Method for recycling a polyol

Abstract

The present invention relates to a method for recycling a polyol, comprising the steps of a) providing a mixture comprising at least one polyol and at least one impurity, wherein said at least one impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product, and b) treating the mixture provided in step a) with a porous, fine-grained solid to give a polyol comprising phase, wherein said phase is at least depleted or even free of the at least one impurity.

Description

[0001] Method for recycling a polyol

[0002] The present invention relates to a process for recycling a polyol, specifically, a polyol which is part of a mixture comprising at least one polyol and at least one impurity, wherein said at least one impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product. The present invention also relates to a recycled polyol comprising not more than 7 wt.-% of one or more impurities, and a process for preparing a polyurethane product, wherein the polyurethane product is prepared from the recycled polyol obtained by the process according to the present invention, or the recycled polyol according to the present invention.

[0003] It is widely known that the main components of polyurethane foam can be chemically recycled. This includes technologies based on glycolysis, hydrolysis, aminolysis, or acidolysis, often also referred to as chemolysis. However, the quality of the recycled polyol produced on a commercial scale so far is poor as these products are normally recovered as a mixture of the polyol with oligomers or other components such as 2,4- and / or 2, 6-diaminotoluene (TDA) formed during the depolymerization. Thus, it is beneficial to limit the use of these recycled polyols in PU foam production to a maximum of 30 % to ensure that the physical and mechanical properties of the resulting flexible PU foams are not affected.

[0004] Processes for depolymerization of polyurethane, recovery of the recycled polyol, and re-use of the same are known from the art, for example, from WO 2022 / 042909 A1 . Depolymerization of polyurethane flexible foam can be conducted using acidolysis, glycolysis, aminolysis, or hydrolysis processes.

[0005] However, when the process is scaled-up, several factors which influence the foam production become relevant. One of these factors is the presence of impurities in the polyol, such as the residual toluene diamine. However, also new factors, which influence the foam production, arise upon scale-up, namely the presence of oxidized products and residual oligomers in the recovered polyol product. Several impurities, e.g., toluene diamine oxidation products, are formed during the process and the subsequent work-up process, which remain in the recycled polyol product. Identity, structure, and properties, e.g., toxicity, of the oxidized toluene-diamine products are described in the literature, for example, in A. Meyer, K. Fischer, Oxidative transformation processes and products of p-phenylenediamine (PPD) and p- toluenediamine (PTD) - a review, Environmental Science Europe, 27:11 , 2015; J. de Souza, B. Da Silva, D. Morales, G. de Arago Ubuzeiro, M. Zanoni, Assessment of the autooxidation mechanism of p- toluenediamine by air and hydrogen peroxide and determination of mutagenic environmental contaminant in beauty salon effluent, Science of the Total Environment, 685, 911-922, 2019; and A. Goux, D. Pratt, L. Dunsch, The Reaction Mechanism pf p-Toluenediamine Anodic Oxidation: An In Situ ESR-UV / Vis / NIR Spectroelectrochemical Study, ChemPhysChem, 8, 2101-2106, 2007. These and analogous impurities cause several problems in the production of new polyurethane products and their properties. Firstly, the resulting polyol products are dark yellow, dark brown or even black because the impurities comprised therein typically contain chromophore units. This coloration of course also affects the color of the polyurethane products that are prepared from the recycled polyol products, which is generally undesired. Secondly, these impurities drastically limit the use of recycled polyol in the production of new polyurethane products. A major issue is that there are issues in the foam formulation above a threshold of 0.1 wt.-% of TDA in the recycled polyol, then the new polyurethane cannot be foamed properly. For the remaining amount, polyols obtained from fossil resources would have to be incorporated, which is undesired from an ecological point of view. Therefore, it is important to either avoid the formation of the impurities or to remove them from the recycled polyol as much as possible.

[0006] The levels of individual impurities in the recycled polyol can be determined by using an HPLC method with a reverse chromatography column / LC / MS, which allows the determination of the structure of the separated components.

[0007] The use of antioxidants and inert conditions can decrease the level of oxidized products in the foam production. A lot of standard polyols already contain antioxidants, which also has an influence on the color of the recycled polyol product obtained in the process. The higher use level in recycling processes inevitably results in increased amounts of residual antioxidants along with the oxidized forms that may cause an issue in foam production and subsequent foam physical properties.

[0008] Consequently, there was still a need for providing a recycled polyol with a low degree of impurities.

[0009] It was found that this problem is solved by treating a mixture comprising at least one polyol and at least one impurity with a porous, fine-grained solid to give a polyol comprising phase, wherein said phase is at least depleted or even free of the at least one impurity.

[0010] An object of the present invention is therefore a method for recycling a polyol, comprising the steps of a) providing a mixture comprising at least one polyol and at least one impurity, wherein said at least one impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product, and b) treating the mixture provided in step a) with a porous, fine-grained solid to give a polyol comprising phase, wherein said phase is at least depleted or even free of the at least one impurity.

