WO2001085665A1

WO2001085665A1 - Process for producing acrylic acid

Info

Publication number: WO2001085665A1
Application number: PCT/JP2001/003648
Authority: WO
Inventors: Takashi Nakagawa; Hironori Tashiro; Kouji Tomita; Ikuya Nagao
Original assignee: Idemitsu Petrochemical Co., Ltd.
Priority date: 2000-05-08
Filing date: 2001-04-26
Publication date: 2001-11-15
Also published as: JP4601120B2; TWI242550B; JP2001316326A

Abstract

A process for producing acrylic acid, characterized by subjecting to azeotropic dehydration an acrylic-acid-containing liquid oxidation product obtained by catalytic vapor-phase oxidation to obtain crude acrylic acid, regulating the total concentration of maleic acid and maleic anhydride in the crude acrylic acid to 2,000 ppm or lower, and then distilling the crude acid in the presence of a hydrazine compound. The process enables high-purity acrylic acid to be economically produced from crude acrylic acid obtained by the catalytic vapor-phase oxidation method, while sufficiently removing impurities such as aldehydes, ketones, maleic acid, and the like and inhibiting sludge generation.

Description

Specification

Method for producing acrylic acid

Technical field

The present invention relates to a method for producing acrylic acid, and more particularly to a method for economically producing high-purity acrylic acid by purifying crude acrylic acid obtained by catalytic gas phase oxidation.

Background art

Acrylic acid is a highly reactive compound, and is an important compound used as a raw material for various polymer monomers and various polymerizable esters. This acrylic acid is industrially produced by a method of oxidizing propylene and z or lactone by molecular oxygen in the gas phase in the presence of a solid oxidation catalyst, that is, by catalytic gas phase oxidation. I have. In this method for producing acrylic acid by catalytic gas phase oxidation, since the reaction is carried out in the presence of water vapor, the oxidation product is usually obtained in the form of an acrylic acid-containing oxidation product solution (aqueous solution).

This oxidized solution containing acrylic acid contains a large amount of aldehydes such as furfural and benzaldehyde, which are difficult to separate from acrylic acid, and carboxylic acids such as maleic acid, maleic anhydride and acetic acid, in addition to acrylic acid. ing. In order to recover acrylic acid from this acrylic acid-containing aqueous solution, a method of dehydrating the product solution and then obtaining acrylic acid using a purification means by distillation is generally used.

Here, as the method for dehydrating the oxidation product solution, there are generally a solvent extraction method using a solvent such as ketone and acetate, and an azeotropic dehydration method using a solvent azeotropic with water such as toluene and methylisobutyl ketone. well known. When this solvent extraction method is employed, maleic acids are easily removed, but are not practical in terms of cost and are not economically viable. The azeotropic dehydration method is advantageous and industrially excellent.

Acrylic acid has recently been used in many fields such as superabsorbent resins and polymer flocculants, but its polymerizability has become important, and impurities such as aldehydes contained in crude acrylic acid have become important. Is a major problem. Therefore, it is necessary to remove and purify these impurities, and many methods have been proposed.

For example, Japanese Patent Publication No. 58-372900 discloses that in the dehydration step of crude acrylic acid, hydrazine hydrate is reacted with aldehydes and ketones having the same level of volatility as acrylic acid. However, there has been proposed a method of converting into a hydrazine diazine, which is a condensate, for separation and removal. However, this purification method has a problem that the efficiency of removing aldehydes is not sufficient.

Further, Japanese Patent Application Laid-Open No. 7-228584 discloses a method of adding a hydrazine compound and copper dithiolbamate to crude acrylic acid and distilling the crude acrylic acid at a temperature of 100 ° C. or less. Proposed. By adopting this method, it is intended to purify crude acrylic acid by separating and removing impurities such as aldehydes while suppressing the adhesion of acrylic acid produced by polymerization to the distillation column in the purification process. However, from the viewpoint of removing impurities, that is, the quality of acrylic acid, there is a problem similar to that of the patent.

