JPS60178842A - Purification and separation of methacrylic acid - Google Patents

Abstract

PURPOSE:To produce purified methacrylic acid without trouble caused by maleic acid and high-boiling components in distillation step, in the vapor-phase oxidation of isobutylene, etc. to produce methacrylic acid, by treating the extract with an alkaline substance. CONSTITUTION:Isobutylene, tert-butanol or methacrolein is subjected to the vapor-phase catalytic oxidation, and the obtained reaction product gas containing methacrylic acid is cooled in a quenching tower to obtain an aqueous solution containing methacrylic acid. After removing the low-boiling components, the solution is extracted with a solvent such as esters, aromatic compounds, etc. The obtained extract is treated with an aqueous solution of an alkali or a mixed aqueous solution of alkali and hydrazine to precipitate and remove maleic acid and high-boiling components from the extract, and methacrylic acid is recovered by distillation. The amounts of the alkaline substance and hydrazine are preferably 1.0-1.5mol and 0.2-0.5mol, respectively, based on 1mol of maleic acid contained in the extract liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for removing high-boiling impurities from an aqueous solution of methacrylic acid obtained by cooling imbutylene, tertiary-butanol, or a reaction product gas containing methacrylic acid obtained by catalytic gas-phase oxidation of imbutylene. The purpose of this invention is to provide a method for industrially and efficiently obtaining methacrylic acid free from carbon dioxide.

Extraction operation from a methacrylic acid-containing aqueous solution obtained by cooling the reaction product gas containing methacrylic acid obtained by gas-phase oxidation of inbutylene, tert-butanol, or methacrolein (hereinafter referred to as C4 compound) using a cooling tower. A method for purifying and separating methacrylic acid, comprising: obtaining a methacrylic acid extract, treating the obtained extract with an aqueous alkali solution or a mixed aqueous solution of alkali and hydrazine, and then separating methacrylic acid from the treated solution. Regarding.

In the process for producing methacrylic acid by gas-phase oxidation of the C4 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. A common method is to use it for subsequent purification steps.

Although methods for producing methacrylic acid by gas phase oxidation of C4 compounds have reached the stage of industrialization, problems still remain in these production processes.

One of the problems is that there are many by-product impurities other than methacrylic acid in the reaction product. Examples are acetaldehyde and acetone.

The presence of acrolein, methacrolein, acetic acid, acrylic acid, maleic acid, citraconic acid, aromatic carboxylic acids, etc. is recognized.

Among these impurities, light boiling components such as acetaldehyde, acetone, acrolein, methacrolein, acetic acid, and acrylic acid can be removed relatively easily by normal distillation, but maleic acid and citraconic acid are removed during extraction. The remaining part moves to the extraction phase, making it difficult to separate it from methacrylic acid in the subsequent purification process.

Furthermore, certain types of high-boiling impurities often pose problems, such as promoting the polymerization of methacrylic acid during the methacrylic acid purification process.

Many of these problems are unique to the process of producing methacrylic acid using the C4 oxidation method, and seed lines have been proposed to solve these problems.

For example, in JP-A No. 58-52239.

A method of selectively collecting only the high point impurities before condensing the reaction product gas was proposed,
No. 4 proposes a method of adding a basic substance to the condensate and subjecting it to an extraction operation.

However, all of these methods are not necessarily satisfactory, as they are expensive or provide insufficient results.

In order to solve these problems, the present inventors conducted various studies and found that the methacrylic acid extract was treated with an alkaline substance.
The present invention was accomplished by finding a method to solve the above problems by removing maleic acid and other high-boiling impurities that cause trouble in the distillation process.

The detailed description of the method of the present invention is as follows.

The reaction product gas obtained from the oxidation reaction of inbutylene, tertiary-butanol, or methacrolein is cooled in a quench tower to obtain an aqueous solution containing methacrylic acid. This aqueous methacrylic acid solution is usually first subjected to an operation to remove light boiling point components, and then subjected to an extraction operation with a solvent such as Este V or aromatics.

In addition to the target methacrylic acid, the extract obtained here contains low-boiling components such as acetic acid, acrylic acid, and pyropionic acid, as well as maleic acid and citraconic acid.

Contains aromatic carboxylic acids and other high-boiling components.

The present inventors added an alkaline aqueous solution or a mixed water bath solution of alkali and hydrazine as an alkaline substance to this extract to precipitate the maleic acid and other high boiling point components, and after separating the precipitate, Maleic acid and citraconic acid can be effectively removed by introducing the extract into the subsequent distillation process to produce methacrylic acid.
Furthermore, in the process of purifying methacrylic acid, it has been found that the polymerization troubles of methacrylic acid that conventionally occur during distillation are drastically reduced.

This is due to the fact that by adding an aqueous alkali solution, acids that are more acidic than methacrylic acid selectively form salts, and other high-boiling components undergo some denaturation, and at the same time, high-boiling aldehydes, which are thought to be the main cause of polymerization troubles, This is presumed to be because it reacts with hydrazi/.

As the alkaline substances mentioned here.

Examples 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 preferred. These are preferably used as an aqueous solution of 10 to 50% by weight F.

On the other hand, regarding hydrazine, hydrazine is 50 to 9
It is preferable to use it in the form of an aqueous solution of 0% by weight or in a mixture with an alkaline aqueous solution.

Here, the alkali added to the methacrylic acid extract:
Add 0.5 to 2.0 times the mole of maleic acid contained in the extract, and add 1.0 to 1.5 times the mole of maleic acid contained in the extract.

Regarding hydrazine, 00 to 1.0 times the molar amount of maleic acid contained in the extract is preferably kto, 2 to 0.5.
It is appropriate to add double mole θ.