[0011] In the context of the present invention the term polyurethane (PU) or polyurethane product is used as known to the person skilled in the art and denotes a product obtained by the reaction of (poly)isocyanates with polyols, or by the reaction of (poly)isocyanates with compounds having isocyanate-reactive groups. Further functional groups in addition to the polyurethane can also be formed in the reaction, for example uretdiones, carbodiimides, isocyanurates, allophanates, biurets, ureas, and / or uretonimines. Therefore, in the content of the present invention the term polyurethane or polyurethane product comprises all reaction products derived by isocyanates, in particular (poly)isocyanates, and suitable isocyanate-reactive molecules. These include polyisocyanurates, polyureas, and allophanate-, biuret-, uretdione-, uretonimine- or carbodiimides-containing isocyanate or (poly)isocyanate reaction products. In the context of the present invention a depolymerization of a polyurethane product is used as known to the person skilled in the art and may be any type of reaction leading to a depolymerization of the polyurethane product in question. In detail, said depolymerization may involve a hydrolysis, glycolysis, acidolysis, and / or aminolysis of the urethane bonds in the polyurethane product.

[0012] In the context of the present invention the term a porous, fine-grained solid is used to denote a solid having an outer surface and an inner surface, e.g., pores.

[0013] The mixture is not subject to any limitations regarding its concentration, and viscosity, provided that said mixture can go through the porous, fine-grained solid, e.g., adsorbent, and be collected as polyol comprising phase. Hence, the mixture is typically a solution, emulsion or dispersion comprising at least one polyol and at least one impurity, wherein said at least one impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product.

[0014] During step b), the mixture may be mechanically agitated. Any known technique for mechanical agitation may be used, such as the incorporation of a mechanical stirrer performing axially, tangentially, radially, or both axial and radial agitation. Other techniques may comprise shaking, such as orbital shaking (vortexing). The mechanical agitation, e.g., stirring, may be performed for a time ranging from 0.5 h to 5 h, preferably, from 1 h to 2 h.

[0015] The method according to the present invention in particular allows for a removal or at least significant reduction in the content of the impurities resulting from the oxidation of toluene diamines.

[0016] The method according to the present invention also allows for a removal or at least significant reduction in the content of other impurities, such as additives, for example, surfactants, fillers, stabilizers, dyes, polymers apart from polyurethane, e.g., styrene-acrylonitrile polymers, catalysts, chain length extenders, curing agents and / or flame retardants or further impurities resulting from process variations.

[0017] Changes in color can result from the contamination of the polyol with impurities, from process variations or residual additives used in the original foam production such as dyes and pigments. In the context of the present invention, the color of the samples was determined according to the Gardner color scale. The Gardner color scale is a one-dimensional scale used to measure the shade of the color yellow. This scale describes the yellowing of transparent liquids from 1 to 18, with 1 for light yellow and 18 for dark brown.

[0018] In the context of the present invention a polyol comprising phase is at least depleted or even free of the at least one impurity, when it has a lower content or degree of said at least one impurity than before being subjected to the method according to the present invention.

[0019] Without wishing to be bound to a specific theory, it is believed that the at least one impurity contained in the mixture is adsorbed by the porous, fine-grained solid in step b) of the method according to the present invention, while the at least polyol is not adsorbed and remains in the liquid. This adsorption may happen on the outer and / or inner surface of the porous, fine-grained solid in question, e.g., adsorbent. It is believed that this leads at least to a depletion or even removal of the at least one impurity, and on the other side, to an enrichment of the at least one polyol, in case no additional solvents are used for washing the porous, fine-grained solid, e.g., adsorbent.

[0020] In an embodiment of the method according to the present invention the porous, fine-grained solid is an adsorbent.

[0021] In the context of the present invention the term adsorption is used to denote the adhesion of atoms, ions, or molecules from a gas, liquid or dissolved solid to a surface. Consequently, the term adsorbent denotes the solid on whose surface, outer and inner surface (pores), the adsorption takes place.

[0022] In principle, the method according to the present invention is not subject to any limitation regarding a specific porous, fine-grained solid, e.g., adsorbent, provided that the porous, fine-grained solid, e.g., adsorbent is suitable for providing the polyol comprising phase being depleted or even free of the at least one impurity. Neither is the method according to the present invention subject to any limitation regarding the number of porous, fine-grained solids, e.g., adsorbents, provided that the resulting combination of porous, fine-grained solids, e.g., adsorbents is suitable for providing the polyol comprising phase being depleted or even free of the at least one impurity.

[0023] The surface area of the fine-grained solid can be described in terms of its Brunauer-Emmett-Teller (BET) surface area. The BET surface area is preferably measured in accordance with ISO 9277:2022 using nitrogen as adsorptive. Preferably the BET surface area of the fine-grained solid is at least 50 m2 / g, more preferably at least 100 m2 / g, more preferably at least 250 m2 / g, most preferably at least 600 m2 / g.

[0024] In an embodiment of the method according to the present invention the porous, fine-grained solid, e.g., adsorbent comprises or consists of charcoal, activated acid-washed charcoal, an alkaline earth silicate, an alkali silicate, aluminum diacetate, a zeolite, a bentonite, or a combination thereof.

[0025] In a preferred embodiment of the invention the fine-grained solid comprises charcoal, preferably is charcoal. Among charcoal activated charcoal, especially activated acid-washed charcoal, is particularly preferred.

[0026] In the context of the present invention the term activated charcoal is used synonymous with activated carbon and denotes steam-treated coal (biochar, charcoal), which has a larger surface area due to the treatment.

