Process for preparing toluylenediamine

Abstract

The present invention relates to a process for preparing toluylenediamine, the process comprising: hydrogenation of dinitrotoluene using hydrogen in the presence of a heterogeneous catalyst to produce toluylenediamine, forming a suspension of the heterogeneous catalyst in a liquid phase containing toluylenediamine and water, wherein at least some of the suspension is fed to a catalyst separation in which a liquid phase depleted of heterogeneous catalyst and a phase enriched with heterogeneous catalyst are obtained; continuing the hydrogenation in the presence of the phase enriched with heterogeneous catalyst; and processing the liquid phase depleted of heterogeneous catalyst in order to recover the toluylenediamine contained therein; wherein the dinitrotoluene used in the hydrogenation has a mass fraction of trinitrated compounds selected from the group consisting of 2,4,6-trinitrophenol, 4,5,6-trinitro-ortho-cresol, 2,4,6-trinitro-meta-cresol, 2,3,6-trinitro-para-cresol, 3,4,6-trinitro-ortho-cresol and 2,4,6-trinitrotoluene in the range from 0 ppm to 400 ppm, based on the total mass of the dinitrotoluene.

Description

[0001] 2024PF30062 - Abroad

[0002] - 1 -

[0003] PROCESS FOR THE PRODUCTION OF TOLUYLENEDIAMINE

[0004] The present invention relates to a process for the production of toluenediamine, comprising: hydrogenation of dinitrotoluene with hydrogen to toluenediamine in the presence of a heterogeneous catalyst, forming a suspension of the heterogeneous catalyst in a liquid phase containing toluenediamine and water, wherein at least a portion of the suspension is fed to a catalyst separation step, in which a liquid phase depleted of heterogeneous catalyst and a phase enriched with heterogeneous catalyst are obtained; continuation of the hydrogenation in the presence of the phase enriched with heterogeneous catalyst and work-up of the liquid phase depleted of heterogeneous catalyst to obtain the toluenediamine contained therein;wherein the dinitrotoluene used in the hydrogenation has a mass fraction of trinitrated compounds selected from the group consisting of 2,4,6-trinitrophenol, 4,5,6-trinitro-ortho-cresol, 2,4,6-trinitro-meta-cresol, 2,3,6-trinitro-para-cresol, 3,4,6-trinitro-ortho-cresol and 2,4,6-trinitrotoluene in the range of 0 ppm to 400 ppm, based on the total mass of the dinitrotoluene.

[0005] Organic amino compounds are an important starting material for the production of isocyanates. A significant example is toluenediamine (TDA), which is converted to toluene diisocyanate (TDI). TDI, in turn, is an important starting material for the production of polyurethanes, especially flexible polyurethane foams. The large-scale production of TDA begins with toluene, which is first nitrated to dinitrotoluene (DNT). The DNT obtained in this way is then converted to TDA in a hydrogenation reaction in the presence of catalysts (for example, certain Raney nickel catalysts as described in EP 0223035 Al). This process initially yields a hydrated crude product which, in addition to the target product TDA, also contains higher and lower boiling organic impurities (so-called high-boiling and low-boiling substances).Water is largely removed from this raw product, with ammonia removal (ammonia can be formed during the reaction) potentially preceding the water separation. This is followed by distillative work-up, including isomer separation and purification to separate the high-boiling and low-boiling components. Meta-TDA (a mixture of 2,4- and 2,6-TDA) is used in particular for polyurethane production.

[0006] The nitration of toluene to DNT can be carried out in one stage (without isolating the intermediate mononitrotoluene, MNT) or in two stages (nitration of toluene to MNT in a first stage and nitration of MNT to DNT in a second stage). Of particular industrial relevance is the two-stage isothermal nitration according to the so-called nitrating acid or mixed acid process, in which the toluene is nitrated with nitric acid in 2024PF30062 -Abroad

[0007] - 2 -

[0008] In the presence of sulfuric acid, the reaction is continuous in two isothermally operated reaction stages to form dinitrotoluene, whereby

[0009] a) the reaction mixture obtained in the second stage (nitration of MNT to DNT) is separated by phase separation and the waste acid obtained is re-strengthened with nitric acid, then mixed with toluene and fed back to the first stage (nitration of toluene to MNT), and

[0010] b) the reaction mixture of the first stage is separated in a separation stage into an organic phase containing mononitrotoluene and an aqueous phase containing predominantly sulfuric acid (“waste acid of the first stage”), after the reaction has taken place, and

[0011] c) the organic phase containing mononitrotoluene obtained in b) is fed to the second stage and the mononitrotoluene is reacted with nitric acid in the presence of sulfuric acid to form dinitrotoluene.

[0012] A suitable process is described, for example, in EP 1880989 Al. As also disclosed therein, to achieve commercially available specifications, the crude DNT is usually processed in downstream stages, primarily washing, and thus largely freed from dissolved sulfuric and nitric acid content as well as from by-products formed in the reaction stages, e.g., cresols and their degradation products. According to EP 1880989 Al, typical commercially available DNT products contain > 98.5 wt% DNT, < 0.1 wt% MNT, < 0.1 wt% TNT, and < 0.1 wt% of other by-products, based on the mass of the DNT product mixture.

[0013] US 2008 / 146847 describes a process for the production of TDA in which DNT is reacted with hydrogen in the presence of a catalyst, wherein the DNT used has a carbon dioxide content in physically dissolved or chemically bound form of no more than 0.175 mol%, based on the molar amount of DNT used. The DNT hydrogenation to TDA is carried out industrially in the liquid phase, using catalyst particles suspended in the liquid phase. These catalyst particles are separated from the product mixture and recycled back into the process. Besides filtration, sedimentation is a common method for catalyst separation. For example, US 6,423,872 B2 describes the hydrogenation of aromatic nitro compounds, particularly DNT, at a hydrogen pressure of 5 to 70 bar in the presence of a heterogeneous catalyst in a stirred tank reactor, followed by separation of the catalyst by filtration or settling (sedimentation).The separated catalyst, mixed with fresh catalyst, is reintroduced into the reaction. The document addresses the formation of solid 2024PF30062 - foreign.

[0014] - 3 -

[0015] Deposits form on the walls of the reactor, the settling tank, and / or peripheral equipment. The formation of such deposits hinders the reaction and complicates catalyst reuse, thus inevitably leading to increased catalyst consumption without countermeasures. US 6,423,872 B2 attributes the formation of such deposits to undesired catalyst reactions (formation of nickel aluminates) during long residence times in continuous processes. To solve this problem, the use of nickel catalysts with only very low aluminum contents of no more than 5.5 wt% is proposed. The document does not mention any other reasons for disruptions in the hydrogenation and increased catalyst consumption besides undesired catalyst reactions to nickel aluminates forming solid deposits.

