JPH09151158A - Purification of acetic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying acetic acid by which purified acetic acid is efficiently recovered from an aqueous solution of the acetic acid with a low heat quantity. SOLUTION: A raw material solution 1 at 10-50wt.% acetic acid concentration is introduced into an extractor 2 and an extracting agent 3 containing isopropyl acetate in an amount of 0.6-3.0 times based on the raw material solution 1 is fed to the extractor 2 to extract the acetic acid into the phase of the extracting agent. The extracted solution 4 is then fed to an azeotropic distillation column 6 to carry out the azeotropic distillation of water with the extracting agent. Thereby, the dehydrated purified acetic acid 19 is recovered from the column bottom.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying acetic acid, which efficiently recovers purified acetic acid from a raw material liquid containing acetic acid and water with a low heat amount.

[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, acetic acid is obtained as an aqueous solution, so in order to obtain dehydrated purified acetic acid, water must be removed from this aqueous solution by the cheapest possible method. A distillation method is generally employed to industrially obtain purified acetic acid from an acetic acid aqueous solution. However, when attempting to separate water from acetic acid by a conventional distillation method, the boiling points of water and acetic acid (boiling point 117.8 ° C./standard pressure) are close to each other, so a distillation column with a high plate number of 70 plates or more is required, Moreover, since a large amount of water with a large latent heat of vaporization is distilled off from the top of the tower, large-scale equipment and a large amount of heat are required. Furthermore, since the relative volatility of water with respect to acetic acid is small, it is necessary to increase the reflux ratio at the top of the column, resulting in poor efficiency.

Various proposals have heretofore been made to solve this problem. As an example, for example, an acetic acid aqueous solution (hereinafter, referred to as “raw material liquid”) is azeotropically distilled in the presence of an azeotropic agent that forms a minimum azeotropic mixture with water, and water and an azeotropic agent are added from the top of the column. Is known to distill the lowest azeotrope of the above to obtain concentrated acetic acid from the bottom of the column (for example, Japanese Examined Patent Publication No.
3-16965, Japanese Patent Publication No. 61-31091). Although this method has the advantage that the reflux ratio at the top of the column can be lowered to reduce the amount of heat required for distilling water, it is the same as ordinary distillation in that a large amount of water must be distilled from the top of the column. Therefore, the effect of reducing the amount of heat cannot be said to be sufficient.

An extraction method is known as a method other than azeotropic distillation. In this method, generally, a water-insoluble organic solvent is used as an extractant in contact with a raw material liquid to extract acetic acid into an extractant phase, and acetic acid is separated and purified from this extract by distillation or the like. In this extraction method, the selection of an extractant that has a small partition coefficient with water and dissolves acetic acid well is an important issue.

Regarding the selection of the extracting agent, generally, there are many proposals for using as the extracting agent a solvent having a higher boiling point than acetic acid and dissolving acetic acid well, since a solvent having a high boiling point has a small partition coefficient with water. For example, JP-A-60-25949 discloses that acetic acid is extracted from a raw material liquid by using a high boiling point solvent containing a C ₇ aliphatic ketone as a main component as an extractant, and water contained in the extract liquid is stripped. Acetic acid is distilled off from the high boiling solvent. Also, for example, Japanese Examined Patent Publication No. 59-35
Japanese Patent No. 373 discloses that a tertiary amine having a boiling point higher than that of acetic acid and an oxygen-containing organic solvent having a boiling point higher than that of acetic acid are used in combination for extraction, the extract is distilled and dehydrated, and the dehydrated mixture is distilled again to collect acetic acid. I'm putting it out. Japanese Patent Publication No. 60-16410 discloses
A specific secondary amide is used as an extractant, and acetic acid is separated from the extract by distillation. Also, US Pat. No. 4,143
No. 066 proposes the use of trioctylphosphine oxide as a high boiling solvent that selectively extracts acetic acid.

On the other hand, a method is also known in which a low boiling point solvent and a high boiling point solvent are mixed and used as an extracting agent. For example, Japanese Patent Publication No. 1-38095 uses a mixed solvent of ethyl acetate and diisobutyl ketone. Further, as a method for carrying out extraction and azeotropic distillation in parallel, US Pat. No. 217
In No. 5879, the raw material liquid is divided into two, one is extracted with a low boiling point solvent, the other is azeotropically distilled using an azeotropic agent such as butyl acetate, and the heat of condensation of the azeotropic distillation overhead gas is multiplexed. Used as an effect, the low boiling point solvent in the extract is distilled from acetic acid to reduce the amount of heat.

[0008]

In the above extraction method or a method in which the extraction method and the azeotropic distillation method are commonly used, when a high boiling point solvent is used as the extractant, water in the extractant phase is generally used. However, since a large amount of extractant is required because the partition coefficient with acetic acid is reduced, not only the apparatus becomes large, but also when acetic acid and the extractant are separated by distillation in a later step, the extractant is relatively small. Since acetic acid, which has a large latent heat of vaporization, is distilled off from the top of the column, the amount of heat is increased. Even if this distillation separation is carried out using the lowest azeotropic distillation with water, since the extractant has a higher boiling point than acetic acid, the lowest azeotropic temperature approaches the boiling point of acetic acid, and high-purity acetic acid is highly recovered. Hard to get at a rate.

The method of using a low boiling point solvent and a high boiling point solvent as the extractant is more advantageous than using only the low boiling point solvent, but since the amount of water brought into the extractant phase is large, the load of azeotropic distillation increases. At the same time, the solvent having a higher boiling point and the acetic acid must be separated by distillation, which is not necessarily advantageous in terms of heat quantity. The present invention has been made to solve the above problems, and therefore an object thereof is to provide a method for purifying acetic acid, which efficiently recovers purified acetic acid from a raw material liquid with a low heat amount.

