JPH064580B2 - Method for producing 2,6-dichlorobenzonitrile - Google Patents

Description

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of collecting 2,6-dichlorobenzonitrile obtained by ammoxidation of 2,6-dichlorotoluene.

2. Description of the Related Art 2,6-Dichlorobenzonitrile is not only industrially very important as a herbicide but also industrially extremely important as a raw material for insecticides in recent years.

A method for producing this compound is described in JP-A-60-22845.
There is a method described in Japanese Patent No. 2 publication.

That is, in JP-A-60-228452, a catalyst based on vanadium-molybdenum oxide is used to
In the production of pure dichlorobenzonitrile by ammoxidation of 6-dichlorotoluene, the reaction is carried out in the fluidized bed process and water is sprayed into the reaction gas after it has flowed out of the fluidized bed reactor. , A process for the production of pure dichlorobenzonitrile is described.

In this method, however, no consideration is given to the recovery utilization of unreacted 2,6-dichlorotoluene remaining after the reaction.

In addition, in this method, air of 3.
A large amount of nitrogen, which is 5 to 7.7 times (Examples 1 to 9), is added (therefore, the concentration of 2,6-dichlorotoluene in the raw material gas is 1.93 to 2.03 mol%). ). When such a large amount of nitrogen is added, not only the amount of heat required for preheating the raw material gas and cooling the reaction gas increases, but also the reaction gas can be cooled to recover unreacted 2,6-dichlorotoluene. There was a drawback that made it difficult. In addition, this method had a defect that the yield of 2,6-dichlorobenzonitrile obtained was as low as 60 to 72% (according to Examples 1 to 9).

[Outline of Invention]

Problem to be Solved by the Invention An object of the present invention is to obtain 2,6-dichlorobenzonitrile obtained by ammoxidation of 2,6-dichlorotoluene in the presence of a catalyst in which a metal oxide is supported on a carrier. When producing, the reaction is carried out without adding nitrogen gas for dilution to the raw material gas, high-purity 2,6-dichlorobenzonitrile is obtained in high yield, and unreacted 2, It is to provide a method for recovering 6-dichlorotoluene.

Means for Solving the Problem In the method for producing 2,6-dichlorobenzonitrile according to the present invention, 2,6-dichlorotoluene, air and ammonia are added to a fluidized bed of a catalyst in which a metal oxide is supported on a carrier. In a method for producing 2,6-dichlorobenzonitrile by an ammoxidation method, which comprises contacting a reaction raw material gas containing the above, this reaction is carried out under the simultaneous satisfaction of the following conditions. .

(B) The concentration of 2,6-dichlorotoluene in the reaction raw material gas is 2.6 mol% or more.

(B) The reaction product gas is brought into contact with water to cool it to a temperature in the range of 50 to 90 ° C.
Collecting 6-dichlorobenzonitrile as a slurry in which it is solidified and dispersed in water, and obtaining 2,6-dichlorobenzonitrile from this slurry.

(C) By contacting the cooled reaction product gas after the collection of 2,6-dichlorobenzonitrile with water again to cool it to a temperature in the range of 0 to 40 ° C., the unreacted 2, 2 Collect 6-dichlorotoluene as a dispersion in which it is dispersed in water, and recover 2,6-dichlorotoluene from this dispersion.

Effects of the Invention By carrying out the step of cooling the reaction gas obtained by the ammoxidation by contacting it with water in two steps,
6-dichlorobenzonitrile was collected and
By recovering 6-dichlorotoluene, the content of unreacted 2,6-dichlorotoluene is 1% or less and 2,6-dichlorobenzonitrile is high without using nitrogen for diluting the reaction gas. It can be obtained in an overall yield.

[Specific Description of the Invention]

Ammoxidation Ammoxidation of 2,6-dichlorotoluene is a known technique, and a known technique can be used unless it contradicts the present invention.

The present invention implements this reaction with a fluidized bed catalyst. The concentration of 2,6-dichlorotoluene in the reaction material gas is 2.6 mol% or more, preferably 3 mol%
As shown by the above, the reaction raw material gas consists essentially of 2,6-dichlorotoluene, air and ammonia, and does not substantially contain a diluent such as nitrogen or steam. is there.

The catalyst for the ammoxidation of 2,6-dichlorotoluene is, for example, alumina, silica, vanadium, chromium,
A material carrying an oxide of a heavy metal selected from oxides of molybdenum, antimony and iron is used. For example,
The catalysts described in JP-B-42-7902 and JP-B-43-5386 are used.