[0016] It has now been found that disturbances in hydrogenation and increased catalyst consumption can have completely different causes than the formation of nickel aluminates described in US 6,423,872 B2, namely premature aging of the catalyst and incomplete separation of the catalyst, especially in the case of catalyst separation by sedimentation, both caused by the presence of trinitrated compounds as explained below.

[0017] If catalyst separation is disrupted, this can have serious consequences. In a process like the one described in US 6,423,872 B2, insufficient catalyst separation leads to an insufficient amount of catalyst being recycled back into the hydrogenation process if no countermeasures are taken. This can have serious consequences, including safety-related ones (accumulation of DNT in the hydrogenation reactor due to an insufficient amount of hydrogenation catalyst). While this can generally be countered by increasing the supply of fresh catalyst, this measure results in an overall increase in catalyst consumption and cannot be carried out indefinitely. Furthermore, inadequate catalyst separation leads to the entrainment of catalyst particles into the crude hydrogenation product and complicates its processing, for example, by causing blockages in filters, pipelines, and the like.This leads to the formation of deposits in distillation columns, especially on separating components such as packings, or to undesirable subsequent reactions. Solving this problem requires entirely different approaches than the chemical modification of the catalyst by minimizing its aluminum content, as described in US 6,423,872 B2. 2024PF30062 - Foreign.

[0018] -4 -

[0019] Therefore, there was a need for further improvements in the field of TDA production by hydrogenation of DNT in the presence of suspended catalysts. In particular, it would be desirable to ensure, through suitable measures, that the catalyst remains hydrogenation-active for as long as possible and that the catalyst removal proceeds as smoothly as possible.

[0020] Taking this need into account, the present invention relates to a process for the production of toluenediamine, comprising the following steps:

[0021] (A) Provision of dinitrotoluene;

[0022] (B) Hydrogenation, in particular continuous hydrogenation, of the dinitrotoluene from step (A) with hydrogen to toluenediamine in (at least) one hydrogenation reactor in the presence of a heterogeneous catalyst, forming a suspension of the heterogeneous catalyst in a liquid phase containing toluenediamine and water (namely water formed as a co-product of the hydrogenation and optionally further water introduced into the at least one hydrogenation reactor with the heterogeneous catalyst), wherein at least a part of the suspension is subjected to a catalyst separation, preferably sedimentation or cross-flow filtration, in particular sedimentation, in which a liquid phase depleted of heterogeneous catalyst and a phase enriched with heterogeneous catalyst, which in the case of sedimentation or cross-flow filtration is a suspension enriched with heterogeneous catalyst, are obtained;

[0023] Continuing the hydrogenation in the presence of the phase enriched with heterogeneous catalyst, preferably in the presence of the suspension enriched with heterogeneous catalyst; and

[0024] (C) Work-up of the liquid phase depleted with heterogeneous catalyst to obtain the toluenediamine contained therein;

[0025] wherein the dinitrotoluene provided in step (A) comprises a mass fraction of trinitrated compounds selected from the group consisting of (determined by high-performance liquid chromatography and gas chromatography using the method described below).

[0026] 2,4,6-Trinitrophenol (picric acid), 4,5,6-trinitro-ortho-cresol, 2,4,6-trinitro-metacresol, 2,3,6-trinitro-para-cresol, 3,4,6-trinitro-ortho-cresol and 2,4,6-trinitrotoluene in the range of 0 ppm to 400 ppm, preferably 0 ppm to 300 ppm, particularly preferably 0 ppm to 250 ppm, based on the total mass of the dinitrotoluene. 2024PF30062 - Abroad

[0027] -5 - It was found, quite unexpectedly, that certain impurities, namely the aforementioned trinitrated aromatic compounds (three nitro groups on an aromatic backbone), in excessively high concentrations in the DNT introduced for hydrogenation, have a negative impact on the catalyst lifetime and, particularly when sedimentation is used, on the separation of the catalyst from the suspension obtained in the hydrogenation. The total concentration of these compounds is crucial; it is insufficient to control only the concentration of individual compounds such as 2,4,6-trinitrotoluene (TNT). These phenomena were previously unknown. The trinitrated aromatic compounds listed above are those that can realistically be expected as impurities in DNT.Further isomers of the aforementioned trinitrated aromatic compounds are theoretically conceivable, but are regularly either not present at all in DNT or, at most, in completely negligible traces. Should the unlikely event occur that such trinitrated aromatic compounds not listed above are present in substantial proportions in DNT, it is preferred to limit their content using the measures described in more detail below. Preferably, the mass fraction of such further trinitrated aromatic compounds not listed above (determined by high-performance liquid chromatography and gas chromatography using the method described below) should not exceed 10 ppm, based on the total mass of the DNT.The catalyst separation process according to the invention serves to provide a liquid phase that is as completely free of catalyst as possible, which is fed to the work-up process for the isolation of the TDA contained therein, and a phase of the catalyst enriched (concentrated) with heterogeneous catalyst, which is returned to the hydrogenation reactor (in the case of catalyst separation outside the hydrogenation reactor) or retained in it (in the case of catalyst separation in the hydrogenation reactor, for example by a filter). Further DNT is fed into the hydrogenation reactor and the hydrogenation is continued.In the preferred continuous reaction process, during steady state (after a start-up phase for commissioning the hydrogenation reactor), a specific flow rate of the suspension of the heterogeneous catalyst in a liquid phase containing TDA and water is continuously withdrawn from the hydrogenation reactor and fed to the catalyst separation unit (if catalyst separation is performed outside the reactor), or the catalyst is retained in the hydrogenation reactor by suitable means (e.g., by means of a filter), so that the liquid phase depleted of heterogeneous catalyst is directly withdrawn from the hydrogenation reactor. The phase obtained in the catalyst separation unit, enriched with heterogeneous catalyst, is continuously recycled back into the hydrogenation reactor (if catalyst separation is performed outside the hydrogenation reactor) or remains in the hydrogenation reactor (if catalyst separation is performed outside the reactor).

[0028] - 6 - hydrogenation reactor), and a quantity of DNT, which (neglecting possible losses, e.g., due to by-product formation) corresponds to the quantity of TDA continuously fed for work-up (i.e., one mole of DNT per mole of TDA removed for work-up), is continuously fed into the hydrogenation reactor. In batch reactions for the production of discrete batches, the liquid phase containing TDA and water obtained in a single production run is completely fed to the catalyst separation.

