JPS595569B2 - Continuous production method of terephthalic acid - Google Patents

Description

[Detailed description of the invention] The present invention relates to a continuous process for producing terephthalic acid.

Terephthalic acid is used as a raw material for polyester fibers by oxidizing paraxylene with molecular oxygen such as air in a lower aliphatic carboxylic acid solvent such as acetic acid using a heavy metal catalyst such as cobalt or manganese and a reaction promoter such as bromine. It is produced industrially on a large scale. In the method of producing terephthalic acid by liquid-phase oxidation of paraxylene, the raw material paraxylene, a solvent, and a catalyst are all charged into a reactor before the reaction, an oxygen-containing gas is introduced, and the reaction product is released after the reaction is completed. Batch type for taking out, semi-continuous type for continuously introducing raw material para-xylene and oxygen-containing gas into a reactor charged with solvent and catalyst and taking out the reaction product after the reaction is completed, and same as raw material para-xylene and oxygen-containing gas. There is a continuous method in which a mixed solution of solvent and catalyst is continuously introduced and the reaction product is continuously extracted from the bottom of the reactor. Continuous systems are superior in terms of ease of management and are generally used in industrial plants, and the present invention also relates to a liquid phase oxidation method using continuous systems.

A reactor for producing terephthalic acid generally consists of a cylindrical straight body and a hemispherical or conical top and bottom attached above and below the body. To ensure uniform dispersion of contained gas, etc.
A stirrer is provided inside the reactor, and a continuous baffle is attached from the straight body of the reactor to the bottom. When producing terephthalic acid by oxidizing paraxylene in a lower aliphatic carboxylic acid, the resulting terephthalic acid has extremely low solubility in the lower aliphatic carboxylic acid, and terephthalic acid exists as crystals, so the reaction system becomes a slurry containing terephthalic acid crystals.

Furthermore, since the specific gravity of terephthalic acid crystals is higher than that of the lower aliphatic carboxylic acid solvent, even if the mixture is stirred using a stirrer, the terephthalic acid crystals will settle to the bottom of the reactor. Alternatively, since the raw material mixture containing paraxylene is supplied into the reactor, the temperature near the inlet drops, and the terephthalic acid that has been dissolved in the carboxylic acid gradually precipitates near the inlet. In particular, when there is a buttful, a vortex is generated on the back of the buttful, and terephthalic acid crystals tend to accumulate there, and this phenomenon is particularly noticeable on the back of the buttful attached to the bottom, causing the accumulated terephthalic acid crystal chunks to fall. Eventually, the reaction product outlet is blocked, resulting in the need to stop the reaction and clean the reactor after a relatively short period of operation. Therefore, the main object of the present invention is to provide a continuous production method for terephthalic acid which prevents and suppresses the adhesion and deposition of terephthalic acid crystals in a reactor, thereby allowing continuous operation over a long period of time. That is, the present invention uses a reactor equipped with a butthole only in the straight body of the invention to continuously produce terephthalic acid by liquid-phase oxidation of paraxylene with an oxygen-containing gas in a lower aliphatic carboxylic acid solvent. By carrying out the reaction, the adhesion and accumulation of terephthalic acid crystals is reduced, and by cutting out the baffle at a height corresponding to the position of the para-xylene-containing liquid filling port, It has been discovered that the effect can be further enhanced by making a notch at a height corresponding to the position of the stirring blade closest to the charging port.

Next, the present invention will be explained in detail with reference to drawings showing a reactor in which the present invention can be carried out.

1 and 5 are general views of the apparatus before carrying out the method of the invention. Fig. 2 shows a device having the conditions set forth in claim 1 of the present invention, Fig. 3 shows a device having the conditions set forth in claim 2 of the present invention, and Fig. 4 shows the patent of the present invention. It is an example of the apparatus diagram each equipped with the conditions of Claim 3. In the figure, 1 is a stirrer, 2 is a buffer, 3 is a charging tube for the raw material paraxylene, solvent and catalyst, 4 is a supply tube for oxygen-containing gas, 5 is a reaction liquid extraction tube, 6 is a stirring blade, 7 8 is a gas outlet, 8 is a heat exchanger, 9 is a condenser, 10 is a waste gas outlet, 11 is a reflux liquid return pipe, 12 is a liquid level, and 13 is a liquid level gauge. The reaction method is to fill a reactor with a specified catalyst and solvent, heat and pressurize it, and then turn the stirrer to mix the reaction liquid while introducing an oxygen-containing gas into the reaction liquid, and mix the raw materials para-xylene, Charge the catalyst and solvent into the reactor. The exhaust gas is cooled in a heat exchanger to separate gas and liquid, the waste gas is discharged from the waste gas outlet, and the reflux liquid and reaction liquid are returned to the reactor. The reaction product is sent to the next crystallization tank from the reactant extraction port while adjusting the liquid level height with a liquid level gauge. Among the stirring blades provided in the reactor used in the present invention, the lowest stirring blade is preferably located at the bottom of the reactor.