[0027] It is preferred that the porous, fine-grained solid, e.g., adsorbent used in the method according to the present invention is not soluble in the phase of the mixture provided in step a) and / or in the solvent used in step a) and / or b), because an insoluble porous, fine-grained solid, e.g., adsorbent can be easily removed from the polyol comprising phase obtained in said method, for example by filtration, leaving no by-products originating from the treatment in step b) in the polyol comprising phase. Alternatively, it is also possible to use a carried or supported porous, fine-grained solid, e.g., adsorbent with the porous, fine-grained solid, e.g., adsorbent being one or more adsorbents suitable for step b) and one or more of them being soluble or insoluble in the phase of the mixture provided in step a) and / or in the solvent used in step a) and / or b). For example, it is possible that the porous, fine-grained solid, e.g., adsorbent has been applied to a classical carrier, such as a bead or a plate. In addition or alternatively, it is also possible that the porous, fine-grained solid, e.g., adsorbent has been applied to the wall or any internal parts of the reactor in which the step b) is carried out. Hence, the shape and formulation of the porous, fine-grained solid, e.g., adsorbent are also not subject to any limitations, for example, it can be a powder, granulate, pellet, and one or more porous, fine-grained solid, e.g., adsorbent beds.

[0028] In one embodiment the porous, fine-grained solid, e.g., adsorbent is present as powder, granulate, pellet, one or more porous, fine-grained solid, e.g., adsorbent beds, supported or carried porous, fine-grained solid, e.g., adsorbent, or a combination thereof.

[0029] The particle size distribution of the fine-grained solid preferably measured in accordance with ISO 13320. The particle size distribution can be described a threshold diameter below which a certain percentage of the particle size lies, e.g. the term “X90” means that ninety percent (90%) of the particles in a sample are smaller in diameter than that given number in a volume-weighted particle size distribution. Preferably X90 is at most 500 pm, more preferably at most 300 pm, even more preferably at most 200 pm, most preferably at most 150 pm. It is further preferred for xso to beat most 100 pm, more preferably at most 80 pm, even more preferably at most 50 pm, most preferably at most 30 pm. It is preferred for xio to be at most 25 pm, more preferably at most 15 pm, most preferably at most 10 pm.

[0030] The mixture provided in step a) can be obtained by any process suitable for depolymerizing polyurethane products, such as polyurethane foams, known in the art. The variety of said chemical depolymerization processes are also referred to as chemolysis. The depolymerization may therefore comprise hydrolysis, glycolysis, acidolysis, and / or aminolysis, with hydrolysis being preferred. In detail, said depolymerization comprises the hydrolysis, glycolysis, acidolysis, and / or aminolysis of those bonds or moieties in the polyurethane product, which are sensitive to hydrolysis, glycolysis, acidolysis, and / or aminolysis, such as urethanes, ureas, uretdiones, carbodiimides, isocyanurates, allophanates, biurets, and / or uretonimines.

[0031] When the depolymerization process or chemolysis is a hydrolysis, it is preferred that the polyurethane is reacted with an excess of at least one base, and if necessary, in the presence of at least one phasetransfer catalysts, optionally at elevated pressure and elevated temperature.

[0032] In another embodiment the mixture of step a) results from the hydrolysis, glycolysis, acidolysis, and / or aminolysis of the polyurethanes contained in a polyurethane product. According to the present invention the mixture being subjected to the method comprises at least one polyol and at least one impurity, wherein said at least one impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product. There is a large variety of starting materials for preparing polyurethane products and thus, also a large variety of potential reactions, which said materials may undergo during and / or after the depolymerization of the polyurethane product. Hence, it is not only challenging but close to impossible to further specify the respective and all conceivable impurities resulting from subsequent reactions.

[0033] However, since the relevant starting compounds contain isocyanate groups, and the formed polyurethane products contain urea bonds, the respective products resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product may comprise impurities which may therefore comprise at least two amine and / or imine groups, or at least one urea group in combination with at least two amine groups, preferably at least two aromatic amine and / or imine groups, or at least one diaryl group in combination with at least two aromatic amine groups. The further oxidation of amines and imines may lead to alcohols, aldehydes, or ketones as further impurities, for example a hydroquinone or an aromatic azo compound.

[0034] In a further embodiment the product resulting from the oxidation of toluene diamines comprises at least two amine and / or imine groups, at least one urea group in combination with at least two amine groups, and / or at least one alcohol, aldehyde and / or ketone.

[0035] The mixture provided in step a) may contain further compounds or components as additional impurities, in addition to at the least one impurity which comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product. Examples for said additional impurities comprise additives known to the person skilled in the art, such as surfactants, fillers, stabilizers, dyes, polymers apart from polyurethane, such as styrene-acrylonitrile polymers, catalysts, chain length extenders, curing agents or flame retardants.

[0036] In an embodiment the mixture of step a) of the method according to the present invention further comprises a surfactant, filler, stabilizer, dye, polymer apart from polyurethane, catalyst, chain length extender, curing agent and / or flame retardant.

[0037] In the context of the present invention, polyols are all organic substances having two or more isocyanatereactive groups, preferably OH groups, and also formulations thereof. Preferred polyols include any polyether polyols, polyester polyols, hydroxyl-containing aliphatic polycarbonates, especially polyether polycarbonate polyols, and natural oil-based polyols (NOPs), that are typically used for the production of polyurethane systems, especially PU foams, and any mixtures thereof. The polyols usually have a functionality of 1 .8 to 8 and number-average molecular weights preferably in the range from 500 to 15,000 g / mol. The polyols are preferably used with OH numbers in the range from 10 to 1 ,200 mg KOH / g. The number-average molecular weights are typically determined by gel permeation chromatography (GPC), especially using polypropylene glycol as reference substance and tetrahydrofuran (THF) as eluent. The number average molecular weight can be determined in accordance with the standard ISO 13885-1 . The OH number can be determined, in particular, in accordance with the standard DIN 53240:1971 -12 or ASTM D 4274-21 .