[0029] The term heterogeneous catalyst-enriched phase refers to the catalyst-rich phase or fraction obtained in catalyst separation, for example (i) a filter cake, (ii) the solid phase settled in centrifugation, or (iii) a suspension concentrated with respect to the heterogeneous catalyst in a part of the liquid phase containing toluenediamine and water, as obtained in sedimentation or cross-flow filtration.

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

[0031] The attached illustrations show:

[0032] FIG. 1 shows the relationship between the time required for the deposition of the catalyst and the content of trinitrated compounds in the DNT;

[0033] FIG. 2 shows the relationship between the 2,4,6-trinitrotoluene (TNT) content in the DNT and the toluene mass flow rate supplied to the nitration; and FIG. 3 shows the relationship between the catalyst requirement in the hydrogenation and the content of trinitrated compounds in the DNT. 2024PF30062 - Abroad

[0034] - 7 -

[0035] The following is a brief summary of various possible embodiments of the invention:

[0036] In a first embodiment of the process according to the invention, which can be combined with all other embodiments, hydrogen and the dinitrotoluene from step (A) are continuously supplied to the (at least one) hydrogenation reactor, and the catalyst separation is carried out outside the hydrogenation reactor, wherein the part of the liquid phase containing toluenediamine and water to be freed from the heterogeneous catalyst is continuously removed from the (at least one) hydrogenation reactor, and the phase obtained in the catalyst separation, enriched with heterogeneous catalyst, which is a concentrated suspension (with respect to the heterogeneous catalyst) in the case of catalyst separation by sedimentation or cross-flow filtration, is continuously returned to the hydrogenation reactor.

[0037] In a second embodiment of the method according to the invention, which can be combined with all other embodiments, the hydrogenation is carried out at 50 °C to 250 °C, preferably at 100 °C to 200 °C.

[0038] In a third embodiment of the method according to the invention, which can be combined with all other embodiments, the hydrogenation is carried out at a pressure of 6.0 bar to 101 bar (measured in a gas space above the reacting mixture), preferably 10 bar to 30 bar.

[0039] In a fourth embodiment of the process according to the invention, which can be combined with all other embodiments, the heterogeneous catalyst comprises Pt, Pd, Rh, Ru, Ni, Co, Cu or mixtures thereof, optionally applied to a support material (preferably activated carbon, aluminum oxide or silicon dioxide).

[0040] In a fifth embodiment of the method according to the invention, which can be combined with all other embodiments, the heterogeneous catalyst comprises Raney nickel and is in particular a Raney nickel catalyst.

[0041] In a sixth embodiment of the process according to the invention, which can be combined with all other embodiments, the heterogeneous catalyst is added during hydrogenation, in particular as a suspension in water.

[0042] In a seventh embodiment of the process according to the invention, which can be combined with all other embodiments, provided that these do not exclude the use of an organic solvent in the hydrogenation, the hydrogenation is carried out in the presence of an organic solvent.

[0043] In an eighth embodiment of the method according to the invention, which can be combined with all other embodiments, provided that these do not have the use2024PF30062 -abroad

[0044] - 8 -

[0045] Since an organic solvent is required in the hydrogenation process, the hydrogenation is carried out in the absence of an organic solvent.

[0046] In a ninth embodiment of the method according to the invention, which can be combined with all other embodiments, step (A) comprises:

[0047] (I) (Double) nitration of toluene to dinitrotoluene using a mixture of sulfuric acid and nitric acid, wherein (after the second nitration) a two-phase product mixture containing an aqueous sulfuric acid phase and an organic dinitrotoluene phase is obtained;

[0048] (II) Separation of the aqueous sulfuric acid phase and the organic dinitrotoluene phase; and

[0049] (III) Washing of the organic dinitrotoluene phase, wherein the washing includes (at least) an alkaline washing stage using a base.

[0050] In a tenth embodiment of the process according to the invention, which is a particular embodiment of the ninth embodiment, step (A)(1) is carried out in one stage. In an eleventh embodiment of the process according to the invention, which is a further particular embodiment of the ninth embodiment, step (A)(1) is carried out in two stages, wherein in a first stage toluene is nitrated to mononitrotoluene with a mixture of sulfuric acid and nitric acid, and the mononitrotoluene is nitrated to dinitrotoluene in a second stage with further nitric acid in the presence of further sulfuric acid.

[0051] In a twelfth embodiment of the process according to the invention, which is a particular embodiment of the ninth to eleventh embodiments, in a normal operating state in step (A)(1) of the nitration, a toluene mass flow of ITITOIH.NENN is continuously supplied and a dinitrotoluene mass flow of ITIDNT.NENN is continuously withdrawn, wherein the toluene mass flow ITITOIH.NENN is divided (in particular uniformly) among n nitration reactors connected in parallel, wherein n is a natural number in the range of 2 or more, in particular from 2 to 10.

[0052] where, during times when only a toluene mass flow rate rriToiH, IST <——• rriToiH, NENN is supplied to the nitration in step (A)(1), the toluene mass flow rate ITITOIH ST (not n

[0053] evenly distributed among the n parallel-connected nitration reactors, but only among or n parallel-connected nitration reactors, where o is a natural number in the range from 1 to n-1 (and where, in particular, o is chosen such that the toluene mass flow rate supplied to each of the o parallel-connected nitration reactors deviates as little as possible from l / n-1).2024PF30062 -Abroad

[0054] - 9 -

[0055] In a thirteenth embodiment of the process according to the invention, which is a special embodiment of the ninth to twelfth embodiments, a molar ratio of total nitric acid to toluene used of 2.0 : 1 to 2.2 : 1, in particular of 2.0 : 1 to 2.1 : 1, is maintained in step (A)(1).

[0056] In a fourteenth embodiment of the process according to the invention, which is a particular embodiment of the ninth to thirteenth embodiments, the base is added in the (at least one) alkaline washing stage in step (III) in such an amount that a pH value (measured in the aqueous phase obtained after phase separation) in the range of 5.0 to 9.5, preferably 6.0 to 9.0, particularly preferably 7.5 to 9.0 is established.

[0057] In a fifteenth embodiment of the process according to the invention, which is a special embodiment of the ninth to fourteenth embodiments, the base is selected from an alkali metal or alkaline earth metal carbonate (in particular soda), an alkali metal or alkaline earth metal hydroxide (in particular sodium hydroxide) or ammonia.

[0058] In a sixteenth embodiment of the method according to the invention, which can be combined with all other embodiments, step (C) comprises a distillative separation of water and a distillative separation of ortho-toluenediamine (as well as organic by-components) and optionally also a (separate) separation of ammonia, which is in particular upstream of the water separation.

