JPH0138095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for extracting and separating acetic acid from an aqueous acetic acid solution.

Generally, when extracting and separating acetic acid from its aqueous solution, the most important thing is the selection of an extractant, and among the properties necessary for an extractant, the most important one is good distribution of acetic acid. Lower alkyl esters such as ethyl acetate, ketones such as methyl ethyl ketone, methyl isobutyl ketone, methyl cyclohexanones, and isophorone, and alcohols such as butanol, isoamyl alcohol, and cyclohexanol are known as solvents with good distribution. However, solvents that have a large partition coefficient relative to acetic acid generally have a high mutual solubility in water, and as an extractant, in addition to having a large partition coefficient, it is necessary to have as little compatibility with water as possible to enable efficient extraction operations. is necessary. Furthermore, when separating acetic acid from the extract, it is necessary that the separation operation be sufficiently easy. Up to now, no extraction solvent for acetic acid has been known that is fully satisfactory in these respects. A method has also been proposed that uses a mixed solvent such as isopropyl ether/ethyl acetate to compensate for the drawbacks of a single solvent, but this is a combination of solvents with a lower boiling point than acetic acid, and the entire amount must be evaporated during the separation process. From the viewpoint of energy conservation, it has been difficult to significantly improve the performance as an extractant.

In view of the current situation, the present inventor conducted studies with the aim of providing a fully satisfactory method for separating and recovering acetic acid with extremely low energy. The present invention was completed based on the discovery that excellent results can be obtained by focusing on three boiling points and using a mixed solvent that combines these under specific conditions.

That is, the present invention relates to an acetic acid recovery method in which acetic acid is extracted from an aqueous solution using a mixed solvent and separated from the extract by distillation, and the method is characterized in that the mixed solvent is an ethyl acetate/diisobutyl ketone system. It is.

Although ethyl acetate has a large partition coefficient and a relatively large azeotrope with water, its selectivity is low, and therefore a large amount of water is carried into the extract, consuming a large amount of energy in the dehydration process.

In order to compensate for these drawbacks of ethyl acetate and improve the selectivity of ethyl acetate, the present invention uses a mixed solvent containing diisobutyl ketone, a solvent with a higher boiling point than acetic acid, as the second solvent component.
According to the present invention, by combining ethyl acetate, which is a solvent with a high partition coefficient and a low boiling point, and diisobutyl ketone, which is a solvent with a high selectivity and a high boiling point, a mixed solvent with a well-balanced distribution coefficient and selectivity can be obtained. Can be done. Although there are no particular restrictions on the mixing ratio, it is preferable to use more diisobutyl ketone, which has a higher boiling point than acetic acid, for the purpose of reducing the evaporation heat load of the solvent. Usually the proportion of ethyl acetate in the mixed solvent is between 5 and 50% by weight, especially between 20 and 30%.

When using a mixed solvent of ethyl acetate/diisobutyl ketone, it is only necessary to evaporate water and ethyl acetate in a dehydration tower, and diisobutyl ketone is extracted together with acetic acid into the pot, separated from acetic acid in an acetic acid recovery tower, and recycled as is. used.

Next, using the schematic flow sheet shown in Figure 1,
A case will be described in which the method of the present invention is carried out continuously. The treated stock solution is fed into the extraction tower from line 1,
The mixed solvent is charged countercurrently from line 2 to the extraction column. The extract extracted from line 3 contains acetic acid and saturated water, so it is first charged to a dehydration tower. In the dehydration tower, ethyl acetate () and water equivalent to the saturated solubility are removed from the top of the tower.
A mixture of diisobutyl ketone (2) and acetic acid is withdrawn from the bottom of the column via line 6. The dehydration tower liquid is charged to the acetic acid recovery tower through line 6, and acetic acid is recovered from the top of the tower. The concentration of acetic acid is considerably higher than that of Therefore, the minimum reflux ratio can be small, and the amount of steam required in the acetic acid recovery tower can be small.
From the bottom of the tower, diisobutyl ketone () is in line 1.
1, mixed with ethyl acetate () extracted from the top of the dehydration tower, and recycled to the extraction tower as a circulating extraction solvent. The treated wastewater from which acetic acid has been extracted in the extraction tower is extracted from line 4 and charged into a solvent recovery tower, where a trace amount of solvent dissolved in the wastewater is recovered from the top of the tower. The recovered solvent is returned to the extraction solvent circulation line 2 via line 12.

As shown by the broken line in FIG. 1, as reflux to the dehydration tower, diisobutyl ketone () extracted from the bottom of the next acetic acid recovery tower is refluxed to the decanter, not as the upper layer of the distillate in the decanter. It is also possible to reduce the solubility of water in the upper layer of the decanter and reflux it.

Example 1 Acetic acid was extracted from a 27 wt % acetic acid aqueous solution using a mixed solvent of diisobutyl ketone/ethyl acetate (70/30 wt ratio). As a result, if the amount of solvent (by weight) is three times that of the acetic acid aqueous solution, the theoretical plate 34
It was found that the acetic acid concentration in ruffinate could be lowered to 0.06 wt% by step. The composition of the extract at this time was 3.29wt% water, 8.22wt% acetic acid, and 89.29wt% solvent.
It was hot.

Example 2 A collective sample of the extract obtained in Example 1 was used to perform dehydration distillation. At the 25th stage of the glass old tower (40φ x 40N), 480
The extract liquid was charged at a rate of g/H. The composition at this time was 7.42 wt% acetic acid, 2.39 wt% water, 27.06 wt% ethyl acetate, and 63.13 wt% diisobutyl ketone. The top pressure was 330 mmHg, and the reflux ratio was 0.4 (wt
0.01wt% acetic acid from the top of the tower
Distillate of 6.62wt% water and 93.37wt% ethyl acetate is 137
g/H. In addition, from the bottom of the can, 343 g/h of canned liquid containing 0.01 wt% ethyl acetate, 0.08 wt% water, 10.77 wt% acetic acid, and 89.14 wt% diisobutyl ketone was obtained.
Obtained with.

Example 3 The same glass old tower as in Example 2
In the 20th stage, a liquid containing 1.15 wt% acetic acid and 88.5 wt% diisobutyl ketone, which had been adjusted to have the same composition as the flask liquid obtained in Example 2, was charged, and acetic acid and diisobutyl ketone were separated and distilled. Bottom pressure 200
When operated at mmHg and a reflux ratio of 1.2 (wt ratio), it was possible to separate diisobutyl ketone in the distillate at 0.005 wt% and acetic acid at the bottom of the can at 0.5 wt%.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an example of continuous implementation of the present invention.

Claims (1)

[Claims] 1. A method for recovering acetic acid, which comprises extracting acetic acid from an aqueous solution using a mixed solvent of ethyl acetate and diisobutyl ketone, and separating acetic acid from the extract by distillation.