Process for producing thioether-substituted aromatic diamines

Abstract

The invention is directed to an improved process for producing at least one thioether-substituted, preferably thioalkylated, aromatic diamine X. Thioether-substituted aromatic diamines are aromatic diamines with at least one thioether group bound to the aromatic ring via the sulfur atom. They are of particular interest for use as curing agents. Preferred thioether-substituted aromatic diamines are monomethylthiotoluene diamine ("MMTDA") and dimethylthiotoluene diamine ("DMTDA"). In the process according to the invention, an aromatic diamine A is reacted with at least one organic disulfide B in the presence of at least one Lewis-acid catalyst D and at least one polyol E. A and E are obtained by depolymerization of at least one polyurethane PU. Preferably, the organic phase, comprising A, of the depolymerization raw product RP is employed in the reaction of the aromatic diamine with the organic disulfide B. The yield of mono- versus di-thioether substituted aromatic diamines may advantageously be controlled by drying the employed organic phase.

Description

[0001] Process for producing thioether-substituted aromatic diamines

[0002] The invention is directed to an improved process for producing at least one thioether-substituted, preferably thioalkylated, aromatic diamine X. Thioether-substituted aromatic diamines are aromatic diamines with at least one thioether group bound to the aromatic ring via the sulfur atom. They are of particular interest for use as curing agents. Preferred thioether-substituted aromatic diamines are monomethylthiotoluene diamine (“MMTDA”) and dimethylthiotoluene diamine (“DMTDA”).

[0003] In the process according to the invention, an aromatic diamine A is reacted with at least one organic disulfide B in the presence of at least one Lewis-acid catalyst D and at least one polyol E. A and E are obtained by depolymerization of at least one polyurethane PU. Preferably, the organic phase, comprising A, of the depolymerization raw product RP is employed in the reaction of the aromatic diamine with the organic disulfide B. The yield of mono- versus di-thioether substituted aromatic diamines may advantageously be controlled by drying the employed organic phase.

[0004] Background of the Invention

[0005] Thioalkylated aromatic diamines have favorable physical properties when comparing with nonthioalkylated aromatic diamines such as being liquid instead of solid, which leads to easier handling of the material. Thioalkylated aromatic diamines also possess less hazardous characteristics in comparison to their corresponding aromatic diamines, which means that the toxicity of thioalkylated aromatic diamines is relatively lower and no health hazard is expected from them.

[0006] Thioalkylated aromatic diamines and other thioether-substituted aromatic diamines may be prepared by reaction of aromatic diamines with organic disulfides in the presence of Lewis acids or organometallic catalysts. According to US 5,302,755 A, a poly(oxyalkylene)polymer can be added to allow practical and effective re-use for the Lewis acid or organometallic catalyst. US 5,382,695 A discloses that the addition poyl(oxyalkylene)amines serve as inhibitors for the Lewis acid catalyst used in the thioalkylation reaction and can therefore be added to the reaction mixture during the distillation (i.e. after the thioalkylation reaction is complete) in order to inhibit the decomposition of a dithioalkylated to the monothioalkylated aromatic amine.

[0007] However, such poly(oxyalkylene)polymers have the disadvantage that they have to be manufactured separately and require to be soluble in the solvents used. Thus, it would be an advantage if a process for producing thioalkylated aromatic diamines was at hand with which the problems of the state of the art could be avoided and thioalkylated aromatic diamines and other thioether-substituted aromatic diamines could be manufactured more easily.

[0008] In addition, the thioalkylation of aromatic diamines in many cases results in a mixture of mono- and dithioalkylated isomers. It is, however, preferred to have a process that allows to obtain either the mono- or di-thioether-substituted product with low contents of the other product. Even more preferable is a process to obtain the di-thioalkylated aromatic diamine with a low content of mono-thioalkylated aromatic diamine. The problem underlying the present invention is therefore the provision of a process that provides the above mentioned advantages and solves the mentioned problems.

[0009] Short Description of the Invention

[0010] Surprisingly, a process for producing at least one thioether-substituted aromatic diamine X, preferably for producing at least one thioalkylated aromatic diamine X, was now found, which solves these problems. The present invention hence relates to a process for producing at least one thioether-substituted aromatic diamine X comprising i) depolymerizing at least one polyurethane PU to obtain at least one aromatic diamine A and at least one polyol E, ii) reacting at least a part of the aromatic diamine A with at least one organic disulfide B and optionally further additives C in the presence of at least one Lewis-acid catalyst D and in the presence of the at least one polyol E, to obtain the at least one thioether-substituted aromatic diamine X.

[0011] The at least one thioether-substituted aromatic diamine X is, in a preferred embodiment, a thioalkylated aromatic diamine X.

[0012] Namely, according to the invention, it was surprisingly found that at least one aromatic diamine A stemming from depolymerization of at least one polyurethane PU, in mixture with at least one polyol E stemming from depolymerization of the at least one polyurethane PU, can be used as reactants in the synthesis of thioether-substituted aromatic diamines.

[0013] The aromatic diamine A stems from a PU depolymerization step. It is hence obtained from a recycling process and does not need to be manufactured prior to production of the thioether-substituted aromatic diamine X. Polyol E dissolves the at least one Lewis-acid catalyst D well. It also does not require separate manufacturing, as it also stems from the same PU depolymerization step, i.e. from a recycling process as well. The aromatic diamine A as well as the polyol E may be used as the organic phase of the raw product of the depolymerization of PU. They are advantageously obtained as raw product mixture from the depolymerization of PU and do not require further elaborate purification.

[0014] The process according to the present invention is therefore highly energy and resource efficient. Particularly, usage of a recycled material is very advantageous for the environment and does not require addition of virgin polyol or virgin aromatic diamine, thus avoiding cost-effective starting materials. In addition, polyurethane (“PU”) waste stemming from industrial products can be minimized. Thus, the carbon footprint caused by the usual burning of polyurethane waste can be reduced.

[0015] The thioether-substituted aromatic diamine X obtained by the process according to the invention may be a mixture of different isomers and / or compounds with different numbers of thioether residues at the aromatic ring. It was further surprisingly found that, when the organic phase from the PU depolymerization raw product is reacted with the organic disulfide, that the yield of mono- versus dithioether substituted product may advantageously be controlled by adjusting the water content of the thus reacted organic phase. This allows the production of di-thioether substituted aromatic diamines in high yield.

[0016] Detailed Description of the Invention

[0017] Step i)

[0018] In step i) of the process according to the invention, at least one polyurethane PU is at least partially depolymerized to obtain at least one aromatic diamine A and at least one polyol E.

[0019] Polyurethane PU refers to a class of polymers composed of organic units joined by urethane links. A polyurethane is produced by reacting at least one compound with at least two hydroxy groups and at least one compound with at least two isocyanate groups.

[0020] The polyurethane PU subjected to step i). of the process according to the present invention comprises the polyol E and the amine A that are, from a formal point of view, mutually linked to each other via urethane bonds that connect a hydroxy group of the polyol E to the amino group of the A. Upon the at least partial depolymerization of the polyurethane PU in step i), in particular the at least partial hydrolysis of the polyurethane PU in step i), at least a part of the urethane groups comprised by PU are cleaved, thus releasing the polyol E and the aromatic diamine A.

[0021] Typically, the polyurethane PU subjected to step i) of the process according to the invention is a polymer, in which at least two OH-groups of a polyol E are each linked to a NH-group of an aromatic diamine A via a urethane functionality and at least two NH-groups of an aromatic diamine A are each linked to a OH- group of a polyol E via a urethane functionality.

[0022] Polyurethanes are materials of considerable utility in the production of rigid and flexible foams, solid and microcellular elastomers, sealants, coatings and adhesives. The versatility, relatively low cost, and superior properties of polyurethanes have resulted in the rapid growth of the polyurethane industry over the past fifty years. Currently, many thousand tons of polyurethanes are produced each year throughout the world. Unfortunately, most polyurethanes are thermoset materials which are cross-linked to one degree or another. Unlike thermoplastics such as polyethylene, polypropylene, and polystyrene, scrap or waste polyurethanes thus cannot be readily remelted or reprocessed into useful articles. Since it would be highly desirable for economic and environmental reasons to reuse or recover the large volume of scrap or waste polyurethane generated each year rather than burning it or disposing of it in landfills, considerable effort has been devoted to devising processes for recovering useful chemical components from scrap polyurethane materials.

[0023] The polyurethane PU subjected to the process according to step i) of the present invention may be in solid, microcellular, or foam form and may range from a rubbery, elastomeric, flexible material to a hard, rigid substance. Preferably, the polyurethane PU subjected to step i) of the process according to the present invention is provided as a PU foam, more preferably as a flexible PU foam.

[0024] In particular, the polyurethane PU subjected to step i) of the process of the present invention are those prepared from active hydrogen-containing polyols, preferably polyethers, and polyisocyanates. Polyurethanes of this type are well known and are described, for example, in US 5,208,379 A.

