JP2000053612A - Prevention of polymerization of acrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing the polymerization of acrylic acid, capable of giving an excellent polymerization-inhibiting effect even in an acrylic acid-purifying process including a process in which an acrylic acid aqueous solution is dehydrated and distilled using an azeotropic acid. SOLUTION: This method for preventing the polymerization of acrylic acid comprises adding at least one compound selected from ammonia, ammonium salts, aliphatic primary monoamines, aliphatic primary diamines, aliphatic polyamines, aromatic primary amines, and amino acids, and a polymerization inhibitor preferably comprising (1) at least one of phenothiazine and methylene blue and (2) at least one of dialkyldithiocarbamic acid copper salts consisting of dimethyldithiocarbamic acid copper salt, diethyldithiocarbamic acid copper salt, dipropyldithiocarbamic acid copper salt and dibutyldithiocarbamic acid copper salt to crude acrylic acid or its aqueous solution to be fed for the purification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to propylene and / or propylene.
Alternatively, a crude acrylic acid aqueous solution obtained by cooling and / or absorbing a product gas obtained by gas phase catalytic oxidation of acrolein with a molecular oxygen-containing gas into water is dehydrated and distilled using an azeotropic agent that azeotropes with water. In addition, the present invention relates to a method for preventing acrylic acid polymerization in a method for purifying acrylic acid by a process including light-boiling distillation and high-boiling distillation.

[0002]

2. Description of the Related Art Acrylic acid is currently industrially produced by a method of gas-phase catalytic oxidation of propylene and / or acrolein with a molecular oxygen-containing gas. As a method widely used as a method for purifying this acrylic acid, a method in which a crude acrylic acid aqueous solution obtained by cooling and / or absorbing water in an oxidation reaction product gas is used to extract acrylic acid using an extractant, There is a method of performing dehydration distillation using an azeotropic agent that azeotropes with water. The crude acrylic acid from which water has been separated is further purified through steps such as light-boiling separation distillation and high-boiling separation distillation. However, acrylic acid itself has the property of easily and extremely intensely polymerizing due to heat, light, peroxides, etc., so when purifying it by distillation, a large amount of polymer is generated. It is known that not only does the performance of the distillation column decrease due to the above, and the heat transfer performance decreases due to the adhesion of the polymer to the heat transfer surface of the distillation column reboiler, but also the blockage due to the polymer in the distillation column occurs. . These phenomena are a great obstacle in the process for producing acrylic acid, and it is extremely important industrially how to suppress the polymerization.

[0003] For this reason, conventionally, as an important method for preventing polymerization in the purification of acrylic acid, the addition of a so-called polymerization inhibitor has been proposed and implemented. Representative polymerization inhibitors include phenols such as hydroquinone, p-methoxyphenol and 2,6-di-t-butylphenol; amines such as phenothiazine and methylene blue; copper salts such as copper dibutyldithiocarbamate; and other nitro compounds. , Nitroso compounds, N-oxyl compounds and the like are known. For example, Japanese Patent Publication No. 49-3
No. 514 describes that a dibutyldithiocarbamate copper salt is added as a polymerization inhibitor in a distillation / concentration step in the production of an unsaturated carboxylic acid or an ester thereof. In the distillation of acrylic acid, these polymerization inhibitors are generally used in combination, and in some cases, in combination with a molecular oxygen-containing gas. For example, at least one selected from hydroquinone, hydroquinone monomethyl ether, phenothiazine, etc.
Combination of seed, dimethyldithiocarbamic acid copper salt and the like and molecular oxygen (Japanese Patent Application Laid-Open No. 49-85016), combination of phenols and manganese salt and hindered phenol (Japanese Patent Application Laid-Open No. 5-10027), N-oxyl A combination of a compound with a phenothiazine, an aromatic amine, or a phenol compound (JP-A-5-320217) is known. However, the problem of polymerization in acrylic acid refining is greatly affected by the refining process, distillation temperature, residence time, and so on.
Even these conventional methods are not sufficient, and a more effective polymerization prevention method is required at present.

