JPH09124548A - Production of alkylbenzoic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce the subject compound in a high grade without causing the abnormal operation of an installation, while by-producing a small amount of a dicarboxylic acid, by oxidizing an alkylbenzene compound with molecular oxygen in a liquid phase, recovering the alkylbenzene from the obtained reaction product, removing impurities from the recovered alkylbenzene and subsequently reusing the purified compound as the raw material. SOLUTION: This method for producing the alkylbenzoic acid comprises oxidizing an alkylbenzene compound (A) having two or more 1-3C alkyl groups with a molecular oxygen-containing gas in the presence of a soluble heavy metal catalyst in a liquid phase, recovering the compound (A) from the reaction product solution, removing the contained impurities from the recovered component (A) by a distillation treatment, a water-washing treatment, a washing treatment using a 8-14pH alkaline aqueous solution, a treatment using an anion exchange resin, a treatment using a solid adsorbent, a treatment using an alkali solid substance, etc., and subsequently reusing the purified recovered component A. In the method, one carboxyl group of the component A is converted into the carboxyl group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing alkylbenzoic acid by liquid-phase oxidation of alkylbenzenes, and more particularly to troubles and quality of operation of an apparatus due to dicarboxylic acid by-produced when producing alkylbenzoic acid. Regarding how to solve the degradation problem.

[0002]

BACKGROUND ART Oxidation of alkylbenzenes represented by xylene and mesitylene with a molecular oxygen-containing gas in a liquid phase using a heavy metal catalyst soluble in the liquid phase converts one alkyl group into a carboxylic acid to give benzoic acid. Producing acids is described, for example, in US Pat. No. 2,712,549,
U.S. Pat. No. 2,712,551, Japanese Patent Publication No. 52-46217
And Japanese Patent Publication No. 56-8816.

In the above-mentioned US patent, when xylene is oxidized to produce toluic acid, at the same time, toluic acid is further oxidized and insoluble phthalic acid is produced as a by-product in the reaction solution. It is described that phthalic acid is deposited and deposited on the heat transfer surface of the vessel and heat removal becomes impossible, and further that phthalic acid is mixed when recovering toluic acid by crystal separation. Regarding the former problem, a method of flushing the reaction solution to remove heat is adopted, but industrially it is necessary to provide a flush tank, the process becomes complicated, and troubles are expected. Regarding the latter problem, phthalic acid is removed by filtering the reaction solution while it is hot. However, this method cannot remove the phthalic acid dissolved in the reaction solution, and when further cooling to obtain toluic acid, a considerable amount of phthalic acid cannot be avoided from being mixed in the product.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to cause troubles in equipment operation and deterioration of quality due to dicarboxylic acid by-produced in the production of alkylbenzoic acid which is a monocarboxylic acid by liquid-phase oxidation of alkylbenzenes. To provide a solution to the problem.

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the inventor has found many impurity peaks in the alkylbenzene recovered after the oxidation reaction by gas chromatography. It was presumed that either of these promotes the dicarboxylic acid by-product. That is, since dicarboxylic acid increases abnormally by recovering unreacted alkylbenzene and reusing it as a raw material, it is important to suppress dicarboxylic acid generation itself in the oxidation reaction as much as possible. The present invention has been found that the by-product of dicarboxylic acid is suppressed by removing impurities contained when the alkylbenzene is recovered and reused as a raw material.

That is, according to the present invention, one alkylbenzene having at least two alkyl groups having 1 to 3 carbon atoms is oxidized in a liquid phase with a molecular oxygen-containing gas using a soluble heavy metal catalyst to give one alkylbenzene. In the method for producing an alkylbenzoic acid by converting the alkyl group of the above to a carboxylic acid, the impurities contained in the alkylbenzene recovered from the reaction product solution are removed and then reused as a raw material. Is a manufacturing method.

As a method of removing impurities contained in the recovered alkylbenzene, a method of further rectifying the recovered alkylbenzene, a method of washing with sufficient water,
Examples include a method of washing with an alkaline aqueous solution having a pH of 8 to 14, a method of treating with an anion exchange resin, a method of treating with a solid adsorbent, and a method of treating with an alkali solid.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The alkylbenzene used as a raw material has 2 to 6 substituents in the benzene nucleus, and at least 2 substituents have an alkyl group having 1 to 3 carbon atoms. is there. In the present invention, ortho-xylene, meta-xylene, para-xylene, mesitylene, pseudocumene is preferably used methylbenzenes, respectively corresponding ortho-toluic acid, meta-toluic acid, para-toluic acid, 3,5-dimethylbenzoic acid, 3, 4 -
Dimethylbenzoic acid and the like are produced.