[0025] The polyurethane PU employed in the process of the present invention may be derived from any aromatic diisocyanate. Suitable polyisocyanates include, but are not limited to, aromatic diisocyanates which can be optionally substituted. Preferred polyisocyanates are toluene diisocyanates and diisocyanatodiphenyl methanes.

[0026] Modified, masked, or blocked polyisocyanates may, of course, also be utilized. The polyurethane PU subjected to the process according to the present invention may also comprise groups selected from allophanate groups, isocyanurate groups, urea groups. If one or more of these groups is present, at least a part of these groups may be cleaved during step i). The polyurethane PU subjected to the process of the present invention may also include any of the conventional additional reactants or additives known in the art such as for example chain extenders or curatives (relatively low molecular weight active hydrogencontaining compounds such as glycols and di- or polyamines), physical or chemical blowing agents, flame retardants, surfactants, fillers, stabilizers, anti-oxidants, colorants, polymers other than the polyurethane PU polymer (e.g., styrene-acrylonitrile copolymers such as are found in polymer polyols), catalysts, for example catalysts promoting the gelling reaction (isocyanate-polyol), the blowing reaction (isocyanate- water) and / or the dimerization or trimerization of the isocyanate.

[0027] In step i) of the process according to the invention, the polyurethane PU is at least partially depolymerized to obtain at least one aromatic diamine A and at least one polyol E.

[0028] Aromatic diamine A

[0029] In the context of the present invention, the aromatic diamine A is an aromatic amine with two amine groups.

[0030] In a preferred embodiment, the at least one aromatic diamine A has the general structure according to formula (I):

[0031] H2N-W1-NH2(I) wherein the residue W1is a divalent aromatic residue, which optionally contains at least one group selected from an ester group, ether group, a cyano group and a hydroxy group.

[0032] W1preferably is selected from the group consisting of aromatic hydrocarbon residues with 6 to 30 carbon atoms, wherein the aromatic hydrocarbon residue optionally comprises at least one group selected from an ester group, ether group, hydroxy group and cyano group.

[0033] Even more preferably, W1in formula (I) is selected from the group consisting of formulae (l-A), (l-B), (l-C), where the bond identified by “(*)” in formulae (l-A), (l-B), (l-C) denotes the bond to one of the amino groups in formula (I) and the bond identified by “(**)” in formulae (l-A), (l-B), (l-C) denotes the bond to the other amino group in formula (I).

[0034] In formula (l-A), it is preferred that the two bonds identified by “(*)” and “(**)”, respectively, are in para-position at the aromatic ring with respect to each other.

[0035] In formula (l-B), it is preferred that the two bonds identified by “(*)” and “(**)”, respectively, are in 2,4-position or 2,6-position at the aromatic ring with respect to the methyl group.

[0036] In formula (l-C), the aromatic carbon atoms that are not linked to one of the bonds identified by “(*)” or “(**)” can be substituted by a group selected from an alkyl group, wherein the alkyl group is preferably methyl, with the proviso that at least one, preferably at least two, ring atom(s) is present that can react in step ii). More preferably, all of the aromatic carbon atoms in formula (l-C) that are not linked to one of the bonds identified by “(*)” or “(**)” each carry a hydrogen.

[0037] In an even more preferred embodiment, the at least one aromatic diamine A is selected from the group consisting of phenylene diamine, toluene diamine (“TDA”) and di- and polyamines of diphenyl methanes (“MDA”). It is most preferred that the at least one aromatic diamine A is toluenediamine.

[0038] Toluene diamine is at least one of the three isomers (ll-A), (ll-B), (ll-C) defined by the formula C6H3(NH2)2(CH3), a mixture of at least two of these isomers or a mixture of all three of these isomers. (Il-A) is 2,4 diamino toluene.

[0039] (H-B) is 2,6 diamino toluene. (ll-C) is 2,5 diamino toluene.

[0040] (ll-A) (ll-B) (ll-C)

[0041] The most preferred isomers of TDA are 2,4-diamino toluene and 2,6-diamino toluene.

[0042] More preferably, the TDA is a mixture comprising 2,4-diamino toluene and 2,6-diamino toluene, wherein it is preferred that the molar ratio of 2,4-diamino toluene to 2,6-diamino toluene in the mixture is in the range of from 0.01 to 100, more preferably in the range of form 0.1 to 75, more preferably in the range of from 0.5 to 50, more preferably in the range of from 1 to 20, more preferably in the range of from 1 .5 to 5.0, more preferably in the range of from 1.8 to 4.5, even more preferably in the range of from 2.0 to 4.0, even more preferably in the range of from 2.8 to 4.0, and most preferably in the range of from 3.0 to 4.0.

[0043] Polyol E

[0044] A “polyol E” as used in the present invention is an organic compound having two or more OH groups. Such polyols are for example described in JP H04-136017 A, WO 2022 / 042909 A1 , WO 2022 / 042910 A1 , WO 2023 / 072985, WO 2023 / 078802 A1 .

[0045] The structure of the polyol E obtained in step i) of the process according to the invention correlates with the structure of the polyol used to prepare the polyurethane PU that is at least partially depolymerized in step i) of the process according to the invention.

[0046] Preferably, the at least one polyol E is selected from the group consisting of polyether polyols; polyester polyols; hydroxyl-containing aliphatic polycarbonates, in particular polyether polycarbonate polyols;

[0047] More preferably, the at least one polyol E is selected from the group consisting of polyether polyols, polyester polyols, even more preferably the at least one polyol E is selected from polyether polyols.

[0048] Even more preferably, the at least one polyol E is selected from the group consisting of polypropylene glycol and polyethylene glycol. In an even more preferred embodiment, the polyol E comprises a mixture of polypropylene glycol and polyethylene glycol, wherein preferably the ratio of the weight of all polypropylene glycol comprised by E to the weight of all polyethylene glycol comprised by E is in the range of from 99 : 1 to 1 : 99, preferably in the range of from 20 : 1 to 3 : 2. The at least one polyol E preferably has an average functionality of 2 to 8, more preferably 2 to 3.

[0049] “Functionality” means the number of OH groups, per molecule.

[0050] In a mixture of more than one polyol E, “average functionality” refers to the number of all isocyanatereactive groups, preferably all OH groups, in the mixture, divided by the amount of substance (mol) of all polyols in the mixture.

[0051] The at least one polyol E preferably has an average molecular weight in the range of from 500 to 15000 g / mol. More preferably, the average molecular weight is in the range from 500 to 9000 g / mol, even more preferably from 2000 to 4000 g / mol. The average molecular weight (also denoted “number average molecular weight”) is preferably determined by gel permeation chromatography (“GPC”), using polypropylene glycol as reference and tetrahydrofuran (“THF”) as eluent.

[0052] The at least one polyol E preferably has an OH number in the range from 10 to 1200 mg KOH / g. The OH numbers are determined in accordance with the DIN standard DIN 53240:1971 -12.

[0053] Polyether polyols

[0054] Polyether polyols, from which the at least one polyol E is preferably selected, are known to the skilled person. Polyether polyols possess at least two hydroxyl end groups. In addition, the polyether polyol may also be amine-functionalized. Preferably, however, the polyether polyol is not amine-functionalized.

[0055] The polyol E has preferably a general formula (III): HX2-V1-X1H, wherein the residue V1is a divalent hydrocarbon residue, which optionally contains at least one group selected from an ester group, an ether group, a thioether group, an amine group, a cyano group, a hydroxy group.

[0056] The polyol E preferably has a general structure that is selected from the group consisting of formulae (lll-A), (lll-B), (lll-C), even more preferably formula (lll-A):

[0057] (IH-A) (lll-B) (lll-C) wherein q2, qs, q4, qs, qe, q?, qs each independently is an integer > 2, preferably in the range of from 2 to 1000, more preferably in the range of from 5 to 500, even more preferably in the range of from 10 to 200, wherein V2, V3, V4, V5, V6, V7, V8each independently is a group with the formula -CnH2n-, wherein n is an integer and n = 1 to 100, preferably n = 2 to 50, more preferably n = 2 to 10, even more preferably n = 2 to 6, even more preferably n = 2 to 4, even more preferably n = 2 to 3, preferably V2, V3, V4, V5, V6, V7, V8each independently is selected from the group consisting of -CH2CH2-, -CH2-CH(CH3)-, -CH(CH3)-CH2-, -CH2CH2CH2-, and wherein the residues V2in the polyol E according to the general structure (lll-A) are the same or different, and wherein the residues V3in the polyol E according to the general structure (lll-B) are the same or different, and wherein the residues V4in the polyol according to the general structure (lll-B) are the same or different, and wherein the residues V5in the polyol E according to the general structure (lll-B) are the same or different, and wherein the residues V6in the polyol E according to the general structure (lll-C) are the same or different, and wherein the residues V7in the polyol E according to the general structure (lll-C) are the same or different, and wherein the residues V8in the polyol E according to the general structure (lll-C) are the same or different.

