JPH10316614A - Production of aromatic polycarboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide equipment for producing a high-quality aromatic carboxylic acid in high yield. SOLUTION: Disk turbine type agitating blades in plural stages 11, 12 and 13 are used and the diameter of the agitating blades 11 in the lowest stage is regulated to 1.1-1.5 times that of the other agitating blades 12 and 13 to produce a high-quality aromatic carboxylic acid in high yield in equipment for oxidizing an aromatic alkyl in the liquid phase with air, etc., and producing the aromatic carboxylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an aromatic carboxylic acid, and more particularly to a method for producing terephthalic acid obtained by oxidizing para-xylene.

[0002]

2. Description of the Related Art A key point in designing an oxidation reactor for producing an aromatic carboxylic acid is a reaction efficiency between an aromatic alkyl as a raw material and oxygen. In order to improve the above, a number of patents have been filed, including regulations on the type and preparation amount of the catalyst, the type of the stirring blade, and the nozzle position. Among them, known examples relating to the structure of the reaction tank are shown below.

In Japanese Patent Publication No. 51-41624, the dispersion and mixing of the reactants in the reaction vessel are improved by defining the spacing between the stirring blades, the supply pipes for a plurality of raw materials, and the stirring power per unit volume. Therefore, it is introduced that a product having a small amount of impurities can be efficiently recovered.

In Japanese Patent Application Laid-Open No. 58-52243, the position at which a mixture of an aromatic alkyl and a solvent is supplied to a reaction vessel is defined. By reducing the burning loss of acetic acid as a solvent by defining the water concentration of the acetic acid.

In Japanese Patent Application Laid-Open No. 59-190946, a bromine compound, which is a kind of catalyst, is supplied to a raw material supply pipe and a vicinity of a pipe for extracting a slurry obtained by the reaction to reduce coloring and unreacted impurities. It is introduced that the product can be obtained.

In Japanese Patent Application Laid-Open No. 2-9839, the position and number of the oxidizing gas supply nozzles, the type and position of the stirrer and the baffle are specified, the engineering quality of the aromatic carboxylic acid produced, and the burning loss of acetic acid. And improving the reaction yield.

[0007]

Most of aromatic carboxylic acids such as terephthalic acid are crystallized in an oxidation reactor. Here, the efficiency of the oxidation reaction is improved and 4
By reducing impurities such as -CBA, p-toluic acid, etc., the load on the subsequent purification step is reduced, which is economically beneficial.

[0008] In the oxidation reaction tank, the cause of the generation of impurities is a local lack of oxygen in the reaction tank. In order to prevent this, the bubbles are finely crushed so that the air becomes uniform in the tank. Need to be dispersed.

Next, it is necessary to disperse not only bubbles but also raw materials such as xylene to be oxidized, a catalyst, a solvent, and the like in the tank so that the oxidation reaction proceeds smoothly.

Means for improving the efficiency of the oxidation reaction include:
Although there are many types, burning loss of acetic acid increases, energy intensity deteriorates, and economical effects are adversely affected. A means is desired to improve the efficiency of the reaction without adversely affecting economics.

[0011]

In view of the above problems, in the present invention, the oxidation reaction is improved by increasing the diameter of the lowermost stirring blade of the oxidation reaction tank to be larger than the diameter of the other stirring blades. Achieved without increasing burning loss and applying excessive stirring power. In addition, the effect is further enhanced by dividing and supplying air or high-concentration oxygen, an oxide such as xylene, a catalyst and a solvent in the longitudinal direction of the reaction tank.

In an oxidation reactor for producing an aromatic carboxylic acid, particularly terephthalic acid, it is necessary to uniformly disperse the raw material, catalyst, solvent, bubbles, and crystals obtained in the reactor, thereby increasing the reaction efficiency. It is important to increase and reduce the generation of impurities.

The amount of air or high-concentration oxygen supplied to the above oxidation reaction tank is 3 to 10 c in terms of a superficial linear velocity.
m / s, which is extremely large as compared with aeration reactors in other processes. If the ventilation rate is so large, air cannot be crushed by means such as a perforated nozzle or sparger,
Since the bubbles do not disperse, the bubbles are generally broken by stirring.
In order to effectively crush the air, it is necessary to select a flat-type stirring blade having a strong shearing force. Among them, the disk turbine type stirring blade is considered to be the most suitable stirring blade for use in the aeration reaction tank because air bubbles can be prevented from bleeding because the air bubbles stay in the disk portion.

Normally, all or most of the air or high-concentration oxygen supplied to the oxidation reaction tank is supplied from the lower part of the lowermost stirring blade. In order to increase the gas-liquid contact time (residence time of bubbles in the liquid phase), the position is most appropriate. In order to uniformly disperse the bubbles in the liquid phase, it is effective to finely crush the bubbles immediately after the supply of air. In order to break the bubbles, it is necessary to apply a large stirring power to that point, that is, the lowermost stirring blade. The power of the stirrer is determined by the rotation speed and the diameter of the stirring blade. Therefore, by increasing the diameter of the stirring blade only in the lowermost stage, it is possible to improve the crushing of bubbles and, as a result, the reaction efficiency. The diameter of the lowermost impeller is larger than the diameter of the other impellers.
By increasing the ratio by 1.1 to 1.5 times, preferably 1.15 to 1.3 times, the amount of impurities can be reduced without increasing the stirring power and increasing the burning loss of the solvent. An aromatic carboxylic acid can be obtained.

