Method and system for obtaining aniline

Abstract

The present invention relates to the obtaining of aniline from polyurethane products or waste streams of isocyanate production. The polyurethane products are based on an isocyanate component comprising methylene diphenylene diisocyanate or a mixture of methylene diphenylene diisocyanate and polymethylene polyphenylene polyisocyanate; the waste streams originate from the production of said isocyanates. The invention comprises a method having the steps of (A) chemolysis of the polyurethane product or waste stream, (B) optional processing of the chemolysis product and (C) pyrolysis of the optionally processed chemolysis product. The invention also relates to a system for obtaining aniline, comprising (a) a chemolysis device, (b) an optional processing device and (c) a pyrolysis device.

Description

[0001] Process and plant for the production of aniline

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

[0003] The present invention relates to the recovery of aniline from polyurethane products or waste streams from isocyanate production. The polyurethane products are based on an isocyanate component comprising methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate; the waste streams originate from the production of said isocyanates. The invention comprises a process comprising the steps of (A) chemolysis of the polyurethane product or waste stream, (B) optional workup of the chemolysis product, and (C) pyrolysis of the optionally worked-up chemolysis product. The invention further comprises a plant for recovering aniline comprising (a) a chemolysis device, (b) an optional workup device, and (c) a pyrolysis device.

[0004] Polyurethanes are versatile products that find a wide range of 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 typically divided into rigid foams (which can be used, for example, as insulating materials, such as in refrigerators or house 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 have in common the basic polyurethane structure, which is formed by the polyaddition reaction of a polyvalent isocyanate (hereinafter referred to as isocyanate) and a polyol and is suitable, for example, for a polyurethane based on a diisocyanate O=C=NRN=C=O and a diol HO-R'-OH (where R and R' are organic radicals).

[0005] - [O-R'-O-(O=C)-HN-R-NH-(C=O)] - Many polyurethanes contain additional structural units in addition to the basic polyurethane structure. These include, in particular, urea, isocyanurate, allophanate, and biuret structural units.

[0006] An important isocyanate is so-called MDI. MDI is a collective term for methylenediphenylene diisocyanate (mMDI - "monomeric MDI") and polymethylenepolyphenylene polyisocyanate, which refers to the higher homologues of mMDI (also called "polymeric MDI", pMDI). Methylenediphenylene diisocyanate exists in several isomers, of which 2,4'-methylenediphenylene diisocyanate and 4,4'-methylenediphenylene diisocyanate are the most important.

[0007] Pure mMDI and mixtures of mMDI and pMDI are of technical importance. Such mixtures are widely used, for example, in the production of rigid foams. The industrial production of MDI starts from aniline, which undergoes an acid-catalyzed reaction with formaldehyde, resulting in mixtures of methylenediphenylenediamine ("monomeric MDA", mMDA) and polymethylenepolyphenylenepolyamine ("polymeric MDA", pMDA). These mixtures are usually phosgenated without prior separation, thus yielding corresponding mixtures of mMDI and pMDI. Typically, fractions of essentially pure mMDI are distilled from these mixtures, leaving mixtures of pMDI and mMDI with a higher pMDI content than the starting mixtures.

[0008] In the early days of polyurethane chemistry, efforts were made to obtain as much mMDI as possible. Initially, there were hardly any technical applications for pMDI, so that pMDI (or its precursor pMDA) was sometimes even considered a waste product that needed to be minimized. This was achieved, for example, by attempting to maximize the mMDA yield at the MDA stage and distilling it from the unwanted pMDA as far as possible. With the aim of making such unwanted pMDA technically usable, Frank J. Weigert described the hydrogenolysis of mMDA, but not pMDA, to aniline and toluidine in the article "Acid-Catalyzed Pyrolysis of Aniline-Formaldehyde Oligomers" published in Ind. Eng. Chem. Prod. Res. Dev. 1979, 18 (3), 232-234. It is suggested that the obtained results could be important for the Lewis acid-catalyzed depolymerization of coal (see abstract).

[0009] This situation from previous decades no longer exists today. Blends 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 various types of polyurethanes, either as a largely pure monomer (mMDI) or—even more significantly in terms of quantity—as a mixture of mMDI and its higher homologues (pMDI). Precisely because of the great commercial success of MDI-based polyurethanes, large quantities of polyurethane waste (e.g., from the insulation materials of no longer used refrigerators) are also generated, which must be put to sensible use.

[0010] The technically simplest way to recycle carbon-containing waste, such as polyurethane waste, is to incinerate it, using the released combustion heat for other processes, such as industrial manufacturing. While this generates valuable energy and thus reduces the need to burn fossil fuels (which is welcome in itself, as it conserves valuable oil, coal, and gas reserves), it does not allow for a closed raw material cycle. This is only possible through material recycling.

[0011] Another method of recycling polyurethane waste, so-called "physical recycling," in which polyurethane waste is mechanically shredded and used in the manufacture of new products, essentially allows for material recycling. However, this type of recycling has limitations, e.g., due to quality losses of the recovered product compared to the original polyurethane. Therefore, there has been no shortage of attempts to recover the raw materials underlying polyurethane production by splitting back the urethane bonds (and any additional bonding structures such as isocyanurate, urea, allophanate, or biuret bonds). Such splitting can be carried out thermally (more precisely: thermo-chemically, i.e., by pyrolysis, "thermo-chemical recycling") or chemically (chemolysis, "chemical recycling").In chemical recycling, functional groups, in this case particularly 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), whereby long polymer chains are cleaved into shorter polymer chains or oligomers and / or monomers. Cleavage of CC bonds generally does not occur. In contrast, thermo-chemical (pyrolytic) cleavage occurs by heating the starting material in the presence of a catalyst (referred to below as a pyrolysis catalyst to avoid confusion), which also results in the cleavage of CC bonds.

[0012] Thermochemical recycling is described, for example, in WO 2022 / 253873 A1. Upon decomposition of an MDI-based rigid foam, it yields a pyrolysis product comprising, among other substances, aniline, toluidine, and mMDA. Polyols (in the above example, HOR'OH) cannot be recovered undecomposed using this process.

[0013] WO 2024 / 046793 A1 describes a process for the thermal treatment of a multicomponent plastic waste material comprising a first polymer material and a second polymer material. The process comprises a first thermal treatment of the first polymer material in a first reactor at a first temperature and a second thermal treatment in a second reactor at a second temperature higher than the first temperature. In the article "Effects of hard- and soft-segment composition on pyrolysis characteristics of MDI, BD, and PTMG-based polyurethane elastomers," published in Journal of Analytical and Applied Pyrolysis, 2017, 126, 337-345, A. Watanabed et al. describe the pyrolysis of flexible and rigid foam at 800°C to form isocyanates, diamines, and many other fragments from the polyurethane polyol. The processing of such a complex product mixture is difficult. A mass balance has not been determined.

[0014] In the 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, 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 resulting GC / MS chromatograms show that the thermochemolysis products are specific for the diol and dicarboxylic acid units of the polymer.

[0015] Polyols can also be recovered through chemical recycling, in which urethane bonds are cleaved through transurethanization and / or hydrolysis reactions. Relatively chemically inert polyols, such as polyether polyols, can be recovered as such. For more chemically reactive polyols, such as polyester polyols, the underlying monomeric building blocks can be recovered. In addition, amines can be obtained by hydrolytic cleavage of the urethane bond (in the above example, H2N-R-NH2), which can be phosgenated after further processing to form isocyanates (in the above example, O=C=NRN=C=O).