[0038] Polyether polyols are polyethers containing usually two or three, but in some cases also up to eight, hydroxy end groups. Polyether polyols are primarily produced by ring-opening polymerization or copolymerization from ethylene oxide, propylene oxide or tetrahydrofuran. Polyether polyols having only two hydroxy end groups are obtained for example when initiators such as water, ethylene glycol or propylene glycol are used. On the other hand, polyether polyols of higher functionalities are obtained when glycerol or trimethylolpropane (three functionalities), pentaerythritol (four functionalities), D-glucitol (six functionalities) and sucrose (eight functionalities) are used as initiators. Polyether polyols having functionalities of three to eight and molar masses of 400 to 1 ,200 g / mol are used for hard / rigid foams, materials, and coatings. Polyether polyols having functionalities of two to three and molar masses of 1 ,000 to 6,500 g / mol are on the other hand used for the production of flexible polyurethane and polyester foams and of elastomers. They are sold under names such as Carbowax™, Jeffox®, Plurocol®, Polyglycol, Polymeg®, Terathane® and Vibrathane®.

[0039] Polyester polyols are preferably based on esters of polybasic aliphatic or aromatic carboxylic acids, preferably having 2 to 12 carbon atoms. Examples of aliphatic carboxylic acids are succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, and fumaric acid. Examples of aromatic carboxylic acids are phthalic acid, isophthalic acid, terephthalic acid and the isomeric naphthalenedicarboxylic acids. The polyester polyols are obtained by condensation of these polybasic carboxylic acids with polyhydric alcohols, preferably of diols or triols having 2 to 12, more preferably having 2 to 6, carbon atoms, preferably trimethylolpropane and glycerol.

[0040] Polyether polycarbonate polyols are preferably polyols containing carbon dioxide bound in the form of carbonate. Since carbon dioxide forms as a by-product in large volumes in many processes in the chemical industry, the use of carbon dioxide as comonomer in alkylene oxide polymerizations is of particular interest from a commercial point of view. Partial replacement of alkylene oxides in polyols with carbon dioxide has the potential to distinctly lower the costs for production of polyols. Moreover, the use of carbon dioxide as comonomer is very advantageous in environmental terms since this reaction constitutes the conversion of a greenhouse gas to a polymer. The preparation of polyether polycarbonate polyols by addition of alkylene oxides and carbon dioxide onto H-functional starter substances by use of catalysts is well known. Various catalyst systems can be used here: The first generation was that of heterogeneous zinc or aluminum salts, as described, for example, in US 3900424 or US 3953383. In addition, mono- and binuclear metal complexes have been successfully used for copolymerization of carbon dioxide and alkylene oxides, as described, for example, in WO 2010 / 028362 A, WO 2009 / 130470 A1 , WO 2011 / 163133 A1 , or WO 2013 / 022932 A1 . The most important class of catalyst systems for the copolymerization of carbon dioxide and alkylene oxides is that of double metal cyanide catalysts, also referred to as DMC catalysts, as described, for example, in US 4500704, or US 2009 / 306239 A1 . Suitable alkylene oxides and H-functional starter substances are those also used for preparing carbon ate -free polyether polyols, as described above. As you can see, there is a large variety of possible polyols that can be recycled by using the method according to the present invention. Nevertheless, the polyols that can be recycled using the method according to the present invention can be characterized in that they have a number average molecular weight Mnin the range from 500 to 15,000 g / mol, determined in accordance with ISO 13885-1 , and / or a hydroxyl value (OH value) in the range from 45 to 60, determined in accordance with standard DIN 53240:1971 -12 or ASTM D 4274-21 .

[0041] In an embodiment the polyol (recycled polyol or polyol to be recycled) has a number average molecular weight Mnin the range from 500 to 15,000 g / mol, determined in accordance with ISO 13885-1 .

[0042] In another embodiment the polyol (recycled polyol or polyol to be recycled) is characterized by a hydroxyl value (OH value) in the range from 45 to 60, determined in accordance with standard DIN 53240:1971 -12 or ASTM D 4274-21.

[0043] In a further embodiment the polyol (recycled polyol or polyol to be recycled) is one or more from the list comprising polyether polyols, polyester polyols, polyether polycarbonate polyols, natural oil-based polyols, polymer polyols, or a combination thereof.

[0044] The method according to the present invention is preferably performed in the presence of a solvent comprising or consisting of a non-polar aprotic solvent. A non-polar aprotic solvent can be used in the method according to the present invention for ease of handling, for example better solubility of any components in the mixture of step a).

[0045] In the context of the present invention the term non-polar aprotic solvent is used as known to the person skilled in the art and denotes a solvent that lacks an acidic proton and an overall dipole in the molecule.

[0046] Suitable non-polar aprotic solvents are, for example, substances of the following classes or substances containing any of the following moieties: aromatic hydrocarbons (e.g., C5-C10 alkyl aromatic), aliphatic hydrocarbons (alkanes (paraffins), linear C5-C10 alkane, and olefins), and cyclic hydrocarbons (e.g., cyclic C5-C10 alkane, preferably cyclohexane).

[0047] In yet another embodiment the step b) of the method according to the present invention is performed in the presence of a solvent comprising or consisting of a non-polar aprotic solvent.

[0048] In a preferred embodiment the step b) of the method according to the present invention is performed in the presence of a solvent comprising or consisting of a linear or cyclic C5-C10 alkane, a C5-C10 alkyl aromatic, or a combination of any these. In principle, the method according to the present invention is not subject to any limitation regarding the amount of solvent used. For example, it is conceivable that additional solvent is added in performing step b) for washing out the porous, fine-grained solid, e.g., adsorbent.

