JPH07228548A - Method for purifying acrylic acid - Google Patents

Abstract

PURPOSE:To efficiently obtain a high-purity acrylic acid useful as a raw material, etc., for water absorbing resins such as paper diaper while preventing polymerization in distillation by adding a specific compound to an acrylic acid obtained by a vapor phase catalytic oxidation method and distilling the acrylic acid at a specific temperature to purify the acrylic acid. CONSTITUTION:(A) A hydrazine compound such as hydrazine hydrate or phenylhydrazine and (B) dithiocarbamic acid such as dimethyldithio carbamate such as copper dimethyldithio carbamate or copper ethylene dithiocarbamate are added to an acrylic acid obtained by a vapor phase catalytic oxidation method and containing by-products, e.g. aldehydes such as furfural or benzaldehyde, ketones such as acetone and distillation is carried out at <=100 deg.C so as to purify the acrylic acid obtained by the vapor phase catalytic oxidation method to provide the objective high-purity acrylic acid. Furthermore, a phenol compound such as phenol or hydroquinone in addition to the components A and B is preferably added to the acrylic acid.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for purifying acrylic acid. More specifically, it relates to a vapor phase catalytic oxidation method for purifying acrylic acid by distillation.

[0002]

BACKGROUND OF THE INVENTION A method for producing acrylic acid by vapor phase catalytic oxidation is well known as an industrial production method. However, in the production process, aldehydes such as furfural and benzaldehyde, and acetone. It is known that ketones and the like are produced as by-products.

In recent years, acrylic acid has been in increasing demand as a raw material for water-absorbent resins such as paper diapers, but high purity is required for such applications. Therefore, acrylic acid is industrially purified by distillation. However, it is difficult to remove impurities in acrylic acid by vapor-phase catalytic oxidation as described above, especially furfural, by ordinary distillation, and when such a raw material is used as a raw material for an acrylic acid polymer without removing such impurities, the reaction is delayed during the polymerization reaction, Problems such as a decrease in the degree of polymerization and coloring of the polymer may occur.

In order to solve this problem, a method of adding a hydrazine compound during the distillation of acrylic acid has been proposed. Although this method is effective in removing the impurities, it has a problem of causing polymerization of acrylic acid during distillation. The formation of the polymer not only causes a decrease in heat transfer performance due to the adhesion to the heat transfer surface of the distillation column reboiler, but may also cause a reduction in the capacity of the distillation column and a blockage in the distillation column. A method capable of suppressing the formation of a polymer has been desired. An object of the present invention is to provide a method capable of efficiently purifying acrylic acid by vapor phase catalytic oxidation while suppressing the production of a polymer.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies on a method for purifying acrylic acid by vapor phase catalytic oxidation, and found that a hydrazine compound and copper dithiocarbamate were added to acrylic acid by vapor phase catalytic oxidation. After that, it was found that the method of distilling could achieve the above-mentioned object, and further studies were conducted to complete the present invention.

That is, the present invention relates to a method for purifying acrylic acid, which is characterized in that a hydrazine compound and copper dithiocarbamate are added to acrylic acid in the vapor phase catalytic oxidation method and then distilled at 100 ° C. or lower.

The present invention will be described in detail below. Acrylic acid used in the present invention is a so-called vapor-phase catalytic oxidation acrylic acid obtained by vapor-phase catalytic oxidation of propylene and / or acrolein, and is usually an impurity such as furfural, which is a by-product in the production process.
It includes aldehydes such as benzaldehyde and ketones such as acetone.

Examples of the hydrazine compound include hydrazine hydrate, phenylhydrazine, hydrazine sulfate and hydrazine hydrochloride. The amount of the hydrazine compound added is not particularly limited because it depends on the amount of impurities, etc.
~ 5000 ppm, preferably about 200 ppm-300
It is 0 ppm. By this, contained in acrylic acid,
It is possible to remove the above-mentioned impurities that adversely affect when acrylic acid is used as a raw material for the polymerization reaction, particularly furfural, which is likely to accompany acrylic acid during distillation.

Examples of the copper dithiocarbamate used include copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate, copper dibutyldithiocarbamate, etc., copper dialkyldithiocarbamate, copper ethylenedithiocarbamate, copper tetramethylenedithiocarbamate, penta Examples include cyclic copper alkylenedithiocarbamate such as copper methylenedithiocarbamate and copper hexamethylenedithiocarbamate, and cyclic copper oxydialkylenedithiocarbamate such as copper oxydiethylenedithiocarbamate. In terms of availability, copper dialkyldithiocarbamate is preferable.

The amount of copper dithiocarbamate added depends on the amount of impurities, etc., and is not particularly limited, but is usually about 1 to 100 ppm, preferably about 5 to 80 ppm, and more preferably about 10 ppm to acrylic acid.
It is 50 ppm. If the amount of copper dithiocarbamate is too small, the effect of preventing polymerization is not sufficient especially at the initial stage of distillation. Excessive addition has no particular problem in terms of polymerization prevention effect,
When distilling, the concentration of copper dithiocarbamate in the can is too high, which may cause corrosion of the apparatus, which is not preferable.

