JPS5949213B2 - Method for producing aromatic dicarboxylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high quality aromatic dicarboxylic acids by liquid phase oxidation of dialkylbenzenes or oxidized intermediates thereof.

A method for producing aromatic dicarboxylic acids is a method in which dialkylbenzene or its oxidized intermediate is oxidized in a liquid phase using a molecular oxygen-containing gas in the presence of a cobalt-manganese-bromine catalyst using a lower aliphatic carboxylic acid as a solvent. It has been known.

In particular, the above method for producing terephthalic acid by liquid phase oxidation of paraxylene is of high industrial value. However, when terephthalic acid is produced using the above method, the resulting terephthalic acid contains para-toluic acid, 4-
It contains not only unoxidized substances such as carboxybenzaldehyde (hereinafter abbreviated as 4CBA) but also coloring impurities of unknown structure. Therefore, when such terephthalic acid is used as a raw material for polymerizing polyester such as polyethylene terephthalate, the color tone of the obtained polyester becomes extremely poor, so that the terephthalic acid needs to be further purified by some method. However, it is extremely difficult to separate the impurities, particularly colored substances, from such terephthalic acid and requires complicated purification steps. For the above reasons, it has been strongly desired to develop a method for producing terephthalic acid with a lower content of coloring impurities than before. Therefore, as the method developed above, cobalt
A method of liquid phase oxidation of dialkylbenzene using molecular oxygen in the presence of a bromo-amine catalyst (Japanese Patent Publication No. 49-3
However, since this method has extremely low oxidation activity and many side reactions, the terephthalic acid obtained by this method contains a large amount of 4CBA and coloring impurities and cannot be purified. Therefore, it is difficult to use it in the production of polyester fibers.

In view of the above circumstances, the present inventors have worked diligently to obtain terephthalic acid with an extremely good color tone and high purity of polyester, and to find an industrially advantageous method for producing the same. As a result of repeated studies, the method of the present invention was completed.

That is, the present invention uses a lower aliphatic carboxylic acid as a solvent and oxidizes dialkylbenzene or its oxidized intermediate with a molecular oxygen-containing gas in the presence of a cobalt-manganese-prone catalyst to produce an aromatic dicarboxylic acid. This method is characterized by the presence of alicyclic amines or quaternary ammonium salts in the oxidation reaction system. In the method of the present invention, the alicyclic amines present in the oxidation reaction system include cyclohexylamine, piperidine, pyrrolidine, piperazine, morpholine, 1,8-diazabicyclo(
0,5,4) undecene-1, etc.

As quaternary ammonium salts, it is preferable to use quaternary ammonium hydroxides such as tetraethylammonium hydroxide and tetrabutylammonium hydroxide, but they can also be used as salts with fatty acids or mineral acids. Note that aromatic amines other than those mentioned above are not preferred because they either interfere with the oxidation reaction or have almost no effect even if they do not interfere. In the present invention, the alicyclic amines and quaternary ammonium salts have an atomic ratio of 0.02 to 10.0, especially 0.02 to 10.0, in terms of basic nitrogen atoms in these compounds, to all bromine atoms in the system. It is preferable to make it exist so that it may be in the range of .2 to 5!0.

If the amount of alicyclic amines or quaternary ammonium salts used is larger than the above range, the amount of oxidized intermediates will increase due to a decrease in oxidation activity, and the inhibitory effect on the formation of coloring impurities will be reduced, and vice versa. This is because if the amount used is smaller than the above range, it will be difficult to achieve the intended purpose of the present invention. In the present invention, it is preferable for the alicyclic amines and quaternary ammonium salts to be present in the oxidation reaction system from the initial stage of the oxidation reaction, since the effect of suppressing the formation of coloring impurities is greater.

Therefore, for example, in a batch or semi-continuous reaction system, alicyclic amines or quaternary ammonium salts may be added before the start of the oxidation reaction, whereas in a continuous reaction system, the starting materials and catalyst may be added simultaneously or separately. It may be supplied to the reaction system. Note that if alicyclic amines or quaternary ammonium salts are brought into direct contact with the catalyst solution, some compounds may react violently with heat generation, so it is recommended to dilute them with water or lower fatty acids as a solvent before adding. preferable.

In the present invention, as the starting material dialkylbenzene or its oxidized intermediate used in the production of aromatic dicarboxylic acid, valaxylene, paratoaldehyde and baratoluic acid are particularly preferred, but paradiisopropylbenzene and paracymene may also be used. Further, for obtaining aromatic dicarboxylic acids other than terephthalic acid, for example, meta-xylene, meta-tolyl aldehyde, meta-tolylic acid, etc. may be used.

