JPH0948744A - Purification of acetic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To collect purified acetic acid from the mixture of acetic acid and water in high efficiency. SOLUTION: After azeotropic distillation of the mixture 1 of acetic acid and water in the presence of the 1st azeotropic agent using the 1st distillation tower 2, the concentrated water containing acetic acid is extracted from the bottom of the tower as first tower bottom liquid 14. The 1st tower bottom liquid 14 is purified by azeotropic distillation in second distillation tower 15 in the presence of the 2nd azeotropic agent which has a lowest azeotropic temperature with water lower than that of the 1st azeotropic agent and the dehydrated pure acetic acid 27 is collected from the tower bottom.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying acetic acid which efficiently recovers purified acetic acid from a mixture of acetic acid and water with low energy.

[0002]

2. Description of the Related Art Conventionally, as an industrial production method of acetic acid, a fermentation method, a carbonylation method of methanol by a liquid phase homogeneous reaction using rhodium and iodine as catalysts, manganese naphthenate, cobalt naphthenate, nickel naphthenate, etc. Oxidation of hydrocarbons such as butane and naphtha by solid-gas heterogeneous reaction using oil-soluble salt catalyst, and oxidization of ethylene to form acetaldehyde, and then acetaldehyde is converted to manganese acetate or copper acetate and cobalt acetate. A two-stage ethylene oxidation method in which acetic acid is obtained by oxidizing in a liquid phase homogeneous system using a mixture of a catalyst and ethylene, and a method in which acetic acid is synthesized by reacting ethylene and oxygen in the gas phase with metallic palladium and heteropolyacid as a main catalyst. (Japanese Patent Application No. 6-65161
No.) are known.

By any of these methods, the reaction product contains water in addition to acetic acid. Distillation is generally used to industrially obtain purified acetic acid from a mixture of acetic acid and water. However, when water is separated from acetic acid by a conventional distillation method, the boiling points of water and acetic acid are close to each other, so that not only is a distillation column with a high number of stages of 70 or more required, but also such a distillation column is required. Even if it is used, since the relative volatility of water with respect to acetic acid is small, it is necessary to make the reflux ratio at the top of the column sufficiently large, resulting in extremely poor efficiency. Moreover, since water having a large latent heat of vaporization is distilled from the top of the column, a large amount of energy is consumed for operating the distillation column. In particular, when the concentration of water in the raw material mixture is high, the volumetric efficiency of the apparatus is reduced and the production capacity of purified acetic acid is significantly reduced.

In order to solve this problem, when distilling a mixture of acetic acid and water (hereinafter referred to as "raw material liquid"), in the presence of a suitable azeotropic agent which forms a minimum azeotropic mixture with water. A method has been proposed in which azeotropic distillation is performed, a minimum azeotropic mixture of water and an azeotropic agent is distilled from the top of the column, and concentrated acetic acid is obtained from the bottom of the column (for example, Japanese Patent Publication No. 43-16965). Japanese Patent Publication No. 61-31091, etc.). These methods of separating water by azeotropic distillation using an azeotropic agent not only reduce the reflux ratio at the top of the column to save energy required for distillation, but also improve the recovery rate of purified acetic acid from the bottom of the column. There are advantages.

[0005]

However, even if the above-mentioned conventionally known azeotropic distillation method is used to obtain highly purified acetic acid, the reflux ratio is inevitably large, and therefore, a large amount is required. It requires a large amount of heat, and if it is attempted to prevent the azeotropic agent from mixing with the acetic acid at the bottom of the column, the recovery rate must be reduced. Therefore, an object of the present invention is to provide a method for purifying acetic acid from a raw material liquid (mixture of acetic acid and water) to obtain purified acetic acid efficiently with low energy.

