JPH0136459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for producing aniline by hydrogenation of nitrobenzene.

U.S. patent for method for hydrogenating aromatic nitro compounds in liquid phase to produce corresponding aromatic amines
Proposed in No. 2292879. This method uses a nickel, cobalt, or copper catalyst supported on a finely divided carrier, suspended in a mixture of a nitro compound and its hydrogenation product, an amine, which is then charged with hydrogen. The reaction is carried out through The specification states that the activity of the catalyst is maintained at a high level by conducting the reaction under conditions such that the water produced in the reaction is continuously distilled off from the reaction system together with the amine, and that the aromatic amine is It is described that the activity of the catalyst is increased by using it as a solvent and reacting the amine at a relatively high concentration.

In addition, Patent Publication No. 15779/1979 states that in a liquid phase reaction, the concentration of the produced aromatic amine used as a solvent is maintained at 95% by weight or more in the liquid phase, as in the above-mentioned US patent, and the reaction is carried out as much as possible. By carrying out the reaction at around normal pressure and at a temperature at or near the boiling point, the water produced by the reaction can be easily removed from the system, and the product distilled off from the reactor has an aromatic aroma with a low content of nitro compounds. It has been proposed that this is advantageous because it provides group amines.

Keeping the amine concentration in the reaction solution high, that is, charging only the amount of nitro compounds commensurate with the consumption of the reaction, lowers the content of unreacted nitro compounds in the product that is distilled out of the system. It is also generally recommended to use a large amount of solvent to control the temperature in reactions that generate a large amount of heat, such as the present reaction, and to control the heat of reaction using the latent heat of vaporization.

From this point of view, it seems advantageous to maintain the amine concentration in the reaction solution as close to 100% as possible and to reduce the concentration of the nitro compound.
However, if the reaction is carried out with a low concentration of nitro compounds in the reaction system, the amount of amine produced per unit time will naturally decrease, resulting in a decrease in production efficiency.More importantly, in the amine solvent, When the concentration of the nitro compound is lowered, nuclear hydrogenation of the aromatic ring is more likely to occur as a side reaction, and impurities such as cyclohexylamine, cyclohexanone, cyclohexylideneaniline, and cyclohexylaniline are more likely to be produced. The rate of these by-products increases as the concentration of nitro compounds in the reaction system decreases.

In order to suppress these by-product impurities, the aforementioned Japanese Patent Publication No. 50-15779 proposes adding organic bases such as alkanolamines. For example, in the case of producing aniline by hydrogenating nitrobenzene, triethanolamine is added. However, even in this case, about 0.02% or less of nitrobenzene and 0.5
% or less of impurities of the hydrogen additive. Furthermore, it has been described that when triethanolamine is not added, the amount of impurities is even higher and it is difficult to separate the aniline layer and the aqueous layer of the condensed product. By the method of Example 1 of Japanese Patent Publication No. 50-15779,
As a result of additional trials using a silicon earth-nickel catalyst,
The distilled condensed aniline contained 0.05% or more of unreacted nitrobenzene and 0.6% or more of nuclear water additives.

As described above, the disadvantage of the method of Japanese Patent Publication No. 50-15779 is that in order to reduce unreacted nitrobenzene, the concentration of aniline in the reaction solution is brought closer to 100% and the concentration of nitrobenzene is lowered. On the other hand, if the aniline concentration is approached to the lower limit of 95%, unreacted nitrobenzene will increase in the condensed aniline. Therefore, in order to provide the aniline obtained by this method as high-purity aniline of commercial standard, it is necessary to perform some kind of complicated purification process that is almost the same as that incorporated in the conventional aniline production process. It won't happen. In addition, in this method, although not disclosed in the specification, as the reaction continues, high-boiling point impurities and tar-like substances rapidly accumulate in the reaction solution, which reduces the activity of the catalyst and shortens the catalyst life. The inventors have also found that this makes it difficult to carry out long-term drug reactions.