[0049] In an embodiment the step b) of the method according to the present invention is performed in the presence of 30 to 200 wt.-% of a solvent, relative to the total weight of the mixture provided in step a).

[0050] In principle, the method according to the present invention is not subject to any limitation regarding the number of runs. For example, it is possible that the method is performed in one single run with the mixture initially provided in step a). In alternative, it is also possible to perform in two or more successive runs, wherein the polyol comprising phase obtained from step b) of the first run is used as the mixture which is subjected to the second run of the method, and so on.

[0051] The larger the amount of the porous, fine-grained solid, e.g., adsorbent, is, the more viscous is the resulting mixture in step b) of the method according to the present invention, and the higher are the disposal costs for the porous, fine-grained solid, e.g., adsorbent. Therefore, for economic reasons, the upper limit of the porous, fine-grained solid, e.g., adsorbent, is considered 20 wt.-%, relative to the total weight of the mixture provided in step a). However, from a technical point of view, it is also possible to use more than 20 wt.-% the porous, fine-grained solid, e.g., absorbent, relative to the total weight of the mixture provided in step a).

[0052] In yet a further embodiment the step b) is performed in the presence of up to 20 wt.-% of the porous, fine-grained solid, preferably adsorbent, relative to the total weight of the mixture provided in step a). It is preferred, that the step b) is performed in the presence of 1 to 20 wt.-%, in particular in the presence 5 to 20 wt.-%, of a porous, fine-grained solid, preferably adsorbent, relative to the total weight of the mixture provided in step a).

[0053] The method according to the present invention allows to provide a recycled polyol having a reduced content of one or more impurities. Specifically, the method allows to provide a recycled polyol having 7 wt.-% at the most, preferably from 3 wt.-% to 5 wt.-% at the most, of the one or more impurities, based on the total weight of the recycled polyol.

[0054] Another object of the present invention is therefore a recycled polyol comprising 7 wt.-% at the most, e.g., from more than 0 to 7 wt.-% at the most, of one or more impurities, e.g., all impurities, based on the total weight of the recycled polyol, wherein said impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product.

[0055] Preferably, the recycled polyol comprises 1 to 7 wt.-% at the most, of one or more impurities, e.g., all impurities, or 2 to 6 wt.-% at the most, based on the total weight of the recycled polyol. It is preferred that the recycled polyol comprises up to 5 wt.-% at the most, e.g., from more than 0 to 5 wt.-% at the most, of the one or more impurities, e.g., all impurities, based on the total weight of the recycled polyol, based on the total weight of the recycled polyol.

[0056] Preferably, the recycled polyol comprises from 3 to 5 wt.-% at the most of the one or more impurities, e.g., all impurities, based on the total weight of the recycled polyol. In particular, the recycled polyol comprises from 3 wt.-% to 5 wt.-% at the most of all impurities, based on the total weight of the recycled polyol.

[0057] It is also preferred that said recycled polyol is obtained by the method according to the present invention.

[0058] The recycled polyol according to the present invention and the recycled polyol obtained by the method according to the present invention each have a reduced content of the one or more impurities. Therefore, they are suitable for use in the preparation of a polyurethane product.

[0059] Yet another object of the present invention is a process for preparing a polyurethane product, wherein the polyurethane product is prepared from the recycled polyol according to the present invention and / or the recycled polyol obtained by the method according to the present invention.

[0060] In principle, said process is not subject to any limitation regarding the type, structure, shape or application field of the polyurethane (PU) product to be prepared. A preferred PU product is a PU foam. In the context of the present invention the term PU foam is understood to comprise flexible PU foams, and preferably comprises hot-cure flexible PU foams, high resilient cold-cure PU foams, viscoelastic PU foams, hypersoft and / or ester type flexible PU foams. Such flexible PU foams can be used as packaging foams, or in mattresses, furniture cushions, automobile seat cushions, headrests, dashboards, automobile interior trims, automobile roof liners, and sound absorption materials.

[0061] The basic processes for preparing a polyurethane product, starting from a polyol, are known to the person skilled in the art. Therefore, it does not need any further explanation, description, mention or listing of the other reactants, catalysts, additive etc. involved in this reaction and the reaction conditions applied.

[0062] Rather, in this respect, reference is made to the relevant textbooks, and review articles, which are known or at least available to the person skilled in the art. A basic overview can be found, for example, in G.

[0063] Oertel, Polyurethane Handbook, 2nd Edition, Hanser / Gardner Publications Inc. , Cincinnati, Ohio, 1994, pp. 177-247. Further information on the starting materials, catalysts and auxiliary materials and additives that can be used can be found, for example, in the Plastics Handbook, Volume 7, Polyurethanes, Carl- Hanser-Verlag Munich, 1st edition 1966, 2nd edition, 1983 and 3rd edition, 1993.

[0064] The present invention is further illustrated in the following examples. Figures:

[0065] Figures 1-2 show the chromatograms of the untreated recycled polyols B1 and B2.

[0066] Figure 3 is a comparison of the signals of the UV-active impurities in a chromatogram of the sample of the untreated recycled polyol B1 (bottom curve) with the corresponding signals of the treated recycled polyol BT1 (top curve).

[0067] Examples:

[0068] I. Chemicals

[0069] Activated charcoal (acid-washed) was purchased from Sigma-Aldrich.

