JPS58140039A - Purification method of acrylic acid - Google Patents

Abstract

PURPOSE:To prevent the polymerization of acrylic acid and obtain the acrylic acid in high yield in a process of separating acetic acid as an impurity in the crude acrylic acid by the distillation, by adjusting the concentration ratio between the water and the acrylic acid contained in the overhead distillate of a distillation column. CONSTITUTION:A reaction product gas obtained by catalytically oxidizing propylene and/or acrolein in the vapor phase is introduced from a line 1 into an absorber 2, where the reaction product is condensed or absorbed in water to give a liquid phase containing 5-55wt%, preferably 20-50wt%, acrylic acid. The resultant liquid is then introduced into an extraction column 4 and extracted with an extractant, e.g. methyl isobutyl ketone. The resultant extract is then fed to a distillation column 7 for separating the extractant, and crude acrylic acid, containing acetic acid, etc., and obtained from the bottom is fed to a distillation column 10 for separating the acetic acid. The acetic acid is obtained from the top, and the acrylic acid containing no acetic acid is obtained from the bottom. The distillation in the distillation column 10 is carried out by adjusting the concentration ratio between the water and the acrylic acid contained in the overhead distillate acetic acid of the distillation column 10 to <=0.30, preferably <=0.20, by weight.

Description

Detailed Description of the Invention The present invention relates to a method for purifying acrylic acid. According to the method of the present invention, when acetic acid, which is an impurity in crude acrylic acid, is distilled and separated, Acrylic acid can be recovered in high yield while preventing polymerization of acrylic acid.

When propylene and/or acrolein is oxidized in a gas phase, in addition to the main component acrylic acid, byproducts such as water, acetic acid, acrolein, acetone, formic acid, formaldehyde, and maleic acid are often produced as reaction products. Among the known by-products, acetic acid is contained in an amount of about 2 to 25% by weight relative to the target acrylic acid trap (for example,
(Refer to Japanese Patent Publication No. 18967/1983). If acetic acid remains in the acrylic acid product, the non-polymerizable acetic acid deteriorates the physical properties of the acrylic acid polymer, causing problems such as residual odor. Therefore, separating acetic acid from the above reaction product is
This is an important step, but acrylic acid polymerizes very easily.
A technology for preventing this polymerization and continuously distilling and separating the product acrylic acid and acetic acid over a long period of time at a high recovery rate has not yet been established.

For example, in the method for purifying acrylic acid described below, the step of separating acetic acid by distillation requires a large number of stages and a large reflux ratio due to the molecular similarity between acrylic acid and acetic acid, which requires a large amount of energy. The process is continuous because acrylic acid is very easy to polymerize even if polymerization inhibitors such as hydroquinone, hydroquinone monomethyl ether, phenothiazine, phenol, dienylamine, and methylene blue are added. In particular, when acrylic acid is polymerized in an acetic acid separation and distillation column, there are few problems with polymers that are soluble in water and/or acrylic acid. And/or when a polymer called "bog corn polymer" which is insoluble in acrylic acid is generated, the separation efficiency of the distillation column decreases, such as by increasing the bottom pressure of the distillation column and increasing the bottom temperature. If the formation of the polymer is severe, there is a risk of blockage of the distillation column and deformation of the trays, so the acrylic acid production plant must be shut down, and the distillation column must be dismantled to remove the polymer. Sometimes it is necessary.

The present inventors have conducted extensive studies to solve the above problems, and have found that if specific distillation conditions are selected in the step of distilling and separating the impurity acetic acid in crude acrylic acid, the polymerization of acrylic acid in the distillation column will occur. He discovered that acrylic acid could be recovered in high yield while preventing the above-mentioned problems, and completed the present invention. That is, the present invention condenses or absorbs a reaction product obtained by vapor phase catalytic oxidation of propylene and/or acrolein in water to form a liquid phase containing 5 to 55 wt. The next three steps: (1) Extracting acrylic acid using an extractant (2)
) Separating the extractant from the extract by distillation (3) In the method for purifying acrylic acid comprising the step of separating acetic acid by distillation, the distillation conditions for the step of separating the acetic acid by distillation are changed to The purpose of the present invention is to provide a method for purifying acrylic acid in which operation is performed while maintaining the concentration ratio of water/acrylic acid contained in the effluent at a weight ratio of 0.30 or less as 4+[.

