(s), wherein preferably, the solvent system comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the solvent system being 100 weight-%. The method of any one of embodiments 1 to 32, wherein the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the residue being

[0206] 100 weight-%; and / or wherein the precipitated polyester obtained in (d) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the precipitated polyester being 100 weight-%.

[0207] 34. The method of any one of embodiments 1 to 33, wherein in optional step (b) the same solvent system as in (c) is used.

[0208] 35. The method of any one of embodiments 1 to 34, wherein the polyester is based on 1,4- butanediol or 1,2-ethandiol, more preferably the polyester according to (i) is selected from the group consisting of a polymer based on 1,4-butanediol and terephthalic acid (polybutylene terephthalate, PBT), a polymer based on 1,2-ethanediol and terephthalic acid (polyethylene terephthalate, PET), a copolymer of 1,4-butanediol, adipic acid and terephthalic acid (polybutylenadipat-terephthalat, PBAT), a polymer of 1,2-ethanediol and 2,5- furandicarboxylic acid (polyethylene furanoate, PEF) and mixtures of two or more of these (co)polymers, more preferably, the polyester comprises at least PET and / or PBT, more preferably the polyester is PET or PBT or a mixture of PET and PBT.

[0209] 36. The method of any one of embodiments 1 to 35, wherein the colorant is selected from the group consisting of dye and optical brightener and mixtures of dye and optical brightener.

[0210] 37. The method of any one of embodiments 1 to 36, wherein the second polymer is selected from the group consisting of polyurethane (Pll), polyethylene glycol (PEG), polytetrahydrofuran (pTHF), mixtures of these polymers and copolymers of these polymers, wherein the second polymer is more preferably Pll or a copolymer of Pll and PEG and / or pTHF, more preferably spandex (copolymer of Pll and PEG or of Pll and pTHF).

[0211] 38. The method of any one of embodiments 1 to 37, wherein the filler is selected from the group consisting of glass fiber, coal fiber, carbon black, inorganic salts (for example, talc, disodium carbonate), adhesive, thickener, antifoam agent, finishing agent (for example water / oil / stain repellent, flame retardant, anticrease agent, biocide), binder, surfactant (for example, softener, scouring agent, antistatic agent), desizing agent, bleaching agent, oxidant, UV filter, emulsionant, fixing agent, washing dispersant, profiling agent.

[0212] 39. The method of embodiment 38, wherein the polyester comprises, preferably is PBT and the filler is one or more selected from the group consisting of glass fiber, coal fiber, carbon black, inorganic salts (for example, talc, disodium carbonate), adhesive, thickener, antifoam agent, finishing agent (for example water / oil / stain repellent, flame retardant, anticrease agent, biocide), binder, surfactant (for example, softener, scouring agent, antistatic agent), desizing agent, bleaching agent, oxidant, UV filter, emulsionant, fixing agent, washing dispersant, profiling agent, preferably the filler is one or more selected from glass fiber, coal fiber, carbon black, inorganic salts (for example, talc, Na2CO3). The method of embodiment 39, wherein the polyester comprises, preferably is PET and the filler is one or more selected from the group consisting of glass fiber, coal fiber, carbon black, inorganic salts (for example, talc, disodium carbonate), adhesive, thickener, antifoam agent, finishing agent (for example water / oil / stain repellent, flame retardant, anticrease agent, biocide), binder, surfactant (for example, softener, scouring agent, antistatic agent), desizing agent, bleaching agent, oxidant, UV filter, emulsionant, fixing agent, washing dispersant, profiling agent, preferably the filler one or more selected from adhesive, thickener, antifoam agent, finishing agent (for example water / oil / stain repellent, flame retardant, anticrease agent, biocide), binder, surfactant (for example, softener, scouring agent, antistatic agent), desizing agent, bleaching agent, oxidant, UV filter, emulsionant, fixing agent, washing dispersant, profiling agent. The method of any one of embodiments 1 to 40, wherein the polymer blend further comprises a fourth polymer (iv), wherein the fourth polymer is different from the polyester (ii), from the third cellulose based polymer of (iii) and from the second polymer of (ii), wherein the fourth polymer is selected from polypropylene (PP), polyethylene (PE), polyamide (PA), and mixtures of two or more thereof. The method of embodiment 41 , wherein the fourth polymer, if present in the polymer blend, is part of the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c) and subjected to biogas preparation in (e). The method of any one of embodiments 1 to 42, wherein T1 is a temperature in the range of from 110 to < 170°C, preferably a temperature in the range of from 110 to 165 °C, more preferably a temperature in the range of from 120 to 160 °C, more preferably a temperature in the range of from 120 to 150 °C, more preferably in the range of from 151 to 160°C. The method of any one of embodiments 1 to 43, wherein T2 is a temperature in the range of from > 170°C to 200 °C, preferably a temperature in the range of from 175 to 190 °C, more preferably a temperature in the range of from 180 to 190 °C. The method of any one of embodiments 1 to 44, wherein (a), optionally (b), (c) and optionally (d) are done at a pressure in the range of from 800 to 200,000 hPa. 46. The method of any one of embodiments 1 to 45, wherein the contacting in (b) is done for a period of time of at least 5 minutes, preferably in the range of from 5 minutes to 10 hours, more preferably in the range of from 5 minutes to 5 hours, more preferably in the range of from 5 minutes to 4 hours.