[0058] According to the present invention “-CnH2n-” comprises linear and branched alkylene residues, preferably selected from the group consisting of methylene, ethylene, n-propylene, / so-propylene, more preferably selected from the group consisting of ethylene, n-propylene, / so-propylene.

[0059] Polyether polyols, from which the at least one polyol E is preferably selected, are obtainable by known methods. Such materials are generally made by the catalytic ring-opening polymerization of one or more cyclic ethers such as epoxides, oxetanes, or oxolanes. Initiators having two or more active hydrogens such as polyhydric alcohols, amines, or acids may be employed to vary the functionality (number of active hydrogens) of the polyether. If more than one type of cyclic ether is used, they may be reacted either simultaneously (to yield a random-type copolymer) or sequentially (to yield a block-type copolymer). Illustrative cyclic ethers include propylene oxide, ethylene oxide, butylene oxide, tetrahydrofuran, and oxetane. Examples of polyether polyols include polypropylene glycol, polyethylene glycol, polytetramethylene glycol, polytrimethylene glycol, ethylene oxide-capped polypropylene glycol, random copolymers of ethylene oxide and propylene oxide.

[0060] Polyether polyols, from which the at least one polyol E is preferably selected, may also be obtained by anionic polymerization of alkylene oxides (“AO”) in presence of alkali metal hydroxides, alkali metal alkoxides or amines as catalysts and by addition of at least one starter molecule (“SM”), which preferably contains two or three reactive hydrogen atoms in banded form, or by cationic polymerization of AO in the presence of Lewis acids, such as, for example, antimony pentachloride or boron trifluoride etherate, or by double meta cyanide catalysis.

[0061] Suitable AO contain from two to four carbon atoms. Examples are tetrahydrofuran, 1 ,3-propylene oxide, 1 ,2-propylene oxide, 1 ,2-butylene oxide and 2,3-butylene oxide. Ethylene oxide and 1 ,2-propylene oxide are preferably used. The alkylene oxides can be used individually, cumulatively, in blocks, in alternation or as mixtures.

[0062] Starter molecules SM used may especially be compounds having at least two, preferably two to eight, hydroxyl groups, or having at least two primary amino groups in the molecule.

[0063] Preferred starter molecules SM are selected from the group consisting of water; di-, tri- or tetrahydric alcohols, in particular selected from ethylene glycol, propane-1 ,2-diol, propane-1 ,3-diol, diethylene glycol, dipropylene glycol, glycerol, trimethylolpropane, pentaerythritol; fatty acid triglycerides, wherein at least two of the fatty acids carry at least one -OH group, preferably castor oil, which is a triglyceride, wherein at least two, preferably each of the three fatty acid residues are 12-hydroxy-9-octadecenoic acid (known as “ricinoleic acid”); higher polyfunctional polyols, especially sugar compounds, for example glucose, sorbitol, mannitol and sucrose; polyhydric phenols, resols, for example oligomeric condensation products of phenol and formaldehyde, and Mannich condensates of phenols, formaldehyde and dialkanolamines, and melamine, or amines such as aniline, ethylene diamine (“EDA”), toluene diamine (“TDA”), diphenylmethane diamine (“MDA”, which is preferably diphenylmethane 2,4’-diamine or diphenylmethane 2,2’-diamine), 1 ,5-pentamethylene diamine (“PMDA”).

[0064] The choice of the suitable starter molecule SM depends on the particular field of use of the resulting polyether polyol in the polyurethane production (for example, polyols used for production of flexible polyurethane PU foams are different from those used in the production of rigid polyurethane PU foams).

[0065] Polyether polyols, from which the polyol E is preferably selected, may also be obtained from natural sources.

[0066] In a preferred embodiment of the process according to the invention, the polyol E comprises a mixture of polypropylene glycol and polyethylene glycol, wherein preferably the ratio of the weight of all polypropylene glycol comprised by E to the weight of all polyethylene glycol comprised by E is in the range of from 99 : 1 to 1 : 99, preferably in the range of from 20 : 1 to 3 : 2.

[0067] In a further preferred embodiment of the invention, the polyol E comprises, preferably consists of, a mixture of polypropylene glycol and polyethylene glycol, wherein the fraction of all polypropylene glycols in the mixture is in the range of 60 wt-% to 95 wt-%, based on the total weight of all polyols E, and the fraction of all polyethylene glycols in the mixture is in the range of 5 wt-% to 40 wt-%, based on the total weight of all polyols E.

[0068] Polyester polyols

[0069] Polyester polyols, which is another group of polyols from which the polyol E is preferably selected, are based on esters of polybasic aliphatic or aromatic carboxylic acids, preferably having two to twelve carbon atoms.

[0070] Examples of aliphatic carboxylic acids are succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, 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 two to twelve, more preferably two to six, carbon atoms, preferably tri methylolpropane and glycerol.

[0071] Polyester polyols, from which the polyol E is preferably selected, may also be obtained from natural sources.

[0072] Hydroxyl-containing aliphatic polycarbonates

[0073] Hydroxyl-containing aliphatic polycarbonates, which is another group of polyols from which the polyol E is preferably selected, are polyols containing carbon dioxide bound in the form of carbonate [-O-C(=O)-O]. 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 the production of polyols. Moreover, the use of CO2 as co-monomer is very advantageous in environmental terms since this reaction constitutes the conversion of a greenhouse gas to a polymer. The preparation of these 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 3,900,424 A or US 3,953,383 A. In addition, mono- and binuclear metal complexes have been used successfully for copolymerization of CO2 and alkylene oxides (WO 2010 / 028362 A1 , WO 2009 / 130470 A1 , WO 2013 / 022932 A1 or WO 2011 / 163133 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” (US 4,500,704 A, WO 2008 / 058913 A1). Suitable alkylene oxides and H-functional starter substances are those also used for preparing carbonate-free polyether polyols, as described above.

[0074] At least Partial Depolymerization in step i) In step i) of the process according to the invention, at least one polyurethane PU is at least partially depolymerized to obtain at least one aromatic diamine A and at least one polyol E. “Depolymerization” means in the context of this invention the cleavage of at least a part of the urethane groups in the polyurethane PU, preferably with water molecules (as nucleophiles), to obtain at least one aromatic diamine A and at least one polyol E.

[0075] Depolymerizations of polyurethanes are known to the skilled person and for example described in WO 2023 / 083968 A1 , WO 2023 / 072985 A1 , WO 2023 / 099420 A1 , WO 2023 / 208946 A1 , WO 2022 / 171586 A1 , and WO 2023 / 194469 A1 .

[0076] “At least partial depolymerization” according to the invention is understood to encompass any depolymerization reaction of PU which leads to the cleavage of at least a part of the urethane groups in the PU polymer subjected to step i) to give at least one aromatic diamine A and at least one polyol E.

[0077] In a preferred embodiment, at least 10 % of all urethane groups of the PU subjected to step i) of the process according to the invention are cleaved in step i) to give at least one aromatic diamine A and at least one polyol E. Even more preferred at least 20 %, even more preferred at least 25 %, even more preferred at least 30 %, even more preferred at least 40 %, even more preferred at least 50 %, even more preferred at least 60 %, even more preferred at least 70 %, even more preferred at least 80 %, even more preferred at least 90 %, even more preferred at least 95 %, even more preferred at least 98 %, even more preferred at least 99 %, even more preferred at least 99.9 % of all urethane groups of the PU subjected to step i) of the process according to the invention are cleaved in step i) to give at least one aromatic diamine A and at least one polyol E. This relative amount of the urethane groups cleaved during step i) may be determined by the skilled person according to his knowledge, for example by NMR, IR. It may be determined by comparing the respective number of urethane functions in the PU and / or the reaction mixture before and after step i).

[0078] Preferably, the polyurethane PU is subjected to essentially full depolymerization according to step i), meaning that essentially all of the urethane groups in the PU subjected to step i) are cleaved.

[0079] One of the advantages of the process according to the present invention is its applicability to a broad range of polyurethanes PU. Hence, the at least one polyurethane PU to be subjected to step i) of the process of the present invention is not especially limited, as long as it is based on at least one aromatic diamine A and at least one polyol E. Preferably the polyurethane PU subjected to step i) is polyurethane waste.

[0080] In a particular embodiment, the at least partial depolymerization according to step i) of the process according to the invention is carried out at a temperature in the range of from 20 °C to 300 °C, preferably in the range of from 100 °C to 250 °C, more preferably in the range of from 120 °C to 220 °C, more preferably in the range of from 140 °C to 200 °C. In a particular embodiment, the at least partial depolymerization according to step i) of the process according to the invention is carried out at a pressure in the range of from 1 bar to 30 bar, preferably in the range of from 2 bar to 20 bar, more preferably in the range of from 3 bar to 15 bar.

