JPH0753685B2 - Recovery method of by-product acetic acid in methacrylic acid production - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering by-product acetic acid in the production of methacrylic acid.

Prior Art When isobutylene, tertiary butanol, isobutyraldehyde or methacrolein is reacted with a gas containing molecular oxygen in the gas phase in the presence of an oxidation catalyst, acetic acid, methacrolein, acrylic acid in addition to methacrylic acid which is a target product A high temperature reaction product gas consisting of carbon monoxide, carbon dioxide, unreacted oxygen, a large amount of nitrogen and water is obtained. The methacrylic acid aqueous solution obtained by quenching the produced gas by an appropriate method is distilled or stripped to remove light boiling substances such as methacrolein, and then extracted by selectively extracting methacrylic acid with an appropriate solvent. A method is known in which the solvent is further separated from the liquid by distillation to obtain methacrylic acid.

On the other hand, the extraction residual liquid contains a large amount of by-produced acetic acid-based organic matter, and the waste liquid discharged outside the system is incinerated or biochemically treated with activated sludge. Is being processed. Further, since acetic acid is used as an absorbent of methacrolein, a method of recovering acetic acid by-product by further distilling and / or extracting the extract (Japanese Patent Laid-Open No. 56-92831) and the like are known.

Problems to be Solved by the Invention Acetic acid contained in the reaction gas is by-produced in a large amount of 20 to 40 mol with respect to 100 mol of methacrylic acid, and partially mixed in the extraction liquid side when selectively extracting methacrylic acid. However, most of acetic acid remains on the extraction residual liquid side together with other organic substances.

In the production of methacrylic acid, acetic acid can be used as an absorbing solvent for methacrolein as described above, and it is useful to recover this.

The concentration of acetic acid in the extraction residual liquid in the recovery of acetic acid is as low as 1 to 10% by weight, and high boiling substances such as terephthalic acid and methacrylic acid polymer are also included as non-volatile residues. Therefore, the method of collecting acetic acid by distilling with a large amount of water by the distillation method requires a significantly large amount of energy,
Furthermore, it cannot be said to be an industrially effective method due to problems such as scaling of the reboiler and clogging of the tower due to precipitation of solids.

Also, when extracting, because the acetic acid concentration is low,
It is necessary to use an extraction solvent with a considerably high extraction power, and an extraction solvent with a high extraction power can easily extract organic substances other than the target acetic acid, and especially non-volatile residues are polymerized, clogged, and reboiled during solvent separation after extraction. The use of an extraction solvent that extracts even the non-volatile residue was not preferable because it is likely to cause scaling.

Means for Solving the Problems The inventors of the present invention have conducted diligent research to solve the above problems, and found that the extraction solvent has a large extraction power of acetic acid and a small extraction power of non-volatile residue. The present invention has been completed.

That is, the method of recovering by-product acetic acid in the production of methacrylic acid of the present invention is carried out by reacting isobutylene, tertiary butanol, isobutyraldehyde or methacrolein with a gas containing molecular oxygen in the presence of an oxidation catalyst to carry out methacrylic acid reaction. In the method for producing an acid, after removing the light boiling substance from the methacrylic acid aqueous solution obtained by rapidly cooling the reaction product gas,
To recover acetic acid by extracting ethyl acetate as a by-product acetic acid by adding ethylbenzene to the extraction residual liquid obtained by extracting and separating methacrylic acid and azeotropically distilling the extract liquid and extracting the distillate with water. It is characterized by.

In the present invention, the methacrylic acid aqueous solution obtained by quenching the reaction product gas is mainly composed of methacrylic acid, and acetic acid, formic acid, propionic acid, acrylic acid, methacrolein, acetone, other aldehydes, and organic acid. An aqueous solution containing the like.

The methacrylic acid aqueous solution is subjected to distillation or stripping to remove light boiling substances such as methacrolein, and heptane, octane, toluene, and xylene are selectively extracted with methacrylic acid as a solvent or a mixture of several solvents. Then, the solvent is distilled off from the extract to obtain methacrylic acid.