[0010]

In order to solve the above-mentioned problems, the present invention provides an extraction device according to claim 1, wherein an acetic acid aqueous solution having a concentration of acetic acid in the range of 10% by weight to 50% by weight is used as a raw material liquid. The extractant containing isopropyl acetate in the range of 0.6 to 3.0 times the weight of the raw material liquid is supplied to the extraction device and brought into contact with the raw material liquid to extract acetic acid into the extractant phase. Separated into an extract containing acetic acid and an extraction residual liquid, and supplying this extract to an azeotropic distillation column,
Provided is a method for purifying acetic acid, in which dehydrated purified acetic acid is recovered from the bottom of this azeotropic distillation column.

In the method for purifying acetic acid according to claim 1, an azeotropic mixture of isopropyl acetate and water is distilled from the top of the azeotropic distillation column, and the distillate is condensed to produce a poor isopropyl acetate-rich mixture. It is preferable to separate into a water phase and a water rich water phase, and at least a part of this poor water phase is circulated to the extraction device as an extractant.

In the purification method, the extraction residual liquid of the extraction device and at least a part of the rich water phase are supplied to a recovery distillation column, and isopropyl acetate and water contained in these supply liquids are azeotropically distilled, The distillate that distills from the top of the column is condensed and separated into a poor water phase rich in isopropyl acetate and a rich water phase rich in water, and at least a part of the poor water phase is discharged as an extractant concentrate, and a recovery distillation column It is preferable to discharge water from the bottom of the column.

Further in this case, the extractant concentrate is
It is preferable to introduce it into an esterification reactor together with acetic acid, convert isopropyl alcohol produced by hydrolysis of isopropyl acetate into isopropyl acetate, and recover the isopropyl alcohol.

According to the present invention, in the method for purifying acetic acid according to claim 1, an azeotropic mixture of isopropyl acetate and water is distilled from the top of the azeotropic distillation column, and the distillate is condensed. Separation into a poor water phase rich in isopropyl acetate and a rich water phase rich in water, supplying at least a part of this rich water phase to the stripper, from the top of this stripper, distilling isopropyl acetate contained in the feed solution, Provided is a method for purifying acetic acid in which this distillate is combined with the azeotropic mixture distilled from the azeotropic distillation column.

In the above-mentioned purification method, the extraction residual liquid of the extraction device is supplied to an extractant recovery column, isopropyl acetate contained in the supply liquid is distilled from the top of the column, the distillate is condensed, and then the condensed product is condensed. At least part of the liquid is preferably circulated to the extraction device.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. (Example 1) FIG. 1 is a process drawing showing the method for purifying acetic acid of Example 1. The apparatus of this step is roughly composed of an extraction apparatus 2, an azeotropic distillation column 6, a recovery distillation column 20 and an esterification reactor (hereinafter abbreviated as “reactor”) 32. Of these, the extraction apparatus 2 is a plate-type liquid-liquid countercurrent extraction column, and the azeotropic distillation column 6 and the recovery distillation column 20 are at the tops of the condensers 8, 22, decanters 9, 23, and the bottom of the column, respectively. And a reboiler 16 and a reboiler 30, respectively.

In FIG. 1, first, a raw material liquid having a concentration of acetic acid in the range of 10% by weight to 50% by weight is introduced from the line 1 to the vicinity of the top of the extraction device 2. From the vicinity of the bottom of the extractor 2, an extractant containing isopropyl acetate as a main component is supplied through a line 3. The amount of isopropyl acetate supplied is 0.6 weight times that of the raw material liquid 1 to 3.
It is within the range of 0 weight times.

In the extraction device 2, the raw material liquid 1 and the extraction agent 3
Both of them are in liquid countercurrent contact with each other, and the acetic acid in the raw material liquid 1 is extracted into the extractant phase and extracted from a large amount of isopropyl acetate, acetic acid and a small amount of water, and a large amount of water. It is separated into an extraction residual liquid containing a small amount of isopropyl acetate.
The separated extract containing acetic acid is supplied to the azeotropic distillation column 6 through the line 4 from the top of the column. On the other hand, the extraction residual liquid 5 is discharged from the tower bottom of the extraction device 2.

The extraction liquid 4 from the extraction device 2 contains isopropyl acetate, acetic acid, and water distributed at the time of extraction. When this extract liquid 4 is supplied to the azeotropic distillation column 6, isopropyl acetate and water contained therein form a minimum azeotrope mixture and distill out from the column top as an azeotropic column top gas 7. Thus, purified acetic acid 17 substantially containing neither water nor isopropyl acetate is obtained from the bottom of the azeotropic distillation column 6.

Azeotropic tower top gas 7 distilled from the azeotropic distillation tower
Is cooled by the cooler 8 and condensed, and is introduced into the first decanter 9 as an overhead condensate. This first decanter 9
The lower part of the tank is divided by a weir 10 into a poor water phase chamber 11 and a rich water phase chamber 12. The tower top condensate introduced into the first decanter 9 is introduced into the fermented water phase chamber 12, where the fertilized water phase having a high specific gravity containing water as a main component and a part of isopropyl acetate, and a water containing isopropyl acetate as a main component. The liquid-liquid separation is carried out due to the difference in specific gravity with the poor water phase having a low specific gravity containing a part of

When the height of the interface between the rich water phase and the poor water phase is adjusted while continuously extracting a regulated amount of the rich water phase from the bottom of the rich water phase chamber 12, only the poor water phase crosses over the weir 10. The water flows into the poor water phase chamber 11, whereby the rich water phase (12) and the poor water phase (11) are separated by the weir 10. Hosui phase extracted from the bottom of Hosui phase room 12 (1
Part 2) is optionally refluxed via the line 15 in the vicinity of the top of the azeotropic distillation column 6 by selecting the feed stage, and at least part is discharged via the line 14.

