Method for refining aniline

Abstract

The present invention relates to a process for purifying aniline, comprising the following steps: a) providing a crude aniline fraction; b) extracting the crude aniline fraction with an aqueous extractant containing an alkali metal hydroxide in a concentration range of 0.009% to 2.05% by mass and an alkali metal salt different from the alkali metal hydroxide in a concentration range of 2.40% to 25.0% by mass, relative to the total mass of the aqueous extractant, to obtain, after phase separation, an organic aniline phase and an aqueous aminophenolate phase; and c) distilling the organic aniline phase from step b) to obtain a purified aniline stream, a gaseous stream containing organic impurities having a boiling point lower than that of aniline, and a liquid stream containing aniline and organic impurities having a boiling point higher than that of aniline.

Description

[Technical field]

[0001] The present invention relates to a process for the purification of aniline, comprising the steps of: a) providing a crude aniline fraction; b) extracting the crude aniline fraction with an aqueous extractant containing an alkali metal hydroxide in a concentration range of 0.009% to 2.05% by weight and an alkali metal salt different from the alkali metal hydroxide in a concentration range of 2.40% to 25.0% by weight, based on the total weight of the aqueous extractant, to obtain after phase separation an organic aniline phase and an aqueous aminophenolate phase; and c) distilling the organic aniline phase from step b) to obtain a purified aniline stream, a gaseous stream containing organic impurities having a boiling point lower than aniline and a liquid stream containing aniline and organic impurities having a boiling point higher than aniline. [Background technology]

[0002] Aniline is an important intermediate, for example, in the production of di- and polyisocyanates of the diphenylmethane series (MDI) and is generally produced on an industrial scale by catalytic hydrogenation of nitrobenzene in the gas or liquid phase (see, for example, US Pat. No. 5,399,623, US Pat. No. 5,499,633, US Pat. No. 5,499,663, and US Pat. No. 5,523,366). In this reaction, in addition to the target product aniline, secondary components, such as, for example, phenol or aminophenols, are also formed, which must be removed before the aniline can be further used in downstream processes. Of particular concern is the removal of such secondary components, whose boiling points are very similar to the target product produced, since in this case distillation is rather troublesome. In particular, the removal of phenol (boiling point at standard pressure: 182° C.) in the production of aniline (boiling point at standard pressure: 184° C.) is a major challenge for distillation technology, which is reflected in the use of long distillation columns with a large number of separation stages and high reflux ratios and therefore high energy requirements. Vacuum distillation to remove phenol from aniline is described, for example, in US Pat. No. 5,499,623.

[0003] For this reason, there is no shortage of approaches to separate phenol (and other phenolic compounds) from aniline in other ways, in particular by conversion to phenolate salts by reaction with a suitable base, which are formed as non-volatile, readily water-soluble compounds that are substantially easier to separate from aniline than the phenolic compounds themselves.

[0004] For example, patent document 6 describes a method in which aniline is sent to the distillation only after it has been contacted with a solid alkali metal hydroxide in a fixed bed, or the distillation is carried out in the presence of a solid alkali metal hydroxide in a proportion of 0.1% to 3% by weight relative to the amount of aniline to be distilled. This simplifies the removal of important components such as aminophenols. However, this method has the disadvantage that a high molar excess of solid alkali metal hydroxide is used relative to the acidic secondary components to be removed, and the alkaline compound cannot be dosed accurately. On the one hand, in the case of excessive dosing, this can lead to corrosion problems, breakdowns and a highly viscous bottom phase in the distillation column, and on the other hand, in the case of underdosing, it can lead to incomplete removal of important components.

[0005] Patent document 7 describes a method for separating compounds having phenolic hydroxyl groups from aromatic amines, in which a base is added to the amine to be purified before distillation in a molar ratio of 0.5:1 to 10:1 relative to the phenolic compound, optionally in the presence of a polyol, for example polyethylene glycol. However, especially in the case of aniline produced in very large quantities, the addition of such a polyol is economically disadvantageous and there is a risk of contaminating the product with polyol (fragments). However, without the use of such polyols, frequent process interruptions due to salt precipitation would be expected.

[0006] US Pat. No. 5,399,633 describes a method for purifying aniline by adding an aqueous alkali metal hydroxide solution before or during distillation, in which problems caused by solids deposition, fouling and / or strong viscosity increase during distillation are prevented by partially draining the bottom phase of the distillation, washing it with water or a dilute alkali metal hydroxide solution and recycling the washed organic phase back to the distillation. The disadvantage here is that additional process steps are required to maintain reliable operation. Moreover, the method generates an additional organically polluted wastewater stream that needs to be worked up and disposed of.

[0007] Patent document 9 describes a method for purifying aromatic amines, in which the crude amine obtained after removal of the process water is treated with an aqueous alkali metal hydroxide solution and the process product thus obtained is distilled. The bottom product of the distillation column is partially or completely discharged and is then passed through two evaporators (E 1 ) and (E 2 ) to some extent. The objective is to achieve maximum reduction of the beneficial amines in the bottoms of the distillation column with minimum equipment cost and energy consumption.

[0008] In the above-mentioned method, aromatic amines are distilled in the presence of a base. In this procedure, problems caused by corrosion, solids deposition, and / or fouling during distillation must be prevented by complex and / or expensive measures. Moreover, such methods are not very suitable for purifying crude aniline with a high aminophenol content, because the aminophenolates formed during the reaction with the base are only soluble in aniline to a very small extent and therefore form solids that cause fouling and deposition in the subsequent aniline column.

[0009] Methods for removing phenol and other phenolic compounds by extraction with an aqueous base are also known. Even to remove other non-acidic impurities, aniline must be distilled at least to some extent. Such methods are described, for example, in US Pat. No. 5,399,623, US Pat. No. 5,399,637, US Pat. No. 5,399,643, or even in US Pat. No. 5,399,651. Among these, US Pat. No. 5,399,651 is considered in more detail as an example. This document describes a method for ensuring that the aqueous phase is always the lower phase in the subsequent phase separation by selecting the concentration and temperature of the alkali metal hydroxide solution used for the extraction. In this way, phase separation problems, especially phase inversion, are avoided during the extraction. Preferred alkali metal hydroxide concentrations are between 0.71% and 35% by weight. However, higher concentrations, for example 50% by weight, are also described. Lower concentrations, for example up to 0.1% by weight, can also be used, provided that a sufficiently high temperature (maximum 140° C., preferably maximum 100° C., particularly preferably maximum 95° C.) ensures that the aqueous phase is always the lower phase. In the respective examples, the extraction was carried out at 90° C. Thus, there must be either a sufficiently high alkali metal hydroxide concentration or a sufficiently high temperature, both of which are associated with costs. The patent application does not reveal how the density difference between the aqueous and organic phases required for good phase separation can be achieved without these measures.

[0010] According to the teaching of WO 02 / 04336, the alkali metal hydroxide solution used for the extraction can be recycled after the extraction, possibly after additional purification and / or concentration, and reused for the extraction. It cannot be derived from this document how this can be done specifically, and in particular how an alkali metal hydroxide solution contaminated with organic impurities (especially phenolates) can be economically purified so as to allow a problem-free recycling. As an alternative to recycling to the extraction, this document discloses that the alkali metal hydroxide solution used for the extraction, possibly after additional purification, is fed to a wastewater stream, which is sent, for example, after a subsequent workup, to a water treatment plant. In this case, losses of alkali metal hydroxide are unavoidable. Thus, in summary, this patent application does disclose a method that makes it possible to reliably guarantee that the aqueous phase is always the lower phase (avoidance of phase inversion), but the price of this is the disadvantage of a high alkali metal hydroxide concentration or a high extraction temperature. Moreover, there is no practical concept of recycling excess alkali metal hydroxide.

[0011] Patent Document 14 describes a method for purifying phenol-containing aniline, in which aniline is extracted with a dilute alkali metal hydroxide solution. Preferably, the concentration of alkali metal hydroxide in the aqueous phase is set in the range of 0.1% to 0.7% by mass after mixing aniline with the alkali metal hydroxide solution. The molar ratio of alkali metal hydroxide to phenol is preferably in the range of 3 to 500.

