JP4552941B2 - Method for purifying and producing aniline - Google Patents

Description

  The present invention relates to a method for purifying and producing aniline.

  Aniline is generally produced by hydrogenating nitrobenzene in the gas phase or liquid phase in the presence of a catalyst. In this reaction, by-products such as phenol and derivatives thereof are usually generated in addition to the target product. The reaction product is usually cooled and condensed, separated into oil and water, and the oil phase and the aqueous phase are distilled to obtain aniline. The crude aniline that is the oil phase has, for example, the composition shown in Table 1.

  The product aniline obtained by distilling the crude aniline has a problem of coloring the product aniline due to contamination with coloring impurities although the ingredients are not clear. In order to solve this, a method is known in which crude aniline is contacted with solid caustic soda and then distilled to obtain aniline that is not colored (see Patent Document 1). However, this method has problems that the viscosity of high boiling waste oil is high and difficult to handle, and that high concentration caustic soda is handled at a high temperature (about 100 ° C. to 150 ° C.), so that the distillation tower is easily corroded. Have.

On the other hand, as impurities in aniline, phenol is desired to be 30 ppm or less, and high boiling point content is desired to be 0.1% or less. These concentrations are defined in JIS K 4109.
The boiling point of phenol (181.4 ° C.) and the boiling point of aniline (184.4 ° C.) are very close to each other. When these separations are carried out in a normal distillation column, energy consumption increases, which is not economical.

  In addition, it is known that aniline having a phenol concentration of 30 ppm or less can be obtained by contacting a crude aniline containing phenol with an alkali aqueous solution having an alkali concentration of 0.1 to 0.7% by weight. (See Patent Document 2). However, the purification method is insufficient to obtain aniline of higher quality (for example, phenol concentration of 5 ppm or less), and the crude aniline contains a large amount of phenol (for example, phenol concentration of 300 ppm or more). During the process, the phenols could not be removed sufficiently.

JP-A-49-35341 JP-A-8-295654

  An object of the present invention is to provide a purification method and a production method of aniline capable of obtaining high-quality aniline without causing a problem of handling high boiling waste oil and corrosion of a distillation tower.

The present invention provides the following inventions.
(1) The contact of aniline obtained by hydrogenation of nitrobenzene with a mixture of crude aniline and aqueous alkali solution and oil-water separation of the mixture is performed twice or more, and the oil phase obtained is distilled to obtain aniline. Purification method.
(2) The total amount of water contained in the aniline subjected to the contact treatment and the water contained in the alkaline aqueous solution, or the water contained in the aniline subjected to the contact treatment, the water contained in the alkaline aqueous solution, and further added water The purification method according to (1), wherein the alkali concentration determined from the total amount and the amount of alkali is 0.1 to 0.7% by weight.
(3) The purification method according to the above (1), wherein the alkaline aqueous solution is an alkaline aqueous solution prepared by using the recovered water obtained from the top of the distillation column by distilling the aqueous phase obtained by oil-water separation.
(4) The total amount of water contained in the aniline subjected to the contact treatment and the water contained in the alkaline aqueous solution, or the water contained in the aniline subjected to the contact treatment, the water contained in the alkaline aqueous solution, and further added water The purification method according to (3), wherein the alkali concentration determined from the total amount and the amount of alkali is 0.1 to 4.5% by weight.
(5) The purification method according to any one of (1) to (4), wherein the alkaline aqueous solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution.
(6) Nitrobenzene is hydrogenated to obtain crude aniline, and contact treatment comprising mixing of the crude aniline and aqueous alkali solution and oil-water separation of the mixture is performed twice or more, and the obtained oil phase is distilled. The manufacturing method of aniline which has the process of obtaining aniline.

  According to the present invention, high-quality aniline can be easily obtained without causing problems with handling of high-boiling waste oil and corrosion of the distillation tower, and even if the crude aniline contains phenols at a high concentration of 300 ppm or more. Phenols can be effectively removed.

  The alkali used in the present invention refers to a basic compound of alkali metal or alkaline earth metal, and specific examples thereof include sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate. Is mentioned. Sodium hydroxide or potassium hydroxide is preferably used from the viewpoint of reactivity, liquid separation, and the like.

