Method for obtaining aniline by thermal cleavage of urethanes or amines

Abstract

The present invention relates to a method comprising the obtaining of aniline from a starting material selected from (i) a urethane based on an isocyanate and an alcohol, wherein the isocyanate comprises methylene diphenylene diisocyanate or a mixture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate, or (ii) an aromatic amine, wherein the aromatic amine comprises methylene diphenylene diamine or a mixture of methylene diphenylene diamine and polymethylene polyphenylene polyamine, with said method comprising a thermal cleavage of the starting material in a reactor in the presence of a catalyst at a temperature of 180 °C to 290 °C, forming a gaseous method product containing aniline and withdrawing the gaseous method product from the reactor, wherein the catalyst comprises an ammonium salt.

Description

[0001] METHOD FOR PROCUREMENT OF ANILINE BY THERMAL CHUNKING OF URETHANES OR AMINES

[0002] The project that led to this application has received funding under grant agreement no. 101036854 from the European Union’s Horizon 2020 research and innovation programme.

[0003] The present invention relates to a process comprising the production of aniline (and optionally toluidine, in particular para-toluidine) from a starting material selected from (i) a urethane based on an isocyanate and an alcohol, wherein the isocyanate comprises methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate, and in particular is, or (ii) an aromatic amine, wherein the aromatic amine comprises methylenediphenylenediamine or a mixture of methylenediphenylenediamine and polymethylenepolyphenylene polyamine, and in particular is, the process comprising a thermal cracking of the starting material in a reactor in the presence of a catalyst at a temperature of 180 °C to 290 °C to form a gaseous process product containing aniline and to remove the gaseous process product from the reactor, wherein the catalyst comprises an ammonium salt.

[0004] Urethanes, and especially polyurethanes, are versatile products with diverse applications in industry and everyday life. Polyurethane products are typically divided into polyurethane foams and so-called "CASE" products, where "CASE" is a collective term for polyurethane coatings (e.g., paints), adhesives, sealants, and elastomers. Polyurethane foams are usually further subdivided into rigid foams (which can be used, for example, as insulating materials, such as in refrigerators or building construction) and flexible foams (which can be used, for example, as cushioning materials, such as in upholstered furniture or car seats).Despite their differences, all these products share the basic polyurethane structure, which is formed by the polyaddition reaction of a multivalent isocyanate (hereinafter referred to as isocyanate) and a polyol, and is exemplified by a polyurethane based on a diisocyanate O=C=NRN=C=O and a diol HO-R'-OH (where R and R' denote organic residues). This can be illustrated. Many polyurethanes contain additional structural units besides the basic polyurethane structure. In particular, urea, isocyanurate, allophanate, and biuret structural units should be mentioned here.

[0005] An important isocyanate is the so-called MDL. MDI is a collective term for methylenediphenyl diisocyanate (mMDI – “monomeric MDI”) and polymethylene-polyphenylene polyisocyanate, which refers to the higher homologs of mMDI (also called “polymeric MDI”, pMDI). Methylenediphenyl diisocyanate exists in several isomers, of which 2,4'-methylenediphenyl diisocyanate and 4,4'-methylenediphenyl diisocyanate are the most important.

[0006] Pure mMDI and mixtures of mMDI and pMDL are technically important. Such mixtures are widely used, for example, in the production of rigid foams. The industrial production of MDI starts with aniline, which undergoes an acid-catalyzed reaction with formaldehyde, yielding mixtures of methylenediphenylenediamine ("monomeric MDA," mMDA) and polymethylenepolyphenylenepolyamine ("polymeric MDA," pMDA). Analogous to MDI, the collective term MDA is used for both mMDA and pMDA. These mixtures are usually phosgenated without prior separation, thus obtaining corresponding mixtures of mMDI and pMDI. Typically, fractions of essentially pure mMDI are distilled off from these mixtures, leaving behind mixtures of pMDI and mMDI with an increased pMDI content compared to the starting mixtures.

[0007] In the early days of polyurethane chemistry, efforts were focused on obtaining as much mMDI as possible. Initially, there were hardly any technical applications for pMDI, so it (or its precursor pMDA) was sometimes even considered a waste product that needed to be minimized. This was achieved, for example, by trying to maximize the yield of mMDA at the MDA stage and distilling it off from the unwanted pMDA as much as possible. Against the backdrop of making such unwanted pMDA technically usable, Frank J. Weigert described the hydrogenolysis of mMDA, but not pMDA, to aniline and toluidine in 1979 in the article "Acid-Catalyzed Pyrolysis of Aniline-Formaldehyde Oligomers," published in Ind. Eng. Chem. Prod. Res. Dev. 1979, 18 (3), 232-234 [1]. It is suggested that the results obtained could be significant for the Lewis acid-catalyzed depolymerization of coal (see summary).The pyrolysis of pMDI at 375 °C in the presence of various catalysts (oxide mixtures, zeolites, metal oxides, Pd / C, and inorganic acids; see Table III) is also described. The products are liquid mixtures containing aniline and toluidine. The best selectivity for aniline (82%) is obtained with HY faujasite at 58% conversion. The best conversion (58%) is obtained with TiCh at an aniline selectivity of 55%. This situation from previous decades no longer applies. Mixtures of pMDI and mMDI have numerous technical applications, such as the use described above in the production of rigid foams. Therefore, large quantities of MDI are produced every year and processed into polyurethanes of various types, either as essentially pure monomer (mMDI) or—even more significantly in terms of volume—as a mixture of mMDI and its higher homologues (pMDI).Precisely because of the great economic success of MDI-based polyurethanes, large quantities of polyurethane waste (e.g. from the insulation materials of no longer used cooling devices) are also generated, which must be put to sensible use.

[0008] The technically simplest way to utilize carbon-containing waste such as polyurethane waste is its incineration, using the released heat for other processes, such as industrial manufacturing. While this generates valuable energy and thus reduces the need to burn fossil fuels (which is desirable in itself, as it conserves valuable oil, coal, and gas reserves), it does not close the material cycles. Only material recycling can achieve this.

[0009] Another method of processing polyurethane waste, known as "physical recycling," involves mechanically shredding polyurethane waste and using it in the production of new products, thus enabling material recovery. However, this type of recycling has its limitations, such as a reduction in the quality of the recovered product compared to the original polyurethane. Therefore, numerous attempts have been made to recover the raw materials underlying polyurethane production by breaking down the urethane bonds (and any additional bonding structures present, such as isocyanurate, urea, allophanate, or biuret bonds). Such breakdown can be achieved through pyrolysis or chemically (chemolysis, "chemical recycling").In chemical recycling, functional groups, in this case especially the urethane bonds, are converted into other functional groups (especially amine and alcohol groups) through a chemical reaction with chemolysis reagents (especially alcohols, amines, and / or water), thereby cleaving long polymer chains into shorter polymer chains or oligomers and / or monomers. C-C bonds are generally not cleaved in this process. In contrast, pyrolytic cleavage occurs by heating the starting material under near-complete or near-complete exclusion of oxygen in the presence of a catalyst, and this process does result in the cleavage of C-C bonds.

[0010] Pyrolytic recycling is described, for example, in WO 2022 / 253873 Al and yields a pyrolysis product, including aniline, toluidine, and mMDA, when an MDI-based rigid foam is decomposed. Polyols (HOR'OH in the example above) cannot be recovered intact using this process.

[0011] PJ Whitman, FF Fru Ila, GH Temme and FA Stuber describe a mechanistic study in Tetrahedron Letters, 1986, 27, 1887-1890 [2] and discuss the possibility of C-C bond cleavage during the acid-catalyzed condensation of aniline and formaldehyde to poly(aminophenyl)methanes. A proton-induced dealkylation mechanism at the ipso position is described.