[0081] The at least partial depolymerization according to step i) of the process according to the present invention is preferably carried out in a reaction vessel.

[0082] In a preferred embodiment of the process according to the invention, the at least partial depolymerization of the at least one polyurethane PU according to step i) of the present invention is carried out in the presence of water, even more preferably in aqueous solution. In the context of the present invention, such depolymerization in the presence of water, even more preferably in aqueous solution is also referred to as “hydrolysis” or “hydrolytic depolymerization”:

[0083] After step i), and before being employed in step ii), the polyol E and the diamine A may be purified from the raw material mixture using extraction techniques or other techniques known to the skilled person. It is, however, preferred to directly employ raw product mixture, in particular the organic phase of the raw product mixture, comprising the polyol E and the diamine A obtained after step i), in step ii), wherein this raw product mixture, in particular the organic phase of the raw product mixture, in a preferred embodiment is at least partially dried before being employed in step ii). This drying step is further described below (paragraph “Drying”).

[0084] Base p

[0085] Preferably, at least one base p is employed in the at least partial depolymerization in step i). This is in particular preferred where the at least partial depolymerization of the at least one polyurethane PU according to step i) is carried out in aqueous solution.

[0086] Preferably, the at least one base p is selected from the group consisting of alkali metal phosphates, alkali earth metal phosphates, alkali metal hydrogen phosphates, alkali earth metal hydrogen phosphates, alkali metal carbonates, alkali earth metal carbonates, alkali metal silicates, alkali earth metal silicates, alkali metal hydrogen carbonates, alkali earth metal hydrogen carbonates, alkali metal carboxylates, in particular alkali metal acetates, alkali earth metal carboxylates, in particular alkali earth metal acetates, alkali metal sulfites, alkali earth metal sulfites, ammonium hydroxide, alkali metal hydroxides, alkali metal oxides, alkali earth metal hydroxides, alkali earth metal oxides.

[0087] More preferably, the at least one base p is selected from the group consisting of alkali metal phosphates, alkali metal hydrogen phosphates, alkali metal carbonates, alkali metal silicates, alkali metal hydrogen carbonates, alkali metal carboxylates, wherein the carboxylate is in particular acetate, alkali metal sulfites, ammonium hydroxide, alkali metal hydroxides, alkali metal oxides, alkali earth metal hydroxides, alkali earth metal oxides.

[0088] The alkali metal comprised by base p is preferably selected from the group consisting of potassium, sodium, lithium, more preferably selected from the group consisting of potassium, sodium. The alkali earth metal comprised by base p is preferably selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, more preferably selected from the group consisting of magnesium, calcium.

[0089] Even more preferably, the at least one base is selected from the group consisting of potassium carbonate, sodium carbonate.

[0090] In a preferred embodiment, the ratio of the total weight of all bases p used in step i) relative to the total weight of all polyurethanes PU subjected to step i) is in the range of 50 : 1 to 0.5 : 1 , preferably 10 : 1 to 0.8 : 1 , more preferably 4 : 1 to 1 : 1 , most preferably 1 .2 : 1 .

[0091] Phase transfer catalyst

[0092] In a further preferred embodiment, the at least partial depolymerization in step i) of the process according to the present invention is catalyzed with at least one phase transfer catalyst selected from the group consisting of quaternary ammonium salts Q, organic sulfonates, preferably at least one phase transfer catalyst selected from the group consisting of quaternary ammonium salts Q.

[0093] The quaternary ammonium salt Q preferably has the general structure R1R2R3R4NX, wherein R1, R2, R3, and R4are the same or different and each is a hydrocarbyl groups selected from alkyl, aryl, arylalkyl, and X is selected from the group consisting of hydroxide, carbonate, hydrogen carbonate, hydrogen sulfate, carboxylate, wherein the carboxylate is preferably acetate, halide, wherein the halide is preferably selected from chloride and bromide, alkyl sulfate, wherein the alkyl sulfate is preferably selected from methylsulfate, ethylsulfate. Preferably, X = hydroxide, hydrogen sulfate. Most preferably, X = hydrogen sulfate.

[0094] The quaternary ammonium salt Q preferably contains an ammonium cation with 6 to 30, preferably 6 to 20, more preferably 6 to 16, even more preferably 12 to 16, carbon atoms.

[0095] The organic sulfonate preferably contains at least 7 carbon atoms.

[0096] In a preferred embodiment, the at least partial depolymerization in step i) is catalyzed with at least one quaternary ammonium salt Q, and even more preferably the at least one quaternary ammonium salt Q comprises a cation selected from the group consisting of tetrabutylammonium cation, benzyltrimethylammonium cation. Even more preferably, the at least one quaternary ammonium salt Q is selected from the group consisting of tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, tetrabutylammonium hydrogen sulfate (“TBAHS”).

[0097] In those cases in which at least one quaternary ammonium salt Q is used in step i), it is further preferred that the weight of all quaternary ammonium salt Q used in step i) is at least 0.5 weight percent (= “wt.-%”), based on the total weight of the polyurethane PU subjected to step i), more preferably in the range of from 0.5 wt.-% to 15 wt.-%, even more preferred in the range of from 0.75 wt.-% to 10 wt.-%, particular preferred in the range of from 0.90 wt.-% to 8 wt.-%, especially preferred in the range of from 1 .0 wt.-% to 7 wt.-%, even more preferred 5.0 wt.-%.

[0098] Reaction conditions in step i)

[0099] The skilled person is aware of how to carry out the at least partial depolymerization according to step i) of the process according to the invention.

[0100] Step i) is preferably carried out as hydrolysis, namely in particular by contacting water W, preferably at least one base p, and the polyurethane PU that is subjected to the at least partial depolymerization reaction. This contacting is, in particular, carried out in a reactor, in which the respective reaction components are mixed and reacted with each other. Such reactor is in particular selected from a continuous stirred-tank reactor, autoclave.

[0101] Step i) may, in an alternative embodiment, also be carried out in a reactor that is specifically designed for continuous processing, such as an extruder (e.g. screw extruder, planetary-gear extruder), kneader, etc.

[0102] The reaction conditions applied in step i) are known to the skilled person.

[0103] It is preferred that the at least partial depolymerization according to step i) is carried out at a temperature in the range of from 20 °C to 300 °C, preferably in the range of from 90 °C to 250 °C, more preferably in the range of from 100 °C to 250 °C, more preferably in the range of from 110 °C to 220 °C, even more preferably in the range of from 120 °C to 220 °C, and most preferred in the range of from 140 °C to 200 °C.

[0104] It is further preferred that the at least partial depolymerization according to step i) is carried out for 30 minutes to 20 hours, preferably 30 minutes to 16 hours, more preferred 30 minutes to 14 hours, even more preferred 45 minutes to 10 hours, particularly preferred 60 minutes to 8 hours, even more preferred 60 minutes to 6 hours.

[0105] It is further preferred that that the at least partial depolymerization according to step i) is carried out at atmospheric pressure or under elevated pressure, in particular under a pressure of from 1 bar abs. to 30 bar abs., preferably 2 bar abs. to 20 bar abs., more preferred 3 bar abs. to 15 bar abs.

[0106] Comminuting step

[0107] To facilitate handling of the PU in step i), it is preferable to carry out a preceding step [i.e. before step i)] in which the PU is comminuted. This comminution is even more preferably selected from the group consisting of chopping, pulverizing, grinding. By this preferred pretreatment step, PU is obtained that is in the form of relatively small particles or granules. This pretreatment step is in particular advantageous, if the PU that is subjected to the process of the present invention is in solid form. In this case, the initial pulverization step is highly advantageous so as to maximize the surface area available for reaction, thereby reducing the reaction time required to achieve the desired level of depolymerization.

[0108] In a further preferred embodiment of the present invention, and in particular if the PU that is subjected to the process according to the invention is a foam, the PU may be partially or fully compressed prior to subjecting it to step i).

[0109] The progress of the depolymerization of PU in step i) may be monitored by nuclear magnetic resonance (“NMR”) or infrared (“IR”) spectroscopy. In particular, these processes may be used to monitor the amount of urethane groups in the polyurethane PU employed in step i) and the amount of urethane groups in the polyurethane PU and / or the reaction mixture after the reaction has progressed.

[0110] Even more preferred, step i) is carried out until essentially no urethane groups may be detected any more.

[0111] Raw product RP

[0112] In a preferred embodiment, the at least partial depolymerization according to step i) is carried out as a hydrolysis, i.e. in aqueous solution.

[0113] In this preferred embodiment, an aqueous raw product RP comprising aromatic diamine A and polyol E, wherein RP comprises an organic phase RPo and an aqueous phase RPw is obtained.

[0114] The hydrolytic raw product RP comprises an organic phase RPo and an aqueous phase RPw.

[0115] The aqueous phase RPw is essentially formed by the water and preferably the base p comprised by the raw product RP after step i). In particular, the aqueous phase RPw comprises preferably the main part of the base p that is comprised by the raw product RH after step i).