[0012] To meet current purity requirements, two or more extraction steps are generally required, which adds further complexity, as described, for example, in US Pat. No. 5,399,633. Furthermore, all these methods generate large amounts of wastewater streams containing phenolates, which also need to be carefully worked up and disposed of.

[0013] Patent document 16 deals very generally with the improvement of the aniline workup. It describes a process in which part of the bottoms of the aniline distillation column is discharged from said column and converted separately, i.e. into a gas phase in a second evaporator different from the original evaporator of the column. The gas phase thus obtained is recycled to the pure aniline column, from which the heavy boiler fraction that cannot be evaporated is removed. The disadvantage of this process is that low boilers and water must be removed separately by additional distillation upstream of the original aniline distillation column in a method with a complex mechanism of dehydration columns.

[0014] Finally, US Pat. No. 5,399,633 describes a process for purifying an aqueous amine solution in two distillation columns connected in series. One column is operated at 2 bar to 20 bar, the other at 0.1 bar to 10 bar. Here, the heat of condensation of the steam leaving the column operating at the higher pressure is used to heat the bottom of the column operating at the lower pressure. The amine is obtained as bottom product. The process is therefore not suitable for removing high boilers (e.g. aminophenols) or phenol from aniline. The high pressure also requires high bottom temperatures which can lead to a certain decomposition of the products and therefore to a reduction in yield or fouling. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] European Patent Application Publication No. 0696573 [Patent Document 2] European Patent Application Publication No. 0696574 [Patent Document 3] European Patent Application Publication No. 1882681 [Patent Document 4] International Publication No. 2013 / 139737 [Patent Document 5] DE 1935363 [Patent Document 6] Japanese Patent Publication No. 49-035341 [Patent Document 7] European Patent No. 1670747 [Patent Document 8] European Patent Application Publication No. 1845079 [Patent Document 9] European Patent Application Publication No. 2028176 [Patent Document 10] European Patent Application Publication No. 1845080 [Patent Document 11] European Patent Application Publication No. 2263997 [Patent Document 12] Patent Publication No. 08-295654 [Patent Document 13] European Patent Application Publication No. 2641892 [Patent Document 14] Japanese Patent No. 3804082 [Patent Document 15] Patent Publication No. 2007-217405 [Patent Document 16] JP2005-350388A [Patent Document 17] European Patent Application Publication No. 1602640 Summary of the Invention [Problem to be solved by the invention]

[0016] Therefore, further improvements were needed in the field of aniline purification. With regard to the removal of phenolic compounds, attention has been paid mainly to phenol itself so far, and less to aminophenols. The known methods using bases have the disadvantages outlined above when purifying crude aniline fractions with a high aminophenol content. When using bases in the distillation, the above-mentioned problem of solids formation occurs. When omitting bases, the removal of phenol, which is always also present, is difficult. When alkaline extraction is used, large amounts of base are required. The concentration and / or amount of the base solution used (usually sodium hydroxide or potassium hydroxide) cannot be arbitrarily reduced without interfering with the extraction efficiency and / or the subsequent phase separation. [Means for solving the problem]

[0017] Quite surprisingly, it has been found that the above-mentioned problems can be solved or at least significantly reduced if a base extraction is located upstream of the distillation of the crude aniline, in which, in addition to the alkali metal hydroxide used as basic component, an alkali metal salt different from the alkali metal hydroxide is also used, in particular if the aqueous phase obtained after phase separation is subjected, after acidification, to back-extraction with an organic stream, such as the high-boiler-rich bottom stream obtained in the distillation.

[0018] Thus, taking into account the outlined needs, the subject of the present invention is a method for producing a method for the production of a medicament for the treatment of a cancer, comprising the steps of: a) providing a crude aniline fraction 1 (comprising an aqueous component and an organic component) containing aniline and organic impurities, where the organic impurities comprise phenol, organic impurities having a boiling point lower than aniline (called "low boilers"), and aminophenols, and also further organic impurities having a boiling point higher than aniline (called "high boilers"), and where the concentration of aminophenols relative to the total weight of the organic components of the crude aniline fraction is in the range of 0.001% to 1.00% by weight, preferably in the range of 0.001% to 0.50% by weight, particularly preferably in the range of 0.001% to 0.10% by weight; b) the crude aniline fraction from step a) is subjected to a step of subjecting the crude aniline fraction to Alkali metal hydroxides, in particular sodium hydroxide or potassium hydroxide, in a concentration range of 0.009% to 2.05% by weight, preferably 0.010% to 2.00% by weight, particularly preferably 0.010% to 1.00% by weight, very particularly preferably 0.50% to 1.00% by weight, very particularly preferably 0.76% to 1.00% by weight, and alkali metal salts other than alkali metal hydroxides, in particular sodium or potassium chloride or sodium or potassium sulfate, in a concentration range of 2.40% by weight to 25.0% by weight, preferably 4.00% by weight to 25.0% by weight, particularly preferably 5.00% by weight to 25.0% by weight, very particularly preferably 10.0% by weight to 20.0% by weight and very particularly preferably 12.0% by weight to 17.0% by weight, to obtain, after phase separation, an organic aniline phase 5 and an aqueous aminophenolate phase 6 which are reduced in aminophenols (and of course also in phenol); c) distilling the organic aniline phase 6 from step b) to obtain a purified aniline stream 8, a gaseous stream 7 containing organic impurities having a boiling point lower than that of aniline, and a liquid stream 9 containing aniline and organic impurities having a boiling point higher than that of aniline; and preferably comprising steps d) to f) including a concentration step, an acid treatment step and an extraction step, wherein these steps exist in a first variant (steps d.1) to f.1), see also FIG. 2a) and a second variant (steps d.2) to f.2), see also FIG. 2b), which differ in terms of the order of the steps and the manner in which the individual material streams are conducted, the first variant being d.1) concentrating the liquid stream 9 from step c) containing aniline and organic impurities having a boiling point higher than that of aniline by evaporation of the aniline to obtain an aniline-containing distillate stream 17 and a bottoms stream 18 containing organic impurities having a boiling point higher than that of aniline; e.1) treating the aqueous aminophenolate phase 6 obtained in step b) with an acid 21 to convert the aminophenolate to aminophenol (preferably in parallel with the addition of acid), f.1) extraction of the aminophenols formed by the acid treatment with an organic stream comprising the bottom stream 18 from step d.1) containing organic impurities with a higher boiling point than aniline to obtain, after phase separation, an organic phase 19 and an aqueous phase 20, in which an alkali metal hydroxide is added to the aqueous phase, said aqueous phase being used as a component of the extractant 4 used in step a); and the second variant includes d.2) treating the aqueous aminophenolate phase 6 obtained in step b) with an acid 21 to convert the aminophenolate to aminophenol (preferably in parallel with the addition of acid), e.2) extraction of the aminophenols formed by the acid treatment with an organic stream comprising the liquid stream 9 from step c) containing aniline and organic impurities with a boiling point higher than that of aniline to obtain, after phase separation, an organic phase 19 and an aqueous phase 20, in which an alkali metal hydroxide is added to the aqueous phase, said aqueous phase being used as a component of the extractant 4 used in step a); f.2) concentrating the organic phase 19 from step e.2) by evaporation of aniline to obtain an aniline-containing distillate stream 17 and a bottoms stream 18 containing organic impurities having a boiling point higher than aniline; The method for purifying aniline comprises the steps of:

[0019] Both the first and second variants, which are preferably implemented variants, can be combined with all other embodiments of the invention described below.

[0020] The process according to the invention, using a mixture of an alkali metal hydroxide and an alkali metal salt different from the alkali metal hydroxide as extractant, makes it possible to ensure a smooth phase separation even in the case of relatively low alkali metal hydroxide concentrations, without having to resort to relatively high extraction temperatures (as taught, for example, in US Pat. No. 5,399,363). The additional use of an alkali metal salt different from the alkali metal hydroxide in the extraction according to step b) makes it possible to reliably ensure that the aqueous phase during phase separation is consistently the lower ("heavy") phase, in particular without restricting the choice of temperature and without increasing the use of relatively expensive alkali metal hydroxide. Furthermore, in a preferred configuration of the process according to the invention, it is possible to back-extract organic components from the aqueous phase after acidification, which makes it possible to recycle essential components of the extractant after replacing the consumed base. Furthermore, it is possible, and is the subject of a preferred embodiment, to feed the organic components removed in the back-extraction into a waste stream (obtained in all cases), which makes disposal of an additional waste stream unnecessary.

