JP2008222623A - Method for stopping reaction of liquid-phase reaction - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stopping a reaction, which controls formation of impurities in the production of an aromatic amine by a hydrogenation reaction of a nitro group-containing aromatic compound in a liquid phase. <P>SOLUTION: In a liquid-phase reaction for producing an aromatic amine by a hydrogenation reaction of a nitro group-containing aromatic compound, in a state in which the supply of a hydrogen gas and a catalyst to a liquid-phase reaction vessel (reactor) 2 and the discharge of a reaction solution 16 containing the catalyst from the liquid-phase reaction vessel 2 are continued, the supply of the nitro group-containing aromatic compound to the liquid-phase reaction vessel 2 and the supply of the catalyst are stopped and then when the concentration of the nitro group-containing aromatic compound in the reaction solution 16 reaches 30 ppm or after that, the supply of the hydrogen gas to the liquid-phase reaction vessel 2 is stopped. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for stopping a reaction in a liquid phase reaction, and more particularly to a method for stopping a reaction in the production of an aromatic amine by a hydrogenation reaction of a nitro group-containing aromatic compound in a liquid phase.

In the reaction of producing aniline by hydrogenation reaction of nitrobenzene in the liquid phase, it is common to use aniline, which is a reaction product, as a reaction solvent, and to react nitrobenzene, which is a reaction raw material, with hydrogen in the presence of a catalyst. (See Patent Document 1).
Further, for example, as a method of interrupting the liquid phase reaction for maintenance, inspection, cleaning, etc. of the reactor, for example, after reducing the supply amount of the reaction raw material and catalyst in advance and reducing the output of the reactor, A method of stopping the supply of the reaction raw material and the catalyst at a time can be mentioned.
JP-A-2-279657

  However, in a reaction system in which aniline is produced by a hydrogenation reaction of nitrobenzene in the liquid phase, for example, when only the supply of hydrogen gas into the reactor is stopped, aniline, nitrobenzene and a catalyst are contained in the reactor. It is present, and the reactor is heated and pressurized, resulting in a hydrogen deficient state. In addition, when the supply of nitrobenzene, hydrogen gas, and catalyst into the reactor is stopped at once, nitrobenzene and the catalyst are present in the reactor for a while after the supply is stopped, as in the above case. In the state where the temperature in the reactor is increased and the pressure is increased, the state where hydrogen is deficient is obtained. In such a state, there is a problem that a nitroso compound which is an unstable substance is easily generated, and impurities are increased due to the formation of the nitroso compound, and the purity of aniline is lowered.

  In the above reaction system, for example, when only the supply of nitrobenzene to the reactor is stopped, aniline, hydrogen gas, and a catalyst are present in the reactor, and the reactor is heated and heated. In this state, nitrobenzene is deficient. In such a state, nuclei hydrogenated aniline, polycyclic aromatic compounds such as dimers and trimers are likely to be formed, impurities increase, and the purity of aniline decreases.

  Further, in the above reaction system, for example, when only the supply of the catalyst into the reactor is stopped, the unreacted nitrobenzene supplied excessively remains in the reactor. This nitrobenzene is vaporized by the heat in the reactor and can be recovered as a vapor together with the reaction product aniline. However, since the boiling points of nitrobenzene and aniline are close to each other, it is difficult to completely separate them. Yes, the purity of aniline decreases.

  Therefore, an object of the present invention is to provide a method for stopping a reaction in which the production of impurities is suppressed in the production of an aromatic amine by the hydrogenation reaction of a nitro group-containing aromatic compound in a liquid phase.

  In order to achieve the above object, the liquid phase reaction stopping method of the present invention is a liquid phase reaction for producing an aromatic amine by hydrogenation reaction of a nitro group-containing aromatic compound. In a state where the supply of the catalyst and the discharge of the reaction liquid containing the catalyst from the reactor are continued, the supply of the nitro group-containing aromatic compound into the reactor and the supply of the catalyst are stopped, and then The supply of hydrogen gas into the reactor is stopped when the concentration of the nitro group-containing aromatic compound in the reaction solution reaches 30 ppm or thereafter.

  According to this liquid phase reaction stopping method, the supply of the nitro group-containing aromatic compound is stopped while the supply of the hydrogen gas and the catalyst into the reactor is continued. Moreover, mixing of the nitro group-containing aromatic compound into the reaction product can be suppressed. In addition, when the concentration of the nitro group-containing aromatic compound in the reaction solution reaches 30 ppm or after that, the supply of hydrogen gas into the reactor is stopped and the reaction solution is cooled down. Production of polycyclic aromatic compounds such as nuclear hydrogenated products, dimers and trimers can be suppressed.

