JPH0729977B2 - Method for purifying methacrylic acid - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel method for purifying methacrylic acid. More specifically, in the process of producing methacrylic acid by vapor-phase catalytic oxidation reaction of isobutylene, tertiary butanol, methacrolein or isobutyraldehyde, from a methacrylic acid aqueous solution obtained by cooling the methacrylic acid-containing gas discharged from the oxidation reactor. The present invention relates to a purification method for obtaining high-purity and high-quality methacrylic acid.

[Conventional technology and problems]

In the reaction gas obtained by catalytically oxidizing isobutylene, tertiary butanol, methacrolein or isobutyraldehyde with molecular oxygen in the presence of water vapor in a one-step or two-step reaction, in addition to the desired methacrylic acid, for example, Formic acid, acetic acid, propionic acid, maleic acid, citraconic acid,
Carboxylic acids such as benzoic acid, toluic acid and terephthalic acid, and aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, methacrolein, benzaldehyde, tolualdehyde and furfural are contained as by-products. Most of these impurities can be made into highly pure products by ordinary purification means such as extraction and distillation. However, it is difficult to remove impurities contained in a trace amount, for example, it is difficult to completely remove maleic acid, citraconic acid and aldehydes. In particular, when aldehydes are contained, absorption is observed in the ultraviolet region, polymerization is suppressed during the polymerization reaction, and a long reaction time is required,
The obtained polymer is not preferable because it often causes inconvenient phenomena such as coloring.

As a method for removing aldehydes contained in methacrylic acid, amines such as hydrazine, ethylenediamine, aniline and polyamine (JP-A-49-51217 and JP-A-52-12301) are used.
7), ethylene glycol (JP-A-58-128336), bisulfite (JP-A-59-44337, 59-44338, 59-9302).
7, 60-25244), mercaptans (JP-A-60-663)
5), methods for adding resorcin, pyrogallol, α-naphthol (JP-A-60-130546) and the like are known. However, amines are not sufficiently effective in removing aldehydes and are apt to cause polymerization in the distillation step after treatment. The removal effect of glycol, bisulfite, and mercaptans is weak,
It is necessary to add a large amount, which causes secondary contamination of methacrylic acid by the added substance and loss of reaction. In addition, phenols such as resorcin are those that exhibit their removal effect only in the presence of strongly acidic substances such as sulfuric acid and hydrochloric acid.
In addition to complicated operations, it is necessary to select and use high-grade equipment materials in actual equipment.

[Means for solving problems]

The present inventors have solved the above-mentioned problems, and as a result of researching a method for simply and effectively removing a trace amount of maleic acid and aldehydes contained in methacrylic acid, as a result, metaaminophenol and metaphenylenediamine are among these impurities. The present invention has been completed by finding out that it exerts an excellent effect on the removal. That is, the present invention relates to isobutylene, the third
In producing methacrylic acid by a gas phase catalytic oxidation reaction of primary butanol, methacrolein or isobutyraldehyde, crude methacrylic acid obtained by the reaction is subjected to catalytic treatment with metaaminophenol and / or metaphenylenediamine and then purified by distillation. A method for purifying methacrylic acid, which is a feature of the present invention, is provided.

[Specific Description of the Invention]

Methacrylic acid is usually obtained by catalytic oxidation of isobutylene, tertiary butanol, methacrolein or isobutyraldehyde with one or two catalyst layers.
In such a method, methacrylic acid is purified by solvent extraction from an aqueous solution containing methacrylic acid obtained by cooling and agglomerating and collecting the reaction product gas, and then through a distillation operation in an extraction solvent separation step, a light boiling point separation step and a heavy material separation step. To be done.

The crude methacrylic acid to be treated in the method of the present invention may be any of those in the above steps, such as an aqueous methacrylic acid solution, a methacrylic acid-containing extract, methacrylic acid after extraction solvent separation, and methacrylic acid after light boiling point separation. Alternatively, any of methacrylic acid and the like after separation of heavy substances can be applied,
In order to obtain the maximum removal effect with the minimum amount of additive,
After separation of light-boiling substances, that is, after separating the extraction solvent, methacrylic acid after removing low-boiling components such as acetic acid, acrylic acid, propionic acid and isobutyric acid, or subsequently a part of maleic acid, a polymerization inhibitor, a polymer It is desirable to apply to methacrylic acid which is subjected to final precision distillation after separating other high boiling point components as bottoms. The method of the present invention can also be applied to unreacted methacrylic acid recovered in the step of producing methyl methacrylate from methacrylic acid and methanol with a cation exchange resin.