[0016] Various approaches to chemical recycling have been developed in the past. The most important ones are briefly summarized below:

[0017] 1. Hydrolysis of polyurethanes by reaction with water to produce amines and polyols with formation of carbon dioxide.

[0018] 2. Glycolysis of polyurethanes by reaction with alcohols, whereby 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 usually referred to in the literature as glycolysis, regardless of the exact type of alcohol used, although this term actually only applies to glycol or glycol derivatives. (In the context of the present invention, therefore, the term alcoholysis is generally used.) Glycolysis can be followed by hydrolysis. If the hydrolysis is carried out with the direct product of the glycolysis process (i.e., without prior separation of polyols and carbamates), it is referred to as

[0019] 3. by hydroglycolysis (more precisely: hydroalcoholysis) of urethane bonds by reaction with alcohols and water. It is, of course, also possible to add alcohol and water from the beginning, whereby the processes of glycolysis and hydrolysis described above occur in parallel.

[0020] 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 be cleaved, and the R-NH groups can be replaced by the amine used in the aminolysis, releasing the amine R-NH2 corresponding to the isocyanate originally used. If amino acids with primary or secondary amino groups are used, the alcohol groups of the amino alcohol used can naturally also react with urethane bonds, resulting in the formation of carbamates. According to the teachings of most of the prior art, aminolysis can be followed by hydrolysis in a separate step.

[0021] 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 A1 and is referred to there as aminohydrolysis.

[0022] A summary of the chemical polyurethane recycling processes known up to the beginning of 2018 is provided in 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 [1],

[0023] 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 processing concepts has been and remains the subject of numerous studies; see, for example, WO 2020 / 260387 A1 and WO 2022 / 063764 A1 on the processing of alcoholysis products. The focus of these applications is on tolylene 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. In contrast to tolylene diisocyanate (TDI), which is widely used in so-called flexible foams, MDI (e.g., originating from waste streams in MDI production) or an MDI-based polyurethane product (e.g., originating from old, used, so-called"Endo Z / e^ products or from offcuts arising in the production of, for example, polyurethane foams) upon hydrolysis forms an amine (MDA) that is only very poorly soluble in water. This makes its isolation by extractive processes, in particular the separation of polyols (which is important in the case of the recycling of polyurethane products), complex. Switching to distillative separation processes is not possible in the case of the presence 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.

[0024] There was therefore a need for further improvements in the recycling of MDI-containing waste streams, and especially of MDI-based polyurethane products. In particular, it would be desirable to recover aromatic amines from which MDI can be produced, and in the case of MDI-based polyurethane products, with the option of also recovering the polyols underlying the polyurethane product (or, in the case of polyols with reactive groups in the polymer chain, their monomeric building blocks).

[0025] Taking this need into account, a first subject matter of the present invention is a process comprising the recovery of aniline (and optionally further valuable products) from a starting material selected from (i) a polyurethane product based on an isocyanate component and a polyol component (hereinafter also: MDI-based polyurethane product) or (ii) an isocyanate-containing waste stream arising in the production of an isocyanate component, wherein the isocyanate component comprises methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate, the process comprising the steps:

[0026] (A) chemical cleavage (chemolysis) of the starting material to obtain a first chemolysis product containing (i) methylenediphenylenediamine or (ii) a mixture of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine;

[0027] (B) optionally, processing the first chemolysis product comprising a (partial to complete) separation of components other than methylenediphenylenediamine and polymethylenepolyphenylenepolyamine to obtain a second chemolysis product; and

[0028] (C) pyrolytic (= thermo-chemical) cleavage (pyrolysis) of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine contained in the first or (when carrying out step (B)) in the second chemolysis product at a pyrolysis temperature of 200 °C to 700 °C, preferably 225 °C to 600 °C, particularly preferably 400 °C to 550 °C, in the presence of a pyrolysis catalyst to obtain a pyrolysis product containing aniline (and optionally benzene, toluene and / or toluidine).

[0029] A further subject of the present invention relates to a plant for obtaining aniline (and optionally further valuable products) from a starting material selected from (i) a polyurethane product based on an isocyanate component and a polyol component or (ii) an isocyanate-containing waste stream arising in the production of an isocyanate component, wherein the isocyanate component comprises methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate, the plant comprising the devices:

[0030] (a) a chemolysis apparatus comprising (at least) one chemolysis reactor for chemically splitting (chemolysis) the starting material to obtain a first chemolysis product containing (i) methylenediphenylenediamine or (ii) a mixture of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine;

[0031] (b) optionally, a processing device downstream of the chemolysis device for processing the first chemolysis product with (partial to complete) separation of components other than methylenediphenylenediamine and polymethylenepolyphenylenepolyamine to obtain a second chemolysis product;

[0032] (c) a pyrolysis device downstream of the chemolysis device or, if the reprocessing device is present, the reprocessing device comprising

[0033] (cl) facilities for introducing the first or second chemolysis product into (at least) one pyrolysis reactor, wherein (c.ll) the (at least one) pyrolysis reactor is designed for the pyrolytic (= thermo-chemical) cleavage (pyrolysis) of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine contained in the first or second chemolysis product to obtain gaseous (in the gas phase) pyrolysis product and non-gaseous (not in the gas phase, i.e. solid or (viscous) liquid) pyrolysis residue,

[0034] (c.lll) (at least) one cooling device for cooling the pyrolysis product to obtain (i) a pyrolysis condensate containing aniline (and optionally benzene, toluene and / or toluidine) and (ii) optionally a gas phase of uncondensed components of the pyrolysis product, and

[0035] (c.IV) (at least) one collector for receiving the pyrolysis condensate (wherein the (at least one) cooling device and the (at least one) collector may be arranged in a common device).

[0036] Completely surprisingly, it was discovered that a combination of chemolysis and pyrolysis allows the recovery of aniline—and, in the case of polyurethane products as starting materials, also of polyols or their monomeric building blocks. Unlike PMDA, aniline can be easily purified by distillation, opening up the possibility of producing new PMDA through acid-catalyzed reaction of aniline with formaldehyde without any loss of quality. Recovered polyols or their monomeric building blocks can also be purified using conventional processes and subsequently used for new purposes, particularly in the production of new polyurethanes.

[0037] Polyurethane products within the meaning of the present invention are the polyaddition products obtained by reacting polyfunctional isocyanates (= isocyanate component of polyurethane production) with polyols (= polyol component of polyurethane production). Polyurethane products generally contain other structures in addition to the basic polyurethane structure outlined above, for example, urea, isocyanurate, allophanate, and biuret structural units. The presence of such structures deviating from the pure basic polyurethane structure in addition to 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 polyfunctional isocyanates with polyols in the presence of a blowing agent, in particular rigid polyurethane foams.In the context of the present invention, a rigid polyurethane foam is understood to mean a polyurethane foam which has a compressive stress at 10% compression (GIO) of 10 kPa or more, measured in accordance with DIN EN 826:2013-05.

