JPS6069053A - Extraction and separation of methacrylic acid - Google Patents

Abstract

PURPOSE:To produce the titled compound preventing the formation of emulsion and deposition of polymer in an extraction column, by contacting an aqueous solution of methacrylic acid with an extractant and/or solvent in an extraction column, and removing the precipitated polymer by a packed filter. CONSTITUTION:The objective compound is produced by contacting an aqueous solution of methacrylic acid with an extraction solvent such as benzene and/or a solvent phase of an extraction column, removing the precipitated polymer with a packed filter, separating the product into two layers with a decanter, and supplying the water layer to the extraction column. EFFECT:The formation of the emulsion and the deposition of polymer in the extraction column can be prevented by the use of a packed filter. The filter can be used for a long period. The solid deposited in the filter can be dissolved easily, and the filter can be regenerated by removing the liquid from the filter and washing the filter with an aqueous solution of an alkali.

Description

Detailed Description of the Invention The present invention relates to a method for extracting and separating methacrylic acid, and more specifically, methacrylic acid obtained by subjecting imbutylene, tertiary butyl alcohol, methacrolein and/or isobutyraldehyde to a gas phase catalytic oxidation reaction. When extracting and separating methacrylic acid from an aqueous solution of methacrylic acid using an extraction column,
This is an extraction and separation method for methacrylic acid, which is characterized in that an aqueous methacrylic acid solution is brought into contact with an extraction solvent and/or an extraction column solvent phase in advance, and precipitated polymers are removed using a packed filter.

Isobutylene, tl! I! Methacrylic acid obtained by subjecting tertiary butyl alcohol, methacrolein, and/or isobutyraldehyde, etc. to a gas phase catalytic oxidation reaction is usually obtained by absorbing the reaction product produced by the gas phase oxidation reaction with water,
After distilling the absorption liquid to remove low-boiling substances such as acetone and methacrolein, water and methacrylic acid are separated in an extraction process.
Next, the extraction solvent and methacrylic acid are separated and purified by distillation, but if the above method is operated continuously for a long period of time, the inside of the extraction column and the elevation control section will be damaged during the extraction process using the extraction column. A large amount of polymers accumulates, and the extraction column becomes inoperable in a relatively short period of time. This creates the inconvenience of having to clean the inside of the column after every 3 to 7 days of operation, and emulsions tend to form in the upper part of the extraction column, which often causes 72 deg. Every time this happens, we have no choice but to temporarily stop the operation of the extraction tower.

The emulsion produced here is different from the emulsion that occurs when the rotation speed of a rotary extraction tower is extremely high, for example, and is foam-like with a particle size of about 1 mm. Also, an emulsion phase is formed in addition to the solvent phase and aqueous phase present in the extraction column.

Once this emulsion phase is generated, it is impossible to continue operating the extraction column unless it is taken out of the extraction column.

As a means to solve this problem, a method is known in which extraction is carried out after contact with activated carbon or various ion exchange resins (Japanese Patent Laid-Open No. 50-52021), but this method In order to achieve the desired contact effect with an aqueous solution of methacrylic acid, a fairly long contact time is required, and in the case of industrial operation, an extremely large amount of granular adsorbent and large equipment are required, and it is difficult to replace or regenerate the adsorbent. It has various drawbacks, such as the need to perform it frequently.

As a result of intensive studies by the present inventors to solve these inconvenient problems, we found that the presence of high-boiling substances, mainly polymers of methacrylic acid, causes the formation of emulsions. is brought into contact with the extraction solvent and/or the extraction tower solvent phase, and the precipitated polymers are removed with a packed filter, separated into two layers using a decanter, and the aqueous layer is supplied to the extraction tower. The present inventors have discovered that the formation of emulsions and the accumulation of polymers can be eliminated, leading to the completion of the present invention.

That is, the gist of the present invention is that when extracting and separating methacrylic acid from an aqueous methacrylic acid solution obtained by a gas phase catalytic oxidation reaction using an extraction tower, the aqueous methacrylic acid solution is brought into contact with an extraction solvent and/or an extraction tower solvent phase in advance, There is a point pressure to remove precipitated polymers using a packed filter.

The temperature at which the aqueous methacrylic acid solution is brought into contact with the extraction solvent and/or the extraction column solvent phase may be room temperature, but is preferably in the range of 30 to 50°C.

In the present invention, it is necessary to appropriately select a filter for removing precipitated polymers. These polymers form a bulky solid substance together with the extraction solvent and methacrylic acid, but since the polymers themselves have fine particles and are sticky, they cannot be used in ordinary glass filters or sintered metal filters.

If a vapor filter or the like is used, it will become clogged in a very short period of time, and if the differential pressure of the filter is increased, polymers will leak, which is not practical.

If a coarse wire mesh filter or P cloth is used, an emulsion will be formed in the decanter due to the polymers passing through the filter, making it difficult to separate into two layers.

Filters that can be backwashed with water do not completely remove the cake on the filtration surface, and the backwashing liquid contains polymers, extraction solvents, and methacrylic acid. disadvantageous to

The inventors of the present invention conducted studies to obtain a filter that does not become clogged in a short period of time and causes less loss of extraction solvent, and as a result, it was discovered that a packed filter exhibits particularly excellent effects in the present invention.゛This is a stainless steel sponge made of McMahon backing and ultra-fine stainless steel wire.
Alternatively, it is a filter filled with wire mesh rings, etc., and since the void ratio of these packings is very large, approximately 90 to 98%, bulky solids made of extraction solvent, methacrylic acid aqueous solution, and polymers are filled as is. Can be captured in the voids of objects. It can be used for a much longer time than the previously mentioned filters, and there is no leakage of polymers or formation of emulsions in the decanter during this time.