[0021] In all industrially relevant processes for the production of aniline, water is formed as a by-product (water of reaction). That is to say, a two-phase crude product consisting of an aqueous phase (containing the water of reaction) and an organic phase (containing the formed aniline and organic impurities) is always initially obtained in the production of aniline. The aniline-containing phase remaining after partial or complete, preferably complete removal of the aqueous phase from the crude product (by so-called phase separation, known to the skilled person) is referred to in the context of the present invention as the "crude aniline fraction". As known to the skilled person, due to a certain residual solubility of the two phases in each other, such separation of the aqueous phase from the organic phase of a two-phase process product is never perfect in the sense that a residue-free separation of the organic components from the aqueous components would be possible. Thus, the term "complete removal of the aqueous phase" or "complete phase separation" in the context of the present invention only means that no fraction of the aqueous phase is intentionally left in the organic phase. Thus, even with complete removal of the aqueous phase, the crude aniline fraction contains the aqueous components as well as the organic components.

[0022] The term "aminophenol" in the present nomenclature includes all isomers (and therefore refers to the entire set of all isomers present), although in this case, as a rule of thumb, only ortho- and para-aminophenols are always present in detectable amounts.

[0023] The mass concentrations of organic compounds specified in the context of the present invention relate to values ​​determined by gas chromatography, when these are measured values ​​(not values ​​calculated from known raw materials). Quantification of the concentration of low molecular weight organic compounds by gas chromatography is a method known to those skilled in the art that does not require further explanation in this respect. In the context of the present invention, the total mass of the organic components is the reference variable.

[0024] The ranges and preferred ranges specified in step b) above for the mass concentration of the alkali metal hydroxide on the one hand and the mass concentration of the alkali metal salt different from the alkali metal hydroxide on the other hand can in principle be combined with each other if desired. That is, for example, it is possible to use an alkali metal hydroxide in a concentration range of 0.010% by mass to 2.00% by mass (the second widest range) and an alkali metal salt different from the alkali metal hydroxide in a concentration range of 12.0% by mass to 17.0% by mass (the narrowest range). This also applies to the individual lower and upper limits. Thus, for example, it is also possible to use an alkali metal hydroxide in a concentration range of 0.010% by mass to 2.00% by mass (the second widest range) and an alkali metal salt different from the alkali metal hydroxide in a concentration range of 2.40% by mass (the lower limit of the widest range) to 17.0% by mass (the upper limit of the narrowest range). However, it is particularly preferred to combine mutually corresponding ranges with one another, i.e., for example, to combine a preferred range for the concentration of an alkali metal hydroxide with a preferred range for the concentration of an alkali metal salt other than the alkali metal hydroxide, or to combine a very preferred range for the concentration of an alkali metal hydroxide with a very preferred range for the concentration of an alkali metal salt other than the alkali metal hydroxide, etc.

[0025] "Low boilers" in the context of the present invention are understood to be organic compounds (and possibly azeotropes) that have a boiling point lower than aniline. In terms of boiling behavior, water of course belongs to the low boilers, but water is generally and also considered separately in the context of the present invention, since it is not an organic impurity that can contribute to secondary reactions, but rather a by-product of aniline production (hydrogenation of nitrobenzene, ammonolysis of phenol) or is introduced with the reagents used (reduction of nitrobenzene with base metals such as iron in the presence of hydrochloric acid, ammonolysis with aqueous ammonia). Typical low boilers in the context of the present invention are cyclohexylamine, cyclohexanone, cyclohexanol and benzene. "High boilers" in the context of the present invention are therefore understood to be organic compounds (and possibly azeotropes) that have a boiling point higher than aniline. Typical high boilers are aminophenols, toluidines, phenylenediamines, diphenylamines, N-cyclohexylaniline, or even unconverted starting materials from the production, such as nitrobenzene. In principle, the classification of a substance as low or high boiler depends on the pressure and, in this case, on the pressure conditions selected for the distillation in step c) (a substance may be a low boiler at one particular pressure and a high boiler at another pressure). However, the examples given above of typical low and high boilers correspond to the allocations made in the entire pressure range relevant in step c). However, phenol has a very similar boiling behavior to aniline and can be separated in step c) as low or high boiler depending on the pressure present.

[0026] "Purified aniline stream" is understood in the context of the present invention to be an aniline stream which has been subjected to removal of low and high boilers by distillation. The purified aniline stream obtained according to the present invention contains an aniline content in the range of 99.5000% by mass to 99.9999% by mass, preferably in the range of 99.9000% by mass to 99.9999% by mass, particularly preferably in the range of 99.9500% by mass to 99.9999% by mass, based on its total mass. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 illustrates an embodiment of a method according to the present invention. [Figure 2a] FIG. 4 illustrates a further embodiment of the method according to the invention, comprising the first variant described above. [Figure 2b] FIG. 4 illustrates a further embodiment of the method according to the invention, comprising the second variant described above. [Diagram 3] FIG. 1 shows the extent of phenol and aminophenol reduction in the extraction of aniline containing phenol and aminophenol using various extractants and the relative phase separation time compared to extraction with pure water. [Figure 4] FIG. 1 shows the partition coefficients of phenol and ortho-aminophenol between the organic and aqueous phases in a two-phase mixture at various pH values. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The following first provides a summary of various possible embodiments of the invention; however, this list of embodiments should not be considered exhaustive.

[0029] In a first embodiment of the invention, which can be combined with both the first and the second variant (see above), step c) comprises a distillation in a distillation column equipped with a side draw, in which a purified aniline stream is withdrawn as a side draw, a gaseous stream containing organic impurities having a lower boiling point than aniline is withdrawn as an overhead stream, and a liquid stream containing aniline and organic impurities having a higher boiling point than aniline is withdrawn as a bottom stream from the distillation column equipped with a side draw.

[0030] In a second embodiment of the invention, which can be combined with both the first and the second variant (see above), step c) comprises a distillation in two distillation columns connected in series, in which in the first distillation column a gaseous stream containing organic impurities having a boiling point lower than aniline is withdrawn as an overhead stream and the bottom stream obtained in the first distillation column is led as feed to a second distillation column in which a purified aniline stream is obtained as an overhead stream and a liquid stream containing aniline and organic impurities having a boiling point higher than aniline is obtained as a bottom stream.

[0031] In a third embodiment of the invention, which can be combined with both the first and the second variant (see above), step c) comprises a distillation in three distillation columns, in which an overhead stream containing water and organic impurities is withdrawn from the first distillation column and separated into an aqueous phase and an organic phase, the organic phase is led to a second distillation column from which a gaseous stream containing organic impurities having a lower boiling point than aniline is withdrawn as overhead stream, and the bottom stream obtained in the first distillation column is led as feed to a third distillation column, in which a purified aniline stream is obtained as overhead stream and a liquid stream containing aniline and organic impurities having a higher boiling point than aniline is obtained as bottom stream.

[0032] In a fourth embodiment of the invention, which is a specific configuration of the first to third embodiments (i.e. can be applied to each of these three embodiments), a gaseous stream containing organic impurities having a boiling point lower than aniline is partially liquefied and the liquid phase thus obtained, after removal of any water present, is recycled (as reflux) to the distillation column from which the gaseous stream containing organic impurities having a boiling point lower than aniline was withdrawn as overhead, and where the gaseous phase remaining after the partial liquefaction (containing, in addition to non-condensable gases, organic impurities having a boiling point lower than aniline) is discharged from the distillation.

[0033] In a fifth embodiment of the invention, which can be combined with both the first and the second variant (see above), a distillation column is used for the concentration in step d.1) or in step f.2).