A known method for purifying acrylic acid to which the method of the present invention is applied will be explained according to FIG.
Alternatively, a reaction product gas obtained by gas phase catalytic oxidation of acrolein is introduced into the absorption tower 2 via line 1. Absorption tower 2
Then, the reaction product gas is absorbed by water (and/or cooled and condensed), and 5 to 55 weight of acrylic acid aqueous solution is passed through line 3.
from there to the extraction tower 4. In the extraction tower, the oil is passed through line 5.
Extraction is performed by introducing the In addition to acrylic acid, some of the by-products such as acetic acid, acrolein, and acetone are dissolved in the extraction phase as impurities without being separated, and this is led to the oil separation and distillation column 7 through the line 6. The raffinate phase is an aqueous solution consisting of mostly water, some extractant and the residue of the by-products of formaldehyde. The raffinate phase is extracted from line 8 and disposed of after recovering the oil therein. In the oil agent separation and distillation column 7, extractant and water are obtained from the top of the column, and acetic acid and crude acrylic acid containing remaining water are obtained from the bottom of the column.The bottom portion is passed through line 9 to the acetic acid separation and distillation column 10.
Here, from the top of the column, a distillate containing acetic acid as a main component, water, an oil agent, and an acrylic acid is obtained, and from the bottom of the column, acrylic acid substantially free of acetic acid is obtained. Furthermore, this acrylic acid can be fed to a product distillation column to obtain even more pure product acrylic acid.

In the method of the present invention, the distillation conditions of the acetic acid separation and distillation column are such that the concentration ratio of water/acrylic acid contained in the top acetic acid distillate of the skeleton distillation column is 0.30 or less, preferably 0.30 or less in weight ratio. 20
By making the following adjustments, polymerization of acrylic acid in the distillation column can be substantially prevented for a long period of time, thereby enabling long-term continuous operation of the acrylic acid production plant.

Adjusting the water/acrylic acid concentration ratio contained in the acetic acid distillate at the top of the skeleton distillation column to a small value is contrary to the objective of obtaining the product acrylic acid in a lower yield, but this By using the method of the invention, it became possible for the first time to prevent the polymerization of acrylic acid in the acetic acid separation and distillation column, making it possible to operate an acrylic acid manufacturing plant continuously for a long period of time, and making it possible to improve the productivity of acrylic acid. In order to carry out the method of the present invention more advantageously, it is preferable to distill water to the top of the extractant distillation column along with the extractant to reduce the water concentration in the bottom liquid as much as possible.

The method of the present invention can be carried out by controlling the amount of the top distillate of the acetic acid separation and distillation column. For example, by decreasing the amount of the overhead distillate, the concentration ratio of water/acrylic acid in the No. 4 distillate can be decreased, and conversely, by increasing the amount of the distillate, the water/acrylic acid concentration ratio can be decreased. The concentration ratio of acrylic acid increases. Part or all of the top distillate of the acetic acid separation and distillation column can be recycled to the extraction column or absorption column to recover and purify acrylic acid. This method is preferable because it improves the recovery rate of acrylic acid.

The method of the present invention is applied when the acrylic acid concentration is 5 to 5.
A 55% by weight aqueous solution, preferably a 20-50% by weight aqueous solution. In the extraction column, the extractant used is a known solvent, and D is preferable even though it has a large partition coefficient during extraction, such as inopropyl acetate, methyl propionate, ethyl propionate, methyl acrylate, and acrylic. Ethyl acid, methyl ethyl ketone, methyl ibutyl ketone, etc. are used. The operating conditions of the extractant distillation column are a pressure of 40 to 200 wHg s and a hot water temperature at the bottom of the column of 100°C or less, preferably 90 to 60°C. The operating conditions for the acetic acid separation and distillation column are pressure.

40 to 200 ■Hg, bottom temperature: 100°C or higher], preferably 90 to 70°C. Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples. In addition, the concentration in the example is .% by weight.

