JPH0694432B2 - Purification method of methacrylic acid aqueous solution - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel method for purifying an aqueous methacrylic acid solution. More specifically, a high melting point substance contained in methacrylic acid obtained by catalytically oxidizing isobutylene, tertiary butanol, methacrolein or isobutyraldehyde with a molecular oxygen-containing gas in the presence of steam,
It relates to a method for removing high molecular weight substances and polymers.

[Conventional technology]

Isobutylene, tert-butanol, methacrolein or isobutyraldehyde (these are simply referred to as raw materials hereinafter) is used in the presence of water vapor in a single stage or 2 stages with molecular oxygen.
Methacrylic acid obtained by catalytic oxidation in a step reaction can be made into a high-purity product by an ordinary purification means such as extraction and distillation.

However, this method has many problems in its implementation. That is, when methacrylic acid is produced by catalytically oxidizing a raw material, unreacted C ₄ hydrocarbons such as methacrolein, nitrogen, carbon dioxide gas, carbon monoxide, and steam are included in the oxidation reaction purified gas in addition to methacrylic acid. ,oxygen,
Further, by-products such as aldehydes, ketones, organic acids and polymers are contained. In order to separate and purify methacrylic acid from this reaction product gas, the oxidation reaction product gas is cooled with water to obtain an aqueous solution of methacrylic acid, and this aqueous solution is then extracted with an organic solvent, and the extraction phase is distilled or Treatment with a combination of unit operations gives methacrylic acid.
When obtaining this methacrylic acid aqueous solution, many of the above by-products are condensed and collected together with methacrylic acid and water. Of these, substances having a relatively light boiling point can be easily removed by distillation or the like. Further, since aromatic carboxylic acid having a high melting point and low solubility such as terephthalic acid is partially precipitated as a solid, it can be separately removed by an appropriate method. However, in addition to these aromatic carboxylic acid residues, maleic acid, citraconic acid, polymers of methacrolein and methacrylic acid, etc. (hereinafter simply referred to as non-volatile residues) are dissolved in the aqueous methacrylic acid solution, and Appeared as scum generation at the liquid-liquid interface during acid-liquid extraction, contamination and clogging with tar-like substances in the extraction column, and / or precipitation of carbon-like substances on the extraction residue side and clogging of pipes I'm having trouble driving.

As a method of solving such a problem, a method of preventing or suppressing the generation of a non-volatile residue considered to be a causative substance, or a method of removing the non-volatile residue generated as a symptomatic treatment can be considered. As the former proposal, for example, Japanese Patent Publication No. Sho 48-10452,
Although there are JP-A-48-26717, JP-A-49-104884, JP-A-49-54317, etc., as described in the specification of JP-A-52-48609, generation of non-volatile residue is completely suppressed. It is virtually impossible. On the other hand, the latter proposals include (1) a method of treating an aqueous methacrylic acid solution with activated carbon or a special ion exchange resin before extraction (Japanese Patent Laid-Open No. 50-52021), and (2) as methacrylic acid is extracted by an extraction operation. A method in which additives are added in advance as water-soluble adducts in order to prevent the non-volatile residue from precipitating in the extraction residual phase (aqueous phase) and to increase the solubility in the aqueous phase (JP-A-50-151805). , JP-A-58-128337, JP-A-SHO
58-99434, JP-A-59-44337 and JP-A-59-44338),
(3) A method of forcibly generating scum before extraction and differentiating it (JP-A-54-66617, JP-A-56-16438 and JP-A-56-796)
34), (4) Method of selectively dissolving and removing from the reaction product gas with hot water before forming an aqueous solution of methacrylic acid (JP-A-52-4)
8609) and so on.

However, the method (1) complicates the process, causes various troubles during long-time operation, and generates a large amount of waste water for cleaning the equipment, which is difficult to industrially adopt. Simplifies the operation, but even if the aromatic carboxylic acid having a high acidity can be alkali-modified, it is difficult to sufficiently modify many polymers, and therefore the above problems cannot be fundamentally solved, and According to the examination by the inventors,
There is still an industrial drawback, such as a part of the alkali-modified substance being entrained in the organic phase and precipitated, which causes a new problem of clogging of the pipe. The method (3) requires a sufficient extraction of methacrylic acid to generate the total amount of scum, but since the solvent is mixed in one step, its effect is small and not a satisfactory treatment. The operation is complicated. Since the method (4) is a treatment before quenching the reaction product gas, there is no means for removing the polymer newly generated during quenching. The studies conducted by the present inventors have found that the polymer is formed in the reaction process and that formed in the subsequent quenching step, and is approximately half-half. Therefore, it cannot be a fundamental measure for performing the extraction operation for a long time.

