Process for the treatment of a substance mixture containing aromatic amines, in particular a substance mixture of crude anilines

Abstract

The present invention relates to a process for treating a substance mixture comprising an aromatic amine, in particular a crude aniline substance mixture. In particular, the present invention relates to a process for treating a substance mixture comprising an aromatic amine, wherein the aromatic amine is aniline or 2,4-diaminotoluene, preferably aniline, wherein the substance mixture is a first substance mixture and comprises the aromatic amine and a compound having a higher boiling point than the aromatic amine, the process comprising the steps: I) distillative separation of the first substance mixture in a first distillation unit (110, 1130) to separate at least partially the aromatic amine, thereby additionally obtaining a first bottoms product, and discharging the first bottoms product from the first distillation unit (110, 1130). The bottoms product from the first distillation unit (110, 1130) is diluted after discharge with condensed overhead product from a distillation unit different from the first distillation unit and / or with a composition comprising methanol.

Description

[0001] This patent application is a divisional application of the parent application with the same title, which has the same application number 201380023422.4 and was filed on April 29, 2013. Technical Field

[0002] This invention relates to a method for processing a mixture of substances comprising an aromatic amine, wherein the mixture is a first mixture comprising an aromatic amine and a compound having a boiling point higher than that of the aromatic amine. The method comprises the steps of: I) distilling the first mixture in a first distillation unit to at least partially separate the aromatic amine, thereby additionally obtaining a first bottoms product, which is discharged from the first distillation unit. This bottoms product can then be diluted with waste material that would otherwise be generated during the production operation, thereby reducing the loss of aromatic amines in the bottoms product. According to the invention, the aromatic amine is aniline or 2,4-diaminotoluene, preferably aniline. Background Technology

[0003] Aromatic amines are important intermediates that must be produced inexpensively and on a large scale. Aromatic amine production facilities are therefore typically designed to achieve extremely high production capacities. These facilities ensure high productivity through extremely long reaction cycles and uninterrupted operation between the start-up and shutdown processes of hydrogenation for the regeneration of the hydrogenation catalyst.

[0004] The main application of 2,4-diaminotoluene is in the production of toluene diisocyanate (TDI). Industrially, it is produced through the hydrogenation of 2,4-dinitrotoluene.

[0005] The primary application of aniline is in the production of methylene diphenyl diamine (MDA), which is used to produce methylene diphenyl diisocyanate (MDI). Aniline is typically produced on an industrial scale by the catalytic hydrogenation of nitrobenzene using hydrogen. Reaction methods described in EP 0 944 578 A2 (isothermal operation) and EP 0 696 574 B1, EP 0 696 573 B1, and EP 1 882681 A1 (adiabatic operation) are particularly preferred. The production of MDA is described in numerous patents and publications (see, for example, HJ Twitchett, Chem. Soc. Rev. 3(2), 209 (1974), MV Moore in: Kirk-Othmer Encycl. Chem. Technol., 3rd edition, New York, 2, 338-348 (1978)).

[0006] The common feature of the isothermal process used to produce aniline is that the raw material nitrobenzene is vaporized at high temperature in a hydrogen stream.

[0007] The reaction is typically carried out by feeding a gaseous nitrobenzene / hydrogen mixture into a hydrogenation reactor, where it is reacted at high temperature and atmospheric pressure over a fixed-bed catalyst, optionally with a subsequent supplementary reactor (Nachreaktor).

[0008] The released heat of reaction is extracted from the reactor via a heat exchanger and is typically used to produce heating steam.

[0009] The reaction products, aniline and water, leave the reactor in gaseous form and are condensed from the hydrogen stream through a multi-stage condenser. Excess hydrogen is recycled, replenished with fresh hydrogen, and then vaporized together with nitrobenzene and introduced as a mixture into the hydrogenation reactor.

[0010] Hydrogen contains gaseous impurities due to this cycle operation. To remove these impurities, a sub-stream is extracted from the hydrogen cycle and incinerated in a thermal exhaust gas purification process.

[0011] The condensed reaction products are separated into an organic phase (crude aniline) and an aqueous phase (aniline-water), which are then subjected to further processing. Crude aniline also contains water and dissolved organic byproducts, which are separated by distillation.