[0012] In their article "Ammonium Y zeolite applied as a thermochemolysis reagent for identification of polyethers and polyesters", published in Journal of Chromatography A, 2013, 1271, 2Y1-220 [3], M Blazsö et al. discuss the use of ammonium Y zeolites as a thermochemolysis reagent for the identification of polyethers, polyesters, and polyether- or polyester-based thermoplastic polyurethanes (see abstract). The obtained GC / MS chromatograms show that the thermochemolysis products are specific for the diol and dicarboxylic acid units of the polymer.

[0013] Chemical recycling allows for the recovery of polyols by cleaving urethane bonds through re-urethanization and / or hydrolysis reactions. Relatively inert polyols, such as polyether polyols, can be recovered as such. For more reactive polyols, such as polyester polyols, the underlying monomeric building blocks can be recovered. In addition, hydrolytic cleavage of the urethane bond can yield amines (in the example above, H₂N-R-NH₂), which, after further processing, can be phosgenated to isocyanates (in the example above, to O=C=NRN=C=O).

[0014] Various approaches to chemical recycling have been developed in the past. The most important ones are briefly summarized below:

[0015] 1. Hydrolysis of polyurethanes by reaction with water to obtain amines and polyols with the formation of carbon dioxide.

[0016] 2. Glycolysis of polyurethanes by reaction with alcohols, wherein the polyols incorporated into the urethane groups are replaced by the alcohol used and thus released. This process is usually referred to in the literature as transesterification (more precisely: transurethanization). This type of chemical recycling is commonly referred to as glycolysis in the literature, regardless of the exact type of alcohol used, although this term is actually only applicable to glycol or glycol derivatives. (Therefore, in connection with the present invention, the term alcoholysis is generally used.) Hydrolysis can follow glycolysis. If the hydrolysis is carried out with the direct product of the glycolysis (i.e., without prior separation of polyols and carbamates), it is called hydrolysis.

[0017] 3. Hydroglycolysis (more precisely: hydroalcohollysis) of urethane bonds through reaction with alcohols and water. It is of course also possible to add alcohol and water from the beginning, in which case the glycolysis and hydrolysis processes described above occur in parallel.

[0018] 4. Aminolysis of urethane bonds by reaction with primary or secondary amines, whereby the polyols incorporated into the urethane groups can be replaced by the amine used and thus released. In this case, the urethane groups are converted to urea groups. Similarly, the R-NH (C=O) bonds in the urethanes can also be cleaved, and the R-NH groups replaced by the amine used in the aminolysis, releasing the amine R-NH₂ corresponding to the originally used isocyanate. If amino acids with primary or secondary amino groups are used, the alcohol groups of the amino alcohol used can also react with urethane bonds, potentially leading to the formation of carbamates. According to most of the prior art, aminolysis can be followed by hydrolysis in a separate step.

[0019] 5. A reaction procedure corresponding to hydroglycolysis, in which amines or amino alcohols and water are used as reagents without prior separation of the released polyols, is described in WO 2023 / 083968 Al and is referred to there as aminohydrolysis.

[0020] A summary of the chemical polyurethane recycling processes known up to the beginning of 2018 is provided by the review article "Recycling of polyurethanes from laboratory to industry, a journey towards the sustainability" by D. Simon et al. in Waste Management 2018, 76, 147 - 171 [4],

[0021] A major challenge in the chemical recycling of polyurethanes is the clean separation of the resulting chemolysis products into polyols and carbamates formed by alcoholysis, or into polyols and amines. The development of viable recovery concepts has been and continues to be the subject of numerous investigations; see, for example, WO 2020 / 260387 Al and WO 2022 / 063764 Al concerning the recovery of alcoholysis products. The focus of these applications is on toluene diisocyanate and polyether polyol-based polyurethane products. However, particular challenges arise when the isocyanate component used in the production of the polyurethane contains the isocyanate MDI discussed above. Unlike toluene diisocyanate (TDI), which is widely used in so-called flexible foams, an MDI-based polyurethane product (for example, originating from old, used, so-called "end-of-life" (EoL) products or from the production of, for example,When polyurethane foams are hydrolyzed (as a byproduct of cutting), an amine (MDA) is formed, which is only very poorly soluble in water. This makes its isolation through extractive processes, especially the separation of polyols (which is important in the case of polyurethane product recycling), complex. Switching to distillation processes is not possible in the case of pMDA (which is regularly the case in the recycling of rigid foams) due to its high boiling point, which makes the isolation of pMDA in high purity very difficult.

[0022] There was therefore a need for further improvements in the field of recycling MDI-based polyurethane products. In particular, it would be desirable to recover aniline, from which MDA and subsequently MDI can be produced. Aniline is significantly easier to isolate and purify than MDA, so a process that enables the recovery of aniline can be advantageous compared to a process that relies on isolating MDA in its purest possible form, even though the latter process does not require the production of new MDA. Furthermore, a process that, unlike the pyrolysis of MDI-based polyurethane products, also allows for the recovery of the underlying polyols (or, in the case of polyols with reactive groups in the polymer chain, their monomeric building blocks) would be desirable.

[0023] Taking this need into account, an object of the present invention is a process comprising the production of aniline (and optionally toluidine, in particular para-toluidine) from a starting material selected from (i) a urethane based on an isocyanate and an alcohol, wherein the isocyanate comprises methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate, and in particular is, or (ii) an aromatic amine, wherein the aromatic amine comprises methylenediphenylenediamine or a mixture of methylenediphenylenediamine and polymethylenepolyphenylene polyamine, and in particular is, the process comprising a thermal cracking of the starting material in a reactor in the presence of a catalyst at a temperature of 180 °C to 290 °C, preferably 220 °C to 270 °C, particularly preferably 195 °C to 255 °C.forming a gaseous process product containing aniline and removing the gaseous process product from the reactor, wherein the catalyst comprises (at least) an ammonium salt (and preferably does not comprise any further catalysts other than ammonium salts, with the exception of the reducing agents explained in more detail below).

[0024] It was found, quite unexpectedly, that when using ammonium salts as catalysts, both MDI-based urethanes (either polyurethanes such as rigid foams or their low-molecular-weight urethanization products obtained in an alcoholysis reaction) and MDA (obtained from MDI-based polyurethanes by chemolysis or derived from MDA production waste) can be cleaved at relatively low temperatures – compared to a “classical” pyrolysis – to form aniline. In the case of MDA, this is even successful in the presence of polyols, so that an incomplete separation of MDA / polyol mixtures obtained in chemolysis does not preclude the application of the process according to the invention.

[0025] In the context of the present invention, thermal cleavage of the starting material is understood to mean the reaction of the starting material in the presence of the catalyst and, in particular, without the addition of chemical cleavage reagents (such as the aforementioned alcohols, amines, and / or water) to form (at least) aniline. Thus, in the context of the present invention, thermal cleavage comprises the cleavage of C-C bonds. In contrast to "classical" pyrolysis, however, it is not only possible to operate at comparatively low temperatures, but even to forego the exclusion of oxygen (although the exclusion of oxygen can be advantageous).