Poor water phase (11) flowing into the poor water phase chamber 11
Is partially refluxed via the line 13 to the vicinity of the top of the azeotropic distillation column 6 by selecting the feed stage, and the balance is the line 3
And is circulated and supplied as an extractant for the extraction device 2 via.

In the extraction residual liquid 5 discharged from the bottom of the extraction apparatus 2 and the rich water phase 14 discharged from the rich water phase chamber 12 of the decanter 9, in addition to isopropyl acetate distributed in water,
It contains isopropyl alcohol produced by hydrolysis of isopropyl acetate. Therefore, in order to efficiently recover these, the extraction residual liquid 5 and the rich water phase 14 are both supplied to the supply stage of the recovery distillation column 20.

In the recovery distillation column 20, isopropyl acetate, isopropyl alcohol, and water form the minimum azeotropic mixture and are azeotropically distilled, and distill out from the column top as a recovery column gas 21. The recovery tower top gas 21 is cooled by a cooler 22 and condensed, and a second decanter 23 is formed as a condensate.
Will be introduced. Like the first decanter 9, the second decanter 23 is divided into a poor water phase chamber 25 and a rich water phase chamber 26 by a weir 24 in the lower part of the tank.

The condensate introduced into the second decanter 23 is
It is introduced into the fermented water phase chamber 26, in which the fermented water phase (26) having a high specific gravity and containing water as a main component and a part of the azeotropic agent (isopropyl acetate and isopropyl alcohol) and one of the water having the azeotropic agent as a main component. Liquid-liquid separation is carried out due to the difference in specific gravity between the poor water phase (25) containing a part and a low specific gravity.

This rich water phase (26) is withdrawn from the bottom of the rich water phase chamber 26 via line 27, and the recovery distillation column 2
It is refluxed by selecting a supply stage near the top of column 0. However, if liquid-liquid separation does not occur in the decanter 23 due to a high concentration of isopropyl alcohol in the condensate, the contents of the rich water phase chamber 26 do not need to be refluxed to the recovery distillation column 20 from the line 27, and The contents of the water phase chamber 25 are merged and processed.

The poor water phase (25) in the decanter 23 is partially recovered via the line 29 as a part of the recovery distillation column 2
A supply stage is selected and refluxed near the top of column 0, but the rest is extracted as extractant concentrated liquid 28 and sent to reactor 32.

By the azeotropic distillation in the recovery distillation column 20, the isopropyl acetate and isopropyl alcohol contained in the extraction residual liquid 5 of the extraction device 2 and the rich water phase 14 discharged from the rich water phase chamber 12 of the decanter 9 are removed from the line. 28
Is collected as an extractant concentrated liquid, and water is discharged as drainage 31 from the bottom of the tower.

The extractant concentrate 28 is then introduced into the reactor 32 in order to react the isopropyl alcohol contained therein with acetic acid to recover it as isopropyl acetate. Acetic acid for this esterification reaction is azeotropic distillation column 6
The bottom liquid 17 of the above is partially branched and supplied via a line 18.

The reactor 32 is filled with an acid catalyst for the esterification reaction, for example, a strongly acidic ion exchange resin or heteripolyacid such as phosphotungstic acid. Reaction liquid 34 rich in isopropyl acetate obtained by this reaction
Can be circulated and used, for example, by supplying it to the azeotropic distillation column 6.

As described above, according to the purification method of Example 1 described with reference to FIG. 1, from the raw material liquid 1 in which the concentration of acetic acid is in the range of 10% by weight to 50% by weight, water and isopropyl acetate are substantially contained. Unpurified acetic acid is recovered as the bottom liquid 19 of the azeotropic distillation column 6, and the water contained in the raw material liquid 1 is discharged from the bottom of the recovery distillation column 20 as drainage 31.

In this purification method, it is not necessary to distill a large amount of water or acetic acid to be distilled from the top of the column, and the boiling points of the azeotropic distillation column 6 and the recovery distillation column 20 are sufficiently higher than those of acetic acid. Since the lowest minimum azeotrope is distilled, the reflux ratio can be reduced, the calorific consumption can be reduced, and acetic acid can be recovered at a high recovery rate.

(Example 2) FIG. 2 is a process diagram showing a method for purifying acetic acid according to Example 2. The apparatus of this step is roughly composed of an extraction device 42, an azeotropic distillation column 46, a stripper 60 and an extractant recovery column 64. Of these, the extraction device 42
It is a plate-type liquid-liquid countercurrent extraction column similar to the extraction device 2 of Example 1, and the azeotropic distillation column 46, like the azeotropic distillation column 6 of Example 1, has a cooler 48 at the top thereof. The decanter 49 and the reboiler 56 are attached to the bottom of the tower. The stripper 60 is a distillation apparatus having a reboiler 61 attached to the bottom of the tower, and the extractant recovery tower 64 is a cooler 6 at the top of the tower.
5, a reflux drum 66, and a reboiler 67 attached to the bottom of the tower.

In FIG. 2, first, a raw material liquid having an acetic acid concentration within the range of 10% by weight to 50% by weight is introduced from the line 41 to the vicinity of the top of the extraction device 42. From the vicinity of the bottom of the extractor 42, an extractant containing isopropyl acetate as a main component is partially supplied through a line 43 and the rest is supplied through a line 70. The supply amount of this isopropyl acetate is within the range of 0.6 to 3.0 times the weight of the raw material liquid 41.

In the extraction device 42, the raw material liquid 41 and the extracting agents 43 and 70 are both liquid and counter-currently contacted to each other.
The acetic acid in 1 was extracted into the extractant phase, and an extract containing a large amount of isopropyl acetate, acetic acid and a small amount of water, and an extraction residual liquid containing a large amount of water and containing a small amount of isopropyl acetate. Is separated into The separated extract containing acetic acid is supplied to the azeotropic distillation column 46 through the line 44 from the top of the column. On the other hand, the extraction residual liquid 45 is discharged from the tower bottom of the extraction device 42.