[0213] 47. The method of any one of embodiments 1 to 46, wherein the contacting in (c) is done for a period of time of at least 0.1 hours, preferably in the range of from 1 minute to 10 hours, more preferably in the range of from 1 minute to 2 hours, more preferably in the range of from 5 minutes to 1 hour.

[0214] 48. The method of any one of embodiments 1 to 47, wherein the contacting in (b) and / or (c) is done with a in mass based ratio solvent system : polymer blend provided in (a) or residue obtained in (b) in the range of 1:1 to 100:1 , preferably in the range of from 1 :1 to 20:1.

[0215] 49. The method of any one of embodiments 1 to 48, wherein at least steps (b) and (c), preferably all steps, are done in an inert atmosphere, preferably in the presence of an inert gas, wherein the inert gas is preferably selected from the group consisting of argon, helium, neon, nitrogen and mixtures of two or more of these inert gases, preferably comprises at least nitrogen, more preferably the inert gas is nitrogen.

[0216] 50. The method of any one of embodiments 1 to 49, wherein at least steps (b) and (c), preferably all steps, are done batch-wise or continuous.

[0217] 51. The method of any one of embodiments 1 to 50, further comprising, work-up of the cellulose based polymer obtained in (d) or (w.2) before (e) by applying one or more treatments) selected from the group consisting of: mechanical treatment, preferably selected from the group consisting of milling, beating, shredding, tearing and mixtures of two or more of these treatments; thermal treatment, preferably selected from the group consisting of freezing, heating or boiling and mixtures of two or more of these treatments, preferably in combination with application of excess pressure (excess pressure = pressure > 1013 mbar); incubation in an aqueous alkaline solvent, which preferably comprises water and one or more alkali, preferably sodium, salt selected from the group consisting of sodium hydroxide, sodium carbonate, sodium monochloroacetate and a mixture of two or more thereof; incubation in an acidic solvent, preferably in one or more acid(s) selected from the group consisting of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid and formic acid; incubation in an ionic liquid, preferably in one or more ionic liquid(s) selected from the group consisting of 1-allyl-3-methylimidazolium chloride ([AMIM]CI), 1 -butyl-3- methylimidazolium chloride ([BMIM]CI), 1-butyl-3-methylimidazolium acetate ([BMIM][OAc]) and 1,5-diazabicyclonon-5-enium acetate ([DBNH][OAc]); incubation in N-methylmorpholine-N-oxide (NMMO); sonication; radiation; addition of an enzyme, preferably selected from the group consisting of cellulase, protease, pectinase, glucosidase, glucanotransferases, PET hydrolase (PETase) and lipase and mixtures of two or more of these enzymes, more preferably selected from the group consisting of p-1 ,4-exoglucanase, p-1 ,4-endoglucanase, p-1 ,4-cello- biohydrolase, p-glucosidase, pyrolase and mixtures of two or more of these enzymes; and microbial cultivation, preferably by adding a cellulolytic bacterial or fungal strain or mixed culture.

[0218] 52. The method of any one of embodiments 1 to 51 , wherein neither before (b) nor in-between steps (b) and (c) nor before step (c) the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) is contacted with an acidic component and / or a basic component.

[0219] 53. A method for preparing biogas from cellulose based polymer separated from a polymer blend comprising

[0220] (i) separation of cellulose based polymer from a polymer blend comprising cellulose based polymer and at least one further polymer different from the cellulose based polymer, thereby obtaining a separated cellulose based polymer fraction;

[0221] (ii) treating the cellulose based polymer fraction obtained in (i) with a solvent system, thereby obtaining a treated cellulose based polymer fraction;

[0222] (iii) preparing biogas from the treated cellulose based polymer fraction obtained in (ii).

[0223] 54. The method of embodiment 53, wherein neither before step (i) nor during step (i) nor inbetween steps (i) and (ii) the polymer blend or the separated cellulose based polymer fraction is contacted with an acidic component and / or a basic component. The method of embodiment 53 or 54, wherein the solvent system used in (ii) is free of acidic and / or basic components, wherein preferably the solvent system comprises less than 10 weight-%, preferably less than8 weight-%, more preferably less than6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic components, based on the total weight of the solvent system being 100 weight-%. The method of any one of embodiments 53 to 35, wherein the treated cellulose based polymer fraction obtained in (ii) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the treated cellulose based polymer fraction being 100 weight-% The method of any one of embodiments 53 to 56, wherein the solvent system comprises gamma-valerolactone, wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least