[0006]

[Means for Solving the Problems] The above-mentioned problems are solved by introducing a raw material liquid into a first distillation column and performing azeotropic distillation in the presence of a first azeotropic agent capable of forming a minimum azeotropic mixture with water. , The overhead gas distilled from the top of the tower is cooled and condensed, and the obtained overhead condensed liquid is liquid-liquid separated into a water-rich rich water phase and an azeotropic agent-rich poor water phase,
At least a part of this rich water phase is discharged out of the system, at least a part of the poor water phase is refluxed to the first distillation column, and the hydrous acetic acid concentrated from the bottom of the first distillation column is used as the first bottom liquid. The first bottom liquid can be introduced into a second distillation column to form a minimum azeotrope with water, and the azeotrope is the minimum azeotrope of the first azeotropic agent and water. Azeotropically distilling in the presence of a second azeotrope having a lower minimum azeotrope temperature, cooling the overhead gas leaving the overhead to condense, the resulting overhead condensate being rich in water Liquid-liquid separation into a rich water phase and a poor water phase rich in azeotropic agent, and discharging at least part of this rich water phase out of the system,
The problem can be solved by providing a method for purifying acetic acid, in which at least a part of the poor water phase is refluxed to the second distillation column to obtain dehydrated purified acetic acid from the bottom of the second distillation column. In the above,
The water concentration of the first tower bottom liquid is preferably concentrated to be in the range of 1% by weight to 15% by weight.

The above-mentioned first azeotropic agent is an alkyl ester, a ketone, an alcohol, an aromatic hydrocarbon, an ether and a polyhydric alcohol derivative having a boiling point of 100 ° C. or higher which can be separated from water by liquid-liquid separation. It is preferably at least one selected from the group consisting of The second azeotropic agent is composed of alkyl esters, ketones, alcohols, aromatic hydrocarbons, alicyclic hydrocarbons and ethers which can be liquid-liquid separated from water and have a boiling point of less than 100 ° C. It is preferably one or more selected from the group.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a process chart showing an embodiment of the present invention. The equipment of this process is
It comprises a first distillation column 2 and a second distillation column 15. The first distillation column 2 is provided with a cooler 6 and a decanter 7 at the top of the column and a reboiler 13 at the bottom of the column. Similarly, in the second distillation column 15, a condenser 19 and a decanter 20 are provided at the top of the column.
A reboiler 26 is attached to the bottom of the tower.

In FIG. 1, first, a raw material liquid 1 which is a mixture of acetic acid and water is introduced into a first distillation column 2 and a reboiler 1
It is heated by 3 to the distillation temperature. The first distillation column 2 is further provided with a first azeotropic agent (butyl acetate in this embodiment,
(Boiling point 126.2 ° C.) is supplied as a liquid from line 3 to the vicinity of the top of the column. This first azeotropic agent azeotropes with water in the first distillation tower 2, and the overhead gas 5 distilled from the overhead is cooled by a cooler 6 and condensed, and introduced into a decanter 7 as an overhead condensate. To be done.

The decanter 7 has a weir 8 which divides the lower part of the tank into a compartment 9 and a compartment 10. The overhead condensate introduced into the decanter 7 is introduced into one of the compartments 10,
Here, a heavy water phase having a large specific gravity containing water as a main component and a part of the first azeotropic agent (butyl acetate), and a poor water phase having a small specific gravity containing a first azeotropic agent as a main component and a part of water The liquid and liquid are separated by the difference in specific gravity. When at least a part of the rich water phase is continuously extracted from the bottom of the compartment 10 via the line 11 and the height of the interface between the rich water phase and the poor water phase is adjusted, only the poor water phase causes the weir 8 to flow. It goes over and flows into the other compartment 9. At least a part of the poor water phase rich in the first azeotropic agent flowing into the compartment 9 is refluxed to the first distillation column 2 via the line 3. In some cases, part of the rich water phase is also refluxed from the line 4 near the top of the first distillation column by selecting a supply stage.

At this time, since a part of the first azeotropic agent is dissolved in the enriched water phase discharged from the line 11 to the outside of the system, the amount of the first azeotropic agent refluxed to the first distillation column 2 is increased. Will gradually run out. Then, the additional first azeotropic agent is introduced into the decanter 7 via the line 12 to replenish the shortage.

By azeotropic distillation in the first distillation column 2 (hereinafter referred to as "first distillation"), a large amount of water contained in the raw material liquid 1 is discharged from the line 11, and the first distillation is performed. From the bottom of the tower 2, concentrated hydrous acetic acid is withdrawn as the first bottom liquid 14. By this first distillation,
The first bottom liquid 14 is concentrated until the water concentration falls within the range of 1% by weight to 15% by weight.

