JPH05246941A - Method for purifying acrylic acid in high yield in production of acrylic acid - Google Patents

Abstract

PURPOSE:To produce high-purity acrylic acid by catalytically oxidizing propylene and/or acrolein in a vapor phase to give a reaction product and efficiently separating by-products, especially acetic acid. CONSTITUTION:Propylene and/or acrolein is catalytically oxidized with a molecular oxygen-containing gas to give a mixed gas 1, which is introduced to an acrylic acid collecting column 101 and brought into contact with water to give an aqueous solution 4 of acrylic acid containing by-products such as acetic acid. Then the aqueous solution is distilled with an azeotropic solvent 5 by an azeotropic distillation column 102 to separate acrylic acid 5. In the distillation, a mixed solvent of (A) diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl-tert-butyl ketone and/or n-propyl acetate and (B) toluene, heptane and/or methylcyclohexane is used as the azeotropic solvent and a mixture substantially comprising acetic acid, water and the azeotropic solvent is distilled from a column top 6 of an azeotropic separating column 102 to obtain high-purity acrylic acid substantially not containing the mixture from a column bottom 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing acrylic acid by catalytic vapor-phase oxidation of propylene and / or acrolein (hereinafter sometimes referred to as "propylene etc.") with a molecular oxygen-containing gas. More specifically, it relates to a method for efficiently separating by-products, particularly acetic acid, from a reaction product obtained by catalytic gas-phase oxidation to produce acrylic acid with high purity. More specifically, water is added to the above product to form an aqueous solution,
The present invention relates to a method for producing high-purity acrylic acid by further adding an azeotropic solvent to remove by-products by an azeotropic phenomenon.

[0002]

2. Description of the Related Art When propylene or the like is subjected to catalytic gas phase oxidation with a molecular oxygen-containing gas in the presence of an oxidation catalyst, acetic acid, formic acid, acetaldehyde,
As a reaction product, a mixed gas containing by-products such as formaldehyde and raw materials such as unreacted propylene and acrolein is obtained. Conventionally, in the method of industrially producing acrylic acid by catalytic vapor-phase oxidation of propylene and the like with a molecular oxygen-containing gas, the mixed gas obtained by this catalytic vapor-phase oxidation is introduced into an acrylic acid collection tower to produce water. The product is obtained by contacting with, cooling, absorbing and collecting to obtain an aqueous solution containing acrylic acid and by-products such as acetic acid, and separating and purifying acrylic acid from this aqueous solution by a distillation method.

However, acetic acid is a relatively large amount of various by-products, and in order to distill and separate this by-product, the distillation temperature is high (acetic acid has a boiling point of 118.1 ° C. under normal pressure), so acrylic acid is used. Is easily polymerized, and acrylic acid and acetic acid have a small relative volatility, and it is difficult to simply separate them by distillation. Therefore, in order to utilize the azeotropic phenomenon of ternary system consisting of acetic acid-water-azeotropic solvent or ternary system or more, the reaction product is brought into contact with water to obtain an aqueous solution, and an azeotropic solvent is further added for distillation. , A method of distilling a mixture of acetic acid-water-azeotropic solvent from the top of the tower and obtaining acrylic acid from the bottom of the tower.

In Japanese Examined Patent Publication No. 63-10691, toluene is used as an azeotropic solvent. However, in this method, most of acetic acid can be separated by azeotropy, but some cannot be separated and is extracted together with acrylic acid from the bottom of the azeotropic separation column. Therefore, an acetic acid separation column is further provided to separate the remaining acetic acid, and two columns, an azeotropic separation column and an acetic acid separation column, are required.

Further, in JP-B-46-34691 and JP-B-46-18967, ethyl acetate, butyl acetate, dibutyl ether, ethyl acetate, hexane are used as azeotropic solvents.
Azeotropic distillation is carried out using heptane, ethyl methacrylate, propyl acrylate, etc., the azeotropic solvent, acetic acid and water are distilled from the top of the column, and acrylic acid is obtained from the bottom of the column. However, according to the study by the present inventor, in these methods, the separation of acetic acid is not sufficient just by removing the high-boiling impurities by distilling the acrylic acid obtained from the bottom of the column, and to obtain an acrylic acid product. Turned out to be inadequate.