[0224] 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of gamma-valerolactone, based on the total weight of the solvent system being 100 weight-%. The method of any one of embodiments 53 to 57, wherein the solvent system comprises dimethyl sulfoxide, wherein more preferably at least 50 weight-%, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of dimethyl sulfoxide, based on the total weight of the solvent system being 100 weight-%. The method of any one of embodiments 53 to 58, wherein the solvent system comprises gamma valerolactone and dimethyl sulfoxide, wherein more preferably at least 50 weight- %, more preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of gamma valerolactone and dimethyl sulfoxide, based on the total weight of the solvent system being 100 weight-%. Biogas, preferably biogas comprising methane, obtained or obtainable from the method of any one of embodiments 1 to 52 or 53 to 59. Use of biogas according to embodiment 60, preferably of methane comprised in the biogas, preferably after purification and / or concentration, as carbon and / or hydrogen source. Use of biogas according to embodiment 61 , preferably biogas comprising at least 40 vol- ume-% methane, as source of energy, preferably as source of thermal energy, for one or more of the steps (b) to (d). Polyester obtained or obtainable from the method of any one of embodiments 1 to 52 or 53 to 61. Use of the polyester of embodiment 63 for textile applications, fiber applications, packaging applications, plastic applications, automotive applications, electronic applications, preferably for the production of food packaging, beverage packaging, clothing, foot wear, wire, cable, wherein preferably for textile applications, fiber applications, packaging applications, plastic applications, more preferably for the production of food packaging, beverage packaging, clothing and foot wear. A method for preparing a product comprising

[0225] (I) providing polyester of embodiment 63;

[0226] (II) preparing a textile, a fiber, a packaging, a plastic, an automotive part, an electronic part from the polyester provided in (I). The method of any one of embodiment 1 to 52, wherein (b) comprises:

[0227] (b.1) contacting the polymer blend with the solvent system at a temperature T1 of

[0228] < 170 °C, thereby obtaining a solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and a residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler;

[0229] (b.2) separating the solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, obtained in (b.1) from the residue, preferably by a physical separation method, thereby obtaining a separated solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, compared to the solvent system provided in (a); and

[0230] (b.3) separating the second polymer from the solvent system, thereby obtaining a separated fraction comprising the second polymer. Method, preferably according to any one of embodiments 1 to 52 or 53 to 64, comprising the further step: converting the second polymer and / or the re-obtained polyester, to obtain one or more monomer, polymer or polymer product. Method according to embodiment 67, wherein the monomer is a di- or polyol; preferably butandiol; aldehyde; preferably formaldehyde; di- or polyisocyanate; preferably methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), toluene diisocyanate (TDI), hexamethylenediisocyanate (HDI) or isophoronediisocyanate (IPDI); amide; preferably caprolactam; alkene; preferably styrene, ethene and norbornene; alkyne, (di)ester; preferably methyl methacrylate; mono or diacid; preferably adipic acid or terephthalic acid; diamine; preferably hexamethylenediamine, nonanediamine; or sulfones; preferably 4,4'-dichlorodiphenyl sulfone. Method according to embodiment 67 or 68, wherein the polymer is and / or the polymer product comprises polyamide (PA); preferably PA 6 or PA 66; polyisocyanate polyaddition product; preferably polyurethane (Pll), thermoplastic polyurethane (TPU), polyurea or polyisocyanurate (PIR); low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyvinyl acetate (PVA), polystyrene (PS), poly acrylonitrile butadiene styrene (ABS), poly styrene acrylonitrile (SAN), poly acrylate styrene acrylonitrile (ASA), polytetrafluoroethylene (PTFE), poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA), polybutadiene (BR, PBD), poly(cis-1 ,4-isoprene), poly(trans-1 ,4-iso- prene), polyoxymethylene (POM), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene adipate coterephthalate (PBAT), polyester (PES), polyether sulfone (PESLI), polyhydroxyalkanoate (PHA), poly-3-hydroxybutyrate (P3HB), poly-4-hy- droxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO), polylactic acid (PLA), polysulfone (PSU), polyphenylene sulfone (PPSLI), polycarbonate (PC), polyether ether ketone (PEEK), poly(p-phenylene oxide) (PPO), poly(p-phenylene ether) (PPE); or copolymer or mixture thereof. Method according to any one of embodiments 67 to 69, wherein the polymer and / or the polymer product is / are or is / are a part of: a part of a car; preferably cylinder head cover, engine cover, housing for charge air cooler, charge air cooler flap, intake pipe, intake manifold, connector, gear wheel, fan wheel, cooling water box, housing, housing part for heat exchanger, coolant cooler, charge air cooler, thermostat, water pump, radiator, fastening part, part of battery system for electromobility, dashboard, steering column switch, seat, headrest, center console, transmission component, door module, cover for car A, B, C or D pillar, spoiler, door handle, exterior mirror, windscreen wiper, windscreen wiper protection housing, decorative grill, cover strip, roof rail, window frame, sunroof frame, antenna panel, headlight and taillight, engine cover, cylinder head cover, intake manifold, airbag, cushion, or coating; a cloth; preferably shirt, trousers, pullover, boot, shoe, shoe sole, tight or jacket; an electrical part; preferably electrical or electronic passive or active component, circuit board, printed circuit board, housing component, foil, line, switch, plug, socket, distributor, relay, resistor, capacitor, inductor, bobbin, lamp, diode, LED, transistor, connector, regulator, integrated circuit (IC), processor, controller, memory, sensor, microswitch, microbutton, semiconductor, reflector housing for light-emitting diodes (LED), fastener for electrical or electronic component, spacer, bolt, strip, slide-in guide, screw, nut, film hinge, snap hook (snap-in), or spring tongue; a consumer, agricultural product or pharmaceutical product; preferably tennis string, climbing rope, bristle, brush, artificial grass, 3D printing filament, grass trimmer, zipper, hook and loop fastener, paper machine clothing, extrusion coating, fishing line, fishing net, offshore line and rope, vial, syringe, ampoule, bottle, sliding element, spindle nut, chain conveyor, plain bearing, roller, wheel, gear, roller, ring gear, screw and spring dampers, hose, pipeline, cable sheathing, socket, switch, cable tie, fan wheel, carpet, box or bottle for cosmetics, mattress, cushion, insulation, detergent, dishwasher tabs or powder, shampoo, body wash, shower gel, soap, fertilizer, fungicide, or pesticide; a packaging for the food industry; preferably mono- or multi-layer blown film, cast film (mono- or multi-layer), biaxially stretched film, or laminating film; or a part of a construction; preferably a rotor blade, insulating material, frame, housing, wall, coating, or separating wall. Method according to any one of embodiments 67 to 70, wherein the content of the second polymer and / or the polyester in the monomer, polymer and / or polymer product is 1 weight-% or more, preferably 2 weight-% or more, more preferably 5 weight-% or more, more preferably 15 weight-% or more, more preferably 30 weight-% or more, more preferably 40 weight-% or more, more preferably 60 weight-% or more, more preferably 80 weight-% or more, more preferably 90 weight-% or more, more preferably 95 weight-% or more; and / or wherein the content of the second polymer and / or the polyester in the monomer, polymer and / or polymer product is 100 weight-% or less, preferably 95 weight-% or less, more preferably 90 weight-% or less, more preferably 50 weight-% or less, more preferably 25 weight-% or less, more preferably 10 weight-% or less; and preferably wherein the content is determined based on identity preservation and / or segregation and / or mass balance and / or book and claim chain of custody models, preferably based on mass balance, preferably the International Sustainability and Carbon Certifica- tion (ISCC) standard.

