JPS62145044A - Purification of methacrylic acid - Google Patents

Abstract

PURPOSE:When the solvent is separated from the solvent extract which is obtained by extraction of an aqueous methacrylic acid solution containing lower aliphatic carboxylic acids, lower carboxylic acids are side-cut from the middle of the concentration in the solvent separation column to improve the separation efficiency of methacrylic acid of high purity. CONSTITUTION:The reaction mixture resulting from catalytic oxidation of isobutylene or tert.-butanol is counter-currently brought into contact with the extraction solvent in the extraction column A and the extract containing methacrylic acid and lower aliphatic acids is fed to the solvent-stripping column B. In the column B, The solvent is distilled off from the top and purified methacrylic acid is taken out of the bottom. Further, lower aliphatic acids are stripped off from the middle 9 of the concentration part in the column B and the fraction is fed to the low-boiling fraction separation column B. In the column D, the concentrated aliphatic carboxylic acids are distilled off from the top through pipe 12 and the bottom fraction is recycled to the upper part of the recovery part in the solvent separation column B.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for separating and purifying methacrylic acid from an aqueous mixture containing methacrylic acid.

[Conventional technology]

In the production of methacrylic acid, for example by catalytic air oxidation of imbutylene, tertiary butanol, methacrolein or isobutyraldehyde, various by-products, especially acetic acid and acrylic acid, are produced along with the main product methacrylic acid. A large amount of aliphatic carboxylic acids such as propionic acid and isobutyric acid are produced.

Crude methacrylic acid is generally obtained as an aqueous solution of a mixture of these by condensing the reaction product gas. Purifying methacrylic acid by directly distilling this methacrylic acid aqueous solution is difficult because water has a lower boiling point than methacrylic acid.
Since it is necessary to distill off the entire amount of water, which increases energy costs and has poor separation efficiency, the method usually used is to extract methacrylic acid with a suitable oil and then separate the oil and methacrylic acid. It will be done. In particular, there is a proposal (Japanese Patent Publication No. 513-52007) in which cyclohexane or n-hexane is selected as an extractant so that methacrylic acid is transferred to the extraction layer and acetic acid and acrylic acid are transferred to the aqueous layer during the extraction operation. However, extensive extraction processing alone cannot reduce impurities such as acrylic acid to a level that meets market needs, so it is necessary to further increase the purity. It is also already well known that after extraction, methacrylic acid is purified through purification steps such as recovery of the extractant and separation of methacrylic acid by distillation. However, it has been difficult to completely remove the impurity acids because they have relatively close boiling points to methacrylic acid and are affected by gas phase association.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for purifying methacrylic acid that efficiently separates lower aliphatic carboxylic acid impurities such as propionic acid, acrylic acid, and isobutyric acid, which have been insufficiently separated in conventional techniques.

[Means for solving problems]

The inventors focused on this point and conducted intensive studies, and found that when the extraction solvent and methacrylic acid are separated by distillation, acrylic acid, propionic acid, and acetic acid accumulate in the solvent molecule a column. They discovered that acrylic acid, propionic acid, and isobutyric acid can be efficiently removed to a virtually harmless level by side-cutting and separating them by distillation, thereby completing the present invention.

That is, the present invention extracts methacrylic acid with a solvent from an aqueous methacrylic acid solution containing lower aliphatic carboxylic acids such as propionic acid, acrylic acid, and isobutyric acid, and then separates and recovers the solvent from the methacrylic acid to produce a bottom liquid. In purifying the resulting crude methacrylic acid by distillation, the lower aliphatic carboxylic acids are side-cut from the middle stage of the concentrating section of the solvent separation column for distilling the extraction solvent from the methacrylic acid, and the side-cut liquid is heated to a low boiling point. The lower aliphatic carboxylic acids concentrated from the top of the column by being supplied to the separation column are separated and removed, while the low boiling point bottoms of the separation column mainly containing methacrylic acid are recycled to the upper stage of the recovery section of the solvent separation column. The present invention provides a characteristic method for purifying methacrylic acid.

The present invention will be explained in more detail below.