Next, the first bottom liquid 14 is introduced into the second distillation column 15 in order to further concentrate and recover purified acetic acid. The first bottom liquid 14 introduced into the second distillation column 15 is heated to the distillation temperature by the reboiler 26. Further, in the second distillation column 2, a second azeotropic agent (isopropyl acetate in this embodiment, boiling point 88.6 ° C.) is used as a liquid in a line 16
Is supplied from near the top of the tower.

The second azeotropic agent (isopropyl acetate) is
A minimum azeotrope can be formed with water, and the azeotrope has a lower minimum azeotrope temperature than the lowest azeotrope of the first azeotropic agent (butyl acetate) and water. That is, the minimum azeotropic temperature of the first azeotropic agent (butyl acetate) and water under standard pressure is 90.2 ° C, while that of the second azeotropic agent (isopropyl acetate) is 76.6 ° C. is there.

The second azeotropic agent azeotropes with water in the second distillation column 15, and the overhead gas 18 distilled from the overhead is cooled by the cooler 19 and condensed, and the decanter 20 as the overhead condensate is obtained. Will be introduced to. Like the decanter 7, the decanter 20 has a weir 21 that divides the lower part of the tank into a compartment 22 and a compartment 23.

The overhead condensate introduced into the decanter 20 is
It is introduced into one of the compartments 23, where a water-rich main component having a large specific gravity and containing a part of the second azeotropic agent (isopropyl acetate) and a second azeotropic agent as a main component and a part of water. Liquid-liquid separation is carried out due to the difference in specific gravity between the poor water phase containing a small specific gravity. If at least a part of the rich water phase is continuously extracted from the bottom of the compartment 23 via the line 24 to adjust the height of the interface between the rich water phase and the poor water phase, only the poor water phase will cause the weir 21 to flow. It goes over and flows into the other compartment 22. At least a part of the poor aqueous phase rich in the second azeotropic agent flowing into the compartment 22 is refluxed to the second distillation column 15 via the line 16.
In some cases, part of the rich water phase is also refluxed from the line 17 to the vicinity of the top of the second distillation column 15 by selecting a supply stage.

At this time, when a part of the second azeotropic agent is dissolved in the enriched water phase discharged from the line 24 to the outside of the system, the second azeotropic agent refluxed to the second distillation column 15 The quantity will gradually become insufficient. In this case, the additional second azeotropic agent is introduced into the decanter 20 via the line 25 to replenish the deficiency.

By azeotropic distillation in the second distillation column 2 (hereinafter referred to as "second distillation"), the first bottom liquid 14
The water remaining in the (hydrous acetic acid) is discharged from the line 24, and purified acetic acid containing no water is withdrawn as a second bottom liquid 27 from the bottom of the second distillation column 15.

In the above embodiment, butyl acetate was used as the first azeotropic agent, but the first azeotropic agent used in the present invention forms a minimum azeotrope with water and separates liquid and liquid from water. Any material may be used as long as it can. Preferably, the first azeotropic agent has a boiling point of 100 ° C. or higher. Examples thereof include alkyl esters such as propyl acetate, isobutyl acetate, butyl acetate and ethyl butyrate, ketones such as methyl propyl ketone, methyl butyl ketone and methyl isobutyl ketone, alcohols such as butyl alcohol and isoamyl alcohol. , Toluene, m-xylene, p-xylene, aromatic hydrocarbons including ethylbenzene, butyl ether, ethers including isoamyl ether, polyhydric alcohol derivatives including ethylene glycol dimethyl ether, or any two of these The above mixture can be mentioned.

In the above embodiment, isopropyl acetate was used as the second azeotropic agent 25. However, the second azeotropic agent used in the present invention can form a minimum azeotropic mixture with water, Any azeotropic mixture may be used as long as it has a minimum azeotropic temperature lower than the minimum azeotropic mixture of the first azeotropic agent and water and can be liquid-liquid separated from water. Preferably, the second azeotropic agent has a boiling point of less than 100 ° C. Examples thereof include, for example, alkyl esters including ethyl acetate and isopropyl acetate, ketones including methyl ethyl ketone, alcohols such as sec-butanol, aromatic hydrocarbons including benzene, and alicyclic compounds including cyclohexane. Examples thereof include hydrocarbons, ethers including ethyl ether, isopropyl ether, and the like, or a mixture of any two or more thereof.