[0004]

The problem to be solved by the present invention is to purify acrylic acid by distillation from an aqueous solution of acrylic acid obtained by subjecting propylene and / or acrolein to gas-phase catalytic oxidation with a molecular oxygen-containing gas. Is to provide a more effective polymerization prevention method. In particular, an object of the present invention is to provide a method for preventing polymerization in a process employing an azeotropic dehydration method instead of an extraction method as a method for removing water.

An aqueous acrylic acid solution obtained by subjecting propylene and / or acrolein to gas-phase catalytic oxidation with a molecular oxygen-containing gas is subjected to dehydration distillation using an azeotropic agent, and then purified by light-boiling distillation and high-boiling distillation. Acrylic acid
Acrylic acid is extracted using an extractant, followed by light-boiling separation distillation,
It has higher polymerizability than acrylic acid purified by high-boiling separation distillation, and when a conventionally known polymerization inhibitor such as phenothiazine, copper salt of dibutyldithiocarbamate, hydroquinone or p-methoxynol is used alone or in combination. However, the polymerization inhibitory effect is not expected to exhibit a satisfactory effect as compared with the purification of an aqueous acrylic acid solution obtained using an extractant. In view of such circumstances, the present inventors have intensively studied to find a method capable of obtaining an excellent polymerization inhibitory effect even in a purification step of acrylic acid including a step of dehydration distillation using an azeotropic agent. When the specific substance is present in the aqueous acrylic acid solution, the azeotropic dehydration method may be used to purify the aqueous acrylic acid solution using an extractant in the presence of the known polymerization inhibitor. The present inventors have found that they exhibit a polymerization prevention effect substantially equivalent to that of the present invention, and have completed the present invention.

[0006]

SUMMARY OF THE INVENTION The present invention provides an acrylic acid solution comprising a step of dehydrating and distilling an aqueous solution of acrylic acid obtained by subjecting propylene and / or acrolein to gas-phase catalytic oxidation with a molecular oxygen-containing gas using an azeotropic agent. In the purification of
At least one selected from the group consisting of ammonia, ammonium salts, aliphatic primary monoamines, aliphatic primary diamines, aliphatic polyamines, aromatic primary amines, and amino acids is added to crude acrylic acid or an aqueous solution thereof for purification. A method for preventing polymerization of acrylic acid, which comprises adding a seed and a polymerization inhibitor for acrylic acid.

[0007]

Embodiments of the present invention will be described below in detail. In the present invention, a crude acrylic acid aqueous solution obtained by cooling and / or absorbing a product gas obtained by gas-phase catalytic oxidation of propylene and / or acrolein with a molecular oxygen-containing gas and / or absorbing it with water is azeotroped with water. The target is a purification method in which dehydration distillation is performed using an azeotropic agent. The crude acrylic acid aqueous solution may be obtained by a one-stage oxidation method of propylene, or may be obtained by a two-stage oxidation method via acrolein,
Further, it may be obtained by a method of recycling a part of the exhaust gas from the acrylic acid absorption tower to an oxidation reaction, or a method of recycling the exhaust gas obtained by rendering this exhaust gas harmless through an exhaust gas combustor.

The main composition of the crude acrylic acid aqueous solution varies depending on the catalyst used and the reaction conditions.
%, Water 20 to 50%, and acetic acid 4 to 10%. Further, the aqueous solution contains aldehydes such as formaldehyde, acetaldehyde, acrolein, furfural, benzaldehyde, organic acids such as propionic acid and maleic acid, and many other by-products. The method of removing water from the crude acrylic acid aqueous solution is a conventionally known method, for example, using toluene, methyl isobutyl ketone, xylene, ethylbenzene, heptane and a mixture thereof as an azeotropic agent, and about 10 to 30 kPa. Perform azeotropic dehydration under vacuum. By this treatment, the water concentration in the bottom liquid is usually 1000 ppm or less. From the top of the azeotropic dehydration tower, light boiling components of water, acetic acid, azeotropic solvents and other by-products are distilled off. However, in the extraction method, some of the components dissolved and removed on the water side are not sufficiently removed and remain in the bottom liquid.

