JPH0780810B2 - Method of treating methacrylic acid aqueous solution - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for treating an aqueous methacrylic acid solution in the production of methacrylic acid.

[Prior art]

When isobutylene, tertiary butyl alcohol, isobutyraldehyde, or methacrolein is catalytically oxidized with molecular oxygen in the presence of an oxidation catalyst in a one- or two-step reaction, formic acid, acetic acid, and propione in addition to methacrylic acid, which is the target product, are obtained. A high-temperature reaction product gas composed of acid, acrylic acid, methacrolein, aldehydes having 1 to 3 carbon atoms, carbon monoxide, carbon dioxide, unreacted oxygen, nitrogen, steam and the like can be obtained.
When this produced gas is cooled by an appropriate method, a gas phase and a liquid phase are formed, and then methacrylic acid is separated and purified in the following steps.

The gas phase containing nitrogen, oxygen, carbon monoxide, carbon dioxide, water vapor, and methacrolein usually absorbs and separates methacrolein, which is an active ingredient, using an absorbent such as water or an organic solvent. On the other hand, with formic acid, acetic acid, propionic acid, acrylic acid and water, a liquid phase containing methacrylic acid as a main component, which contains a small amount of aldehydes such as methacrolein,
After stripping methacrolein, which is the active ingredient, with other aldehydes to separate and collect it, extract it with a solvent that selectively extracts methacrylic acid, and extract a small amount of formic acid, acetic acid, propionic acid, acrylic acid contained in the extraction phase. Methacrylic acid is separated and purified by removing acid and water by azeotropic distillation with a solvent.

When this methacrylic acid is selectively extracted, solid matter often precipitates in the extraction column, causing problems such as clogging in the column in stable operation of the process.

That is, a solid material typified by terephthalic acid is originally hardly soluble in a methacrylic acid aqueous solution, but since the precipitation rate is slow, it becomes a solid material and is supplied to an extraction tower before being sufficiently precipitated,
Although there is a degree of difference depending on the type of the extraction solvent, contact between the methacrylic acid aqueous solution and the extraction solvent causes solids to precipitate in the extraction column and adhere to the column.

As a conventional technique for solving these problems, a method of contacting with a solvent before feeding to an extraction column and filtering a precipitated solid matter (Japanese Patent Laid-Open No. 56-16438, 56-79634, 60-69053),
A method in which a basic substance is added to the extraction tower to decompose the solid matter or shift it to the extraction residual liquid side as a salt (JP-A-58-99434), and bisulfite is added to the extraction tower before it is supplied to the extraction tower. A method of adding and suppressing the precipitation of solids in the extraction tower (Japanese Patent Laid-Open No. 58-128337) is known.

[Problems to be solved by the invention]

In the above-mentioned method, even if an organic compound such as terephthalic acid dissolved in the methacrylic acid aqueous solution can be removed before the extraction of methacrylic acid, the deposition rate is slow and the equipment becomes large, It also requires special chemicals,
It did not solve the essential problem of depositing solids in the extraction tower.

[Means for solving problems]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems.

That is, in the method for treating an aqueous solution of methacrylic acid of the present invention, methacrylic acid is produced by subjecting isobutylene, tertiary butanol, isobutyraldehyde or methacrolein to a gas phase reaction with a gas containing molecular oxygen in the presence of an oxidation catalyst. In the method, an organic compound selected from aromatic carboxylic acids and / or aromatic aldehydes is added to the methacrylic acid aqueous solution after removal of light boiling substances such as methacrolein from the methacrylic acid aqueous solution obtained by quenching the reaction product gas. And / or metal powder is added to precipitate an organic compound such as terephthalic acid contained in the aqueous solution, and then the organic compound is separated and removed.

The extraction solvent added to the aqueous solution of methacrylic acid in the present invention is a substance that selectively extracts methacrylic acid, and examples thereof include one or a mixture of heptane, octane, toluene, and xylene.