Next, when dehydrating and concentrating the raw material liquid which is a mixture of acetic acid and water, the first azeotropic agent preferably has a boiling point of 100 ° C. or higher, and preferably the first azeotropic agent having a boiling point of less than 100 ° C. The action and effect of the purification method of the present invention using the second azeotropic agent having the lowest azeotropic temperature lower than the lowest azeotropic mixture of the boiling agent and water will be described. Now, regarding examples of azeotropic agents capable of forming a minimum azeotropic mixture with water, referring to the boiling point (° C.) of the azeotropic agent and the concentration (% by weight) of water in the minimum azeotropic mixture by race, Tables 1 to 4 below.

[0022]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

From the above tables, it can be seen that generally the concentration of water in the azeotrope tends to increase as the boiling point of the azeotropic agent increases. Therefore, when water is removed from a mixture of acetic acid and water, an azeotropic mixture having a relatively high water concentration can be formed in a region where the water concentration in the mixture is relatively high, that is, an azeotrope having a high boiling point. The selection of the agent is advantageous in terms of distillation efficiency.

On the other hand, the water content at the bottom of the distillation column is 1
When the acetic acid is concentrated to the range of 15% by weight to 15% by weight, using an azeotropic agent having a boiling point of 100 ° C. or higher which is the boiling point of water is more than separation of acetic acid and water. , Which makes it difficult to separate the acetic acid having a boiling point of 118.2 ° C. from the azeotropic agent. Actually, even if the number of distillation columns is increased and the reflux ratio is increased in order to obtain concentrated purified acetic acid under these conditions, acetic acid is mixed in the overhead distillate and the acetic acid at the bottom is The inclusion of the azeotropic agent cannot be substantially prevented.

Therefore, in the method for purifying acetic acid of the present invention, in the first distillation column 2 for concentrating the raw material liquid 1 having a relatively low acetic acid concentration, in order to remove a large amount of water as efficiently as possible, the minimum azeotropic distillation Relatively high temperature, preferably boiling point 1
Using the first azeotropic agent having a temperature of 00 ° C. or higher, azeotropic distillation is performed until the water content of the first bottom liquid 14 is in the range of 1% by weight to 15% by weight.

Next, the first bottom liquid 14 is added to the second distillation column 1
5, a second azeotropic agent having a relatively low minimum azeotropic temperature, preferably having a boiling point of less than 100 ° C., in order to widen the boiling point difference with acetic acid and increase the recovery rate of purified acetic acid from the bottom of the column. Is used for azeotropic distillation. This makes it possible to satisfy the contradictory requirements of the distillation efficiency and the degree of purification, and to obtain purified acetic acid with a high recovery rate. At this time, if the water concentration of the first bottom liquid 14 exceeds 15% by weight, the efficiency of the second distillation decreases, and if the first distillation is concentrated until the water concentration becomes less than 1% by weight, the first distillation This is not preferable because the efficiency of is reduced. By adjusting the conditions of the first distillation so that the water concentration of the first bottom liquid 14 is within the range of 1% by weight to 15% by weight, the distillation efficiency and the degree of purification are compatible with each other.
Purified acetic acid can be obtained with higher efficiency.

Both the first azeotropic agent and the second azeotropic agent are liquid-liquid separated at the top of the respective distillation columns due to the difference in specific gravity between the rich water phase rich in water and the poor aqueous phase rich in azeotropic agent. It goes without saying that this liquid-liquid separation must be possible, but in order to perform this liquid-liquid separation efficiently, the distribution ratio with water is sufficiently small and It is preferable that the difference in specific gravity between and is sufficiently large. Further, since the distribution rate depends on the temperature, it is preferable that the liquid temperature in the first decanter and the second decanter is maintained within the range of -20 ° C to 70 ° C.

