Method for producing aniline or an aniline-derived product

Abstract

The invention relates to a method for producing aniline or an aniline-derived product, comprising the following steps: (A) providing aminobenzoic acid; (B) decarboxylating the aminobenzoic acid in a reactor at a reaction temperature in the region of 170 °C to 350 °C to form aniline and carbon dioxide, wherein the decarboxylation is carried out at a reaction pressure, at which the boiling point of aniline is reached or, preferably, exceeded, such that a first liquid, optionally solid, particle-containing phase and a second gaseous phase are formed in the reactor, wherein a gaseous flow containing aniline and carbon dioxide is discharged from the reactor; and (C) condensing and optionally cleaning the aniline contained in the gaseous flow; and (D) optionally, converting the aniline obtained in (C) into a aniline-derived product.

Description

[0001] Process for the production of aniline or a

[0002] The invention underlying this application was financially supported by the German Federal Ministry of Food and Agriculture within the project "Bio-based production of intermediates for polyurethanes - Phase II (Bio4PURPro)" (grant number 22019918).

[0003] The present invention relates to a process for the preparation of aniline or an aniline derivative, comprising the steps of (A) providing aminobenzoic acid; (B) decarboxylating the aminobenzoic acid in a reactor at a reaction temperature in the range from 170°C to 350°C to give aniline and carbon dioxide, wherein the decarboxylation is carried out at a reaction pressure at which the boiling point of aniline is reached or exceeded, so that a first, liquid phase, optionally containing solid particles, and a second, gaseous phase are formed in the reactor, wherein a gaseous stream containing aniline and carbon dioxide is discharged from the reactor; and (C) condensing and optionally purifying the aniline contained in the gaseous stream; and (D) optionally converting the aniline obtained in (C) to give an aniline derivative.

[0004] The production of aniline by decarboxylation of aminobenzoic acid is generally known in the art. For example, see international patent applications WO 2015 / 124686 A1 and WO 2015 / 124687 A1 and the literature cited therein. The starting compound, aminobenzoic acid, can be obtained chemically or, preferably, by fermentation.

[0005] The chemical production of aminobenzoic acid is well known. One suitable synthesis route is the reaction of phthalimide with sodium hypochlorite. Phthalimide, in turn, can be obtained from phthalic anhydride and ammonia.

[0006] The fermentative production of aminobenzoic acid is also known and described in the literature; see, for example, the aforementioned applications WO 2015 / 124686 A1 and WO 2015 / 124687 A1 and the literature cited therein.

[0007] WO 2015 / 124686 A1 describes the decarboxylation of fermentatively or chemically produced anthranilic acid by extraction of aniline formed in the decarboxylation with a non-system organic solvent (an alcohol, phenol, amide, ether or aromatic hydrocarbon; in particular, 1-dodecanol is highlighted as a suitable solvent).

[0008] WO 2015 / 124687 A1 describes the decarboxylation of fermentatively produced anthranilic acid, among other things, in water or in a non-system organic solvent, in particular 1-dodecanol, optionally in a mixture with aniline (see page 18, lines 28 and 29). Furthermore, this document also describes the possibility of carrying out the decarboxylation in aniline (without 1-dodecanol; see Figures 35 and 37 to 38 and the corresponding text), optionally in the presence of 10 mass% water (see Figure 36 and the corresponding text).

[0009] WO 2018 / 002088 A1 describes a process in which aminobenzoic acid is decarboxylated in a mixture with crude aniline. The crude aniline originates from the process itself, as a portion of the product stream is recycled into the process rather than being fed into the purification stage. Catalysts described for carrying out the decarboxylation include aqueous acids such as sulfuric acid, nitric acid, and hydrochloric acid; solid acids such as zeolites and Si-Ti molecular sieves; solid bases such as hydroxyapatites and hydrotalcites; and polymeric acids such as ion exchange resins (especially Amberlyst).

[0010] WO 2020 / 020919 A1 describes the decarboxylation of aminobenzoic acid in aniline. It is suggested that aniline itself acts as a catalyst (i.e., has autocatalytic properties). External catalysts are deliberately omitted. The reaction is carried out under conditions in which aniline is in liquid form. In certain embodiments, a gas stream is withdrawn from the reactor to remove the carbon dioxide formed as a by-product. Since minor amounts of aniline are also entrained with this gas stream, it is preferable to selectively condense the entrained aniline and feed it into the reaction or workup.

[0011] The as yet unpublished patent application with the file number EP 21177307.2 relates to a process for the preparation of aniline or an aniline derivative, in which aminobenzoic acid is reacted in the presence of an inorganic heterogeneous metal oxide catalyst containing a mass fraction of Al2O3 of 40.0% to 100%, based on the total mass of the metal oxides, wherein the mass fraction of Al2O3, based on the total mass of the inorganic heterogeneous metal oxide catalyst, is 25% to 100%. None of the previously described processes is entirely satisfactory in terms of economic efficiency, particularly with regard to the complexity of the overall process (the actual preparation of the aniline and its workup by distillation). Likewise, optimization of the aniline yield (by optimizing the conversion and suppressing the by-product 2-aminobenzanilide) is desirable.Accordingly, there was a need for improvements in the production of aniline or aniline derivatives by decarboxylation of aminobenzoic acid.

[0012] In response to this need, the present invention provides a process for producing aniline or an aniline derivative comprising the steps:

[0013] (A) providing aminobenzoic acid;

[0014] (B) decarboxylating the aminobenzoic acid in a reactor, wherein the aminobenzoic acid is introduced into the reactor (i) as a solid, (ii) molten, or (iii) dissolved or suspended in a solvent and is converted to aniline and carbon dioxide at a reaction temperature in the range from 170°C to 350°C, preferably 185°C to 300°C, particularly preferably at 190°C to 260°C, wherein the reaction is carried out at a reaction pressure at which the boiling point of aniline is reached or, preferably, exceeded, so that a first, liquid phase, optionally containing solid particles, and a second, gaseous phase are formed in the reactor, wherein a gaseous stream containing aniline and carbon dioxide is discharged from the reactor; and

[0015] (C) condensing and optionally purifying the aniline contained in the gaseous stream; and

[0016] (D) optionally, converting the aniline obtained in (C) to an aniline derivative.

