Value chain return process for recovery of polymeric methylene phenylene amines (pMDA) as hcl salts thereof from depolymerization of waste polyurethane and polyisocyanurate rigid foams

Abstract

The present invention relates to a value chain return process comprising the depolymerization of a polyurethane based on polymeric methylene diphenyl diisocyanate (pMDI) and a rigid polyisocyanurate foam to obtain a mixture (M1); removing volatile compounds from the mixture (M1) by distillation to obtain a mixture (M2) comprising pMDA and at least one polyol; dissolving the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5 * 10 <-30 > Cm to 7.8 * 10 <-30 > Cm; and subsequently adding HCl and isolating the pMDA-HCl salt. The invention also relates to polymeric methylene phenylene amines (pMDA) and polymeric methylene diphenyl diisocyanates (pMDI), which are obtained or can be obtained according to said method, and to the use thereof for producing polyurethanes or polyisocyanurate.

Description

[0001] The present invention relates to a value chain return method for rigid polyurethane foams, which allows the recovery of polymethylene polyphenyleneamine as its HCl salt from the depolymerization of waste rigid polyurethane foams for reuse as a starting material in the synthesis of polymethylene polyphenylene isocyanate (pMDI) for the synthesis of new rigid polyurethane foams.

[0002] In particular, the present invention relates to a value chain return method that includes depolymerizing a polyurethane and polyisocyanurate rigid foam based on polymethylene diphenyl diisocyanate (pMDI) to obtain a mixture (M1); distilling off volatile compounds from the mixture (M1) to obtain a mixture (M2) containing pMDA and at least one polyol; dissolving the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm; and subsequently adding HCl and separating the pMDA-HCl salt. The present invention also relates to polymethylene polyphenyleneamine (pMDA) and polymethylene diphenyl diisocyanate (pMDI) obtained or obtainable according to the method and their use for the preparation of polyurethanes or polyisocyanurates.

[0003] In the past thirty years, the demand for plastics worldwide has increased enormously. For example, in the past 10 years, the amount of plastics produced worldwide has increased by almost 50%. In 30 years, it has even become almost four times, reaching a volume of 359 million metric tons in 2018. From these facts, it becomes clear that after the production of such a large amount of plastics, there is a need to dispose of or recycle the waste plastics. Recycling should be preferred because valuable materials (such as compounds that can act as monomers) can thus be added back to the value chain (for example, by direct reuse in plastic production). For the purpose of imparting various functions to the resin, plastics are used together with incorporated additive components. For example, since the resin itself has high flammability, the resin is mixed with a flame retardant in a proportion of up to 25% by weight from the viewpoint of preventing the spread of fire. In terms of resource conservation and from an economic viewpoint, the possibility of returning the flame retardant to the industrial cycle seems promising.

[0004] In addition, waste polyurethane (PU) rigid foams are generated in the industrial production of rigid polyurethane foams. For example, such PU rigid foam waste is obtained when casting PU rigid foam blocks and then cutting, trimming or sizing the blocks to obtain the desired PU workpieces. In addition, PU rigid foam rejects, such as non-conforming products, are also generated.

[0005] Disposal of the waste products by burning, for example, has a negative impact on the environment and on the carbon footprint.

[0006] In order to reduce waste and reduce the negative impact on the environment, processing technologies for recycling materials from plastic waste need to be developed. The recycling method should preferably reduce both material waste and the carbon footprint. Additionally, it should be an economical and energy-efficient method for delivering valuable materials including high-tech features.

[0007] Among the above plastics, polyurethane (PU) is an important representative. Generally speaking, polyurethane is produced by the polyaddition of (poly)isocyanates and polyols. The characteristic link is the urethane group. Polyurethanes exist in many types, such as foams, elastomers or thermosetting plastics, with foams being particularly important.

[0008] (Poly)isocyanate and polyol polyaddition leads to the formation of linear, branched or crosslinked polyurethanes. As an alternative form of alcohol, the most important group of NCO-reactive compounds are amines that cause the formation of disubstituted or trisubstituted ureas. Ureas are also formed by the reaction of water with isocyanates, where the carbamic acid formed in the first step of the reaction spontaneously decomposes into an amine and eliminates carbon dioxide. This amine then reacts with the excess isocyanate to produce symmetrically substituted ureas. This reaction is the basic reaction for producing polyurethane foams.

[0009] These foams can be formed with a wide range of densities and can have flexible or rigid foam structures. Generally speaking, "flexible foams" are those foams that regain their shape after deformation. In addition to being able to deform reversibly, flexible foams also tend to have a limited resistance to the applied load and tend to have mostly open cells. "Rigid foams" are those foams that generally retain the deformed shape and do not significantly recover after deformation. Rigid foams tend to have mostly closed cells. Whether a PU soft foam or a PU rigid foam is formed during polyaddition mainly depends on the types of polyisocyanates and polyol components used. For example, the starting materials can affect the crosslinking of the polymer, and the crosslinking of the polymer means that the polymer consists of a three-dimensional network. The long flexible chain segments contributed by the polyol cause the formation of PU soft foams. PU rigid foams are obtained from short chains with many crosslinked parts. More details regarding the polyurethane rigid foams suitable for use according to the present invention can be found in: Kunststoffhandbuch, Band 7, Polyurethane, Carl-Hanser-Verlag, 3. Auflage, 1993, Kapitel 6. For rigid foams, pMDI is generally used as the polyisocyanate component.

[0010] Polyurethane rigid foams provide excellent insulation properties. Therefore, they are very important in the construction industry and are commonly used as insulation materials, for example, for building insulation or for refrigerators.

