JPH08283192A - Separation of acetic anhydride from acetic acid - Google Patents

Abstract

PURPOSE: To industrially advantageously separate acetic anhydride and acetic acid from their mixture. CONSTITUTION: A mixture of acetic anhydride and acetic acid is introduced into an intermediate stage of a distillation column and water is introduced into the column from its top and the mixture is distilled to recover purified acetic anhydride from the column bottom.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention provides a method for industrially separating both components from a mixture of acetic anhydride and acetic acid.

[0002]

Acetic anhydride is known as a useful chemical agent. When industrially handling acetic anhydride, a mixture with acetic acid is often generated. For example, in the production of acetic anhydride, there are a reaction product solution in the method of thermally decomposing ketene and absorbing it in acetic acid, a mixture of unreacted acetic anhydride and by-product acetic acid produced when acetic anhydride is used in a dehydration reaction, and the like. .

[0003]

Therefore, it is necessary to separate both components from this mixture, but since acetic anhydride and acetic acid have similar properties, efficient separation is not easy. Purification of acetic anhydride from a mixture with various compounds by a distillation method or an extraction method is often performed, but there is almost no report on separation from acetic acid, and it is a problem to be solved.

[0004]

Means for Solving the Problems As a result of intensive research for solving the above problems, the present inventor distills a mixture of acetic anhydride and acetic acid in the middle stage of the distillation column while introducing water from the top of the column respectively. When the purified acetic anhydride was recovered from the column bottom by performing the above, it was found that the acetic anhydride and acetic acid can be efficiently separated, and the present invention has been completed.

In carrying out the present invention, a mixture of acetic anhydride and acetic acid is charged in the middle stage of the distillation column, and the greatest feature of the present invention is that water is introduced from the top of the distillation column. Due to the presence of such water, the distillation is efficiently performed, and a remarkable effect is exhibited without any fear of corrosion of the distillation column. The presence of water in the handling of acetic anhydride is not preferable from general chemical common sense, but in the present invention, the presence of water does not adversely affect acetic anhydride and the initial effect is obtained. .

If the amount of water introduced is too small, the effects of the present invention cannot be obtained, such as the corrosion of the distillation column becomes severe. On the other hand, if the amount of water is too large, the loss of acetic anhydride becomes remarkable. Is 0.01 to 5% by weight, preferably 0.1
The proportion is controlled to be 0.5% by weight.

The mixture of acetic anhydride and acetic acid to be distilled is not particularly limited in its composition and production history.
0-95% by weight, preferably 60-90% by weight, acetic acid 5-
Mixtures having a composition in the proportion of 50% by weight, preferably 10-40% by weight, are advantageous.

The distillation column used in carrying out the method of the present invention may be any column, and may be a column column type, a packed column type, or a spray type column, as long as it can perform either atmospheric distillation or reduced pressure distillation. The falling film type, the agitated liquid film type, and the like may be used, but those having a small pressure loss are desirable, and the packed column type and the stage column type are usually practical. The number of theoretical plates in the distillation column is 2
About 0 to 70 steps is desirable.

In the distillation, a mixture of acetic anhydride and acetic acid is fed from the middle stage of the distillation column, that is, from the top to the 40th stage, and water is introduced from the top (the 0th to 30th stage). By heating the reboiler at the bottom of the column, highly purified acetic anhydride is obtained from the bottom of the column. An acetic acid solution containing acetic anhydride distills from the top of the column. A reflux ratio of about 1 to 10 is practical,
The reflux liquid is recycled to the top of the tower.

The amount of water added was 100% with respect to the charged amount of the mixture of 100.
2 to 10, the bottom bottom output is 30 to 95, and the top distillation is 5
It is about 70.

[0011]

[Operation] Separation of acetic anhydride and acetic acid is performed by distilling a mixture of acetic anhydride and acetic acid in the middle stage of the distillation column while introducing water from the top of the column and recovering purified acetic anhydride from the bottom of the column. Is done efficiently.

[0012]

EXAMPLES The present invention will be described in more detail with reference to examples. Example 1 A mixture of acetic anhydride and acetic acid (composition of 80% by weight of acetic anhydride and 20% by weight of acetic acid) was fed to the 15th plate (from the top of a column) of a plate distillation column (made of SUS) having a theoretical plate number of 30 plates. 100 kg per hour
Of water at the rate of 1 K / h on the second stage from the top of the tower
It was supplied at a rate of g. Distillation was carried out under normal pressure with a reflux ratio of 4.

Acetic anhydride (purity 99.5% or more) was obtained from the bottom of the column at a rate of 72 kg per hour. The composition of the overhead distillate was a mixture of 30% by weight of acetic anhydride and 70% by weight of acetic acid. At this time, the tower top temperature was 122 ° C and the tower bottom temperature was 149 ° C.
Moreover, there was no concern about corrosion inside the distillation column.

Example 2 Example 1 was repeated except that the mixing stage of a mixture of acetic anhydride and acetic acid (composition of 80% by weight of acetic anhydride and 20% by weight of acetic acid) was changed to 20, and the amount of water added was changed to 0.6 kg. Do the same experiment,
Acetic anhydride (purity of 99.5% or more) is added from the bottom of the tower 72 per hour.
It was obtained in the proportion of Kg. The composition of the overhead distillate was a mixture of 30% by weight of acetic anhydride and 70% by weight of acetic acid. At this time, the column top temperature was 122 ° C and the column bottom temperature was 149 ° C, and there was no concern about corrosion inside the distillation column.

Comparative Example 1 When the use of water was omitted in Example 1, the purity of acetic anhydride decreased to 98.0%, and metal corrosion was observed near the upper part of the distillation column when the operation was continued for 10 days. .

[0016]

INDUSTRIAL APPLICABILITY In the present invention, a mixture of acetic anhydride and acetic acid is introduced into the middle stage of the distillation column and distilled while introducing water from the top of the column, and purified acetic anhydride is collected from the bottom of the column to obtain a distillation column. No corrosion and efficient separation of acetic anhydride and acetic acid.

Claims (1)

[Claims] 1. Distillation is carried out while introducing a mixture of acetic anhydride and acetic acid into the middle stage of the distillation column, respectively introducing water from the top of the column,
A method for separating acetic anhydride and acetic acid, which comprises recovering purified acetic anhydride from the bottom of the column.