[0070] Activated charcoal Norit® SX2 was purchased from Sigma-Aldrich.

[0071] Cyclohexane (> 99.5%) and bentonite (order number 0113.2) were purchased from Roth. Magnesol® Polysorb 30 / 40 was purchased from Dallas Group of America.

[0072] Tonsil® 9191 FF was purchased from Slid Chemie.

[0073] Filter sheet Seitz K300 was purchased from Pall Corporation.

[0074] II. Analytical methods

[0075] 1. Determination of diaminotoluene content using HPLC (method I)

[0076] The determination of diaminotoluene was carried out using reversed phase HPLC / DAD. The method I described here was used for both diaminotoluene isomers, i.e. , 2,4-diaminotoluene and 2,6- diaminotoluene. In the following, the method I is described in detail for the exemplary determination of 2,6-diaminotoluene content. Regardless thereof, the method I described hereinafter can be carried out accordingly for the determination of 2,4-diaminotoluene content as well.

[0077] A suitable amount of the sample was weighed into a volumetric flask and filled up with a solution of 50 mM aqueous (NH4)CIO4 (pH 9.25) and acetonitrile (8:2 vol / vol).

[0078] For quantification, the reference materials of 2,6-diaminotoluene (purity > 97%) were weighed into a volumetric flask and filled up with a solution of water / acetonitrile (1 :1 vol / vol) (cone, of diaminotoluene = 0.013 mg / mL). This stock solution was used to prepare the calibration solutions. Therefore, the corresponding amount of the stock solution was transferred into a volumetric flask and filled up with a solution of 50 mM aqueous (NH4)CIO4 (pH 9.25) and acetonitrile (8:2 vol / vol). The concentration of the calibration solutions was 0.004 pg / mL - 13.0 pg / mL. Aliquots of the solutions were analyzed according to the following conditions:

[0079] Column: Luna C18(2) 4.6 mm x 250 mm / 5.0|jm, Phenomenex

[0080] Eluent: A: water

[0081] B: 50 mM (NH4)CIO4 pH: 9.25 in water

[0082] C: acetonitrile

[0083] Injection volume: 25.0 pL

[0084] Temperature: 30 °C

[0085] Detector: diode array detector (DAD), 220 nm

[0086] Total: 50 min

[0087] Table 1 : Time dependent gradient of the three solvents with respective mass flow

[0088] 2,6-Diaminotoluene diaminotoluene was eluated at approx. 17.2 min under the conditions shown above.

[0089] 2. Determination of UV-active impurities using HPLC (method II)

[0090] The determination of UV-active impurities, for example TDA oxidation products, was carried out using reversed phase HPLC / DAD under the following conditions:

[0091] Column: Dionex lonPac CS14, 250 x 4 mm, 8 pm, Thermo Scientific, P / N 044123

[0092] Pre-column: Dionex lonPac CG14, 50 x 4 mm, 8 pm, Thermo Scientific, P / N 044124

[0093] Column oven: Jasco CO-2060 plus

[0094] Column temperature: 25 °C

[0095] Pump: Jasco PU-2080 Low gradient mixer: Jasco LG-2080-02

[0096] Flow rate: 1.0 mL / min

[0097] Mobile phase A: 1000 mL purified water + 1 .3 mL trifluoroacetic acid (TFA)

[0098] Mobile phase B: 1000 mL acetonitrile (CAN) + 1 .3 mL TFA

[0099] Detector 1 : Jasco UV-2075 plus

[0100] Wavelength: 235 nm

[0101] Detector 1 outlet: 1 V / AU

[0102] Detector 2: Sedex 100 I Evaporative Light Scattering Detector (ELSD)

[0103] Detector 2 outlet: 1 V

[0104] Detector 2 range: Gain 5

[0105] Detector 2 temperature: 90 °C

[0106] Autosampler: Jasco AS-2075 plus

[0107] Injection volume: 40 pL

[0108] Hush medium: 80 mL acetronitrile + 20 mL purified water

[0109] Run time: 40 min

[0110] Solvent / diluent: 400 mL acetonitrile + 600 mL purified water + 2 mL TFA

[0111] 3. Estimation of the color of the samples

[0112] The color of the samples was determined using the Gardner color scale (DIN ISO 4630).

[0113] III. Example A1 : Preparation of the 2,6-diaminotoluene containing polyol

[0114] In a 1000 ml four-necked flask equipped with a KPG stirrer and internal thermometer 872.7 g ARCOL® Polyol 1104 and 7.04 g of 2,6-diaminotoluene (2,6-TDA) were stirred at 110 °C and under air atmosphere for 2 hours. The obtained polyol was clear and dark brown. The content of 2,6-diaminotoluene, determined by HPLC (method I) was 0.8 wt.-%.

[0115] IV. Examples A2-A5: T reatment of the 2,6-diaminotoluene containing polyol of example A1 with different porous, fine-grained solids The 2,6-TDA containing polyol prepared in example A1 was treated with four different porous, finegrained solids, e.g., adsorbents each using cyclohexane as solvent. In a 100 ml four-necked flask equipped with a KPG stirrer and internal thermometer 25 g of the 2,6-TDA containing polyol prepared in example A1 , 50 wt.-% cyclohexane, and 6.7 wt.-% of the respective porous, fine-grained solids, e.g., adsorbent, relative to the weight of the polyether of A1 were stirred at room temperature for 3 hours under inert conditions. After that time, the suspension was filtered, the solvent removed, and the color of each obtained polyol containing phase A2 to A5 was estimated by the Gardner color scale. The 2,6-TDA content of the starting polyol A1 and of each polyol containing phase A2 to A5 was determined using method I (see the table 2 below).