[0116] The organic phase RPo also contains water (and in particular also base P) to some extent due to the Nernst distribution law according to which any compound will always distribute between two immiscible phases.

[0117] The raw product RP comprises an organic phase RPo and an aqueous phase RPw, in which the organic phase Pocomprises at least a part of the aromatic diamine A and at least a part of the polyol E, and wherein the organic phase RPo also contains water. Preferably, the water content in the organic phase RPo is less than 10 wt-%, preferably less than 5 wt.-%, in the organic phase RPo, based on the total amount of the organic phase RPo. At least a part of Po of the organic phase RPo is then separated from the aqueous phase RPw to obtain an organic phase Po comprising at least a part of the aromatic diamine A obtained in step i) and optionally at least a part of the polyol E obtained in step i).

[0118] This separation may be carried out by methods known to the skilled person.

[0119] In a preferred embodiment where step i) of the process according to the invention is carried out as hydrolysis, an organic solvent is added to RP before the separation of Po from RPw- This addition improves the phase separation of organic phase RPo and aqueous phase RPw of the raw product and facilitates separation of the products due to different solvation in the at least one organic solvent. The organic solvent should be immiscible with water (meaning that it establishes two phases in mixture with water).

[0120] The organic solvent is preferably selected from the group consisting of hydrocarbons (such as cyclohexane, toluene, xylene, hexane, pentane, cyclopentane), halogenated hydrocarbons (such as dichloromethane, chloroform), ether (tetra hydrofuran, diethyl ether, methyl fe / Y-butyl ether), ketone (methyl ethyl ketone), acetonitrile.

[0121] The at least partial depolymerization according to step i) hence leads to a crude product mixture comprising the polyol E and the aromatic diamine A.

[0122] In those cases, in which a phase transfer catalyst is employed in step i), and in particular if at least one quaternary ammonium salt Q is used in step i), the organic phase RPo in particular also comprises at least a part of the quaternary ammonium salt Q or decomposition products DQ formed from Q during the reaction according to step i).

[0123] This preferred embodiment of the process of this invention will result in the effective hydrolytic cleavage of the urethane (and, in those cases where PU comprises them, urea bonds) present in the polyurethane PU being treated so as to generate the aromatic diamine A and the polyol E, wherein the polyol E preferably is a polyether polyols. In particular in those cases where the polyurethane PU was prepared using chain extenders or curatives, further products such as low molecular weight glycols, diols which are different from the polyol E, or such as diamines which are different from the aromatic diamine A may also be obtained.

[0124] Likewise, since the process according to the present invention may be applied for recycling of polyurethane PU from a wide range of sources and wastes, the polyurethane PU subjected to the process according to the present invention may contain further additives and processing aids that are then found in the hydrolytic raw product RP and in particular in the organic phase RPo and the aqueous phase RPw comprised by the raw product RH that is obtained after step i).

[0125] In a particular embodiment of the present invention, the raw product RP obtained after step i) hence contains at least one component K, wherein K is selected from the group consisting of foam catalysts, inorganic fillers, polymeric fillers, flame retardants, carboxylates such as formiate, acetate, polydimethylsiloxane, organic pigments, polymeric filers, which are preferably SAN polymers.

[0126] Foam catalysts, inorganic fillers, polymeric fillers, organic pigments may optionally be found in the organic phase Po, while carboxylates such as formate, acetate, polydimethylsiloxane, inorganic fillers, polymeric filers, preferably SAN polymers, flame retardants may optionally be found in the aqueous phase RPw-

[0127] Hence, in a preferred embodiment,

[0128] (a) the organic phase RPo comprised by the raw product RP that is obtained after step i), further comprises at least one component Ko selected from the group consisting of foam catalysts, inorganic fillers, polymeric fillers, organic pigments, antioxidants, dyes, and / or

[0129] (b) the aqueous phase RPw comprised by the raw product RP that is obtained after step i), further comprises at least one component K selected from the group consisting of dyes, polydimethylsiloxane, polymeric filers, inorganic fillers, flame retardants, carboxylates, wherein the carboxylates are preferably at least one of formate, acetate.

[0130] In case of the preferred embodiment (b), it is even more preferred that at least a part, preferably all, of the components Kw are separated from the aqueous phase RPw before, during or after, even more preferably before or after, Po is separated from RPo, so that the amount of components Kw in RPw is minimized, preferably RPw is essentially free of components Kw-

[0131] In case of the preferred embodiment (a), it is even more preferred that at least a part, preferably all, of the components Ko are separated from the organic phase RPo before, during or after, even more preferably before or after, Po is separated from RPo, so that the amount of components Ko in RPo is minimized, preferably RPo is essentially free of components Ko.

[0132] In some embodiments, the raw product RP may also comprise solids S. These solids S may be particles of only partially depolymerized PU, or additional polymer filles (such as styrene-acrylonitril polymers, abbreviated as “SAN polymers”), for example in those cases where the polyurethane PU is composed of polyol, in particular polyether polyol, building blocks that contain such polymers (SAN polymers), in dispersed or covalently bound form. Hence, the raw product RP optionally comprises solids S.

[0133] In a preferred embodiment, the composition of the raw product RP is as follows: In this preferred embodiment, the organic phase RPo in the raw product RP comprises

[0134] (a) more than 40 wt.-%, preferably 45 to 90 wt.-%, more preferred 50 to 80 wt.-%, even more preferred 55 to 80 wt.-% and even more preferred 60 to 75 wt.-%, most preferred 65 wt.-%, by weight of the organic phase RPo, of polyols E, (p) 10 to 40 wt.-%, preferably 15 to 35 wt.-%, more preferred 20 to 30 wt.-% and most preferred 22 to 27 wt.-%, by weight of the organic phase RPo, of amines A,

[0135] (y) water W in an amount of less than 20 wt.-%, preferably 0.1 to 15 wt.-%, more preferred 1 to 10 wt.-%, even more preferred 3 to 8 wt.-%, most preferred 5 wt.-%, by weight of the organic phase RPo,

[0136] (5) in those cases where at least one inorganic base p was preferably used in step i), less than 15 wt.-%, preferably 0.1 to 10 wt.-%, more preferred 0.5 to 8 wt.-% and most preferred 1 to 5 wt.-%, by weight of the organic phase RPo, of the inorganic base ,

[0137] (e) in those embodiments where at least one quaternary ammonium salt Q was used in step i) as phase transfer catalyst, in sum < 15 wt.-%, preferably 0 to 10 wt.-%, more preferred 0.01 to 6 wt.-%, even more preferred 0.05 to 6 wt.-%, particularly preferred 0.5 to 4 wt.-% and most preferred 1 to 2.5 wt.-%, by weight of the organic phase RPo, are constituted by the sum of quaternary ammonium salt Q and decomposition products DQ of the quaternary ammonium salt Q, wherein DQ are the corresponding amine AQ and the corresponding alcohols PQ,

[0138] (0 in those cases where the PU subjected to step i) contained the respective compound Ko, the compounds Ko in a total amount of less than 15 wt.-%, preferably 0.1 to 10 wt.-%, more preferred 0.5 to 8 wt.-% and most preferred 1 to 5 wt.-% by weight of the organic phase Po, wherein the compound Ko is selected from the group consisting of foam catalysts, inorganic fillers, polymeric fillers, organic pigments, antioxidants, dyes, wherein the amounts of components (a) to (Q plus optionally further components comprised sum up to a maximum of 100 wt.-% of the organic phase RPo.

[0139] Step ii)

[0140] According to step ii) of the process according to the present invention, at least a part of the aromatic diamine A reacts with at least one organic disulfide B and optionally further additives C in the presence of at least one Lewis-acid catalyst D and in the presence of the at least one polyol E, in order to obtain at least one thioether-substituted, preferably thioalkylated, aromatic diamine X.

[0141] The conditions to be applied in step ii) of the process according to the present invention are known to the skilled person and described e.g. in US 4,982,002 A and US 5,302,755 A.

[0142] It is preferred that the content of the aromatic diamine A in the reaction mixture in step ii) is in the range of from 5 wt.-% to 75 wt.-%, preferably in the range of from 10 wt.-% to 66 wt.-%, more preferably in the range of from 20 wt.-% to 60 wt.-%, based on the total weight of the reaction mixture. It is further preferred that the content of polyol E applied in the reaction mixture in step ii) is in the range of from 1 wt.-% to 95 wt.-%, preferably in the range of from 3 wt.-% to 60 wt.-%, more preferably in the range of from 5 wt.-% to 50 wt.-%, even more preferably in the range of from 6 wt.-% to 40 wt.-%, the most preferably in the range of from 7 wt.-% to 30 wt.-%, based on the total weight of the all aromatic diamines A comprised by the reaction mixture in step ii).