[0026] A catalyst used for the thermal decomposition of the starting material, as defined in the present invention, is, in accordance with common usage in the field, a substance that increases the reaction rate. However, it is not essential for the present invention that the catalyst used can be recovered unchanged after the thermal decomposition has been carried out. When, within the scope of the present invention, reference is made to a catalyst (or more specifically, for example, "an ammonium halide"), this also includes embodiments in which several catalysts (for example, several different ammonium halides or a mixture of an ammonium halide and another catalyst) are used, unless expressly stated otherwise (e.g., by the phrase "exactly one"). Expressions such as "a catalyst" and the like are not intended to be understood as meaningless or imprecise.Therefore, the term "at least one catalyst" is always to be understood as "at least one catalyst" unless explicitly stated otherwise. Polyurethane products within the meaning of the present invention are the polyaddition products obtained by reacting polyhydric isocyanates (the isocyanate component of polyurethane production) with polyols (the polyol component of polyurethane production). Polyurethane products generally contain, in addition to the polyurethane basic structure outlined above, other structures, for example, urea, isocyanurate, allophanate, and biuret structural units. The presence of such structures, which deviate from the pure polyurethane basic structure, alongside polyurethane structures does not exceed the scope of the present invention. Polyurethane products within the meaning of the present invention are preferably polyurethane foams obtained by reacting polyhydric isocyanates with polyols in the presence of a blowing agent, and in particular, rigid polyurethane foams.Within the scope of the present invention, a rigid polyurethane foam is understood to be a polyurethane foam which has a compressive stress at 10 % compression (GIO) of 10 kPa or more as measured in accordance with DIN EN 826:2013-05.

[0027] In the terminology of the present invention, the term polyols encompasses all polyols known to those skilled in the art in connection with polyurethane chemistry, such as, in particular, polyether polyols, polyester polyols, polyether ester polyols, and polyether carbonate polyols. The expression "a polyol" naturally also includes embodiments in which two or more different polyols are used in the manufacture of a polyurethane product. Therefore, when, for example, "a polyether polyol" (or "a polyester polyol," etc.) is mentioned below, this terminology naturally also includes embodiments in which two or more different polyether polyols (or two or more different polyester polyols, etc.) are used in the manufacture of a polyurethane product. The entirety of all polyols used in the manufacture of a polyurethane product is referred to as the polyol component (of the polyurethane product).The polyol component comprises at least one polyol. Polyols that are relatively unreactive can be recovered (essentially) chemically unchanged. This applies particularly to polyether polyols. In the case of polyols with chemically relatively reactive groups in the polymer chain, such as polyester polyols, the polyols originally used in polyurethane production cannot usually be recovered as such, but their underlying alcohol monomers (e.g., 1,6-hexanediol) can, and these are then considered the recovered polyols. In addition, the acid component used in the production of a polyester polyol (e.g., adipic acid) can also be recovered. As will be explained in more detail below, the polyols in the polyol component are preferably polyether polyols, which can be recovered as such.In the terminology of the present invention, the term isocyanate encompasses all isocyanates known to those skilled in the art in connection with polyurethane chemistry and refers in particular to methylenediphenyl diisocyanate or a mixture of methylenediphenyl diisocyanate (mMDI) and polymethylenepolyphenyl polyisocyanate (pMDI). The expression "one or more isocyanates" naturally also includes embodiments in which two or more different isocyanates (e.g., mixtures of MDI and TDI) are used in the manufacture of a polyurethane product, unless otherwise expressly stated, for example by the phrase "exactly one isocyanate". The entirety of all isocyanates used in the manufacture of a polyurethane product is referred to as the isocyanate component (of the polyurethane product). The isocyanate component contains at least one isocyanate.It contains exactly one (1) isocyanate, which according to the invention is selected from mMDI or - preferably - a mixture of mMDI and pMDI.

[0028] An amine corresponding to an isocyanate is that amine by whose phosgenation the isocyanate can be obtained according to R-NH2 + COCI2 —> RN=C=O + 2 HCl.

[0029] In the context of the present invention, an organic chemolysis reagent means an organic compound that has functional groups which can react with urethane bonds by cleaving them, in particular alcohol and amine groups.

[0030] When the present invention refers to a device / assembly (e.g., in expressions such as "a reactor," etc.), this also includes embodiments in which several devices / assemblies of the aforementioned type are connected in series or in parallel (the example expression is therefore to be read as "at least one reactor"), unless expressly stated otherwise (e.g., by the phrase "exactly one"). The same applies to substances (see the above explanations regarding catalysts, polyols, and isocyanates).

[0031] The term distillation, as used in the context of the present invention, also includes rectification.

[0032] The following is a brief summary of various possible embodiments of the invention:

[0033] In a first embodiment of the process according to the invention, which can be combined with all other embodiments, the (at least one) ammonium salt comprises an ammonium halide (in particular ammonium iodide or ammonium chloride), an ammonium hexafluorosalt (in particular ammonium hexafluorophosphate), ammonium thiosulfate, ammonium hydrogen carbonate, ammonium carbonate, ammonium sulfate, ammonium hydrogen sulfate, ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and / or an ammonium carboxylate (in particular ammonium formate, preferably in combination with another ammonium salt), wherein the use of ammonium halides, ammonium hexafluorosalts, ammonium thiosulfate, ammonium hydrogen carbonate, and / or ammonium carboxylates is particularly preferred. The use of ammonium iodide and / or ammonium chloride is especially preferred.

[0034] In a second embodiment of the process according to the invention, which can be combined with all other embodiments, the catalyst comprises a reducing agent in addition to the ammonium salt.

[0035] In a third embodiment of the process according to the invention, which is a special embodiment of the second embodiment, the reducing agent is selected from a thiosulfate (in the case of an ammonium / umthiosulfate, in particular together with a further ammonium salt) and / or a formate (in the case of an ammonium / umformate, in particular together with a further ammonium salt).

[0036] In a fourth embodiment of the method according to the invention, which can be combined with all other embodiments, the reactor is selected from a rotary tube reactor, a fluidized bed reactor, a fixed bed reactor, a fluidized flow reactor, a kneading reactor, an extruder, a reactor with rotating mixing tools, in particular a stirred tank reactor, a thin-film or falling film evaporator or a combination of two or more of the aforementioned reactor types (whereby two or more reactors of the same type can also be connected in series).

[0037] In a fifth embodiment of the process according to the invention, which can be combined with all other embodiments, the removal of the gaseous process product from the reactor is carried out continuously.

[0038] In a sixth embodiment of the method according to the invention, which is a special embodiment of the fifth embodiment, the removal of the gaseous process product from the reactor is ensured by a gas flow guided through the reactor and / or by suction.

[0039] In a seventh embodiment of the method according to the invention, which is a special embodiment of the sixth embodiment, a residence time of the gaseous process product in the reactor, specified as the period between the time of formation of the gaseous process product and the time of its removal from the reactor, is set from 0.1 seconds to 600 seconds, preferably from 0.5 seconds to 300 seconds, particularly preferably from 0.5 seconds to 200 seconds.

[0040] In an eighth embodiment of the method according to the invention, which is a special embodiment of the sixth and seventh embodiments, the gas stream comprises nitrogen, argon, carbon dioxide and / or nitric oxide.

[0041] In a ninth embodiment of the method according to the invention, which can be combined with all other embodiments, aniline is added to the starting material before thermal cracking.

[0042] In a tenth embodiment of the method according to the invention, which can be combined with all other embodiments, the proportion of oxygen gas in the reactor during the thermal cracking of the starting material (determinable by means of commercially available oxygen sensors) is 0 vol.% to 2.0 vol.%, preferably 0 vol.% to 0.5 vol.%, particularly preferably 0 vol.% to 0.1 vol.%, based on the total volume of the gas phase in the reactor.

[0043] In an eleventh embodiment of the method according to the invention, which can be combined with all other embodiments, an absolute pressure of 0.8 to 1.2 bar is present during the thermal cracking of the starting material in the gas phase of the reactor, preferably atmospheric ambient pressure.

[0044] In a twelfth embodiment of the method according to the invention, which can be combined with all other embodiments, a non-gaseous (solid, liquid or pasty) residue is formed during the thermal cracking of the starting material.