In the liquid phase reaction stopping method of the present invention, the catalyst is removed from the reaction liquid remaining in the reactor after the supply of hydrogen gas is stopped, and then the reaction liquid from which the catalyst has been removed is used as the liquid phase reaction. It is preferred to recycle it as a source of aromatic amine at the start of the process.
According to the reaction stopping method of the liquid phase reaction, the generation of impurities when the liquid phase reaction is stopped can be suppressed, and the mixing of impurities into the reaction solution remaining in the reactor after the reaction is stopped can also be suppressed. Therefore, the reaction liquid remaining in the reactor after the reaction is stopped can be reused as a reaction liquid in a new liquid phase reaction by performing a simple treatment of removing the catalyst.

In the liquid phase reaction termination method of the present invention, it is preferable that the nitro group-containing aromatic compound is nitrobenzene and the aromatic amine is aniline.
In this case, in the production of aniline by the hydrogenation reaction of nitrobenzene, high purity aniline can be obtained, and the content of impurities other than aniline can be obtained from the reaction solution remaining in the reactor after the reaction is stopped by simple treatment. Can be reduced.

According to the liquid phase reaction stopping method of the present invention, in the liquid phase reaction for producing an aromatic amine by hydrogenation reaction of a nitro group-containing aromatic compound, generation of impurities at the time of stopping the reaction, It is possible to prevent impurities from being mixed into the reaction solution remaining inside.
Therefore, the liquid phase reaction termination method of the present invention is suitable for use in producing high-purity aromatic amines, and also suitable for use in reducing costs by reusing reaction liquids during aromatic amine production. It is.

FIG. 1 is a schematic configuration diagram showing an embodiment of a reaction apparatus used in the liquid phase reaction stop method of the present invention. Hereinafter, the method for stopping the reaction of the liquid phase reaction of the present invention will be described with reference to FIG.
In FIG. 1, a reaction apparatus 1 is a reaction apparatus that can be effectively applied to a hydrogenation reaction of a nitro group-containing aromatic compound in a liquid phase, and includes a liquid phase reaction tank 2 as a reactor, Aromatic amine supply line 3, hydrogen gas supply line 4, catalyst supply line 5, nitro group-containing aromatic compound supply line 6, reaction liquid circulation line 7, heat exchanger 8, and reaction product take-out line 9.

The liquid phase reaction tank 2 is a reaction tank capable of performing a gas-liquid contact reaction in the liquid phase, and is not particularly limited as long as it is such a reaction tank, and various reaction tanks may be mentioned. For example, the illustrated liquid phase reaction tank 2 includes a pressure-resistant aerated stirring tank including a stirring blade 10.
The downstream end of the aromatic amine supply line 3 is disposed in the liquid phase reaction tank 2, and the upstream end thereof is connected to an aromatic amine (solvent) source. A control valve 11 for adjusting the amount of aromatic amine supplied into the liquid phase reaction tank 2 is provided in the middle of the aromatic amine supply line 3.

  An aromatic amine is a target compound for a liquid phase reaction, and is a compound that is also used as a solvent for a liquid phase reaction, and is not limited thereto. For example, aniline, (o-, m-, p-) toluidine, Xylidines (for example, 2,3-, 2,4-, 2,5-xylidine, etc.), aromatic monoamines such as (1-, 2-) naphthylamine, for example (o-, m-, p-) And aromatic diamines such as diaminobenzene.

For example, in a liquid phase reaction in which aniline is produced by hydrogenation reaction of nitrobenzene, the target compound aniline is supplied from the aromatic amine supply line 3 as a solvent.
The aromatic amine supplied from the aromatic amine supply line 3 is obtained by removing the catalyst from the reaction liquid remaining in the liquid phase reaction tank 2 when the liquid phase reaction is stopped, as will be described later. It may be.

The downstream end of the hydrogen gas supply line 4 is disposed below the stirring blade 10 and in the bottom of the liquid phase reaction tank 2. A plurality of nozzles (or spargers) 12 are provided at the downstream end of the hydrogen gas supply line 4. A hydrogen gas (raw material gas) source is connected to the upstream end of the hydrogen gas supply line 4.
A control valve 13 for adjusting the supply amount of hydrogen gas into the liquid phase reaction tank 2 is provided in the middle of the hydrogen gas supply line 4.

The downstream end of the catalyst supply line 5 is disposed in the liquid phase reaction tank 2, and the upstream end thereof is connected to a catalyst source. An adjustment valve 14 for adjusting the amount of catalyst supplied into the liquid phase reaction tank 2 is provided in the middle of the catalyst supply line 5.
Examples of the catalyst include solid catalysts. Examples of the solid catalyst include transition metal elements belonging to Groups 8 to 10 of the periodic table, such as palladium, platinum, rhodium, iridium, ruthenium, and nickel, such as alloys such as palladium-platinum, such as palladium-carbon. Examples include composites. Of these, palladium and palladium-platinum are preferable, and palladium is particularly preferable.