[0143] It is further preferred that the content of the Lewis-acid catalyst D applied in the reaction mixture in step ii) is in the range of from 1 wt.-% to 95 wt.-%, preferably in the range of from 1 wt.-% to 45 wt.-%, more preferably in the range of from 2 wt.-% to 25 wt.-%, even more preferably in the range of from 3 wt.-% to 20 wt.-%, most preferably in the range of from 4 wt.-% to 15 wt.-%, based on the total weight of all aromatic diamines A comprised by the reaction mixture in step ii).

[0144] In a preferred embodiment the molar amount of substance of organic disulfide B applied in the reaction mixture in step ii) is in the range of from 0.5 molar equivalents to 4 molar equivalents, preferably is in the range of from 0.9 molar equivalents to 2.1 molar equivalents, more preferably is in the range of from 1.0 molar equivalents to 2.0 molar equivalents, based on the total amount of substance of all aromatic diamines A comprised by the reaction mixture in step ii).

[0145] It is preferred that the step ii) according to the invention is carried out at a temperature in the range of from 20 °C to 300 °C, preferably in the range of from 90 °C to 220 °C, preferably in the range of from 100 °C to 200 °C, more preferably in the range of from 110 °C to 200 °C, even more preferably in the range of from 120 °C to 180 °C, and most preferably in the range of from 140 °C to 180 °C.

[0146] Organic disulfide B

[0147] Organic disulfide B is an organic chemical compound with the molecular formula R1S — SR2, wherein R1and R2are each independently organic residues, preferably each alkyl. R1and R2of R1S — SR2are different or identical, preferably identical.

[0148] Organic disulfides which may be reacted with the aromatic amines are saturated and unsaturated aliphatic, cycloaliphatic and aromatic disulfides in which the hydrocarbyl groups optionally bear inert substituents, such as chloro substituents.

[0149] Further preferred substituents R1and R2are selected from the group consisting of methyl, ethyl, propyl, n-butyl, sec-butyl, tert-buty I, 2-chlorophenyl, cyclopentyl, cyclohexyl, phenyl, benzyl, p-tolyl and p- chlorophenyl disulfides.

[0150] In a preferred embodiment, the organic disulfide B is a dialkylated disulfide. In this preferred embodiment where B is a dialkylated disulfide, R1and R2of R1S — SR2are each alkyl, preferably selected from Ci to Cs-alkyl, more preferred from Ci to Chalky I, even more preferred from Ci to Cs-alkyl. Most preferred R1and R2of R1S — SR2are each methyl. Hence, the most preferred organic disulfide B is dimethyl disulfide. Where the organic disulfide B is a dialkylated disulfide, the obtained thioether-substituted aromatic diamine X is a thioalkylated aromatic diamine.

[0151] The hydrocarbyl disulfide component of the reaction mixture is generally included in at least the stoichiometric amount required to produce the desired hydrocarbylthio aromatic amine. For example, at least one equimolar amount is used when a mono(hydrocarbylthio)aromatic amine is desired and at least two equimolar amounts are used when a di(hydrocarbylthio)aromatic amine is desired.

[0152] The reaction of the aromatic amine with the organic disulfide is generally conducted at a temperature in the range of 20 °C to 300 °C and preferably at a pressure of atmospheric from 1 bar to 69 bar.

[0153] Lewis acid Catalyst D

[0154] In step ii) of the process according to the invention, a Lewis acid catalyst D is employed. The Lewis acid catalyst D is an inorganic compound, which is based on main group metals such as aluminum, boron, silicon and tin, furthermore, many early and late d-block metals such as titanium, zirconium, iron, copper and zinc.

[0155] Hence, preferably Lewis acid catalyst D comprises at least one atom selected from aluminum, boron, silicon, tin, titanium, zirconium, iron, copper, zinc.

[0156] Suitable Lewis acid catalysts D for step ii) according to the invention are Lewis acid catalysts D, such as metal halides. Preferred Lewis acid catalysts are copper chloride, copper bromide, copper iodide (Cui), ammonium iodides, hydrogen iodide, zinc iodide, ferrous iodide, cobaltous iodide, aluminum chloride, boron trifluoride, ferric chloride, zinc chloride, zinc iodide. Metal alkyl compounds, such as triethylaluminum, diethylaluminum chloride, ethyl aluminum dichloride, and the organometallic compounds derived from the reaction of the aromatic amine with the metal alkyls and reactive metals such as aluminum may also be utilized.

[0157] Further Additives C

[0158] The polyurethane PU used is the process of the present invention may also include any of the conventional additional reactants or additives known in the art, such as for example chain extenders or curatives (relatively low molecular weight active hydrogen-containing compounds such as glycols and di- or polyamines), physical or chemical blowing agents, flame retardants, surfactants, fillers, stabilizers, antioxidants, colorants, polymers other than the polyurethane polymer (e.g., styrene-acrylonitrile copolymers such as are found in polymer polyols), catalysts, for example catalysts promoting the gelling reaction (isocyanate-polyol), the blowing reaction (isocyanate-water) and / or the dimerization or trimerization of the isocyanate. The polyurethane PU may be in solid, microcellular, or foam form and may range from a rubbery, elastomeric, flexible material to a hard, rigid substance.

[0159] Drying Surprisingly, it was discovered that, depending on the water content of the organic phase Po in the raw product RP obtained from the at least partial depolymerization in aqueous solution, selective thioether- substitution, preferably thioalkylation, in reaction step ii) is achieved.

[0160] In particular, as described above, in a preferred embodiment of the process according to the invention, in step i),the depolymerization of the at least one polyurethane PU is carried out in aqueous solution, to obtain an aqueous raw product RP comprising aromatic diamine A and polyol E. RP comprises an organic phase RPo and an aqueous phase RPw in which o the organic phase RPo comprises at least a part of the aromatic diamine A and at least a part of the polyol E, o and wherein the organic phase RPo also contains water.

[0161] It was surprisingly found that this organic phase RPo may also be deployed directly in step ii) of the process according to the invention. In addition, it was found out, that the yield in di-thioether substituted, preferably di-thioalkylated, aromatic diamine XDI and mono-thioether-substituted, preferably monothioalkylated, aromatic diamine XMono obtained in step ii) may be controlled by the amount of water in the organic phase RPo deployed in step ii).

[0162] A “di-thioether substituted aromatic diamine XDI” is a compound in which two aromatic carbon atoms are linked to a “-S-R1” or “-S-R2” substituent.

[0163] A “di-thioalkylated aromatic diamine XDI” is a compound in which two aromatic carbon atoms are linked to a “-S-R1” or “-S-R2” substituent, with R1, R2are each alkyl, preferably each selected from Ci to Cs-alkyl, more preferably each selected from Ci to Chalky I, even more preferably each selected from Ci to C3- alkyl, most preferred are each methyl. An exemplary compound is dimethyl thio-toluene diamine (CAS: 106264-79-3).

[0164] A “mono-thioether substituted aromatic diamine XMono” is a compound in which one aromatic carbon atom is linked to a “-S-R1” or “-S-R2” substituent.

[0165] A “mono-thioalkylated aromatic diamine XMono” is a compound in which one aromatic carbon atom is linked to a “-S-R1” or “-S-R2” substituent, with R1, R2are each alkyl, preferably each selected from Ci to Cs-alkyl, more preferably each selected from Ci to C4-alkyl, even more preferably each selected from Ci to Cs-alky I, most preferred are each methyl. An exemplary compound is mono(methyl thio)-toluene diamine.

[0166] A “thioether substituted aromatic diamine X” is a compound in which at least one aromatic carbon atom is linked to a “-S-R1” or “-S-R2” substituent.

[0167] A “thioalkylated aromatic diamine X” is a compound in which at least one aromatic carbon atom is linked to a “-S-R1” or “-S-R2” substituent, with R1, R2are each alkyl, preferably each selected from Ci to Cs-alkyl, more preferably each selected from Ci to Chalky I, even more preferably each selected from Ci to C3- alkyl, most preferred are each methyl. In a preferred embodiment of the process according to the invention, the thioether-substituted aromatic diamine X is rich in di-substituted, preferably di-thioalkylated, aromatic diamine.

[0168] Hence, in this more preferred embodiment, at least a part Po of the organic phase RPo is separated from the aqueous phase RPw to obtain an organic phase Po comprising at least a part of the aromatic diamine A obtained in step (i) and at least a part of the polyol E obtained in step (i).

[0169] The organic phase Po is at least partially dried to obtain a dried organic phase P01. In a preferred embodiment, the drying is continued until the amount of water in P01 is < 90 wt.-%, preferably < 80 wt.-%, more preferably < 70 wt.-%, more preferably < 60 wt.-%, more preferably < 50 wt.-%, more preferably < 40 wt.-%, more preferably < 30 wt.-%, more preferably < 20 wt.-%, more preferably < 10 wt.-%, more preferably < 5 wt.-%, more preferably < 1 wt.-% the amount of water in organic phase Po.