In the present invention, an organic compound such as terephthalic acid dissolved in a methacrylic acid aqueous solution in a supersaturated state is treated with an aromatic carboxylic acid and / or an aromatic aldehyde in a step prior to an extraction column for selectively extracting methacrylic acid. Of an organic compound such as terephthalic acid in an extraction tower by adding an organic compound and / or a metal powder selected from the group to accelerate the precipitation rate in the methacrylic acid aqueous solution and to separate by separation. And adhesion can be avoided.

The organic compound selected from aromatic carboxylic acids and aromatic aldehydes in the present invention is a substance which is hardly soluble in the methacrylic acid aqueous solution, and examples thereof include aromatic carboxylic acids such as terephthalic acid and isophthalic acid, and terephthalic acid. Aromatic aldehydes such as aldehydes and isophthalaldehyde are listed. Since the solid matter deposited and separated in the process is an organic compound containing terephthalic acid as a main component, it is possible to use a part of the separated and recovered terephthalic acid in a circulating manner. As a preferable method.

Examples of the metal powder to be added to the methacrylic acid aqueous solution in the present invention include stainless powder, and the particle size of the metal powder when used is not particularly limited, but is preferably 5 to 50 μm.
The range is m.

As a method for adding the organic compound and / or the metal powder, the organic compound and / or the metal powder may be directly charged into a storage tank of the methacrylic acid aqueous solution or the like, but industrially continuously and at a constant ratio to the methacrylic acid aqueous solution. It is preferable to add, and it is more preferable to stir. The addition ratio is 100 ppm to 1% by weight, and industrially preferably 500 to 4,000 ppm with respect to the methacrylic acid aqueous solution. Also,
The temperature for precipitating an organic compound such as terephthalic acid may be room temperature, but if possible, a temperature range that is about 10 ° C. lower than the temperature in the extraction column when selectively extracting methacrylic acid is preferably used.

An example of an embodiment of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is an example of a flow chart relating to the method for treating an aqueous methacrylic acid solution of the present invention.

After removing light boiling substances such as methacrolein from the aqueous solution of methacrylic acid obtained by quenching the high-temperature reaction product gas obtained by gas-phase reacting methacrolein with a gas containing molecular oxygen in the presence of an oxidation catalyst. The aqueous methacrylic acid solution is continuously fed into the stirring tank 1 through the line 11. At the same time the line
A part of the high-concentration slurry in which an organic compound such as terephthalic acid is deposited is circulated and joined to 11 from the bottom of the solid sedimentation and concentration tank 2 in the subsequent step by a line 18.

In the stirring tank 1, after precipitating an organic compound such as terephthalic acid which is dissolved in a supersaturated state, the mixed liquid exiting the stirring tank 1 is guided by a line 12 and the terephthalic acid etc. To allow the organic compound to settle as a solid.

A residence time of 1 hour in the agitation tank 1 is sufficient, and is preferably about 1 hour from the viewpoint of a continuous process. The aqueous solution of methacrylic acid from which organic compounds such as terephthalic acid have been removed by precipitation is sent as a supernatant liquid to the upper part of the extraction column 3 through the line 13, and methacrylic acid is extracted from the line 14 by the extraction solvent absorbed in the extraction column 3 to extract methacrylic acid. It flows out from the top line 15.

The size of the solid matter settling / concentrating tank 2 may be determined within an allowable range of the amount of solid matter flowing out to the line 13. If a residence time of 1 hour is provided, almost no solid matter will flow out, but a line 13 may be provided with a filter or the like for the sake of completeness.

The high-concentration slurry of the precipitated organic compound such as terephthalic acid extracted from the bottom of the solid matter settling / concentrating tank 2 is partially dissolved in the methacrylic acid aqueous solution by the line 18 in a supersaturated state as described above. Circulates as a seed slurry for precipitation. In this case, although not shown in this flow chart, the high-concentration slurry may be directly circulated in the stirring tank 1. The remaining high-concentration slurry is drawn out of the system through line 17. If necessary, the slurry extracted from the line 17 may be filtered to collect the methacrylic acid aqueous solution.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1 A reaction product gas obtained by vapor-phase catalytic oxidation of methacrolein in the presence of air and water vapor using a heteropolyacid-based oxidation catalyst was cooled to about 260 ° C. with an indirect cooler, and then quenched. Introduced.