As another method for producing acrylic acid, the final distillation column in the continuous method for producing acrylic acid is 25 to 100. At the temperature of C, the crude acrylic acid and the specific amines are added in an amount of 0.1 to 2% based on the total moles of aldehyde and maleic acid and maleic anhydride in the crude acrylic acid. A feed stream containing a minimum effective level of a molar ratio of 0 is provided, and at the top of the final distillation column, an act of supplying the other specific amines at a molar ratio of 0.01 to 1.0 as the standard. There is a method for producing lylic acid (Japanese Patent Application Laid-Open No. 7-33059, Japanese Patent Application Laid-Open No. 9-124659). Furthermore, a crude acrylic acid that has been subjected to azeotropic dehydration treatment is added with a dehydrating agent such as hydracine and at least one kind of an amine such as an aliphatic amine, a heterocyclic amine or an aromatic monoamine, and then purified by distillation. A method for producing acrylic acid (Japanese Patent Application Laid-Open No. 9-200814), a method for producing high-purity acrylic acid by distilling crude acrylic acid in the presence of hydrazine and ammonia. A method of reducing polymerized deposits in a productization tower by a method of evaporating an aqueous solution of acrylic acid before azeotropic dehydration (Japanese Patent Application Laid-Open No. 10-88752). For this purpose, there is no difference from using amines, hydrazines, etc.] (Japanese Patent Application Laid-Open No. H11-217350).

In any case, the method for producing acrylic acid uses aldehydes, maleic acid, maleic anhydride as hydrazines, amines, ammonia, etc. as impurities contained in crude acrylic acid. By the addition, it is intended to be removed as a reaction product. However, in these methods for producing acrylic acid, there is known a problem that the dealdehyde reaction with hydrazines or the like is inhibited by maleic acids.

For this reason, a method has been adopted to ensure the reactivity of aldehydes and hydrazines by removing maleic acid with a chemical such as amine. However, the efficiency of the dealdehyde is not sufficient, such as the remaining of maleic acid or its reaction product, and it is necessary to use an excess of the dealdehyde, and the purification degree is limited. In addition, in these methods, the reaction product of the additive forms sludge, and there may be a problem in long-term continuous operation. Furthermore, these methods have the problem that the resulting water content in the acrylic acid is increased. The present invention relates to a method for producing high-purity acrylic acid from crude acrylic acid obtained by a catalytic gas phase oxidation method, comprising an aldehyde, a ketone and a maleic acid. It is an object of the present invention to provide a highly economical method that can remove impurities such as acids in a minute, suppress generation of sludge, and enable long-term continuous operation.

Disclosure of the invention

The present inventors have studied the above-mentioned problems in the production of acrylic acid, such as the relationship between additives such as dehydrating agents and amines, the amount of sludge formed, and the amount of impurities remaining in purified acrylic acid. As a result of diligent investigations into the results, when maleic acids were removed from crude acrylic acid to a specific level, the amount of additives used in the distillation and purification of atarilic acid could be significantly reduced, and sludge generation was reduced. In addition, it was found that the purity was significantly improved. The present invention has been made based on these findings.

That is, the present invention

(1) Crude acrylic acid obtained by azeotropic dehydration of an acrylic acid-containing oxidation product solution obtained by catalytic gas phase oxidation is converted into maleic acid and maleic anhydride in the crude acrylic acid. A process for producing acrylic acid, wherein the total concentration is 2, OOO ppm or less and distillation is performed in the presence of hydrazines.

(2) The method for producing acrylic acid according to (1), wherein the total concentration of maleic acid and maleic anhydride is 500 to 1,0 O O pm.

(3) The method for producing acrylic acid according to (1) or (2), wherein the hydrazine compound is a compound represented by the following general formula (1) or a hydrate thereof.

R 1-N-N H (1)

R [Wherein, I ¹ and R ² each represent a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a phenyl group, a substituted phenyl group or an alicyclic hydrocarbon group. ]

(4) The method for producing acrylic acid according to any one of (1) to (3), wherein the hydrazines are added at the time of distillation before the distillation column and / or in the distillation column. It is.

(5) The method for producing acrylic acid according to (4), wherein the amount of the hydrazine added is 1 to 8 molar equivalents relative to the aldehydes contained in the crude acrylic acid.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail. The crude acrylic acid obtained by the catalytic gas-phase oxidation in the present invention is obtained by azeotropic dehydration of the acrylic acid-containing oxidation product obtained by the catalytic gas-phase oxidation of propylene and Z or lactone. Crude acrylic acid is used. The acrylic acid-containing production solution may be a reaction product solution obtained by a one-stage oxidation method of propylene, or may be a product solution obtained by a two-stage oxidation method. These acrylic acid-containing product liquids are obtained in the form of an aqueous acrylic acid solution because steam is used for the reaction.