[0038] 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, polyetherester polyols, and polyethercarbonate polyols. The term "a polyol" naturally also encompasses embodiments in which two or more different polyols were used in the production of the polyurethane product. Therefore, if reference is made below, for example, to "a polyether polyol" (or "a polyester polyol," etc.), this terminology naturally also encompasses embodiments in which two or more different polyether polyols (or two or more different polyester polyols, etc.) were used in the production of the polyurethane product. The totality of all polyols used in the production of the polyurethane product is referred to as the polyol component (of the polyurethane product).The polyol component comprises at least one polyol. The term "polyol from the polyol component" refers either to a polyol that was used in the production of the polyurethane product and recovered (essentially chemically unchanged) by the process according to the invention, as in the case of polyether polyols, or, in the case of polyols with comparatively chemically reactive groups in the polymer chain, such as polyester polyols, to the alcohol monomer underlying the polyol, e.g., 1,6-hexanediol. As explained in more detail below, however, the polyols of the polyol component are preferably polyether polyols, which can be recovered as such in the chemolysis and separated prior to pyrolysis.

[0039] In the terminology of the present invention, the term "isocyanates" encompasses all isocyanates known to the person skilled in the art in connection with polyurethane chemistry and means, in particular, methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate (mMDI) and polymethylenepolyphenylene polyisocyanate (pMDI). The term "one / n isocyanate" naturally also encompasses embodiments in which two or more different isocyanates (e.g., mixtures of MDI and TDI) were used in the preparation of the polyurethane product, unless expressly stated otherwise, for example, by the phrase "exactly one isocyanate." The totality of all isocyanates used in the preparation of the polyurethane product is referred to as the isocyanate component (of the polyurethane product). The isocyanate component contains at least one isocyanate.If it contains exactly one (1) isocyanate, this is selected according to the invention from mMDI or, preferably, a mixture of mMDI and pMDI. In the terminology of the present invention, carbamates refer to the urethanes optionally formed by the reaction with an alcohol in step (A).

[0040] An amine corresponding to an isocyanate refers to the amine by whose phosgenation the isocyanate can be obtained according to R-NH2 + COCl2 —> RN=C=O + 2 HCl.

[0041] In the context of the present invention, an organic chemolysis reagent means an organic compound which has functional groups which can react with urethane bonds to cleave them, in particular alcohol and amine groups.

[0042] Pyrolytic cleavage in the sense of the present invention is understood to mean thermochemical cleavage at elevated temperature (200 °C to 700 °C, preferably 225 °C to 600 °C, particularly preferably 400 °C to 550 °C), in particular with substantial to complete exclusion of oxygen.

[0043] When, within the scope of the present invention, reference is made to a device / apparatus (e.g., in expressions such as "a pyrolysis reactor", "a collector", "a cooling device", etc.), this also includes embodiments in which several devices / apparatuses of the type mentioned are connected in series or in parallel (the expressions mentioned by way of example are therefore to be read as "at least one pyrolysis reactor", "at least one collector", "at least one cooling device", etc.), unless expressly stated otherwise (e.g., by the formulation "exactly one").

[0044] First, a brief summary of various possible embodiments of the invention follows:

[0045] In a first embodiment of the process according to the invention, which can be combined with all other embodiments, the chemical cleavage in step (A) comprises a reaction of the starting material with

[0046] (AI) an organic chemolysis reagent and water or

[0047] (AH) Water without the use of an organic chemolysis reagent.

[0048] In a second embodiment of the process according to the invention, which is a particular embodiment of the first embodiment, the organic chemolysis reagent in (AI) is selected from (i) an alcohol, (ii) a primary or secondary amine,

[0049] (iii) an amino alcohol containing a primary or secondary amino group or

[0050] (iv) a mixture of two or more of the aforementioned chemolysis reagents. In a third embodiment of the process according to the invention, which is a particular embodiment of the first and second embodiments, the starting material is an isocyanate-containing waste stream arising in the production of an isocyanate component.

[0051] In a fourth embodiment of the process according to the invention, which is a particular embodiment of the third embodiment, step (A) comprises the reaction of the isocyanate-containing waste stream with (A.ll) water without the use of an organic chemolysis reagent.

[0052] In a fifth embodiment of the process according to the invention, which is a particular embodiment of the fourth embodiment, a chemolysis catalyst is used in step (A).

[0053] In a sixth embodiment of the process according to the invention, which is a particular embodiment of the fifth embodiment, the chemolysis catalyst is selected from a (particularly alkali metal or alkaline earth metal) hydroxide, a (particularly alkali metal or alkaline earth metal) carboxylate (particularly acetate), a tin compound (particularly dibutyltin dilaurate or tin(II) octoate [= tin(II) 2-ethylhexanoate]), a zinc compound (particularly zinc acetate), a (particularly alkali metal or alkaline earth metal) carbonate, a (particularly alkali metal or alkaline earth metal) hydrogencarbonate, a (particularly alkali metal or alkaline earth metal) orthophosphate, a (particularly alkali metal or alkaline earth metal) IV ionohydrogen orthophosphate, a (particularly alkali metal or alkaline earth metal) orthovanadate, a titanium alcoholate, a tertiary amine, cesium fluoride or a mixture of two or more of the aforementioned chemolysis catalysts.

[0054] In a seventh embodiment of the process according to the invention, which is a particular embodiment of the fifth and sixth embodiments, the chemolysis catalyst is used in an amount such that a mass ratio (i.e. the ratio m(chemolysis catalyst) / m(isocyanate-containing waste stream), with m = mass) of chemolysis catalyst and isocyanate-containing waste stream is in the range from 0.001 to 0.05, preferably 0.001 to 0.02.

[0055] In an eighth embodiment of the process according to the invention, which is a particular embodiment of the fourth to seventh embodiments, step (A) is carried out at a temperature in the range of 90 °C to 230 °C.

[0056] In a ninth embodiment of the process according to the invention, which is a particular embodiment of the fourth to eighth embodiments, step (B) is carried out and comprises a separation of water and / or any chemolysis catalyst used. In a tenth embodiment of the process according to the invention, which is a particular embodiment of the fourth to ninth embodiments, water and the isocyanate-containing waste stream are used in a mass ratio (i.e., in the ratio m(water) / m(isocyanate-containing waste stream), where m = mass) of 0.5 to 10.

[0057] In an eleventh embodiment of the process according to the invention, which is a particular embodiment of the first and second embodiments, the starting material is a polyurethane product based on an isocyanate component and a polyol component.

[0058] In a twelfth embodiment of the process according to the invention, which is a particular embodiment of the eleventh embodiment, step (A) comprises reacting the polyurethane product with (Al) an organic chemolysis reagent and water.

[0059] In a thirteenth embodiment of the process according to the invention, which is a particular embodiment of the twelfth embodiment, the mass ratio of (1) organic chemolysis reagent and water on the one hand and (2) the polyurethane product on the other hand (i.e.

[0060] [m(organic chemolysis reagent) + m(water)] / m(polyurethane product), with m = mass) in the range of 0.5 to 2.5, with the mass of water being 3.0% to 22% of the mass of the organic chemolysis reagent.

[0061] In a fourteenth embodiment of the process according to the invention, which is a further particular embodiment of the eleventh embodiment, step (A) comprises the reaction of the polyurethane product with (A.ll) water without the use of an organic chemolysis reagent.