A known method is applied to the oxidation reaction of alkylbenzene. As the reaction solvent, a solvent that is not easily oxidized, such as benzene, may be used, but it is preferable to use the raw material alkylbenzene itself as the solvent. Organic acid salts of cobalt, manganese, cerium, etc. are effective as the solvent-soluble heavy metal catalyst, and cobalt naphthenate, manganese naphthenate, cobalt toluate, etc. are preferable.
The metal concentration in the reaction liquid of the catalyst is 10 to 3000 ppm, preferably 30 to 300 ppm. Although the oxidation reaction temperature depends on the type of alkylbenzene, it is generally 100 to 20.
0 ° C., preferably 120 to 180 ° C. The pressure is a pressure above which the reaction liquid can maintain a liquid phase at the reaction temperature, and is preferably 2 to 50 Kg / cm ² G. Air is usually used as the molecular oxygen-containing gas, and is blown so that oxygen is sufficiently dispersed in the reaction system. In order to avoid the explosion limit, the oxygen concentration in the exhaust gas at the outlet in the steady state is 6
The amount of air blown in is adjusted to be less than or equal to%. The reaction type is usually a tank reactor equipped with a stirrer,
Although the reaction can be carried out in a batch system, a semi-batch system, and a continuous system, it is industrially preferable to carry out the reaction in a continuous system.

The product stream after the reaction is recovered by distillation to recover unreacted alkylbenzene and generated alkylbenzoic acid, or once cooled to separate the generated alkylbenzoic acid by crystallization and then distilled to recover unreacted alkylbenzene. . The recovered alkylbenzene fraction can be used again as a reaction raw material without any treatment, but as the number of times of recycling actually increases, the production of dicarboxylic acid gradually increases as described above. This is considered to be due to the accumulation of impurities that promote the by-product of dicarboxylic acid in the recycled alkylbenzene, and many impurity peaks are observed by gas chromatography as described above.

As a method for removing impurities contained in the recovered alkylbenzene, a method for removing impurities by distillation can be mentioned. The alkylbenzene fraction after the raw material recycling reaction is rectified in a distillation column having 10 or more theoretical plates to concentrate the alkylbenzene to a purity of 98% or more and then subjected to the oxidation reaction again to obtain dicarboxylic acid. The amount of by-product is the same as that of fresh raw materials. Instead of redistillation, washing with water is also effective. For 100 parts of the same alkylbenzene fraction as described above, 300 parts to 10 parts, preferably 100 parts to 30 parts of water is sufficiently contacted and mixed, and then the water layer is separated by a decanter to carry out the oxidation reaction of the alkylbenzene layer. By providing, the by-product of dicarboxylic acid is suppressed.

Rinsing with alkaline water is also effective. pH8 ~
Alkaline aqueous solution of 14 is added to the alkylbenzene fraction 100
100 parts to 0.1 parts, preferably 50 parts to 3 parts
After sufficient contact mixing with the parts, the alkaline aqueous layer is drained, and the recovered alkylbenzene is subjected to an oxidation reaction. The alkali is preferably an inorganic alkali such as caustic soda, caustic potash, sodium carbonate, sodium bicarbonate, and aqueous ammonia solution. Further, an amine-based aqueous solution also exhibits the same effect, but higher amines which are easily dissolved in the organic layer are less preferable.

It is also effective to directly add an alkali solid to the alkylbenzene fraction without using an aqueous solution. By contacting the recovered alkylbenzene with an insoluble inorganic alkali such as solid caustic soda, caustic potash, calcium oxide, and magnesium oxide, an alkylbenzene raw material with less dicarboxylic acid by-product can be obtained. Similarly, anion exchange resins such as Amberlit.
e) A-400 or Dowex 1-X1
Etc. are effective. It is also effective to contact with a general solid adsorbent, and for example, activated carbon, activated alumina, silica gel, zeolite, etc. are effective. These treatment agents can be used with various industrial contact methods such as stirring and mixing with the alkylbenzene in a solid liquid, or forming a fixed bed and continuously passing it. The amounts of the alkali solid, the anion exchange resin and the solid adsorbent used are appropriately selected according to the capacity of each treatment material.

Next, the present invention will be described more specifically with reference to Examples. However, the present invention is not limited to these.