[0059] In a seventeenth embodiment of the method according to the invention, which can be combined with all other embodiments, step (C) comprises filtration and / or centrifugation, in particular prior to the first distillative separation according to the sixteenth embodiment.

[0060] The embodiments and further possible configurations of the invention briefly described above are explained in more detail below. All embodiments described above and the further configurations of the invention described below are, unless the context clearly indicates otherwise to a person skilled in the art or unless expressly stated otherwise, freely combinable with one another. 2024PF30062 - Abroad

[0061] - 10 -

[0062] PROVISION OF THE DNT

[0063] In step (A) of the process according to the invention, the DNT to be hydrogenated is provided. It is advantageous and preferred that the production of the DNT takes place in the same production facility (i.e., at the same location) as its hydrogenation in step (B). This allows the DNT to be transported to the hydrogenation site via pipelines. The production of DNT at a first production facility and its transport to a second production facility located further away from the first (at a different location) for the production of the TDA is, although not preferred, also possible and encompassed by the term "provision of DNT".

[0064] Regardless, the preparation of DNT is preferably carried out by (double) nitration of toluene with nitric acid in the presence of sulfuric acid. This double nitration can be carried out in one or two stages (in one step or in two steps). In the one-stage process, both nitro groups are introduced into the toluene parent material (under adiabatic conditions) without isolating the intermediate MNT. The process yields a two-phase product mixture comprising an aqueous acid phase (consisting essentially of sulfuric acid) and an organic dinitrotoluene phase (consisting essentially of DNT). Such a process is described, for example, in EP 0708076 A2.

[0065] In the two-stage process, toluene is nitrated to MNT in a first stage with a mixture of sulfuric and nitric acids (under isothermal conditions). This yields a first two-phase product mixture comprising an aqueous acid phase (consisting mainly of sulfuric acid) and an organic mononitrotoluene phase (consisting mainly of MNT). The acid phase is separated, and the MNT phase is fed to the second stage. There, the MNT formed in the first stage is nitrated to DNT with further nitric acid in the presence of further sulfuric acid (again under isothermal conditions). The second stage yields a second two-phase product mixture comprising an aqueous acid phase (consisting mainly of sulfuric acid) and an organic dinitrotoluene phase (consisting mainly of DNT). A suitable process is described in EP 1880989 Al.

[0066] Both processes have in common, therefore, that in one step (I), toluene is (double) nitrated to dinitrotoluene using a mixture of sulfuric and nitric acids, whereby after the introduction of the second nitro group (i.e., in the two-stage process, after the second stage), a two-phase product mixture is obtained, containing an aqueous sulfuric acid phase and an organic dinitrotoluene phase. In both processes, the organic phase is preferably dispersed in the aqueous phase(s) during the nitration(s), which is achieved by sufficiently large phase ratios (mass ratio of aqueous to organic phase) and intensive nitration.

[0067] - 11 -

[0068] Thorough mixing (by static mixers – particularly in the single-stage process – or dynamic mixers – particularly in the two-stage process) is ensured. In both processes, a molar ratio of total nitric acid to toluene of 2.0:1 to 2.2:1, particularly 2.0:1 to 2.1:1, is preferably maintained in step (I). In the two-stage process, a molar ratio of nitric acid to nitrifiable aromatic (toluene in the first stage, mononitrotoluene in the second stage) of 1.0:1 to 1.1:1 is particularly maintained in each stage. The basic procedure for both processes is known from the prior art and therefore need not be described in detail here. In particular, the aforementioned upper limits for the molar ratio of nitric acid to nitrifiable aromatic should not be exceeded if possible, in order to keep the content of critical trinitrated compounds as low as possible.

[0069] The two-phase product mixture obtained in step (I) is separated in step (II) into the aqueous sulfuric acid phase and the organic dinitrotoluene phase. This can be done using commercially available phase separation apparatus (separators, decanters) or centrifuges. It is recommended to analyze the aqueous sulfuric acid phase for nitric acid at least periodically. In the case of the two-stage process, this applies to the aqueous sulfuric acid phase of each stage. The measured value can then be compared with the known molar ratio of nitric acid to nitrifiable aromatic. In case of a discrepancy, the input flow rates of nitric acid and / or nitrifiable aromatic can be adjusted accordingly.

[0070] Finally, in step (III), the organic dinitrotoluene phase is processed by means of a single- or multi-stage washing process, wherein the washing process includes (at least) one alkaline washing stage using a base. The washing process preferably comprises a first wash with water (so-called acidic wash for separating the majority of acid residues in the crude DNT), a second wash with base (so-called alkaline wash for neutralizing the remaining acidic components), and a third wash with water (so-called neutral wash), wherein each of these three washes can again be carried out in one or more stages (i.e., comprising several washing stages connected in series). In the at least one alkaline washing stage, the base is preferably added in such an amount that a pH value (measured in the aqueous phase obtained after phase separation) in the range of 5.0 to 9.5, preferably 6.0 to 9.0, and particularly preferably 7.5 to 9.0, is achieved.Alkaline washing is important for the separation of the aforementioned critical cresols. Maintaining the described pH values ​​contributes to their sufficient removal in the DNT (Dissolved Nucleus Tribulus). An alkali metal or alkaline earth metal carbonate (especially soda ash) is preferably used as the base.

[0071] - 12 -

[0072] Alkali metal or alkaline earth metal hydroxide (especially sodium hydroxide) or ammonia is used.

[0073] The large-scale production of chemical products often takes place in several parallel reaction lines (also called reaction trains). This avoids the construction of excessively large reactors that are difficult to control. In such reaction lines, several reactors (as well as the associated peripheral equipment such as heat exchangers, pumps, etc.) are connected in parallel, meaning that the total quantity of reactants is distributed (especially evenly) among the available reactors. Parallel reaction lines can also lead to a common workup sequence. Such parallel operation of reactors can also be advantageous in the production of DNT (dissolved nitrogen).

[0074] In large-scale production, the entire reactor system (whether a single reactor or several operating in parallel) is designed to convert a specific quantity of toluene (TolH) within a specific timeframe. The resulting quantity of DNT is often referred to as the nominal capacity of a production plant, encompassing the reactor(s). Production at nominal capacity is also known as the standard operating condition. In standard operating condition, therefore, in step (I) of the nitration process, a toluene mass flow rate of ITITOIH, NENN is continuously supplied, and a dinitrotoluene mass flow rate of ITIDNT.NENN is continuously removed.