Among the above-mentioned inclusions listed as impurities other than acetic acid, formic acid (bp 100.8 ° C.), acetaldehyde (bp 20.8 ° C.), formaldehyde (bp-1)
Both 9.5 ° C.) and acrolein (bp 52.5 ° C.) have low boiling points, and can be sufficiently removed without using the above azeotropic distillation.

[0007]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, an object of the present invention is to eliminate by-products such as acrylic acid and acetic acid obtained by collecting a mixed gas after catalytic gas phase oxidation with water. Acrylic acid aqueous solution containing, azeotropic distillation by adding the selected azeotropic solvent, distilling the azeotropic solvent, acetic acid and water from the tower top,
In obtaining acrylic acid from the bottom of the column, a azeotropic solvent substantially,
An object of the present invention is to provide a method for purifying high-purity acrylic acid in which all of acetic acid and water are distilled out from the top of the tower and substantially only acrylic acid is extracted from the bottom of the tower.

Another object of the present invention is that the liquid extracted from the bottom of the column can be used as it is as a raw material for the production of acrylic acid ester, and further, it can be distilled to remove high-boiling impurities to obtain a sufficiently high quality. It is an object of the present invention to provide a method for obtaining high-purity acrylic acid, which allows acrylic acid products to be obtained.

Still another object of the present invention is to use a mixture of two or more azeotropic solvents as the azeotropic solvent.
It is to find a particularly good combination azeotropic solvent system, and especially to find its excellent mixing ratio. Still another object of the present invention is to obtain acetic acid obtained from the top of an azeotropic separation column.
It is intended to provide an industrially advantageous method in which a water-azeotropic solvent mixture is separated into water for forming the acrylic acid aqueous solution and an azeotropic solvent for azeotropic distillation and these can be recycled. It is what Another object of the present invention is to
It will be understood according to what will be described below, and its effects will be easily understood by those skilled in the art.

[0010]

The present invention achieves the above objects, and the central technical idea is to use the following solvent A and solvent B as an azeotropic solvent as a mixed solvent. By using such a combination of the selected solvents A and B, a mixture of acetic acid, water and an azeotropic solvent is distilled out substantially from the top of the azeotropic separation column, and the mixture is extracted from the bottom of the column. It became possible to take out highly pure acrylic acid containing substantially no acetic acid, water and azeotropic solvent. Solvent A: at least one selected from the group consisting of diethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl tert-butyl ketone, n-propyl acetate
Solvent B: Solvent B: at least one solvent selected from the group consisting of toluene, heptane, and methylcyclohexane

[0011]

The present invention embodies such a technical idea by various embodiments, and a typical embodiment will be described below based on the flow sheet shown in FIG. 1 and some embodiments. However, the technical scope of the present invention is not limited by the description, and other embodiments also include the technical scope of the present invention as long as they do not deviate from or contradict the gist of the present invention. include.

A mixed gas obtained by catalytic vapor-phase oxidation of propylene or the like with a gas containing molecular oxygen is introduced from a line 1 to an acrylic acid collection column 101, and brought into contact with water introduced from a line 2 to make acrylic acid from a line 4. An acrylic acid aqueous solution containing by-products such as acetic acid and the like is obtained. As the water supplied from the line 2 to the acrylic acid collection tower 101, water may be supplied from the line 13 and used, but as will be described later, the solvent recovery tower 1
It is preferable to use an acetic acid aqueous solution discharged from the bottom of 03.

In the case of the flow sheet shown in FIG. 1, the acrylic acid aqueous solution discharged from the bottom of the acrylic acid collection column 101 via the line 4 is supplied to the azeotropic separation column 102 as it is. However, if necessary, an acrolein stripping tower (not shown) is installed, the acrylic acid aqueous solution from line 4 is supplied to the acrolein stripping tower, and the acrolein dissolved in the acrylic acid aqueous solution is stripped, and then acrylic acid is discharged. The aqueous solution may be supplied to the azeotropic separation column 102. In this case, it is advisable to recover the acrolein that has diffused and circulate it in the reaction system.

In the azeotropic separation column 102, an acrylic acid aqueous solution is supplied from a line 4 and an azeotropic solvent is supplied from a line 5 for azeotropic distillation, and the azeotropic solvent, acetic acid and water are distilled from the top of the column, Obtain acrylic acid from the bottom.