[0017] Carrying out the reaction at a reaction pressure at which the boiling point of aniline is reached or, preferably, exceeded means that the reaction pressure and reaction temperature are coordinated so that the temperature in the reactor is above the boiling point of aniline at the pressure prevailing in the reactor, or at least equal to the boiling point. Aniline boils at 184 °C at atmospheric pressure. Therefore, if the reaction is carried out, for example, at atmospheric pressure (1.013 bar) or a pressure only slightly different therefrom, a reaction temperature of 184 °C or more must be selected. If the reaction is carried out at reduced pressure, a lower reaction temperature corresponding to the pressure reduction (but not lower than 170 °C) can be selected. If the reaction is carried out at elevated pressure, a higher reaction temperature corresponding to the pressure increase (but not more than 350 °C) must be selected.

[0018] As a result, aniline formed by decarboxylation evaporates spontaneously in the process according to the invention. The aniline thus passes, at least in its vast majority, into the second, gaseous phase and is removed from the reactor with the gaseous stream containing aniline and carbon dioxide. It cannot be ruled out that minor amounts of the aniline formed (in particular up to 5.0%, preferably up to 2.0%, particularly preferably up to 1.0% of the theoretical yield of aniline, where "theoretical yield" refers to a 100% conversion of the aminobenzoic acid to aniline, where 1 mol of aminobenzoic acid is converted to 1 mol of aniline) remain in the first, liquid phase, which may contain solid particles, and are then discharged and disposed of, for example, with a purge stream (see below for details). This does not exceed the scope of the present invention.

[0019] Surprisingly, it was discovered that carrying out the decarboxylation under conditions in which the resulting aniline passes into the gas phase and is removed in gaseous form represents a simple process design option, characterized by high conversion and high selectivity for the target product, aniline. In the process according to the invention, the "crude aniline" resulting from the reaction is already distilled, which considerably simplifies further purification, if necessary at all.

[0020] The attached drawings show reactors suitable for the continuous implementation of the process according to the invention:

[0021] FIG. 1: shows a stirred tank reactor;

[0022] FIG. 2: a rotary tube reactor; and

[0023] FIG. 3: a trough reactor (= conveyor reactor). First, a brief summary of various possible embodiments of the invention follows:

[0024] In a first embodiment of the invention, which can be combined with all other embodiments, the reaction of the aminobenzoic acid is carried out at a reaction pressure (measured in the second phase) in the range from 0.10 bar to 10 bar, preferably 0.50 bar to 5.0 bar and particularly preferably 0.90 bar to 1.1 bar (in particular ambient pressure).

[0025] In a second embodiment of the invention, which can be combined with all other embodiments, provided that they are not limited to a batch process, the aminobenzoic acid is continuously fed to the reactor during the reaction of the aminobenzoic acid in step (B) and aniline and carbon dioxide are continuously removed from the reactor.

[0026] In a third embodiment of the invention, which is a particular embodiment of the second embodiment, the reactor is a stirred tank reactor with an inlet for the aminobenzoic acid, an outlet for the gaseous stream and an outlet for a liquid stream, optionally containing solid particles (the conversion of the aminobenzoic acid thus takes place [largely] with backmixing).

[0027] In a fourth embodiment of the invention, which is a particular embodiment of the third embodiment, a mass fraction of aniline in the range from 5.0% to 90%, preferably 10% to 70%, based on the total mass of aminobenzoic acid and aniline is present in the first phase.

[0028] In a fifth embodiment of the invention, which is another particular embodiment of the second embodiment, the reactor comprises a reaction tube with an inlet for the aminobenzoic acid, an outlet for the gaseous stream and an outlet for a liquid stream, optionally containing solid particles (the conversion of the aminobenzoic acid thus takes place [largely] without backmixing).

[0029] In a sixth embodiment of the invention, which is a special embodiment of the fifth embodiment, the reaction tube is rotated about its longitudinal axis (i.e., it is a so-called rotary tube reactor, wherein the reaction tube may be inclined to the horizontal and may optionally contain internals such as lifting bars, baffle plates or a conveyor screw) or the reaction tube is arranged stationary, wherein a conveyor screw rotates in the reaction tube, which does not completely fill the cross-section of the reaction tube (i.e., it is a so-called trough reactor or conveyor channel reactor).

[0030] In a seventh embodiment of the invention, which is a particular embodiment of the fifth and sixth embodiments, a mixture containing 0.1 mass% to 30 mass% of aniline, preferably 1.0 mass% to 7.5 mass%, based on the total mass of the mixture, is continuously withdrawn from the reactor via the outlet for the liquid stream, optionally containing solid particles.

[0031] In an eighth embodiment of the invention, which is a particular embodiment of the second to seventh embodiments, an average residence time tv from the entry of an aminobenzoic acid molecule into the reactor to the removal of an aniline molecule formed therefrom via the gaseous stream from the reactor is set to 1.00 min to 500 min, preferably 5.00 min to 120 min.

[0032] In a ninth embodiment of the invention, which can be combined with all other embodiments, provided that these are not restricted to a continuous process, the reaction of the aminobenzoic acid is carried out discontinuously in batches, wherein the aminobenzoic acid is initially introduced into the reactor and / or added to the reactor (continuously or at intervals) over a period tz and, after addition of the total amount of a batch of aminobenzoic acid, this is reacted in the reactor for a (post-)reaction time tR at the reaction temperature and the reaction pressure.

[0033] In a tenth embodiment of the invention, which is a particular embodiment of the ninth embodiment, the reactor is a stirred tank reactor.

[0034] In an eleventh embodiment of the invention, which is a particular embodiment of the ninth and tenth embodiments, at the beginning of the (post-)reaction time tR, a mass fraction of aniline in the first phase, based on the total mass of aminobenzoic acid and aniline, is in the range from 0.1% to 90%, preferably 5.0% to 90%, particularly preferably 10% to 70%.

[0035] In a twelfth embodiment of the invention, which is a particular embodiment of the ninth to eleventh embodiments, 50% to 100% of the total amount of a batch of aminobenzoic acid is added to the reactor (continuously or at intervals) over the period tz, where tz is 30% to 70% of the total duration tz + tR. In a thirteenth embodiment of the invention, which is a particular embodiment of the ninth to twelfth embodiments, the (post-)reaction duration tR is in the range from 1.00 min to 500 min, preferably 5.00 min to 120 min.

[0036] In a fourteenth embodiment of the invention, which can be combined with all other embodiments, the gaseous stream comprising aniline and carbon dioxide in step (B) passes through a condenser for condensing any aminobenzoic acid entrained in the gaseous stream (so that any aminobenzoic acid entrained is predominantly condensed, preferably to at least 90%, and then recycled to the first phase in the reactor, while aniline passes through the condenser predominantly, preferably to at least 90% - in particular if a (destination or rectification) column is arranged between the reactor and the condenser - in gaseous form).