[0011] Recycling rigid polyurethane foam into valuable monomer compounds remains challenging. In principle, polyurethanes can be depolymerized into polyol compounds and polyamine compounds by glycolysis or hydrolysis (see: Plastics recycling and Polyurethanes, in Ullmann’s Encyclopedia of Industrial Chemistry, 2020, DOI: 10.1002 / 14356007.a21_057.pub2 and Waste Management, 2018, 76, 147 - 171). Separation of the polyol and amine components in the glycolysis or hydrolysis method can be achieved, for example, by an extraction / phase separation method, or if the PU is based on the diisocyanates MDI (methylene diphenyl diisocyanate) or TDI (toluene diisocyanate), the corresponding amines MDA (methylene diphenyl diamine) and TDA (toluene diamine) have vapor pressures that allow separation from the polyol component via distillation under reduced pressure. Unfortunately, the methods of extraction and phase separation from the glycolysis or hydrolysis method fail for pMDA. It also cannot be separated by distillation because pMDA has a negligible vapor pressure.

[0012] DE 2854940A1 discloses a method for precipitating toluene diamine HCl salt. This can be achieved if water is removed by azeotropic distillation using toluene before. Then in a fractional precipitation, toluene diamine HCl is gradually precipitated by adding gaseous HCl and separated by filtration. The disadvantage of this method is that multiple precipitation steps are required to remove toluene diamine hydrochloride from the polyol fraction. This method also requires precise quantitative control of the amount of HCl used in each precipitation step and control of the amine content in each step. In addition, it is not disclosed that this method can work when the amine component is a higher molecular weight amine compound such as pMDA.

[0013] To avoid the fractional precipitation of polyamine HCl salts, DE 3034680 discloses a method in which most of the diamine component from the hydrolysis of polyurethane depolymerization is continuously distilled from the reaction mixture under reduced pressure at a temperature above 200 °C. Since this removal is incomplete, the diamine remaining in the polyol component (less than 1%) is then precipitated by first dissolving it in toluene and adding HCl to precipitate the diamine HCl salt. The significant disadvantage of this method is that it is only applicable to diamines from the hydrolysis of polyurethanes with significant vapor pressure and not to pMDA which cannot be distilled under such conditions.

[0014] Another method is to hydrogenate the polyurethane in a protonic organic solvent using a hydrogenation catalyst, as described in ChemSusChem, 2021, DOI: 10.1002 / cssc.202101705). This is also the only method disclosed so far in which pMDA can be separated from the polyol component after the depolymerization of pMDI-based rigid polyurethane foams. After hydrogenation under 50 bar hydrogenation, the reaction mixture is first purified by column chromatography to obtain a polyol fraction containing pMDA. Then it is dissolved in aqueous HCl / saline to form the pMDA HCl salt. Then the aqueous phase containing the dissolved pMDA HCl salt is extracted several times with dichloromethane to extract the polyol. Then, the dissolved pMDA HCl salt is neutralized with aqueous NaOH to form free pMDA dissolved in this aqueous phase, and this free pMDA must be separated by further extraction with dichloromethane. The disadvantages of this method are the large consumption of organic solvents in the initial column chromatography and the fact that both the polyol and pMDA have to be extracted in this system. In addition, a stoichiometric amount of NaOH is required to release the free pMDA before extraction.

[0015] Therefore, depolymerizing pMDI-based rigid polyurethane foams in a way that allows the polyol and pMDA to be obtained in a simple and effective manner would have high economic value. In addition, an object of the present invention is to provide a method that can be applied in a simple manner and on an industrial scale.

[0016] This object has been achieved by the value chain return method, which comprises the following steps:

[0017] a) Depolymerizing a polyurethane and polyisocyanurate rigid foam based on polymeric methylene diphenyl diisocyanate (pMDI) to obtain a mixture (M1);

[0018] b) Distilling off the volatile compounds from the mixture (M1) to obtain a mixture (M2) containing pMDA and at least one polyol;

[0019] c) Dissolving the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm;

[0020] d) Adding HCl and separating the pMDA-HCl salt.

[0021] "Value chain return" is intended to mean that the low molecular weight products obtained by the method of the present invention can be reintegrated into the value chain for producing polyurethanes or used as raw materials in another value chain.

[0022] It has surprisingly been found that in the value chain return method according to the present invention, after the depolymerization of pMDI-based polyurethane foam, by distilling off volatile compounds from the depolymerization mixture and then dissolving the remaining polyol-pMDA mixture in an organic solvent having a dipole moment less than 10*10 -30 Cm, and adding HCl to precipitate pMDA as its HCl salt to separate the pMDA-HCl salt, pMDA can be easily separated from the polyol component as its HCl salt in a single step. According to the method of the present invention, pMDA can be separated from the depolymerization mixture and directly reused for the synthesis of new pMDI in a simple manner and with a minimum number of steps.

[0023] The method of the present invention produces a polyamine containing an amino group attached to a carbon atom to which the isocyanate group was bonded in the initial polyisocyanate, and the polyamine is an oligomeric and polymeric methylene polyphenyleneamine. The polyols typically used for preparing polyurethane and polyisocyanurate rigid foams based on polymeric methylene diphenyl diisocyanate (pMDI) can preferably also be re-separated. Thus, the method preferably further produces, for example, polyester polyols, low molecular weight polyols such as ethylene glycol or propylene glycol, or high molecular weight polyether polyols based on glycerol, sorbitol, ethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0024] The method is capable of reusing pMDA in the form of its HCl salt, which can be easily converted into new polyisocyanate pMDI, for example by phosgenation, for the production of new pMDI based on waste polyurethane rigid foam. In addition, the polyol component can also be recycled for the synthesis of new polyurethanes by removing the organic solvent from the liquid phase obtained in the precipitation of the pMDA-HCl salt.