[0170] Then, in step ii), o the at least one organic disulfide B and the at least one Lewis-acid catalyst D are mixed with P01, and o at least a part of the aromatic diamine A comprised by P01 are reacted with the at least one organic disulfide B in the presence of the at least one Lewis-acid catalyst D, to obtain the at least one di-thioether-substituted, preferably at least one di-thioalkylated, aromatic diamine XDI.

[0171] The drying may be achieved by means known to the skilled person. In a preferred embodiment, the drying of Po is achieved by distillation. In another preferred embodiment, the drying is achieved with a drying agent such as a drying agent selected from the group of carbonate, sulfate, chlorides, molecular sieve.

[0172] In a preferred embodiment, the obtained at least one di-thioether-substituted aromatic diamine XDI has a carbon footprint of < 3.5, preferably < 2.9, kg CO2 equivalents / kg of all obtained XDI, as determined according to DIN EN ISO standard 14067:2018.

[0173] In another embodiment of the process according to the invention, the thioether-substituted aromatic diamine X is rich in mono-thioether-substituted, preferably mono-thioalkylated, aromatic diamine.

[0174] Hence, in this more preferred embodiment, at least a part Po of the organic phase RPo is separated from the aqueous phase RPw to obtain an organic phase Po comprising at least a part of the aromatic diamine A obtained in step (i) and optionally at least a part of the polyol E obtained in step (i).

[0175] The organic phase Po is then not dried, but employed directly in step ii).

[0176] Then, in step ii), o the at least one organic disulfide B and the at least one Lewis-acid catalyst D are mixed with Po, and o at least a part of the aromatic diamine A comprised by Po are reacted with the at least one organic disulfide B in the presence of the at least one Lewis-acid catalyst D, to obtain the at least one mono-thioether-substituted, preferably mono-thioalkylated, aromatic diamine Xiviono-

[0177] In a preferred embodiment, the obtained at least one mono-thioether-substituted aromatic diamine XMOHO has a carbon footprint of < 3.5, preferably < 2.9, kg CO2 equivalents / kg of all obtained XMono, as determined according to DIN EN ISO standard 14067:2018.

[0178] Carbon footprint can be determined according to DIN EN ISO standard 14067:2018. Using the obtained aromatic diamine A from the depolymerization process according to the invention leads to a reduction of at least 1 kg CO2 equivalents / kg in comparison to fossil-based aromatic diamine A. The carbon footprint of the aromatic diamine A can be brought below the above-mentioned thresholds in a plethora of ways, e.g. by recycling the organic thiol obtained from the heterolytic cleavage of the at least one organic disulfide B in step ii), and / or recycling at least one Lewis-acid catalyst D in step ii). Recycling of the organic thiol means using the organic thiol obtained in step ii) to form the at least one organic disulfide B, for example by reaction with elemental sulfur. The newly formed the at least one organic disulfide B can then be used again in step ii). As the at least one Lewis-acid catalyst D in inherently not consumed during the reaction, its recycling means reintroduction into step ii) in repetitions of the process according to the invention. Preferably at least 50 wt.-%, more preferably at least 80 wt.-%, most preferably at least 90 wt.-% of the at least one Lewis-acid catalyst D are recycled.

[0179] Unless stated otherwise, all percentages (%) given are percentages by weight.

[0180] The examples adduced hereinafter describe the present invention by way of example, without any intention that the invention, the scope of application of which is apparent from the entirety of the description and the claims, be restricted to the embodiments specified in the examples.

[0181] Step i): Process to obtain crude product from depolymerization of polyurethane

[0182] A reactor from Parr instrumental company equipped with a PTFE liner and a mechanical stirrer, was charged with 250 g of standard flexible polyurethane foam (shredded to a size of < 2mm) and 750 g of 40 wt.-% aqueous K2CO3 solution was added. Thereafter 12.5 g tetrabutylammonium hydrogen sulfate (“TBAHS”) was added, the reactor closed and heated to 150 °C for 6 h. After the desired reaction time was over, the dark-brown reaction mixture was allowed to cool down, the reactor was opened and the reaction mixture was transferred into a 2 L separation funnel, then left to stand for 2 h. The layers were then separated.

[0183] Example 1: Thioalkylation with the isolated recycled amine and the isolated recycled polyol

[0184] Isolation of recycled amine and recycled polyether polyol

[0185] Water was removed from the organic phase and the remaining solid was extracted with cyclohexane. The cyclohexane solution was washed with 1 N aqueous HCI solution, dried over magnesium sulfate and the solvent was removed. The solid was extracted with warm toluene to obtain the amine and the polyether polyol.

[0186] Thioalkylation

[0187] A multi-necked round bottom flask equipped with a magnetic stirrer, a condenser and a heat sensor for measuring the internal temperature, was charged with 20 g of toluenediamine (“TDA”) and 6 g of polyol was added. Thereafter 3 g of Copper(l) iodide (Cui) was added to the same flask while another multinecked round bottom flask was charged with 50 ml of dimethyl disulfide (“DMDS”). A tube line was fitted between the flasks with a flexible tube pump. The whole reaction setup was purged with nitrogen and the first flask was heated to 140 °C.

[0188] After the addition of DMDS over a period of 3 hours under inert atmosphere, the reaction was further continued another 4 hours. After the desired reaction time was over, the final product was characterized by GC-MS and it was confirmed that there was no recycled TDA left. Only 8.9 wt.-% of monothioalkylated isomers and 90.5 wt.-% of di-thioalkylated isomers were found.

[0189] The continuation of Cui addition together with DMDS resulted in full conversion to 11 wt.-% of monothioalkylated isomers and 89 wt.-% of di-thioalkylated isomers

[0190] The product purification can be carried out by distillation under reduced pressure.

[0191] Example 2: Thioalkylation with wet, crude reaction mixture from polyurethane depolymerization The organic phase separated from the aqueous phase of the crude reaction mixture from polyurethane depolymerization in step i) was further processed as follows: A multi-necked round bottom flask equipped with a magnetic stirrer, a condenser and a heat sensor for measuring the internal temperature, was charged with 5 g of the organic phase from PU depolymerization according to step i). Another multi-necked round bottom flask was prepared with DMDS. A tube line was fitted between the flasks with a flexible tube pump. The whole reaction setup was purged with nitrogen and the first flask was heated to 140 °C.

[0192] Thereafter, 2.5 g of Cui was added to the first flask and 50 ml of DMDS was added through the tube line over a period of 3 hours under inert atmosphere. The reaction was further continued for another 4 hours. After the desired reaction time was over, the final product was characterized by GC-MS and 50 wt-% of TDA was still detected. Furthermore, only 40.2 wt.-% of mono-thioalkylated isomers were observed, whereas no di-thioalkylated isomers were formed.

[0193] The product purification may be carried out by distillation under reduced pressure.

[0194] Example 3: Thioalkylation with dried, crude mixture from polyurethane depolymerization

[0195] The organic phase separated from the aqueous phase of the crude reaction mixture from polyurethane depolymerization in step i) was further processed as follows:

[0196] Dichloromethane (“DCM”) and MgSC were added to the separated organic phase from step i) to dry the separated organic phase. The organic layerwas then filtered and concentrated to obtain 50 g of the dried organic phase.

[0197] A multi-necked round bottom flask equipped with a magnetic stirrer, a condenser and a heat sensor for measuring the internal temperature, was charged with 50 g of the dried organic phase. Another multinecked round bottom flask was prepared with DMDS. A tube line was fitted between the flasks with a flexible tube pump. The whole reaction setup was purged with nitrogen and the first flask was heated to 140 °C.

[0198] Thereafter 2.5 g of Cui was added to the first flask and 50 ml of DMDS was added through the tube line over a period of 3 hours under inert atmosphere. The reaction was continued for another 4 hours and after 7 hours of reaction time, the final product was characterized by GC-MS. 9.9 % of TDA was still detected. 53.9 wt.-% of mono-thioalkylated isomers and 34 wt.-% di-thioalkylated isomers were detected.

[0199] Example 4: Thioalkylation with dried, crude mixture from polyurethane depolymerization with increased amount of Cui and longer reaction time

[0200] The organic phase separated from the aqueous phase of the crude reaction mixture from polyurethane depolymerization in step i) was further processed as follows: Magnesium sulfate (MgSC ) was added into the separated organic phase solution from the PU depolymerization in dichloromethane (“DCM”) and was stirred at room temperature. The organic phase solution from a PU depolymerization was then filtered and dried to obtain the dried organic phase.

[0201] A multi-necked round bottom flask equipped with a magnetic stirrer, a condenser and a heat sensor for measuring the internal temperature, was charged with 50 g of the dried organic phase. Another multinecked round bottom flask was prepared with DMDS. A tube line was fitted between the flasks with a flexible tube pump. The whole reaction setup was purged with nitrogen and the first flask was heated to 140 °C.