[Problems to be solved by the invention]

An object of the present invention is to provide a method for easily removing a non-volatile residue from a methacrylic acid aqueous solution at a high removal rate.

Another object of the present invention is to provide a method for purifying an aqueous methacrylic acid solution so that the extraction and extraction of methacrylic acid from the aqueous methacrylic acid solution can eliminate contamination and blockage in the extraction tower. It is in.

[Means for solving problems]

As a result of intensive studies on the method for removing the non-volatile residue, the inventors have found that the above-mentioned object can be achieved by contacting the methacrylic acid aqueous solution with a semipermeable membrane under pressure to perform membrane treatment. This has led to the present invention.

The purification method of the methacrylic acid aqueous solution of the present invention is isobutyl,
Tertiary butanol, isobutyraldehyde or methacrolein are subjected to vapor phase catalytic oxidation with a molecular oxygen-containing gas in the presence of water vapor, and the resulting reaction product gas is cooled to obtain a methacrylic acid-containing aqueous solution having a molecular weight cutoff of 500. ~ 2,0
Using a semi-permeable membrane made of 00 polysulfone, polyacrylonitrile or polyamide, the linear velocity parallel to the membrane surface is 1 to 4 m.
/ sec, ultrafiltration treatment is performed to remove the non-volatile residue in the methacrylic acid-containing aqueous solution.

The aqueous solution of methacrylic acid in the present invention is prepared by using a gas containing molecular oxygen in the presence of water vapor as a raw material in one or two stages.
It is an aqueous solution containing methacrylic acid obtained by cooling and condensing the oxidation product gas obtained by catalytic oxidation in a stage, or the aqueous solution obtained by removing ketones and aldehydes such as acetone and methacrolein, which are light-boiling components, by stripping or the like. .

In the present invention, the semipermeable membrane used for the ultrafiltration treatment of the methacrylic acid aqueous solution is made of polysulfone, polyacrylonitrile or polyamide having a molecular weight cut off of 500 to 2,000. A semipermeable membrane that does not meet the above requirements cannot efficiently remove non-volatile residues from a methacrylic acid-containing aqueous solution with a high removal rate.

For ultrafiltration, methacrylic acid aqueous solution is generally 5
It is brought into contact with the semipermeable membrane under pressure at a temperature between ℃ and 80 ℃.
Generally, the higher the processing temperature, the larger the amount of permeate that can be obtained. At a temperature lower than 5 ° C, the amount of permeated liquid is practically small, and at a temperature higher than 80 ° C, it is not preferable from the viewpoint of stability of the methacrylic acid aqueous solution. In addition, in membrane treatment,
Depending on the form of the semi-permeable membrane used, 5-60 kg / cm ² (cage pressure,
same as below. ) The pressure is increased to contact the semipermeable membrane.
If the pressure is too low, the liquid permeation rate is low, while if the pressure is too high, the membrane may be easily consolidated or damaged, which is not preferable.

Further, in the present invention, the methacrylic acid aqueous solution is continuously passed through the semipermeable membrane under the above conditions until at least 50% or more, preferably 70 to 98%, of the methacrylic acid aqueous solution is recovered as the membrane permeate. It is desirable to make pressure contact while circulating, and if necessary, water is appropriately added to supplement the permeated amount. The flow rate of the methacrylic acid aqueous solution to be treated with respect to the membrane surface is
0.5 to 8 m / sec, preferably 1 to 4 m / se at a linear velocity parallel to the film surface
Let c. When the linear velocity is less than 0.5 m / sec, the concentration polarization of the impermeable component on the membrane surface becomes large and prevents the permeation of methacrylic acid, and when it is more than 8 m / sec, the power cost of the pump is unnecessarily increased, which is preferable. Absent.

The methacrylic acid aqueous solution, which has been subjected to ultrafiltration treatment to remove non-volatile residues, removes the low-boiling components of aldehydes by a conventional method, then extracts it with an organic solvent and sends it to the step of separating methacrylic acid for treatment. To be done. Alternatively, methacrylic acid is separated by liquid extraction with an organic solvent without removing the low boiling point component from the methacrylic acid aqueous solution, and the organic solvent is recovered from the extraction phase together with the low boiling point component, and the low boiling point component is recovered from the recovered organic solvent. The boiling point may be separated by distillation.

〔The invention's effect〕

When methacrylic acid is separated from the aqueous solution of methacrylic acid from which the non-volatile residue has been removed as described above by liquid-liquid extraction with an organic solvent by a conventional method, carbonaceous matter and / or tar that precipitate in the extraction column The generation of scum floating on the interfaces between liquids and liquids was virtually absent, and the problem that was a major obstacle to continuing long-term operation was solved.