[0025] The method according to the present invention includes steps a), b), c), and d), but may also include additional steps. The method may, for example, include further purification steps or heat treatments. According to another embodiment, the present invention also relates to the method disclosed above, wherein the method includes a further purification step.

[0026] Suitable processing steps are in principle known to those skilled in the art. Suitable processing and / or purification steps can be carried out between step a) and b), between step b) and c), or between step c) and d). In the context of the present invention, step b) can also be carried out directly after step a). Step c) can also be carried out directly after step b). Step d) can also be carried out directly after step c).

[0027] Suitable purification steps include, for example, washing steps and drying steps.

[0028] Accordingly, according to another embodiment, the present invention also relates to the method as disclosed above, wherein the method comprises step d1):

[0029] d1) purifying the pMDA-HCl salt by washing with fresh solvent and / or drying at elevated temperature and / or drying under vacuum.

[0030] According to a preferred embodiment, the method comprises a further step of treating the salt obtained in step d). The pMDA-HCl salt can, for example, be subjected to a phosgenation step to obtain polymeric methylene diphenyl diisocyanate.

[0031] Accordingly, according to another embodiment, the present invention also relates to the method as disclosed above, wherein the method comprises step e):

[0032] e) phosgenating the pMDA HCl salt to obtain pMDI.

[0033] According to the present invention, the pMDA HCl salt may also be subjected to phosgenation in a mixture comprising additional components such as fresh pMDA or solvent.

[0034] In the context of the present invention, the pMDA-HCl salt obtained in step d) can also be treated with formaldehyde. Accordingly, according to another embodiment, the present invention also relates to the method as disclosed above, wherein the method comprises step e*):

[0035] e*) condensing the pMDA HCl salt with formaldehyde, preferably with formaldehyde and aniline, to obtain pMDA.

[0036] According to step a), polyurethanes and polyisocyanurate rigid foams based on polymeric methylene diphenyl diisocyanate (pMDI) are depolymerized to obtain a mixture (M1).

[0037] According to the present invention, any polyurethanes and polyisocyanurate rigid foams based on polymeric methylene diphenyl diisocyanate (pMDI) can be used for depolymerization. Generally, waste foams are used as starting materials in step a) of the method of the present invention.

[0038] The rigid polyurethane foam used in the present invention is generally obtained from: articles generated at some time after the rigid polyurethane foam has been used for the purpose for which it was manufactured, or waste rigid polyurethane foam from the production process. Before undergoing step a) of the method of the present invention, the articles can be subjected to mechanical comminution, i.e., for example, by chopping, screening, or separation by density ratio, i.e., by air, liquid, or magnetism, to further sort and size the articles appropriately. Optionally, these fragments can then be treated to remove impurities, such as paper labels. Depending on the composition of the rigid polyurethane foam, it can be subjected to extraction to remove soluble additives such as flame retardants, surfactants, or catalysts, so as to retain the pure polymeric polyurethane material before hydrolysis to avoid hydrolysis of the additives or their ultimate entry into MDA.

[0039] The properties of the foam used as starting material in the method according to the present invention can vary within a wide range.

[0040] Generally speaking, rigid polyurethane foam is produced by the reaction between a polyisocyanate component and a polyol component.

[0041] The properties of the rigid polyurethane foam are affected by the types of polyisocyanate and polyol components used. For example, the starting materials can affect the crosslinking of the polymer, and the crosslinking of the polymer means that the polymer consists of a three-dimensional network. Rigid polymers are generally obtained from short chains with many crosslinked parts.

[0042] According to the present invention, polyurethane and polyisocyanurate rigid foams based on polymeric methylene diphenyl diisocyanate (pMDI) are used in step a). For representative compositions of these PU rigid foams, see WO 2015 / 121057 and WO2013 / 139781.

[0043] Commonly used polyols in large amounts are, for example, polyester polyols, low molecular weight polyols such as ethylene glycol or propylene glycol, or high molecular weight polyether polyols based on glycerol, ethylene glycol, polypropylene glycol, polytetramethylene glycol, and polyester polyols.

[0044] In an embodiment of the present invention, the rigid polyurethane foam is based on a polyfunctional isocyanate based on polymeric diphenylmethane diisocyanate (MDI). Suitable diphenylmethane diisocyanates are, in particular, 2,2'-MDI or 2,4'-MDI or 4,4'-MDI or oligomeric MDI (which is also known as polyphenyl polymethylene isocyanate), or a mixture of two or three of the foregoing diphenylmethane diisocyanates, or crude MDI generated in MDI production, or a mixture of at least one MDI oligomer and at least one of the foregoing low molecular weight MDI derivatives.

[0045] According to the present invention, the polymeric diphenylmethane diisocyanate (MDI) may comprise up to 80% by weight of monomeric MDI, preferably less than 50% by weight, more preferably less than 30% by weight, and in particular less than 20% by weight.

[0046] Polyurethane rigid foams are generally also made from modified polyisocyanates (i.e., products obtained by chemical reaction of organic polyisocyanates and having two or more reactive isocyanate groups per molecule). In particular, mention may be made of polyisocyanates containing ester, urea, biuret, urethane, carbodiimide, isocyanurate, uretdione, carbamate and / or allophanate groups. These groups can also be depolymerized in the process according to the invention.

[0047] Polyurethanes based on methylene bis(phenyl isocyanate) (MDI) and polyurethanes based on polymeric methylene bis(phenyl-isocyanate) are technical polymers and are produced on a large scale, for example as described in Polyurethanes, in Ullmann’s Encyclopedia of Industrial Chemistry, 2012, DOI: 10.1002 / 14356007.a21_665.pub2).

[0048] In step a) according to the present invention, the polyurethane rigid foam based on pMDI can be depolymerized using any suitable method, for example via hydrolysis, preferably in the presence of a catalytically active organic nitrogen component such as a tertiary amine or an N-heterocycle.