[0012] First, low-boiling minor components (e.g., cyclohexylamine, cyclohexanone, benzene) are distilled off via the top of the column, and water is distilled off in the side stream as an aniline-water azeotrope. This side stream is two-phase and is returned to the aforementioned phase separation.

[0013] The low-boiling-point minor component, which also contains aniline, is removed from the top of the column and can be used directly in the incineration unit or condensed first and then incinerated together with other residues.

[0014] The bottom product (aniline + high-boiling-point substances) undergoes high-boiling-point byproduct removal (e.g., N-cyclohexylaniline, N,N-diphenylamine, phenol) in the second distillation column. Pure aniline is then distilled off via the top of the column. The high-boiling-point substances are enriched at the bottom of the column and further concentrated in the third distillation column (residue column).

[0015] Aniline is recovered at the top of the residue column and fed into the second column along with the bottom product from the first column. The bottom product from the residue column is transferred to a residue container. Here, the residual aniline acts as a solvent to maintain the pumpability of the residue. Furthermore, the residue is stored at high temperatures to avoid precipitation or excessive viscosity. High-boiling-point substances, along with the residual aniline acting as a diluent, are supplied from the residue container to incineration.

[0016] The dissolved aniline in the water separated during phase separation is removed by distillation and sent as wastewater to the plant's biological wastewater treatment. Aniline is distilled out as an azeotrope with water and returned to the aforementioned phase separation process.

[0017] All stages of the process for producing aniline are carried out in a continuous operation mode.

[0018] On the one hand, the quality of the hydrogenation process for aromatic nitro compounds is determined by the quality of the product. On the other hand, the quality of the hydrogenation process is determined by whether the entire process can operate continuously without significant production interruptions. The cessation of hydrogenation, the regeneration of the hydrogenation catalyst, and the restart of the hydrogenation process are generally referred to as the steady-state process in the hydrogenation cycle.

[0019] Because all stages of this aniline production process are carried out continuously during the hydrogenation cycle, the post-processing of crude aniline should also operate without failure. Finally, achieving a high yield of the desired product is also important, which means avoiding byproducts in the reaction and minimizing production losses in the unit. Such losses occur, for example, during product distillation, because the high-boiling minor components can only be concentrated to a certain extent at the bottom of the column to prevent the residue from solidifying or partially precipitating and forming unwanted precipitates. A significant proportion of the product is therefore always incinerated along with the minor components.

[0020] EP 0 794 170 A1 discloses a method for separating high-boiling substances during the production of diaminotoluene. Crude, dehydrated diaminotoluene is fed into a distillation unit comprising a packed column with a circulating evaporator for the bottom product. In one embodiment ( Figure 1 The packed tower has a falling film evaporator arranged downstream therefrom, into which the bottom discharge of the packed tower is fed. In another embodiment ( Figure 2 In this configuration, a falling film evaporator is positioned upstream of the packed column. Vapor from the falling film evaporator is fed into the packed column. In both cases, the aim is to minimize the loss of valuable product (m-diaminotoluene) along with the high-boiling residue using the falling film evaporator. In both cases, the bottom product of the falling film evaporator (consisting primarily of high-boiling residue) is mixed with the condensed o-diaminotoluene stream taken from the top of the packed column.

[0021] EP 0 696 574 B1 discloses in Examples 9 and 10 a method for diluting the bottom product of a distillation column with an aniline-rich phase obtained by distilling a nitrobenzene hydrogenation product comprising reaction water in a distillation column and diluting the bottom product of the distillation column with a condensate of the top product of the same distillation column.

[0022] EP 1 005 888 B1 describes a rinsing apparatus for removing residue from the bottom of an evaporator and its use in the post-distillation treatment of saline solutions. The disadvantages are that the rinsing agent used inevitably incurs costs, which must then be expensively incinerated. Furthermore, this rinsing apparatus is unsuitable when the bottom of the column is predominantly hot, thus requiring the use of high-boiling-point solvents or when the bottom must be cooled to prevent the rinsing agent from vaporizing. Water is preferred in this method, but its suitability as a washing agent for organic residues is limited. Moreover, in practice, it is not always possible to prevent the washing agent from entering the column and impairing the quality of the top product and / or further post-treatment of the top product. Summary of the Invention

[0023] Therefore, the object of this invention is to provide a method to ensure the smooth operation of the post-treatment tower while minimizing aniline loss.