[0045] In a thirteenth embodiment of the method according to the invention, which is a special embodiment of the twelfth embodiment, the residue is continuously discharged from the reactor.

[0046] In a fourteenth embodiment of the method according to the invention, which can be combined with all other embodiments, the temperature during thermal cracking is 220 °C to 270 °C.

[0047] In a fifteenth embodiment of the method according to the invention, which can be combined with all other embodiments, the temperature during thermal cracking is 195 °C to 255 °C.

[0048] In a sixteenth embodiment of the process according to the invention, which can be combined with all other embodiments, provided that these do not provide for the direct transfer of the gaseous process product to a distillation, the gaseous process product removed from the reactor is cooled to a temperature at which aniline condenses, obtaining a liquid process product containing aniline, which is then subjected to a work-up to obtain aniline comprising (at least) a distillation.

[0049] In a seventeenth embodiment of the process according to the invention, which can be combined with all other embodiments, provided that these do not exclude the direct transfer of the gaseous process product to a distillation, the gaseous process product removed from the reactor is subjected to a work-up for the recovery of aniline comprising (at least) a distillation without condensation.

[0050] In an eighteenth embodiment of the process according to the invention, which is a special embodiment of the sixteenth and seventeenth embodiments, toluidine is formed in addition to aniline in the thermal cracking, wherein the processing of the gaseous or liquid process product includes a separation of aniline and toluidine.

[0051] In a nineteenth embodiment of the process according to the invention, which is a special embodiment of the sixteenth to eighteenth embodiments, the aniline obtained in the processing of the gaseous or liquid process product is reacted with formaldehyde under acid catalysis to form methylenediphenylenediamine and polymethylenepolyphenylenepolyamine.

[0052] In a twentieth embodiment of the process according to the invention, which is a special embodiment of the nineteenth embodiment, the methylenediphenylenediamine and the polymethylenepolyphenylenepolyamine are phosgenated, followed by work-up to obtain methylenediphenylene diisocyanate and a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate.

[0053] In a twenty-first embodiment of the process according to the invention, which is a particular embodiment of the twentieth embodiment, the methylenediphenylene diisocyanate and / or the mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate is reacted with a polyol to form a polyurethane.

[0054] In a twenty-second embodiment of the process according to the invention, which is a particular embodiment of the twenty-first embodiment, the polyol is obtained by splitting a polyurethane product. Such splitting can be the process according to the invention itself, but also recycling processes already known from the literature. In a twenty-third embodiment of the process according to the invention, which can be combined with all other embodiments except those that exclude the use of a polyurethane product as a starting material, the urethane is a polyurethane product and the alcohol is a polyol.

[0055] In a twenty-fourth embodiment of the process according to the invention, which can be combined with all other embodiments except those directed to the use of a polyurethane product as a starting material, the urethane is a cleavage product derived from the isocyanate, obtained by chemical cleavage (chemolysis) of a polyurethane product based on the isocyanate (and optionally further isocyanates different from mMDI and pMDI) and a polyol with an organic chemolysis reagent.

[0056] In a twenty-fifth embodiment of the process according to the invention, which is a special embodiment of the twenty-fourth embodiment, the organic chemolysis reagent comprises a chemolysis alcohol and / or a chemolysis amino alcohol.

[0057] In a twenty-sixth embodiment of the process according to the invention, which is a special embodiment of the twenty-fourth and twenty-fifth embodiments, the chemical cleavage (chemolysis) yields a chemolysis product containing the cleavage product derived from the isocyanate and the polyol, wherein the chemolysis product is subjected to thermal cleavage without separation of the cleavage product and the polyol.

[0058] In a twenty-seventh embodiment of the process according to the invention, which is a further particular embodiment of the twenty-fourth and twenty-fifth embodiments, the chemical cleavage (chemolysis) yields a chemolysis product containing the cleavage product derived from the isocyanate and the polyol, wherein the chemolysis product is separated into a fraction containing the cleavage product derived from the isocyanate and into a fraction containing the polyol, and wherein the fraction containing the cleavage product derived from the isocyanate is subjected to thermal cleavage.

[0059] In a twenty-eighth embodiment of the process according to the invention, which can be combined with all other embodiments except those which exclude the use of an aromatic amine as a starting material, the aromatic amine is obtained from a waste stream of a process for the production of methylenediphenylenediamine and / or polymethylenepolyphenylenepolyamine.

[0060] In a twenty-ninth embodiment of the process according to the invention, which can be combined with all other embodiments except those which exclude the use of an aromatic amine as a starting material, the aromatic amine is obtained by chemical cleavage (chemolysis) of methylenediphenyl diisocyanate and / or polymethylenepolyphenyl polyisocyanate, which originates from a waste stream of a process for the production of methylenediphenyl diisocyanate and / or polymethylenepolyphenyl polyisocyanate, with water.

[0061] In a thirtieth embodiment of the process according to the invention, which can be combined with all other embodiments except those which exclude the use of an aromatic amine as a starting material, the aromatic amine is obtained by chemical cleavage (chemolysis) of a polyurethane product based on the isocyanate (and optionally further isocyanates different from mMDI and pMDI) and a polyol.

[0062] In a thirty-first embodiment of the process according to the invention, which is a special embodiment of the thirtieth embodiment, the chemical cleavage comprises a reaction of the polyurethane product with an organic chemolysis reagent and water.

[0063] In a thirty-second embodiment of the process according to the invention, which is a particular embodiment of the thirty-first embodiment, the organic chemolysis reagent comprises a chemolysis alcohol, a chemolysis amine and / or a chemolysis amino alcohol.

[0064] In a thirty-third embodiment of the process according to the invention, which is a further special embodiment of the thirty-first embodiment, the chemical cleavage (chemolysis) comprises a reaction of the polyurethane product with water without the use of an organic chemolysis reagent.

[0065] In a thirty-fourth embodiment of the process according to the invention, which is a special embodiment of the thirty- to thirty-third embodiments, the chemical cleavage (chemolysis) yields a chemolysis product containing the aromatic amine and the polyol, wherein the chemolysis product is subjected to thermal cleavage without separation of the aromatic amine and polyol.

[0066] In a thirty-fifth embodiment of the process according to the invention, which is a further particular embodiment of the thirty- to thirty-third embodiments, the chemical cleavage (chemolysis) yields a chemolysis product containing the aromatic amine and the polyol, wherein the chemolysis product is separated into a fraction containing the aromatic amine and a fraction containing the polyol, and wherein the fraction containing the aromatic amine is subjected to thermal cleavage. In a thirty-sixth embodiment of the process according to the invention, which is a particular embodiment of the thirty-fifth embodiment, the separation of the chemolysis product into a fraction containing the aromatic amine and a fraction containing the polyol comprises (at least) an extraction and / or (at least) a distillation.

[0067] In a thirty-seventh embodiment of the process according to the invention, which is a further particular embodiment of the thirty-fifth embodiment, the separation of the chemolysis product into a fraction containing the aromatic amine and into a fraction containing the polyol comprises acidification of the chemolysis product with an acid to form a protonated aromatic amine, followed by separation of the protonated aromatic amine leaving the fraction containing the polyol, wherein the separated protonated aromatic amine is converted into the aromatic amine by reaction with a base, in particular after introduction of the protonated aromatic amine into the reactor.

[0068] In a thirty-eighth embodiment of the method according to the invention, which is a special embodiment of the thirty-seventh embodiment, the acid is selected from hydrogen chloride gas, hydrochloric acid or sulfuric acid.