These solid catalysts may be supported on a carrier. Examples of the carrier include activated carbon, alumina, lipophilic carbon black, silica gel, diatomaceous earth, and the like, and preferably activated carbon. Examples of the solid catalyst supported on the carrier include a palladium catalyst supported on activated carbon.
The catalyst is usually supplied little by little into the liquid phase reaction tank 2, and in particular, the above-mentioned solid catalyst is supplied in the form as it is, and a large amount is supplied into the liquid phase reaction tank 2 in a short time. It is difficult. For this reason, the catalyst is supplied into the liquid phase reaction tank 2 as a high-concentration slurry dispersed in a dispersion medium.

The dispersion medium is not particularly limited, and examples thereof include water and an aromatic amine as a reaction solvent.
The high concentration slurry in which the catalyst is dispersed in the dispersion medium only needs to have fluidity that can be supplied from the catalyst supply line 5, for example. Further, the concentration of the slurry is suitable for supply from the catalyst supply line 5 from the viewpoint of enabling the supply of the catalyst necessary for initiating the liquid phase reaction in as short a time as possible and suppressing the generation of impurities. It is preferable to set as high as possible within the range in which fluidity is maintained.

The downstream end of the nitro group-containing aromatic compound supply line 6 is disposed in the liquid phase reaction tank 2, and the upstream end thereof is connected to the nitro group-containing aromatic compound (raw material liquid) source. Has been. A control valve 15 for adjusting the supply amount of the nitro group-containing aromatic compound into the liquid phase reaction tank 2 is provided in the middle of the nitro group-containing aromatic compound supply line 6.
The nitro group-containing aromatic compound is not particularly limited because it is appropriately selected according to the aromatic amine that is the target compound. For example, nitrobenzene, (o-, m-, p-) nitrotoluene, nitroxylenes (For example, 3-nitro-o-xylene, 4-nitro-m-xylene, 2-nitro-p-xylene, etc.), (1-, 2-) nitronaphthalene, (o-, m-, p-) di And nitrobenzene.

For example, when aniline is produced, nitrobenzene is used as the nitro group-containing aromatic compound.
The reactor 1 includes a control valve 11 of the aromatic amine supply line 3, a control valve 13 of the hydrogen gas supply line 4, a control valve 14 of the catalyst supply line 5, and a control valve 15 of the nitro group-containing aromatic compound supply line 6. A control unit (CPU) for controlling opening / closing or opening is provided.

The reaction liquid circulation line 7 forms a circulation path for circulating the reaction liquid 16 in the liquid phase reaction tank 2 through the outside of the liquid phase reaction tank 2 and into the liquid phase reaction tank 2 again.
In the middle of the reaction liquid circulation line 7, there are a pump 17 for circulating the reaction liquid 16 and a heat exchanger 8 for heating or cooling the reaction liquid 16 in order from the upstream side to the downstream side. Intervened.

  A part of the reaction liquid 16 in the liquid phase reaction tank 2 is taken into the reaction liquid circulation line 7, and then the pressure is raised by the pump 17 and taken into the heat exchanger 8. The reaction liquid 16 taken into the heat exchanger 8 is sent again to the liquid phase reaction tank 2 through the reaction liquid circulation line 7. In this way, a part of the reaction solution 16 in the liquid phase reaction tank 2 circulates in the reaction solution circulation line 7 through the heat exchanger 8.

The heat exchanger 8 heats or cools the reaction solution 16 taken from the liquid phase reaction tank 2 into the reaction solution circulation line 7.
The pump 17 forcibly feeds the reaction solution 16 taken into the reaction solution circulation line 7 to the heat exchanger 8. Even if the pump is disposed downstream of the heat exchanger 8 on the reaction liquid circulation line 7 and forcibly feeds the reaction liquid 16 discharged from the heat exchanger 8 into the liquid phase reaction tank 2. Good. Moreover, you may each arrange | position at both the upstream from the heat exchanger 8 on the reaction liquid circulation line 7, and a downstream.

In addition, the pump 17 disposed on the upstream side of the heat exchanger 8 on the reaction liquid circulation line 7 is preferably disposed on the upstream side of a branch point of a reaction liquid extraction line 18 described later.
The reaction liquid extraction line 18 is a line branched from the reaction liquid circulation line 7. The upstream end of the reaction liquid extraction line 18 is connected between the pump 17 of the reaction liquid circulation line 7 and the heat exchanger 8. A filter 19 for removing the catalyst from the reaction solution 16 is disposed in the middle of the reaction solution extraction line 18.