From the above viewpoints, regarding the examples of the azeotropic agent suitable as the first azeotropic agent and the second azeotropic agent used in the method for purifying acetic acid of the present invention, the minimum azeotropic temperature with water under the standard pressure is shown. (° C.), the concentration of water (% by weight) in the lowest azeotropic mixture, and the mutual solubility of water and the azeotropic agent (A) at 30 ° C. are shown in Table 5 and Table 6, respectively.

[0029]

[Table 5]

[Table 6]

The azeotropic agent to be actually used takes into consideration the minimum azeotropic temperature with water, the distribution ratio with water at the liquid-liquid separation temperature, the specific gravity difference with water, volatility, and availability. Selected. Of these, butyl acetate is particularly preferable as the first azeotropic agent. Since butyl acetate has a relatively large proportion of water in the azeotrope, it can distill a relatively large amount of water with a small amount of reflux from the top of the tower, and has a relatively small distribution rate. Good separation from aqueous phase.

Further, isopropyl acetate is particularly preferable as the second azeotropic agent. Isopropyl acetate has a boiling point of 100.
Since the proportion of water in the azeotropic mixture is relatively large in the azeotropic agent below ℃, a relatively large amount of water can be distilled from the top of the tower with a small amount of reflux, and the distribution rate is also relatively small. Therefore, the separation of the rich water phase and the poor water phase is good. Furthermore, since the boiling point of the azeotropic agent itself is sufficiently lower than that of acetic acid, the recovery rate of purified acetic acid in the second distillation column is improved.

The type of apparatus used in the method for purifying acetic acid of the present invention is not particularly limited. For example, the first distillation column and the second distillation column may be of any type conventionally used such as a tray type and a packed type. The cooler, decanter, and the like incidental to these are not particularly limited to the types shown in the above-described embodiment, and they may be formed integrally with the distillation column body or formed separately. It may be either.

[0033]

EXAMPLES Next, examples according to the above-described embodiment will be shown.
In the following examples, all "parts by weight" are values when the raw material liquid is 100 parts by weight. (Example 1) In this example, using the apparatus shown in FIG. 1, the raw material liquid 1 which is a mixture of acetic acid and water is purified to obtain purified acetic acid 27. The composition of this raw material liquid 1 was acetic acid (15.6% by weight) and water (84.4% by weight). Butyl acetate was used as the first azeotropic agent, and isopropyl acetate was used as the second azeotropic agent.

The above raw material liquid 1 (100 parts by weight) was introduced into the first distillation column 2. As the first distillation column 2, the concentration section 30
Raw material liquid 1 was introduced at a temperature of 90 ° C. using a glass-made Oldershaw-type distiller composed of 30 stages and a collecting section. From the vicinity of the top of the first distillation column 2, a poor water phase 3 (31) composed of butyl acetate (98.6% by weight) and water (1.4% by weight) was used.
5.0 parts by weight) was supplied for distillation.

The overhead gas 5 is cooled to 20 ° C. by a cooler 6,
The first decanter 7 separated the liquid into a poor water phase 3 (315.0 parts by weight) and a rich water phase (122.5 parts by weight). The poor water phase 3 is refluxed to the first distillation column 2 as described above, and a part (38.0 parts by weight) of the rich water phase is also passed through the line 4 near the top of the first distillation column 2, Reflux to a stage different from the poor aqueous phase 3. The rest of the Hosui phase (84.5 parts by weight) was discharged from the system through line 11.

The composition of this rich water phase was water (97.7% by weight), butyl acetate (2.3% by weight), and no acetic acid was contained. Butyl acetate (1.9 parts by weight) required to continue the first distillation was replenished via line 12.

Since water (82.5 parts by weight) was discharged from the line 11 by the above-mentioned first distillation, about 98% by weight of the water (84.4 parts by weight) in the raw material liquid 1 was eventually converted to this first portion. It has been separated and removed by one distillation. First distillation column 2
From the bottom of the column, a bottom liquid 14 (17.5 parts by weight) consisting of an acetic acid aqueous solution having a water concentration of 10.8% by weight was obtained. Butyl acetate, which is an azeotropic agent, was not contained in this bottom liquid 14.

The above-mentioned bottom liquid 14 was supplied to a second distillation column 15 composed of a glass Oldershaw type distillation apparatus having 30 stages of concentration section and 30 stages of recovery section. From the vicinity of the top of the second distillation column 15, a poor water phase 16 (19.8 parts by weight) consisting of isopropyl acetate (98.1% by weight) and water (1.9% by weight) was supplied for distillation. went.

