JPS5912096B2 - Polycarbonate polycarbonate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing aromatic polycarboxylic acids.

Conventionally, an aromatic compound having at least two aliphatic substituents is oxidized in a lower aliphatic monocarboxylic acid solvent by blowing an oxygen-containing gas into the liquid phase in the presence of a catalyst containing a heavy metal to produce an aromatic polycarboxylic acid. Methods of manufacturing are known.

One of the problems when this method is carried out industrially is crystal deposition and partial blockage of the produced polycarboxylic acid 5 in the oxygen-containing gas injection section.

This phenomenon is particularly problematic when a bubble column is used as the reactor. In other words, in a bubble column, in order to uniformly blow gas into the vessel, the blowing section has a shape 10 with a large number of small holes (usually about 1 to 5% in diameter), for example, about 30 to 100. There is a tendency for aromatic polycarboxylic acid crystals to adhere near the area, resulting in some small pores being blocked. When this crystal adhesion and blockage occur, the pressure of oxygen-containing gas blowing increases, gas dispersion becomes uneven, and the reaction is adversely affected, and if the crystal adhesion is significant, many As a result, all of the air inlet ports become clogged, making it impossible to inject the oxygen-containing gas. This tendency is particularly noticeable at the beginning of continuous reactions, making it difficult to get a good start and posing a major industrial problem. 20 Possible methods to improve these drawbacks include, for example, blowing preheated air to prevent crystal adhesion, but even this method can prevent significant crystal adhesion at the start. A fully satisfactory result could not be obtained.

Therefore, there has been a need for a method for stably supplying 25 oxygen-containing gas at a constant pressure. In view of the above circumstances, the present inventors conducted various studies on a method 30 for stably blowing oxygen-containing gas over a long period of time when aromatic polycarboxylic acids are continuously produced in a bubble column. The inventors discovered that a good supply of oxygen-containing gas could be achieved by blowing a small amount of alkali into the charged gas, and completed the present invention.

That is, the gist of the present invention is to prepare an aromatic compound having at least two 35 aliphatic substituents in a solvent of a lower aliphatic monocarboxylic acid in the presence of a catalyst containing a heavy metal, and blow an oxygen-containing gas into the liquid phase. A method for continuously producing an aromatic polycarboxylic acid by converting an acid into a 0-carboxylic acid, characterized by blowing an alkaline aqueous solution of sodium hydroxide or potassium hydroxide into an oxygen-containing gas. It consists in a method for producing aromatic polycarboxylic acids.

To explain the present invention in detail, the method for producing aromatic polycarboxylic acids, which is the object of the present invention, involves adding an aromatic compound having at least two substituents to a lower aliphatic monocarboxylic acid using a catalyst containing heavy metals. Any method may be used as long as it produces an aromatic polycarboxylic acid by blowing an oxygen-containing gas into a liquid phase in the presence of.

Representative examples of the aromatic compound having at least two substituents include para-xylene, meta-xylene, and reaction intermediates thereof.

On the other hand, examples of lower aliphatic monocarboxylic acids used as solvents include acetic acid, propionic acid, etc.
Among them, acetic acid is preferred. The amount of this solvent used is typically
It is selected from 0.5 to 20 parts by weight, preferably 1 to 10 parts by weight, per 1 part by weight of the oxidizable material. Furthermore, examples of the catalyst include well-known heavy metal catalysts such as cobalt and manganese.

The amount of catalyst added is usually about 0.01 to 10% by weight based on the solvent. Furthermore, in the present invention, organic accelerators such as bromine compounds or aldehydes, ketones, alcohols, paraldehydes, etc. may be added as necessary. The reaction is usually carried out at 100 to 250°C and normal pressure to 200 atm, preferably normal pressure to 100 atm. In the present invention, the aromatic compound as described above is oxidized by blowing an oxygen-containing gas into the liquid phase of a reactor, such as a bubble column, in the presence of a solvent and a catalyst. For example, 5~
With an oxygen content of 100% by volume, air is usually used.

The total amount of oxygen supplied into the reactor is 1 mole of oxidized material.
-100 mol, preferably 3-100 mol. Further, when blowing gas into the reactor, it is particularly preferable to heat the oxygen-containing gas in advance to a temperature similar to or slightly higher than the reaction temperature before blowing into the reactor. The oxygen-containing gas is normally blown in at a pressure 1 to 10 kg/i higher than the reaction pressure.

The present invention prevents the deposition of crystals near the oxygen-containing gas injection port or the clogging of small holes by blowing an alkali into the gas.

Alkali may be added regularly for a certain period of time, but usually it is added as an aqueous solution into the injection pipe when the injection pressure increases due to blockage of the injection port, for example, when it increases by about 3 to 50%. Bye. When alkali is added into the gas injection pipe, it is entrained in the gas and acts on the injection port.
The crystals adhering to each inlet are dissolved and the inlets are opened. Examples of the alkali include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, etc., and sodium hydroxide is particularly preferred.