A part of the reaction liquid 16 is continuously introduced from the reaction liquid circulation line 7 to the reaction liquid extraction line 18 and the filter 19, and the reaction liquid 16 is introduced into the reaction liquid extraction line 18 and the filter 19. The amount (extraction amount) is adjusted by a control valve 20 disposed between the branch point of the reaction solution circulation line 7 and the reaction solution extraction line 18 and the filter 19.
The filter 19 separates and removes solids such as a catalyst from the reaction solution 16 that passes through the reaction solution extraction line 18. The filtrate (reaction liquid 16) after filtration is stored, for example, and re-used as an aromatic amine source to be supplied from the aromatic amine supply line 3 into the liquid phase reaction tank 2 when the liquid phase reaction is resumed. Used.

On the other hand, the catalyst collected by the filter medium of the filter 19 is recovered from the catalyst recovery line 21. The recovered catalyst is reused as, for example, a catalyst supplied from the catalyst supply line 5 into the liquid phase reaction tank 2 after being activated as necessary.
The upstream end portion of the reaction product take-out line 9 is connected to the top of the liquid phase reaction tank 2. The reaction product take-out line 9 includes an unreacted source gas (hydrogen gas) supplied in excess from the liquid phase reaction tank 2, and a reaction product (aromatic amine) entrained in the unreacted source gas. Then, a part of the unreacted nitro group-containing aromatic compound is taken in as vapor.

The reaction product take-out line 9 includes a gas phase reaction tank 22 for completely reacting an unreacted nitro group-containing aromatic compound and unreacted hydrogen gas at the downstream end thereof.
The nitro group-containing aromatic compound undergoes a gas-liquid contact reaction with hydrogen gas in the liquid phase reaction tank 2, but usually has a conversion rate to an aromatic amine of 80 to 80 in order to suppress generation of impurities due to sequential reaction. It is suppressed to 99.9%. For this reason, as described above, a part of the unreacted nitro group-containing aromatic compound is taken into the reaction product extraction line 9 as a vapor.

However, since the gas phase reaction tank 22 is provided at the downstream end of the reaction product take-out line 9, the unreacted raw material gas (hydrogen gas) taken in from the reaction product take-out line 9 and unreacted The nitro group-containing aromatic compound can be contact-reacted in the gas phase.
In the gas phase reaction tank 22, the aromatic amine generated by the gas phase reaction is taken out from the aromatic amine take-out line 23. The aromatic amine taken out from the aromatic amine take-out line 23 is mixed with impurities because the nitro group-containing aromatic compound is completely reacted with hydrogen gas by the gas phase reaction in the gas phase reaction tank 22. Is highly suppressed.

Next, with reference to the reaction apparatus 1 shown in FIG. 1, one embodiment of the reaction stopping method of the liquid phase reaction of the present invention will be described taking as an example a method for producing aniline by reaction of nitrobenzene and hydrogen gas.
In the liquid phase reaction for producing aniline by hydrogenation reaction of nitrobenzene, for example, aniline as a solvent is supplied into the liquid phase reaction tank 2 in a hydrogen atmosphere, and the liquid temperature of aniline is increased to a predetermined temperature. In addition, the pressure in the liquid phase reaction tank 2 is increased to a predetermined value, and further, hydrogen gas and nitrobenzene, which are reaction raw materials, and a catalyst are supplied into the liquid phase reaction tank 2. .

The liquid temperature of the reaction liquid 16 in the liquid phase reaction tank 2 is preferably set to 150 to 250 ° C., more preferably 180 to 230 ° C. Moreover, the pressure (gauge pressure) in the liquid phase reaction tank 2 is preferably set to 0.3 to 1.5 MPa-G, more preferably 0.5 to 1.0 MPa-G.
When the liquid phase reaction is continuously operated, the supply amount of each component during steady operation, the concentration in the liquid phase reaction tank 2 and the like are appropriately determined according to the size of the liquid phase reaction tank 2, the amount of aniline produced, and the like. Is set.

The supply amount of hydrogen gas from the hydrogen gas supply line 4 into the liquid phase reaction tank 2 is preferably 1 to 5 times the stoichiometric ratio required for the hydrogenation reaction of nitrobenzene. Preferably, it is set to about 3 times the amount.
The supply amount of nitrobenzene from the nitro group-containing aromatic compound supply line 6 into the liquid phase reaction tank 2 is such that the concentration of nitrobenzene in the reaction solution 16 is preferably 0.2 to 2.0% by weight, for example. More preferably, it is suitably set so as to be 0.2 to 1.0% by weight.