Furthermore, since it is no longer necessary to consider the non-volatile residue when selecting the extraction solvent, it is possible to use a solvent having a high selectivity for methacrylic acid (these solvents have considerable selectivity for the non-volatile residue). Therefore, it is extremely advantageous from the standpoint of the apparatus and the energy of solvent recovery.

〔Example〕

 Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 Using a heteropolyacid-based oxidation catalyst, methacrolein was added to
The reaction product gas obtained by vapor-phase catalytic oxidation in the presence of air and water vapor was cooled to 250 ° C. by an indirect cooler and then introduced into a quench tower.

The quench tower has a tower diameter of 6 inches, a height of 3 mm, and a Raschig ring of 2 mm. In the quenching tower, a part of the condensate from the oxidation reaction product gas in the tower is cooled by a cooler and then supplied to the top of the tower, and is brought into parallel flow contact with the reaction product gas to condense and collect the target methacrylic acid. went. The resulting aqueous solution of methacrylic acid was 32.0 parts of methacrylic acid, 3.7 parts of a polymeric substance, 0.5 parts of aldehydes, 6.0 parts of organic acids, and the remaining water. This methacrylic acid aqueous solution was treated at 40 ° C with a membrane area of 0.2 m ² (fraction molecular weight 5
(Polyamide film of 00) was supplied at a rate of 10 l / H and treated at an operating pressure of 16 kg / cm ² . The amount of permeate was 55 l / m ^2, and the composition of the permeate was 30.2 parts of methacrylic acid and 0.
It was 07 parts, 0.5 parts of aldehydes and 5.0 parts of organic acids. From the methacrylic acid aqueous solution, low boiling point components of aldehydes were removed by distillation, and then continuously transferred to a rotating disk type extraction tower.
It was supplied at 0.0 kg / H, and methacrylic acid was recovered by liquid extraction with 10.0 kg / H n-hexane.

Substantially no scum was generated at the interface of the methacrylic acid liquid extraction tower even after 2 months of continuous operation, and no carbon-like substances or tar-like substances were precipitated in the extraction residual liquid. We were able to continue the operation in a stable situation. Further, after the operation was completed, the tower was disassembled and the inside was inspected in detail. As a result, almost no contamination such as the rotating plate, the partition plate and the shaft was observed.

Example 2 The same treatment as in Example 1 was performed except that the operating pressure for ultrafiltration was 50 kg / cm ² . The amount of the permeated liquid was 65 l / m ² , and the composition of the permeated liquid was 31.3 parts of methacrylic acid, 0.03 part of a polymeric substance, 0.5 part of aldehydes, and 5.0 parts of organic acids. Further, the subsequent extraction treatment was also carried out with n-hexane as in Example 1. Continuous operation was possible in an extremely stable state, and scum and carbon-like substances or tar-like substances were not generated even after 2 months, and no pollution was found in the tower inspection after the operation was completed.

Comparative Example 1 Methacrylic acid was recovered by liquid extraction with n-hexane under the same conditions as in Example 1 without subjecting the same aqueous solution of methacrylic acid as in Example 1 to ultrafiltration. Immediately after the start of operation, a large amount of scum was generated at the interface, so the operation was continued while extracting scum with the liquid from the nozzle near the interface. On the other hand, it was observed that a floc black substance was entrained on the side of the residual liquid. At the first week of continuous operation, a tendency toward clogging at the bottom of the tower was observed and a flooding phenomenon occurred, so operation was stopped, internal inspection was performed after draining, and a considerable amount of tar-like substances were found on the rotating plate, partition plate, shaft, etc. It was found that they adhered and blocked the flow path.

Front Page Continuation (72) Inventor Katsuji Yoguchi 4-10-11 Kamo, Takaishi-shi, Osaka (56) References JP-A-58-99434 (JP, A) JP-A-60-104034 (JP, A) Special Kaisho 53-101303 (JP, A) New Experimental Chemistry Course 19 High Polymer Chemistry 2 (Maruzen 1981, page 969)

Claims (1)

[Claims] 1. A methacrylic acid-containing product obtained by subjecting isobutylene, tertiary butanol, isobutyraldehyde or methacrolein to gas phase catalytic oxidation with a gas containing molecular oxygen in the presence of water vapor, and cooling the resulting reaction product gas. The aqueous solution was subjected to ultrafiltration treatment using a semipermeable membrane composed of polysulfone, polyacrylonitrile or polyamide having a molecular weight cutoff of 500 to 2,000 and a linear velocity parallel to the membrane surface of 0.5 to 8 m / sec. A method for purifying an aqueous solution of methacrylic acid, which comprises removing a non-volatile residue in an aqueous solution containing.