[0034] In a sixth embodiment of the invention, which can be combined with both the first and the second variant (see above), the gas phase remaining in step c) after the partial liquefaction (containing, in addition to the non-condensable gases, organic impurities having a boiling point lower than that of aniline) is condensed and the condensate obtained is used as an additional component of the organic stream used in step f.1) or in step e.2).

[0035] In a seventh embodiment of the invention, which can be combined with both the first and the second variant (see above), the organic phase obtained after phase separation in step f.1), or the bottoms stream obtained in step f.2) containing organic impurities having a boiling point higher than that of aniline, Incinerate the

[0036] In an eighth embodiment of the invention, which can be combined with both the first and the second variant (see above), the alkali metal salt used which is different from an alkali metal hydroxide is (i) an alkali metal chloride or (ii) an alkali metal sulfate.

[0037] In a ninth embodiment of the invention, which is a particular configuration of the eighth embodiment, in step e.1) or in step d.2), the acid used in case (i) is hydrochloric acid and the acid used in case (ii) is sulfuric acid.

[0038] In a tenth embodiment of the invention, which can be combined with all other embodiments, the extraction of the crude aniline fraction in step b) is carried out countercurrently in several steps, preferably in two steps.

[0039] In an eleventh embodiment of the present invention, which can be combined with all other embodiments, the organic aniline phase obtained in step b) is mixed with an aqueous solution of an alkali metal hydroxide before the distillation in step c) and the mixture thus obtained is subjected to the distillation of step c) without prior removal of its aqueous components.

[0040] In a twelfth embodiment of the present invention, which can be combined with all other embodiments, the crude aniline fraction is obtained by hydrogenation of nitrobenzene in the presence of a catalyst and removal of the water formed in the hydrogenation.

[0041] In a thirteenth embodiment of the present invention, which is a specific configuration of the twelfth embodiment, the hydrogenation of nitrobenzene is carried out in the gas phase and the resulting gaseous reaction products are condensed.

[0042] In a fourteenth embodiment of the present invention, which is a particular configuration of the thirteenth embodiment, the condensation of the gaseous reaction products is carried out in two stages with successive decreases in temperature (i.e. "partial condensation" and "total condensation"), where only after the second condensation stage a phase separation is carried out to remove the water formed in the hydrogenation.

[0043] In a fifteenth embodiment of the present invention, which is a particular configuration of the fourteenth embodiment, the condensate obtained in the first condensation stage is combined with the organic phase remaining after removal of water in the phase separation after the second condensation stage and is used (partially or completely) as crude aniline stream in step a).

[0044] In a sixteenth embodiment of the present invention, which is a further particular configuration of the fourteenth embodiment, the crude aniline stream provided in step a) is withdrawn either from the condensate obtained in the first condensation stage or from the organic phase remaining after removal of water in the phase separation after the second condensation stage.

[0045] In a 17th embodiment of the present invention, which is a further specific configuration of the 13th embodiment, the condensation of the gaseous reaction products is carried out in one stage, in which the condensation is followed by a phase separation to remove the water formed in the hydrogenation, and the organic phase remaining after removal of the water is used (partially or completely) as a crude aniline stream in step a).

[0046] In an eighteenth embodiment of the present invention, which is a specific configuration of the twelfth to seventeenth embodiments, hydrogenation is carried out adiabatically.

[0047] In a nineteenth embodiment of the present invention, which is a further specific configuration of the twelfth to seventeenth embodiments, the hydrogenation is carried out isothermally.

[0048] In a twentieth embodiment of the present invention, which is a specific configuration of the eighteenth embodiment, the catalyst comprises copper on a silicon dioxide support.

[0049] In a twenty-first embodiment of the present invention, which is a specific configuration of the nineteenth embodiment, the catalyst comprises palladium on an aluminum oxide support.

[0050] In a twenty-second embodiment of the present invention, which can be combined with all other embodiments, the alkali metal of the alkali metal hydroxide and of the alkali metal salt different from the alkali metal hydroxide is in each case sodium or potassium.

[0051] In a 23rd embodiment of the present invention, which can be combined with all other embodiments, in step b) the molar ratio of alkali metal hydroxide to phenolic hydroxyl groups is set in the range from 0.80 to 50, preferably in the range from 0.95 to 10, particularly preferably in the range from 1.0 to 5.0 and very particularly preferably in the range from 1.0 to 2.4.

[0052] In a 24th embodiment of the present invention, which can be combined with all other embodiments, the extraction in step b) is carried out at a temperature in the range from 20°C to 95°C, particularly preferably from 25°C to 85°C, very particularly preferably from 25°C to 70°C and very particularly preferably from 25°C to 40°C.

[0053] In a 25th embodiment of the invention, which can be combined with all other embodiments comprising steps d) to f) (in the first or second variant), the extraction of the aminophenols formed by the acid treatment with an organic stream (step f.1 or step e.2) is carried out in a mixer-settler apparatus (mixer-settler) comprising a mixing unit and a separation unit, in which the treatment of the aqueous aminophenolate phase 6 obtained in step b) with acid 21 to convert the aminophenolates to aminophenols is carried out in such a way that the aqueous aminophenolate phase 6 obtained in step b) is mixed with acid 21 and the organic stream (comprising stream 18 or stream 9) in a mixing unit (acid and organic stream are added simultaneously to the aqueous aminophenolate phase, i.e. the extraction with the organic stream is carried out in parallel with the acid treatment), followed by phase separation into an organic phase 19 and an aqueous phase 20 in a separation unit.

[0054] In a twenty-sixth embodiment of the present invention, which can be combined with all other embodiments, The alkali metal hydroxides used are: Sodium hydroxide or potassium hydroxide in a concentration range of 0.009% to 2.05% by weight, preferably 0.010% to 2.00% by weight, particularly preferably 0.010% to 1.00% by weight, very particularly preferably 0.50% to 1.00% by weight, very particularly preferably 0.76% to 1.00% by weight; and the alkali metal salts used which are different from alkali metal hydroxides are Sodium chloride or potassium chloride in a concentration range of 4.00% to 25.0% by weight, preferably 5.00% to 25.0% by weight, particularly preferably 10.0% to 20.0% by weight, very particularly preferably 12.0% to 17.0% by weight, or Sodium sulfate or potassium sulfate in a concentration range of 2.40% by weight to 25.0% by weight, preferably 4.00% by weight to 25.0% by weight, in particular 5.00% by weight to 25.0% by weight, very particularly preferably 10.0% by weight to 20.0% by weight and very particularly preferably 12.0% by weight to 17.0% by weight, Either:

[0055] The embodiments briefly outlined above and further possible embodiments of the invention are described in more detail below. The embodiments can be combined with each other if desired, unless the context makes clear to the contrary.

[0056] Figure 1 shows a simple configuration of the method according to the invention. The reference symbols have the following meaning:

[0057] Apparatus or method steps: 1000 mixer, 2000 Base extraction including phase separation, 3000 distillation tower, 3100 Bottom evaporator of distillation column 3000.

[0058] Material flow: 1 crude aniline fraction, 2 Alkali metal hydroxide solution, 3. an alkali metal salt solution different from an alkali metal hydroxide solution (preferably an alkali metal chloride solution or an alkali metal sulfate solution); 4 aqueous extractant, 5. Aminophenol (and phenol) reduced organic aniline phase; 6 aqueous aminophenolate phase, 7. Distillation column overhead stream (low boilers, water, non-condensable gases), 8. Purified aniline, 9. Discharge from the bottom evaporator; 10 Distillate from bottom evaporator.

[0059] Since the currently customary industrial processes of the prior art for the preparation of aniline (in particular the hydrogenation of nitrobenzene, to a lesser extent the reduction of nitrobenzene with base metals such as iron and, today, the ammonolysis of phenol or chlorobenzene), all ultimately result, with differences, in a phenol- and aminophenol-containing crude aniline, the process according to the invention can be rationally applied to all of these preparation processes and therefore the crude aniline provided in step a) can likewise originate from all of these processes.