Further, the supply amount of the catalyst from the catalyst supply line 5 into the liquid phase reaction tank 2 is more preferably such that the catalyst content in the reaction solution 16 is preferably 10 to 1000 ppm, for example. It sets suitably so that it may become 10-200 ppm.
As an example of the supply rate of each component during steady operation, for example, when the supply rate of nitrobenzene from the nitro group-containing aromatic compound supply line 6 into the liquid phase reaction tank 2 is 1000 kg / h, The hydrogen gas supply rate from the hydrogen gas supply line 4 to the liquid phase reaction vessel 2 is 50 to 250 kg / h, and the catalyst supply rate from the catalyst supply line 5 to the liquid phase reaction vessel 2 is 0.001 to 0.001. Adjust each to 0.02 kg / h.

The circulation amount of the reaction liquid 16 in the reaction liquid circulation line 7 during the steady operation is not particularly limited, and heat exchange is performed so that the liquid temperature of the reaction liquid 16 in the liquid phase reaction tank 2 is maintained in the above range. The amount is appropriately adjusted in consideration of the amount introduced into the vessel 8.
In addition, the amount of introduction (extraction) of the reaction solution 16 into the reaction solution extraction line during steady operation is not particularly limited, but normally, the amount of catalyst in the reaction solution 16 introduced into the reaction solution extraction line is a new catalyst. The amount is appropriately adjusted so as to be equal to the amount of catalyst supplied from the supply line 5 into the liquid phase reaction tank 2.

  In the liquid phase reaction stopping method of the present invention, first, if necessary, the control valve 13 on the hydrogen gas supply line 4, the control valve 14 on the catalyst supply line 5, and the nitro group-containing aromatic are controlled by the CPU. Adjust the opening of the control valve 15 on the compound supply line 6, adjust the supply amounts of hydrogen gas, nitrobenzene, and catalyst into the liquid phase reaction tank (reactor) 2, respectively, to reduce the reaction load, Transition from steady operation to low output operation.

At the time of low output operation, for example, the supply amounts of hydrogen gas, nitrobenzene, and catalyst are preferably reduced to 20 to 80%, more preferably 50% or less, in the steady operation.
In addition, as an example of the supply rate of each component at the time of low output operation, for example, when the supply rate of nitrobenzene from the nitro group-containing aromatic compound supply line 6 to the liquid phase reaction tank 2 is 200 to 800 kg / h The hydrogen gas supply rate from the hydrogen gas supply line 4 to the liquid phase reaction vessel 2 is set to 10 to 200 kg / h, and the catalyst supply rate from the catalyst supply line 5 to the liquid phase reaction vessel 2 is set to 0. Adjust each to be 0002 to 0.016 kg / h.

The circulation amount of the reaction liquid 16 in the reaction liquid circulation line 7 during the low output operation is not particularly limited, but the liquid temperature of the reaction liquid 16 in the liquid phase reaction tank 2 is within the above range as in the steady operation. The amount is appropriately adjusted in consideration of the amount introduced into the heat exchanger 8 so as to be maintained.
The amount of introduction (extraction) of the reaction liquid 16 to the reaction liquid extraction line during the low output operation is not particularly limited, but usually in the reaction liquid 16 introduced into the reaction liquid extraction line as in the steady operation. Is appropriately adjusted so as to be equivalent to the amount of catalyst newly supplied from the catalyst supply line 5 into the liquid phase reaction tank 2.

Next, while maintaining the concentration of nitrobenzene in the reaction solution 16 at the concentration (for example, 0.2 to 2.0% by weight) at the time of steady operation, the reaction solution in the liquid phase reaction tank 2 is maintained as necessary. The liquid level of 16 is lowered. The liquid level of the reaction liquid 16 in the liquid phase reaction tank 2 is appropriately adjusted so that the operation of the stirring blade 10 is not hindered.
Next, the supply of the nitro group-containing aromatic compound from the nitro group-containing aromatic compound supply line 6 and the catalyst while the supply of hydrogen gas from the hydrogen gas supply line 4 is continued to the liquid phase reaction tank 2 The supply of the catalyst from the supply line 5 is stopped.

  The time difference between the supply stop of the nitrobenzene and the supply stop of the catalyst is preferably short in order to suppress the by-production of the nuclear hydrogenated product of aniline and the polycyclic aromatic compound. Specifically, the time difference between the supply stop of the nitrobenzene and the stop of the supply of the catalyst is preferably 10 although it varies depending on the supply rate of the catalyst, the capacity of the liquid phase reaction tank 2 (capacity of the reaction solution 16), and the like. Within minutes. Note that either the nitrobenzene supply stop or the catalyst supply stop may be operated first, or the operations may be performed simultaneously.

Furthermore, after the supply of nitrobenzene and the catalyst is stopped, when the concentration of nitrobenzene in the reaction solution 16 reaches 30 ppm, or after that, the supply of hydrogen gas from the hydrogen gas supply line 4 is stopped and the liquid phase reaction is stopped. Let
The supply of hydrogen gas is stopped when the concentration of nitrobenzene in the reaction solution 16 reaches 1 ppm or after that.