The composition of the acrylic acid-containing oxidation product solution varies depending on the type of oxidation method, oxidation reaction conditions, and the like. However, in general, the content of each component, Atta acrylic acid 5 0-8 0 weight ^_0/0, water 2 0-5 0 weight ^_0/0, maleic acid 0.3 to 2 wt%, Funorefuranore 1 It is about 0 to 500 ppm, and about 100 to 500 ppm of benzanoledaldehyde. In the present invention, first, crude acrylic acid is obtained by removing water from the acrylic acid-containing oxidation product solution by an azeotropic dehydration method, which is an economical dewatering means. This azeotropic dehydration treatment method is not particularly limited, and a known method in the method for producing atalylic acid can be employed. For example, as an azeotropic agent, toluene, xylene, ethynolebenzene, heptane, methyl isobutyl ketone, diisobutyl ketone, disobutylene or a mixture thereof is used under a reduced pressure of about 10 to 25 kPa. Perform azeotropic dehydration treatment.

By this azeotropic dehydration treatment, the water concentration in the bottom liquid of the azeotropic dehydration column becomes less than 1,000 ppm. Water, acetic acid, azeotropic agents and low-boiling aldehydes are removed from the top of the azeotropic dehydration tower. It is desirable that the water and the azeotropic agent do not dissolve in each other, the distillate is led out of the system, and the oil phase is returned to the azeotropic column as a reflux liquid and recycled. By this azeotropic dehydration treatment, crude acrylic acid is obtained from the bottom of the column. Further, light components such as acetic acid may be removed as necessary.

Next, the crude acrylic acid is guided to a heavy component separation treatment, for example, a heavy component separation column, and a distillate is obtained by ordinary distillation means. In this distillate, crude acrylic acid containing impurities such as water, acetic acid, an azeotropic agent, and aldehydes, which are low-boiling substances, can be obtained. In addition, the bottom liquid becomes acrylic acid having a high concentration of maleic acids such as maleic acid and maleic anhydride. .

Here, the distillation conditions in the heavy component separation column are such that the total concentration of maleic acid and maleic anhydride in the crude acrylic acid is 2,000 ppm or less, preferably 1,500 ppm. Hereinafter, it is more preferably set to be 1, OOO ppm. In the method for producing acrylic acid of the present invention, it is preferable to reduce the concentration of maleic acid in the heavy component separation column. However, as will be apparent from the examples described later, 500 to 1, OOO ppm , It is possible to produce high-purity acrylic acid in the next distillation step. It became clear.

In other words, in the method for producing high-purity acrylic acid, the presence of maleic acid is present as a problem, and this is generally a chemical method. However, surprisingly, the present inventors have clarified that the problem can be solved by a simple means of physical removal at a certain level. Therefore, it is a major feature of the present invention that the distillation column which requires enormous cost and does not require distillation conditions, such as the use of maleic acids as much as possible, can be carried out economically.

The distillation separation for separating and removing the heavy components is not particularly limited, but is usually performed at a pressure of 5 to 15 kPa and a bottom temperature of about 60 to 90 ° C. Done in

Next, the crude acrylic acid having a reduced maleic acid concentration is processed in a distillation column, which is a final purification treatment. This distillation treatment is performed in the presence of hydrazines. What is important in the present invention is that (a) the concentration of maleic acid in the crude acrylic acid supplied to the distillation column is 2, OO Oppm or less. (Mouth) Hydrazines are added to crude acrylic acid under these conditions.

Here, the conditions for adding the hydrazine to the crude acrylic acid having a reduced maleic acid concentration are not particularly limited, and the hydrazine can be added to a stage before the distillation column and / or into the distillation column. For example, a method in which crude acrylic acid is previously mixed and then supplied to a distillation column, supplied simultaneously at a supply port, or supplied separately can be adopted. Here, in order to mix and supply in advance, a method using a crude acrylic acid tank having a stirrer or a pump circulation line or a method of providing a static mixer or a line mixer in the supply line can be adopted.

There are no particular restrictions on the hydrazines to be added, but Preferred examples include the compound represented by the formula (1) or a hydrate thereof.

R N-N H (1)

R

[Wherein, R ¹ and R ² each represent a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, a fuunyl group, a fuunyl group having a substituent, or an alicyclic hydrocarbon group. ]

Specific examples of hydrazines include hydrazine, phenylhydrazine, tolylhydrazine, a, monomethylphenylhydrazine, a, α-diphenylhydrazine,] 3-naphthylhydrazine, or a hydrate of these. Can be illustrated. In addition, a plurality of these hydrazines or hydrates thereof may be used.