In addition, when regenerating the filter, solids can be easily dissolved by draining the liquid inside the filter and washing it with an alkaline aqueous solution, and surprisingly, the solids are initially mixed with the extraction solvent and methacrylic acid aqueous solution. Even though it is made of the king of polymers, the alkaline cleaning solution only contains an extraction solvent that is soluble in water. This is thought to be due to the extraction solvent being separated from the captured bulky solids over time, and the loss of extraction solvent during regeneration can be ignored, making it a very economical regeneration method.

Examples of extraction solvents suitable for the present invention include hydrocarbons having 4 to 8 carbon atoms and/or ketones having 4 to 80 carbon atoms, ethers, esters, etc., which are effective for extracting and separating methacrylic acid. Examples include n-hexane, n-hebutane, benzene, toluene, xylene, ethylbenzene, cyclohexane, methyl isobutyl ketone, Improvyl ether, ethyl acetate, methyl methacrylate, and mixtures thereof.

These extraction solvents may be supplied to the mixing tank in a purified state as shown in Figure IK and brought into contact with the aqueous methacrylic acid solution, or as shown in Figure 2, a part of the solvent phase distilled from the top of the extraction column may be used. Alternatively, all of them may be used for contact. When all of the extraction solvent phase containing methacrylic acid distilled from the top of the extraction column is supplied to a mixing tank with an aqueous solution of methacrylic acid, the extracted methacrylic acid is added to the upper layer of the decanter (organic layer) and is separated and recovered in the subsequent solvent recovery step. The solvent after separating the methacrylic acid can be recycled to the extraction column and/or the mixing tank with the aqueous methacrylic acid solution.

FIG. 12 FIG. 2 shows an example of a polymer removal process employing the present invention, and will be described below.

The explanation of FIG. 1 is as follows.

An extraction solvent is supplied to the mixing tank 1 through 5, an aqueous methacrylic acid solution is passed through 12, and mixing is performed.7'A5°The mixed liquid is sent to the filter 2 through 6, and after removing polymers,
After step 7, the mixture is separated into two layers using decanter 3. The organic layer is sent to the solvent recovery step through 8, and the aqueous layer is sent to the extraction column 4 through 9.

The extraction column overhead solvent phase is sent through 10 to a solvent recovery step;
From 11, the extraction solvent is supplied to the extraction column.

The explanation of FIG. 2 is as follows.

A methacrylic acid aqueous solution is passed through 5 into a mixing tank 1, and a solvent phase at the top of the extraction column is supplied through 10 to perform mixing. The mixed solution is sent to a filter 2 through 6 to remove polymers, and then passed through 7 to a decanter 3 where it is separated into two layers. The organic layer is sent to the solvent separation step through 8, and the aqueous layer is sent through 9 to the extraction column 4.
supply to The extraction solvent is fed through 11 to the extraction column.

The present invention will be explained below with reference to Examples.

Example 1 Tertiary butyl alcohol was oxidized in two stages using a molybdenum-bismuth-antimony catalyst and a phosphorus-molybdenum catalyst in the presence of air and steam, and the resulting fermentation reaction product was recovered with water. After that, low-boiling substances are removed by distillation,
A 20 wt'J aqueous methacrylic acid solution was obtained. According to the flow in Figure 2, "Accordingly, the methacrylic acid aqueous solution and the top solvent phase of the extraction column were added to the mixing tank maintained at 45°C at a rate of 5 kg/hr, respectively.
.

Supply at a rate of 2.9 ky/hr, mix,
After removing the precipitated polymers with a filter, the mixture was separated into two layers using a decanter. The organic layer was sent to a solvent recovery step, and the aqueous layer was fed to the top of a 46 m/mφ x 40-stage rotating disk type extraction column.

A mixed extraction solvent of toluene/methyl methacrylate = 1/1 (weight ratio) was supplied to the bottom of the column at a rate of 2.5 kg/hr.

The filter used here to remove polymers is
50μ in a cylinder of 35.2 m/mφX1000m/m
19 filled with stainless steel sponge 74Pr, and on top of that, 3181nch McMahon backing 190
It is a filling type filter packed with 76cIIL of /r, 4
When operated at 5℃, the replacement time for this filter was 1
20 hours, and the differential pressure of the filter at the time of replacement was 5301
It was 1H,P. For comparison, a 50 μ wire ring filter (filtration area: 7 cm) was used to remove polymers, and it was found that the filter replacement time was 4 hours, which was considerably shorter than the filled filter.

[Brief explanation of drawings]

1 and 2 show a preferred operational flow sheet of the present invention. Country 1 Figure 2

Claims (1)

[Claims] When extracting and separating methacrylic acid from an aqueous methacrylic acid solution obtained by a gas phase catalytic oxidation reaction, the aqueous methacrylic acid solution is brought into contact with an extraction solvent and/or an extraction column solvent phase, and precipitated polymers are removed using a packed filter. A method for extracting and separating methacrylic acid, which is characterized by supplying methacrylic acid to an extraction column.