[0069] In a thirty-ninth embodiment of the process according to the invention, which is a particular embodiment of the thirty-seventh and thirty-eighth embodiments, the base is selected from an alkali metal hydroxide (in particular sodium hydroxide or potassium hydroxide, preferably sodium hydroxide), an alkaline earth metal hydroxide (in particular magnesium hydroxide or calcium hydroxide), an alkali metal or alkaline earth metal carbonate (in particular sodium, potassium, magnesium or calcium carbonate), aqueous ammonia or ammonia gas.

[0070] In a fortieth embodiment of the process according to the invention, which is a further particular embodiment of the thirtieth embodiment, the chemical cleavage comprises a reaction of the polyurethane product with an organic chemolysis reagent, wherein a chemolysis product is obtained which is separated into a fraction containing (at least) a cleavage product derived from the isocyanate and into a fraction containing the polyol, and wherein the fraction containing the (at least one) cleavage product derived from the isocyanate is reacted with water to form a fraction containing the aromatic amine.

[0071] In a forty-first embodiment of the process according to the invention, which is a particular embodiment of the fortieth embodiment, the organic chemolysis reagent comprises a chemolysis alcohol, a chemolysis amine, and / or a chemolysis amino alcohol. In a forty-second embodiment of the process according to the invention, which is a particular embodiment of the twenty-seventh or thirty-five to forty-first embodiments, the fraction containing the polyol, optionally after work-up to purify the polyol contained therein, is used in the production of a polyurethane by reaction with an isocyanate.

[0072] In a forty-third embodiment of the process according to the invention, which is a particular embodiment of the forty-second embodiment, the isocyanate used in the production of the polyurethane comprises the methylenediphenyl diisocyanate and / or mixture of methylenediphenyl diisocyanate and polymethylenepolyphenyl polyisocyanate obtained according to the twentieth embodiment.

[0073] In a forty-fourth embodiment of the method according to the invention, which is a special embodiment of the twenty-fourth to twenty-seventh or the twenty-ninth to forty-threeth embodiments, the chemical cleavage (chemolysis) is carried out in the presence of a chemolysis catalyst.

[0074] In a forty-fifth embodiment of the process according to the invention, which is a particular embodiment of the forty-fourth embodiment, the chemolysis catalyst is selected from a (in particular alkali metal or alkaline earth metal) hydroxide, a (in particular alkali metal or alkaline earth metal) carboxylate (in particular acetate), a tin compound (in particular dibutyltin dilaurate or tin(II) octoate [= tin(II) 2-ethylhexanoate]), a zinc compound

[0075] (in particular zinc acetate), a (in particular alkali metal or alkaline earth metal) carbonate, a (in particular alkali metal or alkaline earth metal) hydrogen carbonate, an (in particular alkali metal or alkaline earth metal) orthophosphate, a (in particular alkali metal or

[0076] alkaline earth metal (IV) ionohydrogen orthophosphate, an (especially alkali metal or alkaline earth metal) orthovanadate, a titanium alkoxide, a tertiary amine, cesium fluoride or a mixture of two or more of the aforementioned chemolysis catalysts.

[0077] The embodiments and further possible configurations of the invention briefly described above are explained in more detail below. All embodiments described above and the further configurations of the invention described below are, unless the context clearly indicates otherwise to a person skilled in the art or unless expressly stated otherwise, freely combinable with one another. PROVISION OF THE STARTING MATERIAL

[0078] In a first embodiment of the present invention, the starting material (i) is a urethane based on an isocyanate and an alcohol, wherein the isocyanate comprises methylenediphenylene diisocyanate (mMDI) or a mixture of methylenediphenylene diisocyanate (mMDI) and polymethylenepolyphenylene polyisocyanate (pMDI) and in particular is (i.e., in particular, does not comprise any other isocyanates besides mMDI and, if applicable, pMDI).

[0079] In a preferred embodiment, the urethane is a polyurethane product; that is, the alcohol in this embodiment is a polyol. As explained above, this polyol is a polyol originally used in polyurethane production (in the case of less reactive polyols such as polyether polyols) and / or reaction products of such a polyol (in the case of reactive polyols such as polyether ester polyols or polyester polyols). Polyether polyols are preferred. The polyurethane products can be either used (so-called end-of-life) polyurethanes or waste (e.g., offcuts) from polyurethane production. Polyurethane foams, in particular rigid polyurethane foams, are preferred.

[0080] In another preferred embodiment, the urethane is a cleavage product derived from the isocyanate (i.e., a low molecular weight urethane or a low molecular weight urea) obtained by chemical cleavage (chemolysis) of a polyurethane product based on the isocyanate (and optionally other isocyanates different from mMDI and pMDI) and a polyol with an organic chemolysis reagent (in particular a chemolysis alcohol and / or a chemolysis amino alcohol).

[0081] The chemical cleavage (chemolysis) yields a chemolysis product containing the cleavage product derived from the isocyanate and the aforementioned polyol (which can also be a mixture of different polyols), as well as optionally further reaction products. The thermal cleavage according to the invention can be carried out without prior separation of the cleavage product and the polyol (and any other reaction products that may be present). However, it is also possible to separate the chemolysis product obtained in the chemical cleavage (chemolysis) into a fraction containing the cleavage product derived from the isocyanate and a fraction containing the polyol (and any other reaction products that may be present) using methods known per se, and to subject the fraction containing the cleavage product derived from the isocyanate to thermal cleavage.

[0082] Methods for carrying out the chemical cleavage and the separation of the resulting chemolysis product into a fraction containing the cleavage product derived from the isocyanate and into a fraction containing the polyol are known and are described, for example, in WO 2020 / 260387 Al, WO 2022 / 063764 Al, WO 2022 / 263336 Al and WO 2023 / 072985 Al.

[0083] In a second embodiment of the present invention, the starting material is (ii) an aromatic amine, wherein the aromatic amine comprises methylenediphenylenediamine (mMDA) or a mixture of methylenediphenylenediamine (mMDA) and polymethylenepolyphenylenepolyamine (pMDA) and in particular is (i.e., in particular, does not comprise any other amines besides mMDA and optionally pMDA).

[0084] The aromatic amine can originate from a waste stream. Such a waste stream can arise in a process for the production of methylenediphenylenediamine and / or polymethylenepolyphenylene polyamine. Alternatively, a waste stream from a process for the production of methylenediphenyl diisocyanate (mMDI) and / or polymethylenepolyphenylene polyisocyanate (pMDI), which undergoes chemical cleavage (chemolysis) with water (hydrolysis), can also serve as a source. Examples of mMDI / pMDI-containing waste streams include by-product-rich distillation fractions from the processing of crude MDI or defective batches that are unsuitable for their intended use due to deviations from specified values. Such MDI-containing waste streams can be reacted with the process according to the invention to yield aniline, which can be easily separated from by-products and purified by distillation.

[0085] In another embodiment, the aromatic amine is obtained by chemical cleavage. a polyurethane product based on the isocyanate (and optionally other isocyanates different from mMDI and pMDI) and a polyol is obtained. As explained previously in general terms and also in connection with the first variant, this polyol is a polyol originally used in polyurethane production (in the case of less reactive polyols such as polyether polyols) and / or reaction products of such a polyol (in the case of reactive polyols such as polyether ester polyols or polyester polyols). Polyether polyols are preferred. As in the first variant, the polyurethane products can be either used (so-called end-of-life) polyurethanes or waste (e.g., offcuts) from polyurethane production. Polyurethane foams, in particular rigid polyurethane foams, are preferred.