[0075] When several nitration reactors are operated in parallel, each fed with the starting material toluene (their number being denoted by n, where n is a natural number of 2 or more, in particular from 2 to 10), the total toluene mass flow rate, ITITOIH (in normal operating conditions: ITITOIH, NENN), supplied to the nitration process is distributed (in particular, evenly) among these n parallel-connected nitration reactors. In the case of the two-stage process described above, there are two nitration reactors for each of the n production lines, one for the first stage and one for the second, which are themselves connected in series (so that the total number of all nitration reactors in the two-stage process is 2n).The toluene is divided between the n parallel nitration reactors of the first stage, each of which is followed by a nitration reactor for the second stage (where a phase separation apparatus for separating the aqueous acid phase obtained in the first stage is located between the nitration reactor of the first stage and the nitration reactor of the second stage).

[0076] It can occasionally happen that a production plant operates at less than its nominal capacity, for example, because demand for the product (here DNT) is temporarily below expectations. During such periods, only a toluene mass flow rate ITITOIH, ACTUAL < ITITOIH, NOMINAL is supplied to the nitration process in step (I), and a correspondingly reduced mass flow rate of DNT is withdrawn from the nitration process. [The last sentence appears to be incomplete and possibly nonsensical. It has been omitted from the translation.]

[0077] - 13 -

[0078] Mass flow rate ITITOIH ST significantly below ITITOIH.NENN, i.e., ITITOIH ST is at most rr)ToiH,NENN, the following possibilities arise:

[0079] n

[0080] a) All n nitration reactors can continue to operate with a corresponding reduction in the toluene mass flow rate supplied to each nitration reactor. b) At least one of the n nitration reactors is taken out of service, so that only o nitration reactors remain in operation, where o is a natural number in the range of 1 to 77⁻¹.

[0081] It was found, quite unexpectedly, that the choice of the aforementioned options affects the content of critical trinitrated compounds in the produced DNT. This is particularly significant for TNT, as its content cannot be reduced by alkaline scrubbing. It was found that alternative b) mentioned above has a positive effect on the content of critical trinitrated compounds in the DNT and is therefore preferable to alternative a). Without being bound to any specific theory, it is suggested that this is due to the fact that, in alternative b), the toluene mass flow rate supplied to each of the nitration reactors is closer to the toluene mass flow rate during normal operation, which also results in a residence time that is closer to that of normal operation.In other words, in alternative b), the reaction conditions are closer to the conditions for which the production plant was designed (= optimized), which results in reduced by-product formation compared to alternative a). It is particularly advantageous to select the number of nitration reactors in operation such that the toluene mass flow rate supplied to each of the parallel-connected nitration reactors deviates as little as possible from (l / z) • ITITOIH.NENN.

[0082] ANALYSIS METHOD FOR DETERMINING THE CONTENT OF TRINITRITED COMPOUNDS

[0083] Regardless of the exact design of step (A), it is essential to the invention that the provided DNT meets the requirements with regard to the previously defined critical trinitrated compounds, i.e., that the mass fraction of trinitrated compounds is selected from the group consisting of

[0084] 2,4,6-Trinitrophenol (picric acid), 4,5,6-Trinitro-ortho-cresol, 2,4,6-Trinitro-meta-cresol, 2,3,6-Trinitro-para-cresol, 3,4,6-Trinitro-ortho-cresol and 2,4,6-Trinitrotoluene

[0085] The concentration of DNT in the provided DNT, based on its total mass, is in the range of 0 ppm to 400 ppm, preferably 0 ppm to 300 ppm, and particularly preferably 0 ppm to 250 ppm. This depends on the total mass fraction of all these compounds. 2024PF30062 - Abroad

[0086] - 14 -

[0087] To verify whether the provided DNT meets these requirements, all methods known in the prior art can generally be used. In case of doubt, i.e., in the event of significant deviations between different methods, the analytical method described below is decisive:

[0088] (I) A representative sample of the DNT to be tested is melted at 80 °C. While stirring, 1.0 ml of the melted DNT at 80 °C is taken and added to 2.5 ml of a 5% sodium carbonate solution (in distilled water) heated to 50 °C. The resulting DNT-sodium carbonate mixture is stirred at 50 °C. After stopping the stirring, one waits until the phases separate. Then, 1.0 ml of the supernatant aqueous phase is extracted with 200 pl of dichloromethane and centrifuged.

[0089] It is recommended to optimize the exact conditions of step (I) based on a recovery rate of at least one of the four cresols mentioned above: 4,5,6-trinitro-ortho-cresol, 2,4,6-trinitro-meta-cresol, 2,3,6-trinitro-para-cresol, and 3,4,6-trinitro-ortho-cresol. This is achieved by either synthesizing at least one of the cresols or isolating a mixture of several or all cresols from the alkaline wash water as described below. The cresol or cresol mixture thus obtained is dissolved in molten DNT, which has been freed from all acidic compounds by alkaline washing, in such an amount that a mass fraction of the cresol or cresol mixture of approximately 250 ppm is reached, based on the total mass of the DNT, with the exact value being recorded. This cresol-DNT mixture is then analyzed as described here.Should the measured value of cresols be significantly lower than the recorded value, the stirring speed and / or duration of the soda treatment should be adjusted, in particular reduced, until no significant deviation occurs.

[0090] (II) 500 pl of the aqueous phase obtained are diluted with 500 pl of sodium hydrogen phosphate solution (5% in distilled water). The diluted sample is measured by high-performance liquid chromatography (HPLC) using a UV / VIS detector (diode array detector; DAD) (injection volume 5 pl, oven temperature 40 °C, flow rate 0.8 mL / min). Two eluent mixtures, A and B, are used:

[0091] Eluent mixture A: Mixture of water and acetonitrile in a mass ratio of 95 : 5;

[0092] 1.6 g / L NaH₂PÜ₄ at a concentration of 1.6 g / L and tetrabutylammonium hydrogen sulfate at a concentration of 1.6 g / L. Eluent mixture B: mixture of water and acetonitrile in a mass ratio of 40 : 60.