[0231] The present invention is further illustrated by the following reference examples, comparative examples, and examples. Examples

[0232] Chemicals

[0233] ** PET having Hansen parameters according to the 5thEdition 5.1.03 (2008) of the HANSEN Solubility Parameters in Practice (HSPiP) of 5D = 18.2, 5P = 6.4 and 5H = 6.6

[0234] Reference Example 1 : Removal of colorants and / or second polymer (Spandex)

[0235] Polymeric material (in any processing form, e.g. textile, flakes etc.) was cut / shredded into pieces and placed in a reaction vessel (e.g. flask, tube, reaction vessel). GVL was added (in mass based ratio polymeric material : GVL 1:1 to 1:100, preferred 1:1-1 :20) and the mixture was heated by use of a suitable heating system (e.g. oil bath, heating blocks, mini-plant vessels) under inert gas atmosphere to a temperature in the range of from 60 to 160 °C. After 0.5-8 h the mixture was filtered, whereby GVL enriched in colorant and / or Spandex and (optionally colorant depleted and optionally at least partially filler depleted) polymeric material pieces were obtained, wherein the later were washed with a small amount of GVL. For an easy removal of GVL and a faster drying process of the (optionally colorant depleted and optionally at least partially filler depleted) polymeric material pieces, small amounts of acetone were optionally used in a second washing step. The thus obtained polymeric material pieces were dried (for example in a vacuum compartment dryer).

[0236] Reference Example 2: Separation of PET from Cotton

[0237] Polymeric material comprising PET and cotton - either treated according to Reference Example 1 in case of presence of Spandex and / or colorants- or fresh polymeric material comprising PET and cotton - in shredded form was placed in a reaction vessel (e.g. flask, tube, reaction vessel). Degassed GVL was added (in mass-based ratio GVL: polymeric material 1 :1 to 100:1 , preferred 1 :1-10:1) and the mixture was heated at 1013 mbar under inert gas atmosphere by use of a suitable heating system (e.g. oil bath, heating blocks, mini-plant vessels) to 185 °C so that a mixture was obtained, wherein PET was fully dissolved and dissolvable parts of filler, if present, were dissolved, but solid particles remained in the mixture. After 5-60 min the mixture was filtered (e.g. heated pressure filtration), whereby a filter cake with undissolved polymeric materials (cotton and undissolvable parts of filler, if present) and a filtrate with PET were obtained. The filter cake was optionally further washed with a small amount of hot GVL. As the filtrate started to cool-down the PET precipitated. The precipitate was filtrated, wherein the part of filler, if present, which was soluble in GVL but did not precipitate during cooling, was removed with the filtrate. The precipitated PET was washed with a small amount of GVL. For an easy removal of GVL and a faster drying process of the re-obtained colour-depleted PET powder, small amounts of acetone were optionally used in a second washing step. The filter cake (the residue of the polymer blend comprising the third cellulose based polymer) was also washed with a small amount of GVL. For an easy removal of GVL and a faster drying process of the cotton pieces, small amounts of acetone were optionally used in a second washing step and a washing with water of the filter cake was done so that the resulting cotton pieces had a content of less than 2 weight-% of organic solvents, based on the total weight of the filter cake being 100 weight- %.The thus obtained cotton pieces were dried (for example in a vacuum compartment dryer).