The method of adding the hydrazine compound and copper dithiocarbamate is not particularly limited, but for example,
Examples thereof include a method of directly adding each to acrylic acid, and a method of adding each or both of them by dissolving them in a suitable organic solvent. The addition temperature can be appropriately determined. These may be added, for example, immediately after the production of acrylic acid, but it is preferable to add them immediately before performing the distillation. Industrially, the acrylic acid is fed to the distillation apparatus in the stock solution or by distillation to the side of the distillation can. It is usually dissolved in the refluxed liquid and supplied.

Further, in the present invention, it is preferable to add a phenol compound in addition to the hydrazine compound and copper dithiocarbamate because the effect of the present invention is further improved. Examples of the phenol compound used include phenol, hydroquinone, metoquinone (p-methoxyphenol), catechol and cresol.

The amount of the phenol compound added may vary depending on the amount of impurities, etc., but is usually about 10 p with respect to acrylic acid.
pm-500 ppm, preferably about 50 ppm-300
It is ppm. Further, other additives such as phenothiazine and manganese salt may be further added. These can be added in the same manner as described above.

The acrylic acid thus added with the hydrazine compound and copper dithiocarbamate is subjected to distillation,
Impurities are removed. The method is not particularly limited, but various methods such as simple distillation and precision distillation can be applied. Specifically, the method and the like shown in the examples of JP-A-49-30312 can be applied. Further, the distillation can be applied to both continuous and batch systems.
Industrially, the continuous type is preferable.

As the material of the liquid contact surface of the apparatus in the distillation, for example, stainless steel such as SUS304 and SUS316 can be used. The distillation temperature is 100 ° C. or lower, preferably 80 ° C. or lower, more preferably 70 ° C. or lower.

The residence time of acrylic acid depends on the distillation temperature, but when the distillation temperature is 80 to 100 ° C., it is usually 5 hours or less, preferably 3 hours or less, more preferably 1 hour or less. When the distillation temperature is 70 to 80 ° C, usually 20
The time is not more than 10 hours, preferably not more than 10 hours, more preferably not more than 5 hours. When the distillation temperature is 70 ° C. or lower, it is usually 40 hours or less, preferably 20 hours or less, more preferably 10 hours or less. The concentration rate of the distillation bottom liquid may vary depending on the type of distillation, the distillation temperature and time, the type and amount of impurities, etc. Normally, it is possible to control the concentration of copper dithiocarbamate to 1% by weight or less. It is preferable in terms of preventing corrosion.

[0017]

EFFECTS OF THE INVENTION According to the method of the present invention, the purification of acrylic acid by vapor phase catalytic oxidation can be efficiently carried out while preventing the polymerization during distillation. As a result, impurities contained in the vapor-phase catalytic oxidation acrylic acid and having a bad influence when acrylic acid is used as a raw material for the polymerization reaction can be removed, and its industrial value is great.

[0018]

EXAMPLES Examples will be given below to specifically explain the present invention, but the present invention is not limited to these examples. Example 1 20 kg of copper dibutyldithiocarbamate was added to 1 kg of crude acrylic acid containing 200 ppm of furfural as an impurity.
0.1 pm (vs. crude acrylic acid) and hydrazine hydrate
It was added so as to be wt% (vs. crude acrylic acid), vacuum distillation was carried out at 50 Torr and 69 ° C. using an evaporator, and concentrated 200 times in 1 hour. Almost no formation of a polymer was observed in the kettle liquid during and after the distillation. In addition, when furfural in the distillate was analyzed, 1
It was below ppm.

Examples 2 to 5 The same operation as in Example 1 was carried out except that the addition amount of copper dibutyldithiocarbamate and the kind of the addition additive and the addition amount thereof were changed as shown in Table 1. The results are shown in Table 1. In addition, the addition amount is based on the amount of crude acrylic acid.

[0020]

[Table 1] * ◎: Not recognized at all ○: Almost not found

Comparative Examples 1 to 5 The same operation as in Example 1 was carried out except that copper dibutyldithiocarbamate was not added and the kind of additive to be added and the addition amount thereof were changed as shown in Table 2. The results are shown in Table 2.
In addition, the addition amount is based on the amount of crude acrylic acid.

[0022]

[Table 2]

Claims (5)

[Claims] 1. A hydrazine compound and copper dithiocarbamate are added to acrylic acid by a vapor phase catalytic oxidation method, and then 10
A method for purifying acrylic acid, which comprises distilling at 0 ° C. or lower. 2. The method according to claim 1, further comprising adding a phenol compound. 3. Copper dithiocarbamate is copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate, copper dibutyldithiocarbamate, copper ethylenedithiocarbamate, copper tetramethylenedithiocarbamate, copper pentamethylenedithiocarbamate, hexamethylenedithiocarbamate. A copper oxyacid or a copper oxydiethylenedithiocarbamate.
The method described. 4. The method according to claim 1, wherein the phenol compound is phenol, hydroquinone, methoquinone, catechol or cresol. 5. The method according to claim 1, wherein the hydrazine compound is hydrazine hydrate, phenylhydrazine, hydrazine sulfate and hydrazine hydrochloride.