[0093] NaH2PÜ4 at a concentration of 1.6 g / L and tetrabutylammonium hydrogen sulfate at a concentration of 1.6 g / L. 2024PF30062 - Abroad

[0094] - 15 -

[0095] A silica gel-based HPLC column (nonpolar, monomeric C18 (octadecyl) modification, endcapped, 16% carbon) with a length of 250 mm, an inner diameter of 4 mm, and a particle size of 5 pm is used. A Eurospher 100 C185 / Lim HPLC column is suitable. However, any HPLC column capable of separating picric acid and the aforementioned cresols can be used; it is not necessary to use exactly the same chromatography column as described here to determine the content of trinitrated compounds relevant to the present invention. The eluent mixtures A and B are used with the following gradient profile:

[0096] Table 1: Gradient profile of eluent mixtures A and B

[0097]

[0098] Signals with a retention time in the range of 37 to 42 minutes are assigned to picric acid (2,4,6-trinitrophenol) and the cresols (i.e., 4,5,6-trinitro-ortho-cresol, 2,4,6-trinitro-meta-cresol, 2,3,6-trinitro-para-cresol, and 3,4,6-trinitro-ortho-cresol) and used for their quantification. For this purpose, calibration measurements are performed with pure substances. The pure substances can be prepared and purified as described in the literature (see especially New J. Chem., 2014, 38, 3699-3707), semi-preparatively isolated from the wash water of the alkaline washing step described above as described below, or purchased commercially. The purity of the calibration substances (whether intentionally prepared or isolated) is determined by means of 1 H-NMR spectroscopy, acid number determination and determination of water content according to the Karl Fischer method.

[0099] Semi-preparative isolation from the wash water of the alkaline washing stage is carried out by HPLC under the conditions described in (II). Depending on the HPLC system used, scale-up may be necessary; the steps required for this are well-known in the field. Insufficient separation performance of the HPLC can lead to contamination of the calibration substance by foreign isomers. This problem can be addressed by calibrating synthesized pure isomers and quantifying their proportion in the isolated mixture, so that even 2024PF30062 -Ausland

[0100] - 16 - Isomer mixtures with defined isomer ratios can be used for calibration. 1 H-NMR spectroscopy can also be used as an absolute method to determine the isomer ratio of different calibration substances or the proportion of impurities.

[0101] (III) The dichloromethane phase obtained by centrifugation as described in (I) is analyzed for its TNT content by gas chromatography (GC). A polysiloxane column (14% cyanopropyl phenyl methylpolysiloxane) with a length of 60 m, a diameter of 0.320 mm, and a film thickness of 0.25 pm is used. Agilent DB-1701 acid is suitable. However, any GC column capable of cleanly detecting TNT (sufficiently separated from any other components that may be present) is suitable. The injector temperature is 250 °C and the heating rate is as follows: start at 80 °C for 1 min, then heat to 150 °C at 50 °C / min, hold at 150 °C for 14 min, then heat to 200 °C at 25 °C / min, hold at 200 °C for 5 min. Dichloromethane is used as the solvent (100 pL sample to 2.5 mL dichloromethane). Quantification is performed by comparison with calibration measurements of pure substances.The total content of critical trinitrated compounds can be easily determined from the analysis results of the aqueous phase and the dichloromethane phase.

[0102] It is recommended to identify optimized operating parameters in preliminary trials (particularly regarding the distribution of the toluene mass flow across different reactors, the selection of a suitable molar ratio of nitric acid to total toluene used, and the design of the scrubbing process, especially the alkaline scrubbing; see the above explanations regarding these points) by means of which the required DNT quality can be reliably ensured. Once such operating parameters are established, analytical control of the DNT quality (whereby, in case of doubt, the analytical method mentioned above is decisive) can be omitted or limited to random samples and cases of unforeseen deviations from the established operating parameters.

[0103] In the event that the DNT should not meet the aforementioned criteria despite all measures, for example, a further alkaline wash can be carried out and / or such DNT can be blended with DNT of higher purity. 2024PF30062 - Abroad

[0104] - 17 -

[0105] HYDRATION OF DNTZU TDA

[0106] In step (B) of the process according to the invention, the DNT from step (A) is hydrogenated to TDA with hydrogen, optionally in the presence of an inert gas (i.e., a gas that does not react with reactants, any intermediates, and end products under the prevailing pressure and temperature conditions, at least not to a significant extent), in (at least) one hydrogenation reactor. Preferred reaction conditions are described below.

[0107] The hydrogenation process is carried out continuously. During continuous operation, hydrogen and the dinitrotoluene from step (A) are continuously supplied to the hydrogenation reactor.

[0108] The portion of the liquid phase containing toluenediamine and water, which is to be freed from the heterogeneous catalyst, is continuously removed from the hydrogenation reactor, freed from the catalyst, and the resulting phase enriched with heterogeneous catalyst (for example, a suspension concentrated with respect to the heterogeneous catalyst) is continuously returned to the hydrogenation reactor (in the case of catalyst separation outside the hydrogenation reactor).

[0109] or

[0110] The catalyst is retained in the hydrogenation reactor and the liquid phase, depleted of heterogeneous catalyst, is directly removed from it (during catalyst separation in the hydrogenation reactor).

[0111] The hydrogenation takes place in the liquid phase with a heterogeneous catalyst suspended in the liquid phase. The heterogeneous catalyst is preferably introduced into the hydrogenation reactor as a suspension in water. Suitable catalysts include hydrogenation catalysts known from the prior art, preferably those in which the heterogeneous catalyst comprises Pt, Pd, Rh, Ru, Ni, Co, Cu, or mixtures thereof, optionally applied to a support material (preferably activated carbon, aluminum oxide, or silicon dioxide). Raney nickel is particularly preferred as the catalyst. The Raney nickel can be doped, in particular with iron and / or chromium. Raney nickel catalysts as described in EP 1512459 Al can also be used. Such catalysts contain 0 to 15 wt% aluminum, 50 to 100 wt% nickel, 0 to 50 wt% iron, and 0 to 30 wt% cerium, cerium mischmetal, vanadium, niobium, tantalum, chromium, molybdenum and / or manganese.Catalysts consisting of 0 to 10 wt% aluminum, 60 to 100 wt% nickel, 0 to 30 wt% iron, and 0 to 30 wt% cerium, cerium mischmetal, vanadium, niobium, tantalum, chromium, molybdenum, and / or manganese are preferred. Catalysts consisting of 0 to 10 wt% aluminum, 70 to 100 wt% nickel, 0 to 20 wt% iron, and 0 to 2024PF30062 -Ausland are particularly preferred.

[0112] - 18 -

[0113] 25 wt% cerium, cerium mischmetal, vanadium, niobium, tantalum, chromium, molybdenum and / or manganese. The wt% values ​​refer to the total mass of the Raney nickel catalyst.