According to the above method, the supply of hydrogen gas is not stopped immediately after the supply of nitrobenzene is stopped, but is stopped when the concentration of nitrobenzene in the reaction solution 16 reaches 30 ppm, or thereafter. Nitrobenzene in the reaction solution 16 can be consumed for the hydrogenation reaction, and contamination of the nitrobenzene into the reaction solution 16 can be reduced.
The concentration of nitrobenzene in the reaction solution 16 can be analyzed, for example, by collecting the reaction solution 16 from the liquid phase reaction tank 2 and performing gas chromatography or colorimetric analysis.

Also, for example, the liquid phase reaction is stopped from a state in which the contents of aniline (solvent), hydrogen gas (raw material gas), nitrobenzene (raw material liquid), and catalyst in the liquid phase reaction tank 2 are known in advance. The concentration of nitrobenzene can also be calculated based on the elapsed time after execution of the liquid phase reaction stop operation from the measurement result by tracking the change with time in the concentration of nitrobenzene.
Further, for example, in the gas phase reaction of nitrobenzene and hydrogen gas in the gas phase reaction tank 22, the gas phase reaction tank 22 depends on the amount of nitrobenzene introduced from the liquid phase reaction tank 2 to the gas phase reaction tank. Therefore, the concentration of nitrobenzene in the reaction solution 16 can also be calculated by observing the amount of temperature change in the gas phase reaction tank 22.

  The supply of hydrogen gas is stopped within 10 minutes after the concentration of nitrobenzene in the reaction solution 16 has reached 0 ppm, and more preferably immediately after reaching 0 ppm. By stopping the supply of hydrogen gas until 10 minutes after the concentration of nitrobenzene in the reaction solution 16 reaches 0 ppm, the by-product of aniline nuclear hydrogenated products and polycyclic aromatic compounds is suppressed. it can.

After the supply of the nitro group-containing aromatic compound, the catalyst, and the hydrogen gas is completely stopped, the reaction liquid 16 can generate impurities even if it is stored in the liquid phase reaction tank 2 at high temperature and high pressure. Although it is suppressed, it is preferably transferred and stored outside the system of the reactor 1.
After the liquid phase reaction is stopped, the reaction liquid 16 remaining in the liquid phase reaction tank 2 is taken out of the reaction apparatus 1 through the reaction liquid circulation line 7 and the reaction liquid extraction line 18. At this time, the reaction solution 16 passes through the filter 19 on the reaction solution extraction line 18, whereby the catalyst in the reaction solution 16 is separated and removed.

The reaction liquid 16 taken out from the system of the reaction apparatus 1 through the reaction liquid take-out line 18 is stored, for example, and is transferred from the aromatic amine supply line 3 into the liquid-phase reaction tank 2 when resuming the liquid-phase reaction. And reused as a source of aromatic amine to supply.
After the liquid phase reaction is stopped, the reaction liquid 16 remaining in the liquid phase reaction tank 2 usually includes an aromatic amine as a reaction solvent, a catalyst, a nitro group-containing aromatic compound as a reaction raw material, and hydrogen. Since this contains gas, aromatic amine nuclear hydrogenated byproducts, and multimers (dimers, trimers, etc.), this reaction solution 16 is used as a reaction solution when resuming the liquid phase reaction. In order to reuse, it is necessary to remove the catalyst, and further remove the nitro group-containing aromatic compound and by-products. However, in the method for stopping the liquid phase reaction, since the mixture of the nitro group-containing aromatic compound and the by-product into the reaction liquid 16 remaining in the liquid phase reaction tank 2 is suppressed, By simply passing through a simple treatment of removing water, it can be reused as an aromatic amine source when the liquid phase reaction is resumed.

  In the liquid phase reaction stop method for producing aniline by the hydrogenation reaction of nitrobenzene described above, the supply of hydrogen gas and catalyst into the reactor is continued, and the reactor is heated and pressurized In this situation, only the supply of the catalyst is stopped while the supply of nitrobenzene is stopped, or the supply of hydrogen gas and nitrobenzene to the reactor is continued, and the reactor is heated and pressurized. Is prevented. When the supply of nitrobenzene is stopped, aniline nuclear hydrogenated products and polycyclic aromatic compounds are produced as impurities, and when the supply of catalyst is stopped, nitroso compounds are produced as impurities in addition to the above impurities. However, according to the reaction stopping method described above, the generation of these impurities can be suppressed.