The amount of hydrazine added can be appropriately selected depending on the concentration of impurities contained in crude acrylic acid supplied to the distillation column. Specifically, it is 1 to 8 times, preferably 3 to 5 times [each molar equivalent], relative to the impurity aldehydes.

There are no particular restrictions on the means for distilling the crude acrylic acid, and various distillation columns are used. Examples of the distillation conditions include a pressure of about 5 to 10 kPa and a liquid temperature at the bottom of the column of 60 kPa. A condition of about 90 ° C is adopted. High-purity acrylic acid as a distillate overhead is obtained in the range of about 60 to 90% by volume of the crude acrylic acid supplied. In this purified acrylic acid, impurities such as furfural, penzaldehyde, and maleic acid can be reduced to 1 ppm or less by selecting purification conditions.

The method for producing acrylic acid according to the present invention comprises an azeotropic dehydration treatment and a heavy component separation treatment. Process, such as processing and distillation. These steps, equipment, processing conditions, and the like differ depending on the processing means, equipment size, crude acrylic acid composition, recovery rate, and the desired purity of the purified atalilic acid, and are appropriately determined except for those specified in the present invention. Can be In addition, since acrylic acid is a compound which is easily polymerized, it is preferable to employ conditions such as distillation under conditions of low pressure and low temperature as much as possible.

In addition, the distillation operation in the method for producing acrylic acid of the present invention may be batch distillation, but continuous distillation is preferred from the viewpoint of industrial and productivity. In order to prevent polymerization of acrylic acid, if necessary, compounds known as polymerization inhibitors, phenols such as hydroquinone, methoxyphenol, hydroquinone monomethinoleate ether, phenothiazine, etc. Amines such as diphenylamine, copper salts such as dibutyl dithiopotassium copper rubinate, manganese salts such as manganese acetate, double-mouthed compounds, nitroso compounds and the like can be added.

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The gas chromatographic method was used for the determination of impurities in acrylic acid. Example 1

(1) Azeotropic dehydration treatment

A small distillation unit (azeotropic dehydration unit) filled with a filler is used to convert the acrylic acid-containing oxidation product solution obtained by propylene one-step catalytic gas phase oxidation to a diameter of 2.

6 mm, length: 60 O mm], toluene was continuously supplied at a rate of 35 ml / hr and at a rate of 135 ml / hour as an azeotropic solvent, and the pressure at the top: 1 An azeotropic dehydration treatment was performed under the conditions of 7.5 kPa and a temperature of 85 ° C to obtain crude acrylic acid ①. In this crude acrylic acid, furfuranore: 470 ppm, benzanoledide: 450 ppm, maleate Acids: 11,1000 ppm was contained.

(2) Separation distillation of heavy components

The crude acrylic acid 得 obtained in (1) above was transferred to a small distillation apparatus (heavy component separation tower) filled with a filler [diameter: 2.6 mm, length: 600 mm]. Feed continuously at the rate of 0 ml Z-hour, pressure at the top: 5.3 kPa, temperature: 65 ° C, bottom pressure: 10.0 kPa, bottom temperature: 8

2. Distillation was performed under the conditions of C to obtain crude acrylic acid ② as a distillate. This crude acrylic acid II contained furfural: 230 ppm, benzaldehyde: 60 ppm, and maleic acids: 880 ppm. That is, it was removed so that the maleic acid content was less than 2,000 ppm.

(3) Distillation of acrylic acid

Hydrazine monohydrate: 590 ppm (4 molar equivalents to aldehydes (sum of furfural and benzaldehyde)) was added together with the crude acrylic acid obtained in (2) above. A small distillation device (atrial acid distillation column) filled with packing material (diameter: 2.6 mm, length: 600 mm)

Feed continuously at a speed of 30 m 1 Z hour, pressure at the top of the column: 5.3 kPa, temperature: 65 ° C, bottom pressure: 10.0 kPa, bottom temperature: Distillation was performed at 79 ° C. to obtain a purified high-purity acrylic acid in an amount of 75% by volume based on the feed liquid as a top distillate.

Furfural, benzaldehyde, and maleic acid in the obtained high-purity acrylic acid were all 1 ppm or less, and the water content was 570 ppm. Furfural in the bottom of the distillation column was 1 Oppm, benzaldehyde was 15 Oppm, and maleic acid was 5 Oppm. At this time, no precipitate was observed at the bottom of the distillation column.