Example 1 In a 500 ml autoclave equipped with a stirrer made of SUS316, 150 g of raw material metaxylene and 0.5 g of cobalt cobalt naphthenate were charged, pressurized with nitrogen gas to 5 Kg / cm ² G, and then heated to 140 ° C. The temperature was raised to. Reaction pressure is 10 Kg /
While maintaining cm ² G, about 50 L / Hr (normal pressure conversion) of air was blown in so that the outlet oxygen concentration would not exceed 6%.
At this time, the stirring rotation speed by the stirring blade was controlled to 1000 rpm so that sufficient gas contact could be achieved. The reaction was carried out for 2 hours while keeping the reaction temperature at 140 to 150 ° C. After the reaction, the reaction solution was cooled to room temperature and the product was taken out to obtain a reaction solution containing a small amount of white precipitate. Analysis showed that this white precipitate weighed 4.1 g and was 87 w
It contained t% isophthalic acid. The amount of isophthalic acid dissolved in the reaction solution was 0.3 g, and the total amount of isophthalic acid produced was 3.9 g. The results of this reaction were that the conversion of metaxylene was 37.5% and the selectivity to metatoluic acid was 73.5 mol%. The selectivity of the produced isophthalic acid with respect to the meta-xylene consumed in the reaction was 5.4 mol%.

Almost all of the reaction solution was distilled under reduced pressure of 100 mmHg to recover 87 g of a meta-xylene fraction. From the recovered meta-xylene, 70 g was taken and combined with fresh meta-xylene, 150 g of raw material was again used as the raw material, and the oxidation reaction was carried out under the same conditions as above. Repeating this operation, 70 g of the meta-xylene fraction after the 4th reaction was placed in a separating funnel, 70 g of water was added and shaken vigorously to remove the aqueous phase, and then to the 5th oxidation reaction again. I served. The reaction results of each time are shown in Table 1 below. It can be seen that washing with water suppressed the production of isophthalic acid to the initial production level.

[0017]

Table 1 Number of Reactions Meta-xylene m-toluic acid Isophthalic acid conversion rate (%) Selectivity rate (mol%) Selectivity rate (mol%) 1 37.5 73.5 5.4 2 38.7 72.2 6. 1 3 36.3 73.4 6.9 4 39.2 71.5 7.6 5 (after washing with water) 38.1 71.2 5.3

Examples 2 to 4 In the same manner as in Example 1, the conversion rate of the oxidation reaction of alkylbenzene was adjusted to 35 to 40%, the reaction and recovery were repeated, and the recovered alkylbenzene of the fourth reaction was used in the fifth reaction. In Example 2, washing with an aqueous alkaline solution (70 g of para-xylene with 10 g of 5% NaOH and washing at room temperature)
In Example 3, anion exchange resin (10 g of Amberlite 400 was used for 70 g of ortho-xylene and treated at 50 ° C.), and in Example 4 solid adsorbent (for 70 g of mesitylene, 5 g of activated carbon tsurumicol was used. And treated at 60 ° C.) and then subjected to the reaction. The reaction results of each example are shown in Table 2. It can be seen that the dicarboxylic acid production was suppressed to the initial production level by each treatment.

[0019]

Table 2 Example 2 Example 3 Example 3 Reaction raw material Paraxylene Ortho-xylene Mesitylene First-time reaction results Raw material conversion rate (%) 35.1 37.4 40.2 Selectivity (mol%) Monocarboxylic acid 72. 4 69.5 61.2 Dicarboxylic acid 4.7 5.2 5.2 8.5 4th reaction result Raw material conversion (%) 36.0 38.2 41.1 Selectivity (mol%) Monocarboxylic acid 71.5 70 .1 59.8 Dicarboxylic acid 8.2 8.5 11.3 5th reaction result (after each treatment) Raw material conversion rate (%) 35.5 38.0 40.5 Selectivity (mol%) Monocarboxylic acid 71 .2 69.8 60.3 dicarboxylic acid 4.3 5.3 5.3 8.0

[0020]

EFFECTS OF THE INVENTION After removing impurities contained in alkylbenzene recovered from a reaction product solution by the method of the present invention and reusing it as a raw material, a dicarboxylic acid is first produced as shown in each Example. It is possible to solve the problems such as heat removal in the reactor during the operation of the apparatus and the problem of deterioration of quality due to mixing of dicarboxylic acid into the product.