The bottom liquid obtained by the azeotropic dehydration method is further subjected to light-boiling separation distillation and then to high-boiling separation distillation, and the resulting acrylic acid is extracted with an aqueous solution using a mixed solvent of xylene and methyl ethyl ketone. Subsequently, compared with acrylic acid obtained by performing light-boiling separation distillation and high-boiling separation distillation, the polymerizability is higher when a polymerization test is performed under the same conditions.

However, by adding a very small amount of amines to acrylic acid obtained by the azeotropic dehydration method having high polymerizability, polymerization can be greatly suppressed. Although the reason for this is not fully understood, trace amounts of by-products removed in the extraction step in the extraction method remain in the azeotropic dehydration method and act as a substance that promotes polymerization. This is presumed to be due to the fact that this substance was converted into a substance that did not react and promote polymerization. The behavior of this substance, which is presumed to be the same as a specific peak detected together with formaldehyde, acrolein, and the like, by performing derivative analysis with 2,4-dinitrophenylhydrazine by liquid chromatography, matches the behavior. That is, acrylic acid in the extraction method does not have this peak, but exists in acrylic acid in the azeotropic dehydration method, and disappears by treatment with amines. One of the amines to be added is ammonia or an ammonium salt such as ammonium acetate or ammonium acrylate. The aliphatic primary monoamines include methylamine, ethylamine, propylamine, isopropylamine, n-butylamine, sec-butylamine, tert-butylamine, n-hexylamine, cyclohexylamine, and n-butylamine.
Octylamine, 2-ethylhexylamine and the like can be mentioned. Aliphatic primary diamines include ethylenediamine, trimethylenediamine, 1,4-diaminobutane,
Hexamethylene diamine and the like can be mentioned. Examples of the aliphatic polyamines include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 3- (methylamino) propylamine, diaminopropylamine,
N-methyl-3,3'-iminobis (propylamine)
And the like. Examples of the aromatic primary amines include aniline, toluidine, anisidine, aminophenol, phenylenediamine and the like. Amino acids include glycine, alanine, methionine and the like.

The effect of the addition of amines was also confirmed in the bottom liquid of the azeotropic dehydration tower, the bottom liquid of the light-boiling separation tower, and the distillate, which are process liquids in the purification step. It is considered that this substance has already been generated in the stage of the aqueous oxidation reaction solution and cannot be sufficiently separated from acrylic acid by the distillation operation. From the viewpoint of reducing the polymerization problem in the entire purification process, it is desirable that the addition treatment of the amines is performed on the upstream side of the process, that is, at the stage of the liquid feed or the liquid withdrawn from the bottom of the azeotropic dehydration column.

The amount of the amines to be added may be an amount capable of substantially treating a polymerization accelerating substance considered to be present in a very small amount, and is about 0.001 to about 0.5% by weight, preferably about 0.001% by weight, based on acrylic acid. About 0.005 to about 0.2% by weight is sufficient.

Since amines alone are not considered to act directly as a polymerization inhibitor, they need to be used together with conventionally known polymerization inhibitors. As the polymerization inhibitor that can be used, known ones used in the purification of crude acrylic acid or an aqueous solution thereof are used. And at least one member selected from the group consisting of copper dibutyldithiocarbamate is indispensable. More preferably, phenol,
Hydroquinone, p-methoxyphenol, benzoquinone, 1,2-naphthoquinone, cresol, catechol,
2,5-di-t-butylhydroquinone, 2,6-di-
t-butylphenol, 6-t-butyl-m-cresol, 2,6-di-t-butyl-p-cresol, 4-t
-Butylcatechol, 2,4-dimethyl-6-t-butylphenol, 2-t-butylhydroquinone, 2-t
Phenols such as -butyl-4-methoxyphenol may be present. Further, an oxygen-containing gas such as air may be used in combination. The amount of the polymerization inhibitor other than the amines is not particularly limited as long as it is within a known range, but is usually about 0.0001 to about 0.5% by weight, preferably about 0.001 to about 0.2% by weight. %. The addition position of these polymerization inhibitors is not particularly limited as long as it is present in the crude acrylic acid to be subjected to the purification operation or in an aqueous solution thereof.
For example, it is added from a reflux line of a distillation column in which acrylic acid exists, such as a dehydration distillation column, a light boiling separation column, and a commercialization column.