[0037] In a fifteenth embodiment of the invention, ortho-aminobenzoic acid is provided in step (A). This embodiment can be combined with all other embodiments, provided they do not provide for the provision of a different aminobenzoic acid isomer in step (A).

[0038] In a sixteenth embodiment of the invention, para-aminobenzoic acid is provided in step (A). This embodiment can be combined with all other embodiments, provided they do not provide for the provision of a different aminobenzoic acid isomer in step (A).

[0039] In a seventeenth embodiment of the invention, which is a particular embodiment of the fifteenth embodiment, step (A) comprises (i) the reaction of phthalimide or phthalic acid monoamide with an alkali metal hypohalide (in particular sodium hypochlorite) in a basic medium followed by an acid treatment or (ii) the hydrogenation of 2-nitrobenzoic acid.

[0040] In an eighteenth embodiment of the invention, which is a particular embodiment of the sixteenth embodiment, step (A) comprises (i) the reaction of terephthalic acid monoamide with an alkali metal hypohalide (in particular sodium hypochlorite) in a basic medium followed by an acid treatment or (ii) the hydrogenation of 4-nitrobenzoic acid.

[0041] In a nineteenth embodiment of the invention, which is a particular embodiment of the first to sixteenth embodiments, step (A) comprises fermenting a raw material containing a fermentable carbon-containing compound and a nitrogen-containing compound in the presence of microorganisms. In a twentieth embodiment of the invention, which is a particular embodiment of the nineteenth embodiment,

[0042] • the fermentable carbon-containing compound is selected from starch hydrolysate, sugar cane juice, sugar beet juice, hydrolysates from lignocellulose-containing raw materials or a mixture of two or more of the aforementioned carbon-containing compounds, and

[0043] • the nitrogen-containing compound is selected from ammonia gas, ammonia water, (at least) one ammonium salt, soy protein, urea or a mixture of two or more of the aforementioned nitrogen-containing compounds.

[0044] In a twenty-first embodiment of the invention, which is a particular embodiment of the nineteenth and twentieth embodiments, the microorganisms are selected from Escherichia coli, Pseudomonas putida, Corynebacterium glutamicum, Ashbya gossypii, Pichia pastoris, Hansenula polymorpha, Kluyveromyces marxianus, Yarrowia polytica, Zygosaccharomyces bailii or Saccharomyces cerevisiae.

[0045] In a twenty-second embodiment of the invention, which is a particular embodiment of the first to twenty-first embodiments, step (B) is carried out without addition of a catalyst and without addition of aniline.

[0046] In a twenty-third embodiment of the invention, which is a further particular embodiment of the first to twenty-first embodiments, step (B) is carried out in the presence of a catalyst selected from

[0047] (a) an aqueous mineral acid (such as, in particular, sulfuric acid, nitric acid, and hydrochloric acid), (b) a zeolite (in particular of type Y in the protonated form [H-form]), (c) a Si-Ti molecular sieve, (d) a hydroxyapatite, (e) hydrotalcite, (f) an ion exchange resin (in particular Amberlyst), and / or (g) an inorganic heterogeneous metal oxide catalyst containing a mass fraction of Al2O3 of 40.0% to 100%, based on the total mass of the metal oxides, wherein the mass fraction of Al2O3, based on the total mass of the inorganic heterogeneous metal oxide catalyst, is 25% to 100%. In a twenty-fourth embodiment of the invention, which is a particular embodiment of the twenty-third embodiment, the process comprises step (B)(iii), wherein the solvent comprises (and is, in particular, aniline).

[0048] In a twenty-fifth embodiment of the invention, which is a further particular embodiment of the first to twenty-first embodiments, the process comprises step (B)(iii), wherein the solvent comprises aniline (in particular is aniline) and no (foreign) catalyst is added.

[0049] In a twenty-sixth embodiment of the invention, which can be combined with all other embodiments (provided they do not provide for the use of aniline as solvent), in particular insofar as they relate to the use of a continuously flowing reaction tube in step (B), step (B)(iii) is included, wherein the solvent remains in the first phase to an extent of at least 90%, preferably at least 95%, particularly preferably at least 99% at the reaction temperature and the reaction pressure.

[0050] In a twenty-seventh embodiment of the invention, which is a particular embodiment of the twenty-sixth embodiment, the solvent is selected from a hydrocarbon (in particular having twelve or more carbon atoms), a silicone oil, an ether-based oil (in particular tri-, tetra- or pentaglyme), a molten salt, sulfolane, diphenyl ether, a haloaromatic (in particular trichlorobenzene) or an aniline-based amide (in particular 2-aminobenzanilide), with a hydrocarbon or 2-aminobenzanilide being preferred.

[0051] In a twenty-eighth embodiment of the invention, which can be combined with all other embodiments, step (D) is carried out and comprises one of the following implementations:

[0052] (1) Acid-catalyzed reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series;

[0053] (2) Acid-catalyzed reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series, followed by their reaction with phosgene to form di- and polyisocyanates of the diphenylmethane series; or

[0054] (3) Conversion of the aniline to an azo compound. The embodiments briefly described above and other possible configurations of the invention are explained in more detail below. All embodiments and other possible configurations can be combined with one another in any way, unless the context clearly indicates otherwise to a person skilled in the art or something else is expressly stated.

[0055] In step (A) of the process according to the invention, the aminobenzoic acid to be reacted is provided. This can be produced at the site of decarboxylation or introduced externally. In the process according to the invention, ortho- or para-aminobenzoic acid is preferably used as the starting material for the decarboxylation, with ortho-aminobenzoic acid (anthranilic acid) being particularly preferred. The aminobenzoic acid can be produced by any of the processes known in the art. Both chemical (non-fermentative) and biotechnological (fermentative) routes for the production of aminobenzoic acid are known. Both production methods can be used within the scope of the process according to the invention. Since these are well-known and can all be easily applied within the scope of the decarboxylation according to the invention, they are only briefly outlined below:

[0056] Particularly suitable chemical synthesis routes are (i) a Hofmann rearrangement of the corresponding imides or monoamides with an alkali metal hypohalide (especially sodium hypochlorite) in basic medium followed by acid treatment and (ii) hydrogenation of the corresponding nitrobenzoic acids. In the former case (i), phthalimide or phthalic acid monoamide or terephthalic acid monoamide serve as starting materials, and in the latter case (ii), 2-nitrobenzoic acid or 4-nitrobenzoic acid.