Therefore, the above-mentioned reaction stopping method produces high-purity aniline in which the generation of impurities is suppressed and the reaction is performed, for example, when the liquid phase reaction is interrupted for maintenance, inspection, cleaning, etc. of the reactor. This method is suitable as a method for suppressing the mixing of impurities into the reaction solution remaining in the vessel.
As mentioned above, although one embodiment of the method for stopping the reaction of the liquid phase reaction of the present invention has been described by taking the example of the method for producing aniline by the reaction of nitrobenzene and hydrogen gas, the present invention is not limited to the above reaction. In addition, the present invention is widely applied to a method for producing an aromatic amine by a reaction between a nitro group-containing aromatic compound and hydrogen gas.

Next, although an example and a comparative example are given and the present invention is explained, the present invention is not limited by the following example.
Example 1
Hydrogen gas was supplied from a hydrogen gas supply line 4 into a liquid phase reaction tank (aeration stirring tank type reactor) 2 of the reaction apparatus 1 shown in FIG. 1, and the inside of the liquid phase reaction tank 2 was replaced with hydrogen gas. Next, 350 parts by weight of aniline from aromatic amine supply line 3 and catalyst (palladium supported on activated carbon at a ratio of 5% by weight) from catalyst supply line 5 are placed in liquid phase reaction tank 2 at 0.035 weight. Parts were supplied respectively.

  Next, the aniline in the liquid phase reaction tank 2 is taken into the heat exchanger 8 through the reaction liquid circulation line 7 and heated, whereby the liquid temperature of aniline in the liquid phase reaction tank 2 is increased to 230 ° C. Warm up. After the temperature rise, nitrobenzene is supplied into the liquid phase reaction tank 2 from the nitro group-containing aromatic compound supply line 6 at a supply rate of 75 parts by weight per hour, and the total pressure (gauge pressure) in the liquid phase reaction tank 2 is supplied. ) Was maintained at 0.7 MPa-G, hydrogen gas was supplied from the hydrogen gas supply line 4 in an amount three times that of the stoichiometric amount to initiate a liquid phase reaction.

  During the liquid phase reaction, 75 parts by weight of the reaction liquid 16 in the liquid phase reaction tank 2 was withdrawn per hour, and the reaction liquid circulation line 7 was circulated. A condenser (on the reaction product take-out line 9) that keeps the liquid volume, temperature, and pressure of the reaction liquid 16 constant, and supplies an excessively supplied hydrogen gas and vapor containing aniline accompanying it. The reaction was continued for 3 hours while condensing in a receiver (not shown) and withdrawing into a receiver.

After the liquid phase reaction was continued for 3 hours, the supply of nitrobenzene was stopped, and the reaction solution 16 was sampled at regular intervals for 60 minutes after the supply of nitrobenzene was stopped, and the components were analyzed. In addition, the amount of the reaction liquid 16 in the liquid phase reaction tank 2 decreased to about 60% when 60 minutes passed from the supply stop of nitrobenzene.
Component analysis result of reaction solution (detection limit 0.1ppm)
-Before stopping supply of nitrobenzene Reaction product (solvent): 83.6% aniline
Reaction raw material: Nitrobenzene 330ppm
Impurities: 1290 ppm N-cyclohexylcyclohexamine, 15.1% N-phenylcyclohexylamine, 4300 ppm N-phenylbenzenamine.

-After 30 minutes, reaction product (solvent): aniline 79.4%
Reaction raw material: Nitrobenzene 0.1 ppm or less Impurities: N-cyclohexylcyclohexamine 1900 ppm, N-phenylcyclohexylamine 19.1%, N-phenylbenzeneamine 4700 ppm.

-After 60 minutes, reaction product (solvent): aniline 70.0%
Reaction raw material: Nitrobenzene 0.1 ppm or less Impurities: N-cyclohexylcyclohexamine 3700 ppm, N-phenylcyclohexylamine 26.4%, N-phenylbenzeneamine 6400 ppm.

From the above results, even after the supply of nitrobenzene was stopped, the supply of hydrogen gas was continued, nitrobenzene was consumed by the hydrogenation reaction, and when the concentration of nitrobenzene was 0 ppm (or below the detection limit concentration). It was found that it was necessary to stop the hydrogen supply and stop the reaction promptly.
Example 2
Hydrogen gas was supplied from a hydrogen gas supply line 4 into a liquid phase reaction tank (aeration stirring tank type reactor) 2 of the reaction apparatus 1 shown in FIG. 1, and the inside of the liquid phase reaction tank 2 was replaced with hydrogen gas. Next, 30 parts by weight of aniline from the aromatic amine supply line 3 and hydrogen gas from the hydrogen gas supply line 4 are supplied into the liquid phase reaction tank 2, and the aniline in the liquid phase reaction tank 2 is further reacted. The solution was taken into the heat exchanger 8 through the liquid circulation line 7 and heated. Thereby, the liquid temperature of the aniline was raised to 208 degreeC, maintaining the total pressure (gauge pressure) in the liquid phase reaction tank 2 at 0.7 MPa-G.