[0062] In a fifteenth embodiment of the process according to the invention, which is a particular embodiment of the fourteenth embodiment, water and polyurethane product are used in a mass ratio (i.e. in the ratio m(water) / m(polyurethane product), with m = mass) of 0.5 to 10.

[0063] In a sixteenth embodiment of the method according to the invention, which is a particular embodiment of the twelfth and thirteenth embodiments, step (A) is carried out in such a way that

[0064] (A.1.1) the organic chemolysis reagent and water are added to the polyurethane product and the chemical cleavage is carried out to obtain the first chemolysis product (hydroalcoholysis and / or aminohydrolysis), wherein the first chemolysis product comprises, in addition to (i) methylenediphenylenediamine or (ii) the mixture of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine, additionally (iii) (at least) one polyol from the polyol component, or

[0065] (A.1.2) in a first step of chemical cleavage, the organic chemolysis reagent is added to the polyurethane product and reacted with it (alcoholysis and / or aminolysis), followed by separation into a carbamate or urea phase and a polyol phase containing (at least) one polyol from the polyol component, and wherein in a second step of chemical cleavage, the carbamate or urea phase is reacted with water to obtain the first chemolysis product (hydrolysis).

[0066] In a seventeenth embodiment of the process according to the invention, which is a particular embodiment of the sixteenth embodiment, when carrying out step (A.1.2), step (B) is included and comprises a separation of excess water.

[0067] In an eighteenth embodiment of the process according to the invention, which is a particular embodiment of the sixteenth and seventeenth embodiments, when carrying out step (A.1.1), step (B) is included and comprises a separation of a polyol phase containing (at least) one polyol from the polyol component.

[0068] In a nineteenth embodiment of the process according to the invention, which is a particular embodiment of the fourteenth and fifteenth embodiments, step (B) is included and comprises a separation of a polyol phase containing (at least) one polyol from the polyol component.

[0069] In a twentieth embodiment of the process according to the invention, which is a particular embodiment of the eighteenth and nineteenth embodiments, the (at least one) polyol from the polyol component (which originates from step (B) when carrying out (A.1.1) or (A.11) and from the first step of (A.1.2) when carrying out (A.1.2)), optionally after purification, is reacted with an isocyanate to form a polyurethane.

[0070] In a twenty-first embodiment of the process according to the invention, which is a particular embodiment of the eleventh to twentieth embodiments, a chemolysis catalyst is used in step (A) (ie in (A.1.1) or in the first step of (A.1.2) or in the second step of (A.1.2) or in the first and second steps of (A.1.2) or in (A.11)).

[0071] In a twenty-second embodiment of the process according to the invention, which is a particular embodiment of the twenty-first embodiment, the chemolysis catalyst is selected from a (particularly alkali metal or alkaline earth metal) hydroxide, a (particularly alkali metal or alkaline earth metal) carboxylate (particularly acetate), a tin compound (particularly dibutyltin dilaurate or tin(II) octoate [= tin(II) 2-ethylhexanoate]), a zinc compound (particularly zinc acetate), a (particularly alkali metal or alkaline earth metal) carbonate, a (particularly alkali metal or alkaline earth metal) hydrogencarbonate, a (particularly alkali metal or alkaline earth metal) orthophosphate, a (particularly alkali metal or alkaline earth metal) monohydrogen orthophosphate, a (particularly alkali metal or alkaline earth metal) orthovanadate, a titanium alcoholate, a tertiary amine,Caesium fluoride or a mixture of two or more of the aforementioned chemolysis catalysts.

[0072] In a twenty-third embodiment of the process according to the invention, which is a particular embodiment of the twenty-first and twenty-second embodiments, the chemolysis catalyst is used in an amount such that a mass ratio of chemolysis catalyst and polyurethane product or of chemolysis catalyst and carbamate or urea phase (i.e. the ratio m(chemolysis catalyst) / m(polyurethane product or carbamate or urea phase) of 0.001 to 0.05, preferably 0.001 to 0.02, is present.

[0073] In a twenty-fourth embodiment of the process according to the invention, which is a particular embodiment of the eleventh to twenty-third embodiments, step (A) is carried out at a temperature in the range from 90°C to 250°C, preferably from 95°C to 220°C, particularly preferably from 100°C to 195°C, most particularly preferably from 115°C to 160°C. (If step (A) is carried out in several steps, the temperature in each of these steps is within the stated range.)

[0074] In a twenty-fifth embodiment of the process according to the invention, which can be combined with all other embodiments, the pyrolysis catalyst is selected from inorganic salts, minerals, metal oxides, mixed oxides, clays, zeolites, or a mixture of two or more of the aforementioned compounds. (The pyrolysis catalyst is preferably a metal oxide, particularly preferably a mixed oxide of Al2O3 and MgO.)

[0075] In a twenty-sixth embodiment of the process according to the invention, which can be combined with all other embodiments, step (C) comprises:

[0076] (Cl) introducing the first chemolysis product or (when carrying out step (B)) the second chemolysis product and the pyrolysis catalyst into (at least) one pyrolysis reactor,

[0077] (C.ll) decomposition of the first chemolysis product or the second chemolysis product in the (at least one) pyrolysis reactor to obtain gaseous (in the gas phase) pyrolysis product and non-gaseous (not in the gas phase, ie solid or (viscous) liquid) pyrolysis residue, and

[0078] (C.lll) Cooling the pyrolysis product to obtain (i) a pyrolysis condensate containing aniline (and optionally benzene, toluene and / or toluidine) and (ii) optionally a gas phase of uncondensed components of the pyrolysis product.

[0079] In a twenty-seventh embodiment of the process according to the invention, which is a particular embodiment of the twenty-sixth embodiment, in step (C. II) the pyrolysis product formed is continuously discharged from the (at least one) pyrolysis reactor.

[0080] In a twenty-eighth embodiment of the process according to the invention, which is a particular embodiment of the twenty-seventh embodiment, the removal of the pyrolysis product from the reactor is ensured by a gas stream passed through the (at least one) pyrolysis reactor and / or by suction.

[0081] In a twenty-ninth embodiment of the process according to the invention, which is a particular embodiment of the twenty-eighth embodiment, a residence time of the pyrolysis product, indicated as the period between the time of formation of the pyrolysis product and the time of its removal from the reactor, is set to 0.1 seconds to 600 seconds, preferably 0.5 seconds to 300 seconds, particularly preferably 0.5 seconds to 200 seconds.

[0082] In a thirtieth embodiment of the process according to the invention, which is a particular embodiment of the twenty-eighth and twenty-ninth embodiments, the gas stream is passed through the (at least one) pyrolysis reactor, wherein the gas stream comprises nitrogen, argon, carbon dioxide and / or nitrogen monoxide.

[0083] In a thirty-first embodiment of the process according to the invention, which is a particular embodiment of the thirtieth embodiment, the gas stream additionally comprises methane, gaseous water, hydrogen and / or the optionally present gas phase of non-condensed constituents of the pyrolysis product.