The extraction liquid 44 from the extraction device 42 contains isopropyl acetate, acetic acid, and water distributed at the time of extraction. When this extract liquid 44 is supplied to the azeotropic distillation column 46, isopropyl acetate and water contained therein form a minimum azeotropic mixture and distill out from the column top as an azeotropic column top gas 47. From the bottom of the azeotropic distillation column 46,
Purified acetic acid containing virtually no water or isopropyl acetate 58
Is recovered.

Azeotropic overhead gas 47 distilled from the azeotropic distillation column
Is combined with the azeotropic gas mixture 62 from the top of the stripper 60, which will be described later, cooled by the cooler 48 to be condensed, and introduced into the decanter 49 as a top condensate.
The lower part of the tank of the decanter 49 is divided into a poor water phase chamber 51 and a rich water phase chamber 52 by a weir 50. The overhead condensate introduced into the decanter 49 is introduced into the high-water phase chamber 52, where the high-concentration high-concentration water containing water as a main component and a part of isopropyl acetate is introduced due to the difference in specific gravity as in the case of Example 1. Liquid-liquid separation is performed into a phase (52) and a poor water phase (51) having a low specific gravity and containing isopropyl acetate as a main component and a part of water.

The rich water phase extracted from the bottom of the rich water phase chamber 52 contains water as a main component, and contains isopropyl acetate distributed in water and isopropyl alcohol produced by hydrolysis of isopropyl acetate. Therefore, in order to recover these efficiently and discharge the water containing no impurities to the outside of the system, a part of this rich water phase (52) is optionally passed through the line 55 to the top of the azeotropic distillation column 46. A supply stage is selected in the vicinity to be refluxed, and the rest is supplied to the vicinity of the top of the stripper 60 via a line 54.

From the top of the stripper 60, an azeotropic mixed gas 62 of isopropyl acetate, isopropyl alcohol and water is distilled out. The azeotropic mixed gas 62 is combined with the azeotropic overhead gas 47 distilled from the azeotropic distillation column 46, condensed, and then introduced into the decanter 49 to form a poor water phase (51) and a rich water phase (52). To be separated. From the bottom of the stripper 60, water containing no impurities is discharged out of the system as drainage 63.

The poor water phase (51) separated from the combined product of the azeotropic overhead gas 47 distilled from the azeotropic distillation column 46 and the azeotropic mixed gas 62 distilled from the top of the stripper 60 is a poor water phase. From the phase chamber 51, a part is refluxed via a line 53 in the vicinity of the top of the azeotropic distillation column 46 by selecting a supply stage and the rest is
It is circulated and supplied from the vicinity of the bottom of the tower to the extraction device 42 as a part of the extraction agent via a line 43.

The extraction residual liquid 45 discharged from the bottom of the extraction device 42 contains water as a main component and contains acetic acid, isopropyl acetate, and isopropyl alcohol distributed in the aqueous phase. The extraction residual liquid 45 is supplied to the supply stage of the extractant recovery tower 64 in order to recover the extractant.

In the extractant recovery column 64, isopropyl acetate and an azeotropic mixture of isopropyl alcohol and water are distilled out as a recovery gas 68 from the top of the column. This recovered gas 6
8 is condensed in the cooler 65 and introduced into the reflux drum 66. From the reflux drum 66, a part of the reflux drum 66 is refluxed by selecting a supply stage in the vicinity of the top of the extractant recovery tower 64 via a line 69, and the rest is passed through a line 70 to the extraction device 42. As a part of the extractant, it is circulated and supplied by selecting a supply stage. From the bottom of the extractant recovery tower 64, water containing no extractant is discharged as wastewater 71 out of the system.

By the method for purifying acetic acid of Example 2 described with reference to FIG. 2 above, substantially no water and isopropyl acetate are added from the raw material liquid 41 having an acetic acid concentration within the range of 10% by weight to 50% by weight. Purified acetic acid containing no is recovered as the bottom liquid 58 of the azeotropic distillation column 46, and the stripper 6
Water containing no impurities is discharged as drainage 63 from the bottom of the column 0, and water containing no extractant is discharged from the bottom of the extractant recovery column 64 to the outside of the system as drainage 71.

In this purification method, it is not necessary to distill a large amount of water or acetic acid to distill it from the top of the column, and the azeotropic distillation column 46,
Since the minimum azeotropic mixture having a boiling point sufficiently lower than that of acetic acid is distilled out from both the stripper 60 and the top of the extractant recovery column 64, the reflux ratio can be reduced, the heat consumption is low, and the recovery is high. The advantage is that acetic acid can be recovered at a rate.

In the method for purifying acetic acid of the present invention, an aqueous solution having a concentration of acetic acid in the range of 10% by weight to 50% by weight is used as the raw material liquid. This concentration range is the optimum range due to the selection of isopropyl acetate as the extractant, and if the acetic acid concentration is less than 10% by weight, a large amount of isopropyl acetate, which serves as the extractant, must be used to increase the recovery rate of acetic acid. First, an azeotropic distillation column (Fig. 1
6 or 46) in FIG. 2 consumes a large amount of heat. The acetic acid concentration in the raw material liquid is 50% by weight.
If it exceeds, the amount of water distributed in the extraction liquid in the extraction device becomes relatively large relative to the amount of water in the extraction residual liquid,
The selective resolution of acetic acid is substantially reduced.