[0049] Accordingly, according to another embodiment, the present invention also relates to the method as disclosed above, wherein in step a), the depolymerization is achieved via hydrolysis in the presence of a catalytically active organic nitrogen component.

[0050] The catalytically active organic nitrogen compounds generally consist of organic compounds containing at least one nitrogen functional group according to formula I or formula II

[0051]

[0052] wherein R 1 and R 2 , R 3 , R 4 and R 5 are independently of one another selected from substituted or unsubstituted C 1 -C 12 -alkyl, C 1 -C 12 -alkenyl, C 5 -C 8 -cycloalkyl and aryl, and the residues R 1 , R 2 and R 3Alternatively, both R4 and R5 can form a ring or be part of a ring system.

[0053] Preferably, the active organic nitrogen compound is selected from tertiary amines such as, for example, triethylamine, tributylamine, pyridine, 1-methylimidazole, dimethylbenzylamine, dicyclohexylmethylamine, dimethylcyclohexylamine, N,N,N',N'-tetramethyldiamino diethyl ether, bis-(dimethylaminopropyl)-urea, N-methyl- or N-ethylmorpholine, N-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N,N-tetramethylbutanediamine, N,N,N,N-tetramethylhexanediamine-1,6, pentamethyldiethylenetriamine, bis(2-dimethylaminoethyl) ether, dimethylpiperazine, N-dimethylaminoethylpiperidine, 1,2-dimethylimidazole, 1-azabicyclo-(2,2,0)-octane, 1,4-diazabicyclo.-(2,2,2).octane (Dabco) and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine, dimethylaminoethanol, 2-(N,N-dimethylaminoethoxy)-ethanol, N,N',N”-tris-(dialkylaminoalkyl) hexahydrotriazine, e.g. N,N',N”-tris-(dimethylamino-propyl)-s-hexahydrotriazine and triethylenediamine.

[0054] In a preferred embodiment, the active organic nitrogen compound has a boiling point below 200 °C at ambient pressure.

[0055] In a preferred embodiment, the active organic nitrogen compound is selected from pyridine, 1-methylimidazole or triethylamine.

[0056] Accordingly, in another embodiment, the present invention also relates to the method as disclosed above, wherein the catalytically active organic nitrogen compound is selected from the group consisting of pyridine, 1-methylimidazole and triethylamine.

[0057] According to the present invention, for rigid polyurethane foams, the active nitrogen compound is preferably used in an amount of 1 to 100 weight equivalents, more preferably in an amount of 2 to 20 weight equivalents.

[0058] According to the present invention, preferably, water is used in combination with the active organic nitrogen compound for hydrolysis. For rigid polyurethane foams, water is generally used in an amount of 0.1 to 100 weight equivalents, preferably in an amount of 1 to 10 weight equivalents.

[0059] Hydrolysis is generally carried out at a temperature in the range of 50 °C to 250 °C, preferably in the range of 80 °C to 200 °C, more preferably in the range of 100 °C to 180 °C.

[0060] Hydrolysis is generally carried out at a pressure in the range from ambient pressure to 100 bar, preferably from 1 to 20 bar, depending on the vapor pressures of water and the active organic compound at the selected temperature.

[0061] The hydrolysis time is generally selected between 0.1 h and 100 h, preferably between 2 h and 50 h, more preferably between 1 h and 20 h.

[0062] Hydrolysis can be carried out in all reactors suitable for the reaction, such as, for example, a stirred batch reactor or a tubular reactor, and can be carried out discontinuously or continuously.

[0063] According to step a), a mixture (M1) is obtained which comprises pMDA and at least one polyol and generally also comprises further volatile compounds and may also comprise unreacted starting materials. Preferably, the mixture (M1) comprises pMDA and at least one polyol and generally also comprises further volatile compounds. If the mixture obtained in step a) comprises solid residues, these residues can be separated off by suitable separation steps such as, for example, a filtration step.

[0064] The process according to the invention further comprises step b) of removing the volatile compounds by distillation from the mixture (M1) to give a mixture (M2) which comprises pMDA and at least one polyol;

[0065] In step b) according to the invention, all the volatile compounds after depolymerization are removed by distillation. Generally speaking, the "volatility" of a liquid can be described using its vapor pressure, where a high vapor pressure indicates high volatility and vice versa. In the context of the present invention, the volatile components after depolymerization are mainly active organic nitrogen compounds and the water used in the hydrolysis.

[0066] The distillation can be carried out at a pressure from 1 bar to 0.001 bar, preferably between 1 bar and 0.01 bar.

[0067] The distillation can be carried out at a temperature from 20 °C to 250 °C, preferably between 50 °C and 200 °C.

[0068] Accordingly, according to a further embodiment, the invention also relates to the process as disclosed above, wherein step b) is carried out at a pressure in the range from 1 bar to 0.001 bar and at a temperature in the range from 20 °C to 250 °C.

[0069] The active organic nitrogen compounds separated off in step b) can be reused for further depolymerization.

[0070] In step b), a mixture (M2) comprising pMDA and at least one polyol is obtained. The high-boiling / non-volatile fraction remaining in the distillation consists of the polyol component and pMDA and is further used in step c) of the present invention.

[0071] According to step c), the mixture (M2) is dissolved in an organic solvent (S1) having a dipole moment less than 10*10 -30 Cm.

[0072] In step c) according to the present invention, the remaining polyol-pMDA mixture is dissolved in an aprotic organic solvent having a dipole moment in the range of 0.5*10 - 30 Cm to 7.8*10 -30 Cm, preferably in the range of 0.5*10 -30 to 6.27*10 -30 Cm.