  In the present invention, the contact treatment between the crude aniline and the aqueous alkaline solution is performed twice or more. The more the number of contact treatments, the more effective purification is possible, but too many times are uneconomical, and the number of contact treatments is preferably 2 to 4 times, particularly preferably 2 times. The contact treatment is a treatment in which an aqueous alkaline solution having a predetermined concentration is added to and mixed with crude aniline, and the resulting mixture is separated into oil and water. Water is by-produced in the hydrogenation reaction of nitrobenzene. The crude aniline may be used while containing this water, or may be used after removing the water. The concentration of the alkaline aqueous solution is adjusted in consideration of the water that the crude aniline may contain. Separately, water for adjusting the concentration may be added.

  In the present invention, the alkali concentration of the aqueous phase is preferably about 0.1 wt% to 0.7 wt%, more preferably about 0.15 wt% to 0.65 wt%. If the alkali concentration is low, a large amount of alkaline aqueous solution is required to sufficiently remove phenols, which is not economical. On the other hand, if the alkali concentration is high, the upper and lower sides of the oil phase and the aqueous phase are reversed, the liquid separation property is deteriorated, and the amount of alkali brought into the next process is increased. Here, the alkali concentration in the present invention is the total amount of water contained in the aniline subjected to the contact treatment and the water contained in the aqueous alkaline solution, or the water contained in the aniline subjected to the contact treatment, the alkaline aqueous solution. It is calculated | required from the total amount of the water contained and water to add, and the amount of alkali. That is, the alkali concentration (% by weight) = amount of alkali / (amount of alkali + total amount of water) × 100. Examples of the aniline that is subjected to the contact treatment here include crude aniline and aniline that is further subjected to the contact treatment after the contact treatment.

  For the preparation of the aqueous alkaline solution, it is preferable to use an aqueous phase (recovered water) recovered from the top of the distillation column by distilling the aqueous phase obtained by the oil-water separation. The recovered water usually contains about 0.1 to 7% by weight of ammonia, which is a byproduct of the hydrogenation reaction, so that the specific gravity is lower than 1. By using this recovered water, the concentration of the aqueous alkali solution used can be increased, and even when the alkali concentration is increased to about 4.5% by weight, the upper and lower sides of the oil phase and the aqueous phase are not reversed, and the liquid is separated. Sex does not deteriorate. For removal of phenols, a higher alkali concentration is preferred. The aqueous alkali solution prepared using the recovered water is preferably used for the second and subsequent contact treatments.

  The amount ratio of alkali to phenols depends on the concentration of phenols in the crude aniline, but when the alkali is an alkali metal basic compound, the molar ratio of alkali metal to phenols is usually 3 to 500, preferably 10 to 200. When the alkali is a basic compound of an alkaline earth metal, the molar ratio of the alkaline earth metal to the phenol is usually 1.5 to 250, preferably 5 ~ 100. If the amount of alkali is small, sufficient phenols cannot be removed. If the amount is large, the amount of alkali increases, which is not economical.

  The mixing time of the crude aniline and the aqueous alkaline solution is not particularly limited as long as the contact between the crude aniline and the aqueous alkaline solution is sufficiently performed.

  After mixing, the mixture is allowed to stand, oil-water separation is performed, and the water phase and the oil phase are distilled to separate aniline, water, low-boiling substances, and high-boiling substances. The oil phase portion is usually distilled at a pressure of about 8 to 30 kPaA and a temperature of about 110 to 140 ° C. to obtain a purified aniline having no coloring and having a phenol concentration of 30 ppm or less (usually hardly contained).

  At this time, the viscosity of the high-boiling waste oil does not become so high that it becomes difficult to handle or corrosion due to alkali hardly occurs.

  The method of the present invention can be easily carried out by a continuous method or a batch method.

  An example of a process flow diagram (PFD) according to the purification method of the present invention is shown in FIG. The reactor 1 is a reactor in which nitrobenzene is hydrogenated to obtain crude aniline. The reaction gas from the reactor 1 is cooled by the cooler 2 to condense the reaction product. Gas-liquid separation is performed in the gas-liquid separation tank 3, and the gas phase 13 is circulated and used while being partially purged. The aqueous alkaline solution 9 is added to the liquid phase, mixed and brought into contact. The mixture is oil-water separated in the oil / water separation tank 4, and the aqueous phase is sent to the water phase storage tank 7. The alkaline aqueous solution 10 is added to the oil phase via the oil phase storage tank 5, mixed, and brought into contact. The mixture is oil-water separated in the oil / water separation tank 6, the water phase is sent to the water phase storage tank 7, and the oil phase is sent to the oil phase storage tank 8. The alkaline aqueous solution is not limited to the method of adding to the liquid feed line, and may be added to the gas-liquid separation tank 3 and / or the oil phase storage tank 5.