Further, even if they are alkaline and have the effect of preventing crystal adhesion, nitrogen-containing compounds such as aliphatic amines have an adverse effect on the product and should be avoided.

These alkalis are usually added as a 1 to 30% by weight aqueous solution.

The amount of alkaline aqueous solution added at one time is the amount necessary to lower the increased blowing pressure of the oxygen-containing gas to around the predetermined pressure set at the beginning, and it is preferably as small as possible, depending on the reaction conditions and Although it varies somewhat depending on the reaction form, for example, in the case of a reaction tank of about 20 mm, an alkali of the above-mentioned type and concentration of about 1 to 30 mm is usually sufficient.

This addition is normally done in response to an increase in the pressure of the oxygen-containing gas being blown into the gas, but the method for this response is to use an electric circuit to increase the pressure to a certain level and then use a valve to control the addition of the alkaline aqueous solution. Alternatively, it may be added manually by reading a pressure gauge.

Next, the present invention will be specifically explained with reference to the drawings.

As shown in FIG. 1, for example, a liquid in which paraxylene and a cobalt catalyst are dispersed in an acetic acid solvent is continuously supplied into a bubble column 1 through a conduit 3, and compressed from the bottom of the bubble column 1 by a compressor 4. The air passes through the conduit 9 and enters the air inlet 2.
will be introduced. A pressure gauge 5 is provided in the air conduit 9, and as the pressure rises, a valve 7 opens and the alkaline aqueous liquid introduced from the 6 is blown in together with the air. Immediately after the addition of the alkaline aqueous solution, the valve 7 is closed and a certain amount of the alkaline aqueous solution is set in the valve 6 again. The reaction continues in this manner, and the reaction product is taken out of the system through the conduit 10 and stored in the tank 8. As described above, according to the present invention, aromatic polycarboxylic acids such as terephthalic acid can be continuously produced in a bubble column using a very simple method, which is extremely advantageous industrially. Next, the present invention will be explained in more detail with reference to Examples.

In the examples, "parts" indicate "parts by weight."

Example 100 parts of paraxylene, 95% acetic acid (5% water) 3 were placed in a titanium pressure-resistant reactor 1 with an internal volume of 23 m3, which had an air inlet in the bottom of the tank with 80 holes with a diameter of 8' arranged as shown in Figure 2.
00 parts, 0.14 parts of cobalt acetate tetrahydrate as an oxidation catalyst, 0.29 parts of manganese acetate tetrahydrate, and 0.0 parts of sodium bromide.
6000 kg of a mixed solution of raw materials, solvent, and catalyst containing 13 parts was charged through tube 3 at a pressure of 24 kg/c? - After heating to 210°C with G, start supplying air heated to 230°C from tube 9 and gradually increase the air supply amount to 7500Nm3/Hr.

When the oxidation reaction of the charged paraxylene is completed, the raw material mixture is supplied from the tube 3 at 8400 kg/Hr, and when the liquid volume in the reaction tank reaches a predetermined amount, the reaction liquid slurry is started to be withdrawn from the tube 10. The amount of liquid in the reaction tank was kept constant and continuous reactions were carried out. In the reaction, air is supplied so as to keep the flow rate constant using the flow rate control valve 11. When the air blowing pressure gauge 5 reaches 28k9/Crii-G, the valve 7 opens and the 5% water of 2.51 is supplied. The sodium oxide aqueous solution is instantly blown into the air, and the valve 7 is immediately closed again.
A device in which 5% aqueous sodium hydroxide solution was set at 1:6 was attached to the air blowing pipe. The pressure in the air blowing tube was 26.5 kg/Cd-G when the air supply amount was increased to 7500 Nm3/Hr after the start of the reaction, but it rose to 27.5 kg/Cd-G at the end of the batch reaction, and continued to increase in the continuous reaction. Approximately 30 minutes after switching to , it rose to 28k9/G. At this point, the flow rate control valve is fully open and the air flow rate is 750.
It started to drop from 0Nm3/Hr, but the alkali feeder was activated and the pressure in the air blowing pipe was 26.8kg/Cd.
It descended instantly to -G. After that, the pressure increases again and about 1
After 0 minutes, the alkali feed device is activated and the pressure is 26.8k9/
After that, the alkali feeding device was operated twice in about 30 minutes. Thereafter, this operation was repeated to allow the reaction to proceed for two weeks, and the reaction progressed smoothly.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of an example of carrying out the method of the present invention, where 1 indicates a bubble column and 2 indicates a blowing section.

Claims (1)

[Claims] 1 An aromatic compound having at least two aliphatic substituents is oxidized in a lower aliphatic monocarboxylic acid solvent in the presence of a catalyst containing a heavy metal by blowing an oxygen-containing gas into the liquid phase to produce an aromatic polycarbonate. 1. A method for continuously producing an aromatic polycarboxylic acid, which comprises blowing an alkaline aqueous solution of sodium hydroxide or potassium hydroxide into the oxygen-containing gas.