Example 1 Aqueous acrylic acid solution obtained by condensing the product gas obtained by gas-phase catalytic oxidation reaction of propylene and removing acrolein, acetaldehyde, etc. It contained .9%. This crude acrylic aqueous solution was fed to the extraction tower at 34.4 Kf per hour. Methyl isobutyl ketone was supplied to the bottom of the extraction column as an extraction solvent at a rate of 20 Kf/hour to obtain 35.64 ml of extract. This extract is introduced into an extractant separation distillation column. The distillation column was a tray column having 30 plates and was operated at a column top pressure of 320 μHg, and hydroquinone was added as a polymerization inhibitor from the top of the column at 100 F per hour. 0.5% water and acetic acid from the bottom of the tower 4.
93.8% of acrylic acid containing 9% was obtained at 12.414 hours per hour, which was fed to the acetic acid separation and distillation column.

The acetic acid separation and distillation column is a tray column having 40 plates, and the column top pressure cuff is 0 ■Hg%. % purity was obtained at 11.43 Kt/hour. The composition of the top distillate is 5.6% water, 56.1% acetic acid, and 38% acrylic acid.
．． At 3%, the water to acrylic acid ratio was 0.15.

In this way, the acetic acid separation tower was operated continuously for one month.
The bottom pressure of the tower was 103■Hg at the start of operation, rarely 10
6-C, but there was no problem with driving at all.

Example 2 Using the same equipment as in Example 1, the operating conditions of the oil separation and distillation column were changed, the water concentration in the bottom liquid of the distillation column was set to 0.8%, and this liquid was transferred to the acetic acid separation and distillation column. supplied. The top distillate of the acetic acid separation and distillation column contains 9.2% water and 35.8% acrylic acid.
The distillate cap was 1.119 odors per hour. The ratio of water and acrylic acid was 0.25. After continuous operation for one month under these conditions, the bottom pressure at the start of operation was 1103.
-H, but a small amount of acrylic acid polymer was observed.

Comparative Example 1 The reflux amount of the extractant separation and distillation column was changed, and the top distillate composition of the acetic acid separation and distillation column was set to 17.4% water, 52.2% acetic acid, and 30.4% acrylic acid. Continuous operation was carried out in the same manner as in Example 1. At this time, the ratio of water to acrylic acid was 0.57. After one week of continuous operation, the bottom pressure at the start of operation was 103■
The Hg level dropped to 120■Hg, and a flooding phenomenon occurred, making it impossible to continue operation. After the operation was stopped, the acetic acid separation and distillation column was dismantled, and a large amount of acrylic acid polymer was found on the top shelf and on the column wall near the feed stage.Comparative Example 2 Amount of liquid distilled from the top of the acetic acid separation and distillation column Example 1 except that the
Continuous operation was performed in the same manner. At this time, the composition of the top distillate was 7.3% water, 73.2% acetic acid, and 19.5% acrylic acid.
%, the ratio of water to acrylic acid was 0.37. Two weeks after the start of continuous operation, acetic acid analysis revealed that acrylic acid polymer was found on the upper shelf of the tower and on the tower wall. Furthermore, when the tower top condenser was dismantled and inspected, a large amount of acrylic acid polymer was found to have adhered to the condensing tubes, and half of the condensing tubes were almost completely blocked.

From the above Examples and Comparative Examples, it is clear that the method of the present invention is superior.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. 2... Absorption tower 7... Extractant separation and distillation column IO... Acetic acid separation and distillation column Patent applicant Mitsubishi Yuka Co., Ltd. Agent Patent attorney Hidetoshi Furukawa Patent attorney Masahisa Hase

Claims (1)

[Claims] A reaction product obtained by gas phase catalytic oxidation of propylene and/or acrolein is condensed or collected in water to form a liquid phase containing 5 to 55% of acrylic acid by weight, and the liquid is at least Next three steps; <1) Step of extracting acrylic acid using extractant (2)
) Separating the extractant from the skeleton exudate by distillation (a) In the method for purifying acrylic acid, which consists of the step of separating acetic acid by distillation, the distillation conditions for the step of separating the skeleton acetic acid by distillation are set at the top of the column. A method for purifying acrylic acid, characterized in that the operation is carried out while maintaining the water/acrylic acid ratio contained in the acetic acid distillate at a weight ratio of 0.30 or less.