JPH0780809B2 - 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-step or two-step reaction, formic acid, acetic acid, and propione in addition to methacrylic acid, which is a target, 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, it is separated into a gas phase and a liquid phase.

The gas phase containing nitrogen, oxygen, carbon monoxide, carbon dioxide, water vapor, and methacrolein usually absorbs and separates methacrolein as 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,
Methacrolein, which is an active ingredient, is stripped together with other aldehydes and separated and collected.

[Problems to be solved by the invention]

When methacrolein is separated and recovered from the liquid phase, solid matter often precipitates in the stripping tower, which causes operational problems such as clogging in the tower. That is, solids typified by terphthalic acid are originally poorly soluble in the methacrylic acid aqueous solution, but since the precipitation rate is slow, they are supplied to the stripping tower before the solids are sufficiently precipitated, and the solids are precipitated. Then it adheres to the diffusion 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 and / or metal powder selected from aromatic carboxylic acids and / or aromatic aldehydes is added to a methacrylic acid aqueous solution obtained by quenching a reaction product gas, and the solution is contained in the aqueous solution. It is characterized in that an organic compound such as terephthalic acid is deposited and then separated and removed.

According to the above-mentioned treatment method of the present invention, an organic compound such as terephthalic acid dissolved in a methacrylic acid aqueous solution in a supersaturated state is replaced with an organic compound selected from aromatic carboxylic acids and / or aromatic aldehydes. By adding the metal powder, it is possible to accelerate the precipitation rate for separation. Thus, it becomes possible to easily separate the organic compounds such as terephthalic acid in the previous step of the stripping tower for removing light boiling components such as methacrolein, avoiding the precipitation and adhesion in the stripping tower and the subsequent steps. It is possible to prevent precipitation and adhesion of the organic compound such as terephthalic acid in the tower.

The organic compound which is an aromatic carboxylic acid and an aromatic aldehyde referred to in the present invention is a substance which is hardly soluble in the methacrylic acid aqueous solution, for example, aromatic carboxylic acids such as terephthalic acid and isophthalic acid, terephthalaldehyde, Aromatic aldehydes such as isophthalaldehyde are mentioned, and the solid substance deposited and separated in the process is an organic compound whose main component is terephthalic acid. Therefore, it is preferable to circulate and use a part of the separated and recovered terephthalic acid. As a 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.

The organic compound and / or metal powder may be added directly to a methacrylic acid aqueous solution storage tank or the like, but industrially continuously and at a constant ratio to the methacrylic acid aqueous solution. It is preferable to put it in, and it is more preferable to stir it. As the addition ratio,
It is 100 ppm to 1% by weight, and particularly preferably 600 to 6,000 ppm by weight based on the methacrylic acid aqueous solution. The temperature for precipitating the organic compound such as terephthalic acid may be room temperature, but if possible, the bottom temperature of the stripping tower when stripping methacrolein etc. from the aqueous solution of methacrylic acid is 50 ° C, or about 10 ° C higher than that. Lower temperatures are 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.

A methacrylic acid aqueous solution obtained by rapidly cooling a high temperature reaction product gas obtained by reacting methacrolein or the like with a gas containing molecular oxygen in the presence of an oxidation catalyst is continuously fed to a stirring tank 1 through a line 11. Further, in line 11, a part of the high-concentration slurry in which an organic compound such as terephthalic acid is deposited is circulated through line 16 from the bottom of the solid sedimentation and concentration tank 2 in the subsequent step.

After precipitating an organic compound such as terephthalic acid which is dissolved in a supersaturated state in the stirring tank 1, the mixed liquid leaving the stirring tank 1 is guided by the line 12 and then in the next solids settling / concentrating tank 2, terephthalic acid, etc. The organic compound of 1. is allowed 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 methacrylic acid aqueous solution from which the organic compounds such as terephthalic acid have been deposited and removed is sent as a supernatant to the upper part of the stripping tower 3 through a line 13. Light boiling substances such as methacrolein are removed from the top line 15 of the stripping tower 3, and methacrylic acid aqueous solution from which the light boiling substances such as methacrolein are removed is stripped in the stripping tower 3.
It is removed by line 14 at the bottom of the tower.

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 organic compound such as terephthalic acid that is extracted from the bottom of the solid sedimentation and concentration tank 2 is a part of the organic compound dissolved in the methacrylic acid aqueous solution in a supersaturated state by the line 16 as described above. Circulate as a seeding slurry for precipitation. In this case, although not shown in FIG. 1, 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. The resulting aqueous methacrylic acid solution contained 30.9 wt% of methacrylic acid, 540 ppm of dissolved terephthalic acid, 9.5 wt% of other organic acids and aldehydes, and the balance 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 45 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 50 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 methacrylic acid aqueous solution supplied to the stripping tower 3 through the line 13, and the stripping tower was packed with 2.4 m of the through-the-pack BX. No deposits were seen in the tower even after a month of operation.

Comparative Example-1 When the aqueous methacrylic acid solution was allowed to stand in Example-1, the amount of 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 conducted except that terephthalic acid was not added. As a result, a solid substance was found in the aqueous methacrylic acid solution in line 13, and the result of the operation for about 2 months was that the inside of the stripping tower A large amount of deposits was seen on the surface and the operation was stopped after that.

〔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 concentration tank 3 stripping tower 11 to 17 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 selected from aromatic carboxylic acids and / or aromatic aldehydes and / or metal powder is added to the resulting aqueous methacrylic acid solution to precipitate an organic compound such as terephthalic acid contained in the aqueous solution. After punishing
A method for treating an aqueous solution of methacrylic acid, which comprises separating and removing.