[0057] Aminobenzoic acid can also be obtained by fermentation (see the patent literature cited above). For this purpose, a raw material containing a fermentable carbon-containing compound and a nitrogen-containing compound is fermented in the presence of microorganisms. It is preferred that

[0058] • the fermentable carbon-containing compound is selected from starch hydrolysate, sugar cane juice, sugar beet juice, hydrolysates from lignocellulose-containing raw materials or a mixture of two or more of the aforementioned carbon-containing compounds, and the nitrogen-containing compound is selected from ammonia gas, ammonia water, (at least) one ammonium salt, soy protein, urea or a mixture of two or more of the aforementioned nitrogen-containing compounds.

[0059] Particularly suitable microorganisms are Escherichia coli, Pseudomonas putida, Corynebacterium glutamicum, Ashbya gossypii, Pichia pastoris, Hansenula polymorpha, Kluyveromyces marxianus, Yarrowia lipolytica, Zygosaccharomyces bailii or Saccharomyces cerevisiae.

[0060] The fermentative route is preferred because it opens a path to a more sustainable and environmentally friendly production of aniline.

[0061] Step (B) of the process according to the invention relates to the actual decarboxylation of the aminobenzoic acid to the desired product (or intermediate) aniline.

[0062] For this purpose, the aminobenzoic acid provided in step (A) is introduced into the decarboxylation reactor (i) as a solid, (ii) molten, or (iii) dissolved or suspended in a solvent. If the aminobenzoic acid is introduced into the reactor in solid form (i), it will melt due to the prevailing temperatures of 170°C to 350°C, preferably 185°C to 300°C, particularly preferably 190°C to 260°C. When melting (ii) the aminobenzoic acid outside the decarboxylation reactor, particular care should be taken to ensure that decarboxylation does not already begin there. This can be ensured by the shortest possible residence times and the lowest possible temperatures.When using aniline as solvent (iii), i.e., when feeding aminobenzoic acid / aniline mixtures into the decarboxylation reactor (hereinafter referred to as reactor), the temperature of the aminobenzoic acid in aniline solution before entering the reactor must be selected between room temperature and 160 °C, depending on the mixing ratio. Upon entering the reactor, the mixture is heated to the reaction temperature, with the aniline added to the aminobenzoic acid predominantly passing into the second, gaseous phase and being removed from the reactor with the gaseous stream containing aniline and carbon dioxide. In parallel, the aminobenzoic acid also decarboxylates to further aniline, which also predominantly passes into the second, gaseous phase and is removed from the reactor with the gaseous stream containing aniline and carbon dioxide.When using solvents (iii) other than aniline, care must be taken to ensure that they remain largely, ideally completely, in the liquid phase, i.e. that they have a correspondingly high boiling point under the reaction conditions chosen (which is regularly the case if their boiling point at ambient pressure is > 200 °C), and that they remain at least 90%, preferably at least 95%, particularly preferably at least 99% in the first phase (the liquid phase, which may contain solid particles suspended therein), in particular at the reaction temperature and the reaction pressure present in the reactor.Suitable solvents include high-boiling compounds that are unreactive toward the functional groups of aniline and aminobenzoic acid (amine and carboxyl groups) under the chosen reaction conditions, such as long-chain hydrocarbons, especially hydrocarbons with twelve or more carbon atoms (individual compounds or mixtures such as paraffin oil), silicone oils, ether-based oils (e.g., tri-, tetra-, or pentaglyme), molten salts, or high-boiling solvents such as sulfolane, diphenyl ether, halogenated aromatics (e.g., trichlorobenzene), 2-aminobenzanilide, or other aniline-based amides. This embodiment is particularly advantageous when the reaction is carried out in continuous-flow reactors because the liquid discharge of the solvent allows for the purge of high-boiling impurities such as by-products, thus preventing their accumulation in the reaction space.

[0063] The reaction pressure can be selected within a wide range, provided that an aniline-containing gas phase (the second phase) forms as described above, and is in particular from 0.10 bar to 10 bar, preferably from 0.50 bar to 5.0 bar, and particularly preferably from 0.90 bar to 1.1 bar. In the context of the present invention, all pressure specifications refer to absolute pressures. The reaction can very particularly preferably be carried out at ambient pressure, which is a particular advantage of the process according to the invention. To determine the pressure, a pressure gauge can be installed in the second (gaseous) phase. A measurement in the first phase is, of course, also possible, although not preferred. In the event of deviating measured values, the value measured in the second phase is decisive.

[0064] In a preferred embodiment, the gaseous stream containing aniline and carbon dioxide removed from the reactor passes through a condenser for the (selective) condensation of any aminobenzoic acid entrained in the gaseous stream. The condenser is operated in particular such that any entrained aminobenzoic acid condenses predominantly to completely, preferably to at least 90%, while aniline passes through the condenser (predominantly) in gaseous form. Condensed aminobenzoic acid is recycled to the first phase (liquid, optionally containing solid particles) in the reactor. In a preferred embodiment, the condenser is in the form of a plug-in condenser located directly above the reactor so that the condensed aminobenzoic acid can drain freely. Condenser types known in the art can be used for this purpose.Particularly suitable designs are characterized by the avoidance of stagnant fluid flow and the ability to be mechanically cleaned. A secondary cooling medium circuit can be used to dissipate heat. A preferred design utilizes evaporative cooling with water to utilize the waste heat for steam generation. When setting suitable operating conditions, the temperature should be sufficiently high to prevent crystallization of the aminobenzoic acid and thus avoid deposits. If necessary, the optimal operating conditions can be determined through simple preliminary tests.

[0065] To minimize the proportion of unwanted recirculated aniline, a (destination or rectification) column can be arranged between the reactor and the condenser. It is preferred that at least 90% of the aniline passes through the condenser in gaseous form, preferably (essentially) completely.

[0066] The decarboxylation can be carried out in the presence of a catalyst. Suitable (non-system) catalysts are

[0067] (a) aqueous mineral acids (such as in particular sulfuric acid, nitric acid and hydrochloric acid), (b) zeolites (in particular of type Y in the protonated form [H form]), (c) Si-Ti molecular sieves, (d) hydroxyapatites, (e) hydrotalcite, (f) ion exchange resins (in particular Amberlyst) and / or (g) inorganic heterogeneous metal oxide catalysts containing a mass fraction of Al2O3 of 40.0% to 100% based on the total mass of the metal oxides, wherein the mass fraction of Al2O3 based on the total mass of the inorganic heterogeneous metal oxide catalyst is 25% to 100%.