In the present invention, the acrylic acid aqueous solution in the azeotropic separation column 102 is supplied from the line 2 to the acrylic acid collection column 101.
It varies depending on the amount of water supplied to the tank and other operating conditions, but under the production conditions for acrylic acid synthesis that is usually performed, acrylic acid is in the range of 50-80% by weight, acetic acid 2-5% by weight, and the balance water. The ones are common. The azeotropic solvent used in the present invention is a mixed solvent of the above-mentioned solvent A and solvent B.

The group of the solvent A and the group of the solvent B are as described above, and since the present invention exerts excellent effects in any combination thereof, selection of the combination is left to a person who carries out the present invention. .. However, all of the solvents A have high hydrophilicity, and the most recommended solvent among such solvents A is the azeotropic composition with water, the azeotropic temperature, and the solvent price. In consideration, methyl isobutyl ketone is most advantageous. Further, the solvent B has a high affinity with acetic acid, and any of them is expected to form an azeotropic mixture with acetic acid, and an optimal solvent may be selected depending on the progress of the reaction.

By using this specific azeotropic solvent, a mixture consisting essentially of acetic acid, water and an azeotropic solvent is distilled from the top of the azeotropic separation column 102, and substantially acetic acid and water are extracted from the bottom of the column. Thus, acrylic acid containing no azeotropic solvent can be obtained. The mixing ratio of the solvent A and the solvent B of the azeotropic solvent supplied from the line 5 is preferably in the range of 50:50 to 75:25 by weight. If the amount of solvent A is too large, the concentration of acetic acid at the bottom of the column will be high, and if the amount of solvent B is too large, the amount of acrylic acid distilled from the top of the column will increase.

A mixture of substantially acetic acid, water and an azeotropic solvent distilled from the top of the azeotropic separation column 102 is received in a storage tank 20, where an organic phase mainly consisting of the azeotropic solvent and mainly acetic acid and water. And an aqueous phase consisting of. The organic phase is circulated to the azeotropic separation column 102 via line 5. On the other hand, the aqueous phase is introduced into the solvent recovery tower 103 through the line 8 and distilled, and the azeotropic solvent is distilled off from the top of the solvent recovery tower 103 in the line 9
After returning to the storage tank 20, the aqueous acetic acid solution consisting essentially of acetic acid and water is extracted from the bottom of the solvent recovery column 103 via the line 14 and discharged out of the system. However, this acetic acid aqueous solution can also be effectively utilized by circulating it from the line 10 to the acrylic acid collection tower 101 and using it as water to be brought into contact with the mixed gas obtained by catalytic vapor phase oxidation. By doing so, it is better not only to collect and circulate the acetic acid aqueous solution but also to use the acetic acid aqueous solution as the water to be brought into contact with the mixed gas obtained by the catalytic gas phase oxidation, rather than using only the water from the line 13. Also, since the efficiency of collecting acrylic acid becomes high, the advantage that the required number of stages of the acrylic acid collecting tower 101 is small can be obtained. It is understood that this is because acetic acid in the acetic acid aqueous solution has a good affinity for acrylic acid. It is desirable to control the amount of water supplied from the line 13 and the amount of aqueous acetic acid solution withdrawn from the line 14 to maintain the overall balance so that the acetic acid concentration does not rise excessively while circulating through the system.

Acrylic acid extracted from the bottom of the azeotropic separation column 102 can be sent to an esterification step via a line 15 and used as it is as a raw material for producing an acrylic ester. In addition, to obtain high-purity acrylic acid products,
After passing through the line 7 to the high boiling separation column 104 for distillation, a high boiling point substance such as a polymer is withdrawn from the bottom of the column through a line 12, and an acrylic acid product is obtained from the top of the column through a line 11.

[0020]

By using the specific azeotropic solvent of the present invention, acrylic acid hardly distills from the top of the azeotropic separation column, and substantially acetic acid, water and the azeotropic solvent form the bottom of the column. It is possible to obtain acrylic acid that does not contain any of the above, and the bottom liquid of the azeotropic separation column can be used as it is as a raw material for producing an acrylate ester. You can now get the product. Therefore, conventionally, the acetic acid separation column was further provided after the azeotropic separation to separate the remaining acetic acid, but the method of the present invention does not require the acetic acid separation column, and the acrylic acid production process can be greatly simplified.