In the present invention, the reason why isopropyl acetate is particularly selected as the extractant is that isopropyl acetate has a relatively small partition coefficient with water during extraction and has a good compatibility with acetic acid, and therefore isopropyl acetate has a good compatibility with water and acetic acid. Has good separation efficiency,
Moreover, the boiling point of the simple substance (88.5 ° C) and the minimum azeotropic temperature with water (76.6 ° C) are the boiling points of acetic acid (117.8 ° C).
This is because not only the amount of heat required for distillation separation can be reduced because it is sufficiently lower, but also the efficiency is improved because it is not necessary to set a large reflux ratio in the distillation separation step.

The amount of isopropyl acetate supplied to the extractor is within the range of 0.6 to 3.0 times the raw material liquid. If it is less than 0.6 times by weight, the recovery rate of acetic acid will be lowered, and if it exceeds 3.0 times by weight, an extra amount of heat will be required to distill and separate isopropyl acetate in an azeotropic distillation column or the like.

The extraction temperature in the extraction device is preferably in the range of 10 ° C to 80 ° C. Within this range, liquid-liquid extraction in the isopropyl acetate phase and the aqueous phase will proceed smoothly. Further, in the embodiment of Example 1 or Example 2, liquid-liquid separation between the poor water phase and the high water phase is performed using a decanter. This liquid-liquid separation can be performed at 0 ° C to 70 ° C.
It can proceed smoothly within the temperature range of ° C.

Since isopropyl acetate is an ester compound, it undergoes hydrolysis in the presence of water to produce isopropyl alcohol. This hydrolysis reaction is an equilibrium reaction as shown by the following formula, and its equilibrium constant is 0.45.

[0050]

(Equation 1)

The isopropyl alcohol produced is itself a compound having a boiling point lower than that of water (boiling point 82.3 ° C.) and, together with water and isopropyl acetate, a minimum azeotropic mixture of the three components (minimum azeotropic temperature 75.5). ℃, azeotropic composition is water 1
1.0 wt%: isopropyl acetate 76.0 wt%: isopropyl alcohol 13.0 wt%)
It can be easily separated from acetic acid by distillation.

However, when isopropyl alcohol gradually accumulates in the circulation system, isopropyl alcohol has a large partition coefficient with water, so that it may interfere with the extraction separation in the extraction device or the liquid-liquid separation in the decanter. Become. Therefore, in the embodiment of the present invention shown in Example 1, the produced isopropyl alcohol is reacted with acetic acid to be converted into isopropyl acetate, which is then recycled.

That is, in the embodiment of Example 1 shown in FIG. 1, in order to convert this isopropyl alcohol into isopropyl acetate and circulate it, the extraction residual liquid 5 of the extraction device 2 and the azeotropic distillation column 6 are used. And a part 14 of the water-rich phase (12) separated by the first decanter 9 of the above is azeotropically distilled in a recovery distillation column 20, and an extractant concentrate 28 obtained from the top of the column and containing isopropyl alcohol is concentrated. It is supplied to the reactor 32 together with acetic acid 18 to convert isopropyl alcohol to isopropyl acetate. The reaction liquid 34 rich in isopropyl acetate obtained by this reaction can be circulated to the extraction device 2, but it is more preferable to circulate it to the azeotropic distillation column 6 because it contains an excess amount of acetic acid.

Although isopropyl alcohol is produced also in the embodiment of Example 2, the reaction step of reacting this isopropyl alcohol with acetic acid to convert it to isopropyl acetate is not adopted in Example 2. This is because when isopropyl alcohol accumulates to a certain concentration in the circulatory system, it becomes a steady state at a constant concentration lower than the equilibrium concentration, and in this steady state there is no obstacle to extraction and separation,
It was found that it was not necessary to convert to isopropyl acetate.

In the embodiment of Example 2, the reason why the concentration of isopropyl alcohol stabilizes at a concentration lower than the equilibrium concentration is not clear, but in the azeotropic distillation column 46 and the extractant recovery column 64 of FIG. There is a vapor phase in
Since the equilibrium constant of hydrolysis in the gas phase is significantly smaller than that in the liquid phase, when the concentration of isopropyl alcohol exceeds a certain value, the reverse reaction, esterification, becomes dominant, and the substantial equilibrium constant is low. It is believed that this is due to shifting to

The apparatus used in the method for purifying acetic acid of the present invention and its form are not limited to those used in the embodiments of Examples 1 and 2. For example, the extraction device, an azeotropic distillation column, a recovery distillation column, a stripper, an extractant recovery column may be any of a plate type, a filling type, a rotary cylinder type, etc., and a condenser attached to them, a decanter, a reboiler, etc. For example, it may be integrated with the tower body,
Alternatively, it may be attached separately. The type of reactor and the structure of the catalyst in Example 1 are not particularly limited as long as the esterification proceeds smoothly.

Next, an operation example in which purified acetic acid is recovered from a raw material liquid in which the concentration of acetic acid is in the range of 10% by weight to 50% by weight in the embodiments of Examples 1 and 2 will be described. In the following operation examples, operation example 1 and operation example 2 are according to the embodiment of example 1 shown in FIG. 1, and operation example 3 is according to the embodiment of example 2 shown in FIG. is there. In the following description, all "parts by weight" are values when the raw material liquid is 100 parts by weight.

(Operation Example 1) In this operation example, the extraction device 2 in FIG. 1 has a downcomer and a porosity of 3
A liquid-liquid countercurrent extraction column (corresponding to 4 to 6 theoretical plates) using 30% to 5% perforated plates was used. Further, as the raw material liquid 1, acetic acid (42.0% by weight) and water (58.
0% by weight).

From the vicinity of the top of the extractor 2, the above raw material liquid 1
(100 parts by weight) and Extractant 3 containing isopropyl acetate as a main component (105.0 parts by weight) were introduced at 30 ° C. from the vicinity of the bottom of the column.