The overhead gas 18 is cooled to 20 ° C. by the cooler 19, and the second decanter 20 separates the liquid phase into a poor water phase 16 (19.8 parts by weight) and a rich water phase (1.9 parts by weight). did. The poor water phase 16 was refluxed to the second distillation column 15 as described above, and the whole rich water phase (1.9 parts by weight) was discharged from the system through the line 24. The isopropyl acetate (0.1 parts by weight) required to continue the second distillation was replenished via line 25. By this second distillation, purified acetic acid (15.6 parts by weight) substantially free of water and an azeotropic agent was obtained as the bottom liquid 27 of the second distillation column 15.

In Example 1 above, Table 7 shows the composition (wt%) of each line shown in FIG. 1 and the load amount (wt part) of each line when the raw material liquid 1 was 100 parts by weight. .

[0041]

[Table 7]

From the above results, according to the method of Example 1, water having a small relative volatility with respect to acetic acid and a large latent heat of vaporization was efficiently separated from the raw material liquid 1, and highly purified purified acetic acid was obtained at a high recovery rate. You can see that it was recovered.

Example 2 The same distillation operation as in Example 1 was carried out using the apparatus shown in FIG. 1, except that methyl isobutyl ketone was used as the first azeotropic agent and benzene was used as the second azeotropic agent. Moreover, the composition of the raw material liquid 1 was changed to concentrate and purify acetic acid. The composition of this raw material liquid 1 was acetic acid (70.0% by weight) and water (30.0% by weight).

The above raw material liquid 1 (100 parts by weight) was introduced into the first distillation column 2 at a temperature of 100 ° C. From the vicinity of the top of the first distillation column 2, a poor water phase 3 (21) composed of methyl isobutyl ketone (98.0% by weight) and water (2.0% by weight) was obtained.
(0.0 parts by weight) was supplied to carry out azeotropic distillation.

The overhead gas 5 is cooled to 20 ° C. by a cooler 6,
Liquid-liquid separation was performed using a first decanter 7 into a poor water phase 3 (210.0 parts by weight) and a rich water phase (63.4 parts by weight). The poor water phase 3 is refluxed to the first distillation column 2 as described above, and a part (34.6 parts by weight) of the rich water phase is also passed through the line 4 near the top of the first distillation column 2. Reflux to a stage different from the poor aqueous phase 3.
The rest of the Hosui phase (28.8 parts by weight) was discharged out of the system through line 11.

The composition of this rich water phase was water (98.1% by weight), methyl isobutyl ketone (1.9% by weight), and did not contain acetic acid. The methyl isobutyl ketone (0.5 parts by weight) required to continue the first distillation was replenished via line 12.

Since water (28.3 parts by weight) was discharged from the line 11 by the above-mentioned first distillation, about 94% by weight of the water (30.0 parts by weight) in the raw material liquid 1 was eventually converted to this first. It has been separated and removed by one distillation. First distillation column 2
From the column bottom, column bottom liquid 14 (71.7 parts by weight) consisting of an acetic acid aqueous solution having a water concentration of 2.4% by weight was obtained. The first bottom liquid 14 did not contain azeotropic agent methyl isobutyl ketone.

Next, the above first bottom liquid 14 is added to the second distillation column 1
5. From the vicinity of the top of the second distillation column 15, a poor water phase 16 (26.0 parts by weight) consisting of benzene (99.9% by weight) and water (0.1% by weight) was supplied for distillation. It was

The overhead gas 18 is cooled to 20 ° C. by a cooler 19, and a second decanter 20 separates a liquid phase into a poor water phase 16 (26.0 parts by weight) and a rich water phase (2.4 parts by weight). did. The poor water phase 16 is refluxed to the second distillation column 15 as described above, and 0.7 part by weight of the rich water phase is refluxed to the second distillation column 15 via the line 17, and the rest (1.7 parts by weight). Part) was discharged from the system through the line 24. During the second distillation, virtually no benzene make-up was required. By this second distillation, purified acetic acid (70.0 parts by weight) substantially free of water and an azeotropic agent was obtained as the bottom liquid 27 of the second distillation column 15.