The aqueous methacrylic acid solution used in the present invention is not limited to any manufacturing method as long as it contains lower aliphatic carboxylic acids such as propionic acid, acrylic acid, and isoacetic acid; A product obtained by catalytically oxidizing rhein or isobutyraldehyde through one or two catalyst layers is used.

For example, an aqueous solution of methacrylic acid obtained by catalytic oxidation of tertiary butanol in two stages contains 31.5% methacrylic acid, 4.0% acetic acid, 0.2% propionic acid, and 0.7% acrylic acid.
, 0.1% isobutyric acid, pond water, low boiling point components and high boiling point components.

As the extraction solvent, known oils of methacrylic acid can be used, such as n-pentane, n-hexane, n-
hebutane, n-octane, cyclohexane, toluene,
Examples include ethylbenzene, isopropyl acetate, methyl methacrylate, etc.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, an aqueous methacrylic acid solution is supplied from a tube 1, and an extraction solvent is supplied from a tube 2 to an extraction column A, and methacrylic acid is extracted by self-flow contact. The raffinate is discharged from tube 3,
In some cases, the solvent dissolved therein is recovered by distillation and then subjected to wastewater treatment or incineration.

The extract containing methacrylic acid, lower aliphatic carboxylic acids, etc. is extracted from the pipe 4 and supplied to the solvent separation column B. Usually, a solvent with a lower boiling point than carboxylic acids is used as an extraction solvent, so the extraction solvent is passed through the solvent separation column, pipe 5 from the top of B.
It is separated and collected through the process. At this time, butyric acid is extracted from the top of the column together with the solvent and separated into the aqueous layer by decanter C, and is either extracted from pipe 7 and disposed of, or used as an absorption solvent for unreacted methacrolein in the second stage oxidation process. Ru. A portion of the oil layer in the decanter C is refluxed to the top of the solvent separation column B through a pipe 6, and the remainder is supplied to the acetic acid recovery column E through a pipe 8.

The lower aliphatic carbonic acids accumulated in the concentration section of the solvent separation column B are extracted from the middle stage 9 of the e-line section and supplied to the low boiling point separation column via the pipe 14. Low mowing) Pipe 1 from the top of the separation tower
2, concentrated propionic acid, acrylic acid and inbutyric acid are distilled out. On the other hand, the bottoms whose concentration of lower aliphatic carboxyl alcohol has decreased is recycled to the upper stage of the recovery section of the solvent separation column B via the pipe 11.

From the bottom of the solvent fraction column B, methacrylic acid whose content of lower aliphatic carboxylic acid has dropped below a practically acceptable concentration is taken out via pipe IO. By distilling this methacrylic acid using a conventional method to remove high-boiling components, highly purified purified methacrylic acid that meets market needs can be obtained.

Acetic acid mixed in the solvent is separated from the oil layer in the decanter 〇, which is supplied to the acetic acid recovery tower E, and the solvent is recycled to the extraction tower A through the pipe 2. On the other hand, acetic acid is discharged from pipe 13 at the bottom of the column and, like the acetic acid in pipe 7, is used to absorb methacrolein. However, depending on the type of solvent used, it may form a two-component azeotrope with acetic acid, so in such cases, acetic acid or the solvent may be azeotropically extracted from the top of the column, and the solvent may be recovered from the bottom of the column.

〔Example〕

EXAMPLES The present invention will be specifically described below with reference to Examples.