[0024] According to the present invention, this objective is achieved by a method for processing a mixture of substances containing an aromatic amine, wherein the aromatic amine is aniline or 2,4-diaminotoluene.

[0025] The mixture is a first mixture comprising an aromatic amine (i.e., aniline or 2,4-diaminotoluene) and compounds with boiling points higher than the aromatic amine. Preferably, the first mixture is dehydrated, wherein the dehydration is achieved by phase separation and / or distillation.

[0026] The method includes the following steps:

[0027] I) The first mixture of substances is separated by distillation in the first distillation unit, at least partially separating the aromatic amine, thereby obtaining a first bottom product and discharging the first bottom product from the first distillation unit;

[0028] The bottom product from the first distillation unit is diluted after discharge with condensed top product from a distillation unit different from the first distillation unit and / or with a composition containing methanol.

[0029] The advantage of this method according to the invention is that, due to dilution, the concentration of the desired aromatic amine in the residue (the bottom product from the first distillation unit) can be reduced, since the amine is no longer needed as a solvent. The high-boiling-point residue can therefore be further concentrated at the bottom of the column, thus increasing the amine yield. Furthermore, the energy-consuming heating of the residue container and the commonly used pipe tracing can be omitted.

[0030] Within the scope of this invention, a "distillation unit" includes a distillation column and associated peripheral equipment, such as an evaporator, which may also be integrated into the distillation column. The first distillation unit may, for example, be a purification distillation column, particularly an aniline purification distillation column. Furthermore, the first distillation unit may be used in conjunction with other distillation units, thereby constructing it as a high-boiling-point column at the end of a multi-stage distillation process. Although the requirements for such a high-boiling-point column are high due to physical boundary conditions (vacuum, temperature, viscosity), advantages arise because the entire stream of aromatic amines is no longer distilled in this column, thus allowing for a smaller, more technically complex apparatus.

[0031] Advantageously, the bottom product is discharged into a container and then diluted there. However, dilution can also be carried out in a pipe located outside the first distillation unit.

[0032] The condensed overhead product from the distillation unit may be obtained from the first distillation unit and / or from a distillation unit different from the first distillation unit.

[0033] The residue (bottom product) is kept liquid, on the one hand by the remaining amine and on the other hand by a sufficient amount of additionally introduced diluent (a methanol-containing composition and / or a low-boiling point produced as the top product of a distillation unit different from the first distillation unit). This also prevents clogging in the pipes and the incinerator. This balance is appropriate because the methanol-containing composition and / or the low-boiling point (which are particularly derived from integrated polyisocyanate-verbund (e.g., MDA operation) and which would otherwise have had to be removed) now enable amine recovery. Within the scope of this invention, the term "low-boiling point" preferably refers to a substance or mixture of substances having a boiling point of ≥ 30°C to ≤ 220°C, preferably ≥ 50°C to ≤ 197°C, particularly preferably ≥ 50°C to ≤ 185°C, and most particularly preferably ≥ 60°C to < 100°C at 1013 mbar.

[0034] Other possible sources of this diluent are low-boiling components separated from amine distillation, aliphatic-rich waste streams from the nitrobenzene process (see DE 10 2009 005324 A1), and low-boiling components separated from the TDA process (e.g., 1,3-diamino-4-methylcyclohexane).

[0035] When low-boiling-point substances and / or methanol-water (e.g., from MDA production) are mixed into the residue container to dilute the residue (bottom product from the first distillation unit), the following advantages occur:

[0036] i) The amine concentration in the residue can be reduced through the dilution effect.

[0037] ii) The high-boiling-point residue can therefore be further concentrated at the bottom of the column, thereby increasing the amine yield.

[0038] iii) Keep the residue liquid by using sufficient low-boiling-point substances and / or methanol, thereby preventing clogging of the spray gun of the thermal exhaust gas purifier (TAP).

[0039] iv) In addition, energy is saved because the residue can be stored at a lower temperature and the pipe tracing can be omitted.

[0040] v) The waste disposal balance is appropriate because the liquid that would otherwise have had to be disposed of was used.

[0041] vi) Because this dilution only affects the residue container, it does not impair distillation.

[0042] Embodiments of the present invention are described below. They can be combined in any way, unless it is clearly apparent from the text that such combinations would be contrary to this.