[0114] The concentration of the catalyst in the liquid phase present in the hydrogenation reactor is preferably 0.01 wt% to 30 wt%, particularly preferably 0.01 wt% to 20 wt%, and most preferably 0.50 wt% to 10 wt%, based on the total mass of the liquid phase. If mixtures of hydrogen and inert gases are used, preferred inert gases are ammonia, noble gases, and / or nitrogen. Hydrogen or the mixture of hydrogen and inert gases is introduced in such a way that a constant pressure is maintained in the hydrogenation reactor; that is, the amount of hydrogen added corresponds to the sum of the hydrogen consumed chemically and, optionally, the hydrogen discharged as a purge stream.In the case of using a mixture of hydrogen and inert gases as a hydrogenation reagent, the ratio of hydrogen to inert gas in the supplied hydrogenation reagent is preferably increased successively in order to prevent the reactor contents from becoming depleted of hydrogen.

[0115] In the process according to the invention, hydrogen is preferably used in excess of the amount required for the hydrogenation of the nitro groups to amino groups. In particular, the excess of hydrogen relative to the amount of substance required for the hydrogenation of the nitro groups to amino groups is at least 0.01%, preferably at least 0.10%, and at most 10%.

[0116] Optionally, inert organic solvents such as alcohols like methanol, propanol, or isopropanol, or ethers like dixoane or tetrahydrofuran, can be used under the reaction conditions. To increase the economic efficiency of the process, a low solvent concentration is generally advantageous. This is typically between 1.0 wt% and 50 wt%, preferably between 20 wt% and 35 wt%, in each case based on the total mass of the liquid phase. However, the avoidance of organic solvents is preferred.

[0117] Furthermore, in the process according to the invention, 0.10% to 10%, preferably 0.20% to 5.0% of the mass flow of hydrogen used can be removed (purge hydrogen). This removal prevents the accumulation of inert compounds or gaseous byproducts.

[0118] The hydrogenation preferably takes place at temperatures of 50 °C to 250 °C, particularly preferably 100 °C to 200 °C, and at a pressure (measured in a gas space above the reacting mixture) of 6.0 bar to 101 bar, preferably 10 bar to 30 bar. 2024PF30062 - Abroad

[0119] - 19 -

[0120] In the hydrogenation reactor, a liquid phase containing TDA and water with a heterogeneous catalyst suspended therein is formed. In a preferred embodiment, at least a portion of the liquid phase containing TDA and water with the heterogeneous catalyst suspended therein is removed from the hydrogenation reactor and freed from the heterogeneous catalyst by sedimentation or cross-flow filtration, particularly preferably by sedimentation. After separation of the catalyst-free portion of the liquid phase by sedimentation or cross-flow filtration, a suspension concentrated with respect to the heterogeneous catalyst remains, which is returned to the hydrogenation reactor. The hydrogenation is continued by adding further dinitrotoluene and hydrogen, optionally (for example, as a result of progressive catalyst inactivation) by adding fresh catalyst, particularly as a suspension in water.

[0121] A suitable hydrogenation reactor for carrying out step (B) is, for example, a stirred tank reactor. Other suitable reactor types include, in particular, trickling film reactors and bubble column reactors.

[0122] Processing for the extraction of toluene diamond

[0123] The portion of the liquid phase containing toluenediamine and water, freed from the catalyst, preferably by sedimentation or cross-flow filtration, particularly preferably by sedimentation, is processed outside the hydrogenation reactor to recover the toluenediamine contained therein in step (C). This can be carried out according to any method known in the prior art. In particular, this processing can include the separation of water and the separation of ortho-toluenediamine (as well as other high- and low-boiling by-products) by distillation or distillations, optionally in conjunction with a separate ammonia separation (carried out in a separate column), which is particularly upstream of the water separation. Suitable methods are well known in the prior art and therefore need not be described in detail here.Such distillation steps may be preceded by an additional solid-liquid separation by filtration and / or centrifugation in order to separate any residual catalyst carried over from the preceding catalyst separation in step (B). 2024PF30062 - Abroad.

[0124] - 20 - Examples:

[0125] Example 1: Dependence of the settling rate on the total concentration of trinitrated compounds

[0126] For examples aa-d, the sedimentation rate was determined using a sedimentation scale.

[0127] A sedimentation balance is a special type of balance with a plate immersed in the suspension being measured. This plate measures the mass of the particles that have just settled on the plate. With a balance equipped with, for example, a serial interface, it is possible to perform quasi-continuous measurements and thus obtain curves that represent the sedimentation rate. Such a sedimentation curve starts at "0" and then shows the mass measured on the submerged plate as sedimentation progresses, asymptotically approaching the final value. The sedimentation balance used comprised the following components:

[0128] • Measuring container: A transparent cylinder or container that holds the suspension to be tested.

[0129] • Immersion body (or measuring plate): A disc or plate that is immersed in the suspension. It is suspended from a sensitive balance.

[0130] • Precision scale with interface to a data acquisition system: Continuously measures the weight of the particles deposited on the immersion body.

[0131] • Data acquisition system: For continuous recording of measured values.

[0132] The sedimentation behavior of the catalyst in a suspension in water was examined for the measurement. Example 1a contained no trinitrated compounds. All other examples contained a mixture of all the above-mentioned trinitrocresols (originating from the wash water of the alkaline washing stage of a DNT production, quantified using the method described above), specifically (relative to the total mass of the aqueous solution without catalyst) 94 ppm in example 1b, 188 ppm in example 1c, and 940 ppm in example 1ld (for comparison). The results are shown in FIG. 1. The ordinate axis represents the mass of catalyst deposited at a given time, relative to the mass of catalyst deposited at the end of the respective experiment.

[0133]

[0134] The time until settling, in minutes (t / min), is plotted on the abscissa. 2024PF30062 - Abroad

[0135] - 21 - Example 2: Dependence of the formation of trinitrated compounds on the mass flow rate of toluene supplied to the nitration

[0136] A toluene stream was fed into a continuously operated nitration reactor designed for operation with a toluene mass flow rate HITO1H,NENN and was fed with lower toluene streams (at a constant ratio of toluene to nitric acid to sulfuric acid) to represent the conditions during part-load operation.

[0137] The results are shown in FIG. 2. The ordinate axis shows the concentration of trinitrotoluene in the alkaline-washed DNT end product in ppm, CTNT / ppm. The abscissa axis shows the normalized toluene mass flow rate, riiToiH.isT / riiToiH.NENN. It was found that the proportion of trinitrotoluene formed increases with the smaller the toluene flow rate supplied to the hydrogenation reactor. This is significant because, unlike cresols, the TNT content cannot be reduced by optimizing the washing process.