[0068] Such a catalyzed reaction can be carried out by adding aniline to the aminobenzoic acid to be reacted (as described in WO 2018 / 002088 A1, although purified aniline can also be used instead of crude aniline). However, it is also possible to carry out the decarboxylation by adding aniline to the aminobenzoic acid to be reacted and omitting a (non-system) catalyst (as described in WO 2020 / 020919 A1). It is also possible to add neither aniline nor a (non-system) catalyst.

[0069] The reaction can be carried out discontinuously or continuously.

[0070] In a discontinuous reaction, the aniline is produced in discrete batches, for which corresponding batches of aminobenzoic acid are reacted. The amount of aminobenzoic acid to be reacted in a batch production can be initially charged in the reactor or added thereto over a period t t (continuously or at intervals). It is also possible to initially charge a portion of the aminobenzoic acid and add the remainder over the period t t . In any case, after the total amount of a batch of aminobenzoic acid has been added, it is reacted in the reactor for a (post-)reaction time t R at the reaction temperature and reaction pressure. It is preferred to add 50% to 100% of the total amount of a batch of aminobenzoic acid to the reactor continuously or at intervals, where t t is 30% to 70% of the total duration of t t + t R . For the (post-)reaction time tR, values ​​from 1.00 min to 500 min, preferably 5.00 min to 120 min, are preferred.Stirred tank reactors are particularly suitable as reactors for carrying out discontinuous aniline production.

[0071] At the start of the (post-)reaction time tR (i.e. after the addition of the aminobenzoic acid has ended and the selected conditions of reaction temperature and pressure have been reached), the mass fraction of aniline in the first phase, based on the total mass of aminobenzoic acid and aniline, is generally in the range of 0.1% to 90%, preferably 5.0% to 90%, particularly preferably 10% to 70%. The exact value depends, among other things, on the type of addition of the aminobenzoic acid. If the aminobenzoic acid is initially charged in the reactor at ambient temperature and only melted in the reactor, then of course only a small proportion of the aminobenzoic acid will have converted when the reaction temperature is reached. If, on the other hand, the aminobenzoic acid is introduced in a molten state into a reactor in which the desired conditions of reaction temperature and pressure already exist, then considerably more aminobenzoic acid will have converted when the addition is complete.Of course, the rate at which aniline formed passes from the first (liquid, possibly containing solid particles) phase to the second (gaseous) phase also plays a role, which in turn depends significantly on the reaction temperature and pressure. In a continuous reaction, the aniline is produced in continuous-flow reactors. After a start-up phase, a steady state is established in which a certain flow rate (for example, specified in kg / h) of aminobenzoic acid is continuously fed to the reactor and corresponding flows of aniline and carbon dioxide are continuously removed from the reactor. Provided no operational disruptions occur, this steady state of continuous conversion of the aminobenzoic acid is maintained until production is to be terminated (e.g. due to necessary maintenance work or simply because there is no demand for aniline at the time).The reactor used must be equally suitable for highly concentrated suspensions (melting solids), low-viscosity liquids and, if applicable, high-viscosity liquids (by-products / residue).

[0072] A suitable reactor type for this purpose is a stirred tank reactor. In contrast to the stirred tank reactor described above in connection with the batch process, it is operated in such a way that, during the conversion of the aminobenzoic acid, aminobenzoic acid is continuously introduced into the reactor and the gaseous stream (containing aniline and carbon dioxide) is continuously removed from the reactor. The stirred tank reactor must therefore have (at least) one inlet for the aminobenzoic acid and (at least) one outlet for the gaseous stream. Such a stirred tank reactor used in a continuous process should also have an outlet for a liquid stream, through which high-boiling by-products and any other impurities present can be discharged in liquid or suspended form.Recovery of reactant or valuable product from this stream can be considered depending on the respective concentrations.

[0073] Such a stirred tank reactor is shown in FIG. 1. The reference numerals have the following meaning:

[0074] When using a stirred tank reactor, the reaction takes place with extensive backmixing, i.e. the composition of the reaction mixture is (essentially) constant over the entire tank contents, in contrast to the continuously flowing reaction tubes considered below, in which the composition of the reaction mixture changes continuously from the inlet of the reactants to the outlet of the products (or until the maximum conversion is achieved). In the process according to the invention, when using stirred tank reactors in a continuous process, a mass fraction of aniline in the range from 5.0% to 90%, preferably 10% to 70%, based on the total mass of aminobenzoic acid and aniline is preferably present in the first phase. These figures refer to a process in which aniline is not additionally used as a solvent.A possible design for the operation of such a stirred tank reactor is described in more detail below:.

[0075] A stream of powdered or molten aminobenzoic acid is continuously metered into the stirred tank reactor. The stirred tank is heated; some time after the start of reactant metering, a liquid level of molten aminobenzoic acid forms in its lower section (establishing the steady state). The aminobenzoic acid decomposes into aniline and carbon dioxide, with the temperature in the tank being selected such that both products are gaseous and continuously leave the stirred tank reactor through an outlet at its upper end. A condenser is located at the gas outlet, the operating temperature of which is selected so that entrained gaseous aminobenzoic acid is condensed as selectively as possible and flows directly back into the stirred tank reactor.The remaining gaseous stream enters a processing stage where the target product, aniline, is separated from carbon dioxide, usually present water, and any low-boiling impurities. In the lower section of the stirred-tank reactor, a small stream of the liquid vessel contents, possibly containing solid particles, is continuously withdrawn to prevent the accumulation of high-boiling impurities in the stirred tank. This stream can optionally also be fed to a processing stage to separate the aminobenzoic acid and aniline contained therein from the residue. Depending on the composition of the separated valuable products, they are added either to the reactant stream of aminobenzoic acid or to the product stream of aniline (before or after its processing).The feed flow of powdered or molten aminobenzoic acid into the reactor must be selected so that the stirred tank is partially filled with liquid, i.e., it must be adjusted to the required residence time for complete reaction of the aminobenzoic acid and evaporation of the formed aniline. During steady-state operation of the continuously operated stirred tank reactor, the level in the stirred tank should remain constant. Optionally, a stream of inert gas (e.g., preheated nitrogen) can be passed through the head space of the stirred tank reactor to reduce the residence time of the gaseous product in the reactor.