In the ammoxidation of 2,6-dichlorotoluene in a catalytic fluidized bed reactor, the conversion rate is important, and when the conversion rate is increased, the selectivity of 2,6-dichlorobenzonitrile tends to decrease sharply. There is. Therefore, the conversion rate range is 80%
〜97% is suitable, and preferably 85% to 95%. When the conversion rate exceeds the upper limit, the selectivity of 2,6-dichlorobenzonitrile decreases and the overall yield of 2,6-dichlorobenzonitrile decreases. If the conversion rate is lower than the lower limit value, the amount of 2,6-dichlorotoluene contained in the 2,6-dichlorobenzonitrile obtained in the first-stage collection column becomes large. For this reason, it is necessary to raise the temperature in the first-stage collecting tower, which results in a large amount of water evaporation, which is disadvantageous in terms of economy.

Although it depends on the activity of the catalyst, it is appropriate that the contact time with the catalyst is 2 seconds to 20 seconds, and preferably 3 seconds to 10 seconds, in order to bring the conversion in the reactor to the above range, though it depends on the activity of the catalyst.

The reaction temperature is suitably 300 ° C to 450 ° C, preferably 350 ° C to 400 ° C. If the reaction temperature is low,
The conversion rate of 2,6-dichlorotoluene decreases. When the reaction temperature exceeds 450 ° C., decomposition is increased and the reaction yield of 2,6-dichlorobenzonitrile is significantly reduced.

During the reaction, the molar ratio of 2,6-dichlorotoluene: ammonia is about 1: 1 to 10, preferably about 1: 2 to 7, and the molar ratio of 2,6-dichlorotoluene: oxygen is 1: 2.
It is about 6 to 6, preferably about 1 to 3 to 5.

Cooling of reaction product gas In the method of the present invention, cooling of the reaction gas flowing out of the reactor is performed, for example, by connecting two cooling devices in series, and contacting the reaction gas with water in each cooling device. Let me
Do it in two steps. In the first cooling device, the temperature of the reaction gas is lowered to 50 ° C to 90 ° C. When the temperature of the reaction gas is lowered,
2,6 contained in 2,6-dichlorobenzonitrile
-The amount of 2,6-dichlorotoluene increases and the content of 2,6-dichlorotoluene decreases. Therefore, depending on the concentration of unreacted 2,6-dichlorotoluene in the reaction gas flowing out of the reactor, The temperature inside the cooling device of the
The concentration of 2,6-dichlorotoluene mixed in dichlorobenzonitrile is 1% or less, preferably 0.5% or less,
Is selected from the range of 50 ° C to 90 ° C.

Most of the 2,6-dichlorotoluene condensed in the first cooling device goes into 2,6-dichlorobenzonitrile, and a very small amount is dissolved in water.

The 2,6-dichlorotoluene that does not condense in the first cooling device is condensed and recovered by cooling the reaction gas to 0 ° C to 45 ° C in the second cooling device. The 2,6-dichlorotoluene recovered by the second cooling device is a mixture with water and can be recovered by being separated from water by liquid-liquid separation. It can be fed to the reactor for ammoxidation as part of the starting 2,6-dichlorotoluene.

Although any known gas-liquid contact device is used as the cooling device, a spray tower for spraying water, a cyclone scrubber, a venturi scrubber, a wet wall tower, a packed tower, or the like is used.

Water is circulated in the cooling device, and the water is cooled by a heat exchanger to adjust the temperature to a required temperature. In order to prevent the accumulation of impurities in the water, it is necessary to extract a part of the circulating water and replenish it with fresh water in order to obtain 2,6-dichlorobenzonitrile having less impurities.

The slurry of 2,6-dichlorobenzonitrile obtained in the first cooling device is solid-liquid separated from water by a known method such as a filter or a centrifuge, and washed with water if necessary,
2,6-dichlorotoluene content of 1% or less 2,6
Obtaining dichlorobenzonitrile.

If necessary, 2,6-dichlorobenzonitrile can be dried by a known method.

Examples The definitions of conversion and overall yield in the following examples are as follows.

DCT: 2,6-dichlorotoluene DBN: 2,6-dichlorobenzonitrile Example 1 Stainless steel fluidized bed reactor with an inner diameter of 81 mm (about 3 inches) and a height of about 4 m was 1.9% vanadium oxide, Chromium oxide 3.0%, iron oxide 9.7% and antimony oxide 35.
7 kg of a fluidized catalyst having 5% supported on silica was filled. The reaction was carried out by supplying 2,6-dichlorotoluene, ammonia and air to the reactor.

