JPH10182548A - Method for producing benzoic acid - Google Patents

Abstract

[PROBLEMS] To produce benzoic acid by oxidizing toluene in a liquid phase with a molecular oxygen-containing gas to suppress the production of by-product tar components and selectively produce benzoic acid in high yield. Provides a way to get: Kind Code: A1 In the presence of a transition metal catalyst containing cobalt, toluene is brought into contact with a molecular oxygen-containing gas in a liquid phase and oxidized to produce benzoic acid.
The temperature is set to 00 to 170 ° C., and the oxygen concentration in the molecular oxygen-containing gas is set to 22 to 40% by volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing benzoic acid by oxidizing toluene in a liquid phase with a molecular oxygen-containing gas.

[0002]

BACKGROUND OF THE INVENTION Benzoic acid is phenol, terephthalic acid,
It is a compound useful as an intermediate material such as a dye, and itself as a food additive, and is industrially produced in large quantities. Although many methods for producing benzoic acid are already known, all of these methods have major defects.

[0003] For example, Kamiya et al.
sis, 25, 326 (1972) and Bull. Che
m. Soc. Japan, 46, 905 (1973), etc.) A method for producing benzoic acid by oxidizing toluene with molecular oxygen in a lower fatty acid solvent such as acetic acid in the presence of a heavy metal compound catalyst involves the production of benzoic acid by corrosion of equipment with lower fatty acids, In addition to the decrease in equipment efficiency due to use, the separation and purification of the target benzoic acid is complicated due to the presence of lower fatty acids in the oxidation products, and equipment for the recovery and purification of lower fatty acids is also required. Is industrially undesirable in many respects.

There is also known a method for producing benzoic acid by oxidizing toluene with molecular oxygen in the presence of a heavy metal compound catalyst and a halogen compound as an oxidation promoter. Corrosion is remarkable, and there is a defect that impurities derived from the halogen compound are mixed into the target benzoic acid.

Therefore, in order to industrially produce a large amount of benzoic acid, a lower fatty acid solvent or a halogen compound is not used,
In many cases, only a heavy metal compound such as a cobalt compound is used as a catalyst, and toluene is oxidized with molecular oxygen in a liquid phase (Hydrocarbon Pro).
sessing 43 vol. 11, p. 174 and U.S. Pat. No. 4,339,599).

[0006] This method is much superior to the above two methods, because the apparatus does not corrode so much and the separation and purification of the target benzoic acid from the oxidation product are relatively easy. But CO, CO in the oxidation reaction
2, formic acid, acetic acid, biphenyls, benzoates,
Since many by-products such as benzyl esters are produced, the selectivity for benzoic acid from toluene is low, which is not industrially satisfactory.

[0007] In particular, high-boiling substances, mainly benzoic acid esters and benzyl esters, form tar-like substances, which not only reduce the selectivity of toluene to benzoic acid, but also reduce the catalyst recovery step after the oxidation reaction. However, there is a large adverse effect such as deterioration of the handleability. In order to suppress the formation of this tar-like substance, a method of keeping the conversion of toluene low, such as lowering the reaction temperature, can be considered, but this is not realistic because the productivity is greatly sacrificed.

[0008]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention suppresses the generation of by-product tar components when oxidizing toluene in a liquid phase with a molecular oxygen-containing gas to produce benzoic acid. And a method for selectively obtaining benzoic acid at a high yield.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, by using a gas having a high oxygen content in the reaction, it was possible to reduce the conversion of toluene without lowering the conversion. They have found that only by-produced tar-like substances can be reduced, and have completed the present invention.

That is, according to the process for producing benzoic acid of the present invention, when toluene is brought into contact with a molecular oxygen-containing gas in the liquid phase in the presence of a transition metal catalyst containing cobalt and oxidized to produce benzoic acid, Reaction temperature 100-170 ° C
And the oxygen concentration in the molecular oxygen-containing gas is 22 to 4
It is characterized by being 0% by volume.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The oxidation catalyst used in the present invention contains a cobalt compound.
It may be used by mixing with a metal component. The cobalt concentration is 10 to 1000 ppm by weight based on the reaction mixture,
In particular, 30 to 100 ppm by weight is preferred, and 10 parts by weight pp
If it is less than m, a sufficient reaction rate cannot be obtained, and the productivity is lowered. If it exceeds 100 ppm by weight, the reaction rate does not increase so much, which is economically disadvantageous. When the second metal component is used in combination, the weight ratio of cobalt (a): second metal component (b) is preferably a: b = 99: 1 to 60:40, more preferably 90:10 to 80. : 20.