[0060] The actual production of purified aniline is preferably carried out by catalytic hydrogenation of nitrobenzene. The crude process product obtained in this case contains, in addition to aniline and secondary components, a significant proportion of water (water of reaction) as a by-product of the hydrogenation, which is partially or completely, preferably completely, removed before further purification. This removal is carried out by phase separation as known to the skilled person. The aqueous phase thereby obtained, in the preferred configuration with complete phase separation (see the explanation above in this respect), contains the majority of the water of reaction (except for residual amounts which cannot be removed by phase separation due to the low solubility of water in aniline), which is removed. In addition to aniline, the remaining organic phase also contains organic impurities and dissolved water.

[0061] Advantageously, the hydrogenation can be carried out in the gas phase, where hydrogen is preferably used in stoichiometric excess. As known to those skilled in the art, the hydrogenation can be carried out adiabatically (without controlled removal of the heat of reaction) or isothermally (for example, with controlled removal of the heat of reaction in a shell-and-tube reactor using a cooling heat transfer medium such as water, oil, or molten salt).

[0062] In the case of adiabatic mode, two or more reactors are generally arranged in series in series. In this case, the reaction gas is cooled after leaving the reactor, since the heat of reaction leads to a significant increase in the temperature of the reaction gas (so-called "adiabatic temperature jump"). After cooling, gaseous nitrobenzene and additional hydrogen can be optionally added again and fed to the additional reactor. In order to suppress the heat of reaction, adiabatic processes generally operate with a particularly large excess of hydrogen. Unconsumed hydrogen is therefore preferably circulated.

[0063] In isothermal processes, a single reactor is generally used, which is actively cooled as described. Despite the generally much smaller excess of hydrogen compared to adiabatic processes, it is usually appropriate to recycle the unconsumed hydrogen.

[0064] The advantage of adiabatically carried out processes is the simpler design of the reactor, since no cooling of the catalyst bed is required. Isothermal processes are correspondingly more expensive, since cooling of the catalyst bed is required. However, due to the feasible reactor sizes, a series arrangement of two or more reactors and corresponding intercoolers is generally not required here.

[0065] The process according to the invention can be used particularly advantageously when the hydrogenation is carried out isothermally using a catalyst comprising palladium on an aluminum oxide support or adiabatically using a catalyst comprising copper on a silicon dioxide support. In both cases, in addition to phenol, relatively large amounts of aminophenols are formed, which can be efficiently removed by the process according to the invention.

[0066] In both procedures the gaseous reaction products initially obtained are condensed. Such condensation can be carried out in one step (i.e. to obtain a single condensate) followed by a phase separation. The organic phase remaining after removal of the reaction water can be fed to step b) as crude aniline fraction.

[0067] However, it is also possible to carry out the condensation in two stages, so that two condensates of different composition are obtained. For this, the initially obtained gaseous crude product stream is subjected to continuously decreasing temperatures, so that initially only the higher boiling components condense together with the aniline. In this way, a first condensate (the so-called "partial condensate") is obtained which is almost water-free and preferably single-phase, so that in this case no phase separation is necessary. This "partial condensate" therefore consists essentially only of aniline and high boilers. Only in the second condensation (the so-called "total condensation"), which is carried out at a lower temperature, do the low boilers and water also condense in addition to further aniline. The removal of the water of reaction by phase separation can therefore still be limited to this "total condensate". The organic phase remaining after the phase separation can advantageously be fed to step b) together with the partial condensate as crude aniline fraction. However, it is also possible to feed only one of the two streams (the organic phase of the partial condensate or of the total condensate obtained after phase separation) as crude aniline fraction to step b).

[0068] Regardless of the exact method of preparing the crude aniline, the invention can be used for the purification of a crude aniline fraction having a concentration of aminophenols in the range of 0.001% to 1.00% by weight, preferably in the range of 0.001% to 0.50% by weight, particularly preferably in the range of 0.001% to 0.10% by weight, relative to the total weight of the organic components of the crude aniline fraction. Since the formation of aminophenols is always accompanied by the formation of phenol, such a crude aniline fraction always also contains phenol, in particular in the range of 0.001% to 1.00% by weight, preferably in the range of 0.001% to 0.50% by weight, particularly preferably in the range of 0.001% to 0.10% by weight, relative to the total weight of the organic components of the crude aniline fraction.

[0069] As long as the requirement according to the invention of additionally using an alkali metal salt different from an alkali metal hydroxide is observed, the extraction in step b) can in principle be carried out using devices and procedures known per se in the prior art. Without wishing to be bound by theory, it is assumed that an alkali metal salt different from an alkali metal hydroxide promotes a simple phase separation, since it ensures a sufficient density difference between the aqueous and organic phases, even when the alkali metal hydroxide concentration in the extractant is relatively low. Such promotion of the separation of two immiscible or very poorly miscible phases should be distinguished from the procedure known in organic chemistry of reducing the solubility of organic compounds in the aqueous phase by saturating the latter with salts, thus increasing the yield of the organic target product in the workup of the aqueous-organic process product (by minimizing the losses due to the residual solubility of this organic target product in the aqueous phase).

[0070] The two components of the aqueous extractant essential to the invention, the alkali metal hydroxide (the original reactive component) and the alkali metal salt different from the alkali metal hydroxide, can be fed in premixed form (which is preferred) or even separately (via separate feed devices). The extraction can be carried out in one or more stages in devices known to the skilled artisan, in particular in so-called "mixer-settler" devices (mixer-settlers). Multi-stage, in particular two-stage, extraction in countercurrent is particularly preferred. After each extraction step the phases are separated and the organic phase depleted in aminophenols (and of course also phenol) obtained after the final (possibly only) extraction step is fed to step c).

[0071] The extraction in step b) is preferably carried out at a temperature in the range from 20°C to 95°C, particularly preferably from 25°C to 85°C, very particularly preferably from 25°C to 70°C and very particularly preferably from 25°C to 40°C.

[0072] According to the invention, the alkali metal hydroxide is used in a concentration range of 0.009% to 2.05% by weight, preferably 0.010% to 2.00% by weight, particularly preferably 0.010% to 1.00% by weight, very particularly preferably 0.50% to 1.00% by weight, very particularly preferably 0.76% to 1.00% by weight, and the alkali metal salt different from the alkali metal hydroxide is used in a concentration range of 2.40% to 25.0% by weight, preferably 4.00% to 25.0% by weight, particularly preferably 5.00% to 25.0% by weight, very particularly preferably 10.0% to 20.0% by weight, very particularly preferably 12.0% to 17.0% by weight, based on the total mass of the extractant. As already mentioned, it is preferable to premix the two components essential to the invention. In the case of an equally possible separate supply of the two components essential to the invention to the extraction device used in step b) (the extractant being initially formed in the extraction device as a result of mixing), the reference variable for the abovementioned mass concentrations is the sum of the individual masses of the two components essential to the invention (which is equal to the mass of the premixed extractant in the preferred embodiment).

[0073] In a preferred embodiment, the total concentration of phenol and aminophenol in the crude aniline fraction is monitored continuously or at intervals, and the composition and / or amount of the extractant is adapted thereto. For the most complete removal of aminophenol (and phenol), the alkali metal hydroxide must be used in at least stoichiometric amounts relative to the phenolic hydroxyl groups, preferably in excess (phenolic hydroxyl groups in the context of the present invention refer collectively to the hydroxyl groups of phenol and aminophenol, which are also referred to collectively as phenolic compounds). However, under certain circumstances, it may be appropriate not to intentionally neutralize all phenolic compounds in step b), but instead to shift part of the removal to the subsequent distillation in step c). In this way, the use of extractant in step b) can be minimized, in case a certain amount of phenolic compounds can be removed without problems by distillation in step c). The relative amount of alkali metal hydroxide advantageously used can therefore vary depending on the exact procedure. In particular, useful molar ratios of alkali metal hydroxide to phenolic hydroxyl groups have been found to be in the range of 0.80 to 50, preferably in the range of 0.95 to 10, particularly preferably in the range of 1.0 to 5.0, very particularly preferably in the range of 1.0 to 2.4. In the context of the present invention, the molar ratio can be directed only towards the objective of reducing the concentration of phenolic hydroxyl groups to the required extent under the present conditions. Furthermore, it is not particularly required to add further alkali metal hydroxide to establish the desired density, as may be absolutely necessary in the prior art methods. In contrast, the adjustment of density, which is optionally required in the method according to the invention, can be carried out in a simple and cost-effective manner by adding an alkali metal salt different from the alkali metal hydroxide.

