JPH062718B2 - Continuous production of tolylenediamine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an industrially advantageous continuous production method of tolylenediamine containing almost no unreacted nitro compound and non-volatile residue by catalytic hydrogenation of dinitrotoluene. .

In recent years, tolylenediamine has been mass-produced as an intermediate of tolylene diisocyanate, which is a raw material for polyurethane resins.

Tolylene diisocyanate is generally produced by nitration of toluene to give dinitrotoluene, and then catalytic hydrogenation to give tolylene diamine, followed by phosgenation to give diisocyanate. A continuous process is suitable for carrying out. Therefore, due to a slight improvement in yield and improvement in utility,
A large resource and energy saving effect is exhibited.

2. Description of the Related Art A number of methods have hitherto been proposed for producing an aromatic amine by a catalytic hydrogenation reaction of an aromatic nitro compound such as dinitrotoluene.

For example, U.S. Pat. No. 2,292,879 discloses a method for producing a corresponding aromatic monoamine such as aniline by hydrogenating an aromatic mononitro compound such as nitrobenzene in a liquid phase. The activity of the catalyst can be kept high by conducting the extraction under the conditions described above, and the amine formed can serve as a reaction solvent, and the activity of the catalyst can be increased by reacting the amine at a relatively high concentration. Have been described.

However, in the production of the above monoamines such as aniline, since the reaction temperature is relatively high and the boiling point of the amine is low, the reaction product water can be easily removed together with the reaction product. Since it is carried out at a relatively high temperature and a relatively low temperature, it is not easy to remove produced water.

Further, in JP-A-35-5763, catalytic nitrophenols and nitrocresols which are catalyst poisons are controlled to carry out catalytic hydrogenation of dinitrotoluene in a molten state without a solvent to remove water produced by the reaction. However, a method of causing the reaction has been proposed.

However, in this method, the hydrogenation reaction time (residence time) is as long as 20 hours or more, therefore the production amount per unit time is low, and it is necessary to supply a large excess of hydrogen gas to remove the produced water. There is a large amount of catalyst used for dinitrotoluene as a noble metal component, and there is a residual amount of unreacted nitro compound of about 100 ppm despite the long reaction time. However, it is not suitable for mass production.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The inventors of the present invention contain an unreacted nitro compound, suppress the formation of a tar-like non-volatile residue, and are economical and suitable for mass production. The present invention has been completed as a result of earnestly studying a dynamic manufacturing method.

Means for Solving the Problems The method of the present invention is a continuous production method of tolylenediamine by catalytic hydrogenation reaction of dinitrotoluene, using a tank reactor equipped with a stirrer, in a tolylenediamine aqueous solution solvent, at least 100 Palladium or palladium-platinum deposited on a lipophilic carbon having an oil absorption of is suspended as a catalyst, dinitrotoluene is fed so that the residence time of the fed dinitrotoluene is 4 to 12 hours, It is a continuous process for producing tolylenediamine, which is characterized in that the reaction is carried out at a temperature of 90 to 150 ° C. under a pressure of 10 kg / cm ² G or less while distilling off the reaction product water from the reaction product.

Here, the residence time is the liquid amount in the entire reaction system with respect to the raw material dinitrotoluene continuously supplied every hour, that is,
It means the total hold-up amount of the reaction system / the feed amount of dinitrotoluene in the system.

Usually, the crude tolylenediamine reaction solution obtained in the tolylenediamine production is subjected to a purification step in order to obtain a satisfactory high quality of the speck when converted to the corresponding diisoianate, but in the method of the present invention, the reaction is not performed. Since the concentration of the unreacted nitro compound in the liquid is 30 ppm or less and the content of the non-volatile residue can be suppressed to a very small amount, the purification is not always necessary.

As a factor for suppressing the concentration of the unreacted nitro compound in the reaction solution to 30 ppm or less, that is, for causing almost complete hydrogenation reaction of dinitrotoluene, there is a mutual relation among pressure-residence time-actual stirring power required (stirring speed). , And the relationship is shown in Figure 1.

Figure 1 shows the correlation between retention time and pressure at the lowest point where the unreacted nitro compound is 30 ppm or less when the hydrogenation of dinitrotoluene is carried out at a reaction temperature of 110 ° C using an ordinary hydrogenation catalyst. This is a plot, and the parameter is the actual power required for stirring (stirring speed).
That is, it is shown that the unreacted nitro compound can be suppressed to 30 ppm or less in the region above the curve shown by the solid line in the figure, and rises to 30 ppm or more in the region below. If the unreacted nitro compound increases, it becomes an impurity in the tolylene diisocyanate formed by the subsequent borogenation, and therefore some purification step must be performed.