The compound used as the oxidation catalyst is preferably soluble in the reaction mixture. However, even if it is hardly soluble or insoluble, it can be used as long as it changes into a soluble compound during the reaction. In particular, when the concentration of benzoic acid in the reaction mixture is high, the conversion to a soluble compound is fast, and even a poorly soluble one can be easily used. Starting not only widens the choice of catalyst species but also shortens the induction period of the reaction.

The oxidation catalyst used in the present invention specifically includes the following compounds. (1) Cobalt salts and manganese salts of aliphatic carboxylic acids such as acetic acid, propionic acid and butyric acid. (2) Cobalt salts and manganese salts of aromatic carboxylic acids such as benzoic acid and toluic acid. (3) Cobalt salts and manganese salts of alicyclic carboxylic acids such as naphthenic acid. (4) Inorganic compounds such as metallic cobalt, metallic manganese, or carbonates, oxides and hydroxides thereof.

Of these, acetate, benzoate, toluate and the like are preferable, all of which are easily available and
High solubility in the reaction mixture. No halogen compound is used as an oxidation promoter.

The reaction temperature is from 100 ° C. to 170 ° C., especially 1
30 ° C to 170 ° C is preferred. If the temperature is lower than 100 ° C., a sufficient reaction rate cannot be obtained because of the low activity of the cobalt catalyst, and the productivity is reduced. If the temperature exceeds 170 ° C., the generation of by-products, especially tar-like substances, is remarkably increased. The selectivity to benzoic acid is greatly reduced.

The reaction pressure is from normal pressure to 10 MPaG, especially from 0.2 to 10 MPaG because the reaction mixture needs to be maintained in a liquid phase.
1 MPaG is preferred. If the reaction pressure is low, the reaction mixture cannot be maintained in the liquid phase, resulting in a decrease in the reaction rate. Further, if the reaction pressure is increased more than necessary, the construction cost of the apparatus increases, which is economically disadvantageous.

Although the oxidation reaction of the present invention is preferably carried out without a solvent, it may be diluted with a compound which is relatively stable against oxidation, such as benzene. In addition, use of a fatty acid such as acetic acid as a solvent is not performed.

The gas containing molecular oxygen as an oxidizing agent is
A gas having an increased oxygen concentration in air, a mixed gas of an inert gas such as carbon dioxide or nitrogen and oxygen, or a mixed gas of an oxidized exhaust gas and oxygen is used.

The above gas is generally introduced into the reactor from a straight, ring-shaped or radial blowing pipe. The blowing pipe has a shape such that the gas is uniformly and efficiently dispersed in the reaction contents. Are preferred.

The flow rate of the blowing gas is 1 km
1 to 50 Nm ³ / hr, preferably 5 to 20 Nm ³ / hr.
Nm ³ / hr is more preferred. If the amount is more than this, the blown gas becomes excessive, contact with the reaction contents is not sufficiently performed, and oxygen in the gas is not efficiently used for the reaction. If the amount is less than this, the productivity of benzoic acid per unit raw material decreases.

Generally, inexpensive air is used as the blowing gas. In the present invention, a gas having an oxygen concentration of 22 to 40% by volume, preferably 25 to 30% by volume, is used. The enrichment of oxygen increases the oxygen concentration in the liquid phase, further oxidizes the reaction intermediate, which is a by-product, and improves the selectivity of the target product, benzoic acid. Absorption is not performed, and the oxygen intensity decreases. That is, when the oxygen concentration exceeds 30% by volume, it becomes difficult to sufficiently absorb oxygen into the liquid phase, and when the oxygen concentration exceeds 40% by volume, a large amount of oxygen is not consumed and exhaust gas is not contained. Spread.
It goes without saying that the productivity of benzoic acid is optimized by adjusting the reaction temperature, the amount of blown gas and the oxygen concentration so that the oxygen concentration in the gas at the outlet of the reactor approaches 0% by volume as much as possible.

In the present invention, the reaction is preferably carried out until the concentration of benzoic acid in the reaction mixture reaches 10 to 50% by weight, preferably 20 to 30% by weight. If the amount is less than 10% by weight, the production amount per unit time is small, which is economically disadvantageous. If the amount exceeds 50% by weight, the toluene concentration becomes low and the reaction rate becomes low, which is also economically unfavorable.

The exhaust gas contains water, formic acid, acetic acid, etc., which are by-produced during the oxidation, in addition to unreacted toluene, so that they are cooled and condensed. Since the condensed liquid is separated into two layers, the toluene layer is returned to the oxidation step, and the acidic wastewater containing formic acid, acetic acid, etc. is subjected to an appropriate detoxification treatment and then discarded.