[0238] Reference Example 3: General procedure for solvent-based approach

[0239] Shredded cotton (textile sample) (125 g) was placed in a reaction vessel (e.g. flask, tube, vessel). The solvent was added (in mass-based ratio solvent : polymeric material 100:1 to 1:1, preferred 10:1-1 :1) and the mixture was heated by use of a suitable heating system (e.g. oil bath, heating blocks, mini-plant vessels) to maximum of a) the respective boiling point of the solvent, or b) to 210 °C, both under an inert gas atmosphere. After 1-60 min the mixture was filtered, whereby the cotton fraction was obtained as filter cake and the solvent as filtrate. For an easy removal of the solvent and a faster drying process, the solvent-treated cotton was washed with water. In case the solvent used is badly miscible in water, acetone can be used in a preceding washing step. The thus obtained cotton was dried (for example under air until weight constancy).

[0240] Reference Example 4: biochemical methane potential (BMP)

[0241] The BMP test was performed by mixing in a flask an inoculum (comprising microorganisms), with the respective sample as substrate (shredded, treated or untreated cotton or cotton derived from Reference Example 2). The mixture was then incubated under oxygen-free conditions at37 °C. The biogas produced was followed overtime and the methane content was analyzed by gas chromatography (GO). The method to be used was the manometric method. This method relied on the measurement of the pressure developed in the flasks due to biogas formation. The pressure in the flasks was registered and allowed to calculate the total volume of gas produced. By taking a sample of the gas and analyzing it in a GO, it was possible to determine the percentage of methane in the gas and hence the volume produced. The results were expressed as Nml methane / g VS (VS: volatile solids, here sample). “N” in “Nml” stands for normal and indicates that the volume was specified at a certain standard pressure and temperature of 1013 mbar and 0 °C. The trials were performed in 500 ml flasks at 37 °C and for approximately 56 days.

[0242] The inoculum used came from a municipal wastewater treatment plant in Uppsala, Sweden.

[0243] The organic loading used was 2 g VS of the test substrate / L and 6 g VS / L of inoculum (=wastewater sludge).

[0244] The BMP test was done for each substrate in triplicate, wherein the resulting methane values were indicated as average value of the three measurements. Besides the BMP done for each substrate in triplicate, a positive control with microcrystalline cellulose and a blank were conducted, wherein the cellulose control assessed the microbial activity present in the inoculum and the blank with only inoculum was included to subtract the methane produced by the inoculum, so that the Nml methane / g VS results below graphically shown in Fig. 1 and listed in Table 1 represent only the methane derived from the substrate.

[0245] Comparative Example 1 (C1): Shredded cotton

[0246] Shredded cotton (textile sample) (125 g) was used in a fermentation process as described in Reference Example 4. The amount of methane obtained is graphically shown in Fig. 1 and listed in Table 1.

[0247] Comparative Example 2 (C2): Treatment with enzyme

[0248] Shredded cotton (125 g) was used in a fermentation process as described in Reference Example 4, wherein cellulase mixture was additionally added. The amount of methane obtained is graphically shown in Fig. 1 and listed in Table 1.

[0249] Comparative Example 3(C3): Treatment with NaOH

[0250] Shredded cotton (textile sample) (125 g) was placed in a reaction vessel (e.g. flask, tube, vessel). 11% NaOH was added (in mass-based ratio NaOH : textile material, 10:1). The mixture was stirred at 50 °C for 1 hour. Thereafter, the supernatant solution was decanted, water was added to the residue (= cotton). The mixture was stirred for 30 minutes at room temperature (20-30 °C) and was subsequently filtered. This step was optionally repeated for several times. The treated cotton was then dried (for example under air until weight constancy).

[0251] The treated and dried cotton was then used in a fermentation process as described in Reference Example 4. The amount of methane obtained is graphically shown in Fig. 1 and listed in Table 1. Examples 1 to 4 (E1, E2, E3, E4): Solvent treatment

[0252] Cotton was obtained from a polymeric material (textile sample) according to Reference Example 2 with DMSO (E1), Cyrene (E2), methyl phenyl acetate (E3) or DMI (E4). The treated and dried cotton was then used in a fermentation process as described in Reference Example 4. The amount of methane obtained is graphically shown in Fig. 1 and listed in Table 1.

[0253] Example 5 (E5): GVL treatment

[0254] Cotton was obtained from a polymeric material (textile sample) according to Reference Example 2. The treated and dried cotton was then used in a fermentation process as described in Reference Example 4. The amount of methane obtained is graphically shown in Fig. 1 and listed in Table 1.

[0255] Table 1

[0256] Methane yield

[0257] It could be seen that cotton after a solvent-based approach (E1-E5) gave almost the same methane yield as when a conventional pretreatment with NaOH was done. And thus, gave more biomethane than a cotton sample which was just shredded and not treated with a solvent-based approach.

[0258] Short description of the Figure

[0259] Fig. 1 shows the amount of methane obtained from BMP of Comparative Examples 1 to 3 and Examples 1 to 5.

[0260] Cited Literature Anacleto, T.M.; Kozlowsky-Suzuki, B.; Wilson, A.E.; Enrich-Prast, A. Comprehensive Meta-Analysis of Pathways to Increase Biogas Production in the Textile Industry. Energies 2022, 15, 5574. https: / / doi.org / 10.3390 / en15155574

[0261] Elnaz Hasanzadeh, Safoora Mirmohamadsadeghi, Keikhosro Karimi, Enhancing energy production from waste textile by hydrolysis of synthetic parts, Fuel, Volume 218, 2018, Pages 41-48, ISSN 0016-2361, https: / / doi.Org / 10.1016 / j.fuel.2018.01.035.