Due to the above three relationships, any area above the solid line in the figure may be selected, but from the viewpoint of mass production and economic efficiency, if the residence time is set to 10 hours or more, the larger capacity will be. However, if the residence time is shortened to 4 hours or less, the pressure will be a high pressure reaction of 10 kg / cm ² G or more, or the actual power required for stirring will be 4.0 K per m ³ .
Must be greater than W. If a high-pressure reaction is to be carried out, the removal of the reaction product water becomes so difficult, and in order to increase the pressure of the equipment and to carry out the reaction product water while continuously removing it as a vapor, a large-capacity gas circulation blower is required. You will need it. Further, in the case of performing strong stirring of 4.0 kW or more, enormous power consumption is involved and it cannot be an industrially advantageous method. Therefore, from this point of view, it is natural that the pressure is preferably as low as 10 kg / cm ² G or less, if the residence time is not taken into consideration.

On the other hand, FIG. 2 shows changes in the tar-like nonvolatile residue content after dehydration with respect to the residence time at a reaction temperature of 110 ° C. in the hydrogenation of dinitrotoluene using the catalyst of the present invention. As shown in Fig.-2, a decrease in the tar-like non-volatile residue is observed with a decrease in the retention time. From this point, it is preferable that the retention time is short, but considering the relationship between the unreacted dinitrotoluene content and Fig.-1, There is a natural limit to shortening the residence time.

Further, the catalytic activity tends to decrease unless the produced water is removed, and the non-volatile residue gradually increases accordingly. Therefore, in order to suppress the non-volatile residue, it is necessary to remove the generated water. On the contrary, if this is strictly controlled, the off gas circulation line and the like require high power and cooling costs.

The present invention has been completed based on these viewpoints.

Usually, in the catalytic hydrogenation reaction of dinitrotoluene,
Logically, the water content in the system is 37% due to the generated water, and as mentioned above, it is difficult to continuously remove the generated water.
In the present invention, the use of the specific catalyst allows the reaction to proceed without degrading the catalytic activity even in a water-containing reaction solution close to the theoretical value. In addition, by setting a residence time in a specific range, 10 kg /
By carrying out the treatment at a cm ² G or less, it is possible to industrially advantageously obtain an unreacted nitro compound and tolylenediamine having a lower content of non-volatile residues than tolylenediamine obtained by a usual method.

The contact used in the process of the present invention is palladium or palladium-platinum catalyst deposited on a non-porous lipophilic carbon having an oil absorption of 100 or more. Oil absorption rate 150 to 3
A 00 lipophilic carbon carrier is preferred. The definition of the oil absorption rate of the carrier is described in JP-B-32-9320.
It is indicated by 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 which causes gelation. Carrier particle size is 20-6
0 mμ and a surface area of 50 to 100 m ² / g are suitable. The method for producing the catalyst can also be adjusted by a conventional method such as a precipitation method of a palladium platinum compound in an aqueous dispersion of a lipophilic carbon carrier as described in the above specification.

A suitable concentration of palladium and palladium and platinum deposited on the lipophilic carbon is 0.1-5% by weight. Palladium may be used alone, but when platinum is used in combination, it is particularly effective in terms of activity and selectivity. In that case, it is desirable to use about 5 to 20% by weight of platinum based on palladium. Further, as described in the above specification, a small amount of an oxide or hydroxide of a metal such as iron or nickel can be mixed.

In the present invention, using such a specific catalyst, the residence time of the supplied dinitrotoluene is within the range of 5 to 12 hours and is determined according to the reaction pressure and the spec of the reaction product. The preferred range of reaction pressure is 5 to 9 kg / cm ²
G, when the actual power required for stirring is 3.0 to 3.5 kW per m ^{3, the} residence time is preferably 5 to 10 hours.

The reaction temperature is in the usual range of 90 to 150 ° C.,
If the temperature is lower than 0 ° C, the reaction is slow, the residence time needs to be long, and the circulation amount of the gas blower needs to be very large in order to remove the produced water out of the system.
The above temperature is required, but if it exceeds 150 ° C., the tar-like non-volatile residue content increases and the yield of tolylenediamine decreases. Therefore, when the reaction pressure is 5 to 9 kg / cm ² G, it is desirable to carry out at 100 to 130 ° C.

Under such conditions, most of the dinitrotoluene continuously introduced into the reaction vessel according to the residence time was rapidly converted to tolylenediamine and water, and the reaction solution was tolylenediamine in which the catalyst was suspended. It becomes an aqueous solution. Then, a part of the generated water is continuously removed as vapor outside the system. The removal of water is carried out by appropriately selecting the reaction temperature in the temperature range of 90 to 150 ° C. in relation to the hydrogen pressure, and by forcibly circulating the off gas preferably by utilizing a part of the reaction heat generated. The water is evaporated and condensed and removed outside the system.