[0084] In a thirty-second embodiment of the process according to the invention, which is a particular embodiment of the twenty-sixth to thirty-first embodiments, the proportion of oxygen gas in the (at least one) pyrolysis reactor during the decomposition in step (C.II) 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 (at least one) pyrolysis reactor. In a thirty-third embodiment of the process according to the invention, which is a particular embodiment of the twenty-sixth to thirty-second embodiments, an absolute pressure of 1.0 bar to 1.2 bar exists in the gas phase of the (at least one) pyrolysis reactor during the decomposition in step (C.II).

[0085] In a thirty-fourth embodiment of the process according to the invention, which is a particular embodiment of the twenty-sixth to thirty-third embodiments, in step (C. II) the pyrolysis residue formed is continuously discharged from the (at least one) pyrolysis reactor.

[0086] In a thirty-fifth embodiment of the process according to the invention, which is a particular embodiment of the twenty-sixth to thirty-fourth embodiments, the (at least one) pyrolysis reactor is selected from a continuously operated stirred tank reactor, a tubular reactor, a fixed bed reactor, a shaft reactor, a moving bed reactor, a belt reactor, a fluidized bed reactor (with beds of inert material or catalyst or a mixture thereof), a screw reactor, a screw conveyor reactor, an entrained flow reactor, a rotary tube reactor, a paddle reactor or a combination of two or more of the aforementioned reactor types.

[0087] In a thirty-sixth embodiment of the process according to the invention, which can be combined with all other embodiments, the pyrolysis product obtained in step (C) is subjected in a step (D) to a workup comprising (at least) one distillation, whereby aniline is obtained.

[0088] In a thirty-seventh embodiment of the process according to the invention, which is a particular embodiment of the thirty-sixth embodiment, in step (C) in addition to aniline, toluidine is additionally formed, wherein step (D) comprises a separation of aniline and toluidine.

[0089] In a thirty-eighth embodiment of the process according to the invention, which is a particular embodiment of the thirty-sixth and thirty-seventh embodiments, the aniline obtained in step (D) is reacted with formaldehyde under acid catalysis to form methylenediphenylenediamine and polymethylenepolyphenylenepolyamine.

[0090] In a thirty-ninth embodiment of the process according to the invention, which is a particular embodiment of the thirty-eighth embodiment, the methylenediphenylenediamine and the polymethylenepolyphenylenepolyamine are phosgenated, followed by workup to obtain methylenediphenylene diisocyanate and a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate. In a fortieth embodiment of the process according to the invention, which is a particular embodiment of the thirty-ninth embodiment, the methylenediphenylene diisocyanate and / or the mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate is reacted with a polyol to form a polyurethane.

[0091] In a forty-first embodiment of the process according to the invention, which is a particular embodiment of the fortieth embodiment, the polyol comprises the (at least one) polyol from the polyol phase obtained in the eighteenth or nineteenth embodiment (and which, when carrying out (A.1.1), originates from step (B) and, when carrying out (A.1.2), from the first step of (A.1.2)), optionally after purification thereof.

[0092] In a first embodiment of the plant according to the invention, which can be combined with all other embodiments, the chemolysis device comprises a device for inerting the starting material.

[0093] In a second embodiment of the plant according to the invention, which can be combined with all other embodiments, the processing device comprises (at least) one extraction device and / or (at least) one distillation device.

[0094] In a third embodiment of the system according to the invention, which can be combined with all other embodiments, the system further comprises:

[0095] (d) a further processing device downstream of the pyrolysis device for obtaining aniline from the pyrolysis condensate.

[0096] The embodiments briefly described above and other possible configurations of the invention are explained in more detail below. All of the embodiments described above and the other configurations of the invention described below can be combined with each other as desired, unless the context clearly indicates otherwise to a person skilled in the art or unless expressly stated otherwise.

[0097] CHEMOLYSIS AND REUSE OF ANY POLYOLS THAT MAY OCCUR

[0098] Suitable starting materials for use in the process and plant according to the invention include both MDI-based polyurethane products and MDI-containing waste streams arising from MDI production. Examples of the latter 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 specifications. Such MDI-containing waste streams can be converted using the process and plant according to the invention to yield aniline, which can be easily separated from by-products and purified by distillation. The MDI-based polyurethane products can be used either as used (so-called end-of-life) polyurethanes or as waste (e.g., offcuts) from polyurethane production. Polyurethane foams, in particular rigid polyurethane foams, are preferred.

[0099] Suitable reaction apparatus (= chemolysis reactors) for carrying out chemolysis include stirred tanks and tubular reactors. Stirred tanks are preferably designed as heatable double-shell stirred tanks. These are equipped, in particular, with a bottom drain and a gear-controlled stirrer, an inlet nozzle for filling with solids, feed pipes for liquids connected to metering pumps, and a gassing pipe for inert gas.

[0100] Regardless of the nature of the starting material, the chemolysis step (step (A)) of the present invention can be carried out by reaction with (I) an organic chemolysis reagent and water or (II) water without the use of an organic chemolysis reagent. In the former case, the organic chemolysis reagent is preferably selected from (i) an alcohol, (ii) a primary or secondary amine, (iii) an amino alcohol containing a primary or secondary amino group, or (iv) a mixture of two or more of the aforementioned chemolysis reagents.

[0101] Particularly suitable alcohols are aliphatic secondary or tertiary (preferably secondary) monoalcohols (e.g. iso-propanol or sec-butanol), aliphatic primary monoalcohols which are bonded to two or three further C atoms at (at least) one C atom in the ß-position or γ-position (preferably β-position) to the hydroxyl group of the monoalcohol (e.g. 2-methyl-l-butanol or 3-methyl-l-butanol), aromatic monoalcohols (e.g. phenol or substituted phenols), aliphatic unbranched monoalcohols having 1 to 4 carbon atoms, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, methyl glycol, triethylene glycol, glycerol, 2-methyl-l,3-propanediol or mixtures of two or more of the aforementioned Alcohols.

[0102] Mono- and / or diamines are particularly suitable as primary or secondary amines. 1,2-ethylenediamine, 1,4-diaminobutane, 1,6-hexamethylenediamine, or a mixture of two or more of the aforementioned amines are preferred. Suitable amino alcohols with primary or secondary amino groups are particularly ethanolamine (2-aminoethanol), N-methylethanolamine, 3-amino-l-propanol, or a mixture of two or more of the aforementioned amino alcohols.

[0103] If the starting material is an isocyanate-containing waste stream arising from the production of an isocyanate component, it is preferable to carry out the chemolysis step as pure hydrolysis, i.e., as a reaction of the isocyanate-containing waste stream with water without the use of an organic chemolysis reagent. Preferably, water and the isocyanate-containing waste stream are used in a mass ratio (i.e., in the ratio m(water) / m(isocyanate-containing waste stream), where m = mass; the masses of water and isocyanate-containing waste stream are to be used in the same unit, e.g., both in kg, so that the mass ratio is dimensionless) of 0.5 to 10.