[0202] Thereafter 5 g of Cui was added to the first flask and 50 ml of DMDS was added through the tube line over a period of 3 hours under inert atmosphere. The reaction was continued for another 9 hours and after 12 hours of reaction time, the final product was characterized by GC-MS. It was confirmed that there was no TDA left. Only 8.8 wt.-% of mono-thioalkylated isomers and 90.9 wt.-% of di-thioalkylated isomers were found.

[0203] Example 5: Thioalkylation with wet, crude mixture from polyurethane depolymerization with increased amount of Cui and longer reaction time

[0204] The organic phase separated from the aqueous phase of the crude reaction mixture from polyurethane depolymerization in step i) was further processed as follows:

[0205] A multi-necked round bottom flask equipped with a magnetic stirrer, a condenser and a heat sensor for measuring the internal temperature, was charged with 50 g of the organic phase. Another multi-necked round bottom flask was prepared with DMDS. A tube line was fitted between the flasks with an addition of a pump. The whole reaction setup was purged with nitrogen and the first flask was heated to 122 °C.

[0206] Thereafter 5 g of Cui was added to the first flask and DMDS was added through the tube line over a period of 3 hours under inert atmosphere. The reaction was continued for another 9 hours and after 12 hours of reaction time, the final product was characterized by GC-MS. After 12 hours reaction time, 8.6 wt.-% of TDA was detected. Furthermore, 58.8 wt.-% of mono-thioalkylated isomers and 32.5 wt.-% of di-thioalkylated isomers were found.

[0207] Results and Conclusion

[0208] 1) Example 1 shows that the recycled polyol / diamine mixture from a PU depolymerization reaction can advantageously be used in the synthesis of mono- and di-thioalkylated isomers of aromatic diamines. In Example 1 , the recycled amine and the polyol were each dried and purified from the hydrolytic raw product obtained from PU depolymerization.

[0209] 2) Examples 2 to 5 surprisingly show that the organic phase from the raw product obtained during PU depolymerization may also be used directly, i.e. without further separation or isolation of the diamines, in the reaction with the alkylated disulfide, and thus may be directly deployed in the synthesis of the mono- and / or di-thioalky lated aromatic diamines. In those cases where a high yield of di-thioalkylated aromatic diamines is desired a drying step is necessary, which may be carried out easily.

[0210] 3) Even more surprisingly, the comparison between Examples 2 and 3 and the comparison between Examples 4 and 5 show that the yield in mono versus di-thioalkylated product may be controlled by drying, i.e. adjusting the water content of the applied organic phase. Where a high yield of the di-thioalkylated aromatic diamine is to be obtained, the organic phase must be dried. Where a high yield of the mono-thioalkylated aromatic diamine is to be obtained, the drying of the organic phase is omitted and the organic phase from the depolymerization raw product may be used directly.

[0211] The present invention thus provides for a convenient and effective process of synthesis of thioethersubstituted, preferably thioalkylated aromatic diamines from recycling products from PU depolymerization. Moreover, it provides for a process for selectively synthesizing mono- or di-thioether-substituted, preferably mono- or di-thioalkylated, aromatic diamines.

Claims

Claims1 . Process for producing at least one thioether-substituted aromatic diamine X comprising: i) at least partially depolymerizing at least one polyurethane PU to obtain at least one aromatic diamine A and at least one polyol E, ii) reacting at least a part of the aromatic diamine A with at least one organic disulfide B in the presence of at least one Lewis-acid catalyst D and in the presence of the at least one polyol E, to obtain the at least one thioether-substituted aromatic diamine X.

2. Process according to Claim 1 , characterized in that the aromatic diamine A is toluene diamine.

3. Process according to Claim 2 , characterized in that the toluene diamine is a mixture comprising 2,4-diamino toluene and 2,6-diamino toluene, wherein it is preferred that the molar ratio of 2,4-diamino toluene to 2,6-diamino toluene in the mixture is in the range of from 0.01 to 100, more preferably in the range of form 0.1 to 75, more preferably in the range of from 0.5 to 50, more preferably in the range of from 1 to 20, more preferably in the range of from 1 .5 to 5.0, more preferably in the range of from 1 .8 to 4.5, even more preferably in the range of from 2.0 to 4.0, even more preferably in the range of from 2.8 to 4.0, and most preferably in the range of from 3.0 to 4.0.

4. Process according to one of Claims 1 to 3, characterized in that the polyol E comprises a mixture of polypropylene glycol and polyethylene glycol, wherein preferably the ratio of the weight of all polypropylene glycol comprised by E to the weight of all polyethylene glycol comprised by E is in the range of from 99 : 1 to 1 : 99, preferably in the range of from 20 : 1 to 3 : 2.

5. Process according to one of Claims 1 to 4, characterized in that, in step i), the at least partial depolymerization of the at least one polyurethane PU is carried out in aqueous solution, to obtain an aqueous raw product RP comprising aromatic diamine A and polyol E, wherein RP comprises an organic phase RPo and an aqueous phase RPw in which o the organic phase RPo comprises at least a part of the aromatic diamine A and at least a part of the polyol E, o and wherein the organic phase RPo also contains water,and wherein at least a part Po of the organic phase RPo is separated from at least a part Pw of the aqueous phase RPw, to obtain an organic phase Po comprising at least a part of the aromatic diamine A obtained in step (i) and at least a part of the polyol E obtained in step (i).

6. Process according to Claim 5, characterized in that an organic solvent is added to RP before the separation of Po from Pw.

7. Process according to Claim 5 or 6, wherein the at least one thioether-substituted aromatic diamine X is a di-thioether-substituted aromatic diamine XDI, characterized in that the organic phase Po is at least partially dried to obtain a dried organic phase P01, and wherein, in step ii), o the at least one organic disulfide B and the at least one Lewis-acid catalyst D are mixed with P01, and o at least a part of the aromatic diamine A comprised by P01 is reacted with the at least one organic disulfide B in the presence of the at least one Lewis-acid catalyst D, to obtain the at least one di-thioether-substituted aromatic diamine XDI.

8. Process according to Claim 7, wherein the drying of Po is continued until the amount of water in P01 is < 90 wt.-%, preferably < 80 wt.-%, more preferably < 70 wt.-%, more preferably < 60 wt.-%, more preferably < 50 wt-.%, more preferably < 40 wt.-%, more preferably < 30 wt.-%, more preferably < 20 wt.-%, more preferably < 10 wt.-%, more preferably < 5 wt.-%, more preferably <1 wt.-% the amount of water in organic phase Po.

9. Process according to Claim 7 or 8, characterized in that the obtained at least one di-thioether-substituted aromatic diamine XDI has a carbon footprint of < 3.5, preferably < 2.9, kg CO2 equivalents / kg of all obtained XDI, as determined according to DIN EN ISO standard 14067:2018.

10. Process according to Claim 5 or 6, wherein the at least one thioether-substituted aromatic diamine X is a mono-thioether-substituted aromatic diamine XMono, characterized in that the organic phase Po is used without further drying in step ii),and wherein, in step ii), o the at least one organic disulfide B and the at least one Lewis-acid catalyst D are mixed with Po, and o at least a part of the aromatic diamine A comprised by Po are reacted with the at least one organic disulfide B in the presence of the at least one Lewis-acid catalyst D, to obtain the at least one mono-thioether-substituted aromatic diamine XMono-11 . Process according to Claim 10, characterized in that the obtained at least one mono-thioether-substituted aromatic diamine XMono has a carbon footprint of < 3.5, preferably < 2.9, kg CO2 equivalents / kg of all obtained XMono, as determined according to DIN EN ISO standard 14067:2018.

12. Process according to one of Claims 1 to 1 1 , wherein the at least partial depolymerization according to step i) is carried out at a temperature in the range of from 20 °C to 300 °C, preferably in the range of from 90 °C to 250 °C, more preferably in the range of from 100 °C to 250 °C, more preferably in the range of from 110 °C to 220 °C, even more preferably in the range of from 120 °C to 220 °C, and most preferred in the range of from 140 °C to 200 °C.

13. Process according to one of Claims 1 to 12, wherein the organic disulfide B has a structure R1S — SR2, wherein R1and R2are different or identical, preferably identical, and wherein R1and R2are each alkyl, preferably each selected from Ci to Cs-alkyl, more preferably each selected from Ci to Chalky I, even more preferably each selected from Ci to Cs-alkyl, most preferred are each methyl.

14. Process according to one of Claims 1 to 13, wherein the reaction according to step ii) is carried out at a temperature in the range of from 20 °C to 300 °C, preferably in the range of from 90 °C to 220 °C, preferably in the range of from 100 °C to 200 °C, more preferably in the range of from110 °C to 200 °C, even more preferably in the range of from 120 °C to 180 °C, and most preferably in the range of from 140 °C to 180 °C.

15. Process according to one of Claims 1 to 14, wherein the Lewis acid catalyst D comprises at least one atom selected from aluminum, boron, silicon, tin, titanium, zirconium, iron, copper, zinc.

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