[0021]

【Example】

Example 1 A mixed gas obtained by catalytic vapor-phase oxidation of propylene with a molecular oxygen-containing gas was introduced into an acrylic acid collection column and brought into contact with water, and an aqueous solution obtained was introduced into an acrolein stripping column to diffuse acrolein, An acrylic acid aqueous solution containing 30% by weight of water and 3.0% by weight of acetic acid was obtained. Number of steps 60 steps, step interval 147
Using an azeotropic separation column 102 equipped with a sieve tray of mm, a distillation pipe at the top of the column, a raw material supply pipe at the center, and a column bottom liquid extraction pipe at the bottom of the column, using methyl isobutyl ketone and toluene as azeotropic solvents Azeotropic distillation operation of this acrylic acid aqueous solution was performed using a mixed solvent (mixing weight ratio of 65:35).

The operating conditions during steady operation are as follows: tower temperature 47 ° C., tower bottom temperature 98 ° C., tower top pressure 100 mmHg, reflux ratio (total moles of reflux liquid per unit time / unit time). (Total number of moles of distillate per unit) was 1.42, and the amount of raw material supplied from the line 4 was 7.59 liters / hour. The aqueous phase in line 8 contains 6.7% by weight acetic acid and 0.5% by weight acrylic acid, while from the bottom of the azeotropic separation column 102 to line 1
The liquid extracted through 5 is 97.0% by weight of acrylic acid,
It contained acetic acid 0.03% by weight, solvent 0.001% by weight, and other 2.97% by weight.

The aqueous phase obtained from the line 8 is the solvent recovery tower 1
03, and the solvent is recovered from the top of the column via line 9, while the aqueous acetic acid solution is taken out from the bottom of the column via line 10. The composition is 7.1% by weight of acetic acid, 0.53% by weight of acrylic acid, and the balance is water, and is an absorption scavenger for contacting with the mixed gas after the catalytic gas phase oxidation by being recycled to the acrylic acid collection tower 101. Used as.

Comparative Example 1 An azeotropic distillation operation of an aqueous acrylic acid solution was carried out in the same manner as in Example 1 except that only methyl isobutyl ketone was used as the azeotropic solvent and the reflux ratio was 1.43. ..

The aqueous phase in the line 8 in the steady operation contained 6.6% by weight of acetic acid and 4.0% by weight of acrylic acid, and the amount of acrylic acid was about 8 times as much as that of Example 1. On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 via the line 15 is 96.9% by weight of acrylic acid, 0.2% by weight of acetic acid, and 0.
The content of acetic acid was higher than that of Example 1 by one digit.

Comparative Example 2 An azeotropic distillation operation of an acrylic acid aqueous solution was carried out in the same manner as in Example 1 except that only toluene was used as the azeotropic solvent and the reflux ratio was 1.23.

The water phase in the line 8 during steady operation contained 6.7% by weight of acetic acid and 5.8% by weight of acrylic acid, and the amount of acrylic acid was about 10 times as much as that of Example 1. On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 via the line 15 contains 97.0% by weight of acrylic acid, 0.03% by weight of acetic acid, 0.01% by weight of solvent, and 2.96% by weight of others. I was out.

Example 2 In Example 1, as the azeotropic solvent, a mixed solvent of methyl isobutyl ketone and heptane (mixing weight ratio 65:35).
Was used, and the azeotropic distillation operation of the acrylic acid aqueous solution was performed in the same manner as in Example 1 except that the reflux ratio was 1.65.

The water phase in line 8 during steady operation contained 6.6% by weight acetic acid and 0.6% by weight acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 96.9% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 3.07% by weight of others.

Example 3 In Example 1, a mixed solvent of methyl tert-butyl ketone and toluene was used as an azeotropic solvent (mixing weight ratio 65: 3).
Azeotropic distillation operation of the acrylic acid aqueous solution was carried out in the same manner as in Example 1 except that 5) was used and the reflux ratio was 1.89.

The water phase in line 8 during steady operation contained 6.7% by weight acetic acid and 0.5% by weight acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 via the line 15 is 97.3% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.67% by weight of others.

Example 4 In Example 1, a mixed solvent of methyl tert-butyl ketone and heptane was used as an azeotropic solvent (mixing weight ratio 65: 3).
Azeotropic distillation operation of the acrylic acid aqueous solution was carried out in the same manner as in Example 1 except that 5) was used and the reflux ratio was 1.99.

The water phase in line 8 during steady operation contained 6.6% by weight acetic acid and 0.5% by weight acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 97.2% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.77% by weight of others.

