JPH066551B2 - Method for purifying and separating methacrylic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention removes high boiling impurities from an aqueous solution of methacrylic acid obtained by cooling a reaction product gas containing methacrylic acid obtained by catalytic gas phase oxidation of isobutylene, tert-butanol, or isobutylene. The present invention relates to a method for industrially efficiently obtaining methacrylic acid that does not contain methacrylic acid.

From a methacrylic acid-containing aqueous solution obtained by cooling a reaction product gas containing methacrylic acid obtained by gas phase oxidation of isobutylene, tert-butanol or methacrolein (hereinafter referred to as C ₄ compound) with a catalyst in a cooling tower. Methacrylic acid is characterized by separating the methacrylic acid from the treatment liquid after treating the obtained extraction liquid with an aqueous alkali solution or a mixed aqueous solution of alkali and hydrazine by an extraction operation. The present invention relates to a purification separation method.

In the process for producing methacrylic acid by vapor phase oxidation of the above C ₄ compound, the gas generated in the reaction is cooled and collected as an aqueous solution, and methacrylic acid is extracted from this aqueous solution using an organic solvent that is not freely miscible with water. In general, the method is used for the subsequent purification step.

Although the method of producing methacrylic acid by vapor-phase oxidation of a C ₄ compound has reached the stage of industrialization, problems still remain in the production process thereof. One of the problems is that many by-product impurities other than methacrylic acid are present in the reaction product. For example, the presence of acetaldehyde, acetone, acrolein, methacrolein, acetic acid, acrylic acid, maleic acid, citraconic acid, aromatic carboxylic acid, etc. is recognized.

Among these impurities, light boiling components such as acetaldehyde, acetone, acrolein, methacrolein, acetic acid,
Acrylic acid, etc. can be relatively easily removed by ordinary distillation operation, but maleic acid and citraconic acid partly move to the extraction phase during extraction, making it difficult to separate from methacrylic acid in the subsequent purification process. Becomes

Further, some of the high-boiling impurities cause problems such as accelerating the polymerization of methacrylic acid in the methacrylic acid refining process.

Many of these problems are peculiar to the process for producing methacrylic acid by the C ₄ oxidation method, and various proposals have been made to solve them.

For example, JP-A-58-52239 proposes a method of selectively collecting only high-boiling-point impurities before condensing a reaction product gas, and JP-A-58-99434 discloses a method in which a basic substance is contained in a condensate. A method of adding and subjecting to an extraction operation has been proposed.

However, none of these methods can be said to be necessarily satisfactory because of high cost or insufficient results.

As a result of various investigations for solving these problems, the present inventors have treated the methacrylic acid extract with an alkaline substance,
The present invention has been completed by finding a method for solving the above problems by removing impurities having a high boiling point which cause troubles in mclayic acid and other distillation steps.

The details of the method of the present invention are as follows.

The reaction product gas obtained by the oxidation reaction of isobutylene, tert-butanol, or methacrolein is cooled in a quench tower to obtain a methacrylic acid-containing aqueous solution. This aqueous solution of methacrylic acid is usually first subjected to an operation of removing light-boiling components, and then subjected to an extraction operation with a solvent such as esters and aromatics.

In the extract obtained here, in addition to the target methacrylic acid, acetic acid, acrylic acid, low-boiling components such as pyropionic acid and maleic acid, citraconic acid, aromatic carboxylic acids and other high-boiling components Contains.

The present inventors added an alkaline aqueous solution or a mixed aqueous solution of alkali and hydrazine as an alkaline substance to this extract to precipitate the maleic acid and other high-boiling components, and extract the precipitate after separation. By introducing the liquid to the subsequent distillation step to purify methacrylic acid, maleic acid and citraconic acid can be effectively removed, and even in the methacrylic acid purification step, polymerization of methacrylic acid that has conventionally occurred during distillation I found that the troubles were drastically reduced.

This is because the addition of an aqueous alkaline solution causes acids having a higher acidity than methacrylic acid to selectively form salts and other high-boiling components to undergo some modification, and at the same time, a high-boiling aldehyde which is considered to be the main cause of polymerization trouble. Is presumed to have reacted with hydrazine.

Examples of the alkaline substance described here include hydroxides, carbonates and bicarbonates of alkali metals such as sodium and potassium, alkaline earth metals such as calcium and magnesium, and sodium hydroxide is particularly preferable. These are preferably used as an aqueous solution of 10 to 50% by weight.

On the other hand, for hydrazine,
It is preferable to use it as an aqueous solution of wt% or as a mixture with an alkaline aqueous solution.

The amount of alkali added to the methacrylic acid extract is 0.5 to 2.0 times, preferably 1.0 to 1.5 times the mol of maleic acid contained in the extract.

Regarding hydrazine, it is suitable to add 0 to 1.0 times mol, preferably 0.2 to 0.5 times mol of maleic acid contained in the extract.

If the addition amount is too large, methacrylic acid is neutralized more than necessary, resulting in a loss, and if it is too small, the removal effect of maleic acid decreases, and at the same time, the occurrence of methacrylic acid polymerization trouble in the refining process cannot be sufficiently prevented. become.

The precipitate (slurry substance) produced by adding the above-mentioned alkaline substance to the extract is discharged out of the system by a usual separation method such as a static tank or a centrifuge.

Next, one specific example of the present invention will be described with reference to FIG.