According to the present invention, as compared with the conventional method, the average bubble diameter of the bubbles present in the reaction tank becomes smaller, and the area of the gas-liquid contact interface increases. As a result, oxygen is effectively absorbed into the liquid phase, improving the efficiency of the reaction.

There is also a means for increasing the number of revolutions of only the lowermost agitating blade, but it is not practical because equipment manufacture becomes difficult and equipment manufacture cost increases.

In order to uniformly disperse a liquid phase component such as a raw material, a catalyst, and a solvent, which are aromatic alkyls, in a tank, a plurality of liquid supply nozzles are provided in a vertical direction of the reaction tank.
Dispersion and mixing of the liquid phase in the tank are improved, and the efficiency of the reaction is also increased.

It has been found that the efficiency of the reaction is further improved by dividing the input amount of air according to the ratio of the required power of each stirring blade.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail with reference to the following examples.
The present invention is not limited to the following embodiments.

FIG. 1 shows an outline of an oxidation reaction tank 10 for producing an aromatic carboxylic acid by oxidizing an aromatic alkyl. The oxidation reaction tank 10 is provided with a stirrer 1, and a plurality of stirring blades 11, 12, and 13 are attached. In the oxidation reaction tank 10, nozzles 2, 6, 7 for supplying air, nozzles 3 for supplying a mixture of aromatic alkyl, solvent and catalyst,
4. A nozzle 5 for extracting the slurry is provided on the side surface of the tank, and a nozzle 8 for extracting the vapor of the solvent generated by the reaction heat and the unreacted gas, and cooling the generated vapor to return the condensed solvent into the reaction tank. A nozzle 9 is provided at the top of the reaction tank tower.

The oxidation reactor 10 is kept at a temperature and pressure sufficient to maintain the solvent and aromatic alkyl in a substantially liquid state.

The stirrer 1 has three stages of stirring blades 11, 12,
13 are attached.

Example 1: The diameter (d / d) of the lowermost stirring blade 11
D = 0.4) is 1.2 times the diameter (d / D = 0.33) of the other stirring blades, and the mixture of para-xylene, solvent and catalyst is supplied to nozzles 3 and 4 (supply ratio 1: 1). From the nozzle 2,
6, 7 (supply ratio 8: 1: 1). Table 1 shows the ratio of the amount of unreacted para-xylene to the amount of impurity contained in terephthalic acid and the amount of para-xylene (PX) supplied at that time.

Here, d / D indicates the ratio of the diameter of the stirring blade to the diameter of the tank.

Comparative Example 1: The diameter of the lowermost stirring blade was set to (d / D
= 0.33). The supply amounts of the mixture of para-xylene, the solvent, the catalyst and the air were the same as in Example 1.

Examples 2 and 3: In comparison with Example 1, in Example 2, the mixture of paraxylene, solvent and catalyst was supplied only to the nozzle 3. In the third embodiment, the supply of air is
And only. The supply amounts of the mixture of para-xylene, the solvent, the catalyst and the air were the same as in Example 1.

Table 1 shows the main operating conditions and the ratio of the content of impurities such as 4-CBA in the obtained terephthalic acid to the unreacted para-xylene in each of Examples and Comparative Examples.

[0028]

[Table 1]

[0029]

According to the present invention, a high-quality aromatic carboxylic acid can be produced without deteriorating economic efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of an oxidation tank according to the present invention.

[Explanation of Signs] 1 ... Stirrer for oxidation reaction tank, 2, 6, 7 ... Air supply nozzle,
3, 4 ... material supply nozzle, 8 ... vapor discharge nozzle, 9 ... condensate reflux nozzle, 10 ... oxidation reaction tank, 11, 12, 13
... stirring blades.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenichiro Nishijima 4-13-17 Nakagawa, Adachi-ku, Tokyo Inside Hitachi Techno Engineering Co., Ltd. (72) Inventor Katsushio Tamahashi 4-6-chome, Kanda Surugadai, Chiyoda-ku, Tokyo Address: Inside Hitachi, Ltd.

Claims (5)

[Claims] An oxidation reaction tank provided with a plurality of stages of disk turbine type impellers, wherein the diameter of the lowest stage impeller is set to be 1.1 to 1.5 times the diameter of the other stage impellers. A method for producing an aromatic carboxylic acid, wherein a raw material is charged and an oxidation step is performed by rotating the impellers in the plurality of stages. 2. The method for producing an aromatic carboxylic acid according to claim 1, wherein the air or high-concentration oxygen supplied to the oxidation reaction tank is divided and supplied in the vertical direction of the oxidation reaction tank. 3. The method for producing an aromatic carboxylic acid according to claim 1, wherein the raw material, the catalyst and the solvent to be supplied to the oxidation reaction tank are divided and supplied in the vertical direction of the oxidation reaction tank. 4. The method according to claim 1, wherein the aromatic carboxylic acid is terephthalic acid. 5. A disk turbine type impeller is provided in a plurality of stages, and the diameter of the lowest stage impeller is set to be 1.1 to 1.5 times the diameter of the other stage impeller. Oxidation reaction tank.