Comparative Example 3 An azeotropic distillation of an aqueous acrylic acid solution was carried out in the same manner as in Example 1 except that the mixing weight ratio of methyl isobutyl ketone and toluene was changed to 85:15 and the reflux ratio was changed to 1.41. Distillation operation was performed. The water phase in line 8 during steady operation contained 5.8 wt% acetic acid and 0.5 wt% acrylic acid. On the other hand, from the bottom of the azeotropic separation tower 102 to the line 1
The liquid extracted through 5 is 97.3% by weight of acrylic acid,
Acetic acid 0.10% by weight, solvent 0.01% by weight, others 2.
It contained 59% by weight.

Example 5 An azeotropic distillation of an aqueous acrylic acid solution was carried out in the same manner as in Example 1 except that the mixing weight ratio of methyl isobutyl ketone and toluene was changed to 50:50 and the reflux ratio was changed to 1.49. Distillation operation was performed.

The water phase in line 8 during steady operation contained 6.7% by weight acetic acid and 0.5% by weight acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is acrylic acid 96.8% by weight, acetic acid 0.0
It contained 3% by weight, 0.001% by weight of solvent, and 3.17% by weight of others.

Example 6 In Example 1, as an azeotropic solvent, a mixed solvent of methyl isobutyl ketone and methylcyclohexane (mixing weight ratio 6) was used.
5:35) and the azeotropic distillation operation of the acrylic acid aqueous solution was performed in the same manner as in Example 1 except that the reflux ratio was 1.25.

The water phase in line 8 during steady operation contained 6.6 wt% acetic acid and 0.5 wt% acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 via the line 15 is 97.3% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.67% by weight of others.

Example 7 Example 1 was repeated except that a mixed solvent of methyl tert-butyl ketone and methylcyclohexane (mixing weight ratio 65:35) was used as the azeotropic solvent and the reflux ratio was 1.60. The azeotropic distillation operation of the acrylic acid aqueous solution was performed in the same manner as in.

The water phase in line 8 during steady operation contained 6.8% by weight acetic acid and 0.5% by weight acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 97.4% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.57% by weight of others.

Example 8 The same as Example 1 except that a mixed solvent of diethyl ketone and toluene (mixing weight ratio 65:35) was used as the azeotropic solvent and the reflux ratio was 1.58. The azeotropic distillation operation of the acrylic acid aqueous solution was performed.

The water phase in line 8 during steady operation contained 6.2% by weight of acetic acid and 0.5% by weight of acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 97.2% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.77% by weight of others.

Example 9 In the same manner as in Example 1, except that a mixed solvent of diethyl ketone and heptane (mixing weight ratio of 65:35) was used as the azeotropic solvent and the reflux ratio was 1.83. The azeotropic distillation operation of the acrylic acid aqueous solution was performed.

The water phase in the line 8 in the steady operation contained 6.0% by weight of acetic acid and 0.4% by weight of acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 via the line 15 is 97.0% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.97% by weight of others.

Example 10 In Example 1, a mixed solvent of diethyl ketone and methylcyclohexane was used as an azeotropic solvent (mixing weight ratio 65: 3).
The azeotropic distillation operation of the acrylic acid aqueous solution was performed in the same manner as in Example 1 except that 5) was used and the reflux ratio was 1.34.

The water phase in line 8 during steady operation contained 6.1% by weight of acetic acid and 0.4% by weight of acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 97.4% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.57% by weight of others.

Example 11 The same as Example 1 except that a mixed solvent of methyl propyl ketone and toluene (mixing weight ratio 65:35) was used as the azeotropic solvent and the reflux ratio was 1.67. Then, the azeotropic distillation operation of the acrylic acid aqueous solution was performed.

The aqueous phase in line 8 during steady operation contained 6.1% by weight acetic acid and 0.4% by weight acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 via the line 15 is 97.3% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.67% by weight of others.

Example 12 Same as Example 1 except that a mixed solvent of methyl propyl ketone and heptane (mixing weight ratio 65:35) was used as the azeotropic solvent and the reflux ratio was 1.94. Then, the azeotropic distillation operation of the acrylic acid aqueous solution was performed.

The water phase in the line 8 in the steady operation contained 6.0% by weight of acetic acid and 0.4% by weight of acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 97.1% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.87% by weight of others.

Example 13 In Example 1, as an azeotropic solvent, a mixed solvent of methylpropylketone and methylcyclohexane (mixing weight ratio: 6) was used.
5:35) and the azeotropic distillation operation of the aqueous acrylic acid solution was performed in the same manner as in Example 1 except that the reflux ratio was 1.58.