[0116] Table 2: Analytical results for the polyols A1-A5

[0117] A comparison of the 2,6-TDA content in the obtained polyols of each example with the corresponding Gardner color number of said polyol showed that there is no correlation between the 2,6-TDA content and the Gardner number. For example, the polyol obtained in example A5 had a rather low Gardner color number, compared to the polyols obtained in the other examples, but nevertheless it still contained 5100 ppm 2,6-TDA. This means that the color of the polyol was not caused by the 2,6-TDA itself. Rather, it is believed that the color was caused by the oxidation products, which are the result of heating the 2,6-TDA containing polyol at 110 °C under air atmosphere (see example A1 above). Based on the 2,6-TDA contents determined in the obtained polyols of each example, activated charcoal (acid washed) was chosen as the most promising adsorbent for a recycled siloxane (see examples B1 and B2 below).

[0118] V. Examples B1 and B2: Treatment of recycled polyols with activated charcoal (acid-washed)

[0119] Two different recycled polyols were used in this example. The recycled polyol B1 was a propylene oxide / ethylene oxide polyether (consisting of 88 % propylene oxide and 12 % ethylene oxide), which was obtained from the depolymerization of a polyurethane product. The recycled polyol B2 was a polyoxypropylene triol (consisting of 100 % propylene oxide), which was also obtained from the depolymerization of a polyurethane product.

[0120] The 2,4- and 2,6-diaminotoluene content in the recycled polyols B1 and B2 was determined before and after treatment with activated charcoal using the method I. The results are summarized in table 3. Thus, the determined content of the individual diaminotoluenes remained essentially constant within the measurement error. The recycled polyols B1 and B2 were also analyzed for the UV-active impurities before and after treatment with activated charcoal using the method II. The results are summarized in tables 4 and 5. The corresponding chromatograms of the untreated recycled polyols B1 and B2 is shown in Figures 1 and 2.

[0121] The polyols B1 and B2 were treated with activated charcoal (acid-washed): In a 1000 ml four-necked flask equipped with a KPG stirrer and internal thermometer 340 g of the respective recycled polyol, 34 g of activated charcoal (acid-washed) and 340 g cyclohexane were stirred at room temperature for 1 .5 hours. After that time, the suspension was filtrated (Seitz K300 filter plate), and the cyclohexane was removed under reduced pressure to give the treated polyols BT1 and BT2. The treated polyols BT1 and BT2 were each clear and light brown. Hence, treatment with activated charcoal (acid-washed) again seemed to be suitable for the removal of UV-active impurities, most likely oxidation products of TDA.

[0122] Table 3: concentration of 2,4- and 2,6-TDA in the untreated recycled polyols B1 and B2

[0123] The content of the UV-active impurities in the untreated recycled polyols B1 and B2 was determined using method II (see the tables 4 and 5 below). The corresponding chromatograms of the untreated recycled polyols B1 and B2 is shown in Figures 1 and 2. A comparison of the concentrations of the UV- active impurities before and after the treatment of the recycled polyols B1 and B2 with activated charcoal acid-washed shows that this treatment led to a significant reduction in the content of UV-active impurities.

[0124] Table 4: Analytical results for the UV-active impurities in the untreated recycled polyol B1 Table 5: Analytical results for the UV-active impurities in the untreated recycled polyol B2

[0125] A comparison of the data before and after treatment shows that the treatment of the recycled polyols B1 and B2 with activated charcoal acid-washed also led to a significant reduction in the content of UV-active impurities in both recycled polyols. In detail, the UV-active impurities in the untreated recycled polyols that eluted at run times between 10 and 13 minutes were no longer detectable in the treated polyols. The content of the other UV-active impurities in the treated recycled polyols was significantly reduced, compared to the untreated recycled polyols.

[0126] These results are illustrated in Figure 3, which is a comparison of the chromatography signals of the UV- active impurities of the untreated recycled polyol B1 (bottom curve) with the corresponding signals of the treated recycled polyol BT1 (top curve). There are signals of the UV-active impurities in the untreated recycled polyol B1 at a run time between 10 bis 13 minutes. In contrast, for the same time frame no signals were detectable in the treated recycled polyol BT1. Further, the integrals of the signals of all UV- active impurities in the treated recycled polyol BT1 , that eluted at run times above 13 minutes, was significantly reduced, compared to the integrals of the corresponding signals for the UV-active impurities in the untreated recycled polyol B1 .

[0127] These results demonstrate that the method according to the present invention allows for the provision of recycled polyols with a content of 7 wt.-% at the most of one or more impurities, based on the total weight of the recycled polyol, wherein said impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product.

[0128] VI. Examples C1-C7: Treatment of recycled polyols with different filter materials

[0129] The recycled polyol C1 was a propylene oxide / ethylene oxide polyether (consisting of 88% propylene oxide and 12% ethylene oxide), which was obtained from the depolymerization of a polyurethane product. Notably, the impurities differ from Examples B1 and B2 due to differences in the source polyurethane materials.