[0073] Suitable solvents are in principle known. According to the present invention, it has been found that aprotic organic solvents (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm are suitable for dissolving at least the polyol component, but will not dissolve the pMDA-HCl salt. For an economical method of separating the pure polyol from the organic solvent used in step c), an organic solvent having a boiling point below 200 °C, more preferably below 150 °C, at ambient pressure is preferably selected.

[0074] In one embodiment, the organic solvent is selected from aliphatic hydrocarbons, halogenated hydrocarbons, ethers, aromatic hydrocarbons, esters, ketones, and mixtures thereof.

[0075] Suitable halogenated hydrocarbons are selected from dichloromethane, chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, chlorobenzene, and mixtures thereof.

[0076] Thus, according to another embodiment, the present invention also relates to the method as disclosed above, wherein the organic solvent (S1) is selected from the group consisting of aliphatic hydrocarbons, halogenated hydrocarbons, ethers, aromatic hydrocarbons, aromatic halogenated hydrocarbon esters, ketones, and mixtures thereof.

[0077] If desired, a mixture of two or more of the aforementioned organic aprotic solvents can be used.

[0078] This step is generally carried out at an elevated reaction temperature of at least 0 °C but generally not higher than 150 °C, preferably 10 °C to 100 °C.

[0079] The method of the present invention further includes step d). According to step d), HCl is added to precipitate pMDA as its HCl salt, and the separation of pMDA-HCl is carried out.

[0080] According to the present invention, HCl can be added as a gas or as a solution of HCl in any suitable solvent for step c). The ratio of HCl used is preferably at least one equivalent of HCl per equivalent of pMDA and at most 100 equivalents of HCl per equivalent of pMDA. Unreacted HCl can also be recycled subsequently from the polyol phase, for example via distillation or flash evaporation.

[0081] Thus, according to another embodiment, the present invention also relates to the method as disclosed above, wherein HCl is added as a gas or as a solution of HCl in a solvent (S1).

[0082] If a solvent is used in this step at a temperature above its boiling point under ambient pressure or under HCl pressure, the extraction is carried out in a pressure vessel (such as an autoclave) at the selected extraction temperature at the vapor pressure of the solvent used at that time.

[0083] Preferably, this step is carried out at an elevated reaction temperature of at least 0 °C but generally not higher than 150 °C, more preferably 10 °C to 100 °C.

[0084] The method of the present invention for separating the thus-formed solid pMDA-HCl can be carried out in conventional equipment and / or is known to those skilled in the art for separating solids from liquids. For the method of the present invention, in principle, any equipment that is substantially suitable for separating solids from liquids at the stated temperature and the stated pressure can be used, such as filtration, decantation, or centrifugation. Suitable equipment for filtration is, for example, disclosed in Filtration, 2. Equipment, in Ullmann's Encyclopedia of Industrial Chemistry, 2013, Wiley-VCH Verlag GmbH & Co. KGaA, DOI 10.1002 / 1436007.n11_n01.pub2.

[0085] Filtration can be carried out discontinuously in batch mode or continuously or semi-continuously.

[0086] After separating the pMDA-HCl salt, the liquid phase to which the organic solvent was added in step c) usually contains a polyol component and, if in excess, also contains HCl. Then, HCl and the organic solvent can be separated from the polyol by distillation, and the polyol component can be reused for the synthesis of new polyurethane rigid foams, the organic solvent can be reused in step c), and HCl can be reused in step d).

[0087] After separation, pMDA-HCl can be further purified. Suitable purification steps can include washing with fresh solvent to remove traces of polyol and / or drying at elevated temperature and / or under vacuum.

[0088] Preferably, the method of the present invention includes step d1):

[0089] d1) Purifying the pMDA-HCl salt by washing with fresh solvent and / or drying at elevated temperature and / or under vacuum.

[0090] The pMDA-HCl salt can be separated, but can also be subjected to additional steps such as, for example, phosgenation to obtain pMDI, which in turn can be separated and used in further processes.

[0091] Preferably, the method of the present invention includes step e):

[0092] e) Phosgenating the pMDA HCl salt to obtain pMDI.

[0093] In step e) according to the present invention, in one embodiment, the pure pMDA-HCl salt obtained in step d) of step d1) can then be directly used as starting material in phosgenation to produce fresh pMDI. Suitable conditions for phosgenation are in principle known to the person skilled in the art. The phosgenation of amine-HCl salts is for example disclosed in US8455695, EP0424836A1 or CN107337615B.

[0094] According to another embodiment, the obtained pMDA-HCl salt can also be reacted with formaldehyde. Thus, the method of the present invention can also include step e*):

[0095] e*) Condensing the pMDA HCl salt with formaldehyde, preferably with formaldehyde and aniline, to obtain pMDA.

[0096] According to this embodiment, the separated pMDA-HCl salt is used in the condensation reaction of aniline with formaldehyde to obtain fresh pMDA, which can then be used again in phosgenation according to the prior art for the production of pMDI, as described for example in Isocyanates,Organic,in Ullmann’s Encyclopedia of Industrial Chemistry,2012,DOI:10.1002 / 14356007.a14_611.

[0097] According to another aspect, the present invention also relates to polymeric methylene polyphenyleneamine (pMDA) obtained or obtainable according to the method disclosed above.

[0098] According to one aspect, the present invention also relates to a polymeric methylene diphenyl diisocyanate (pMDI) obtainable or obtained according to the method disclosed above.

[0099] The polymeric methylene diphenyl diisocyanate (pMDI) obtainable or obtained according to the method of the present invention can be reused as a starting material, for example, in a method for preparing polyurethanes or polyisocyanurates.

[0100] According to another aspect, the present invention also relates to the use of a polymeric methylene diphenyl diisocyanate (pMDI) obtainable or obtained according to the method of the present invention or a polymeric methylene diphenyl diisocyanate (pMDI) according to the present invention for preparing polyurethanes or polyisocyanurates.