Metaaminophenol and / or used in the present invention
Alternatively, the amount of metaphenylenediamine is equimolar or more, preferably 2 times or more, and particularly preferably 3 times or more, with respect to the carboxylic acid group and the aldehyde group based on the unsaturated dibasic acid contained in methacrylic acid. Is. It is difficult to strictly analyze the trace amount of multi-component impurities in the actual liquid in the methacrylic acid production process, and it is usually different depending on what kind of separation and purification process the methacrylic acid to which the present invention is applied has gone through. Is 3 to carboxylic acid group and aldehyde group based on quantifiable unsaturated dibasic acid.
Used in a 10-fold molar range.

The contact treatment of methaminophenol and / or metaphenylenediamine with methacrylic acid may be carried out by mixing both at room temperature, but in order to complete the reaction treatment in a short time, it should be heated to a temperature range of 50 to 100 ° C. Is preferred. The contact treatment time is usually 1 to 60 minutes, but usually methacrylic acid to which methaminophenol and / or metaphenylenediamine is added is heated in the subsequent distillation step, and thus a special heating treatment can be omitted. For example, it can be carried out by a simple operation of adding a predetermined amount of methaaminophenol and / or metaphenylenediamine to the feed liquid, the bottom liquid or the inside of the methacrylic acid distillation column.

〔The invention's effect〕

According to the method of the present invention, it has become possible to efficiently remove maleic acid and aldehydes contained in methacrylic acid under mild conditions by a very simple operation. Further, the obtained high-purity methacrylic acid is not colored, and no abnormal phenomenon of polymerization behavior is observed in the production of the polymer.

〔Example〕

Example 1 To high-purity methacrylic acid, 10 ppm each of furfural, benzaldehyde, and paratolualdehyde and 100 ppm of maleic acid were added as impurities, and a predetermined amount of the reagents shown in Table 1 was added, followed by heat treatment at 80 ° C. for 2 hours. Analyze
The experiment numbers 1 to 5 in the table in which the respective removal rates were calculated are examples of the present invention, and the experiment numbers 6 to 15 are comparative examples. Furfural, benzaldehyde and paratolualdehyde were analyzed by gas chromatography after neutralizing the reaction solution, and maleic acid was analyzed by liquid chromatography.

Polymerization property during distillation: In Table 1, hydroquinone (500 ppm) was added to Experiment Nos. 1 to 6, which had good removal efficiency without using an acid catalyst, and distilled by a conventional method (column top temperature 95 ° C., pressure 60 mmHg ) As a result, in Experiment Nos. 1 to 5, there was no polymerization trouble at the time of distillation, and no impurities were detected in the distilled methacrylic acid, but in Experiment No. 6, polymer formation was remarkably observed and stable distillation was performed. I couldn't.

Example 2 Isobutylene was subjected to vapor phase catalytic oxidation, the distillate was cooled and coagulated and collected, and the resulting aqueous solution of methacrylic acid was settled and filtered to separate a solid component produced as a by-product, and then methacrylic acid was extracted with hexane. . Hexane and low-boiling components were distilled off from this extract to obtain crude methacrylic acid shown in Table 2. To the total amount of maleic acid-based carboxyl groups and furfural and benzaldehyde-based aldehyde groups in crude methacrylic acid, 7-fold moles of metaaminophenol or metaphenylenediamine were added, and simple distillation was performed under the same conditions for distillation. The content of impurities in methacrylic acid is shown in the same Table 2. Almost 100% of maleic acid and furfural and 97% or more of benzaldehyde were found to be removed.

Coloring of distilled methacrylic acid: Table 2 shows the absorbance of distilled methacrylic acid (using a 10 mm glass cell and measuring -log T at 350 nm). It is shown that the coloring was greatly improved by the treatment with meta-aminophenol and meta-phenylenediamine, respectively.

Example 3 A methacrylic acid extract was obtained in the same manner as in Example 2 by subjecting tertiary butanol to gas phase catalytic oxidation. In the crude methacrylic acid obtained by distilling off the extraction solvent from this extract, maleic acid 40
ppm, furfural 130 ppm, and benzaldehyde 160 ppm were contained. To 10 kg of this crude methacrylic acid was added 10 g of metaphenylenediamine, and the mixture was distilled under reduced pressure to remove low boiling point components to obtain 9 kg of a bottom liquid. A slight solid matter was precipitated in the bottom liquid, which was filtered off, and then continuously distilled at a reflux ratio of 0.5 with an Oldasha column having 20 plates to obtain 7.8 kg of methacrylic acid as a product. The amounts of impurities contained in this product were below the detection limit values of the gas chromatograph and the liquid chromatograph, respectively. On the other hand, in methacrylic acid obtained by performing the same treatment without adding additives, maleic acid 20 pp
m, furfural 100 ppm, and benzaldehyde 120 ppm remained.