[0074] It may also be expedient to add further aqueous alkali metal hydroxide to the aniline phase obtained in the extraction and depleted in aminophenols before distilling said phase in step c) and subject the mixture thus obtained to the distillation in step c) without removing its aqueous components. This is equivalent to the combination of a basic extraction according to the invention in the presence of an alkali metal salt different from an alkali metal hydroxide and a distillation in the presence of a base as known from the literature.

[0075] The alkali metal hydroxide used is preferably sodium hydroxide or potassium hydroxide.The alkali metal salt used different from the alkali metal hydroxide is preferably sodium chloride or potassium chloride, or sodium sulfate or potassium sulfate.The alkali metal salt of the hydroxide used should preferably be the same as the alkali metal salt of the alkali metal salt used different from the alkali metal hydroxide, in particular sodium or potassium in each case.

[0076] In step c) the crude aniline pre-purified by extraction in step b) is purified by distillation (high purity). In principle, any distillation apparatus and methods known to the skilled person as suitable for aniline purification can be used.

[0077] In a first configuration option for step c) of the present invention, low boilers and dissolved water on the one hand and high boilers on the other hand are removed in separate distillation columns, i.e. the purification by distillation comprises two distillation columns connected in series. The feed of the first distillation column is the crude aniline fraction pre-purified by basic extraction from step b).

[0078] In the first distillation column (the so-called "lights column"), the low boilers are distilled off at the top, while the aniline and the high boilers accumulate at the bottom. Dissolved water can likewise be withdrawn at the top or even in a side draw. The bottom of the first column forms the feed of a further (second) distillation column (the so-called "aniline column"), in which the aniline is distilled off at the top and the aniline-containing high boiler stream accumulates at the bottom. The aniline distilled off at the top in this embodiment constitutes the purified aniline stream for the purposes of the present invention.

[0079] In the first configuration option, the "low boiler distillation" may preferably be carried out at a top pressure in the range of 1000 mbar (absolute) to 1100 mbar (absolute) and a top temperature in the range of 97° C. to 100° C. The distillation in the aniline column is preferably carried out at a top pressure in the range of 100 mbar (absolute) to 200 mbar (absolute) and a top temperature in the range of 110° C. to 130° C.

[0080] In a second configuration option for step c) of the present invention, dissolved water is removed in a dedicated distillation column (so-called "dehydration column"). The crude aniline fraction pre-purified by basic extraction from step b) is fed to this dehydration column (in this configuration option, the first distillation column). A stream containing water, aniline and low boilers is withdrawn at the top of the dehydration column and then separated into an aqueous phase and an organic phase. The organic phase is fed to a further distillation column ("low boiler column", in this configuration option, the second distillation column), where the low boilers are distilled off at the top. The bottom stream of this low boiler column is recycled to the dehydration column.

[0081] The bottom of the dehydration column forms the feed of a third distillation column (the so-called "aniline column") in which, as in the first configuration option, aniline is distilled off at the top and an aniline-containing high-boiling stream is collected at the bottom. The aniline distilled off at the top, as in the first configuration option, constitutes the purified aniline stream for the purposes of the present invention.

[0082] In the second configuration option, the "dehydration column" may preferably be operated at a top pressure in the range of 100 mbar (absolute) to 400 mbar (absolute) and a top temperature in the range of 100° C. to 150° C. The "low boiler distillation" is preferably carried out at a top pressure in the range of 1000 mbar (absolute) to 1100 mbar (absolute) and a top temperature in the range of 70° C. to 90° C. The distillation in the aniline column is preferably carried out at a top pressure in the range of 250 mbar (absolute) to 350 mbar (absolute) and a top temperature in the range of 140° C. to 160° C.

[0083] However, it is also possible to introduce the crude aniline fraction pre-purified by basic extraction from step b) into a distillation column equipped with a side draw (also called a side draw column) in which low and high boilers (and also dissolved water) are removed in one distillation step, which is the subject of the third configuration option for step c) of the present invention. In one embodiment of the third configuration option, the side draw column has a dividing wall (so-called dividing wall column). In the third configuration option, a purified aniline stream is withdrawn from the distillation column as a side draw, while low boilers (and water) are withdrawn from the top of the column. As in the aniline column of the above configuration option, the aniline-containing high boiler stream accumulates at the bottom of the column. This distillation is preferably carried out at a side draw column top pressure in the range from 200 mbar (absolute) to 500 mbar (absolute) and a side draw column top temperature in the range from 100°C to 150°C.

[0084] In all cases, the low-boiling stream (i.e. the top stream of the first distillation column in the first configuration option, the top stream of the second distillation column in the second configuration option and the top stream of the side draw column in the third configuration option) is initially obtained in gaseous form. This gaseous low-boiling stream is preferably partially liquefied and the liquid phase thus obtained can be advantageously returned as reflux to the first column, optionally after removing any water present. An uncondensed gas phase consisting essentially only of low boilers in addition to a certain proportion of non-condensable gases (under conditions customary in industry), such as, for example, nitrogen, is discharged from the distillation.

[0085] It may be advantageous to subject the aniline-containing high-boiling stream obtained in the above-mentioned configuration option for step c) to a high-boiler concentration in step d.1), thus minimizing the loss of useful product aniline (corresponding to the first variant described above). In this method, the aniline-containing stream is evaporated and can be advantageously recycled to the distillation of step c). This aniline-containing stream is preferably led to the bottom of the distillation column from which the aniline-containing high-boiling stream originally originated. Furthermore, in this step, a bottom stream (high-boiling stream) is obtained that contains organic impurities with a boiling point higher than aniline. The concentration of step d.1) is preferably carried out in a distillation column specially prepared for this purpose.

[0086] In a first variant, the economics of the process according to the invention can be further improved if the extraction step, i.e. the aqueous aminophenolate phase obtained in step b), is treated with an acid in step e.1) to convert the aminophenolate to aminophenol and extracted in step f.1) with an organic stream to obtain an (aminophenol-rich) organic phase and an (aminophenol-reduced) aqueous phase after phase separation. In order to prevent the aminophenol from precipitating as a solid, it is preferred to carry out step f.1) in parallel with step e.1) (= simultaneous addition of acid and organic stream to the aqueous aminophenolate phase). An alkali metal hydroxide can then be advantageously added to this aqueous phase, which can be used as a component of the extractant used in step a). In this way, it is possible to provide the entire amount of the alkali metal hydroxide used in step a). In this way, it is also possible to provide the entire amount of the alkali metal salt different from the alkali metal hydroxide used in step a), i.e. in the form of a salt of the acid used in step e.1), where this salt is in any case present in the (aminophenol-reduced) aqueous phase in this embodiment. A particularly suitable organic stream for extraction is the high boiler bottom stream obtained in step d.1), which can also be mixed for this purpose with other organic streams. For example, in step c), the non-condensable gas phase obtained during the preferably performed partial liquefaction of the gaseous low boiler overhead stream, consisting essentially only of low boilers in addition to a certain proportion of non-condensable gases (under industrially customary conditions), such as nitrogen, can be converted by liquefaction of the condensable fraction into a liquid low boiler stream, said liquid low boiler stream being suitable for mixing with the high boiler bottom stream obtained in step d.1), for the purpose of extracting aminophenols. In any case, the aniline content of the aminophenol-containing organic phase obtained after extraction and phase separation is so low that this organic phase can be incinerated without appreciable economic losses. In step f.1), the aminophenols (and of course also phenol, if present) are returned from the aqueous phase to the organic phase (which in fact originally originates from the organic phase, which is the crude aniline fraction), so that this step is also called back extraction.