Extraction liquid 4 flowing out from the top of the extraction device 2
(168.8 parts by weight) was supplied to the supply stage of the azeotropic distillation column 6 to carry out azeotropic distillation. At the same time, the reaction liquid 34 (3.4 parts by weight) from the reactor 32 was also supplied to the same supply stage. As the azeotropic distillation column 6, an Oldershaw type distiller consisting of 30 stages of concentration section and 30 stages of recovery section was used.

The azeotropic overhead gas 7 of the azeotropic distillation column 6 was cooled to 30 ° C. by the cooler 8 and the obtained condensate was mixed with the first decanter 9
Then, liquid-liquid separation was performed into a poor water phase (11) and a rich water phase (12).
Part of this poor water phase (172.0 parts by weight) is
From the azeotropic distillation column 6 to the vicinity of the top of the column, and the balance (105.
0 part by weight) was circulated and supplied as the extractant 3 to the extractor 2. The rich water phase (12) of the decanter 9 is not refluxed to the azeotropic distillation column 6 and the whole amount (25.3 parts by weight) is supplied to the line 14.
It was supplied to the recovery distillation column 20 from.

In the recovery distillation column 20, the above-mentioned rich water phase (1
Along with 2), the extraction residual liquid 5 (36.2 parts by weight) of the extraction device 2 was also supplied to recover and distill the extractant. As the recovery distillation column 20, an Oldershaw-type distiller having 25 stages of concentration section and 25 stages of recovery section was used.

The top gas 21 of the recovery distillation column 20 is cooled by the cooler 2
Upon cooling at 2, the obtained condensate did not undergo liquid-liquid separation, so a portion (4.0 parts by weight) of the liquid as it is was fed to the line 29.
Reflux to the vicinity of the top of the recovery distillation column 20, and the remaining top liquid (2.5 parts by weight) is used as the extractant concentrate 28 in the reactor 3
Feed to 2. The composition of this extractant concentrate 28 is water 1
It was 1.1% by weight, 67.9% by weight of isopropyl acetate, and 21.1% by weight of isopropyl alcohol.

To the reactor 32, a part (0.9 parts by weight) of the purified acetic acid 17 obtained from the bottom of the azeotropic distillation column 6 was supplied from the line 18 together with the extractant concentrate 28. The reactor 32 was filled with a cationic ion exchange resin (PK-212H manufactured by Mitsubishi Kasei Co.) as an acid catalyst and used.

The reaction solution 34 (3.4 parts by weight) obtained by esterification in the reactor 32 was 8.3% by weight of water and 2 parts of acetic acid.
It contained 5.6% by weight, 50.9% by weight isopropyl acetate, and 15.3% by weight isopropyl alcohol. The conversion rate from isopropyl alcohol to isopropyl acetate in the reactor 32 was 2.3%. The whole amount of the obtained reaction liquid 34 was supplied to the supply stage of the azeotropic distillation column 6.

By the above operation, purified acetic acid 19 (41.0 parts by weight) substantially free of water, isopropyl acetate and isopropyl alcohol was obtained from the bottom of the azeotropic distillation column 6, and the recovery distillation column 20 was operated. Water was discharged as drainage 31 from the bottom of the tower. In the above, Table 1 shows the composition (% by weight) of each line shown in FIG. 1 and the load amount (part by weight) of each line when the raw material liquid 1 is 100 parts by weight.

[0067]

[Table 1]

The above results are obtained by the method of operation example 1.
From raw material liquid 1 containing 42.0% by weight of acetic acid, purified acetic acid of high purity can be efficiently separated by separating it from water without taking out acetic acid as a top distillate of the distillation column, and the extractant can be circulated without waste. It indicates that it could be used.

(Operation Example 2) Acetic acid was purified using the same apparatus and method as in Operation Example 1, except that the composition of the raw material liquid 1 was changed. The composition of the raw material liquid 1 of the operation example 2 was acetic acid (21.0
% By weight) and water (79.0% by weight).

From the vicinity of the top of the extraction device 2, the above-mentioned raw material liquid 1
(100 parts by weight), and extractant 3 (148.0 parts by weight) consisting of 2.8% by weight of water, 96.4% by weight of isopropyl acetate and 0.8% by weight of isopropyl alcohol from the vicinity of the bottom of the column, respectively. It was introduced at 30 ° C. and extracted.

Extract liquid 4 flowing out from the top of the extractor 2
(174.1 parts by weight) was supplied to the supply stage of the azeotropic distillation column 6 for azeotropic distillation. At the same time, the reaction liquid 34 (4.2 parts by weight) from the reactor 32 was also supplied to the same supply stage. The condensate obtained by cooling the azeotropic overhead gas 7 of the azeotropic distillation column 6 to 30 ° C. is liquid-liquid separated into a poor water phase (11) and a rich water phase (12) by the first decanter 9, Part of the water phase (44.0
(Parts by weight) was refluxed to the azeotropic distillation column 6 through the line 13, and the rest (148.0 parts by weight) was circulated and supplied as the extractant 3 to the extraction device 2. The rich water phase (12) was not refluxed to the azeotropic distillation column 6 and the entire amount (8.6 parts by weight) was supplied to the recovery distillation column 20 through the line 14.

In the recovery distillation column 20, together with the above-mentioned rich water phase (line 14), the extraction residual liquid 5 (73.9) of the extraction device 2 was obtained.
(Parts by weight) was also supplied to perform recovery distillation of the extractant. The condensate obtained by cooling the top gas 21 of the recovery distillation column 20 is liquid-liquid separated, and the whole amount (0.3 parts by weight) of the rich water phase (26) is returned to the recovery distillation column 20 as reflux 27, Part of the aqueous phase (25) (4.3 parts by weight) is refluxed to the recovery distillation column 20 through the line 29, and the rest (2.9 parts by weight) is the extractant concentrate 2.
8 was fed to the reactor 32. This extractant concentrate 28
Has a composition of 8.6% by weight of water and 76.4 of isopropyl acetate.
% By weight and 15.0% by weight of isopropyl alcohol. In the reactor 32, a part of the purified acetic acid 17 obtained from the bottom of the azeotropic distillation column 6 (1.
3 parts by weight) was supplied through line 18.