Example 4 Methacrylic acid obtained by the same method as in Example 3 was used. Maleic acid 40 ppm, furfural 140 ppm, benzaldehyde 1
To 10 kg of crude methacrylic acid containing 65 ppm, 5 g of metaaminophenol and 5 g of metaphenylenediamine were added and distilled under reduced pressure to remove low-boiling components, and 8.9 kg of a bottom liquid was obtained. This can solution was treated in the same manner as in Example 3 to produce methacrylic acid 7.7 kg.
Got The impurities contained in this product were below the detection limit.

Example 5 (when applied to an aqueous solution containing methacrylic acid) The aqueous solution of methacrylic acid obtained by the same method as in Example 2 was subjected to settling filtration to separate a solid component produced as a by-product. The resulting aqueous solution of methacrylic acid contained 0.3% maleic acid and 3% furfural.
It contains 00ppm and benzaldehyde 170ppm. To this solution, 5 times mol of meta-aminophenol is added to the total amount of the above impurities, and the mixture is heated at 80 ° C for 2 hours, and then analyzed for impurities.
The respective removal rates were calculated to be 80%, 100%, 8% for maleic acid, furfural and benzaldehyde, respectively.
It was 5%.

Example 6 (when applied to a methacrylic acid extract) The aqueous solution of methacrylic acid obtained by the same method as in Example 2 was subjected to settling filtration to separate the solid component produced as a by-product, and then methacrylic acid was extracted with heptane. The methacrylic acid extract contained 290 ppm and 300 ppm of the total amount of maleic acid-based carboxyl groups and furfural and benzaldehyde-based aldehyde groups, respectively. 200 g of this extract
To this, 1.0 g of metaphenylenediamine was added, and heat treatment was performed at 50 ° C. for 60 minutes. The residual amounts of the aldehyde group and the carboxyl group in this liquid were 0 ppm and 3 ppm, respectively.

Example 7 (when applied after separation of high-boiling substances) Isobutylene was subjected to vapor-phase catalytic oxidation, cooled, condensed, and collected to obtain an aqueous methacrylic acid solution, which was then settled and filtered to separate solid components produced as by-products, and then hexane was added. Methacrylic acid was extracted. Hexane and low-boiling components were removed by distillation from this extract, and methacrylic acid was separated from high-boiling components by continuous distillation at an reflux rate of 0.5 with an Oldasha column having 20 plates. In this methacrylic acid, maleic acid 50ppm, furfural 3
Since it contained 0 ppm and benzaldehyde of 50 ppm, 6 times mol of metaaminophenol was added to this and simple distillation was performed under the same conditions to obtain a product methacrylic acid in which the above impurities were below the detection limit.

Example 8 (when applied to unreacted methacrylic acid after esterification) Separation of solid components from an aqueous solution of methacrylic acid obtained by the same method as in Example 2, solvent extraction, separation of solvent and low boiling point component, and After the methacrylic acid obtained by separating the high-boiling components was esterified with methanol using a cation exchange resin, methyl methacrylate and low-boiling components were distilled off under reduced pressure to obtain unreacted methacrylic acid. To the residual liquid (maleic acid 10 ppm, furfural 10 ppm, benzaldehyde 20 ppm) which is the main component, 5 times mol of metaaminophenol was added, and simple distillation was performed under the same conditions to obtain a product methacrylic acid in which the above impurities were below the detection limit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Koshibe 1-3-16 Shinhiodai, Sakai City, Osaka Prefecture (72) Yoshihiro Sezaki 3-2-12-302 Yayoi Town, Izumi City, Osaka Prefecture

Claims (1)

[Claims] 1. When producing methacrylic acid by a gas-phase catalytic oxidation reaction of isobutylene, tertiary butanol, methacrolein or isobutyraldehyde, crude methacrylic acid and metaaminophenol and / or metaphenylenediamine obtained by the reaction are produced. A method for purifying methacrylic acid, which comprises subjecting to a contact treatment and then purifying by distillation.