[0138] Example 3: Dependence of catalyst consumption in hydrogenation on the concentration of trinitrated compounds in the DNT fed to the hydrogenation. A continuously operated hydrogenation reactor (stirred tank reactor) was charged with DNT containing varying mass fractions of trinitrated compounds of the type mentioned. A heterogeneous Raney nickel catalyst was used, and the DNT was reacted with hydrogen in the molten state without solvent at 150 °C. A portion of the intensively stirred suspension was removed from the hydrogenation reactor and subjected to catalyst separation by sedimentation. The resulting phase, enriched with heterogeneous catalyst (a suspension concentrated with respect to the heterogeneous catalyst in TDA and water), was recycled back into the hydrogenation reactor.In cases of excessive catalyst loss, indicated by catalyst entrainment and increased pressure drop across a downstream filter, fresh catalyst in a water suspension was added. The average amount of fresh catalyst required over time is a measure of catalyst consumption. The results are shown in FIG. 3. The x-axis represents the total concentration of critical trinitrated compounds (TNV) in ppm, LCTNV / ppm. The y-axis represents the catalyst consumption normalized to a standard case, CC, CC / CCstandard. The "standard case" is defined as catalyst consumption at a TNV content of 220 ppm. 2024PF30062 - Foreign.

[0139] - 22 -

[0140] Example 4: Influence of the concentration of trinitrated compounds on the catalyst lifetime

[0141] In addition to the effects of the trinitrated compound content on catalyst separation, particularly the catalyst's sedimentation behavior and the associated problems, as described above, the presence of elevated levels of the trinitrated compounds defined above also has negative effects on catalyst lifetime that are independent of catalyst separation and therefore not caused by sedimentation behavior. If the hydrogenation of DNT is carried out continuously at 150 °C in a stirred reactor without the addition of fresh catalyst, it can be seen that the catalyst lifetime decreases significantly upon the addition of trinitrated compounds. Table 2 below shows the results. Catalyst lifetime is defined as the period during which the hydrogenation can be carried out with complete conversion of DNT.The catalyst lifetime achieved using DNT with a trinitrated compound content of 220 ppm, without any further added trinitrated compounds, was set to 100% and the other catalyst lifetimes were given relative to this.

[0142] Table 2: Results of Example 4 - Catalyst lifetimes at different concentrations of trinitrated compounds. Values ​​in ppm are mass fractions relative to the total mass of DNT used.

[0143]

Claims

2024PF30062 - Abroad - 23 - 1. Process for the production of toluenediamine, comprising (A) Provision of dinitrotoluene; (B) Hydrogenation of the dinitrotoluene from step (A) with hydrogen to toluenediamine in a hydrogenation reactor in the presence of a heterogeneous catalyst to form a suspension of the heterogeneous catalyst in a liquid phase containing toluenediamine and water, wherein at least a part of the suspension is fed to a catalyst separation, yielding a liquid phase depleted of heterogeneous catalyst and a phase enriched with heterogeneous catalyst; Continuing the hydrogenation in the presence of the phase enriched with heterogeneous catalyst; and (C) Work-up of the liquid phase depleted of heterogeneous catalyst to obtain the toluenediamine contained therein; wherein the dinitrotoluene provided in step (A) is a mass fraction of trinitrated compounds selected from the group consisting of 2,4,6-Trinitrophenol (picric acid), 4,5,6-Trinitro-ortho-cresol, 2,4,6-Trinitro-meta-cresol, 2,3,6-Trinitro-para-cresol, 3,4,6-Trinitro-ortho-cresol and 2,4,6-Trinitrotoluene in the range of 0 ppm to 400 ppm, based on the total mass of dinitrotoluene.

2. The process of claim 1, wherein hydrogen and the dinitrotoluene from step (A) are continuously supplied to the hydrogenation reactor and the catalyst separation takes place outside the hydrogenation reactor, wherein the portion of the liquid phase containing toluenediamine and water to be freed from the heterogeneous catalyst is continuously removed from the hydrogenation reactor and the phase obtained in the catalyst separation, enriched with heterogeneous catalyst, is continuously recycled back into the hydrogenation reactor.

3. The process of claim 1 or 2, wherein the hydrogenation is carried out at 50 °C to 250 °C.

4. A method according to any one of claims 1 to 3, wherein the hydrogenation is carried out at a pressure of 6.0 bar to 101 bar. 2024PF30062 - Abroad - 24 - 5. A method according to any one of claims 1 to 4, wherein the heterogeneous catalyst comprises Pt, Pd, Rh, Ru, Ni, Co, Cu or mixtures thereof, optionally applied to a support material.

6. A method according to any one of claims 1 to 5, wherein the heterogeneous catalyst comprises Raney nickel.

7. Method according to any one of claims 1 to 6, wherein the heterogeneous catalyst is added during hydrogenation.

8. Method according to any one of claims 1 to 7, wherein step (A) comprises: (I) Nitration of toluene to dinitrotoluene using a mixture of sulfuric acid and nitric acid, yielding a two-phase product mixture containing an aqueous sulfuric acid phase and an organic dinitrotoluene phase; (II) Separation of the aqueous sulfuric acid phase and the organic dinitrotoluene phase; and (III) Washing of the organic dinitrotoluene phase, wherein the washing includes an alkaline washing stage using a base.

9. The method of claim 8, wherein in a normal operating state in step (A)(1) of the nitration a toluene mass flow of ITITOIH.NENN is continuously supplied and a dinitrotoluene mass flow of ITIDNT.NENN is continuously withdrawn, wherein the toluene mass flow ITITOIH.NENN is divided among n parallel-connected nitration reactors, wherein n is a natural number in the range of 2 or more, in particular from 2 to 10, where, in times when only a toluene mass flow is supplied to the nitration in step (A)(1), the toluene mass flow 'n' rtiToiH sT is distributed on or n parallel connected nitration reactors, where o is a natural number in the range of 1 to / 7-1.

10. Method according to claim s or 9, wherein in step (A)(1) a molar ratio of total nitric acid to toluene of 2.0 :1 to 2.2 : 1 is maintained.

11. A method according to any one of claims 8 to 10, wherein in the alkaline washing stage in step (III) the base is added in such an amount that a measured pH value in the range of 5.0 to 9.5 is achieved. 2024PF30062 - Abroad - 25 - 12. Method according to any one of claims 8 to 11, wherein the base is selected from an alkali metal or alkaline earth metal carbonate, an alkali metal or alkaline earth metal hydroxide or ammonia.

13. A method according to any one of claims 1 to 12, wherein the catalyst separation takes place outside the hydrogenation reactor by sedimentation or cross-flow filtration and the phase enriched with heterogeneous catalyst is a suspension concentrated with respect to the heterogeneous catalyst in a part of the liquid phase containing toluenediamine and water.

14. The method of claim 13, wherein the catalyst separation is carried out by sedimentation.

15. Method according to any one of claims 1 to 14, wherein step (C) comprises filtration and / or centrifugation.

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