[0043] When the production of aromatic amines by gas-phase hydrogenation is mentioned exemplarily below, the method of the present invention is of course also applicable to any mixture of substances containing aromatic amines and produced in different ways, that is, particularly applicable to those mixtures of substances containing aromatic amines produced by liquid-phase methods or those whose feedstocks are reacted in a catalytic fluidized bed.

[0044] In one embodiment of the method of the present invention, the method further includes steps Ia) and Ib), wherein Ia) and Ib) are performed prior to I).

[0045] Ia) A second mixture of substances is provided, wherein the second mixture of substances comprises an aromatic amine, a compound having a boiling point lower than that of the aromatic amine, and a compound having a boiling point higher than that of the aromatic amine, and the content of the aromatic amine is different from the content of the aromatic amine in the first mixture of substances;

[0046] Ib) The second mixture of substances is distilled and separated in an upstream distillation unit, separating compounds with boiling points lower than the aromatic amine as the top product, thereby obtaining the aromatic amine as a side stream and the first mixture of substances as the bottom product. The bottom product yields the mixture of substances to be processed in the method of the present invention, which of course also contains the aromatic amine. In this case, the first distillation unit of the method of the present invention is preferably a residue column.

[0047] In another embodiment of the method of the present invention, the method further includes steps IIa), IIb), and III), wherein IIa) and IIb) are performed before III), and III) is performed before I):

[0048] IIa) A second mixture of substances is provided, wherein the second mixture of substances comprises the aromatic amine, a compound with a boiling point lower than that of the aromatic amine, and a compound with a boiling point higher than that of the aromatic amine, and the content of the aromatic amine is different from the content of the aromatic amine in the first mixture of substances;

[0049] IIb) The second mixture of substances is separated by distillation in a second distillation unit to separate compounds with boiling points lower than the aromatic amine as the top product of the column, thereby obtaining a bottom product containing the aromatic amine.

[0050] III) In the third distillation unit, the bottom product from the second distillation unit is distilled and separated, at least partially separating the aromatic amine as the top product, thereby obtaining the first mixture of substances as the bottom product.

[0051] Therefore, this embodiment produces the following sequence of steps: IIa), IIb), III), I). It is also clear that the names "first distillation unit," "second distillation unit," and "third distillation unit" do not represent the order of these distillation units in the method of the present invention. Rather, the second distillation unit may be a low-boiling column, followed by a third distillation unit as an amine purification column (particularly an aniline purification column), which is connected to the first distillation unit as a high-boiling column.

[0052] In a preferred embodiment of the method of the present invention, the content of aromatic amines in the bottom product from the first distillation unit is ≥ 5% by weight to ≤ 70% by weight, particularly preferably ≥ 10% by weight to ≤ 45% by weight, based on the total weight of the bottom product in each case. This is understood to refer to the content of aromatic amines in the bottom product after discharge and before dilution.

[0053] According to the invention, the bottom product from the first distillation unit, after being discharged, is diluted with the top product from a distillation unit different from the first distillation unit and / or with a composition containing methanol. In a preferred embodiment of the method of the invention, the bottom product from the first distillation unit, after being discharged, is diluted with the top product from a distillation unit different from the first distillation unit and / or with a composition containing methanol such that the resulting mixture has a dynamic viscosity at 20°C of ≥ 0.3 mPas to ≤ 1000 mPas, preferably ≥ 0.5 mPas to ≤ 100 mPas, particularly preferably ≥ 1 mPas to ≤ 50 mPas, and most particularly preferably ≥ 1 mPas to ≤ 10 mPas. Here, this viscosity is measured using a falling ball viscometer according to DIN 53015 / ISO 12058.

[0054] The condensed overhead product from a distillation unit different from the first distillation unit is preferably single-phase at the temperature at which the bottom product from the first distillation unit is diluted after discharge, i.e., containing only water up to the saturation limit, thereby avoiding spontaneous demixing into an aqueous and organic phase. In this way, the diluted bottom product from the first distillation unit also preferably remains single-phase. In another embodiment of the method of the invention, the condensed overhead product from a distillation unit different from the first distillation unit therefore preferably contains ≥ 80% by weight of the total overhead product. < 100% by weight of low-boiling-point substances and ≥ 0% by weight to < 20% by weight of water. The overhead product of this condensation is particularly preferably composed of the above-mentioned proportions of low-boiling-point substances and water.