[0086] In one embodiment, such a chemical cleavage involves reacting the polyurethane product with an organic chemolysis reagent and water. The organic chemolysis reagent comprises, in particular, a chemolysis alcohol, a chemolysis amine, and / or a chemolysis amino alcohol (hydroalcohollysis or m'inohydrolysis). Carrying out the chemolysis as aminohydrolysis is particularly preferred and can advantageously be performed as described in WO 2023 / 083968 Al, in particular on page 16, line 33 to page 19, line 2.

[0087] In another embodiment, the chemical cleavage (chemolysis) involves a reaction of the polyurethane product with water without the use of an organic chemolysis reagent (hydrolysis).

[0088] The chemical cleavage of the polyurethane product with water and optionally an organic chemolysis reagent in any case yields a chemolysis product containing the aromatic amine and the polyol. The thermal cleavage according to the invention can be carried out without separating the aromatic amine and the polyol. However, it is also possible to separate the chemolysis product into a fraction containing the aromatic amine and a fraction containing the polyol using methods known per se (such as those described, for example, in WO 2023 / 083968 Al, in particular on page 19, line 4 to page 20, line 2 and page 20, line 23 to page 22, line 30), and to subject the fraction containing the aromatic amine to thermal cleavage. In one embodiment, such a separation comprises (at least) an extraction and / or (at least) a distillation.It is also possible to acidify the chemolysis product with an acid to form a protonated aromatic amine, followed by the separation of the protonated aromatic amine, leaving behind the fraction containing the polyol. The separated protonated aromatic amine is converted back into the aromatic amine by reaction with a base. The acid used is preferably selected from hydrogen chloride gas, hydrochloric acid, or sulfuric acid. The base required for the conversion back into the aromatic amine is preferably selected from an alkali metal hydroxide (in particular sodium hydroxide or potassium hydroxide, preferably sodium hydroxide), an alkaline earth metal hydroxide (in particular magnesium hydroxide or calcium hydroxide), an alkali metal or alkaline earth metal carbonate (in particular sodium, potassium, magnesium, or calcium carbonate), aqueous ammonia, or ammonia gas.The reaction with the base is preferably carried out by introducing the protonated amine into the reactor for thermal decomposition, then adding the base, and finally adding the catalyst comprising at least one ammonium salt. The base is preferably added stoichiometrically and, in particular, not superstoichiometrically. The reactor can be heated to the reaction temperature before the addition of the protonated amine.

[0089] It is also possible to carry out the chemical cleavage of the polyurethane product in two steps, whereby first a reaction with an organic chemolysis reagent (in particular a chemolysis alcohol, a chemolysis amine, and / or a chemolysis amino alcohol) is performed, and the resulting chemolysis product is separated into a fraction containing (at least) one cleavage product derived from the isocyanate and a fraction containing the polyol. The fraction containing the (at least one) cyanate-derived cleavage product is then reacted (hydrolyzed) with water in a second step to form a fraction containing the aromatic amine. Such a two-step cleavage of the polyurethane product is described, for example, in WO 2020 / 260387 Al, WO 2022 / 063764 Al, and WO 2022 / 263336 Al.

[0090] In all variants and embodiments that include chemical cleavage (chemolysis), it is preferred to carry this out in the presence of a chemolysis catalyst.The chemolysis catalyst is preferably selected from a (especially alkali metal or alkaline earth metal) hydroxide, a (especially alkali metal or alkaline earth metal) carboxylate (especially acetate), a tin compound (especially dibutyltin dilaurate or tin(II) octoate [= tin(II) 2-ethylhexanoate]), a zinc compound (especially zinc acetate), a (especially alkali metal or alkaline earth metal) carbonate, a (especially alkali metal or alkaline earth metal) hydrogen carbonate, an (especially alkali metal or alkaline earth metal) orthophosphate, an (especially alkali metal or alkaline earth metal) IV ionohydrogen orthophosphate, an (especially alkali metal or alkaline earth metal) orthovanadate, a titanium alkoxide, a tertiary amine, cesium fluoride or a mixture of two or more of the aforementioned chemolysis catalysts.

[0091] FURTHER PROCESSING OF RECOVERED POLYOL-CONTAINING FRACTIONS

[0092] The polyol-containing fractions obtained during chemical cleavage (chemolysis) are valuable raw materials that are preferably used for material recovery. For this purpose, the resulting polyol-containing fractions, optionally after processing to purify the polyols they contain, can be used in the production of polyurethanes by reaction with isocyanates. In principle, all isocyanates known to the trade for polyurethane synthesis are suitable. The use of MDI (more precisely: mMDI or mixtures of mMDI and pMDI) is preferred. As mentioned above, MDI is usually obtained by phosgenation of MDA, which in turn is obtained by acid-catalyzed reaction of aniline with formaldehyde. It is particularly preferred to use aniline obtained by the thermal cleavage according to the invention. THERMAL CHUNKING

[0093] The starting material, provided in particular as described above, is subjected to thermal cracking according to the invention. The catalyst used comprises at least one ammonium salt. Preferably, this is selected from an ammonium halide (in particular ammonium iodide or ammonium chloride), an ammonium hexafluorosalt (in particular ammonium hexafluorophosphate), ammonium thiosulfate, ammonium sulfate, or ammonium hydrogen sulfate.

[0094] Ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium hydrogen carbonate, ammonium carbonate and / or an ammonium carboxylate (in particular ammonium formate, preferably in combination with another ammonium salt), wherein the use of ammonium halides, ammonium hexafluorosalts, ammonium thiosulfate, ammonium hydrogen carbonate and / or ammonium carboxylates is particularly preferred. The use of ammonium iodide and / or ammonium chloride is especially preferred.

[0095] In one embodiment, the catalyst comprises a reducing agent in addition to the ammonium salt. This reducing agent is selected, in particular, from a thiosulfate (in the case of an ammonium / umthiosulfate, especially together with another ammonium salt) and / or a formate (in the case of an ammonium / umformate, especially together with another ammonium salt). The use of a reducing agent can improve the selectivity to aniline.

[0096] As regards the reactor used for thermal cracking, it is preferably selected from a rotary tube reactor, a fluidized bed reactor, a fixed bed reactor, a fluidized flow reactor, a kneading reactor, an extruder, a reactor with rotating mixing tools, in particular a stirred tank reactor, a thin-film or falling film evaporator or a combination of two or more of the aforementioned reactor types (where two or more reactors of the same type may also be connected in series).

[0097] The gaseous process product formed in the thermal cracking process is preferably continuously discharged from the reactor. This can be ensured by a gas stream passing through the reactor and / or by suction. A residence time of the gaseous process product in the reactor, defined as the period between the time of its formation and the time of its discharge from the reactor, of 0.1 seconds to 600 seconds, preferably 0.5 seconds to 300 seconds, and particularly preferably 0.5 seconds to 200 seconds, is preferred. If a gas stream is used, it preferably comprises nitrogen, argon, carbon dioxide, and / or nitric oxide. The gas stream is particularly preferably composed of one or more of the aforementioned gases. As already mentioned, the exclusion of oxygen is not strictly necessary for the process according to the invention, but can nevertheless be advantageous.In one embodiment, therefore, during the thermal cracking of the starting material, the proportion of oxygen gas in the reactor (determinable by means of commercially available oxygen sensors) is adjusted to 0 vol.% to 2.0 vol.%, preferably 0 vol.% to 0.5 vol.%, particularly preferably 0 vol.% to 0.1 vol.%, based on the total volume of the gas phase in the reactor.

[0098] The absolute pressure in the gas phase of the reactor is preferably 0.8 to 1.2 bar. Thermal cracking is particularly preferably carried out at atmospheric pressure ("pressureless"). The temperature during thermal cracking is 180 °C to 290 °C, preferably 220 °C to 270 °C, and particularly preferably 195 °C to 255 °C.