[0101] Further embodiments of the present invention can be found in the claims and the examples. It should be understood that the features of the subject matter / method / use according to the present invention described above and elaborated below can be used not only in the combinations specified in each case, but also in other combinations without departing from the scope of the present invention. For example, combinations of preferred features with particularly preferred features or combinations of features not further characterized with particularly preferred features, etc., are thus implicitly covered even if the combination is not explicitly mentioned.

[0102] Exemplary embodiments of the present invention are listed below, but these do not limit the present invention. In particular, the present invention also encompasses those embodiments resulting from the combinations specified by the dependent references and thus below.

[0103] 1. A value chain return method, the value chain return method comprising the following steps:

[0104] a) Depolymerizing polyurethane and polyisocyanurate rigid foams based on polymeric methylene diphenyl diisocyanate (pMDI) to obtain a mixture (M1);

[0105] b) Distilling off volatile compounds from the mixture (M1) to obtain a mixture (M2) containing

[0106] pMDA and at least one polyol;

[0107] c) Dissolving the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm;

[0108] d) Adding HCl and separating the pMDA-HCl salt.

[0109] 2. The method according to embodiment 1, wherein the method comprises step e):

[0110] e) Phosgenate the pMDA HCl salt to obtain pMDI.

[0111] 3. The method according to embodiment 1 or 2, wherein the method comprises a further purification step.

[0112] 4. The method according to any one of embodiments 1 to 3, wherein the method comprises step d1):

[0113] d1) Purify the pMDA-HCl salt by washing with fresh solvent and / or drying at elevated temperature and / or drying under vacuum.

[0114] 5. The method according to any one of embodiments 1 to 3, wherein the method comprises step e*):

[0115] e*) Condense the pMDA HCl salt with formaldehyde, preferably with formaldehyde and aniline, to obtain pMDA.

[0116] 6. The method according to any one of embodiments 1 to 5, wherein in step a), depolymerization is achieved via hydrolysis in the presence of a catalytically active organic nitrogen component.

[0117] 7. The method according to embodiment 6, wherein the catalytically active organic nitrogen compound is selected from the group consisting of pyridine, 1-methylimidazole, and triethylamine.

[0118] 8. The method according to any one of embodiments 1 to 7, wherein step b) is carried out at a pressure in the range of 1 bar to 0.001 bar and at a temperature in the range of 20 °C to 250 °C.

[0119] 9. The method according to any one of embodiments 1 to 8, wherein the aprotic organic solvent (S1) is selected from the group consisting of aliphatic hydrocarbons, halogenated hydrocarbons, ethers, aromatic hydrocarbons, esters, ketones, and mixtures thereof.

[0120] 10. The method according to any one of embodiments 1 to 9, wherein HCl is added as a gas or as a solution of HCl in the solvent (S1).

[0121] 11. Polymeric methylene polyphenyleneamine (pMDA), which is obtained or can be obtained according to the method according to any one of embodiments 1 to 10.

[0122] 12. Polymeric methylene diphenyl diisocyanate (pMDI), which is obtained or can be obtained according to the method according to any one of embodiments 1 to 10.

[0123] Use of a polymeric methylene diphenyl diisocyanate (pMDI) obtained by the method according to any one of embodiments 1 to 10 or obtainable by said method or a polymeric methylene diphenyl diisocyanate (pMDI) according to embodiment 12 for the preparation of polyurethanes or polyisocyanurates.

[0124] 14. A value chain return method, comprising the steps of:

[0125] a) depolymerizing polyurethanes and polyisocyanurate rigid foams based on polymeric methylene diphenyl diisocyanate (pMDI) to obtain a mixture (M1);

[0126] b) distilling off volatile compounds from the mixture (M1) to obtain a mixture (M2) comprising

[0127] pMDA and at least one polyol;

[0128] c) dissolving the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm;

[0129] d) adding HCl and separating the pMDA-HCl salt,

[0130] e) phosgenating the pMDA HCl salt to obtain pMDI.

[0131] 15. A value chain return method, comprising the steps of:

[0132] a) depolymerizing polyurethanes and polyisocyanurate rigid foams based on polymeric methylene diphenyl diisocyanate (pMDI) to obtain a mixture (M1);

[0133] b) distilling off volatile compounds from the mixture (M1) to obtain a mixture (M2) comprising

[0134] pMDA and at least one polyol;

[0135] c) dissolving the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm;

[0136] d) adding HCl and separating the pMDA-HCl salt,

[0137] wherein the method comprises step d1):

[0138] d1) Purify the pMDA-HCl salt by washing with fresh solvent and / or drying at elevated temperature and / or vacuum drying.

[0139] 16. A value chain return method, the value chain return method comprising the following steps:

[0140] a) Depolymerize a polyurethane and polyisocyanurate rigid foam based on polymeric methylene diphenyl diisocyanate (pMDI) to obtain a mixture (M1);

[0141] b) Distill off volatile compounds from the mixture (M1) to obtain a mixture (M2) comprising

[0142] pMDA and at least one polyol;

[0143] c) Dissolve the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm;

[0144] d) Add HCl and separate the pMDA-HCl salt,

[0145] wherein the method comprises step e*):

[0146] e*) Condense the pMDA HCl salt with formaldehyde, preferably with formaldehyde and aniline, to obtain pMDA.