[0104] If necessary, the chemolysis can be supported by the use of a chemolysis catalyst. Suitable chemolysis catalysts include, for example, (particularly alkali metal or alkaline earth metal) hydroxides, (particularly alkali metal or alkaline earth metal) carboxylates (particularly acetates), tin compounds (particularly dibutyltin dilaurate or tin(II) octoate [= tin(II) 2-ethylhexanoate]), zinc compounds (particularly zinc acetate), (particularly alkali metal or alkaline earth metal) carbonates, (particularly alkali metal or alkaline earth metal) hydrogencarbonates, (particularly alkali metal or alkaline earth metal) orthophosphates, (particularly alkali metal or alkaline earth metal) monohydrogen orthophosphates, (particularly alkali metal or alkaline earth metal) orthovanadates, titanium alkoxides, tertiary amines, cesium fluoride, or mixtures of two or more of the aforementioned chemolysis catalysts.In any case, it is preferred to use the chemolysis catalyst in an amount such that a mass ratio of chemolysis catalyst and isocyanate-containing waste stream (i.e. the ratio m(chemolysis catalyst) / m(isocyanate-containing waste stream), with m = mass; wherein the masses of chemolysis catalyst and isocyanate-containing waste stream are to be used in the same unit, i.e., both in kg, so that the mass ratio is dimensionless) is in the range from 0.001 to 0.05, preferably 0.001 to 0.02.

[0105] The hydrolysis of the isocyanate-containing waste stream is preferably carried out at temperatures of 90 °C to 230 °C.

[0106] Preferably, step (B) is included, which involves the removal of water and / or any chemolysis catalyst used. Known methods such as distillation and filtration are suitable for the separation.

[0107] If the starting material is an MDI-based polyurethane product, it may be advantageous to use an organic chemolysis reagent in addition to water ((AI)). It is preferred that the mass ratio of (1) organic chemolysis reagent and water on the one hand and (2) the polyurethane product on the other hand (i.e. [m(organic chemolysis reagent) + m(water)] / m(polyurethane product), with m = mass; all masses are to be used in the same unit, e.g., all in kg, so that the mass ratio is dimensionless) is in the range of 0.5 to 2.5, with the mass of water being 3.0% to 22% of the mass of the organic chemolysis reagent.

[0108] In a first variant, the reaction of the MDI-based polyurethane product with water and an organic chemolysis reagent can be carried out by adding the organic chemolysis reagent and water simultaneously or preferably sequentially to the polyurethane product, whereby the first chemolysis product is obtained after the reaction has ended (hydroalcoholysis and / or aminohydrolysis) - ((A.1.1)). In this case, the first chemolysis product contains, in addition to (i) methylenediphenylenediamine or (ii) the mixture of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine, additionally (iii) (at least) one polyol from the polyol component. Preferably, this embodiment includes step (B) and involves separating a polyol phase containing the (at least) one polyol from the polyol component. Phase separation processes known per se are suitable for this purpose, optionally in conjunction with extraction processes and / or distillation steps.

[0109] However, it is also possible - (A.1.2) - to add (only) the organic chemolysis reagent to the polyurethane product in a first chemical cleavage step and react it with it (alcoholysis and / or aminolysis), followed by separation into a carbamate or urea phase and a polyol phase containing (at least) one polyol from the polyol component. In a second chemical cleavage step, the carbamate or urea phase is then reacted with water to obtain the first chemolysis product (hydrolysis of the carbamates formed in the first step). This embodiment also preferably includes step (B) and involves removal of excess water, preferably by distillative concentration of the hydrolysis product.

[0110] Carrying out the chemolysis as aminohydrolysis is particularly preferred and can advantageously be carried out as described in WO 2023 / 083968 A1, in particular on page 16, line 33 to page 19, line 2. Step (B) of the present invention, which is fundamentally optional but strongly preferred in this embodiment, can also preferably be carried out as described in WO 2023 / 083968 A1, in particular on page 19, line 4 to page 20, line 2 and page 20, line 23 to page 22, line 30. However, even if the starting material is an MDI-based polyurethane product, the chemolysis can be carried out as pure hydrolysis (i.e., without the use of an organic chemolysis reagent) ((A.11)). Here, water and polyurethane product are preferably mixed in a mass ratio (i.e. in the ratio m(water) / m(polyurethane product), with m = mass; whereby the masses of water and polyurethane product are in the same unit, e.g.Both are to be used in kg, so that the mass ratio is dimensionless) of 0.5 to 10. Again, step (B) is preferably included, which involves separating a polyol phase containing (at least) one polyol from the polyol component. Known phase separation processes are suitable for this purpose, optionally in conjunction with extraction processes and / or distillation steps.

[0111] Regardless of the exact manner in which the chemolysis is carried out, it may be advantageous to use a chemolysis catalyst in step (A). Depending on which of the previously described embodiments is used, this relates to (A.1.1) or the first step of (A.1.2) or the second step of (A.1.2) or the first and second steps of (A.1.2) or (A.11). Suitable chemolysis catalysts are the same as those described above for the conversion of isocyanate-containing waste streams. It is preferred to use the chemolysis catalyst in an amount such that a mass ratio of chemolysis catalyst and polyurethane product or of chemolysis catalyst and carbamate or urea phase (i.e. the ratio m(chemolysis catalyst) / m(polyurethane product or carbamate or urea phase), with m = mass; all masses being in the same unit, i.e., for example,all in kg, so that the mass ratio is dimensionless) is in the range of 0.001 to 0.05, preferably 0.001 to 0.02.

[0112] Regardless of the precise configuration of the chemolysis step, it is preferred to maintain a temperature in the range of 90°C to 250°C, particularly preferably from 95°C to 220°C, very particularly preferably from 100°C to 195°C, and extraordinarily very particularly preferably from 115°C to 160°C during the chemical cleavage in step (A). If step (A) is carried out in several steps, the temperature in each of these steps is preferably within the stated range.

[0113] The MDI-based polyurethane product used is preferably one whose polyol component comprises only those polyols which can undergo the chemical cleavage according to step (A) without significant chemical decomposition. Such polyols are, in particular, polyether polyols. Such polyols can be recovered (as such) as described above in step (A) or in step (B). They arise when carrying out (A.1.1) or (A.11) in step (B) and when carrying out (A.1.2) in the first step of (A.1.2). It is preferred to react the polyols thus obtained, optionally after purification (e.g. by distillation and / or stripping), with an isocyanate to form a new polyurethane. If the polyol component comprises partly or exclusively polyols with reactive groups in the polymer chain (e.g.Polyester polyols), these are split in step (A) into monomeric or oligomeric fragments, which also represent valuable raw materials and, after isolation using known processes, can be used in the new production of polyols (which in turn can then be converted back into polyurethanes).

[0114] PYROLYSIS AND REUSE OF PRODUCED AMINES

[0115] In step (C), the first or second chemolysis product (from step (A) or (B)) is pyrolytically (thermochemically) cleaved. The pyrolysis catalyst used for this purpose is preferably selected from inorganic salts, minerals, metal oxides, mixed oxides, clays, zeolites, or a mixture of two or more of the aforementioned compounds.

[0116] Refractory oxides, for example, are suitable. Refractory oxides are metal oxides that are stable at temperatures from 300 °C to 700 °C. Such oxides that act as pyrolysis catalysts include the oxides of aluminum, magnesium, zirconium, titanium, chromium, zinc, tin, and other metals, or combinations of aluminum oxide with magnesium oxide and / or calcium oxide.

[0117] Other suitable inorganic materials include aluminosilicates, silicon-aluminum phosphates, silicalite, spinels and other natural zeolites and clays.