Further, the baffle used in the present invention is preferably attached perpendicularly to the inner wall of the reactor and to the reaction liquid level. The number of buffles is preferably 4 to 8, and the width of the buffles is preferably D/8 to D/15 (D is the inner diameter of the reactor). In addition, the straight body of the reactor as used in the present invention refers to the part of the reactor excluding the top and bottom, where the inner wall is perpendicular to the reaction liquid level, and the bottom part which is not perpendicular to the reaction liquid level. According to the present invention, there is no cross-full added to the .
Generally, it is common sense that a buttful is installed to prevent the liquid from co-rotating due to stirring and to increase the stirring effect, but in the present invention, it is installed at the bottom to give co-rotation to the bottom and prevent terephthalic acid from accumulating. The lower hemisphere is omitted. Furthermore, by providing a notch at a height corresponding to the position of the para-xylene-containing liquid filling port, Batsuful also has a notch at a height corresponding to the position of the stirring blade closest to the para-xylene-containing liquid filling port. By providing a notch in the section, the fed paraxylene is immediately dispersed all around the circumference by the strong centrifugal force of the stirring blades as soon as it exits the charging port. 2 pieces, 4 pieces, 6 pieces, 8 pieces...
・It is common to make a notch in the symmetrical position, and it is possible to make a notch in all the parts or at the = part, but if you make a notch in all the parts, the co-rotation will be too strong and the effect of Batsuful will be reduced. Therefore, it is preferable to set the number to about half, such as 2 out of 4 or 3 out of 6. In particular, it is very effective to cut out the butthole closest to the paraxylene-containing liquid filling port. Furthermore, the length of the notch is preferably about the same width as the stirring blade, since if it is too long, the co-rotation will be too strong and the buffling effect will be diminished. The width of the cutout, that is, the depth of the cutout, needs to be wide enough to suppress adhesion and precipitation of terephthalic acid, but it is preferable to cut out the entire cutout. However, since the shape and rotation speed of the reactor have an influence, it is not limited to the above. When producing terephthalic acid, the stirrer of the reactor is generally used to have three stages of stirring blades, and in the case of the present invention, the para-xylene-containing liquid inlet is preferably provided near the middle stage stirring blade. It is preferable to cut out a buttful at the height of the middle stirring blade. Although the present invention is applicable to any process for producing terephthalic acid by liquid phase oxidation of paraxylene, preferred reaction conditions are as follows.

The reaction is carried out at a temperature range of 80-250°C.

Furthermore, since the reaction is carried out in a liquid phase, it is necessary to apply pressure to keep the raw materials and solvent in a liquid phase at the reaction temperature. Lower aliphatic carboxylic acids such as acetic acid, propionic acid, and butyric acid are used as the solvent, but acetic acid is preferred, and it is sufficient if the solvent is at least twice the weight of the raw material paraxylene. Heavy metal salts such as cobalt and manganese and bromine compounds are used as catalysts. The heavy metal compounds such as cobalt and manganese are preferably those soluble in the reaction solvent such as inorganic salts, naphthenates, and lower fatty acid salts, and the bromine compounds are preferably ammonium salts, sodium salts or potassium salts, or hydrogen bromide. It is also possible to use other promoters such as ketones and aldehydes. The raw material para-xylene charged from the para-xylene-containing liquid charging port may have a solvent diluted with a lower aliphatic carboxylic acid, and may further contain a catalyst. The oxygen-containing gas used as the oxidizing agent may contain an inert gas such as nitrogen, and it is particularly economical and advantageous to use air. The amount of oxygen introduced is 3.5 to 5.0 moles per mole of paraxylene. As mentioned above, we succeeded in significantly extending the continuous operation period in the continuous production method of terephthalic acid by simple improvement of the reactor buffer, which simplifies operation, saves operating personnel, and makes the product terephthalic acid uniform. We were able to achieve extremely advantageous improvements in industrial production, such as an increase in production volume due to increased operating rates, a reduction in wastewater that needs to be treated, and a reduction in fluctuations in the utility sector.