[0262] Kumar, P., Samuchiwal, S. & Malik, A. Anaerobic digestion of textile industries wastes for biogas production. Biomass Conv. Bioref. 10, 715-724 (2020). https : / / do i . org / 10.1007 / s 13399-020-00601 -8

[0263] Xinyi Xiang, Xiaoguang Chen, Ruobin Dai, Ying Luo, Puyue Ma, Shengsheng Ni, Chengyu Ma, Anaerobic digestion of recalcitrant textile dyeing sludge with alternative pretreatment strategies, Bioresource Technology, Volume 222, 2016, Pages 252-260, ISSN 0960-8524, https: / / doi.Org / 10.1016 / j.biortech.2016.09.098

[0264] “Dyes and Pigments” Metin Agikyildiz, Kubra Gunes, Ahmet Gurses Springer, 2016 (ISBN: 10 : 3319338900)

[0265] Industrial Organic Pigments - Klaus Hunger, Thomas Heber, Martin II. Schmidt, Friedrich Reisinger, Stefan Wanne Wiley-VCH, 4th edition, 2018 (ISBN: 978-3-527-32608-2)

[0266] Chemistry and Technology of Natural and Synthetic Dyes and Pigments - Ashis Kumar Samanta, Nasser Awwad, IntechOpen, 2020 (ISBN: 9781789859980, 9781789859973, 9781839687587)

[0267] Encyclopedia of Color, Dyes, Pigments - Volume 1 , Gerhard Pfaff, de Gruyter, 2021 (ISBN: 311058588X)

[0268] Heinrich Zollinger: Color Chemistry: Syntheses, Properties, and Applications of Organic Dyes and Pigments. 3rd edition. WILEY-VCH Verlag, Weinheim 2003 (ISBN: 3-906390- 23-3)

[0269] Klaus Hunger (Ed.): Industrial Dyes: Chemistry, Properties, Applications. WILEY-VCH Verlag, Weinheim 2003 (ISBN: 3-662-01950-7)

[0270] Hermann Rath: Lehrbuch der Textilchemie. einschl. der textilchemischen Technologie. 2nd edition. Springer-Verlag, Berlin, Heidelberg 1963 (ISBN: 978-3-662-00065-6); Wilfried Kratzert, Rasmus Peichert

[0271] Farbstoffe. Quelle & Meyer, Heidelberg 1981 (ISBN: 3-494-01021-8)

[0272] Ullmann’s Encyclopedia of industrial chemistry, Wiley-VCH, 2000, sections “dyes and pigments” and “dyes, general survey” (ISBN: 9783527303854)

Claims

Claims1 . A method for preparing biogas comprising providing a polymer blend, which comprises(i) a polyester and(ii) optionally one or more component(s) selected from the group consisting of a second polymer, a colorant, and a filler;(iii) a cellulose based third polymer; wherein the optional second polymer (ii) and the cellulose based third polymer (iii) are different from each other and different from the polyester of (i); the method comprising:(a) providing the polymer blend and providing a solvent system comprising gamma valerolactone or dimethylsulfoxide or a mixture of gamma valerolatone and dimethyl sulfoxide, which comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the solvent system being100 weight-%;(b) optionally contacting the polymer blend with the solvent system at a temperature T 1 of < 170 °C, thereby obtaining a solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and a residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, optionally the cellulose based third polymer and optionally the filler or a part of the filler;(c) contacting the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) with the solvent system at a temperature T2 of > 170 °C, thereby obtaining a solvent system, which is enriched in dissolved polyester compared to the solvent system provided in (a) and comprises optionally the filler or a part of the filler, and a residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler;(d) optionally precipitating the polyester from the solvent system, which is enriched in dissolved polyester, obtained in (c), thereby obtaining a precipitated polyester and a solvent system, which is depleted in dissolved polyester and which optionally comprises the filler or a part of the filler;(e) preparing biogas from the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c); wherein neither before (b) nor in-between steps (b) and (c) nor before step (c) the polymer blend provided in (a) or the residue of the polymer blend optionally obtained in (b) is contacted with an acidic component and / or a basic component.

2. The method of claim 1 , wherein the residue of the polymer blend, which is depleted of polyester and comprises the cellulose based third polymer and optionally the filler or a part of the filler, obtained in (c) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the residue being 100 weight-%; and / or wherein the precipitated polyester obtained in (d) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the precipitated polyester being 100 weight-%.

3. The method of claim 1 or 2, wherein the cellulose based third polymer is selected from the group consisting of natural cellulose based polymer, synthetic cellulose based polymer and mixtures of one or more natural cellulose based polymer(s) and one or more synthetic cellulose based polymer(s), wherein a natural cellulose based polymer is preferably selected from the group consisting of cotton, cellulose, lignin, linen, viscose and mixtures of two or more thereof and wherein a synthetic cellulose based polymer is preferably viscose, wherein the cellulose based polymer preferably comprises at least cotton, more preferably at least 65 weight-%, more preferably at least 70 weight-%, more preferably at least 75 weight-%, more preferably at least 80 weight-%, more preferably at least 85 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-% of the cellulose based polymer are cotton, based on the total weight of the cellulose based polymer being 100 weight-%, more preferably the cellulose based polymer is cotton.