[0118] The catalyst particularly preferably contains at least one aluminum oxide in the form of an oxide or mixed oxide and is present in a spinel structure, hydrocalcite structure, or Y-Al2O3 structure. The pyrolysis catalyst used is preferably a mixed oxide of Al2O3 and MgO. This, in turn, is very particularly preferably present in a spinel structure or hydrocalcite structure.

[0119] Step (C) preferably comprises the following sub-steps:

[0120] (Cl) introducing the first chemolysis product or (when carrying out step (B)) the second chemolysis product and the pyrolysis catalyst into (at least) one pyrolysis reactor,

[0121] (C.ll) decomposition of the first chemolysis product or the second chemolysis product in the (at least one) pyrolysis reactor to obtain gaseous (in the gas phase) pyrolysis product and non-gaseous (not in the gas phase, i.e. solid or (viscous) liquid) pyrolysis residue, and (C.lll) cooling the pyrolysis product to obtain (i) a pyrolysis condensate comprising aniline (and optionally benzene, toluene and / or toluidine) and (ii) optionally a gas phase of non-condensed constituents of the pyrolysis product.

[0122] Suitable pyrolysis reactors include, for example, continuously operated stirred tank reactors (CSTRs), tubular reactors, fixed-bed reactors, shaft reactors, moving-bed reactors, belt reactors, fluidized-bed reactors with beds of inert material or catalyst or a mixture thereof, screw reactors, screw conveyor reactors, entrained-flow reactors, rotary tube reactors, paddle reactors, or a combination of two or more of the aforementioned reactor types. Reactors into which the pyrolysis material can be continuously introduced are particularly preferred.These are selected in particular from rotary tube reactors, continuously operated stirred tank reactors (CSTR), fixed-bed reactors (in particular with continuous bed exchange (shaft reactors) with an internal heat exchanger, preferably with internal heat exchanger tubes), screw reactors, screw conveyor reactors, entrained-flow reactors, moving-bed or fluidized-bed reactors, or a combination of two or more of the aforementioned reactor types. In a particularly preferred embodiment of the process, the pyrolysis reactor is selected from a screw reactor, a rotary tube reactor, a fluidized-bed reactor, or a combination of two or more of the aforementioned reactor types.

[0123] It is particularly preferred to continuously remove the pyrolysis product formed in step (C.II) from the reactor. This can preferably be ensured by means of a gas stream passed through the pyrolysis reactor and / or by suction. In particular, a residence time of the pyrolysis product, specified as the period between the time of formation of the pyrolysis product and the time of its removal from the pyrolysis reactor, is set to between 0.1 seconds and 600 seconds, preferably between 0.5 seconds and 300 seconds, particularly preferably between 0.5 seconds and 200 seconds. When using a gas stream, this particularly comprises inert gases such as nitrogen, argon, carbon dioxide, and / or nitrogen monoxide.However, it may also be advantageous to additionally use non-inert gases such as methane, gaseous water, hydrogen and / or the optionally present gas phase from non-condensed components of the pyrolysis product as components of the gas stream.

[0124] The proportion of oxygen gas in the pyrolysis reactor during the decomposition in step (C.11) (determined using commercially available oxygen sensors) should be as low as possible and is preferably limited 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. The absolute pressure in the gas phase of the pyrolysis reactor is preferably 1.0 bar to 1.2 bar.

[0125] The pyrolysis residue formed in step (C. II) is preferably continuously discharged from the pyrolysis reactor.

[0126] To obtain aniline, the pyrolysis product obtained in step (C) is preferably subjected to a workup comprising (at least) one distillation in a step (D). The term distillation as used in the context of the present invention also includes rectification. Any other amines formed, such as toluidine, are separated off in step (D). The distillative purification of aromatic amines, such as aniline in particular, is well known and need not be described in detail here.

[0127] The aniline obtained in step (D) can be used for all conventional uses of aniline. The same applies, of course, to any toluidine obtained. The preferred reaction is the reaction of recovered aniline with formaldehyde under acid catalysis (especially hydrochloric acid catalysis) to form methylenediphenylenediamine and polymethylenepolyphenylenepolyamine. These, in turn, are preferably phosgenated to the corresponding isocyanates. After workup, methylenediphenylene diisocyanate and a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate are obtained. All of these processes are well known per se and therefore require no further description here.

[0128] The methylenediphenylene diisocyanate obtained in this way and / or the mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate is suitable for reaction with a polyol to form a polyurethane. Any polyol known in polyurethane chemistry can be used as the polyol, in particular the (at least one) polyol from the polyol phase, which can be obtained in the chemolysis or in step (B) as described above.

[0129] ATTACHMENT

[0130] The invention further provides a plant for obtaining aniline as already described above. Suitable chemolysis reactors have already been described previously in connection with the process according to the invention. In a preferred embodiment, the chemolysis device of the plant comprises a device for rendering the starting material inert. It is further preferred that the optionally present workup device of the plant downstream of the chemolysis device comprises (at least) one extraction device and / or (at least) one distillation device. A further workup device (d) is preferably connected downstream of the pyrolysis device and serves to obtain aniline (and optionally toluidine) from the pyrolysis condensate. This further workup device preferably comprises devices for distilling the pyrolysis condensate.

[0131] Examples:

[0132] Example 1: Chemolysis of a rigid polyurethane foam (step (A) of the present invention)

[0133] In a 1000 ml 4-neck flask equipped with a stirrer, thermometer, and cooling attachment, 200 g of ethanolamine and 2 g of sodium carbonate were placed and heated to 150 °C under nitrogen. 200 g of a rigid polyurethane foam, prepared according to the formulation given in Table 1, were added and dissolved with stirring. After dissolution, the mixture was stirred at 150 °C for 2 hours, and then 17 g of water were added over a period of 30 minutes so that the reaction temperature did not fall below 150 °C. After the addition of water, the mixture was stirred at 150 °C for a further 3 hours. The resulting reaction mixture corresponds to the first chemolysis product.

[0134] Table 1: Formulation of the rigid polyurethane foam used in Example 1

[0135] (1) Polyether polyols from Covestro Deutschland AG

[0136] (2) Polyethersiloxane additive from Evonik AG

[0137] (3) Amine catalyst from Covestro Deutschland AG

[0138] (4) Amine catalyst from Evonik AG

[0139] (5) Physical blowing agent

[0140] (6) Desmodur 44V20L is a mixture of mMDI and pMDI from Covestro Deutschland AG

[0141] (7) Ratio of NCO to OH groups Example 2: Workup of the first chemolysis product (step (B) of the present invention)

[0142] Ethanolamine was first distilled from the first chemolysis product from Example 1a at 150 °C and <20 mbar. The remaining product mixture was mixed with chloroform and water in a mass ratio of 1:1:1 and then intensively mixed with 32% hydrochloric acid to a protonation degree of 105%, calculated based on the amine number of the first chemolysis product. Phase separation into an organic polyol phase and an aqueous amine phase followed. The aqueous amine phase was neutralized with sodium hydroxide (equimolar amount based on the amount of hydrochloric acid previously used). After separation of the aqueous phase, the second chemolysis product was obtained. This had the composition given in Table 2.

[0143] Table 2: Composition of the second chemolysis product

[0144] [a] Determined by 1 H-NMR.