The reaction liquid 34 (4.2 parts by weight) obtained by esterification in the reactor 32 was 6.1% by weight of water and 3% of acetic acid.
It contained 0.6% by weight, 53.5% by weight isopropyl acetate, and 9.9% by weight isopropyl alcohol.
The conversion rate from isopropyl alcohol to isopropyl acetate in the reactor 32 was 4.2%. The whole amount of the obtained reaction liquid 34 was supplied to the supply stage of the azeotropic distillation column 6.

By the above operation, purified acetic acid 19 (20.4 parts by weight) substantially free of water, isopropyl acetate and isopropyl alcohol was obtained from the bottom of the azeotropic distillation column 6, and the recovery distillation column 20 was operated. Wastewater 31 was discharged from the bottom of the tower. In the above, Table 2 shows the composition (weight%) of each line shown in FIG. 1 and the load amount (weight part) of each line when the raw material liquid 1 is 100 parts by weight.

[0075]

[Table 2]

The above results show that the acetic acid concentration of the raw material liquid is 21.
Even in the case of Example 2 in which the amount is 0% by weight, acetic acid can be efficiently separated from water, and purified acetic acid with high purity can be recovered.

(Operation Example 3) This operation example 3 is based on the embodiment of Example 2 shown in FIG. In this operation example, as the extraction device 42, as in the case of the first embodiment, a liquid-liquid countercurrent extraction column having a downcomer and 30 perforated plates with a porosity of 3% to 5% ( A theoretical plate number of 4 to 6) was used. Further, as the raw material liquid 41,
A mixture of acetic acid (35.0% by weight) and water (65.0% by weight) was used.

The above raw material liquid 41 (100 parts by weight) was supplied from the vicinity of the top of the extraction device 42, and isopropyl acetate (94.3% by weight) and isopropyl alcohol (3.0 parts by weight) were supplied from the vicinity of the bottom of the tower. %) And extractant 43 (104.0 parts by weight) consisting of water (2.7% by weight), isopropyl acetate (29.4% by weight), isopropyl alcohol (59.0% by weight), and water (11 .6% by weight)
The recovery liquid 70 (5.4 parts by weight) was supplied from the same supply stage. The temperature of the supply liquid was 30 ° C. for both the raw material liquid and the extractant mixed liquid.

Extraction liquid 4 flowing out from the top of the extraction device 42
4 (157.6 parts by weight) was supplied to the feed stage of the azeotropic distillation column 46 to carry out azeotropic distillation. As the azeotropic distillation column 46, an Oldershaw type distiller consisting of 30 stages of concentration section and 30 stages of recovery section was used.

Azeotropic overhead gas 47 (23) of the azeotropic distillation column 46
1.1 parts by weight) is combined with the azeotropic gas mixture 62 (1.2 parts by weight) from the stripper 60, and the temperature is 30 ° C. in the cooler 48.
The resulting condensate was cooled with a decanter 49 to a poor water phase (5
Liquid-liquid separation was carried out into 1) and the Hosui phase (52). A part (108.0 parts by weight) of the poor water phase is extracted from the line 53 through the azeotropic distillation column 4
It was refluxed in the vicinity of the top of the column of No. 6, and the rest (104.0 parts by weight) was circulated and supplied to the extraction device as the extraction agent 43. The rich water phase (52) does not flow back to the azeotropic distillation column 46, and the total amount (20.3 parts by weight) is supplied from the line 54 to the stripper 60.
Supplied.

As the stripper 60, an Oldershaw type distillation apparatus having 20 stages was used. Stripper 60
The azeotropic mixed gas 62 from the top of the column was combined with the azeotropic overhead gas 47 of the azeotropic distillation column 46 and circulated as described above. From the tower bottom of the stripper 60, water 63 (19.1 parts by weight)
Was discharged. The water 63 did not contain acetic acid, isopropyl acetate, or isopropyl alcohol.

The extraction residual liquid 45 (51.8 parts by weight) discharged from the bottom of the extraction device 42 was water (89.9% by weight), acetic acid (0.9% by weight), isopropyl acetate (3.
1% by weight), isopropyl alcohol (6.2% by weight)
Was included. The extraction residual liquid 45 is transferred to the extraction agent recovery tower 64.
Supplied. As the extractant recovery tower 64, the concentration section 25
An Oldershaw-type distiller having 25 stages of collecting stages and 25 collecting units was used.

Of the 21.7 parts by weight of the condensate at the top of the extractant recovery column 64, 16.3 parts by weight were refluxed to the extractant recovery column 64 from the line 69, and the balance (5.4 parts by weight) was And was circulated to the extraction device 42 as described above. From the bottom of the extractant recovery tower 64, 46.4 parts by weight of water was discharged as drainage 71.

According to the operation example 3, the acetic acid concentration was 3
Purified acetic acid 58 (34.5 parts by weight) substantially free of water, isopropyl acetate and isopropyl alcohol is recovered as the bottom liquid 58 of the azeotropic distillation column 46 from the 5.0% by weight raw material liquid 41. Water containing no impurities was discharged as drainage 63 from the bottom of the stripper 60, and water containing no extractant was also discharged as drainage 71 from the bottom of the extractant recovery tower 64.

In the above description, Table 3 shows the composition (weight%) of each line shown in FIG. 2 and the load amount (weight part) of each line when the raw material liquid 41 is 100 parts by weight.

[0086]

[Table 3]

The above results show that even in the embodiment of Example 2 which does not have an esterification reaction step, isopropyl alcohol does not accumulate in the system to the extent that it interferes with extraction, and acetic acid can be efficiently separated from water. , Indicating that highly purified acetic acid could be recovered.