The obtained reaction product contains, in addition to the target product benzoic acid, intermediate oxides such as benzyl alcohol and benzaldehyde, and by-products such as benzoates, benzyl esters and biphenyls. The reaction product is separated by a known method such as distillation, and the unreacted toluene and intermediate oxide are preferably returned to the oxidation step.
The intermediate oxide is ultimately recovered as benzoic acid as the oxidation proceeds, and there is no loss as a by-product when such circulation is repeated. Other substances are discharged out of the system together with heavy components as tar-like substances. Therefore, the reduction of the tarry substance, which is an effect of the present invention, results in the selective production of benzoic acid.

[0026]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 Toluene 23 was placed in a 500 cc titanium autoclave equipped with a reflux condenser, a stirrer, a gas injection pipe, and a thermometer.
2.5 g, benzoic acid 17.5 g, and cobalt acetate 4
A mixture gas of oxygen and air adjusted to an oxygen concentration of 25% by volume was charged with 0.0635 g of hydrate, and the mixture was sufficiently stirred at a temperature of 150 ° C. and a pressure of 0.5 MPaG.
h, and reacted for 3 hours. After completion of the reaction, the reaction contents were cooled and the reaction contents were taken out. The amount of benzoic acid, benzyl alcohol, benzaldehyde, benzyl ester, benzoate, etc. was determined by GC analysis and titration with an aqueous solution of caustic soda.

Since benzaldehyde and benzyl alcohol are intermediates to benzoic acid, they were evaluated as benzoic acid, and the benzoic acid selectivity was calculated by the following formula (1).

[0029]

(Equation 1)

Benzyl esters and benzoic esters represented by benzyl benzoate, benzyl biphenylcarboxylate and the like were evaluated as tar components.
The tar selectivity was calculated by the following equation (2).

[0031]

(Equation 2)

The oxygen consumption efficiency determined by the following equation (3) was calculated from the oxygen concentration in the outlet gas.

[0033]

(Equation 3)

The results obtained are shown in Table 1.

Example 2 In addition to cobalt acetate, 0.011 of manganese acetate was used as a catalyst.
The reaction was carried out under the same conditions as in Example 1 except that 2 g was added. After completion, the selectivity of benzoic acid and tar was calculated in the same manner. The results obtained are shown in Table 1.

Example 3 A reaction was carried out under the same conditions as in Example 1 except that a mixed gas of oxygen and air whose oxygen concentration was adjusted to 30% by volume was used. The selectivity was calculated. The results obtained are shown in Table 1.

Example 4 A reaction was carried out under the same conditions as in Example 1 except that a mixed gas of oxygen and air whose oxygen concentration was adjusted to 40% by volume was used, and after completion, benzoic acid and tar were similarly treated. The selectivity was calculated. The results obtained are shown in Table 1.

The effects of the present invention are shown more clearly with reference to the following comparative examples.

COMPARATIVE EXAMPLE 1 Except that ordinary air having an oxygen concentration of 21% by volume was used.
The reactions were all carried out under the same conditions as in Example 1, and after completion, the selectivity of benzoic acid and tar was calculated in the same manner. The results obtained are shown in Table 1.

Comparative Example 2 Except for using ordinary air having an oxygen concentration of 21% by volume,
The reaction was carried out under the same conditions as in Example 2, and after completion, the selectivity of benzoic acid and tar was calculated in the same manner. The results obtained are shown in Table 1.

[0041]

[Table 1]

[0042]

As described above in detail, according to the method for producing benzoic acid of the present invention, when benzoic acid is produced by oxidizing toluene in a liquid phase with a molecular oxygen-containing gas. The production of tar components can be suppressed, and benzoic acid can be selectively produced at a high yield.

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[Procedure amendment]

[Submission date] January 27, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

 ──────────────────────────────────────────────────の Continued on the front page (72) Kyohei Segawa, Inventor 4-7-1 Nakai, Nakai, Kokurakita-ku, Kitakyushu-shi, Fukuoka Prefecture −202

Claims (1)

[Claims] 1. A method for producing benzoic acid by contacting toluene in a liquid phase with a molecular oxygen-containing gas in the presence of a transition metal catalyst containing cobalt to produce benzoic acid, at a reaction temperature of 100 to 100.
A method for producing benzoic acid, wherein the temperature is 170 ° C. and the oxygen concentration in the molecular oxygen-containing gas is 22 to 40% by volume.