[0145] Example 3: Pyrolysis of the second chemolysis product (step (C) of the present invention)

[0146] The second chemolysis product from Example 2 was pyrolytically (thermochemically) cleaved as follows:

[0147] First, half (2.5 g) of the pyrolysis catalyst (aluminum oxide catalyst "Puralox SBA 200" from Sasol Germany GmbH), followed by 1 g of the second chemolysis product, and finally the remaining amount (2.5 g) of the pyrolysis catalyst were added to a metal cylinder with an internal volume of 12 ml. A filter paper was placed in the lid of the vessel, and the vessel was sealed after purging with nitrogen. The thus-filled vessel was then placed in a nitrogen-perfused tubular reactor with an internal volume of 70 ml, including 28 ml in the hot zone. The flow rate of the nitrogen gas stream (superficial velocity) in the reactor was 0.013 m / s. The reactor was heated to 500 °C and then left at this temperature for 30 min. Behind the reactor were two condensers cooled with liquid nitrogen to separate the condensable components of the pyrolysis gas produced.The amount of pyrolysis residue was determined by weighing the solid remaining in the metal cylinder and subtracting the amount of catalyst powder used after pyrolysis. The components in the pyrolysis product (=pyrolysis condensate), which formed as an oil, were determined using gas chromatography (GC) with a flame ionization detector. An Agilent 7890A gas chromatograph was used for this purpose. After injection, the sample is evaporated in the built-in glass fiber liner and separated using an Rxi-lms column from Restek, which uses silicon dioxide as the stationary phase. The column is 30 m long, has an inner diameter of 0.32 mm, and operates in a temperature range from -60°C to 330 / 350°C. The GC results were evaluated using the "Chromeieon" software. For the GC analysis, 0.75 g of the pyrolysis oil was diluted with 20.0 g of methanol to which 0.100 g of cumene had been added as an internal standard.Table 3 shows the results obtained.

[0148] Table 3: Results of pyrolysis

Claims

1. A process comprising the recovery of aniline from a starting material selected from (i) a polyurethane product based on an isocyanate component and a polyol component or (ii) an isocyanate-containing waste stream resulting from the production of an isocyanate component, wherein the isocyanate component comprises methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate, the process comprising the steps: (A) chemically cleaving the starting material to obtain a first chemolysis product containing (i) methylenediphenylenediamine or (ii) a mixture of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine; (B) optionally, processing the first chemolysis product comprising separating components other than methylenediphenylenediamine and polymethylenepolyphenylenepolyamine to obtain a second chemolysis product; and (C) pyrolytic cleavage of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine contained in the first or second chemolysis product at a pyrolysis temperature of 200 °C to 700 °C in the presence of a pyrolysis catalyst to obtain a pyrolysis product containing aniline.

2. A process according to claim 1, wherein the chemical cleavage in step (A) comprises reacting the starting material with (AI) an organic chemolysis reagent and water or (AH) water without the use of an organic chemolysis reagent.

3. The process according to claim 2, wherein the organic chemolysis reagent in (AI) is selected from (i) an alcohol, (ii) a primary or secondary amine, (iii) an amino alcohol containing a primary or secondary amino group, or (iv) a mixture of two or more of the aforementioned chemolysis reagents.

4. A process according to claim 2 or 3, wherein the starting material is a polyurethane product based on an isocyanate component and a polyol component.

5. The process of claim 4, wherein step (A) comprises reacting the polyurethane product with (Al) an organic chemolysis reagent and water.

6. The process according to claim 4, wherein step (A) comprises reacting the polyurethane product with (A.ll) water without the use of an organic chemolysis reagent.

7. The method according to claim 5, wherein in step (A) (A.1.1) the organic chemolysis reagent and water are added to the polyurethane product and the chemical cleavage is carried out to obtain the first chemolysis product, wherein the first chemolysis product comprises, in addition to (i) methylenediphenylenediamine or (ii) the mixture of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine, additionally (iii) a polyol from the polyol component, or (Al2) in a first step of chemical cleavage, the organic chemolysis reagent is added to the polyurethane product and reacted with it, followed by separation into a carbamate or urea phase and a polyol phase containing a polyol from the polyol component, and wherein in a second step of chemical cleavage, the carbamate or urea phase is reacted with water to obtain the first chemolysis product.

8. The process according to claim 7, wherein, when carrying out (A.1.1), step (B) is included and comprises separating a polyol phase containing a polyol from the polyol component.

9. The process of claim 6, wherein step (B) is included and comprises separating a polyol phase containing a polyol from the polyol component.

10. The process according to claim 8 or 9, wherein the polyol from the polyol component, optionally after purification, is reacted with an isocyanate to form a polyurethane.

11. A method according to any one of claims 1 to 10, wherein step (C) comprises: (Cl) Introduction of the first chemolysis product or the second Chemolysis product and the pyrolysis catalyst into a pyrolysis reactor, (C.ll) Decomposition of the first chemolysis product or the second Chemolysis product in the pyrolysis reactor to obtain gaseous pyrolysis product and non-gaseous pyrolysis residue, and (C.lll) Cooling the pyrolysis product to obtain (i) a pyrolysis condensate containing aniline and (ii) optionally a gas phase of uncondensed components of the pyrolysis product.

12. Process according to one of claims 1 to 11, in which the pyrolysis product obtained in step (C) is subjected in a step (D) to a work-up comprising a distillation, whereby aniline is obtained.

13. The process according to claim 12, wherein the aniline obtained in step (D) is reacted with formaldehyde under acid catalysis to give methylenediphenylenediamine and polymethylenepolyphenylenepolyamine, the methylenediphenylenediamine and the polymethylenepolyphenylenepolyamine being phosgenated, followed by workup to give methylenediphenylene diisocyanate and a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate.

14. The process according to claim 13, wherein the methylenediphenylene diisocyanate and / or the mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate are reacted with a polyol to form a polyurethane.

15. Plant for the production of aniline from a starting material selected from (i) a polyurethane product based on an isocyanate component and a polyol component or (ii) an isocyanate-containing waste stream arising in the production of an isocyanate component, wherein the isocyanate component comprises methylenediphenylene diisocyanate or a mixture of methylenediphenylene diisocyanate and polymethylenepolyphenylene polyisocyanate, the plant comprising the devices: (a) a chemolysis device comprising a chemolysis reactor for chemically splitting the starting material to obtain a first chemolysis product containing (i) methylenediphenylenediamine or (ii) a Mixture of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine; (b) optionally, a processing device downstream of the chemolysis device for processing the first chemolysis product to separate components other than methylenediphenylenediamine and polymethylenepolyphenylenepolyamine to obtain a second chemolysis product; (c) a pyrolysis device downstream of the chemolysis device or, if the reprocessing device is present, the reprocessing device comprising (cl) means for introducing the first or second chemolysis product into a pyrolysis reactor, wherein (cl I) the pyrolysis reactor is designed for the pyrolytic cleavage of methylenediphenylenediamine and polymethylenepolyphenylenepolyamine contained in the first or second chemolysis product to obtain gaseous pyrolysis product and non-gaseous pyrolysis residue, (c.lll) a cooling device for cooling the pyrolysis product to obtain (i) a pyrolysis condensate containing aniline and (ii) optionally a gas phase of uncondensed components of the pyrolysis product, and (c.lV) a collector for collecting the pyrolysis condensate.

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