The reaction temperature is about 360 ° C., and the contact time between the reaction gas and the catalyst is about 7.5 seconds. The amount supplied to the reactor is 2,6-
Dichlorotoluene 3.0 mol / H ammonia 15 mol /
H, and air 50 mol / H, ammonia / 2,
6-dichlorotoluene molar ratio: 5.0, oxygen /
The molar ratio of 2,6-dichlorotoluene is 3.5.

The reaction product gas flowing out of the reactor has an inner diameter of about 81 mm (about 3 mm
Inch), and introduced into a cooling tower made of stainless steel having a height of about 2 m, and cooled to 70 ° C. by contacting with circulating water having a flow rate of 1 m ³ / H. The temperature of the circulating water is controlled by cooling with water in a heat exchanger provided in the circulation line. The reaction product gas cooled to 70 ° C. in the first cooling tower was introduced into the second cooling tower having the same specifications as the first cooling tower, and contacted with the circulating water cooled with brine to obtain 10 Cooled to ° C.

The first cooling tower was supplied with 1 liter / H of make-up water, the resulting slurry of 2,6-dichlorobenzonitrile was centrifuged, a part of the separated mother liquor was withdrawn, and the rest was subjected to first cooling. I returned to the tower.

A part of the circulating water is withdrawn from the second cooling tower, liquid-liquid separation is performed, and 2,6-dichlorotoluene is recovered and returned to the reactor as a part of the raw material. Excess water was withdrawn and the rest was returned to the second cooling tower.

2,6- in the obtained 2,6-dichlorobenzonitrile
The dichlorotoluene content was 0.1% and the overall yield of 2,6-dichlorobenzonitrile was 81%.
The conversion rate of 2,6-dichlorotoluene was 90%.

Example 2 A test was conducted under the same conditions as in Example 1 except for the following conditions.

Catalyst filling amount: Approximately 5.8 kg Raw material supply amount 2,6-Dichlorotoluene 3 mol / H Ammonia 21 mol / H Air 71 mol / H The results of the test are shown in Table 1.

Example 3 A test was performed under the same conditions as in Example 1 except for the following conditions.

Catalyst filling amount: about 9.1 kg Raw material supply amount 2,6-dichlorotoluene 3 mol / H ammonia 12 mol / H air 57 mol / H The results of the test are shown in Table 1.

Comparative Example 1 A test was conducted under the same conditions as in Example 1 except that the cooling tower was cooled to 40 ° C. using only the first stage.

As shown in Table 1, the test results showed that the yield of 2,6-dichlorobenzonitrile was as low as 76%, and the yield of 2,6-dichlorobenzonitrile was 2,6.
-Dichlorobenzonitrile contains 4% of 2,6-dichlorotoluene, and in order to make it 1% or less, purification such as dissolution in a solvent and recrystallization is necessary.

Example 4 A test was conducted under the same conditions as in Example 1 except that the first-stage cooling tower was cooled to 50 ° C.

The test results were as shown in Table 1.

Comparative Example 2 A test was carried out under the same conditions as in Example 3 except that the catalyst was charged at 7 kg and the cooling tower was used only at the first stage to cool to 25 ° C.

The test results were as shown in Table 1.

Comparative Example 3 A test was performed under the same conditions as in Example 3 except that the cooling tower was used only at the first stage to cool to 25 ° C.

The test results were as shown in Table 1.

Claims (2)

[Claims] 1. A method for ammoxidation comprising contacting a reaction raw material gas containing 2,6-dichlorotoluene, air and ammonia with a fluidized bed of a catalyst comprising a metal oxide supported on a carrier to form a 2,6-dicarboxylic acid. In the method for producing chlorobenzonitrile, the reaction is carried out under the simultaneous satisfaction of the following conditions, and the method for producing 2,6-dichlorobenzonitrile. (B) The concentration of 2,6-dichlorotoluene in the reaction raw material gas is 2.6 mol% or more. (B) The reaction product gas is brought into contact with water to cool it to a temperature in the range of 50 to 90 ° C.
Collecting 6-dichlorobenzonitrile as a slurry in which it is solidified and dispersed in water, and obtaining 2,6-dichlorobenzonitrile from this slurry. (C) By contacting the cooled reaction product gas after the collection of 2,6-dichlorobenzonitrile with water again to cool it to a temperature in the range of 0 to 40 ° C., unreacted 2, Collect 6-dichlorotoluene as a dispersion in which it is dispersed in water, and recover 2,6-dichlorotoluene from this dispersion. 2. The method for producing 2,6-dichlorobenzonitrile according to claim 1, which is carried out under the satisfaction of at least one of the following conditions. (D) The concentration of 2,6-dichlorotoluene in the reaction raw material gas is 3 mol% or more. (E) The conversion rate of 2,6-dichlorotoluene in ammoxidation is in the range of 80 to 97%.