By carrying out the method of the present invention as described above, it is possible to continuously obtain high-purity tolylenediamine containing almost no unreacted nitro compound and tar-like non-volatile residue. It can be said that it is extremely effective in terms of sex.

Next, an example of a preferable method for carrying out the present invention will be described with reference to the reaction apparatus shown in FIG.

In FIG. 3, the tank-type hydrogenation reactor 1 is an iron 200-pressure reaction tank equipped with a stirrer, a hydrogen dispersion pipe, a dinitrotoluene supply pipe, and a jacket for cooling.

Dinitrotoluene is continuously supplied to reactor 1 through line A. Hydrogen gas used for the reaction is supplied to the reactor 1 after being compressed by the compressor 6 through the line B.
Excessive off-gas is discharged from the line 11, the generated steam is condensed in the cooler 7, and the condensed water is separated into the storage tank 8. The excess gas is forcibly circulated by the gas circulation blower 10, and at this time, a part of the off gas is purged from the system through the line 12 to keep the hydrogen purity in the off gas constant. Furthermore, the circulating gas is mixed with the hydrogen gas from the fresh,
It is circulated to the reactor 1.

The catalyst-water slurry liquid adjusted to a predetermined concentration is continuously introduced into the reactor 1 from the storage tank 5, and at the same time, the same amount of reaction liquid slurry as the added catalyst slurry is continuously discharged out of the system through the line 13. The catalyst concentration in the system is kept substantially constant.

Hot water adjusted to a predetermined temperature to remove heat from the reaction,
From the line 14, the jacket of the reactor 1 and the cooler 4 are introduced, and the reaction temperature is kept constant. The reaction liquid is circulated by a circulation pump 2 in a circulation line equipped with a continuous filter 3 and a cooler 4, and returns to the reactor 1. During this period, the aqueous solution of tolylenediamine is continuously discharged to the storage tank 9 so as to keep the liquid level of the reactor 1 constant.

Next, the present invention will be described in more detail by way of examples. Percentages are weight percentages unless otherwise indicated.

[Example-1] Hydrogenation tank type reactor 1 Hydrogenation obtained by depositing 0.8 kg of palladium, 0.1% of platinum and 0.8% of iron on carbon powder having 170 kg of hetolylenediamine, 27 kg of pure water and 260 oil absorption rate. 3 kg of catalyst was charged, stirring was started, and the stirring speed was set to 300 rpm. Further, the circulation pump 2 was driven to circulate at a speed of 2.5 m ^{3 /} hour. While raising the internal temperature to 90 ° C and maintaining the total pressure at 7.0 kg / cm ² G, dinitrotoluene (2,4-dinitrotoluene 7
Composition of 8.1%, 2,6-dinitrotoluene 19.2%, 2,3-dinitrotoluene 1.1%, 3,4-dinitrotoluene 1.4%, and water 0.2%) 30 kg / h, hydrogen gas 26N / h
The catalyst-water-slurry adjusted to a rate of m ³ and a concentration of 1.5% was fed from the catalyst tank 5 at a rate of 0.33 kg / h.

At that time, the internal temperature was raised to 110 ° C., and excess heat of reaction was removed by circulating hot water of about 80 ° C. to the jacket of the reactor 1 and the cooler 4 and kept at that temperature. Excess hydrogen gas and steam were circulated by driving the gas blower 10, and the steam was condensed into water by the cooler 7 and separated into the storage tank 8. The amount of separated water was 8 kg / h. Hydrogen gas amount of the off-gas to be circulated from the gas blower 10 is per hour 91 nm ^3, and discharged to the outside system as a purge gas from line 12 in them per hour to about 4 Nm ³ speed, the hydrogen purity in the recycle gas is maintained to 96% by volume Was done. The circulating gas was mixed with freshly supplied fresh hydrogen gas and introduced into the reactor.

During this period, the aqueous solution of tolylenediamine was continuously discharged into the storage tank 9 at a rate of 23.68 kg / h by means of the reactor 3 so as to keep the liquid level of the reactor 1 constant. Further, the reaction mixture slurry was discharged from the system through the line 13 at a rate of 0.33 kg / h, and the catalyst concentration in the reaction system was kept at 1.5%.