The quenching tower had a tower diameter of 10 inches and a height of 4 m and was filled with 3 m of a 3 / 4B pole ring. A part of the condensed liquid was supplied from the top of the column and brought into countercurrent contact with the reaction product gas. This condensate was stirred for 300 m with light boiling substances such as methacrolein and acetone in a diffusion tower.
mHgABS was removed under reduced pressure to obtain an aqueous solution of methacrylic acid from the bottom of the tower. The resulting aqueous methacrylic acid solution contained 31.5 W% of methacrylic acid, 530 ppm of dissolved terephthalic acid and other organic compounds, and 9.1 wt% of other organic acids and aldehydes.
And the rest was water.

When 1 g of terephthalic acid was added to 1000 g of this aqueous solution,
As shown in FIG. 2, the concentration of supersaturated organic compounds such as terephthalic acid reached equilibrium in only 40 minutes.

Example-2 In Example-1, when 1 g of stainless powder was added to 1000 g of methacrylic acid aqueous solution, the concentration of dissolved organic compounds such as terephthalic acid reached equilibrium in 45 minutes.

Example-3 Using the same methacrylic acid aqueous solution as in Example-1, the first
Methacrylic acid was produced using equipment having the same equipment as the flow shown in the figure (outline is shown in Table 1).

The methacrylic acid aqueous solution was continuously supplied to the stirring tank 1 at 30.0 kg / hr, and when the whole system reached equilibrium, the flow rate and composition of each were measured. The results are shown in Table 2. No solid matter was found in the aqueous methacrylic acid solution in the line 13 supplied to the extraction tower 3, and the rotating disk type extraction tower 3 with a tower diameter of 6 inches and a height of 7 m was used even at an extraction tower temperature of 30 ° C. for about 2 months of operation. No deposit was found in the tower.

Comparative Example-1 When the aqueous methacrylic acid solution was allowed to stand in Example-1, the dissolved organic compounds such as terephthalic acid did not reach equilibrium after 10 hours as shown in FIG.

Comparative Example-2 The same procedure as in Example-3 was carried out except that terephthalic acid was not added. As a result, solid matter was found in the line 13, and about 2
As a result of the operation for a month, a large amount of deposits were found in the stripping tower, and then the operation became impossible.

〔The invention's effect〕

According to the present invention, the precipitation rate of an organic compound such as terephthalic acid which is supersaturated in an aqueous solution of methacrylic acid and the growth rate of its particle size are dramatically increased, and it becomes possible to remove these solids in a short time. Great industrial value in manufacturing.

[Brief description of drawings]

FIG. 1 is an example of a flow chart relating to the method for treating an aqueous methacrylic acid solution of the present invention. FIG. 2 shows the deposition rate of organic compounds such as terephthalic acid which are supersaturated in the aqueous methacrylic acid solution according to the present invention. 1 Stirring tank 2 Solid sedimentation and concentration tank 3 Dispersion tower 11-18 Each line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirozo Segawa 2-1 Kyowa-cho, Nakajo-cho, Kitakanbara-gun, Niigata Prefecture (72) Inventor Katsuji Yoguchi 4-7-411 Kamo, Takaishi-shi, Osaka

Claims (1)

[Claims] 1. A method for producing methacrylic acid by subjecting isobutylene, tertiary butanol, isobutyraldehyde or methacrolein to a gas phase reaction with a gas containing molecular oxygen in the presence of an oxidation catalyst to rapidly cool the reaction product gas. An organic compound and / or metal powder selected from aromatic carboxylic acids and / or aromatic aldehydes is added to the methacrylic acid aqueous solution obtained after removing light boiling substances such as methacrolein from the methacrylic acid aqueous solution obtained by A method for treating an aqueous solution of methacrylic acid, which comprises depositing an organic compound such as terephthalic acid contained in the aqueous solution, and then separating and removing the organic compound.