Example 1 21.0 parts of methacrylic acid, 4.2 parts of acetic acid, l of propion
vO, 05 parts, 7') l) An aqueous solution of methacrylic acid containing 0.5 parts of fluoric acid, 0.04 parts of isobutyric acid, 0.5 parts of aldehydes, and a small amount of other high-boiling substances was added to the methacrylic acid extraction tower A. Methacrylic acid is was extracted. Extraction of each acid is methacrylic acid,
99.2% propionic acid, acrylic acid and inbutyric acid
, acetic acid 18.7%. This methacrylic acid extract was fed to the solvent separation column B (column diameter 70
mm, perforated plate column with 30 stages). Operating conditions: 60 mmHg absolute pressure, 28°C at the top of the column, 95°C at the bottom, and a reflux ratio of 2.5. Heptane and water were recovered from the top of the column, the aqueous layer was separated in decanter C, and acetic acid was removed in acetic acid separation column E. was removed and recycled to extraction column A. On the other hand, from the middle stage of the concentration section of the solvent separation column B, the reflux ratio is 10, and the mixture consists of 44 parts of propionic acid, 34.6 parts of acrylic acid, 8.4 parts of isobutyric acid, 50.8 parts of methacrylic acid, and 0.7 parts of water. Ingredients 0.2kg/H
It was sidecanted at r and fed to a low-boiling separation column. The low-boiling fraction column was operated at an operating pressure of 50 mmHg (absolute pressure), a column top temperature of 75°C, and a column bottom temperature of 91.2°C, with a slag ratio of 5.
8.8 parts of propionic acid and 87.2 parts of acrylic acid were added from the top of the column.
parts, isobutyric acid 18.8 parts 1. *A distillate consisting of 1.4 parts and 1.8 parts of methacrylic acid was added to 0.017 kg/l
I extracted it with r. From the bottom of the tower, 95.3 parts of metagrilic acid,
A bottoms liquid of 0.18 kg/hr consisting of 0.5 parts of propionic acid, 3.1 parts of acrylic acid, and 0.7 parts of isoacetic acid was obtained.

This bottoms was recycled to the upper stage of the solvent fraction column B recovery section. Also, from the bottom of solvent separation column B, 99.9% of methacrylic acid was collected.
part, propionic acid 3 ppm, acrylic acid 6 ppm,
12 ppm of isobutyric acid and 0.59 kg/Hr of methacrylic acid containing 0.1 part of high boiling point substances were obtained.

Comparative Example 1 When methacrylic acid was purified in the same manner as in Example 1 in solvent separation column B without sidecarving the lower aliphatic carboxylic acid, the liquid composition obtained from the bottom of solvent separation column B was is 97.2 parts of methacrylic acid.

The contents were 0.2 part of propionic acid, 2.3 parts of acrylic acid, 0.2 part of isobutyric acid, and 0.1 part of pond water and high boiling point substances. This was purified by passing it through a low-boiling column and a high-temperature separation column according to the conventional method, and the purity of the obtained methacrylic acid was 99.8%, but it contained 30 ppm+ of propionic acid and 75 ppm+ of acrylic acid.
+, Contained 180 ppm of isobutyric acid.

〔Effect of the invention〕

According to the present invention, when purifying methacrylic acid by solvent extraction and distillation of an aqueous solution of methacrylic acid containing lower aliphatic carboxylic acids such as propionic acid, acrylic acid, and acetic acid as impurities, the solvent separation column By sidecanting the lower aliphatic carboxylic acids that accumulate in the carboxylic acid, distilling off the low-boiling fraction in the column, and recycling the bottom liquid to the solvent separation column, simple distillation as in the conventional technology is not sufficient to separate and remove the lower aliphatic carboxylic acids. It became possible to efficiently remove the lower aliphatic carboxylic acid, which had been difficult, and to easily obtain high-grade methacrylic acid.

[Brief explanation of drawings]

FIG. 1 is a flow sheet for explaining one embodiment of the present invention. A: Extraction tower B: Solvent separation tower C: Decanter D: Low-purity # tower E: Acetic acid separation tower Patent applicant Mitsui Toatsu Chemical Co., Ltd. Representative Tadashi Wakabayashi Figure 1

Claims (1)

[Claims] After extracting methacrylic acid with a solvent from an aqueous methacrylic acid solution containing lower aliphatic carboxylic acids such as propionic acid, acrylic acid, and isobutyric acid, the solvent is separated and recovered from the methacrylic acid, and crude methacrylic acid is obtained as a bottom liquid. When purifying by distillation, the lower aliphatic carboxylic acids are side-cut from the middle stage of the concentrating section of a solvent separation column for distilling and separating the extraction solvent from methacrylic acid, and this side-cut liquid is supplied to a low-boiling separation column. methacrylic acid, characterized in that the lower aliphatic carboxylic acids concentrated from the top of the column are separated and removed, while the low-boiling separation column bottoms mainly composed of methacrylic acid are recycled to the upper stage of the solvent separation column recovery section. Purification method.