The stirring speed of the stirrer of the reactor 1 was 300 rpm, and the actual power required for the stirring station in the steady state was 3.0 KW per m ³ . Furthermore, the total hold-up of the reaction solution was 200 kg, of which 160 kg was in the reactor 1 and 40 kg was in the circulation line. The residence time with respect to the amount of dinitrotoluene supplied was 6.7 hours.

Thus, the concentration of the tolylenediamine aqueous solution continuously discharged to the storage tank 9 was 85%, and the remaining 15% was water,
The amount of unreacted nitro compound was 20 ppm.

The tolylenediamine obtained by distilling me by a predetermined method was 99.03% of the theoretical amount, and the remaining 0.97% was a tar-like non-volatile residue.

Example-2 Pressure 4.0 kg / cm ² G, Dinitrotoluene supply rate 20 k / h
g, hydrogen supply rate 17 Nm ^{3 /} h, off gas circulation rate 32 h / h
Nm ^3, except that the purge hydrogen amount per hour 3 Nm ³ (hydrogen purity of 96% by volume in the off-gas) was carried out in the same manner as in Example 1 method. Residence time is 1 for dinitrotoluene supply
It was 0 hours, the water separated in the storage tank 8 was 5.5 kg / h, the tolylenediamine aqueous solution discharged to the storage tank 9 was 15.79 kg / h, the concentration of tolylenediamine was 85%, and the unreacted nitro compound was 2%.
It was 0 ppm. Furthermore, the tolylenediamine obtained by distillation was 98.8% of the theoretical amount, and the remaining 1.2% was a tar-like non-volatile residue.

[Example-3] The off-gas circulation amount circulated from the gas blower was set to 10 per hour.
The conditions were the same as in Example 1 except that Nm ³ was used.

The water collected in the storage tank 8 was 1 kg per hour, the tolylenediamine aqueous solution discharged into the storage tank 9 was 30.97 kg per hour, the concentration of tolylenediamine was 65%, the remaining 35% was water, and the unreacted nitro compound was It was 28 ppm.

Further, the tolylenediamine obtained by distillation was 99% of the theoretical amount, and the remaining 1.0% was a tar-like non-volatile residue.

[Comparative example]

Example 1 was carried out under the same conditions as in Example 1 except that a catalyst obtained by depositing palladium on a finely powdered coconut shell carbon containing 90% or more of particles having a particle size of 100 mesh or less to have a palladium content of 1% was used. . About 1.0 hour after the start of the supply of dinitrotoluene, the tolylenediamine aqueous solution discharged into the storage tank 9 became a black opaque liquid, and the unreacted nitro compound increased to 500 ppm.

The theoretical amount of tolylenediamine obtained by distillation is 9
5%, and the remaining 5% was a tar-like non-volatile residue.

[Brief description of drawings]

Figure 1 shows the minimum point at which the unreacted nitro compound in the reaction solution was below 30 ppm at 110 ° C by the correlation between the residence time and the pressure, and the curves of the parameters are per m ^{3 respectively} . Is the actual power required for stirring. FIG. 2 shows the amount of the tar-like non-volatile residue after dehydration and distillation of the tolylenediamine aqueous solution obtained at the reaction temperature of 110 ° C. according to the method of the present invention, plotted against the residence time. FIG. 3 is a flow chart of a preferred example for carrying out the method of the present invention. 1. A tank reactor with a stirrer, 2. Reaction solution circulation pump,
3. Overkill, 4. Cooler, 5. Catalyst storage tank, 6.
Hydrogen gas compressor, 7. Cooler, 8. Separated water storage tank,
9. Reaction solution storage tank 10. Gas circulation blower A Dinitrotoluene supply line B Hydrogen supply line.

Claims (5)

[Claims] 1. A method for continuously producing tolylenediamine by catalytic hydrogenation reaction of dinitrotoluene, which uses a tank reactor with a stirrer and which has an oil absorption rate of at least 100 in a tolylenediamine aqueous solution solvent. Palladium or palladium-platinum deposited on oily carbon was suspended as a catalyst, and dinitrotoluene was supplied so that the residence time of the supplied dinitrotoluene was 4 to 12 hours, and 10 kg / cm ² G or less. A continuous process for producing tolylenediamine, characterized in that the reaction is carried out at a temperature of 90 to 150 ° C. while distilling off the reaction product water from the reaction product under pressure. 2. The method according to claim 1, wherein the reaction is carried out at a pressure of 5 to 9 kg / cm ² G. 3. The method according to claim 1, wherein the residence time is 5 to 10 hours. 4. The method according to claim 1, wherein the reaction temperature is 100 to 130 ° C. 5. The process according to claim 1, wherein the actual power required for stirring in the tank reactor is 3.0 to 3.5 kW per m ³ .