The present inventors have made extensive studies with the aim of completing a continuous production method for high-purity aniline containing almost no impurities, and have found that by using a specific catalyst under specific reaction conditions, the method described in Japanese Patent Publication No. 50-15779 was We have discovered a method for producing highly pure aniline that contains extremely low amounts of impurities such as unreacted nitrobenzene and nuclear water additives that cannot be obtained by other methods, and have completed the method of the present invention.

That is, the process of the present invention is a process for the continuous production of aniline by hydrogenation of nitrobenzene, in which palladium or palladium-platinum is deposited on lipophilic carbon having an oil absorption of at least 100 in aniline as a solvent. was suspended as a catalyst, and the concentration of nitrobenzene in the reaction solution was adjusted to 0.5.
The reaction is carried out at a temperature of 150 to 250°C while keeping the temperature below % by weight, and the reaction is carried out in the substantial absence of water while continuously distilling off aniline and reaction product water as steam from the reaction product. This is a method for producing high purity aniline.

In the process of the invention, the catalyst used is palladium or palladium-platinum catalyst deposited on non-porous lipophilic carbon with an oil absorption of 100 or higher. Generally, palladium and/or platinum catalysts using commercially available porous activated carbon or alumina as carriers do not give good results in the method of the present invention, and oil absorption rates of 100 or more, preferably in the range of 150 to 300, are not used as carriers. It is necessary to be an oily carbon carrier.
The oil absorption rate of the carrier is defined in Japanese Patent Publication No. 32-9320, and is expressed as the number of parts by weight of raw cottonseed oil having an acid value of 2 to 4 per 100 parts by weight of carbon that causes gelation. . The particle size of the carrier is 20 to 60 mμ, and the surface area is 50 to 100.
m ² /g is appropriate.

In addition, the method for producing the catalyst is as follows: palladium,
It can be prepared by conventional methods such as platinum-compound precipitation. Palladium deposited on lipophilic carbon and concentrations of palladium and platinum range from 0.1 to
5% by weight is suitable, particularly preferably 0.5-1.0% by weight. Palladium may be used alone, but when used in combination with platinum, it is particularly effective in terms of activity and selectivity, and in that case it is desirable to use about 5 to 20% by weight of platinum relative to palladium. Further, as described in the above specification, a small amount of oxides or hydroxides of metals such as iron and nickel may be mixed. The concentration of the catalyst in the reaction mixture system is usually 0.2 to 2.0% by weight.

When the method of the present invention is carried out using the catalyst of the present invention, if water is present in the reaction system, the catalytic activity decreases and at the same time the amount of by-products increases. It is necessary to remove it from the system and conduct the reaction in the substantial absence of water.
Therefore, in the method of the present invention, a very small amount of nitrobenzene is introduced in one pass to carry out the reaction, and the nitrobenzene introduced into the reactor is instantaneously converted to aniline and water, and the reaction products are removed from the system as steam. This is possible by appropriately selecting the reaction temperature within the temperature range of 150 to 250° C. in relation to the hydrogen pressure, and by evaporating almost all of the reaction products with a portion of the reaction heat generated. The steam is then condensed to separate water and aniline, and the water is removed from the system. At that time, it is desirable to return a portion of the aniline condensate to the reactor as necessary to maintain the amount of liquid in the reactor approximately constant to carry out the reaction.

In the method of the present invention, hydrogenation can be carried out under atmospheric pressure, but it is preferably carried out at a pressure of 1.5 to 10 atmospheres. If carried out under atmospheric pressure, impurity by-products tend to increase relatively and the life of the catalyst tends to be shortened, so it is particularly preferable to carry out under 3 to 7 atmospheres. Also, the reaction temperature is in the range of 150-250℃.
Below 150℃, the reaction will be slow and the production per hour will be low, and in order to effectively remove the reaction product water from the system, a temperature of 150℃ or higher is required, but 250℃
Above this amount, the amount of by-products increases. Nitrobenzene is supplied into the aniline solvent in an amount approximately equivalent to the conversion to aniline so that the concentration of nitrobenzene in the reaction solution is 0.5% by weight or less, and the reaction is preferably maintained at a concentration of 0.1% by weight or less.