[0076] In addition to stirred tank reactors, tubular reactors (reaction tubes) are also suitable for carrying out the process according to the invention. These have an inlet for the aminobenzoic acid on one end or near an end and an outlet for the gaseous stream downstream of this in the upper region. Furthermore, as already mentioned for the stirred tank reactors, they have an outlet for a liquid stream (containing high-boiling by-products and any other impurities present), which is expediently arranged on the side opposite the inlet. In such reactors, the reaction proceeds largely without backmixing; i.e. the composition of the reaction mixture flowing through the reactor changes continuously as it passes through the reactor and has the lowest concentration of aminobenzoic acid (= maximum conversion) at the point where the liquid stream exits.It is preferable to carry out step (B) with as little backmixing as possible. The liquid stream discharged via the outlet may contain solid particles, depending on the precise design of the reactor and the reaction procedure.

[0077] A suitable reactor type is the so-called rotary tube reactor. This is a tubular reactor that rotates around its longitudinal axis during operation. Such a rotary tube reactor is shown in FIG. 2. The reference numerals used in connection with FIG. 1 have the same meaning as there. The remaining reference numerals have the following meaning:

[0078] The reactor may also be inclined to the horizontal (ie in the direction of the flowing reaction mass) - not shown in FIG. 2 - and may optionally contain internals such as lifting bars, baffle plates or a conveyor screw.

[0079] A possible design for the operation of such a rotary tube reactor is described in more detail below:

[0080] A stream of powdered or molten aminobenzoic acid is continuously metered into a horizontally or inclined rotary tube reactor at one end. The rotary tube reactor is heated, and the metered reactant is conveyed through the tube depending on the rotational speed and inclination of the rotary tube. The aminobenzoic acid decomposes into aniline and carbon dioxide, with the temperature in the rotary tube being selected such that both products are gaseous and continuously leave the reactor through an outlet at the downstream end of the rotary tube. In the process according to the invention, the rotary tube is partially filled; gaseous product formed during the reaction can therefore flow past the material flowing as a channel at the bottom of the tube to the gas outlet.Downstream of the gas outlet is a condenser whose operating temperature is selected to condense any entrained gaseous aminobenzoic acid as selectively as possible. This condensed stream is recycled to the inlet of the rotary tube reactor in a suitable manner. The remaining gaseous stream enters a processing stage where the target product, aniline, is separated from carbon dioxide, any water present, and any low-boiling impurities.In the channel of the material flowing downstream of the rotary tube, a composition gradient develops along the tube length depending on the reaction progress: While the material in the inlet region consists of solid and / or molten aminobenzoic acid, the liquid stream on the outlet side, possibly containing solid particles, will consist of high-boiling residue (possibly highly viscous) and a small proportion of liquid aminobenzoic acid and aniline. This stream can be treated as previously described for the stirred tank reactor. The feed stream of powdered or molten aminobenzoic acid to the rotary tube reactor must be selected such that the proportion of valuable product in the liquid residue is as low as possible, i.e., it must be adapted to the required residence time for complete reaction of the aminobenzoic acid and evaporation of the formed aniline.The interior of the rotary tube can be empty or equipped with internals, such as vanes that can improve transport, mixing, and heat transfer, or, for example, baffle plates that can increase the amount of reaction mixture present in the rotary tube (so-called hold-up). Optionally, a stream of inert gas (e.g., preheated nitrogen) can be added at the inlet of the rotary tube reactor to reduce the residence time of the gaseous product in the reactor.

[0081] Another reactor type suitable for a reaction process essentially free of backmixing is the so-called trough reactor (also called a conveyor trough reactor). This is a tubular reactor which, unlike the rotary tube reactor, is stationary. A conveyor screw rotates inside the reactor, which does not completely fill the cross-section of the reaction tube (the conveyor screw only fills the lower region of the reactor; only the gas phase is present in the upper region). Such a trough reactor is shown in FIG. 3. The reference numerals already used in connection with FIG. 1 have the same meaning as there. The remaining reference numerals have the following meaning:

[0082] The trough reactor can be inclined to the horizontal (i.e., in the direction of the flowing reaction mass) - not shown in FIG. 3. One possible embodiment of the operation of such a trough reactor is described in more detail below: A stream of powdered or molten aminobenzoic acid is continuously metered into a horizontally or inclined trough reactor at one end. The trough reactor is heated; the metered product is conveyed through the reactor depending on the speed of the conveyor screw and the inclination of the trough. The aminobenzoic acid decomposes to aniline and carbon dioxide, with the temperature in the trough reactor being selected such that both products are gaseous and continuously leave the reactor through an outlet at the top of the trough reactor.The trough reactor is partially filled so that the gaseous product produced during the reaction can flow past the material flowing as a channel at the bottom of the trough in the area of ​​the screw conveyor to the gas outlet. A condenser is located at the gas outlet, the temperature of which is selected so that any entrained gaseous aminobenzoic acid is condensed as selectively as possible and flows directly back into the trough reactor. The remaining gaseous stream enters a processing stage where the target product, aniline, is separated from carbon dioxide, any water present, and any low-boiling impurities.In the channel of material conveyed by the screw at the bottom of the trough reactor, a composition gradient develops along the length of the trough depending on the reaction progress: While the material in the inlet area consists of solid and / or molten aminobenzoic acid, the liquid stream on the outlet side, possibly containing solid particles, will consist of high-boiling residue (possibly highly viscous) and a small proportion of liquid aminobenzoic acid and aniline. This outlet stream can be treated as described above for the stirred tank reactor. The feed flow of powdered or molten aminobenzoic acid to the trough reactor must be selected so that the proportion of valuable product in the liquid residue is as low as possible, i.e., it must be adapted to the required residence time for complete reaction of the aminobenzoic acid and evaporation of the formed aniline.The conveyor screw of the trough reactor can have conveyor elements with different geometries along its length to influence residence time behavior and mass transfer, for example, different pitches or conveying directions of the screw elements. Optionally, a stream of inert gas (e.g., preheated nitrogen) can be added at the inlet of the trough reactor to reduce the residence time of the gaseous product in the reactor.

[0083] For all reactor types with essentially backmixing-free reaction, a mixture containing 0.1 mass% to 30 mass% of aniline, preferably 1.0 mass% to 7.5 mass%, based on the total mass of the mixture, is preferably continuously withdrawn from the reactor via the outlet for the liquid stream, which may contain solid particles.

[0084] For all continuously operated process regimes (i.e. regardless of whether operated with or without backmixing) of step (B), the mean residence time tv from the entry of an aminobenzoic acid molecule into the reactor to the removal of an aniline molecule formed therefrom via the gaseous stream from the reactor is from 1.00 min to 500 min, preferably 5.00 min to 120 min.