[0099] In one embodiment of the process, aniline is added to the starting material before thermal cracking. It has been shown that this improves the selectivity for aniline.

[0100] During the thermal cracking of the starting material, a non-gaseous (solid, liquid, or pasty) residue can be formed in addition to the gas phase. This is preferably continuously discharged from the reactor.

[0101] REPROCESSING OF GAS-FORMED PROCESS PRODUCT CONTAINING ANILINE

[0102] The gaseous process product extracted from the reactor contains the target product aniline and is preferably processed for its purification.

[0103] For this purpose, it can be cooled to a temperature at which aniline condenses, yielding a liquid process product containing aniline, which is then subjected to a work-up process to obtain aniline, comprising (at least) one distillation. It is also possible to subject the gaseous process product removed from the reactor to a work-up process to obtain aniline without condensation, comprising (at least) one distillation. Regardless of the method, substantial amounts of toluidine can be formed during thermal cracking. In this case, the work-up of the gaseous or liquid process product preferably includes a separation of aniline and toluidine. The distillative purification of aromatic amines, such as aniline in particular, is well known and need not be described in detail here. FURTHER PROCESSING OF THE ANILINE RECOVERED

[0104] The aniline obtained can be used in all known applications of aniline in the scientific community (this also applies, of course, to any toluidine obtained). The preferred reaction of aniline with formaldehyde under acid catalysis (especially hydrochloric acid catalysis) yields methylenediphenylenediamine and polymethylenepolyphenylene. The methylenediphenylenediamine and the polymethylenepolyphenylene can then be phosgenated, allowing for further work-up to obtain methylenediphenyl diisocyanate and a mixture of methylenediphenyl diisocyanate and

[0105] The reaction with polymethylene polyphenylene polyisocyanate follows. The methylene diphenyl diisocyanate and / or the mixture of methylene diphenyl diisocyanate and polymethylene polyphenylene polyisocyanate obtained in this way can be reacted with a polyol to form a polyurethane. All these processes are well known and therefore do not require further description here.

[0106] The polyols required for polyurethane production can originate from any process for the production of new polyols. However, they can also be partially or completely recycled polyols, i.e., polyols obtained by splitting a polyurethane product. Such splitting can be the process according to the invention itself, but also recycling processes already known from the literature.

[0107] Examples:

[0108] chemicals

[0109] Analytics

[0110] HPLC

[0111] For HPLC analysis, an Agilent setup with UV detection (DAD, measured at 254 nm) was used. An Agilent EC-C18 column (PN: 699975-302) was employed for separation. The mobile phase consisted of a mixture of acetonitrile and buffer (buffer: water with 1.5 g / L ammonium acetate and 0.25 mL / L glacial acetic acid (pH = 5.4)). The gradient started at 5% acetonitrile, and the solvent composition was maintained for 0.5 min before being gradually increased to 95% acetonitrile over 16.5 min. 95% acetonitrile was then retained until the end of the run (20.5 min). The flow rate was 0.75 mL / min. The column oven was heated to 35 °C. The injection volume was 1 pL. The retention times of the individual components aniline (ANL), p-toluidine (p-TOL), 4,4'-MDA (MDA), and 1,3,5-trichlorobenzene (TCB) were: ANL = 2.70 min; p-TOL = 4.72 min; MDA = 6.40 min; TCB = 12.7 min. FT-IR

[0112] Each ID-IR (FTIR) spectrum was an average of 24 scans and was acquired in the wavelength range of 400 to 4000 cm⁻¹. -1 with a spectral resolution of 4 cm -1 Measured using a Bruker Alpha FTIR.

[0113] 1 H-NIVIR spectroscopy

[0114] The measurements were performed on a Bruker Avance III 400 (400 MHz); the calibration of the chemical shifts was performed relative to the residual proton signal (Δ1H (ppm) DMSO- c / 6: 2.50; Aniline: 7.01 (2H, t), 6.56 (2H, d), 6.49 (1H, t), 4.99 (2H, s); para-Toluidine: 6.82 (2H, d), 6.49 (2H, d), 4.77 (2H, s), 2.13 (3H, s)).

[0115] Experimental procedure:

[0116] Recovery of aniline from 4,4'-MDA under reactive distillation conditions - general operating procedure (GAP 1)

[0117] A 50 mL round-bottom flask is filled with MDA (4.00 g) and catalyst (type and quantity see Table 1). This flask is then connected in series to two other round-bottom flasks, which are mounted as an open system towards the cooled end. The round-bottom flask loaded with the reaction mixture is heated, and the last of the two series-connected flasks is cooled to 0 °C in an ice bath. The glass furnace (Büchi B-585) is then heated to 250 °C at 50 rpm for 1 h. After the reaction, the glass furnace is cooled, and the three glass flasks are separated. The amount of distillate ("total": sum of the two distillation vessels; "0 °C": only the mass in the last distillation vessel at 0 °C) is determined gravimetrically. The distillates are then separated using... 1 The residue in the reaction vessel turns dark violet-brown. It was analyzed by H-NMR (in DMSO-d6) and HPLC.

[0118] Recovery of aniline from pMDA under reactive distillation conditions - general operating procedure (GAP 2)

[0119] A 50 mL round-bottom flask is filled with pMDA (2.00 g) and catalyst (type and quantity see Table 2). This flask is then connected in series to two other round-bottom flasks, which are mounted as an open system towards the cooled end. The round-bottom flask loaded with the reaction mixture is heated, and the last of the two series-connected flasks is cooled to 0 °C in an ice bath. The glass furnace (Büchi B-585) is then heated to 250 °C at 50 rpm for 1 h. After the reaction, the glass furnace is cooled, and the three glass flasks are separated. The amount of distillate ("total": sum of the two distillation vessels; "0 °C": only the mass in the last distillation vessel at 0 °C) is determined gravimetrically. The distillates are then separated using... 1The residue in the reaction vessel turns dark violet-brown. It was analyzed by H-NMR (in DMSO-d6) and HPLC.

[0120] Recovery of aniline from a pMDA / polyol mixture under reactive distillation conditions (AAV 3)

[0121] A 50 mL round-bottom flask is filled with pMDA and polyols (total 2.00 g) and catalyst (type and quantity see Table 3). This round-bottom flask is then connected in series to two other round-bottom flasks, which are mounted as an open system towards the cooled end. The round-bottom flask loaded with the reaction mixture is heated, and the last of the two series-connected round-bottom flasks is cooled to 0 °C in an ice bath. The glass furnace (Büchi B-585) is then heated to 250 °C at 50 rpm for 1 h. After the reaction, the glass furnace is cooled, and the three glass flasks are separated. The amount of distillate ("total": sum of the two distillation vessels; "0 °C": only the mass in the last distillation vessel at 0 °C) is determined gravimetrically. The distillates are then separated using... 1 The residue in the reaction vessel turns dark violet-brown. It was analyzed by 1H NMR (in DMSO-d6) and HPLC.

[0122] Recovery of aniline from pMDI-based polyurethane foam under reactive distillation conditions (AAV 4)

[0123] A 50 mL round-bottom flask is filled with polyurethane foam pellets (2.00 g, containing 82 wt% polyurethane foam and 18 wt% residual moisture) and catalyst (type and quantity see Table 3). This round-bottom flask is then connected in series to two other round-bottom flasks, which are mounted as an open system towards the cooled end. The round-bottom flask loaded with the reaction mixture is heated, and the last of the two series-connected round-bottom flasks is cooled to 0 °C in an ice bath. The glass furnace (Büchi B-585) is then heated to 250 °C at 50 rpm for 1 h. After the reaction, the glass furnace is cooled, and the three glass flasks are separated. The amount of distillate ("total": sum of the two distillation vessels; "0 °C": only the mass in the last distillation vessel at 0 °C) is determined gravimetrically. The distillates are separated using 1Analyzed by 1H NMR (in DMSO-d6) and HPLC. The residue in the reaction vessel turns dark violet-brown. Recovery of aniline from pMDI-based polyurethane foam (end-of-life material) under reactive distillation conditions (AAV 5).