The reaction product gas obtained by the catalytic gas phase oxidation reaction of isobutylene is cooled to obtain an aqueous methacrylic acid solution, and subsequently, low boiling point components contained in this aqueous solution are removed, and then line 1 in FIG. 1 is used. Then, the solution is fed to the methacrylic acid extraction tower 101. Here, the extraction agent is fed from the line 8 to extract methacrylic acid. The extract is fed into the mixer 102 through the line 2 and is contacted with the alkaline aqueous solution or the mixed aqueous solution of alkali and hydrazine fed from the line 4 to neutralize maleic acid and citraconic acid, and at the same time, High boiling components undergo denaturation. On the other hand, the raffinate remaining after the extraction of methacrylic acid is removed from the system through line 3.

The mixed solution containing the precipitate is passed through the line 5 to the stationary tank 103.
The solid precipitate is separated. The slurry of the separated solid precipitate is discharged from the line 7.

On the other hand, the clarified liquid is fed to the light-boiling separation column 104 through the line 6 to separate the solvent and the light-boiling components, which is the line 8
After being supplied to the extraction tower, it is used again. From the bottom of the column 104, crude methacrylic acid from which light boiling components have been removed is taken out through a line 9.

The present invention will be described below with reference to examples.

Example 1 Obtained by carrying out an oxidation reaction of isobutylene and methacrolein using a Bi-Mo-based multi-component catalyst as the first-stage oxidation catalyst and a Mo-based heteropolyacid-based catalyst as the second-stage catalyst. The reaction product gas is cooled and condensed to obtain a methacrylic acid aqueous solution,
Further, light boiling components such as methacrolein in this liquid were removed, and methacrylic acid was extracted from the obtained liquid using isopropyl acetate as an extractant to obtain an extract. This extract is
Methacrylic acid 26% by weight, acetic acid 3% by weight, water 8% by weight,
The composition was 0.6% by weight of maleic acid, 0.1% by weight of citraconic acid, a small amount of high-boiling components, and the balance being isopropyl acetate.

100 kg of this extract was mixed with 0.8 kg of a 30% by weight aqueous sodium hydroxide solution, and the mixture was stirred at room temperature for about 20 minutes. In this case, the amount of sodium hydroxide was 1.2 mol times that of maleic acid in the extract.

After stirring, the white solid substance suspended in this liquid was separated with a filter.

The liquid composition thus obtained had a methacrylic acid content of 26% by weight,
Acetic acid 3% by weight, water 7.5% by weight, maleic acid 0.03% by weight,
The content of citraconic acid was 0.08% by weight, a small amount of high-boiling components, and the balance was isopropyl acetate. In this case, the maleic acid removal rate was 95%, which was a sufficiently satisfactory result.

Further, the obtained liquid was supplied to a light boiling separation column and continuously operated for a long time, but it was found that the fouling due to the adhesion of the polymer to the heat transfer section at the bottom of the column was significantly reduced and the operation could be endured for a long time. .

Example 2 To 100 kg of the same extract as in Example 1, 0.8 kg of 30% by weight aqueous sodium hydroxide solution and 0.16 kg of 80% by weight aqueous hydrazine solution were added and stirred at room temperature for about 20 minutes.

In this case, the amount of sodium hydroxide and the amount of water-hydrazine contained in the extract were 1.2 mol and 0.5 mol, respectively. The composition of the treatment liquid thus obtained was substantially the same as in Example 1.

Further, the obtained liquid was supplied to a light-boiling separation column and continuously operated for a long period of time, but the fouling due to the adhesion of the polymer to the heat transfer section at the bottom of the column was reduced as compared with Example 1. It was observed that it was found that there was an effect of adding hydrazine.

Comparative Example 1 An extract having the same composition as in Example 1 was supplied to a light boiling separation column without adding an alkali to carry out continuous operation. 15
It was judged that it was not possible to continue the operation as it was because the stains due to the adhesion of the polymer to the heat transfer section at the bottom of the column after the time operation were severe.

Comparative Example 2 A liquid obtained by removing light-boiling components such as methacrolein in Example 1 (33% methacrylic acid, 5% acetic acid, 58% water).
%, Maleic acid 1%, citraconic acid 0.5%) sodium hydroxide to the total of maleic acid and citraconic acid 1.
After adding 2 mol times, extraction was performed in the same manner as in Example 1. The composition of the extract was methacrylic acid 26%, acetic acid 3%, water 8%, maleic acid 0.1%, citraconic acid 0.1%, a trace amount of high-boiling components, and the balance being isopropyl acetate.

Thus, when alkali is added before the extraction step, the removal rate of maleic acid, citraconic acid and the like decreases, and the amount of alkali used is also required to be double or more.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of an embodiment of the present invention. 101 ... Methacrylic acid extraction tower 102 ... Mixer 103 ... Stationary tank 104 ... Light boiling separation tower

Claims (1)

[Claims] 1. An extraction operation from a methacrylic acid-containing aqueous solution obtained by cooling a reaction product gas containing methacrylic acid obtained by gas phase oxidation of isobutylene, tert-butanol or methacrolein with a catalyst in a cooling tower. A methacrylic acid extract is obtained by treating the obtained extract with an aqueous alkali solution or an aqueous mixed solution of alkali and hydrazine, and then methacrylic acid is separated from the treated solution. Separation method.