What is important in the present invention is to extract and recover the by-product acetic acid from ethyl benzene as an extraction solvent from the extraction residual liquid containing the by-product acetic acid as a main component after the extraction and separation of methacrylic acid.

Generally, various solvents such as ethylbenzene, toluene, and ethyl acetate can be used as the extraction solvent, but generally, those having a high distribution rate of acetic acid also have a high distribution rate of the non-volatile residue.
However, as shown in FIG. 1, ethylbenzene is applicable to the present invention because it has a high acetic acid distribution rate and a low non-volatile residue distribution rate.

In the extraction of acetic acid in the present invention, the ratio of the flow rates of the extractant (hereinafter abbreviated as S) and the raw material (hereinafter abbreviated as F) is S / F by using an extraction device such as a rotary disk extraction tower, a mixer / settler and the like.
= 0.3 to 3.0, preferably S / F = 1.0 to 2.0, and the extraction temperature at that time is 5 to 50 ° C, preferably 15 to 35 ° C, and the extraction can be completed.

Using ethylbenzene for the extraction of acetic acid according to the invention
Needless to say that the above-mentioned acetic acid has a high partition rate and the nonvolatile residue has a low partition rate, ethylbenzene can be azeotropically distilled with acetic acid in the separation of the acetic acid extract, and the content of the raffinate in the raffinate It is optimally used because it does not azeotrope with other organic substances such as methacrylic acid and acrylic acid.

The extract extracted with ethylbenzene is subjected to azeotropic distillation in a distillation column, and the resulting acetic acid / ethylbenzene mixed liquid is extracted with water in an extraction device similar to the above rotary disk extraction column, mixer / settler, etc. As S /
F = 0.1-1.0, preferably S / F = 0.3-0.6, temperature 10-40 ° C
To obtain a 30 to 60% by weight aqueous acetic acid solution.

The ethylbenzene from which the acetic acid has been separated is circulated and used as an acetic acid extraction solvent together with ethylbenzene in the bottom liquid of the azeotropic distillation column.

The concentration of the obtained acetic acid aqueous solution may be adjusted by distillation or the like, if necessary.

Description of the Drawings The following describes in more detail with reference to the drawings.

FIG. 1 shows the distribution ratio of acetic acid and non-volatile residue in the extraction residual liquid in the acetic acid extraction column of each extraction solvent. Second
The figure shows an example of an embodiment of a method for recovering by-product acetic acid in the production of methacrylic acid according to the present invention.

Line (5) of methacrylic acid aqueous solution from which light boiling substances have been removed
More is supplied to the methacrylic acid extraction tower (1). An extraction solvent such as heptane is supplied from a line (6) to selectively extract methacrylic acid and separate it from the top of the column through a line (7). The extraction residual liquid withdrawn from the bottom of the methacrylic acid extraction tower (1) is supplied in countercurrent to the upper part of the acetic acid extraction tower (2) via the line (8) and ethylbenzene from the line (9) to the lower part. Extract acetic acid.

The extract is sent from the top of the acetic acid extraction column (2) to the distillation column (3) via the line (10) and azeotropically distilled to obtain an azeotropic mixture of acetic acid and ethylbenzene of about 7: 3 as a distillate. , Acetic acid recovery column (4) from the top of the distillation column (3) via line (12)
Send to the bottom of. The remaining ethylbenzene is sent from the bottom of the distillation column (3) to the acetic acid extraction column (2) again as an acetic acid extraction solvent through the lines (13) and (9).

Acetic acid is extracted with water supplied from the line (14) to the upper part of the acetic acid recovery column (4), and is separated into an oil layer and an aqueous layer to obtain an aqueous acetic acid solution from the column bottom through the line (16). The ethylbenzene separated from the top of the acetic acid recovery column (4) merges with the line (13) via the line (15) and is recycled as an extractant to the acetic acid extraction column (2).