[0085] Step (C) of the process according to the invention comprises the condensation and, if appropriate, purification of the aniline withdrawn from the reactor in gaseous form. For this purpose, the gaseous stream withdrawn from the reactor, optionally after passing through a condenser (13 in the figures) as described above to separate any entrained aminobenzoic acid by selective condensation, passes through a condenser (not shown in the figures) operated in such a way that aniline condenses out of the gaseous stream, while carbon dioxide passes through it in gaseous form (possibly with the exception of small amounts dissolved in the condensed aniline). Condenser types known in the art can be used for this purpose. Particularly suitable designs are characterized by the avoidance of stagnant liquid and can be mechanically cleaned. A secondary circuit of a cooling medium can be used to dissipate the heat.In a preferred embodiment, evaporative cooling with water is implemented in order to be able to use the waste heat to generate steam.

[0086] Here too, as already described above for the condenser 13 for selective condensation of any entrained aminobenzoic acid, a (distillation or rectification) column can be connected upstream of the condenser.

[0087] The aniline thus obtained is already characterized by high purity, especially when, as described above, a (distillation or rectification) column is connected upstream of the condenser of step (C). If necessary, it can be further purified by distillation (in particular heteroazeotropic distillation). Methods for this are well known in the art and therefore require no further explanation here. Step (D) of the process according to the invention concerns the optional further conversion of the resulting aniline. Possible further conversions include, in particular, the following:

[0088] (1) The acid-catalyzed reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series;

[0089] (2) the acid-catalyzed reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series, followed by their reaction with phosgene to form di- and polyisocyanates of the diphenylmethane series; and

[0090] (3) the conversion of aniline to an azo compound.

[0091] The further reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series (D)(1) is known per se and can be carried out by any prior art process. The continuous or partially discontinuous preparation of di- and polyamines of the diphenylmethane series from aniline and formaldehyde is disclosed, for example, in EP 1 616 890 A1, US-A-5286760, EP-A-451442, and WO-A-99 / 40059. The reaction takes place under acid catalysis. Hydrochloric acid is preferably suitable as an acid catalyst.

[0092] The further reaction of the resulting di- and polyamines of the diphenylmethane series with phosgene to form di- and polyisocyanates of the diphenylmethane series (D)(2) is also known per se and can be carried out by any known process. Suitable processes are described, for example, in EP 2 077 150 B1, EP 1 616 857 A1, EP 1 873 142 A1, and EP 0 314 985 B1.

[0093] The conversion of the aniline obtained according to the invention into azo compounds, in particular into azo dyes (D)(3), can also be carried out by any known prior art process. Examples include the known preparation of aniline yellow (para-aminoazobenzene; CAS 493-5-7) or indigo (2,2'-bis(2,3-dihydro-3-oxomethylidene); CAS 482-89-3).

[0094] The invention is explained in more detail with reference to the following examples.

[0095] Anthranilic acid (AS, petrochemical): C7H7NO2, purity > 98%, Acros Organics

[0096] Anthranilic acid (AS, biogenic): C7H7NO2, purity: 98%, Covestro Deutschland AG

[0097] 2-Aminobenzanilide (AMD): C13H12N2O, purity 95%, but GmbH

[0098] HPLC: For HPLC analysis, an Agilent setup with UV detection (DAD, measured at 254 nm) was used. An Agilent column (Eclipse XDB-C18; 5 pm; 4.6 x 150 mm) was used for separation. A mixture of MeOH and buffer was used as the mobile phase (volume ratio MeOH:buffer = 40:60, buffer: 0.7 mL of 85% pA H3PO4 was diluted to a final volume of 1 L with HPLC-grade water, with pH adjusted to 3.0 with sodium hydroxide solution before final filling). The flow rate was 0.7 mL / min. The column oven was heated to 40 °C. The injection volume was 0.5 pL. The retention times of the individual components aniline (ANL), anthranilic acid (AS), and 2-aminobenzanilide (AMD) were: ANL = 2.6 min; AS = 5.2 min; amide = 14.9 min.

[0099] The peak areas are converted to area percent (area%). The quantification of the individual components in mass percent (mass%), based on the reaction mixture, was made possible by a previously performed calibration with pure substances. In addition to the mass composition, the conversion of anthranilic acid, the yield of aniline formed, the selectivity of aniline formation, and the selectivity for the formation of 2-aminobenzanilide are determined based on these values. of anthranilic acid under

[0100] The setup includes an 80 mL four-necked flask with a stir bar, a jacketed dropping funnel, a reflux condenser, and an inert gas connection (Ar). First, the dropping funnel is filled with the desired amount of solid AA at room temperature, and the entire apparatus is inertized with a constant Ar flow of 20 standard L / h. The apparatus is operated open at ambient pressure. The reflux condenser is cooled to 5 °C. After inerting, the thermostat of the dropping funnel is set to 155 °C, and a wait of 25 minutes is made until the AA has completely melted. At the same time, the reaction vessel is heated to 210 °C, and the transitions (reaction vessel - dropping funnel; reaction vessel - reflux condenser) are insulated. The AA is then continuously added to the reaction vessel over a specified period of time (ts). After continuous addition, stirring is continued for a specified period of time (ts), and the system is then shut down.The product mass of the reaction vessel is determined and characterized via HPLC analysis regarding AS, ANL, AMD composition.

[0101] AAV 2: Decarboxylation of anthranilic acid with gaseous discharge of the aniline formed (according to the invention)

[0102] The setup includes an 80 mL four-necked flask with a stir bar, a jacketed dropping funnel, a distillation bridge with a distillation vessel, and an inert gas connection (Ar). First, the dropping funnel is filled with the desired amount of solid AA at room temperature, and the entire apparatus is inertized with a constant Ar flow of 20 standard liters / h. The apparatus is operated open at ambient pressure. The distillation vessel is cooled to 5 °C. After inerting, the thermostat of the dropping funnel is set to 165 °C, and a wait of 25 minutes is made until the AA has completely melted. At the same time, the reaction vessel is heated to 210 °C, and the transitions (reaction vessel - dropping funnel; reaction vessel - distillation bridge) are insulated or trace heated. The AA is then continuously added to the reaction vessel over a specified period of time (ts).After continuous dosing, stirring is continued for a specified period (IR), and then the system is shut down. The product masses of the reaction and product vessels are determined, and the fractions are characterized by HPLC analysis for their AS, ANL, and AMD composition.