[0087] The second variant described above also utilizes back extraction in this sense (here, step e.2)). However, in contrast to the first variant, the organic stream here is a liquid stream from step c) containing aniline and organic impurities with a boiling point higher than aniline, while the acid treatment (here, step d.2)) can in principle be carried out similarly to the first variant. In contrast to the first variant, here the organic phase obtained in the back extraction is concentrated (in step f.2)), this step being configured to prevent the reintroduction of aminophenols / phenols into step c) via the distillate of step f.2). However, this is possible without jeopardizing the energy-related advantages of the method, since the amount of the organic phase stream fed to the concentration is relatively small. The advantage of this second variant turns out to be a more robust method modality, which offers a higher degree of freedom. The amount of the organic stream sent to the back extraction (here, stream 9) can be selected in the second variant to be higher than in the first variant, if necessary (the amount of the organic stream (stream 18) mentioned above is essentially determined by the concentration of high boilers in the crude aniline fraction). The aniline contained in stream 9 is not lost, since it is recycled in stream 19 to the distillation column 5000 concentrating high boilers, from where it is passed via stream 17 to the aniline distillation 3000. Thus, in the second variant, the organic stream (here the liquid stream (stream 9) from step c) containing aniline and organic impurities with a boiling point higher than aniline) can be selected independently of the amount of high boilers obtained. Phase separation on a scale relevant for industrial applications can therefore be carried out in e.2) for all compositions of the crude aniline fraction. Also in the second variant, it is preferred to carry out a step of extraction with an organic stream (here, step e.2)) in parallel with the step of acid treatment (here, step d.2)) in order to prevent the aminophenol from precipitating as a solid (= simultaneous addition of acid and organic stream to the aqueous aminophenolate phase).

[0088] Suitable acids for the acid treatment in step e.1) or d.2) are in particular hydrochloric acid or sulfuric acid. The acid is selected corresponding to the choice of alkali metal salt used in step a) that is different from the alkali metal hydroxide, with hydrochloric acid being used in the case of an alkali metal chloride (in particular sodium chloride or potassium chloride) and sulfuric acid being used in the case of an alkali metal sulfate (in particular sodium sulfate or potassium sulfate). The acid treatment in step e.1) or d.2) is preferably carried out up to a pH (at 20°C) in the range of 2.0 to 8.5, preferably up to a pH (at 20°C) in the range of 3.5 to 8.5, particularly preferably up to a pH (at 20°C) in the range of 5.0 to 8.5.

[0089] Figure 2a shows a preferred configuration of the process according to the invention in a first variant with a two-stage condensation of the crude product of the gas-phase aniline hydrogenation, i.e. concentration of the bottom stream of the aniline distillation and extraction of the wastewater obtained in the base extraction with high boilers from the concentration step. Figure 2b shows a corresponding configuration for the second variant. The same reference symbols as in Figure 1 respectively have the same meaning as in that figure. The further reference symbols have the following meaning:

[0090] Apparatus or method steps: 4100 Partially condensed, 4200 mixer, 4300 Fully condensed, 4400 phase separation, 5000 Distillation column for concentrating high boiling point substances, 6000 neutralization, 7000 Extraction involving phase separation.

[0091] Material flow: 11 Gaseous crude product of aniline hydrogenation, 12 Partial condensate, 13 The fraction of the crude product that was not condensed in the partial condensation. 14 Total Condensate, 15 The uncondensed fraction in the total condensation (essentially excess hydrogen), 16 Organic phase of total condensate, 17 aniline-containing distillate stream; 18 a bottom stream containing high boilers (in the second variant according to FIG. 2b: preferably before incineration), 19 High-boiling stream from the extraction (in the first variant according to FIG. 2a: preferably before incineration), 20 Aqueous phase (reduced in aminophenols) (added to stream 3; some may be discharged as wastewater), 21 An acid (preferably hydrochloric acid or sulfuric acid).

[0092] The representation of neutralization and extraction (including phase separation) in the two stages 6000 and 7000 in Figure 2a / Figure 2b does not necessarily mean that these method steps must be performed in two apparatuses. In a preferred embodiment, the extraction is carried out in a so-called "mixer-settler" apparatus, as already mentioned, i.e. an apparatus comprising a mixing unit and a separation unit. In a particularly preferred configuration of this embodiment, the acid (stream 21 in the figure) and the organic stream (streams 18 and 9 in Figures 2a and 2b, respectively) are fed to a mixing unit, followed by phase separation in a separation unit. EXAMPLES

[0093] Example 1: Proof-of-principle experiment on aminophenol reduction and phase separation time (see FIG. 3) The crude aniline to be purified contained 750 ppm of phenol and 500 ppm of aminophenols relative to the total mass of its organic components and was saturated with water. This mixture was extracted in various experiments with water, sodium hydroxide solution, sodium chloride solution and a solution containing sodium hydroxide and sodium chloride, observing a volume ratio of aniline to extractant of 4:1. In this case, the NaOH concentration was adjusted to a constant value of 0.800% by mass with various NaCl concentrations (0%, 1.25%, 2.50%, 5.00%, 10.0% and 20.0% by mass). A series of experiments using sodium sulfate solution instead of NaCl solution was also carried out.

[0094] In the experiment with a salt concentration of 5.00 wt%, it was found that the phase separation was significantly accelerated for both salts, NaCl and Na2SO4. In the experiment with a salt concentration of 10.0 wt%, the time required for phase separation for both salts was comparable to that for the pure water-aniline mixture. At a salt concentration of 2.50 wt%, a significant reduction in the phase separation time was also observed for sodium sulfate.

[0095] In all tests (except when pure water and pure sodium chloride solution were used), ortho-aminophenol was removed from the organic phase to below the detection limit, and added phenol could be removed from the crude aniline to an extent of 75%-85%. No solid formation was observed in any of the tests.

[0096] These results are presented in graphical form in FIG.

[0097] The percentage of phenol / orthoaminophenol reduction is represented on the left vertical axis (Y1) in relation to the height of the bars (e.g. a value of 100 on the left vertical axis means that the corresponding phenolic compound is reduced below the detection limit).

[0098] The relative separation times (duration of phase separation) are represented on the right vertical axis (Y2) in relation to the position of the triangles (separation times for experiments with sodium sulfate) and circles (experiments with sodium chloride and without added further salt). For this, the duration for separation of aniline for the above composition of demineralized water was set to 1 (=reference) and the remaining values ​​are reported relative to this (for example a value of 80 on the right vertical axis means that the phase separation lasted 80 times longer than in the reference case).

[0099] The results of all experimental series are presented on the horizontal axis in the form of bars and symbols (triangles, circles) with the above mentioned meanings. In this figure, the following experimental series are shown from left to right:

[0100] Of crude aniline, (1) a sodium hydroxide solution having no additional salt content; (2) sodium hydroxide solution containing a mass proportion of 1.25% of further salts, (3) 2.50% by weight of a sodium hydroxide solution containing a further salt; (4) sodium hydroxide solution containing a mass proportion of 5.00% of a further salt; (5) Sodium hydroxide solution containing a mass proportion of 10.0% of a further salt, (6) Sodium hydroxide solution containing a mass proportion of 20.0% of a further salt, (7) Water containing 10.0% by mass of salt (without NaOH), and (8) Demineralized water (containing no NaOH or additional salts); Extraction by.

[0101] In experimental row (1), the bars are arranged from left to right as follows: (a) phenol, and (b) ortho-aminophenol, The percentage reduction in β-aminobutyric acid (β-aminobutyric acid) is shown, in both cases no additional salt was added.

[0102] In experimental rows (2) to (6), the bars are arranged from left to right as follows: (a) Phenol with sodium sulfate as the further salt; (b) phenol with sodium chloride as the further salt; (c) ortho-aminophenol with sodium sulfate as the further salt, and (d) ortho-aminophenol with sodium chloride as the further salt; The percentage of reduction in

[0103] In experimental row (7), the bars are ordered from left to right as follows: (a) phenol, with sodium sulfate as the further salt; and (b) ortho-aminophenol with sodium sulfate as the further salt; The percentage of reduction in

[0104] In experimental row (8), the bars are ordered from left to right as follows: (a) phenol, and (b) ortho-aminophenol, The percentage reduction in β-aminobutyric acid (β-aminobutyric acid) is shown, in both cases no additional salt was added.