If the nitrobenzene concentration in the reaction solution exceeds 0.5% by weight, nitrobenzene will be mixed into the distilled aniline, and a new distillation purification process will be required to obtain high-purity aniline. Therefore, it would be very industrially advantageous if the reaction could be carried out at a nitrobenzene concentration of 0.5% by weight or less in the reaction solution; however, the production rate of nuclear hydrogenation by-products represented by N-cyclohexylaniline decreases from around this nitrobenzene concentration. tends to increase rapidly, and this tendency becomes even more pronounced as the concentration of nitrobenzene becomes lower.

The catalyst of the present invention has a particularly strong effect of suppressing nuclear hydrogenation, so when carried out at a nitrobenzene concentration of 0.1% by weight or less, nuclear hydrogenation can be suppressed without adding an inhibitor such as triethanolamine, and unreacted nitrobenzene can be suppressed. High purity aniline containing almost no aniline can be obtained. The amount of liquid in the reaction system is adjusted by taking out the amount of aniline corresponding to the charge amount of nitrobenzene, that is, the amount of aniline converted to aniline from the reaction system as vapor, or by returning a portion of the distilled aniline to the reaction system after separating it from water. do.

Japanese Patent Publication No. 32-9320 describes the characteristics of the catalyst in which palladium and/or platinum is deposited on a lipophilic carbon carrier used in the method of the present invention as an aqueous system in which the organic nitro substance is suspended in water. However, the catalyst that was conventionally thought to be useful in such reactions using water as a medium has been shown to exhibit high activity in hydrogenation using amine as a solvent, as in the present invention. Shows extremely high selectivity in a system in the absence of water, in other words, shows extremely strong activity only for the reduction of nitro groups, while showing almost no activity for the reduction of aromatic nuclei and other impurity-forming reactions. It was completely unexpected and surprising that there would be no such thing.

As described above, by carrying out the method of the present invention, high-purity aniline with extremely low unreacted nitrobenzene content and extremely suppressed nuclear hydrogenated products can be produced in one bath without adding any nuclear hydrogenation inhibitor. Therefore, it can be said that the purification process is almost unnecessary and the effect is extremely large.

Examples are shown below.

Example 1 Equipped with an inlet for continuously supplying nitrobenzene, a catalyst, and hydrogen gas, an outlet for discharging unreacted hydrogen gas and products from the reaction system, a condenser, a stirrer, and a thermometer. Aniline in a stainless steel autoclave with an internal volume of 1
500g and 0.25g of hydrogenation catalyst obtained by depositing 0.8% by weight of palladium, 0.1% by weight of platinum, and 0.8% by weight of iron on carbon powder with an oil absorption rate of 260, and the internal temperature was raised to 190~190g.
Nitrobenzene, catalyst, and hydrogen gas were each fed at 100°/hour at 200°C while maintaining the total pressure at 3 kg/cm ³ G.
water and aniline are continuously discharged from the system together with unreacted hydrogen gas, and this steam is introduced into a condenser connected to the autoclave and equipped with it. Water and aniline were condensed by cooling. During this time, the flow rate of hydrogen gas is adjusted so that an amount of aniline corresponding to the amount produced by the supplied nitrobenzene is distilled out, that is, the weight of the liquid phase containing aniline as the main component in the autoclave is always maintained at around 500 g. I adjusted it as follows. On the other hand, the catalyst concentration in the system was kept constant by extracting the amount of catalyst from the reactor at regular intervals (approximately 10% by weight of the nitrobenzene supplied). At that time, by filtering and analyzing the extracted bottom liquid, it was possible to know the concentration of nitrobenzene in the bottom liquid and the amount of nuclear hydrogenated products such as N-cyclohexylaniline and other by-products produced. The resulting condensate was separated into two layers, yielding a colorless to pale yellow transparent aniline layer. This aniline layer contains approximately 4.5% water, but as a result of analysis by gas chromatography, impurities of cyclohexanol, cyclohexanone, cyclohexylideneaniline, and nitrobenzene were found to be less than 40ppm, less than 100ppm, and less than 30ppm, respectively.
The purity of aniline was 99.98% or more.
Furthermore, a final analysis of the aniline solution in the liquid phase in the reactor during the reaction confirmed that the nitrobenzene concentration was maintained at 0.2% or less. During that time, the nitrobenzene concentration in the liquid phase became too high, and there was no need to make changes such as reducing the amount of nitrobenzene supplied or increasing the amount of catalyst supplied. Although N-cyclohexylaniline was observed in this liquid phase, its content was only 0.05% 9 hours after the start of the reaction.