[0055] In another embodiment of the method of the present invention, the composition containing methanol is a composition containing methanol and water obtained by a process for producing methylene diphenyl diamine (MDA).

[0056] In the production of MDA, a composition called methanol-water is produced. The plants producing aniline and MDA are typically located very close to each other because they are part of the MDI production chain. The transport route of methanol-water from MDA to aniline is therefore very short and can be done via pipeline. Methanol-water is produced during the reaction in the MDA process.

[0057] EP 1 616 890 A1 describes the acidic condensation of aromatic amines and formaldehyde to form MDA. In the absence of an acidic catalyst, formaldehyde—industrially available formaldehyde containing methanol for stabilization—is first condensed with aniline to form a so-called acetal amine and water. The rearrangement to form MDA is acidically catalyzed in the first step to p- and o-aminobenzylaniline. The aminobenzylaniline rearranges in the second step to produce MDA. After the reaction produces the acetal amine, at least some water and all methanol are first removed from the acetal amine in the form of so-called methanol-water, then the acetal amine is mixed with an acidic catalyst, and the resulting acidic reaction mixture is further reacted at a temperature of 20°C to 100°C. Here, the water content is 0% to 20% by weight.

[0058] In another embodiment of the method of the present invention, the methanol-containing composition comprises ≥ 20% by weight to ≤ 95% by weight of methanol based on the total weight of the methanol-containing composition. This proportion is preferably ≥ 50% by weight to ≤ 80% by weight of methanol based on the total weight of the methanol-containing composition. Furthermore, it is preferred that the remainder of the composition contains water and technically unavoidable impurities, particularly salts, etc.

[0059] In another embodiment of the method of the invention, the flow rate of the methanol-containing composition is selected such that the theoretical flow rate of pure methanol is ≥ 30% by weight based on the flow meter of the bottom product discharged from the first distillation unit. This flow rate is preferably ≥ 40% by weight.

[0060] In another embodiment of the method of the invention, it is preferable to dilute only the bottom product from the first distillation unit with a methanol-containing composition, i.e., completely discarding the condensed overhead product fed into the other distillation unit. This is particularly desirable when a sufficient quantity of the methanol-containing composition can be supplied from a nearby MDA facility. This embodiment is also preferred when the addition of the condensed overhead product from the other distillation unit results in spontaneous phase separation of the diluted bottom product from the first distillation unit.

[0061] In another embodiment of the method of the present invention, the bottom product from the third distillation unit is incinerated after dilution. Attached Figure Description

[0062] The invention will be explained in more detail with the aid of the following figures and embodiments, but is not limited thereto.

[0063] Figure 1 The apparatus and method for reprocessing crude products from aniline production are illustrated schematically.

[0064] Figure 2 The illustration schematically shows another apparatus and another method for post-processing the crude product from aniline production. Detailed Implementation Plan

[0065] According to Figure 1 In this process, crude aniline from the production unit / intermediate storage unit (flow 200) and / or from the phase separation vessel 100 (flow 210) arrives at the first distillation unit 110, which is configured as an aniline purification distillation column. An aqueous alkali, preferably an aqueous sodium hydroxide solution (flow 220), may be added if necessary. The purification distillation column 110 operates under reduced pressure; the necessary vaporization energy can be supplied by a steam-heated circulating evaporator. The required reduced pressure is generated using a liquid ring pump. Aniline water serves as the working fluid for the vacuum pump.

[0066] A portion of the pure aniline is introduced into the tower as reflux using a pure aniline pump. The remainder is discharged as product after cooling (feed flow 230).

[0067] The low-boiling-point distillation product is taken out of column 110 as overhead stream 240 and partially condensed. The organic aniline-rich portion of the condensate is returned to the top of the column via phase separator 120. The aqueous portion of the condensate is returned to phase separation vessel 100 as feed stream 250.

[0068] Concentrated high-boiling-point substances remain at the bottom of the column. They are discharged as feed stream 260 and collected in residue receiver 140. Here, they are diluted with methanol-water from the MDA operation (feed stream 270) and optionally sent to heat utilization (feed stream 280) along with low-boiling-point substances.