[0103] The experiments are summarized in the following tables. The following abbreviations are used:

[0104] V = comparison example

[0105] ANL = Aniline

[0106] AS = anthranilic acid

[0107] AMD = 2-aminobenzanilide Table 1: Decarboxylation of anthranilic acid to aniline. Reaction temperature T = 210 °C; inert gas flow (Ar) 20 Nl / h, 45 g anthranilic acid.

[0108] Table 1 (continued).

[0109] n to the tables:

[0110] [a] Mass distribution (numbers are mass-%) of the reaction mixture in the reaction or distillation vessel at t=t ge s, with t ge s = tz + tR;

[0111] [b] Mass fraction in % of the product mixture, based on the total mass of the products in the reaction and distillation vessel;

[0112] [c] Chemical conversion of anthranilic acid;

[0113] [d] Chemical yield of aniline;

[0114] [e] Selectivity to aniline or 2-aminobenzanilide;

[0115] [f] Chemical yield of aniline in % in the distillation vessel;

[0116] [g] Purity of aniline (determined from the mass distribution of ANL, AS and AMD at t=tR in the vessel in question);

[0117] [h] Mass balance of the reaction vessel or the sum of the reaction and distillation vessels.

[0118] As the examples demonstrate, the process according to the invention enables the conversion of aminobenzoic acid with high conversions and low by-product formation, leading to a high yield of aniline. The process according to the invention offers several advantages over the process without distillative product separation. For the same reaction time, a higher conversion of AS and thus a higher yield of ANL can be observed in the case of continuous distillative product removal. For the same conversion of AS, an increased ANL selectivity and thus a higher ANL yield can be observed in the case of continuous distillative product removal. An additional advantage is that the ANL is already obtained in high purity in the case of the process according to the invention and is therefore less prone to secondary reactions or subsequent yield losses in subsequent process steps.

Claims

1. A process for the production of aniline or an aniline derivative comprising the steps of: (A) Provision of aminobenzoic acid; (B) Decarboxylating aminobenzoic acid in a reactor, wherein the aminobenzoic acid (i) is introduced into the reactor as a solid, (ii) molten, or (iii) dissolved or suspended in a solvent and is reacted to form aniline and carbon dioxide at a reaction temperature in the range of 170 °C to 350 °C, the reaction being carried out at a reaction pressure at which the boiling point of aniline is reached or exceeded, such that a first, liquid phase, optionally containing solid particles, and a second, gaseous phase are formed in the reactor, with a gaseous stream containing aniline and carbon dioxide being discharged from the reactor; and (C) Condensing and, if necessary, purifying the aniline contained in the gaseous stream; and (D) optional, conversion of the aniline obtained in (C) to an aniline derivative.

2. The method according to claim 1, wherein the reaction of the aminobenzoic acid is carried out at a reaction pressure in the range of 0.10 bar to 10 bar.

3. A method according to claim 1 or 2, wherein during the reaction of the aminobenzoic acid in step (B) the aminobenzoic acid is continuously supplied to the reactor and aniline and carbon dioxide are continuously removed from the reactor.

4. The method according to claim 3, wherein the reactor is a stirred tank reactor with an inlet for the aminobenzoic acid, an outlet for the gaseous stream and an outlet for a liquid stream, optionally containing solid particles.

5. The method of claim 3, wherein the reactor comprises a reaction tube with an inlet for the aminobenzoic acid, an outlet for the gaseous stream and an outlet for a liquid stream, optionally containing solid particles.

6. Method according to claim 5, wherein the reaction tube is rotated about its longitudinal axis or is arranged in a fixed position, wherein a screw conveyor rotates in the reaction tube which does not completely fill the cross-section of the reaction tube.

7. A method according to claim 1 or 2, wherein the reaction of the aminobenzoic acid is carried out discontinuously in batches, wherein the aminobenzoic acid is placed in the reactor and / or added to the reactor over a period of time tz and, after addition of the total amount of a batch of aminobenzoic acid, it is reacted in the reactor for a reaction time tR at the reaction temperature and reaction pressure.

8. The method of claim 7, wherein the reactor is a stirred tank reactor.

9. Method according to one of the preceding claims, wherein the gaseous stream containing aniline and carbon dioxide passes through a condenser in step (B) for condensation of optionally aminobenzoic acid carried in the gaseous stream.

10. Method according to any one of claims 1 to 9, (a) in which ortho-aminobenzoic acid is provided in step (A) or (ß) in which para-aminobenzoic acid is provided in step (A).

11. The method of claim 10, wherein (a) Step (A) (i) the reaction of phthalimide or phthalic acid monoamide with an alkali metal hypohalide in basic medium followed by an acid treatment or (ii) the hydrogenation of 2-nitrobenzoic acid, or in which (β) Step (A) comprises (i) the reaction of terephthalic acid monoamide with an alkali metal hypohalide in a basic medium followed by acid treatment or (ii) the hydrogenation of 4-nitrobenzoic acid. A process according to any one of claims 1 to 10, wherein step (A) comprises the fermentation of a feedstock containing a fermentable carbon-containing compound and a nitrogen-containing compound in the presence of microorganisms. A process according to any one of claims 1 to 12, wherein (a) step (B) is carried out without the addition of a catalyst and without the addition of aniline; or in which (ß) Step (B) selected in the presence of a catalyst from (a) an aqueous mineral acid (such as, in particular, sulfuric acid, nitric acid, and hydrochloric acid), (b) a zeolite (in particular of type Y in the protonated form [H-form]), (c) a Si-Ti molecular sieve, (d) a hydroxyapatite, (e) hydrotalcite, (f) an ion exchange resin (in particular Amberlyst), and / or (g) an inorganic heterogeneous metal oxide catalyst containing a mass fraction of Al₂O₃ of 40.0% to 100% based on the total mass of the metal oxides, wherein the mass fraction of Al₂O₃ based on the total mass of the inorganic heterogeneous metal oxide catalyst is 25% to 100%; or in which (y) Step (B)(iii) is included, wherein the solvent comprises aniline and no catalyst is added.

14. A process according to any one of the preceding claims, comprising step (B)(iii) wherein at least 90% of the solvent remains in the first phase at the reaction temperature and pressure, wherein the solvent is not aniline.

15. A process according to any one of the preceding claims, wherein step (D) is carried out and comprises one of the following reactions: (1) Acid-catalyzed reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series; (2) Acid-catalyzed reaction of aniline with formaldehyde to form di- and polyamines of the diphenylmethane series, followed by their reaction with phosgene to form di- and polyisocyanates of the diphenylmethane series; or (3) Conversion of the aniline to an azo compound.

Images