In addition, in the method of the present invention, the lower fatty acid used as a solvent is preferably an aliphatic monocarboxylic acid having 2 to 6 carbon atoms, and specific examples thereof include acetic acid, propionic acid, butyric acid, fornic acid, etc., but acetic acid is particularly used. is preferable.

Further, a small amount of water may be present in this solvent in order to promote solubility of the oxidation catalyst described below. Next, specific conditions for implementing the present invention are shown below.

First, air, oxygen gas, or a mixture thereof is used as the molecular oxygen-containing gas. At this time, in order to maintain the reaction system in a liquid phase, it is preferable to pressurize the reaction system with the above gas, and a pressure of 5 to 50 Kf/d is usually used. Next, the catalyst for promoting the oxidation reaction is a cobalt-manganese-promone catalyst as described above, and examples of cobalt and manganese compounds include cobalt, manganese carbonate, chloride, bromide, acetate, and hydroxide. Things are used. The bromine compound is appropriately selected from inorganic bromine compounds such as free bromine, hydrobromic acid, sodium bromide, and potassium bromide, and organic bromine compounds such as bromoform, dipromethane, tetrabromoethane, monobromoacetic acid, benzyl bromide, and xylene bromide. However, it is preferable to use organic bromine because it is less corrosive to the oxidizing equipment and is easy to handle. The method of the present invention can be effectively used in any of the batch, semi-continuous and continuous methods. Since the quality of the terephthalic acid obtained using the method of the present invention is extremely high, it can be used as it is in the production of polyester fibers such as polyethylene terephthalate without going through a purification process, making it extremely practical.

As shown in the examples below, the terephthalic acid obtained by the method of the present invention is determined by the absorbance of an alkaline solution of terephthalic acid and the external color of terephthalic acid, which have been conventionally used as an effective quality measure of terephthalic acid. Although the quality is not significantly superior to that of conventionally known terephthalic acid, it has the interesting feature of providing a polyester with high whiteness.

The present invention will be described in more detail below based on Examples, but the present invention is not limited to these Examples.

In the examples, alkaline solution absorbance refers to absorbance of 340 mμ, which is obtained by measuring a solution prepared by dissolving terephthalic acid crystal 29 in 2N potassium hydroxide aqueous solution 25ME in a glass cell with a thickness of 50 to 100 mμ, using 2N potassium hydroxide aqueous solution as the target liquid.
It means the absorbance under liquid light.

Also, the b value is 1.09 for terephthalic acid or polyester
18mm in diameter and 2.6m1 in thickness at a pressure of 200K'/~
ND-101D manufactured by Nippon Denshoku Co., Ltd.
This is the external color measured with a model colorimeter. The amount of 4-CBA in terephthalic acid was determined by dissolving terephthalic acid in an ammonia buffer and measuring it using a polarographic method.
Examples 1 to 4 In a titanium autoclave equipped with a reflux condenser, an inlet for xylene and air, and a stirrer, 250 parts of 95% acetic acid, 53 parts of cobalt acetate tetrahydrate, 1.11 parts of manganese acetate tetrahydrate, and 0.48 parts of tetrabromoethane, an alicyclic amine, and a quaternary ammonium salt were each supplied in the amounts shown in Table 1, and while stirring at a pressure of 23K2/DGl temperature of 210°C, baraxylene was mixed with air at a rate of 50 parts per hour. Sent.

The amount of air supplied to the reaction system is such that the oxygen concentration in the exhaust gas is between 5 and 5.
It was adjusted to 7%. After reacting in this manner for 1 hour, the contents were taken out and solid and liquid were separated, and the resulting crystals were washed with acetic acid, then water, and dried to obtain terephthalic acid. Table 1 shows the quality of the terephthalic acids and the appearance color of the polyester chips obtained by esterifying these terephthalic acids with ethylene glycol and then polycondensing them. Comparative Example 1 Terephthalic acid was produced in exactly the same manner as in Example 1, except that triethylamine was not added.

The results at this time are also listed in Table 1. Comparative Example 2 Terephthalic acid was produced in exactly the same manner as in Example 1, except that the amount of cobalt acetate tetrahydrate added was 1.64 parts, and manganese acetate tetrahydrate was not added all at once.

Claims (1)

[Claims] 1. Producing an aromatic dicarboxylic acid by oxidizing dialkylbenzene or its oxidized intermediate with a molecular oxygen-containing gas in the presence of a cobalt-manganese-bromine catalyst using a lower aliphatic carboxylic acid as a solvent. 1. A method for producing an aromatic dicarboxylic acid, which is characterized in that an alicyclic amine or a quaternary ammonium salt is present in the oxidation reaction system. 2 Basic nitrogen atom is 0.02 to 10 to bromine atom
．． The method for producing aromatic dicarboxylic acids according to claim 1, wherein the alicyclic amines or quaternary ammonium salts are present so that the atomic ratio is within the range of 0 (atomic ratio).