[0014]

According to the method of the present invention described in detail above, by adding a small amount of amines, it is possible to effectively suppress the polymerization in the purification of acrylic acid by the azeotropic dehydration method. The utility value of is very large.

[0015]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In Examples and Comparative Examples,
The following method was used for the polymerization test. Polymerization test method: 5 g of a sample in which a polymerization inhibitor and an additive were previously adjusted to a predetermined concentration was placed in a test tube with a cap having an inner volume of 20 ml, and a nitrogen gas containing 100 ppm of oxygen was bubbled in a nitrogen box for 5 minutes, and then sealed. Then, this is immersed in an oil bath whose temperature is controlled to 100 ° C., heated for a predetermined time, taken out and cooled. This is diluted with water, the resulting polymer is reacted with a quaternary ammonium salt, and its turbidity is measured using a spectrophotometer to quantify polyacrylic acid. The polymerization rate per hour is calculated from the amount of polyacrylic acid.

Example 1 An aqueous solution of about 55% by weight of acrylic acid obtained by two-stage gas-phase catalytic oxidation of propylene was subjected to dehydration distillation using toluene as an azeotropic agent, followed by light-boiling distillation and further high-boiling distillation. Acrylic acid for ester (phenothiazine 20
225 ppm of 25% aqueous ammonia solution (containing 5 ppm of ammonia) in 0 ppm and containing 50 ppm of p-methoxyphenol.
6 ppm) and copper dibutyldithiocarbamate 25p
pm was added to obtain a sample. Using this sample, a polymerization test was conducted by the above method. Table 1 shows the results.

Comparative Example 1 The acrylic acid for ester obtained by the azeotropic dehydration method used in Example 1 was used as a sample for a polymerization test. Table 1 shows the results.

Comparative Example 2 A polymerization test was carried out using a sample obtained by adding 25 ppm of copper dibutyldithiocarbamate to the acrylic acid for ester obtained by the azeotropic dehydration method used in Example 1 as a sample. Table 1 shows the results.

REFERENCE EXAMPLE An aqueous solution of about 55% by weight of acrylic acid obtained by two-stage gas-phase catalytic oxidation of propylene was extracted and separated using a mixed solvent of methyl ethyl ketone and xylene. Acrylic acid for ester obtained by high boiling separation distillation (phenothiazine 200 ppm, p
(Containing 50 ppm of -methoxyphenol) as a sample, and a polymerization test was carried out. Table 1 shows the results.

[0020]

[Table 1] Azeotropic dehydration method: azeotropic dehydration method acrylic acid extraction method: extraction method acrylic acid CBSC: copper dibutyldithiocarbamate Pz: phenothiazine MQ: p-methoxyphenol

EXAMPLE 2 A can solution (80% by weight of acrylic acid) obtained by subjecting an aqueous solution of about 55% by weight of acrylic acid obtained by two-stage gas phase catalytic oxidation of propylene to dehydration distillation using toluene as an azeotropic agent. ,
Toluene weight 17%, phenothiazine 500 ppm, P
-Methoxyphenol 150 ppm, containing 80 ppm of copper dibutyldithiocarbamate) and 224 ppm of 25% aqueous ammonia were used as a sample, and a polymerization test was performed by the above method. Table 2 shows the results.

Comparative Example 3 A polymerization test was carried out using the liquid in the azeotropic dehydration tower used in Example 2 as a sample. Table 2 shows the results.

[0023]

[Table 2]

Examples 3 to 13 In place of ammonia water in Example 2, ammonium acetate, methylamine, ethylamine, n-propylamine, n-butylamine, tert-butylamine, sec-butylamine, n-hexylamine shown in Table 3 were used. , Cyclohexylamine, n-octylamine and aliphatic monoamines of 2-ethylhexylamine were added, respectively. The results are shown in Table 3.