[0147] 17. A value chain return method, the value chain return method comprising the following steps:

[0148] a) Depolymerize a polyurethane and polyisocyanurate rigid foam based on polymeric methylene diphenyl diisocyanate (pMDI) to obtain a mixture (M1);

[0149] b) Distill off volatile compounds from the mixture (M1) to obtain a mixture (M2) comprising

[0150] pMDA and at least one polyol;

[0151] c) Dissolve the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm;

[0152] d) Add HCl and separate the pMDA-HCl salt,

[0153] e) Phosgenate the pMDA HCl salt to obtain pMDI,

[0154] In step a), depolymerization is achieved via hydrolysis in the presence of a catalytically active organic nitrogen component.

[0155] 18. The method according to embodiment 17, wherein the catalytically active organic nitrogen compound is selected from the group consisting of pyridine, 1-methylimidazole, and triethylamine.

[0156] 19. The method according to any one of embodiments 14 to 18, wherein step b) is carried out at a pressure in the range of 1 bar to 0.001 bar and a temperature in the range of 20 °C to 250 °C.

[0157] 20. The method according to any one of embodiments 14 to 19, wherein the aprotic organic solvent (S1) is selected from the group consisting of aliphatic hydrocarbons, halogenated hydrocarbons, ethers, aromatic hydrocarbons, esters, ketones, and mixtures thereof.

[0158] 21. The method according to any one of embodiments 14 to 20, wherein HCl is added as a gas or as a solution of HCl in the solvent (S1).

[0159] The present invention can be further explained and illustrated based on the following examples. However, it should be understood that including these examples is for illustrative purposes only and is not intended to limit the scope of the present invention in any way. Examples

[0160] 1. Materials used

[0161] Polyol 1: A polyether polyol obtained by the propoxylation of propylene glycol, with an OH value of 56.

[0162] Polyol 2: A polyether polyol obtained by the propoxylation of propylene glycol, with an OH value of 248.

[0163] Polyol 3: A polyether polyol obtained by the propoxylation of glycerol, with an OH value of 42.

[0164] Polyol 4: A polyether polyol obtained by the propoxylation of glycerol, with an OH value of 400.

[0165] Polyol 5: A polyether polyol obtained by the propoxylation of toluenediamine, with an OH value of 400.

[0166] Polyol 6: A polyether polyol obtained by the propoxylation of sorbitol, with an OH value of 490.

[0167] Polyol 7: A polyether polyol obtained by the propoxylation of a mixture of sucrose and glycerol, with an OH value of 490.

[0168] Elastopir: A polyisocyanurate rigid foam from BASF polyurethane, obtained by reacting a polyol component containing a phosphorus-containing flame retardant (Elastopir 1132 / 509) with Lupranat M50 (index = 330).

[0169] Elastocool: A polyurethane rigid foam from BASF polyurethane, obtained by reacting a polyol component (Elastocool F 2030 / 310) with Lupranat M20 (index = 120).

[0170] In the extraction experiment, different pMDI-based PU rigid foams were used. The PU rigid foam Elastopir is based on 70% polymeric MDI and 30% polyol component (a mixture of polyester polyol and polyether alcohol). The PU rigid foam Elastocool is based on 60% pMDI and 40% propylene oxide-based polyether alcohol. The PU rigid foam "end-of-life polymer" is the material used for insulation in refrigerators. The composition is not exactly known, but it is a common polyurethane rigid foam for this application, mainly made of pMDI and short-chain polyether- and polyester alcohols. This can be confirmed in a reverse-engineering manner by applying the method according to the present invention through the hydrolysis and separation of pMDA-HCl.

[0171] 2. With HCl Precipitate polymeric diaminodiphenylmethane ( pMDA ) 。

[0172]

[0173] Weigh polymeric MDA (368 mg, 1.86 mmol) into a 20 mL vial. Rinse the walls with CH 2 Cl 2 (5 mL). Under stirring, add an ethereal solution of HCl (2 M in Et 2 O, 5 mL) to the yellow solution. The formation of a thick precipitate can be observed immediately. [Note: Inject the last 3 mL of the solution directly into the solution to ensure contact with the DCM phase.] After sealing with a screw cap, shake the vial additionally to mix all phases homogeneously. Filter the suspension through a suction filter, and wash the remaining solid with DCM (3 X 5 mL) and Et 2 O (2 X 2 mL). After drying in air for 20 minutes, transfer the yellow solid to a flask and dry it additionally under reduced pressure (room temperature, 2.0·10 -2 mbar) overnight. A highly electrostatic solid (502 mg, 1.85 mmol, >99%) is obtained. Dry the colorless filtrate under reduced pressure (45 °C, 70 mbar). No residue is detected in the flask.

[0174] 3. Separate polymeric diaminodiphenylmethane (pMDA) from polyol in the premixed sample by precipitation with HCl .

[0175] Table 1 summarizes the results obtained. The polymerization 4,4'-diaminodiphenylmethane and polyol were mixed in a 20 mL screw-capped vial. Each sample was dissolved in a specified amount of dichloromethane. After mixing uniformly, an indicated amount of ethereal HCl (2 M in Et 2 O) was added. The samples were diluted with an indicated amount of dichloromethane and mixed by shaking for 20 s. Many precipitates were observable for each sample. All samples were filtered on a suction filter. The remaining solid was washed with dichloromethane (3 × 10 mL) and dried at 60 °C (oven) for five hours to obtain the polymerization 4,4'-diaminodiphenylmethane as the polyhydrochloride. The solvent of all filtrates was removed under reduced pressure (47 °C, minimum pressure 60 mbar). The masses of all fractions can be taken from the table below. By 1 H and 13 C NMR spectra (MeOD-d 4 for the hydrochloride, CDCl 3 for the polyol) were used to analyze all samples.

