JPH0753687B2 - 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 a process for producing methacrylic acid by a gas phase catalytic oxidation reaction of isobutylene, tertiary butanol, methacrolein or isobutyraldehyde, from a methacrylic acid aqueous solution obtained by cooling a methacrylic acid-containing gas discharged from an 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 often causes inconvenient phenomena such as coloring.

As a method for removing aldehydes contained in methacrylic acid, hydrazine, ethylenediamine, aniline, amines such as polyamines (JP-A-49-51217, JP-A-52-23017),
Ethylene glycol (JP-A-58-128336), bisulfite (JP-A-59-44337, 59-44338, 59-93027, 60-252)
44), mercaptans (JP-A-60-6635), resorcin, pyrogallol, α-naphthol (JP-A-60-13054).
Methods for adding 6) 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. Glycol, bisulfite, and mercaptans also have a weak removing effect, and 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 can only be removed in the presence of strongly acidic substances such as sulfuric acid and hydrochloric acid, which complicates the operation and requires the selection and use of high-grade equipment materials in actual equipment. is there.

[Means for solving problems]

The present inventors have solved the above-mentioned problems and studied the method for simply and effectively removing a trace amount of maleic acid and aldehydes contained in methacrylic acid, and as a result, 2,4-diaminodiphenylamine and metatoluyi. The inventors have found that diamine has an excellent effect in removing these impurities, and completed the present invention.

That is, the present invention relates to isobutylene, tertiary butanol,
In producing methacrylic acid by a gas phase catalytic oxidation reaction of methacrolein or isobutyraldehyde, crude methacrylic acid obtained by the reaction is subjected to catalytic treatment with 2,4-diaminodiphenylamine or metatoluylenediamine, and then purified by distillation to obtain methacrylic acid. It provides a purification method.

[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, condensing and collecting the reaction product gas, and then performing distillation operations of an extraction solvent separation step, a light boiling point material 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, acetic acid, acrylic acid, methacrylic acid after removing low-boiling components such as propionic acid and isobutyric acid, or a part of maleic acid subsequently, a polymerization inhibitor, It is desirable to apply it to methacrylic acid that is subjected to final precision distillation after separating polymers and other high-boiling 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.

The amount of 2,4-diaminodiphenylamine or metatoluylenediamine used in the present invention is an equimolar amount or more with respect to the carboxylic acid group and the aldehyde group based on the unsaturated dibasic acid contained in methacrylic acid, preferably The amount is 2 times or more, and particularly preferably 3 times or more. 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 depends on what methacrylic acid to which the present invention is applied has passed through the separation and purification process, Usually, it is used in a range of 3 to 10 times mol based on the carboxylic acid group and aldehyde group based on the quantifiable unsaturated dibasic acid.

The contact treatment between 2,4-diaminodiphenylamine or metatoluylenediamine and 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 is heated to a temperature range of 50 to 100 ° C. Preferably. The contact treatment time is usually 1 to 60 minutes, but usually 2,4-
Since methacrylic acid added with diaminodiphenylamine or metatoluylenediamine is heated in the subsequent distillation step, a special heating treatment can be omitted.

For example, it is possible to carry out a simple operation in which a predetermined amount of 2,4-diaminodiphenylamine or metatoluylenediamine is added to a feed solution, a can solution or a tower of a methacrylic acid distillation tower.

Regarding the distillation of methacrylic acid, the distillation is usually performed in the presence of hydroquinone, phenothiazine, etc. in order to prevent the polymerization.However, the 2,4-diaminodiphenylamine of the present invention itself has a polymerization inhibiting effect, so that the polymerization to be used in combination is performed. It is also possible to reduce or eliminate the inhibitor.

〔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 1 kg of high-purity methacrylic acid was furfural as an impurity,
10 pp each of benzaldehyde and paratolualdehyde
m and 100 ppm of maleic acid were added, a predetermined amount of the reagent shown in Table 1 was added, and the mixture was heated at 80 ° C. for 2 hours and analyzed for impurities, and the removal rate of each was calculated. Grace, experiment number 1 in the table
5 is an example of the present invention, and 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.

Polymerizability at the time of 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 batch distillation was performed according to 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 condensed and collected, and the obtained 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. A 7-fold molar amount of 2,4-diaminodiphenylamine or metatoluylenediamine was added to the total amount of maleic acid-based carboxyl groups and furfural and benzaldehyde-based aldehyde groups in crude methacrylic acid, and simple distillation was performed under the same conditions. The content of impurities in the distilled 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 -logT at 350 nm). It is shown that the coloring was greatly improved by the treatment with 2,4-diaminodiphenylamine and metatoluylenediamine, 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 50
ppm, furfural 110 ppm, benzaldehyde 140 ppm were contained. To 10 kg of this crude methacrylic acid, 10 g of metatoluylene diamine was added, and low-boiling components were removed by distillation under reduced pressure to obtain a can liquid 8.7 kg. A small amount of 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 Oldashaw column having 20 plates to obtain 7.6 kg of methacrylic acid product.
Got 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 the methacrylic acid obtained by performing the same treatment without adding additives, maleic acid 25 pp
m, furfural 90ppm, and benzaldehyde 100ppm remained.

Example 4 (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 solid components produced as by-products. The resulting aqueous solution of methacrylic acid contained 0.3% maleic acid and 3% furfural.
00ppm and benzaldehyde 170ppm were added to this solution, and 5 times mol of metatoluylenediamine was added to the total amount of the above impurities, and the mixture was heat treated at 80 ° C for 2 hours, and then the impurities were analyzed. 90% for acid, furfural and benzaldehyde, 100 each
% And 85%.

Example 5 (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 a 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
Then, 1.0 g of metatoluylenediamine 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 5 ppm, respectively.

Example 6 (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 by-produced, and then hexane was used for extraction. 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 50 ppm, 6-fold mol of 2,4-diaminodiphenylamine 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.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Minoru Koshibe 1-3-16, Shin-Hinodai, Sakai City, Osaka Prefecture (72) Inventor Yoshihiro Sezaki, 3-2-12-302 Yayoi-cho, Izumi City, Osaka Prefecture (56) References JP-A-63-162652 (JP, A) JP-A-52-23017 (JP, A)

Claims (1)

[Claims] 1. When producing methacrylic acid by vapor-phase catalytic oxidation reaction of isobutylene, tertiary butanol, methacrolein or isobutyraldehyde, crude methacrylic acid obtained by the reaction is converted to 2,4-diaminodiphenylamine or metatoluylene diene. A method for purifying methacrylic acid, which comprises subjecting it to a contact treatment with an amine and then purifying it by distillation.