  FIG. 2 shows an example of a PFD in which the water phase and the oil phase obtained by separation are distilled to separate and purify them into aniline, water, low-boiling substances and high-boiling substances. The aqueous phase is distilled from the aqueous phase storage tank 7 via the liquid feed line 11 to the distillation tower 21 and an aqueous solution containing phenols is taken out from the bottom of the tower. This is usually treated as waste water. Water and organic matter are distilled from the top of the column, cooled and condensed, and separated into an aqueous phase and an oil phase by the oil / water separator 24. The aqueous phase is sent to the aqueous phase storage tank 7 and circulated to the distillation tower 21. This aqueous phase contains ammonia, which is a by-product when hydrogenating nitrobenzene, and has a specific gravity of less than 1, so it is preferably used for preparing the alkaline aqueous solution. The oil phase is recovered in the oil phase storage tank 8.

  The oil phase is supplied to the distillation column 22 from the oil phase storage tank 8 via the liquid feed line 12 and distilled, and water, low-boiling substances, etc. are distilled from the top of the column, cooled and condensed, and separated into oil and water. Separator 25 separates the water phase and the oil phase. The aqueous phase containing organic matter is recovered in the aqueous phase storage tank 7. The oil phase is taken out as a low-boiling point product and treated such as combustion. The aniline containing a high boiling point substance is taken out from the bottom of the column, supplied to the distillation tower 23 and distilled, and the high boiling point is taken out from the bottom of the column and treated such as combustion. Purified aniline is taken out from the top.

  Here, the oil phase separated from the top of the distillation column 21 may be recovered not at the oil phase storage tank 8 but at the top of the distillation column 22. Moreover, since the low boiling point substance separated by the oil / water separator 25 contains aniline, it is distilled in a distillation tower (not shown), and an organic substance containing aniline is taken out from the bottom of the tower and recovered in the distillation tower 22. Also good. At this time, an aqueous phase containing a low boiling point substance is taken out from the top of the tower, and the aqueous phase is recovered in the aqueous phase storage tank 7.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to this.

Comparative example 3 (old example 1)
The reaction product obtained by hydrogenating nitrobenzene was separated into oil and water to obtain crude aniline (phenol concentration 174 ppm). Into the mixer, 345 g of crude aniline (oil phase) and 137 g of water were added, and 1.67 g of 25 wt% aqueous sodium hydroxide solution was added so that the sodium hydroxide concentration in the aqueous phase portion was 0.3 wt%. Mixed at 0 ° C. and contacted. Subsequently, oil-water separation was carried out using a separatory funnel, and the phenol concentration in the oil phase was measured and found to be 26 ppm. Next, 172 g of this oil phase and 68 g of water are put into a mixer, and 0.83 g of 25 wt% aqueous sodium hydroxide solution is added so that the sodium hydroxide concentration in the aqueous phase portion is 0.3 wt%. Mixed at 0 ° C. and contacted. Subsequently, oil-water separation was carried out using a separatory funnel, and the phenol concentration in the oil phase was measured and found to be 2 ppm. By distilling this oil phase, aniline which is uncolored and hardly contains phenols can be obtained without causing corrosion.

Example 2
172 g of the oil phase (phenol concentration 26 ppm) obtained in the first contact treatment in Example 1 and the aqueous phase obtained in the first contact treatment in Example 1 were distilled and recovered from the tower top. 68 g of water (aniline concentration: 4% by weight, ammonia concentration: 4% by weight) was put in a mixer, and 25% by weight aqueous sodium hydroxide solution was added so that the sodium hydroxide concentration in the aqueous phase became 0.3% by weight. 83g was added, mixed at 20 ° C and contacted. Subsequently, oil-water separation was carried out using a separatory funnel, and the phenol concentration in the oil phase was measured and found to be 0.6 ppm. By distilling this oil phase, aniline which is uncolored and hardly contains phenols can be obtained without causing corrosion.