[0069] The aqueous phase separated in phase separation vessel 100 contains dissolved aniline and is introduced as feed stream 290 into a distillation unit configured as stripping column 150. The overhead product from this distillation contains an azeotrope of water and aniline and can subsequently be returned to phase separation vessel 100 as feed stream 300. At the bottom of the column, water with aniline removed as much as possible is taken out of the process as wastewater (feed stream 310).

[0070] According to Figure 2 In this process, crude aniline from the production unit / intermediate storage unit (stream 1200) and / or from the phase separation vessel 1100 (stream 1210) arrives at a column referred to in the terminology of this invention as the second distillation unit 1110, which acts as a distillation column or dehydration column for separating low-boiling-point compounds. The dehydration column 1110 operates at atmospheric pressure. The necessary vaporization energy can be supplied by a circulating evaporator heated by steam. The water / aniline azeotrope is enriched on the intermediate trays, and the mixture of water, aniline, and low-boiling-point compounds is enriched at the top of the column. The top product is condensed in a condenser and returned to the top of the column; the uncondensed portion is removed as waste gas.

[0071] The water / aniline azeotrope is taken out of column 1110 as a side stream 1220 and returned to separation vessel 1100 for phase separation.

[0072] The crude aniline at the bottom of column 1110, having had low-boiling-point substances and water removed as much as possible, is supplied as feed stream 1230 to another column, referred to in the terminology of this invention as the third distillation unit 1120, where it is further fractionated. Aniline is enriched at the top of this refining distillation column 1120, while high-boiling-point substances are enriched at the bottom. The pure aniline vapor from the top of this column is condensed.

[0073] The purification distillation column 1120 operates under reduced pressure; the necessary vaporization energy can be supplied by a steam-heated circulating evaporator. The collected pure aniline is introduced as a reflux portion to the top of the column using a pure aniline pump.

[0074] The bottoms of the purification distillation column 1120, enriched with high-boiling-point substances, are fed as stream 1240 into a residue column 1130, referred to in the terminology of this invention as the first distillation unit (residue distillation), for further concentration. The residue column 1130 also operates under reduced pressure. The necessary vaporization energy can be supplied by a falling film evaporator heated by steam. Aniline vapor passes through the top of this column and condenses in a condenser. A portion of the condensate is introduced as reflux into the top of the column by means of a distillate pump. Depending on quality, the remaining condensate can be discharged via a heat exchanger or mixed as stream 1250 into the feed of the pure aniline column 1120.

[0075] Concentrated high-boiling-point substances remain at the bottom of the column. They are discharged as stream 1260 and collected in residue receiver 1140. Here, they are diluted with methanol-water from the MDA operation (stream 1270) and optionally sent to heat utilization (stream 1280) along with other low-boiling-point substances.

[0076] The aqueous phase separated in phase separation vessel 1100 contains dissolved aniline and is introduced as stream 1290 into the fourth distillation unit configured as stripping column 1150. The overhead product from this distillation contains an azeotrope of water and aniline and can subsequently be returned to phase separation vessel 1100 as stream 1300. At the bottom of the column, water with aniline removed as much as possible is removed from the process as wastewater (stream 1310).

[0077] Example:

[0078] Example 1 (Comparative Example): Typical aniline loss (328 tons / year)

[0079] This is how the post-treatment unit, connected to the aniline process, consists of a low-boiling-point column, a pure aniline column, and a residue column. Figure 2 The residue was stored at 35°C and then removed by incineration. Relevant characteristic data are reproduced in Table 1.

[0080] Table 1:

[0081] Flow rate of aniline to residue tower (flow 1240) Proportion of high-boiling-point substances Discharge at the bottom of the tower (1260) Aniline loss 800 kg / h 5% 80 kg / h 40 kg / h

[0082] Example 2 (Comparative Example): Reduced aniline loss (theoretically 56 tons / year) and the resulting blockage of pipes and spray guns in TAP.

[0083] This is how the post-treatment unit, connected to the aniline process, consists of a low-boiling-point column, a pure aniline column, and a residue column. Figure 2The residue was stored at 120°C and then removed by incineration, with a residual aniline content of 30% established at the bottom of the residue tower. The residue discharged from the bottom of the tower was stored at 120°C and then removed by incineration. During this process, although the pipes leading to incineration were heated, deposits occurred in these pipes and blockages occurred in the incineration unit's spray guns. The process had to be frequently interrupted to clean the slag collector located on the suction side of the residue pump and the spray guns in the incineration unit. Heating of the residue container was cut off during these cleaning operations. An increase in viscosity occurred during the cooling of the residue mixture, rendering the mixture no longer pumpable. Relevant characteristic data are reproduced in Table 2.