The present invention will be explained below with reference to Examples.

Example 1 A pressure-resistant reactor with a titanium lining arranged as shown in Fig. 2 (inner volume 13 m3, inner diameter 1.8 m, stirring blade diameter 0.9 m,
4.0 tons of acetic acid, 6.0 kg of cobalt acetate/tetrahydrate, 4.0 kg of manganese acetate/tetrahydrate, and 5.2 k of sodium bromide.
g and pressure 211<g/Cr! IG, temperature 21
The temperature was maintained at 0°C, and a mixed solution of paraxylene, acetic acid, cobalt acetate, manganese acetate, and sodium bromide (the ratio of acetic acid and catalyst was the same as the initial charging solution) was added at 5.0 tons/Hr (of which,
Para-xylene is fed at a rate of 1.0 tons/Hr) while air is fed at a rate of 4.2 Nm3/Kg of para-xylene to react continuously, and the liquid level is maintained at a constant level based on the indication from the liquid level gauge ( liquid level height 4.0 m) and sent to the next crystallization tank.

As can be seen from Figure 2, the reactor used in this example does not have a buffle at the bottom, so the stirring power can be reduced compared to conventional equipment, and the reaction products are removed 50 days after the start of the reaction. The reaction was able to continue without any problems until the outlet was clogged with terephthalic acid crystals and the reaction was stopped. Comparative Example 1 Terephthalic acid was produced under the same conditions as in Example 1 using the reactor shown in FIG. 1, which was also provided with a buffle at the bottom of the reactor.

Compared to the case of Example 1, the stirring power increased by about 10%,
Moreover, on the 14th day after the start of the reaction, the reaction product outlet was clogged with terephthalic acid crystals, and the reaction had to be stopped. Example 2 Terephthalic acid was produced under the same conditions as in Example 1 using the reactor shown in FIG.

The notched buttful is two of four sheets facing inward, and is cut out by the width of the stirring blades with the paraxylene-containing liquid inlet in the center. Compared to the case of Example 1, the stirring power was reduced by about 3%, and on the 73rd day after the start of the reaction, the reaction product outlet was clogged with terephthalic acid crystal lumps, causing no trouble until the reaction was stopped. I was able to continue reacting. Example 3 Terephthalic acid was produced under the same conditions as in Example 1 using the reactor shown in FIG.

The notched buttful is two of the four sheets facing inward, and is cut out by the width of the stirring blade. Example 1
Compared to the case of , the stirring power was reduced by about 3%, and on the 65th day after the start of the reaction, the reaction product outlet was clogged with terephthalic acid crystals, and the reaction continued without any hindrance until the reaction was stopped. I was able to do it. Comparative Example 2 Terephthalic acid was produced under the same conditions as in Example 1 using the reactor shown in FIG.

This reactor differs from the reactor shown in FIG. 2 only in that the baffle extends vertically to the bottom. The stirring power increased by about 8% compared to Example 1, and on the 24th day after the start of the reaction, the reaction product outlet was clogged with terephthalic acid crystal lumps, and the reaction had to be stopped.

[Brief explanation of drawings]

1 and 5 are general views of the apparatus before implementing the method of the present invention, and FIGS. 2, 3, and 4 are claims 1 and 2 of the present invention, This is an example of a diagram of a device provided with each of the conditions in Section 3.

Claims (1)

[Claims] 1. In order to continuously produce terephthalic acid by liquid-phase oxidation of paraxylene with an oxygen-containing gas in a lower aliphatic carboxylic acid solvent, a reactor equipped with a baffle only in the straight body part is used. A method for continuous production of terephthalic acid characterized by carrying out a reaction using terephthalic acid. 2 In continuously producing terephthalic acid by liquid-phase oxidation of paraxylene with an oxygen-containing gas in a lower aliphatic carboxylic acid solvent, a baffle is attached only to the straight body, and the paraxylene-containing liquid in the baffle is A method for continuous production of terephthalic acid, characterized in that the reaction is carried out using a reactor having a cutout at a height corresponding to the position of a charging port. 3 In order to continuously produce terephthalic acid by liquid-phase oxidation of paraxylene with an oxygen-containing gas in a lower aliphatic carboxylic acid solvent, a baffle is attached only to the straight body, and a paraxylene-containing liquid inlet is installed. A method for continuously producing terephthalic acid, characterized in that the reaction is carried out using a reactor in which a baffle is cut out at a height corresponding to the position of a stirring blade closest to the stirring blade.