4. The method of any one of claims 1 to 3, wherein preparing biogas from the residue of the polymer blend according to (e) comprises microbial fermentation, more preferably anaerobically microbial fermentation.

5. The method of any one of claims 1 to 4, comprising after (e)(f) separating methane from the biogas obtained in (e) by one or more purification and / or concentration step(s), thereby obtaining methane (CH4) with a purity of at least 85 volume-%, more preferably at least 90 volume-%, even more preferably at least 95 volume-%, based on the total volume of the gas phase containing CH4 being 100 volume-%.

6. The method of any one of claims 1 to 5, wherein at least 50 weight-%, preferably at least 60 weight-%, more preferably at least 70 weight-%, more preferably at least 80 weight-%, more preferably at least 90 weight-%, more preferably at least 95 weight-%, more preferably at least 99 weight-% of the solvent system consists of gamma-valerolactone and / or DMSO, based on the total weight of the solvent system being 100 weight-%.

7. The method of any one of claims 1 to 6, wherein the polyester is based on 1 ,4-butanediol or 1 ,2-ethandiol, more preferably the polyester according to (i) is selected from the group consisting of a polymer based on 1 ,4-butanediol and terephthalic acid (polybutylene terephthalate, PBT), a polymer based on 1 ,2-ethanediol and terephthalic acid (polyethylene terephthalate, PET), a copolymer of 1 ,4-butanediol, adipic acid and terephthalic acid (polybutylenadipat-terephthalat, PBAT), a polymer of 1 ,2-ethanediol and 2,5-furandicar- boxylic acid (polyethylene furanoate, PEF) and mixtures of two or more of these (copolymers, more preferably, the polyester comprises at least PET and / or PBT, more preferably the polyester is PET or PBT or a mixture of PET and PBT; and / or wherein the second polymer is selected from the group consisting of polyurethane (Pll), polyethylene glycol (PEG), polytetrahydrofuran (pTHF), mixtures of these polymers and copolymers of these polymers, wherein the second polymer is more preferably Pll or a copolymer of Pll and PEG and / or pTHF, more preferably spandex (copolymer of Pll and PEG or of PU and pTHF); and / or wherein the polymer blend further comprises a fourth polymer (iv), wherein the fourth polymer is different from the polyester (ii), from the third cellulose based polymer of (iii) and from the second polymer of (ii), wherein the fourth polymer is selected from polypropylene (PP), polyethylene (PE), polyamide (PA), and mixtures of two or more thereof.

8. A method for preparing biogas from cellulose based polymer separated from a polymer blend comprising(i) separation of cellulose based polymer from a polymer blend comprising cellulose based polymer and at least one further polymer different from the cellulose based polymer, thereby obtaining a separated cellulose based polymer fraction;(ii) treating the cellulose based polymer fraction obtained in (i) with a solvent system comprising gamma valerolactone or dimethyl sulfoxide or a mixture of gamma valerolactone and dimethyl sulfoxide, which comprises less thanlO weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the solvent system being 100 weight-%, thereby obtaining a treated cellulose based polymer fraction;(iii) preparing biogas from the treated cellulose based polymer fraction obtained in (ii); wherein neither before step (i) nor during step (i) nor in-between steps (i) and (ii) the polymer blend or the separated cellulose based polymer fraction is contacted with an acidic component and / or a basic component.

9. The method of claim 8, wherein the treated cellulose based polymer fraction obtained in (ii) comprises less than 10 weight-%, preferably less than 8 weight-%, more preferably less than 6 weight-%, more preferably less than 5 weight-%, more preferably less than 4 weight-%, more preferably less than 3 weight-%, more preferably less than 2 weight-%, more preferably less than 1 weight-% of acidic and / or basic component(s) based on the total weight of the treated cellulose based polymer fraction being 100 weight-%.

10. Biogas, preferably biogas comprising methane, obtained or obtainable from the method of any one of claims 1 to 7 or 8 or 9.11 . Use of biogas according to claim 10, preferably of methane comprised in the biogas, preferably after purification and / or concentration, as carbon and / or hydrogen source; preferably biogas comprising at least 40 volume-% methane, as source of energy, preferably as source of thermal energy, for one or more of the steps (b) to (d).

12. Polyester obtained or obtainable from the method of any one of claims 1 to 7 or 8 or 9.

13. Use of the polyester of claim 12 for textile applications, fiber applications, packaging applications, plastic applications, automotive applications, electronic applications, preferably for the production of food packaging, beverage packaging, clothing, foot wear, wire, cable,wherein preferably for textile applications, fiber applications, packaging applications, plastic applications, more preferably for the production of food packaging, beverage packaging, clothing and foot wear.

14. A method for preparing a product comprising(I) providing polyester of claim 12;(II) preparing a textile, a fiber, a packaging, a plastic, an automotive part, an electronic part from the polyester provided in (I).