[0084] Table 2:

[0085] Flow rate of aniline to residue tower (flow 1240) Proportion of high-boiling-point substances Discharge at the bottom of the tower (1260) Aniline loss 800 kg / h 5 % 57 kg / h 17 kg / h

[0086] Example 3 (An embodiment of the present invention): Dilute the residue with methanol in a container.

[0087] This is how the post-treatment unit, connected to the aniline process, consists of a low-boiling-point column, a pure aniline column, and a residue column. Figure 2 The residue was prepared to establish a residual aniline content of approximately 30% by weight at the bottom of the residue tower. The residue discharged from the bottom of the tower was stored at 35°C and diluted with approximately 0.6 times the amount (mass flow rate) of methanol-water (72% by weight) from the adjacent methylene diphenyl diamine (MDA) operation. No clogging or sedimentation issues were observed in the disposal of the residue treated in this manner. Relevant characteristic data are reproduced in Table 3.

[0088] Table 3:

[0089] Flow rate of aniline to residue tower (flow 1240) Proportion of high-boiling-point substances Discharge at the bottom of the tower (1260) Add methanol to water (1270). Aniline loss 800 kg / h 5 % 57 kg / h 35 kg / h 17 kg / h

Claims

1. A method for processing a mixture of substances containing aniline, wherein the mixture of substances is a first mixture and contains aniline and a compound with a boiling point higher than aniline. The method includes the following steps: I) The first mixture of substances is separated by distillation in the first distillation unit (110, 1130), at least partially separating aniline, thereby obtaining a first bottom product, and discharging the first bottom product from the first distillation unit (110, 1130); Its features are, The bottom product from the first distillation unit (110, 1130) is diluted with a composition containing methanol after discharge and then incinerated. The aniline content in the bottom product from the first distillation unit (110, 1130) is ≥ 10% by weight to ≤ 45% by weight. The methanol-containing composition comprises ≥ 20% by weight to ≤ 95% by weight of methanol. The flow rate of the methanol-containing composition is selected such that the calculated flow rate of pure methanol is ≥ 30% by weight, based on the flow meter of the bottom product discharged from the first distillation unit (110, 1130), and The methanol-containing composition is a methanol- and water-containing composition obtained by a method for producing methylene diphenyl diamine.

2. The method according to claim 1, It further includes steps Ia) and Ib), wherein Ia) and Ib) are performed before I). Ia) A second mixture of substances is provided, wherein the second mixture of substances comprises aniline, a compound with a boiling point lower than that of aniline and a compound with a boiling point higher than that of aniline, and the content of aniline is different from the content of aniline in the first mixture of substances; Ib) The second mixture is distilled in the upstream distillation unit to separate compounds with boiling points lower than aniline as the top product, thereby obtaining aniline as the side stream and the first mixture as the bottom product.

3. The method according to claim 1, It further includes steps IIa), IIb), and III), wherein IIa) and IIb) are performed before III), and III) is performed before I): IIa) A second mixture of substances is provided, wherein the second mixture of substances comprises aniline, a compound with a boiling point lower than that of aniline, and a compound with a boiling point higher than that of aniline, and the content of aniline is different from the content of aniline in the first mixture of substances; IIb) The second mixture of substances is separated by distillation in the second distillation unit (1110) to separate compounds with boiling points lower than aniline as the top product of the column, thereby obtaining a bottom product containing aniline. III) In the third distillation unit (1120), the bottom product from the second distillation unit is distilled and separated, at least partially separating aniline as the top product, thereby obtaining the first mixture as the bottom product.

4. The method according to any one of claims 1 to 3, wherein the bottom product from the first distillation unit (110, 1130) is diluted with a composition containing methanol after discharge so that the resulting mixture has a viscosity at 20°C of ≥ 0.3 mPas to ≤ 1000 mPas.

5. The process according to any one of claims 1 to 3, wherein the column bottoms from the first distillation unit (110, 1130) are diluted after discharge only with a composition comprising methanol.

Images