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[Procedure amendment]

[Submission date] October 23, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction contents]

[0002]

BACKGROUND ART Oxidation of alkylbenzenes represented by xylene and mesitylene with a molecular oxygen-containing gas in the liquid phase using a heavy metal catalyst soluble in the liquid phase converts one alkyl group into a carboxyl group to give benzoic acid. Producing acids is described, for example, in US Pat. No. 2,712,549.
No. 2,712,551, Japanese Patent Publication No. 52-462.
No. 17 and Japanese Patent Publication No. 56-8816 are known.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0003

[Correction method] Change

[Correction contents]

In the above-mentioned US patent, when xylene is oxidized to produce toluic acid, at the same time, toluic acid is further oxidized and insoluble phthalic acid is produced as a by-product in the reaction solution. vessels of the phthalic acid to the heat transfer surface becomes impossible deposits precipitated heat removal, even it has been described that cause problems, such as phthalic acid is mixed when recovering toluic acid crystals separated. Regarding the former problem of heat removal, a method of flushing the reaction solution to remove heat is adopted, but industrially it is necessary to install a flush tank, the process becomes complicated, and troubles are expected. . Regarding the latter problem of phthalic acid contamination, phthalic acid is removed by filtering the reaction solution while hot. However, this method cannot remove the amount of phthalic acid dissolved in the reaction liquid, and when toluic acid is obtained as crystals by further cooling, a considerable amount of phthalic acid is mixed in the product. I can not avoid doing it.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the inventor has found many impurity peaks in the alkylbenzene recovered after the oxidation reaction by gas chromatography. It was presumed that either of these promotes the dicarboxylic acid by-product. That is, since the unreacted alkylbenzene is recovered and reused as a raw material, the amount of dicarboxylic acid increases sequentially.Therefore, it is important to suppress the generation of dicarboxylic acid itself in the oxidation reaction as much as possible. The present inventors have found that the by-product of dicarboxylic acid is suppressed by removing impurities contained when the reacted alkylbenzene is recovered and reused as a raw material, and the present invention has been accomplished.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

That is, according to the present invention, one alkylbenzene having at least two alkyl groups having 1 to 3 carbon atoms is oxidized in a liquid phase with a molecular oxygen-containing gas using a soluble heavy metal catalyst to give one alkylbenzene. a method of manufacturing an alkyl benzoate alkyl groups and converted to <br/> carboxyl group, after removal of the impurities contained in the alkyl benzene fraction which is recovered from the reaction product solution, be reused as a raw material And a method for producing an alkylbenzoic acid.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

[0012] The alkali washing can also be effective. pH 8
Alkaline aqueous solution of 14 to 10
100 parts to 0.1 parts, preferably 50 parts to 0 parts
After sufficient contact mixing with 3 parts, drain the alkaline water layer,
The recovered alkylbenzene is subjected to an oxidation reaction. As alkali, caustic soda, caustic potash, sodium carbonate,
Inorganic alkalis such as sodium bicarbonate and aqueous ammonia are preferred. Further, an amine-based aqueous solution also exhibits the same effect, but higher amines which are easily dissolved in the organic layer are less preferable.

Claims (7)

[Claims] 1. An alkyl group having at least two alkyl groups having 1 to 3 carbon atoms is oxidized in a liquid phase with a molecular oxygen-containing gas using a soluble heavy metal catalyst to form one alkyl group. In the method for producing an alkylbenzoic acid by converting a carboxylic acid into a carboxylic acid, impurities contained in the alkylbenzene recovered from the reaction product solution are removed, and then reused as a raw material. 2. The method for producing alkylbenzoic acid according to claim 1, wherein impurities contained in the recovered alkylbenzene are removed by distillation. 3. The method for producing an alkylbenzoic acid according to claim 1, wherein impurities contained in the recovered alkylbenzene are removed by washing with water. 4. The method for producing an alkylbenzoic acid according to claim 1, wherein impurities contained in the recovered alkylbenzene are removed by washing with an alkaline aqueous solution having a pH of 8 to 14. 5. The method for producing an alkylbenzoic acid according to claim 1, wherein impurities contained in the recovered alkylbenzene are removed by an anion exchange resin. 6. The method for producing alkylbenzoic acid according to claim 1, wherein impurities contained in the recovered alkylbenzene are removed by a solid adsorbent. 7. The method for producing an alkylbenzoic acid according to claim 1, wherein impurities contained in the recovered alkylbenzene are removed with an alkali solid.