[0088]

According to the first aspect of the present invention, in the method for purifying acetic acid according to the present invention, a raw material liquid having an acetic acid concentration of 10% by weight to 50% by weight is introduced into the extraction device, and 0.6 times by weight to 3.0% thereof is introduced.
Extraction is performed with an extractant containing 1 times the weight of isopropyl acetate, and the resulting extract is azeotropically distilled to recover dehydrated purified acetic acid from the bottom of the column. be able to.

According to a second aspect of the present invention, the azeotropic mixture of isopropyl acetate and water is distilled from the top of the azeotropic distillation column, and the distillate is condensed into a poor water phase and a rich water phase. Since it is separated and at least part of this poor water phase is circulated to the extraction device as an extractant, the extractant component can be concentrated and separated from water with a low heat amount, and the loss of the extractant is reduced. be able to.

According to a third aspect of the present invention, the extraction residual liquid of the extraction device and at least a part of the enriched water phase are supplied to a recovery distillation column, and the overhead distillate is condensed to form a poor water phase and a rich water phase. Since the water is discharged from the bottom of the column and the isopropyl alcohol produced in the system is not preferred, it can be concentrated in this poor water phase.

According to the fourth aspect of the present invention, the poor water phase is reacted with acetic acid to convert isopropyl alcohol into isopropyl acetate for recovery, so that the loss of the extractant due to hydrolysis can be suppressed and the system can be suppressed. The undesired isopropyl alcohol concentration within can always be kept low.

According to a fifth aspect of the present invention, in the method for purifying acetic acid according to the first aspect, the distillate from the top of the azeotropic distillation column is condensed and separated into a poor water phase and a rich water phase, At least a part of the rich water phase is supplied to the stripper, isopropyl acetate contained in the feed solution is distilled from the top of the stripper, and the distillate is combined with the azeotropic mixture distilled from the azeotropic distillation column. Since the extractant component can be concentrated and separated from water with a low heat amount, the loss of the extractant can be reduced, and water containing substantially no impurities can be extracted from the bottom of the stripper. It can be discharged as waste water.

According to a sixth aspect of the present invention, the extraction residual liquid of the extraction device is supplied to an extractant recovery column, the extractant component contained in the supply liquid is distilled from the top, and the distillate is extracted by the extraction. Since it circulates to the device, the extractant can be circulated and used without waste.

[Brief description of the drawings]

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

FIG. 2 is a process drawing showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Raw material liquid 2 ... Extractor 3 ... Extractor 6 ... Azeotropic distillation column 9 ... First decanter 11 ... Poor water phase 12 ... Pouring water phase 19 ... Purified acetic acid 41 ... Raw material liquid 42 ... Extractor 43 ... Extractor 46 ... Azeotropic distillation column 49 ... Decanter 51 ... Poor water phase 52 ... Hoyomizu phase 58 ... Purified acetic acid

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location C07C 69/14 C07C 69/14 (72) Inventor Hiroshi Nishino Oita-shi, Oita Prefecture Naka no 2 2 Showa Electric Works Co., Ltd. Oita Factory

Claims (6)

[Claims] 1. An acetic acid aqueous solution having a concentration of acetic acid in the range of 10% by weight to 50% by weight is introduced as a raw material liquid into an extraction device, and the extraction device is 0.6 times by weight to 3.0 times the raw material liquid. An extractant containing isopropyl acetate in the range of weight times is supplied to contact with the raw material liquid, and acetic acid is extracted into the extractant phase and separated into an extract containing acetic acid and an extraction residual liquid,
A method for purifying acetic acid, which comprises supplying this extract to an azeotropic distillation column and recovering purified dehydrated acetic acid from the bottom of the azeotropic distillation column. 2. The method for purifying acetic acid according to claim 1, wherein an azeotropic mixture of isopropyl acetate and water is distilled from the top of the azeotropic distillation column, and the distillate is condensed to give isopropyl acetate. Separation into a rich poor water phase and a rich water rich phase,
A method for purifying acetic acid, characterized in that at least part of this poor water phase is circulated to the extraction device as an extractant. 3. The method for purifying acetic acid according to claim 2, wherein the extraction residual liquid of the extraction device and at least a part of the rich water phase are supplied to a recovery distillation column, and isopropyl acetate contained in these supply liquids is supplied. And water are azeotropically distilled, and the distillate distilled from the top of the column is condensed to separate a poor water phase rich in isopropyl acetate and a rich water phase rich in water, and at least a part of the poor water phase is extracted as an extractant. A method for purifying acetic acid, which comprises discharging as a concentrated liquid and discharging water from the bottom of the recovery distillation column. 4. The method for purifying acetic acid according to claim 3, wherein the extractant concentrate is introduced into an esterification reactor together with acetic acid to convert isopropyl alcohol produced by hydrolysis of isopropyl acetate into isopropyl acetate. A method for purifying acetic acid, which is characterized in that 5. The method for purifying acetic acid according to claim 1, wherein an azeotropic mixture of isopropyl acetate and water is distilled from the top of the azeotropic distillation column, and the distillate is condensed to give isopropyl acetate. It is separated into a rich poor water phase and a water rich rich water phase, at least a part of this rich water phase is fed to a stripper, and isopropyl acetate contained in the feed liquid is distilled from the top of this stripper, and this distillate is distilled off. A method for purifying acetic acid, characterized in that the product is combined with the azeotropic mixture distilled from the azeotropic distillation column. 6. The method for purifying acetic acid according to claim 1, wherein the extraction residual liquid of the extraction device is supplied to an extractant recovery column, and isopropyl acetate contained in the supply liquid is distilled from the top of the column. A method for purifying acetic acid, comprising condensing an output product and circulating at least a part of the condensate to the extraction device.