If the amount added is too large, even methacrylic acid will be neutralized more than necessary, resulting in loss; if it is too small, the removal effect of maleic acid will decrease, and at the same time, it will not be possible to sufficiently prevent polymerization problems of methacrylic acid during the purification process. It's going to happen.

The precipitate produced by adding the above alkaline substance to the extract (
The slurry-like material) is discharged from the system using a standard separation method such as a static tank or a centrifugal filter.

Next, one embodiment of the present invention will be explained with reference to FIG.

The reaction product gas obtained from the catalytic gas phase oxidation reaction of inbutylene was cooled to obtain an aqueous methacrylic acid solution.

Subsequently, after removing low boiling point components contained in this aqueous solution, methacrylic i! is passed through line 1 in FIG.
Feed to the first criminal extraction tower 101. Here, extractant is fed from line 8 and methacrylic acid is extracted.

The extract is sent to the mixer 102 through line 2,
Maleic acid,
/ Traconic acids are neutralized and at the same time other high-boiling components are denatured. On the other hand, the raffinate after extracting methacrylic acid is removed from line 5 to F tank.

The mixed liquid containing the precipitate is passed through line 5 to static tank 103.
The solid precipitate is separated. The separated solid precipitate slurry is discharged via line 7.

On the other hand, the clarified liquid is fed through line 6 to light boiling separation column 104, where the solvent and light boiling components are separated;
It is then supplied to the extraction tower and reused. From the bottom of the column 104, methacrylic acid from which light boiling components have been removed is taken out through line 9.

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

Example 1 An oxidation reaction of isobutylene and methachlorefane was carried out using a Bi-Mo multicomponent catalyst as the first stage oxidation catalyst and a Mo heteropolyacid catalyst as the second stage catalyst. The reaction product gas was cooled and condensed to obtain an aqueous methacrylic acid solution, and the light boiling component of methacrolein curve in this solution was removed, and methacrylic acid was extracted from the obtained solution using inpropyl acetate as an extractant. The extract was mixed with 26 parts of methacrylic acid, 3 parts of acetic acid, and 8 parts of water.
The composition consisted of high boiling point components of 1%, 1%, 1%, 0.6% maleic acid, 0.1%, 1lj-% citraconic acid, and the remainder was isopropyl acetate.

Mix 100% of this extract with F and 0.8% of a 30% sodium hydroxide aqueous solution, and mix +Q for about 20 minutes at room temperature.
It's IT. In this case, the amount of sodium hydroxide used was 1.2 times the amount of maleic acid in the extract by mole.

After stirring, the white solid suspended in this liquid was separated using a sieve filter.

Thus, the salivary fluid composition of 111 is 26jl of methacrylic acid.
i: 111% of 111% of acetic acid, 7.5% of water, 0.03% of maleic acid, 0.08% of citraconic acid, 111% of high boiling point component, the rest is isopropyl acetate. there were. In this case, the removal rate of maleic acid was 95%.

The results showed fully satisfactory results.

Furthermore, this obtained liquid was supplied to a light-boiling separation column and subjected to long-term constant speed &; It turned out that it could withstand hours of operation.

Example 2 Same extraction as Example 1, 50 weight 1 for 100 Kp
7+ was mixed with 0.8 of an i% aqueous sodium hydroxide solution and 0.46 of an 80% aqueous hydrazine solution, and stirred at room temperature for about 20 minutes.

In this case, the amount of sodium monochloride in water is 1.2 times the amount of maleic acid in the extract, and the amount of sodium monochloride in water is 0.
5 times the amount was used. The composition of the treatment liquid thus obtained was approximately the same as in Example 1.

Furthermore, this obtained liquid was supplied to a light boiling separation column and operated continuously for a long time, and it was found that the amount of contamination due to polymer adhesion to the heat transfer section at the bottom of the column was reduced compared to Example 1. It was found that the addition of hydrazine had an effect.

Comparative Example 1 Extraction # having the same composition as in Example 1 was fed into a light boiling separation column without adding alkali, and continuous operation was carried out. 1
After 5 hours of operation, the bottom of the tower was very dirty due to polymer build-up, and it remained as it was! ! , continuing driving is p
It was judged as +1 reason.

Comparative Example 2 The saliva obtained by removing light boiling components such as methacrolein in Example 1 (36% methacrylic acid, 5% acetic acid, 5% water)
8%, maleic acid 1%, citraconic acid 0.5%)
After adding sodium hydroxide in an amount of 1.2 times the total amount of maleic acid and 7 traconic acid.

Extraction was performed in the same manner as in Example 1. The composition of the extract is 26% methacrylic acid, 3% acetic acid, and 8% water.

Maleic acid 0.1%, citraconic acid o, +4. fine fit
The high boiling point component was inglovir acetate, and the remainder was inglovir acetate.

As described above, when an alkali is added before the extraction step, the removal rate of maleic acid, citraconic acid, etc. decreases, and furthermore, the use tR of the alkali is required to be twice or more.

[Brief explanation of drawings]

FIG. 1 is a flow note showing an example of the i aspect of the present invention. 101... Methacrylic acid extraction tower 102.
...River...Mixer 103...River...Stationing tank 104...Light boiling separation tower patent applicant Nippon Kayaku Co., Ltd.

Claims (1)

[Claims] A methacrylic acid extract is extracted from the methacrylic acid-containing aqueous solution obtained by cooling the reaction product gas containing methacrylic acid obtained by gas-phase catalytic oxidation of inbutylene, tert-butanol or methacrolein using a cooling tower. A method for purifying and separating methacrylic acid, comprising: treating the obtained extract with an aqueous alkali solution or an aqueous mixed solution of an alkali and hydrazine, and then separating methacrylic acid from the treated solution.