Example 2 In the same manner as in Example 1, except that hydrazine hydrate was preliminarily mixed with the crude acrylic acid for 5 minutes and then continuously supplied to the acrylic acid distillation column, the overhead was distilled off. As a liquid, purified high-purity acrylic acid was obtained. Furbural, benzaldehyde, and maleic acids in the high-purity acrylic acid obtained were all less than 1 ppm, and the water content was 590 ppm. Furfural in the bottom liquid of the distillation column was 7 ppm, benzaldehyde was 11 ppm, and maleic acids were 43 ppm. At this time, no precipitate was observed at the bottom of the distillation column.

Comparative Example 1

Hydrazine monohydrate containing 1,000 ppm of maleic acid obtained in (1) of Example 1 and crude atalylic acid ①: 1,830 ppm [to aldehydes [Equivalent to 4-fold molar equivalent] was added and continuously supplied to the acrylic acid distillation column in the same manner as in Example 1 to obtain purified acrylic acid as a top distillate. Furfural in the obtained purified acrylic acid was 8 ppm, benzaldehyde was 1 ppm, maleic acid was 15 ppm, and water content was 1,750 ppm. Furfuranore in the bottom of the distillation column was 150 ppm, benzanoledide was 240 ppm, and maleic acids were 31.000 ppm. At this time, a large amount of precipitate was observed at the bottom of the distillation column.

Comparative Example 2

The maleic acid obtained in (1) of Example 1 containing 11,000 ppm of crude atalylic acid and hydrazine monohydrate: 2,740 ppm [6 to hydrazine [Mole equivalent], and purified acrylic acid was obtained as the top distillate in the same manner as in Example 1 except that the mixture was continuously supplied to the acrylic acid distillation column. 5 ppm of furfural, 1 ppm of benzaldehyde, 10 ppm of maleic acid, and 10 ppm of water in the obtained purified acrylic acid Minutes were 2,63 O ppm. Furfurul in the bottom liquid of the distillation column was 110 ppm, benzaldehyde was 180 ppm, and maleic acid was 23, OOO ppm. At this time, a larger amount of precipitate was observed at the bottom of the distillation column than in Comparative Example 1.

Comparative Example 3

The distillation conditions in (2) of Example 1 were changed to obtain crude acrylic acid ③ containing furfural: 290 ppm, benzanoledaldehyde: 130 ppm, and maleic acids: 2,500 ppm. . To this was added hydrazine monohydrate: 850 ppm [4 molar equivalents relative to hydrazines], and the mixture was fed continuously to the acrylic acid distillation column in the same manner as in Example 1. As a result, purified acrylic acid was obtained as a top distillate. The obtained purified acrylic acid contained 2 ppm of fullernole, 1 ppm of benzanoledaldehyde, 4 ppm of maleic acid, and 81 Ppm of water. The bottoms in the distillation column had 40 ppm of phenol, 40 ppm of benzanoledaldehyde, and 4.5 ppm of maleic acid. At this time, a precipitate was observed at the bottom of the distillation column.

Industrial applicability

According to the production method of the present invention, high-purity acrylic acid is converted from crude acrylic acid obtained by catalytic gas-phase oxidation of propylene and / or acrolein. The generation of sludge during distillation purification is suppressed. Thus, it can be manufactured economically advantageously.

Claims

The scope of the claims

1. Crude acrylic acid obtained by azeotropic dehydration of an acrylic acid-containing oxidation product solution obtained by catalytic gas phase oxidation is converted into maleic acid and maleic anhydride in the crude acrylic acid. A process for producing acrylic acid, wherein the total acid concentration is set to not more than 2,000 ppm and distillation is carried out in the presence of hydrazines.

2. The method for producing acrylic acid according to claim 1, wherein the total concentration of maleic acid and maleic anhydride is from 500 to 1,000 ppm.

3. The method for producing acrylic acid according to claim 1, wherein the hydrazine is a compound represented by the following general formula (1) or a hydrate thereof.

R ¹ -N-NH (1)

R

[Wherein, R ¹ and R ² each represent a hydrogen atom,

Group, a phenyl group, a phenyl group having a substituent or an alicyclic hydrocarbon group. ]

4. The process for producing acrylic acid according to any one of claims 1 to 3, wherein the hydrazines are added during the distillation before the distillation column and in the Z or distillation column.

5. The method for producing acrylic acid according to claim 4, wherein the amount of hydrazine added is 1 to 8 molar equivalent times the amount of aldehydes contained in crude acrylic acid.