In Example 2 above, Table 8 shows the composition (wt%) of each line shown in FIG. 1 and the load amount (part by weight) of each line when the raw material liquid 1 was 100 parts by weight. .

[0051]

[Table 8]

From the above results, also by the method of Example 2, water having a small relative volatility to acetic acid and a large latent heat of vaporization is efficiently separated from the raw material liquid 1, and highly purified purified acetic acid is highly recovered. It turns out that it was possible to collect at a rate.

[0053]

In the method for purifying acetic acid of the present invention, the mixture of acetic acid and water is azeotropically distilled in the first distillation column in the presence of the first azeotropic agent, and the water concentration from the column bottom is preferably 1% by weight. % ~ 15
The hydrous acetic acid concentrated to the range of wt% is withdrawn as the first bottom liquid and introduced into the second distillation column to obtain a second azeotropic temperature with water lower than that of the first azeotropic agent. Since azeotropic distillation is performed in the presence of an azeotropic agent to obtain purified acetic acid dehydrated and concentrated from the bottom of the column, purified acetic acid can be efficiently recovered from a mixture of acetic acid and water. If the boiling point of the first azeotropic agent is 100 ° C. or higher and the boiling point of the second azeotropic agent is less than 100 ° C., most of the water can be removed with low energy in the first distillation, and in the second distillation Highly purified acetic acid can be obtained with a high recovery rate while using a simple device.

[Brief description of drawings]

FIG. 1 is a process drawing showing an embodiment of the present invention.

[Explanation of symbols]

 1 ... Acetic acid / water mixture 2 ... First distillation column 3 ... Poor water phase 4, 11 ... Pouring water phase 14 ... First tower bottom liquid 15 ... Second distillation column 16 ... Poor water phase 17, 24 ... Pouring water phase 27 ... Purification Acetic acid

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Nishino Oita City, Oita Prefecture Nakano 2 in Showa Denko Oita Factory

Claims (4)

[Claims] 1. A raw material liquid consisting of a mixture of acetic acid and water is introduced into a first distillation column and azeotropically distilled in the presence of a first azeotropic agent capable of forming a minimum azeotropic mixture with water, The overhead gas that distills from the overhead is cooled and condensed, and the obtained overhead condensate is liquid-liquid separated into a rich water phase rich in water and a poor aqueous phase rich in azeotropic agent, and at least this rich water phase. A part is discharged to the outside of the system, at least a part of the poor water phase is refluxed to the first distillation column, the concentrated hydrous acetic acid is extracted from the bottom of the first distillation column as the first bottom liquid, and then this first One bottom liquid can be introduced into the second distillation column to form a minimum azeotrope with water, the azeotrope being lower than the minimum azeotrope of the first azeotrope and water. Azeotropic distillation in the presence of a second azeotropic agent having a temperature, the overhead gas distilled from the overhead is cooled and condensed, and the obtained overhead condensate is enriched with water. Liquid-liquid separation into a poor water phase rich in azeotropic agent, at least a part of this rich water phase is discharged out of the system, at least a part of the poor water phase is refluxed to the second distillation column, and the second distillation column A method for purifying acetic acid, in which dehydrated purified acetic acid is recovered from the bottom of the column. 2. The method for purifying acetic acid according to claim 1, wherein the raw material liquid is concentrated in the first distillation column until the water concentration of the first bottom liquid is within the range of 1% by weight to 15% by weight. 3. The first azeotropic agent is an alkyl ester, a ketone, an alcohol, an aromatic hydrocarbon, an ether and a polyvalent compound which can be liquid-liquid separated from water and has a boiling point of 100 ° C. or higher. The method for purifying acetic acid according to claim 1 or 2, which is one or more selected from the group consisting of alcohol derivatives. 4. The second azeotropic agent is an alkyl ester, a ketone, an alcohol, an aromatic hydrocarbon, or an alicyclic hydrocarbon which has a boiling point of less than 100 ° C. and which can be liquid-liquid separated from water. The method for purifying acetic acid according to claim 1 or 2, which is one or more selected from the group consisting of compounds and ethers.