Example 3
The reaction product obtained by hydrogenating nitrobenzene was separated into oil and water to obtain crude aniline (phenol concentration 522 ppm). Into the mixer, 174 g of crude aniline (oil phase) and 67 g of water were added, 0.82 g of 25 wt% aqueous sodium hydroxide solution was added so that the sodium hydroxide concentration in the aqueous phase was 0.3 wt%, and 35 ° C. And contact. Subsequently, oil-water separation was carried out using a separatory funnel, and the phenol concentration in the oil phase was measured and found to be 117 ppm. Next, 174 g of this oil phase and 67 g of recovered water (aniline concentration: 4 wt%, ammonia concentration: 4 wt%) obtained in the same manner as in Example 2 were put in a mixer, and the sodium hydroxide concentration in the aqueous phase portion was 0.82 g of 25 wt% aqueous sodium hydroxide solution was added so that the amount of the solution was 0.3 wt%, mixed at 20 ° C, and contacted. Subsequently, oil-water separation was performed using a separatory funnel, and the phenol concentration in the oil phase was measured. As a result, it was 11 ppm. By distilling this oil phase, aniline which is not colored and contains almost no phenol can be obtained without causing corrosion.

Comparative Example 1
In a mixer, 174 g of crude aniline (oil phase) obtained in the same manner as in Example 3 (oil phase phenol concentration: 522 ppm) and 134 g of water were added, and the sodium hydroxide concentration in the aqueous phase portion was 0.3 wt%. Then, 1.61 g of 25 wt% sodium hydroxide aqueous solution was added, mixed at 35 ° C., and contacted. Subsequently, oil-water separation was carried out using a separatory funnel, and the phenol concentration in the oil phase was measured and found to be 56 ppm. By distilling this oil phase, it is quite difficult to obtain aniline which is uncolored and hardly contains phenols.

Comparative Example 2
In a mixer, 174 g of crude aniline (oil phase) obtained in the same manner as in Example 3 (oil phase phenol concentration: 522 ppm) and 67 g of water were added, and the sodium hydroxide concentration in the aqueous phase portion was 0.6% by weight. Then, 1.61 g of 25 wt% sodium hydroxide aqueous solution was added, mixed at 35 ° C., and contacted. Subsequently, oil-water separation was carried out using a separatory funnel, and the phenol concentration in the oil phase was measured and found to be 67 ppm. By distilling this oil phase, it is quite difficult to obtain aniline which is uncolored and hardly contains phenols.

It is a figure which shows an example of the process flow diagram (PFD) which concerns on the purification method of this invention. It is a figure which shows an example of the process flow diagram (PFD) which isolate | separates and isolate | separates the water phase and oil phase which were isolate | separated into aniline, water, a low boiling point thing, and a high boiling point thing, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reactor 2 Cooler 3 Gas-liquid separation tank 4, 6 Oil / water separation tank 5, 8 Oil phase storage tank 7 Water phase storage tank 9, 10 Alkaline aqueous solution 21, 22, 23 Distillation tower 24, 25 Oil / water separator 27 Waste water 28 Low boiling point Product 29 product aniline 30 high boiling point product

Claims (5)

A method for purifying aniline, wherein the contact treatment comprising mixing of the crude aniline obtained by the hydrogenation reaction of nitrobenzene with an aqueous alkaline solution and oil-water separation of the mixture is performed twice or more, and the resulting oil phase is distilled to obtain aniline. An aniline, which is an alkaline aqueous solution prepared using recovered water obtained from the top of a distillation column by distilling an aqueous phase obtained by oil-water separation, from an alkaline aqueous solution used for the second and subsequent contact treatments Purification method .   The total amount of water contained in the aniline subjected to the contact treatment and the water contained in the alkaline aqueous solution, or the total amount of water contained in the aniline subjected to the contact treatment, the water contained in the alkaline aqueous solution, and further added water; The purification method according to claim 1, wherein the alkali concentration determined from the amount of alkali is 0.1 to 0.7% by weight. The total amount of water contained in the aniline subjected to the second and subsequent contact treatments and the water contained in the alkaline aqueous solution or the water contained in the aniline subjected to the second and subsequent contact treatments, the water contained in the alkaline aqueous solution, and further the total amount of the alkali concentration determined from the amount of the alkali of water added is, the purification method of claim 1, wherein a 0.1 to 4.5 wt%. The purification method according to any one of claims 1 to 3 , wherein the alkaline aqueous solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution. Nitrobenzene is hydrogenated to obtain crude aniline, and contact treatment comprising mixing the crude aniline and aqueous alkali solution and oil-water separation of the mixture is performed twice or more, and the resulting oil phase is distilled to obtain aniline. A method for producing aniline having a step, wherein an alkaline aqueous solution used for the second and subsequent contact treatments uses recovered water obtained from the top of a distillation column by distilling an aqueous phase obtained by oil-water separation. A method for producing aniline, which is an aqueous alkali solution prepared in the above .

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