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

Example 1 Using a SUS304 fixed bed reactor, pressure was applied in the presence of an oxidation catalyst.
At 0.5 kg / cm ₂ · G and a temperature of 305 ° C, the reaction product gas obtained by the gas phase catalytic reaction of methacrolein and air was rapidly cooled to 15 ° C. Acid 26.2% by weight, formic acid 1.3% by weight, acetic acid
4.1% by weight, propionic acid, 0.5% by weight, acrylic acid 0.4
% By weight, 2.5% by weight of methacrolein, 0.3% by weight of acetone, 0.4% by weight of other aldehydes, 5% by weight of other organic acids and 59.5% by weight of water. After stripping methacrolein and acetone from this aqueous solution, supply them to the upper part of the methacrylic acid extraction column (1) shown in Fig. 2 at 10 kg / hr, and from the lower part to supply heptane at 10 kg / hr for countercurrent contact. , 13.13 kg / hr from the top of the tower, 6.87 kg / h from the bottom of the tower
Obtained r residual solution. The composition of this raffinate is methacrylic acid.
0.4 wt%, acetic acid 6.0 wt%, acrylic acid 0.4 wt%, water 8
It was 7.4% by weight and other 5.8% by weight.

The extraction residual liquid was supplied at 6.87 kg / hr from the upper part of the acetic acid extraction column (2) and ethylbenzene was supplied from the lower part at 10.3 kg / hr for countercurrent contact. Acetic acid extraction column (2) Extraction liquid from the top 10.57k
The acetic acid extraction rate at this time obtained at g / hr was 55.0%, and the extract was yellow.

The extract was supplied to a distillation column (3) for azeotropic distillation.
The composition of the azeotropic distillate obtained from the top of the column at a rate of 0.34 kg / hr was 66% by weight of acetic acid and 34% by weight of ethylbenzene.

The azeotropic distillate thus obtained was placed at the bottom of the acetic acid recovery column (4) at 0.34
Water was supplied at a rate of 0.17 kg / hr from the top, and 0.39 kg / hr of an acetic acid aqueous solution in which ethylbenzene was separated was obtained from the bottom of the column.
Almost no impurities were detected in the obtained acetic acid aqueous solution,
At this time, the acetic acid concentration was 55.6% by weight. Both the extraction column and the distillation column were able to perform stable continuous operation for 7 days, and scaling inside the column was hardly observed.

Comparative Example 1 Acetic acid was extracted in the same manner as in Example 1 except that ethylbenzene was changed to ethyl acetate, and the acetic acid extraction rate was 65%.
The extract was dark brown. When this extract was distilled in a distillation column (3), solid substances accumulated at the bottom of the column were observed, and after 24 hours, the solids were clogged and the operation could not be performed.

Comparative Example 2 As a result of extracting acetic acid in the same manner as in Example 1 except that ethylbenzene was changed to toluene, the extraction rate of acetic acid was 8.3.
%Met.

EFFECTS OF THE INVENTION According to the present invention, acetic acid conventionally discarded as a waste liquid can be efficiently recovered as a high-purity aqueous acetic acid solution,
It is very beneficial to industry.

[Brief description of drawings]

FIG. 1 shows the distribution ratio of acetic acid and non-volatile residue in the extraction residual liquid in the acetic acid extraction column of each extraction solvent. Second
The figure shows an example of an embodiment of a method for recovering by-product acetic acid in the production of methacrylic acid according to the present invention. (1) Methacrylic acid extraction tower, (2) acetic acid extraction tower (3) distillation tower, (4) acetic acid recovery tower, (5) to (16) each line

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hirozo Segawa 2-1 Kyowa-cho, Nakajo-machi, Kitakanbara-gun, Niigata Prefecture (72) Inventor Katsuji Yoguchi 4-7-4-411 Kamo, Takaishi-shi, Osaka (56) Reference Document JP-A-56-90034 (JP, A)

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. After removing light-boiling substances from the aqueous methacrylic acid solution obtained by extraction, ethylbenzene was added as an extraction solvent to the extraction residue obtained by extracting and separating methacrylic acid to extract by-product acetic acid, and the extract was azeotropically distilled to obtain. A method for recovering by-product acetic acid in the production of methacrylic acid, characterized in that acetic acid is recovered by extracting the distillate obtained by extraction with water.