The water phase in line 8 during steady operation contained 6.2% by weight of acetic acid and 0.5% by weight of acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 97.1% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.87% by weight of others.

Example 14 In Example 1, a mixed solvent of n-propyl acetate and toluene (mixing weight ratio 65:35) was used as an azeotropic solvent,
Azeotropic distillation operation of the acrylic acid aqueous solution was performed in the same manner as in Example 1 except that the reflux ratio was changed to 2.10.

The aqueous phase in line 8 during steady operation contained 6.2% by weight of acetic acid and 0.5% by weight of acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 97.5% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.47% by weight of others.

Example 15 In Example 1, a mixed solvent of n-propyl acetate and heptane (mixing weight ratio 65:35) was used as an azeotropic solvent,
The azeotropic distillation operation of the acrylic acid aqueous solution was performed in the same manner as in Example 1 except that the reflux ratio was 2.14.

The aqueous phase in line 8 during steady operation contained 6.2% by weight of acetic acid and 0.5% by weight of acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 through the line 15 is 97.4% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.57% by weight of others.

Example 16 In Example 1, a mixed solvent of n-propyl acetate and methylcyclohexane was used as an azeotropic solvent (mixing weight ratio 65: 3).
Azeotropic distillation operation of the acrylic acid aqueous solution was carried out in the same manner as in Example 1 except that 5) was used and the reflux ratio was 1.66.

The aqueous phase in line 8 during steady operation contained 6.3% by weight acetic acid and 0.5% by weight acrylic acid.
On the other hand, the liquid extracted from the bottom of the azeotropic separation column 102 via the line 15 is 97.3% by weight of acrylic acid and 0.0% of acetic acid.
It contained 3% by weight, 0.001% by weight of solvent, and 2.67% by weight of others.

[Brief description of drawings]

FIG. 1 is a flow sheet for carrying out the present invention.

[Explanation of symbols]

 101 acrylic acid collection tower 102 azeotropic separation tower 103 solvent recovery tower 104 high boiling separation tower 20 storage tank

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yoji Akazawa, 992, Nishi-oki, Niigata, Himeji, Aboshi-ku, Himeji-shi, Hyogo Pref., Nihon Shatai Co., Ltd. 1 Inside Nippon Shokubai Himeji Factory

Claims (4)

[Claims] 1. A mixed gas obtained by catalytic vapor-phase oxidation of propylene and / or acrolein with a gas containing molecular oxygen is introduced into an acrylic acid collection column and brought into contact with water to produce by-products such as acrylic acid and acetic acid. Obtaining an acrylic acid aqueous solution containing, when the acrylic acid aqueous solution is introduced into an azeotropic separation column to separate acrylic acid by distillation using an azeotropic solvent, diethyl ketone, methyl propyl ketone, methyl isobutyl ketone as an azeotropic solvent, Azeotropic separation using a mixed solvent of at least one solvent A selected from methyl-tert-butyl ketone and n-propyl acetate and at least one solvent B selected from toluene, heptane and methylcyclohexane. Substantially acetic acid from the top of the tower, water, a mixture of azeotropic solvent is distilled off, substantially acetic acid from the bottom of the tower,
A method for producing acrylic acid, which comprises obtaining acrylic acid containing neither water nor an azeotropic solvent. 2. The method according to claim 1, wherein the mixing ratio of the azeotropic solvent, solvent A and solvent B, is in the range of 50:50 to 75:25 by weight. 3. Aqueous acrylic acid solution introduced into the azeotropic separation column comprises acrylic acid 50 to 80% by weight, acetic acid 2 to 5% by weight,
The method according to claim 1 or 2, which is an acrylic acid aqueous solution containing 20 to 40% by weight of water. 4. A mixture of substantially acetic acid, water and an azeotropic solvent obtained from the top of the azeotropic separation column is introduced into a solvent recovery column for distillation, and the azeotropic solvent is contained from the top of the solvent recovery column. While distilling off the fraction and circulating it in the azeotropic separation column, an aqueous acetic acid solution consisting essentially of acetic acid and water is extracted from the bottom of the solvent recovery column and circulated in the acrylic acid collection column for contact gas phase. The method according to any one of claims 1 to 3, which is used as water to be brought into contact with a mixed gas obtained by oxidation.