JP3751657B2 - Method for separating acetic anhydride and acetic acid - Google Patents

Description

[0001]
[Industrial application fields]
The present invention provides a method for industrially advantageously separating both components from a mixture of acetic anhydride and acetic acid.
[0002]
[Prior art]
Acetic anhydride is known as a useful chemical agent. When industrially working with acetic anhydride, a mixture with acetic acid often occurs. For example, in the production of acetic anhydride, there is a reaction product solution in which ketene is thermally decomposed and absorbed into acetic acid, or a mixture of unreacted acetic anhydride and by-product acetic acid produced when acetic anhydride is used in a dehydration reaction. .
[0003]
[Problems to be solved by the invention]
Therefore, it is necessary to separate both components from this mixture. However, 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 distillation or extraction is a common practice, but there is almost no report on separation from acetic acid, which is a problem to be solved.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve such problems, the present inventor conducted distillation while introducing a mixture of acetic anhydride and acetic acid into the middle stage of the distillation column while introducing water from the top of the column, and purified acetic anhydride from the bottom of the column. In the recovery of acetic acid, it has been found that the separation of acetic anhydride and acetic acid can be carried out efficiently, and the present invention has been completed.
[0005]
In practicing the present invention, a mixture of acetic anhydride and acetic acid is charged into 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, distillation is efficiently performed, and a remarkable effect is exhibited that there is no concern about corrosion of the distillation tower. 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 surprisingly does not adversely affect acetic anhydride, and the initial effect is obtained. .
[0006]
If the amount of water introduced is too small, the effect of the present invention cannot be obtained, for example, the corrosion of the distillation column becomes severe. On the other hand, if the amount is too large, the loss of acetic anhydride becomes significant. The ratio is controlled to be 01 to 5% by weight, preferably 0.1 to 0.5% by weight.
[0007]
The mixture of acetic anhydride and acetic acid subjected to distillation is not particularly limited in its composition and production history, but acetic anhydride is 50 to 95% by weight, preferably 60 to 90% by weight, and acetic acid 5 to 50% by weight, preferably 10 to 40%. Mixtures with a composition by weight percentage are preferred.
[0008]
The distillation column used in carrying out the method of the present invention may be any columnar column type, packed column type, spray type, falling film as long as it can be any of atmospheric distillation and vacuum distillation. Any structure such as a formula and a stirring liquid film type can be mentioned, but those having a small pressure loss are desirable, and a packed tower type and a plate tower type are usually practical.
The number of theoretical plates in the distillation column is preferably about 20 to 70.
[0009]
In the distillation, a mixture of acetic anhydride and acetic acid is supplied to the middle stage of the distillation column, that is, 10 to 40 stages from the top, and water is introduced from the top (0 to 30 stages). By heating the reboiler at the bottom, high-purity acetic anhydride purified from the bottom is obtained. An acetic acid solution containing acetic anhydride is distilled from the top of the column. A reflux ratio of about 1 to 10 is practical, and the reflux liquid is recycled to the top of the column.
[0010]
The amount of water added is about 100 to 100, the amount of bottoms discharged is 30 to 95, and the amount of distillates at the top of the column is about 5 to 70.
[0011]
[Operation]
By separating the mixture of acetic anhydride and acetic acid into the middle column of the distillation column, introducing water from the top of the column, and collecting purified acetic anhydride from the bottom of the column, acetic anhydride and acetic acid can be separated efficiently. Is called.
[0012]
【Example】
Next, 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) is 100 kg per hour in the 15th stage (from the top) of a plate-type distillation column (manufactured by SUS) having 30 theoretical plates. Water was supplied at a rate of 1 kg per hour from the top of the column to the second stage. Distillation was performed under normal pressure at a reflux ratio of 4.
[0013]
Acetic anhydride (purity 99.5% or more) was obtained from the bottom of the column at a rate of 72 kg / h. The composition of the column top distillate was a mixture of acetic anhydride 30% by weight and acetic acid 70% by weight.
At this time, the column top temperature was 122 ° C., the column bottom temperature was 149 ° C., and there was no concern about corrosion inside the distillation column.
[0014]
Example 2
The same experiment as in Example 1 was conducted except that the mixture of acetic anhydride and acetic acid (composition of 80% by weight acetic anhydride and 20% by weight acetic acid) was changed to 20 plates and the amount of water was changed to 0.6 kg. Acetic anhydride (purity 99.5% or more) was obtained from the bottom at a rate of 72 kg per hour. The composition of the column top distillate was a mixture of acetic anhydride 30% by weight and acetic acid 70% by weight. At this time, the column top temperature was 122 ° C., the column bottom temperature was 149 ° C., and there was no concern about corrosion inside the distillation column.
[0015]
Control Example 1
When the use of water was omitted in Example 1, the purity of acetic anhydride was reduced to 98.0%, and when the operation was continued for 10 days, metal corrosion was observed near the top of the distillation column.
[0016]
【The invention's effect】
In the present invention, the distillation column is not corroded by performing distillation while introducing a mixture of acetic anhydride and acetic acid into the middle stage of the distillation column, and introducing purified acetic anhydride from the bottom of the column while introducing water from the top of the column. Separation of acetic anhydride and acetic acid is performed efficiently.

Claims (1)

A method for separating acetic anhydride and acetic acid, comprising performing distillation while introducing a mixture of acetic anhydride and acetic acid into the middle stage of the distillation column and introducing water from the top of the column respectively, and collecting purified acetic anhydride from the bottom of the column.