15. The method of any one of claim 1 to 7, wherein (b) comprises:(b.1) contacting the polymer blend with the solvent system at a temperature T1 of< 170 °C, thereby obtaining a solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, and a residue of the polymer blend, which is depleted of said second polymer and / or colorant and optionally in the filler or in a part of the filler, and comprises the polyester, the cellulose based third polymer and optionally the filler or a part of the filler;(b.2) separating the solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, obtained in (b.1) from the residue, preferably by a physical separation method, thereby obtaining a separated solvent system, which is enriched in dissolved second polymer and / or colorant and optionally in the filler or in a part of the filler, compared to the solvent system provided in (a); and(b.3) separating the second polymer from the solvent system, thereby obtaining a separated fraction comprising the second polymer.

16. Method according to any one of claims 1 to 7 or 15, comprising the further step: converting the second polymer and / or the re-obtained polyester, to obtain one or more monomer, polymer or polymer product; wherein preferably, the monomer is a di- or polyol; preferably butandiol; aldehyde; preferably formaldehyde; di- or polyisocyanate; preferably methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyl diisocyanate (pMDI), toluene diisocyanate (TDI), hexamethylenediisocyanate (HDI) or isophoronediisocyanate (IPDI); amide; preferably caprolactam; alkene; preferably styrene, ethene and norbornene; alkyne, (di)ester; preferably methyl methacrylate; mono or diacid; preferably adipic acid or terephthalic acid; diamine; preferably hexamethylenediamine, nonanediamine; or sulfones; preferably 4,4'-di- chlorodiphenyl sulfone; and / orwherein preferably, the polymer is and / or the polymer product comprises polyamide (PA); preferably PA 6 or PA 66; polyisocyanate polyaddition product; preferably polyurethane (Pll), thermoplastic polyurethane (TPU), polyurea or polyisocyanurate (PIR); low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyvinyl acetate (PVA), polystyrene (PS), poly acrylonitrile butadiene styrene (ABS), poly styrene acrylonitrile (SAN), poly acrylate styrene acrylonitrile (ASA), polytetrafluoroethylene (PTFE), poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA), polybutadiene (BR, PBD), poly(cis-1 ,4-isoprene), poly(trans-1 ,4- isoprene), polyoxymethylene (POM), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene adipate coterephthalate (PBAT), polyester (PES), polyether sulfone (PESLI), polyhydroxyalkanoate (PHA), poly-3-hydroxybutyrate (P3HB), poly- 4-hydroxybutyrate (P4HB), polyhydroxyvalerate (PHV), polyhydroxyhexanoate (PHH), polyhydroxyoctanoate (PHO), polylactic acid (PLA), polysulfone (PSU), polyphenylene sulfone (PPSLI), polycarbonate (PC), polyether ether ketone (PEEK), poly(p-phenylene oxide) (PPO), poly(p-phenylene ether) (PPE); or copolymer or mixture thereof; and / or wherein preferably, the polymer and / or the polymer product is / are or is / are a part of: a part of a car; preferably cylinder head cover, engine cover, housing for charge air cooler, charge air cooler flap, intake pipe, intake manifold, connector, gear wheel, fan wheel, cooling water box, housing, housing part for heat exchanger, coolant cooler, charge air cooler, thermostat, water pump, radiator, fastening part, part of battery system for electromobility, dashboard, steering column switch, seat, headrest, center console, transmission component, door module, cover for car A, B, C or D pillar, spoiler, door handle, exterior mirror, windscreen wiper, windscreen wiper protection housing, decorative grill, cover strip, roof rail, window frame, sunroof frame, antenna panel, headlight and taillight, engine cover, cylinder head cover, intake manifold, airbag, cushion, or coating; a cloth; preferably shirt, trousers, pullover, boot, shoe, shoe sole, tight or jacket; an electrical part; preferably electrical or electronic passive or active component, circuit board, printed circuit board, housing component, foil, line, switch, plug, socket, distributor, relay, resistor, capacitor, inductor, bobbin, lamp, diode, LED, transistor, connector, regulator, integrated circuit (IC), processor, controller, memory, sensor, microswitch, microbutton, semiconductor, reflector housing for light-emitting diodes (LED), fastener for electrical or electronic component, spacer, bolt, strip, slide-in guide, screw, nut, film hinge, snap hook (snap-in), or spring tongue; a consumer, agricultural product or pharmaceutical product; preferably tennis string, climbing rope, bristle, brush, artificial grass, 3D printing filament, grass trimmer, zipper, hook and loop fastener, paper machine clothing, extrusion coating, fishing line,fishing net, offshore line and rope, vial, syringe, ampoule, bottle, sliding element, spindle nut, chain conveyor, plain bearing, roller, wheel, gear, roller, ring gear, screw and spring dampers, hose, pipeline, cable sheathing, socket, switch, cable tie, fan wheel, carpet, box or bottle for cosmetics, mattress, cushion, insulation, detergent, dishwasher tabs or powder, shampoo, body wash, shower gel, soap, fertilizer, fungicide, or pesticide; a packaging for the food industry; preferably mono- or multi-layer blown film, cast film (mono- or multi-layer), biaxially stretched film, or laminating film; or a part of a construction; preferably a rotor blade, insulating material, frame, housing, wall, coating, or separating wall.