[0105] Example 2: Proof-of-principle experiment for neutralization of aminophenol-depleted aqueous phase and subsequent extraction of the formed aminophenols (see FIG. 4) An aqueous NaOH solution (concentration 0.800% by mass) was saturated with aniline, followed by the addition of 5000 ppm ortho-aminophenol and 5000 ppm phenol so that the salts of the respective phenolic compounds were present. The various samples were then adjusted with hydrochloric acid at a concentration of 30% by mass to a pH in the range of 6.0-7.0 and below 3.5. The acidified samples were then extracted with a synthetic high boiler waste stream consisting of diphenylamine (as exemplary high boilers) and aniline in a mass ratio of 1:1. Here, depending on the pH and the nature of the phenolic compounds, it was possible to reduce the concentration of all phenolic compounds in the aqueous medium by a factor of 1.5 to 9.0. It can also be seen that the phenolic compounds can be extracted with varying degrees of success depending on the pH value.

[0106] These results are presented in the form of a bar graph in FIG.

[0107] The partition coefficient of each phenolic compound as the ratio of its mass fraction in the organic phase to its mass fraction in the aqueous phase is reported on the vertical axis (Y) in relation to the height of the bar.

[0108] The results of each experimental series are shown on the horizontal axis (X) in the form of two bars at pH values ​​of 3.4 and 6.5, respectively, where the left bar (a) shows the partition coefficient of phenol and the right bar (b) shows the partition coefficient of ortho-aminophenol.

[0109] Example 3: Sequential Experiments Regarding the Method A production sample of crude aniline (containing approximately 2500 ppm phenol and 250 ppm aminophenols) was continuously contacted in a two-stage mixer-settler system with an aqueous solution containing 10% by weight Na2SO4 and 1% by weight NaOH (pH=12) in a volume ratio of 4:1 (ratio of organic phase to aqueous phase) (extraction). An organic raffinate stream and an aqueous extract stream were obtained. The aqueous extract stream was continuously adjusted to a neutral pH by addition of sulfuric acid and contacted in a two-stage mixer-settler with a synthetically produced high-boiling stream (containing 50% by weight aniline and 50% by weight diphenylamine as representative of typical high boilers of the aniline process) in a volume ratio of 2:1 (ratio of aqueous phase to organic phase) (acid treatment and back extraction). The extraction and back extraction were carried out continuously in series at a temperature of 30° C. It was found that phenol and aminophenols could no longer be detected in the aniline raffinate from the extraction. This confirms the proof-of-principle experiments for the continuous process mode as well. During stripping, phenol and aminophenols were found in high concentrations in the high boiler extract. Considering the entire workup process, it was found that on average 85% of the phenol and 95% of the aminophenols could be transferred from the crude aniline stream to the stripping stream (in the high boiler extract). Phase separation proceeded without problems in all separators and, upon addition of the salt Na2SO4, an aqueous phase was obtained as the heavy phase in all separators.

Claims

1. A method for purifying aniline, comprising the steps of: a) providing a crude aniline fraction containing aniline and organic impurities, wherein the organic impurities comprise phenol, organic impurities having a boiling point lower than aniline, and aminophenols, and also further organic impurities having a boiling point higher than aniline, and the concentration of aminophenols relative to the total weight of the organic components of the crude aniline fraction is in the range of 0.001% to 1.00% by weight; b) extracting the crude aniline fraction from step a) with an aqueous extractant containing an alkali metal hydroxide in a concentration range of 0.009% to 2.05% by weight and an alkali metal salt different from the alkali metal hydroxide in a concentration range of 2.40% to 25.0% by weight, based on the total weight of the aqueous extractant, to obtain after phase separation an aminophenol-reduced organic aniline phase and an aqueous aminophenolate phase; c) distilling the organic aniline phase from step b) to obtain a purified aniline stream, a gaseous stream containing organic impurities having a boiling point lower than that of aniline, and a liquid stream containing aniline and organic impurities having a boiling point higher than that of aniline; A method comprising:

2. d. 1) concentrating the liquid stream from step c) containing aniline and organic impurities having a boiling point higher than that of aniline by evaporation of aniline to obtain an aniline-containing distillate stream and a bottoms stream containing organic impurities having a boiling point higher than that of aniline; e. 1) treating the aqueous aminophenolate phase obtained in step b) with an acid to convert the aminophenolate to aminophenol; f.1) extracting the aminophenols formed by the acid treatment with an organic stream comprising the bottom stream from step d.1) containing organic impurities with a boiling point higher than that of aniline to obtain an organic phase and an aqueous phase after phase separation, in which an alkali metal hydroxide is added to the aqueous phase, and this aqueous phase is used as a component of the extractant used in step a); The method of claim 1 , comprising:

3. d. 2) treating the aqueous aminophenolate phase obtained in step b) with an acid to convert the aminophenolate to aminophenol; e.2) extracting the aminophenols formed by the acid treatment with an organic stream comprising the liquid stream from step c) containing aniline and organic impurities having a boiling point higher than that of aniline to obtain an organic phase and an aqueous phase after phase separation, in which an alkali metal hydroxide is added to the aqueous phase, and this aqueous phase is used as a component of the extractant used in step a), f.2) concentrating the organic phase from step e.2) by evaporation of aniline to obtain an aniline-containing distillate stream and a bottom stream containing organic impurities having a boiling point higher than that of aniline, The method of claim 1 , comprising:

4. 4. The method according to claim 2 or 3, wherein the extraction step (step f.1) or step e.2)) is carried out in parallel with the acid treatment step (step e.1) or step d.2)).

5. Step c) comprises: or, wherein the purified aniline stream is withdrawn as a side draw, the gaseous stream containing organic impurities having a boiling point lower than that of aniline is withdrawn as an overhead stream, and the liquid stream containing aniline and organic impurities having a boiling point higher than that of aniline is withdrawn as a bottoms stream from the distillation column equipped with a side draw; or distillation in two distillation columns connected in series, in which in a first distillation column, the gaseous stream containing organic impurities having a boiling point lower than that of aniline is withdrawn as an overhead stream and the bottom stream obtained in the first distillation column is led as a feed to a second distillation column, in which the purified aniline stream is obtained as an overhead stream and the liquid stream containing aniline and organic impurities having a boiling point higher than that of aniline is obtained as a bottom stream; or The process comprises distillation in three distillation columns, wherein an overhead stream containing water and organic impurities is withdrawn from a first distillation column and separated into an aqueous phase and an organic phase, said organic phase being led to a second distillation column from which said gaseous stream containing organic impurities having a boiling point lower than that of aniline is withdrawn as an overhead stream, and the bottom stream obtained in said first distillation column is led as a feed to a third distillation column, in which said purified aniline stream is obtained as an overhead stream and said liquid stream containing aniline and organic impurities having a boiling point higher than that of aniline is obtained as a bottom stream, said gaseous stream containing organic impurities having a boiling point lower than that of aniline is partially liquefied, the liquid phase thus obtained, after optionally removing any water present, being recycled to the distillation column from which said gaseous stream containing organic impurities having a boiling point lower than that of aniline was withdrawn as overhead, and the gaseous phase remaining after partial liquefaction is discharged from the distillation, The method according to any one of claims 2 to 4.

6. 6. The process according to claim 5, wherein the gas phase remaining in step c) after the partial liquefaction is condensed and the resulting condensate is used as an additional component of the organic stream used in step f.1) or step e.2).

7. The alkali metal salt other than an alkali metal hydroxide is (i) an alkali metal chloride, or (ii) an alkali metal sulfate, In step e.1) or step d.2), the acid used in case (i) is hydrochloric acid and the acid used in case (ii) is sulfuric acid; The method according to any one of claims 2 to 6.

8. The alkali metal hydroxide used is sodium hydroxide or potassium hydroxide in the concentration range of 0.009% to 2.05% by weight, The alkali metal salts used which are different from the alkali metal hydroxides are Sodium chloride or potassium chloride in a concentration range of 4.00% by mass to 25.0% by mass, or 2. The method according to any one of claims 1 to 7, wherein the concentration range of sodium sulfate or potassium sulfate is from 40% by mass to 25.0% by mass.

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