  After raising the temperature and increasing the pressure, 0.006 parts by weight of catalyst (palladium supported on activated carbon at a ratio of 5% by weight) is supplied from the catalyst supply line 5 into the liquid phase reaction tank 2, and the catalyst supply is started. Immediately, nitrobenzene was supplied from the nitro group-containing aromatic compound supply line 6 at a supply rate of 9.2 parts by weight per hour to initiate a liquid phase reaction. The hydrogen gas supply amount during the liquid phase reaction was 3 times the stoichiometric amount, and the catalyst supply amount was 0.0000825 parts by weight per hour, and continuous operation was continued. Further, 0.92 part by weight of the reaction solution 16 was extracted from the liquid phase reaction tank 2 per hour, and the reaction solution circulation line 7 was circulated.

The excessively supplied hydrogen gas and the vapor containing aniline accompanying the hydrogen gas were condensed by a condenser (not shown) provided on the reaction product extraction line 9. Further, non-condensed hydrogen gas and reactant gas were collected by the reaction product take-out line 9, and the hydrogen gas was separated and recovered as a reaction product.
Next, the control unit (CPU) controls the opening degree of the control valve 13 of the hydrogen gas supply line 4, the control valve 14 of the catalyst supply line 5, and the control valve 15 of the nitro group-containing aromatic compound supply line 6, respectively. The supply amounts of nitrobenzene, hydrogen gas, and catalyst from each of the lines 4, 5, and 6 were reduced to 50% during the continuous operation.

Subsequently, while continuing to supply hydrogen gas at a supply amount of 50% during continuous operation (low power operation), the control valve 14 is closed, the supply of nitrobenzene is stopped, and the control valve 15 is immediately closed, The catalyst supply was stopped. Further, when the concentration of nitrobenzene in the reaction solution 16 reached 2 ppm, the control valve 13 was closed, the supply of hydrogen gas was stopped, and the liquid phase reaction was stopped.
The concentration of nitrobenzene in the reaction solution 16 is determined in advance by changing the nitrobenzene concentration in the reaction solution over time under the same conditions as those for the continuous operation and low-power operation and the liquid phase reaction stopping operation described above. It measured and computed from the elapsed time after the liquid phase reaction stop operation based on the measurement result.

Next, after the liquid phase reaction in the liquid phase reaction tank 2 was completely stopped, the reaction solution 16 was sampled and its components were analyzed.
Component analysis result of reaction liquid after stopping liquid phase reaction (detection limit 0.1ppm)
Reaction product (solvent): aniline 93.2%
Reaction raw material: Nitrobenzene 0.1 ppm or less Impurities: 2 ppm of benzene, 32 ppm of N-cyclohexylcyclohexamine, 4.3% of N-phenylcyclohexylamine, 1600 ppm of N-phenylbenzeneamine.

  From the above results, even after the nitrobenzene supply is stopped, the hydrogen gas supply is continued and the nitrobenzene is consumed by the hydrogenation reaction, so that mixing of the nitrobenzene into the reaction solution after the reaction is stopped can be remarkably suppressed. I understood. It was also found that the generation of impurities (by-products) can be significantly suppressed by quickly stopping the hydrogen supply and stopping the reaction when the concentration of nitrobenzene reaches 0 ppm (or below the detection limit concentration). .

  The present invention is not limited to the above description, and various design changes can be made within the scope of the matters described in the claims.

FIG. 1 is a schematic configuration diagram showing an embodiment of a reaction apparatus used in the liquid phase reaction stop method of the present invention.

Explanation of symbols

2 Liquid phase reactor (reactor)
16 reaction liquid

Claims (3)

  In the liquid phase reaction to produce aromatic amines by hydrogenation reaction of nitro group-containing aromatic compounds, supply of hydrogen gas and catalyst into the reactor and discharge of the reaction solution including the catalyst from the reactor are continued. In this state, the supply of the nitro group-containing aromatic compound into the reactor and the supply of the catalyst are stopped, and then the concentration of the nitro group-containing aromatic compound in the reaction solution reaches 30 ppm, Alternatively, after that, the supply of hydrogen gas into the reactor is stopped, and the liquid phase reaction stopping method is characterized.   After the supply of hydrogen gas is stopped, the catalyst is removed from the reaction solution remaining in the reactor, and then the reaction solution from which the catalyst has been removed is reused as an aromatic amine supply source at the start of the liquid phase reaction. The method for terminating a liquid phase reaction according to claim 1, wherein:   The method for terminating a liquid phase reaction according to claim 1 or 2, wherein the nitro group-containing aromatic compound is nitrobenzene and the aromatic amine is aniline.

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