[0176] Table 1: Separation of polymeric 4,4'-diaminodiphenylmethane (pMDA) from polyol in the premixed sample by precipitation with HCl Separation . [1]

[0177]

[0178]

[0179] [1] Amount of DCM for dissolution + amount of DCM for dilution

[0180] [2] Isolated as the polyhydrochloride

[0181] [3] The sample contains a small amount of polyol

[0182] 4. Separate the monomer mixture obtained by hydrolysis in an amine base - water mixture, and then precipitate polymeric diaminodiphenylmethane from the polyol with HCl Precipitate polymeric diaminodiphenylmethane .

[0183] Table 2 summarizes the results obtained. In air, a 38 mL ace tube was charged with the polymer. The walls were rinsed with amine base and water. The tube was closed and heated overnight at 160 °C with stirring. After stirring at 160 °C for 18 h, the dark orange solution was cooled to room temperature. The sample was filtered on a small pad of diatomaceous earth (Pasteur pipette) and the pad was rinsed with the amine base used (3 × 4 mL). Under reduced pressure (in the case of pyridine: 47 °C, minimum pressure 60 mbar; in the case of methylimidazole: 90 °C, minimum pressure 1.8·10 –2Remove the solvent under reduced pressure (mbar). Suspend the residue in dry dichloromethane (20 mL [1.00 g] for small-scale reactions; 150 mL for larger-scale reactions). Add the indicated amount of ethereal HCl solution with stirring at room temperature. The formation of a heavy precipitate can be observed. After stirring for five minutes at room temperature, filter the solid through a suction filter, wash with additional dry dichloromethane (3 × 10 mL), and dry under reduced pressure (room temperature, 1.8·10 –2 mbar). Weigh the dried solid and determine the amount of the separated ammonium polyhydrochloride salt. Remove the solvent from the filtrate under reduced pressure (47 °C, minimum pressure of 50 mbar), and the residual oil is determined as the polyol fraction. All products are characterized by 1 H and 13 C NMR.

[0184]

[0185] 5. Solubility of polymeric diaminophenylmethane polyhydrochloride (pMDA HCl) and polyol 7 in different solvents :

[0186] Charge a 20 mL vial with pMDA HCl (~20 mg - 40 mg) or polyol 7 (50 mg - 100 mg). Add the indicated solvent (3 mL - 4 mL), and cap the vial. After allowing to stand at room temperature for four hours, shake all vials for approximately one minute. After standing at room temperature for one day and one weekend (a total of 68 hours), check the solubility of all samples.

[0187]

[0188] The cited prior art

[0189] Kunststoffhandbuch, Band 7, Polyurethane, Carl-Hanser-Verlag, 3. Auflage, 1993, Kapitel 6

[0190] Plastics recycling and Polyurethanes, in Ullmann’s Encyclopedia of Industrial Chemistry, 2020, DOI: 10.1002 / 14356007.a21_057.pub2 and Waste Management, 2018, 76, 147 - 171

[0191] DE 2854940A1

[0192] ChemSusChem, 2021, DOI: 10.1002 / cssc.202101705

[0193] WO 2015 / 121057

[0194] WO 2013 / 139781

[0195] Ullmann’s Encyclopedia of Industrial Chemistry, 2012, DOI: 10.1002 / 14356007.a21_665.pub2

[0196] US8455695

[0197] EP0424836A1

[0198] CN107337615B

Claims

1. A method for value chain return, the value chain return method comprises the following steps: a) Depolymerize polyurethane and polyisocyanurate rigid foams based on polymeric methylene diphenyl diisocyanate (pMDI) to obtain a mixture (M1); b) Distill off volatile compounds from the mixture (M1) to obtain a mixture (M2) comprising pMDA and at least one polyol; c) Dissolve the mixture (M2) in an aprotic organic solvent (S1) having a dipole moment in the range of 0.5*10 -30 Cm to 7.8*10 -30 Cm; d) Add HCl and separate the pMDA-HCl salt.

2. The method according to claim 1, wherein the method comprises step e): e) Phosgenate the pMDA HCl salt to obtain pMDI.

3. The method according to claim 1 or 2, wherein the method comprises a further purification step.

4. The method according to any one of claims 1 to 3, wherein the method comprises the step d1)： d1) Purify the pMDA-HCl salt by washing with fresh solvent and / or drying at elevated temperature and / or vacuum drying.

5. The method according to any one of claims 1 to 3, wherein the method comprises the step e*)： e*) Condense the pMDA HCl salt with formaldehyde, preferably with formaldehyde and aniline, to obtain pMDA.

6. The method according to any one of claims 1 to 5, wherein in step a), the depolymerization is achieved via hydrolysis in the presence of a catalytically active organic nitrogen component.

7. The method according to claim 6, wherein the catalytically active organic nitrogen compound is selected from the group consisting of pyridine, 1-methylimidazole, and triethylamine.

8. The method according to any one of claims 1 to 7, wherein step b) is carried out at a pressure in the range of 1 bar to 0.001 bar and at a temperature in the range of 20 °C to 250 °C.

9. The method according to any one of claims 1 to 8, wherein the aprotic organic solvent (S1) is selected from the group consisting of aliphatic hydrocarbons, halogenated hydrocarbons, ethers, aromatic hydrocarbons, esters, ketones, and mixtures thereof.

10. The method according to any one of claims 1 to 9, wherein HCl is added as a gas or as a solution of HCl in a solvent (S1).

11. Polymeric methylene polyphenyleneamine (pMDA), which is obtained or can be obtained according to the method of any one of claims 1 to 10.

12. Polymeric methylene diphenyl diisocyanate (pMDI), which is obtained or can be obtained according to the method of any one of claims 1 to 10.

13. Use of the polymeric methylene diphenyl diisocyanate (pMDI) obtained or obtainable according to the method of any one of claims 1 to 10 or the polymeric methylene diphenyl diisocyanate (pMDI) according to claim 12 for the preparation of polyurethanes or polyisocyanurates.

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