[0124] A 50 mL round-bottom flask is filled with polyurethane foam pellets (2.00 g, containing 86 wt% polyurethane foam, 10 wt% inorganic and polymeric impurities (e.g., metals and polystyrene), and 4 wt% residual moisture) and catalyst (type and quantity see Table 3). The round-bottom flask is then connected in series to two other round-bottom flasks, which are mounted as an open system towards the cooled end. The round-bottom flask loaded with the reaction mixture is heated, and the last of the two series-connected flasks is cooled to 0 °C in an ice bath. The glass furnace (Büchi B-585) is then heated to 250 °C at 50 rpm for 1 h. After the reaction, the glass furnace is cooled, and the three glass flasks are separated. The quantity of distillate (“total”: sum of both distillation vessels; “0°C”: only the mass in the last distillation vessel at 0°C) is determined gravimetrically. The distillates are processed using 1The residue in the reaction vessel turns dark violet-brown. It was analyzed by H-NMR (in DMSO-d6) and HPLC.

[0125] Table 1: Cleavage of 4,4'-MDA to aniline with different cleavage reagents under various conditions according to AAV l [a]

[0126] Explanations for Table 1:

[0127] [a] Substrate: 4,4'-MDA.

[0128] [b] Percentage based on the mass of the substrate.

[0129] [c] By means of 1 1H NMR determined molar ratio of aniline and toluidine found after the reaction. The toluidine consists of at least 90% of the para-isomer. Table 2: Cleavage of pMDA to aniline with different cleavage reagents under various conditions according to AAV 2. [a] Explanations for Table 2:

[0130] [a] Substrate: pMDA.

[0131] [b] Percentage based on the mass of the substrate. Any added aniline (Ex. 2-15) is excluded from the yield calculation. [c] By means of 1 The molar ratio of aniline and toluidine found after the reaction was determined by 1H NMR. Any added aniline (Ex. 2-15) has been subtracted. The toluidine consists of at least 90% of the para-isomer.

[0132]

[0133] Explanations for Table 3:

[0134] [a] Percentage based on the mass of the substrate.

[0135] [b] Mass fractions of aniline, toluidine and polyols (total corresponds to the total yield of distillates). Ratios determined via 1 ¹H NMR after the reaction. The toluidine consists of at least 90% of the para-isomer.

[0136] [c] Percentage based on the mass fraction “pMDA” in the substrate.

[0137] [d] By means of 1 The molar ratio of aniline to toluidine found after the reaction was determined by 1H NMR. The toluidine consists of at least 90% of the para-isomer.

[0138] [e] Examples carried out in accordance with AAV 3. [f] Examples carried out in accordance with AAV 4.

[0139] [g] Examples carried out in accordance with AAV 5.

[0140] (V) Comparative example

Claims

Patent claims:

1. A process comprising the recovery of aniline from a starting material selected from (i) a urethane based on an isocyanate and an alcohol, wherein the isocyanate comprises methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate, or (ii) an aromatic amine, wherein the aromatic amine comprises methylenediphenylenediamine or a mixture of methylenediphenylenediamine and polymethylenepolyphenylene polyamine, the process comprising thermal cracking of the starting material in a reactor in the presence of a catalyst at a temperature of 180 °C to 290 °C to form a gaseous process product containing aniline and removing the gaseous process product from the reactor, wherein the catalyst comprises an ammonium salt.

2. The method of claim 1, wherein the ammonium salt comprises an ammonium halide, an ammonium hexafluoro salt, ammonium thiosulfate, ammonium hydrogen carbonate, ammonium carbonate, ammonium sulfate, ammonium hydrogen sulfate, ammonium phosphate, ammonium hydrogen phosphate, ammonium dihydrogen phosphate and / or an ammonium carboxylate.

3. The method of claim 1 or 2, wherein the catalyst comprises a reducing agent in addition to the ammonium salt.

4. The method of claim 3, wherein the reducing agent is selected from a thiosulfate and / or a formate.

5. Method according to any one of claims 1 to 4, wherein aniline is added to the starting material prior to thermal cracking.

6. A process according to any one of claims 1 to 5, wherein the gaseous process product removed from the reactor is cooled to a temperature at which aniline condenses, obtaining a liquid process product containing aniline, which is subjected to a work-up for the recovery of aniline comprising distillation, or wherein the gaseous process product removed from the reactor is subjected to a work-up for the recovery of aniline comprising distillation without condensation.

7. The process according to claim 6, wherein the aniline obtained in the work-up of the gaseous or liquid process product is reacted with formaldehyde under acid catalysis to form methylenediphenylenediamine and polymethylenepolyphenylenepolyamine, wherein in particular the methylenediphenylenediamine and the polymethylenepolyphenylenepolyamine are phosgenated, followed by a work-up to obtain methylenediphenylene diisocyanate and a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylenepolyisocyanate, wherein in particular the methylenediphenylene diisocyanate and / or the mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylenepolyisocyanate is reacted with a polyol to form a polyurethane.

8. Method according to any one of claims 1 to 7, wherein the urethane is a polyurethane product and the alcohol is a polyol.

9. A method according to any one of claims 1 to 7, wherein the urethane is a cleavage product derived from the isocyanate obtained by chemical cleavage of a polyurethane product based on the isocyanate and a polyol with an organic chemolysis reagent.

10. The method of claim 9, wherein the chemical cleavage yields a chemolysis product containing the cleavage product derived from the isocyanate and the polyol, wherein the chemolysis product is subjected to thermal cleavage without separation of the cleavage product and the polyol, or wherein the chemolysis product is separated into a fraction containing the cleavage product derived from the isocyanate and into a fraction containing the polyol, and wherein the fraction containing the cleavage product derived from the isocyanate is subjected to thermal cleavage.

11. A method according to any one of claims 1 to 10, wherein the aromatic amine is obtained from a waste stream of a process for the production of methylenediphenylenediamine and / or polymethylenepolyphenylenepolyamine, or wherein the aromatic amine is obtained by chemical cleavage of methylenediphenylene diisocyanate and / or polymethylenepolyphenylene polyisocyanate, which is obtained from a waste stream of a process for the production of methylenediphenylene diisocyanate and / or polymethylenepolyphenylene polyisocyanate, with water.

12. A method according to any one of claims 1 to 10, wherein the aromatic amine is obtained by chemical cleavage of a polyurethane product based on the isocyanate and a polyol.

13. The method of claim 12, wherein the chemical cleavage yields a chemolysis product containing the aromatic amine and the polyol, wherein the chemolysis product is subjected to thermal cleavage without separation of the aromatic amine and the polyol, or wherein the chemolysis product is separated into a fraction containing the aromatic amine and a fraction containing the polyol, and wherein the fraction containing the aromatic amine is subjected to thermal cleavage.

14. The method of claim 12, wherein the chemical cleavage comprises reacting the polyurethane product with an organic chemolysis reagent, wherein a chemolysis product is obtained which is separated into a fraction containing a cleavage product derived from the isocyanate and into a fraction containing the polyol, and wherein the fraction containing the cleavage product derived from the isocyanate is reacted with water to form a fraction containing the aromatic amine.

15. A method according to claim 10, 13 or 14, wherein the fraction containing the polyol, optionally after processing to purify the polyol contained therein, is used in the production of a polyurethane by reaction with an isocyanate.

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