Example 2 Using the same equipment and operation as in Example 1, a reaction was carried out using a hydrogenation catalyst obtained by depositing palladium on carbon powder with an oil absorption rate of 180 to a content of 0.8 weight percent. The impurities in the distilled aniline layer were found to be less than 40 ppm of cyclohexanol, less than 120 ppm of cyclohexanone,
Cyclohexylideneaniline 50ppm or less, and
It contained less than 50 ppm of nitrobenzene, and the purity of aniline was more than 99.97%. Further, the concentration of nitrobenzene in the liquid phase in the reactor during the reaction was maintained at 0.2% or less, and the content of N-cyclohexylaniline was only 0.08% 9 hours after the start of the reaction. During that time, the nitrobenzene concentration in the liquid phase became too high, so there was no need to make changes such as reducing the amount of nitrobenzene supplied or increasing the amount of catalyst supplied.

Comparative Example 1 Completely the same as Example 1 except that a catalyst obtained by depositing palladium at a content of 1% on finely powdered charcoal containing 90% or more of particles with a particle size of 100 mesh or less was used. As a result of using the same equipment and operation, the aniline layer distilled from the reactor contained impurities of 0.06 to 0.07% cyclohexanol, 0.19 to 0.26% cyclohexanone, and 0.08% cyclohexylidene aniline.
~0.11% N-cyclohexylaniline 0.003~
It contained 0.006% and nitrobenzene 0.04-0.06%. Further, N-cyclohexylaniline was produced in the liquid phase in the reactor, and its content reached about 1.4% 9 hours after the start of the reaction. Moreover, the nitrobenzene content in this liquid phase was 1.0 to 1.4%.

Comparative Example 2 The reaction was carried out in the same manner as in Example 1 except that the supply rates of nitrobenzene, catalyst, and hydrogen gas were 130 g (average), 0.033 g (average), and 60 to 90 g/hour, respectively. Impurities in the distilled aniline layer were Slight yellow or less than 30ppm of cyclohexanol, 50ppm or less of cyclohexanone, 10ppm or less of cyclohexylideneaniline, and 500ppm or less of nitrobenzene,
A yellow aniline was obtained with a purity of over 99.95%.

In addition, the aniline solution in the liquid phase inside the reactor during the reaction was sequentially analyzed, and the nitrobenzene concentration was determined to be 0.55 to 0.6.
%. During this period, in order to maintain this nitrobenzene concentration, the supply amount of nitrobenzene was adjusted to 110g to 150g/hour.
g (average) and catalyst supply amount from 0.025 to 0.038 g (average 0.033 g). Also,
Although N-cyclohexylaniline was observed in this liquid phase, it was 0.02% at 9 hours after the start of the reaction.

Claims (1)

[Claims] 1. In the continuous production method of aniline by hydrogenation of nitrobenzene, as the aniline solvent,
Palladium or palladium-platinum deposited on lipophilic carbon having an oil absorption rate of at least 100 is suspended in the solvent as a catalyst, and the concentration of nitrobenzene in the reaction solution is kept below 0.5% by weight. A method for producing high-purity aniline, in which the reaction is carried out at a temperature of ~250°C, and the reaction is carried out substantially in the absence of water while continuously distilling off aniline and reaction product water from the reaction product as steam.