[0025]

[Table 3]

Examples 14 to 17 In Example 2, instead of aqueous ammonia, aliphatic primary diamines of ethylenediamine, trimethylenediamine, 1,4-diaminobutane and hexamethylenediamine shown in Table 4 were added. Table 4 shows the results.

[0027]

[Table 4]

Examples 18 to 24 In Example 2, Table 5 was used instead of monoethanolamine.
Diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 3-methylaminopropylamine, 3,3′diaminodipropylamine, N-
An aliphatic polyamine of methyl-3,3'-iminobis (propylamine) was added, respectively. Table 5 shows the results.

[0029]

[Table 5]

Examples 25 to 29 In Example 2, aniline, toluidine, anisidine, aminophenol,
The aromatic primary amines of phenylenediamine were each added. Table 6 shows the results.

[0031]

[Table 6]

Examples 30 to 32 In Example 2, amino acids of glycine, alanine and methionine were added instead of aqueous ammonia. Table 7 shows the results.

[Table 7]

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kimiki Katahira 5-1 Sokai-cho, Niihama-shi, Ehime Sumitomo Chemical Co., Ltd. (72) Inventor Tatsuya Ono 5-1 Sokai-cho, Niihama-shi, Ehime Sumitomo Chemical F term (reference) 4H006 AA02 AC46 AD12 AD41 BC14 BC50 BE30 BS10

Claims (5)

[Claims] 1. An acrylic acid aqueous solution obtained by gas-phase catalytic oxidation of propylene and / or acrolein with a molecular oxygen-containing gas is subjected to dehydration distillation using an azeotropic agent for purification of acrylic acid. To crude acrylic acid or its aqueous solution, ammonia, ammonium salt,
At least one selected from the group consisting of aliphatic primary monoamines, aliphatic primary diamines, aliphatic polyamines, aromatic primary amines and amino acids, and a polymerization inhibitor of acrylic acid added A method for preventing polymerization of acrylic acid, which comprises: 2. Ammonia, ammonium salt, aliphatic 1
At least one selected from the group consisting of primary monoamines, aliphatic primary diamines, aliphatic polyamines, aromatic primary amines, and amino acids is added to the azeotropic dehydration column feed or bottoms. 2. The method according to claim 1, wherein
The method for preventing polymerization of acrylic acid as described above. 3. The method of claim 1, wherein the acrylic acid polymerization inhibitor is at least one selected from phenothiazine and methylene blue.
The method according to claim 1 or 2, wherein a copper salt of dimethyldithiocarbamate, copper salt of diethyldithiocarbamate, copper salt of dipropyldithiocarbamate and copper salt of dibutyldithiocarbamate are used in combination. 2. The method for preventing polymerization of acrylic acid according to 2. 4. The method of claim 1, wherein the acrylic acid polymerization inhibitor is at least one selected from phenothiazine and methylene blue.
Species and copper dialkyldithiocarbamate consisting of copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dipropyldithiocarbamate and copper dibutyldithiocarbamate,
Phenol, hydroquinone, p-methoxyphenol, benzoquinone, 1,2-naphthoquinone, cresol, catechol, 2,5-di-t-butylhydroquinone, 2,6-di-t-butylphenol, 6-t-butyl-m- Cresol, 2,6-di-tert-butyl-p-cresol, 4-tert-butylcatechol, 2,4-dimethyl-6-tert-butylphenol, 2-tert-butylhydroquinone and 2-tert-butyl-4- The method for preventing polymerization of acrylic acid according to any one of claims 1 to 3, wherein at least one selected from the group consisting of methoxyphenol is present. 5. Ammonia, ammonium salt, aliphatic 1
At least one selected from the group consisting of primary monoamines, aliphatic primary diamines, aliphatic polyamines, aromatic primary amines, and amino acids is 0.001% by weight based on acrylic acid. The method for preventing polymerization according to any one of claims 1 to 4, wherein the amount is from 0.5 to 0.5% by weight.