[0130] The polyol C1 was treated with the different materials as described in the following: In a 100 ml fournecked flask equipped with a KPG stirrer and internal thermometer 50 g of the polyol, 100 wt.-% cyclohexane, and 10 wt.-% of the respective adsorbent, relative to the mass of the polyol, were stirred at room temperature for 1 .5 hours under inert conditions. After that time, the suspension was filtered and the solvent removed under reduced pressure. Notably, the source material C1 (pitch black, Gardener color >18) was significantly more polluted than the polyols used in the previous examples. It was therefore deemed necessary for the above polyol the above procedure to be repeated, i.e. by adding, relative to the weight of the recovered polyol, 10 wt.-% of adsorbent and 100 wt.-% cyclohexane, followed by stirring under inert conditions for 1 .5 hours, and filtration. After the process was carried out again, the number the color of each obtained polyol was estimated by the Gardner color scale.

[0131] The 2,3-, 2,4-, 2,6-, and 3,4-diaminotoluene contents in the recycled polyols C1 to C7 were determined before and after treatment with different materials using the methods I and II. The results are summarized in table 6. The integral sum of oligomers and oxidation product refers to eluation times of 10 to 16 minutes.

[0132] Table 6: Analytical results for the polyols C1 to C7.

[0133] For filter paper, which was used as a comparative adsorbent, the Gardener color only reduced slightly while the TDA-content remained virtually unchanged. C5 and C6 show a further reduction of the Gardener color number, as well as a stronger reduction in the TDA content. The reduction in the TDA- content in this example series is, without being bound by theory, attributed to the duplicated extraction of the polyol. C7 yet a further visual improvement accompanied by an almost complete removal of TDA. Charcoal however outperforms the other adsorbents significantly, both with respect to removal of optical impurities as well as TDA.

Claims

Patent claims1 . A method for recycling a polyol, comprising the steps of a) providing a mixture comprising at least one polyol and at least one impurity, wherein said at least one impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product, and b) treating the mixture provided in step a) with a porous, fine-grained solid to give a polyol comprising phase, wherein said phase is at least depleted or even free of the at least one impurity.

2. The method according to claim 1 , wherein the porous, fine-grained solid is an adsorbent.

3. The method according to claim 2, wherein the porous, fine-grained solid, preferably adsorbent, comprises or consists of charcoal, acid-washed activated charcoal, an alkaline earth silicate, an alkali silicate, aluminum diacetate, a zeolite, a bentonite, or a combination thereof.

4. The method according to claim 2 or 3, wherein the porous, fine-grained solid, preferably adsorbent, comprises or consists of charcoal.

5. The method according to any of the claims 2 to 4, wherein the porous, fine-grained solid, preferably adsorbent, comprises or consists of acid-washed activated charcoal.

6. The method according to claim 2 or 3, wherein the porous, fine-grained solid, preferably adsorbent, comprises or consists of an alkaline earth silicate.

7. The method according to claim 2 or 3, wherein the porous, fine-grained solid, preferably adsorbent, comprises or consists of an alkali silicate.

8. The method according to claim 2 or 3, wherein the porous, fine-grained solid, preferably adsorbent, comprises or consists of aluminum diacetate.

9. The method according to claim 2 or 3, wherein the porous, fine-grained solid, preferably adsorbent, comprises or consists of a zeolite.

10. The method according to claim 2 or 3, wherein the porous, fine-grained solid, preferably adsorbent, comprises or consists of a bentonite.11 . The method according to any of claims 1 to 10, wherein the mixture of step a) results from the hydrolysis, glycolysis, acidolysis, and / or aminolysis of the polyurethanes contained in a polyurethane product.

12. The method according to any of claims 1 to 11 , wherein the product resulting from the oxidation of toluene diamines comprises at least two amine and / or imine groups, at least one urea group in combination with at least two amine groups, and / or at least one alcohol, aldehyde and / or ketone.

13. The method according to any of claims 1 to 12, wherein the mixture of step a) further comprises a surfactant, filler, stabilizer, dye, polymer apart from polyurethane, catalyst, chain length extender, curing agent and / or flame retardant.

14. The method according to any of claims 1 to 13, wherein the polyol has a number average molecular weight Mnin the range from 500 to 15,000 g / mol, determined in accordance with ISO 13885-1.

15. The method according to any of claims 1 to 14, wherein the polyol is characterized by a hydroxyl value (OH value) in the range from 45 to 60, determined in accordance with DIN 53240:1971 -12 or ASTM D 4274-21.

16. The method according to any of claims 1 to 15, wherein the polyol is one or more from the list comprising polyether polyols, polyester polyols, polyether polycarbonate polyols, natural oilbased polyols, polymer polyols, or a combination thereof.

17. The method according to any of claims 1 to 16, wherein the step b) is performed in the presence of a solvent comprising or consisting of a non-polar aprotic solvent.

18. The method according to any of claims 1 to 17, wherein the step b) is performed in the presence of a solvent comprising or consisting of a linear or cyclic C5-C10 alkane, a C5-C10 alkyl aromatic, or a combination of any these.

19. The method according to any of claims 1 to 18, wherein the step b) is performed in the presence of 30 to 200 wt.-% of a solvent, relative to the total weight of the mixture provided in step a).

20. The method according to any of claims 1 to 19, wherein the step b) is performed in the presence of 1 to 20 wt.-% of the porous, fine-grained solid, preferably adsorbent, relative to the total weight of the mixture provided in step a).21 . A recycled polyol comprising 7 wt.-% at the most of one or more impurities, based on the total weight of the recycled polyol, wherein said impurity comprises a product resulting from the oxidation of toluene diamines, and / or a product resulting from the depolymerization of a polyurethane product.

22. A process for preparing a polyurethane product, wherein the polyurethane product is prepared from the recycled polyol obtained by the process according to any of claims 1 to 20, or the recycled polyol according to claim 21 .

Images