JPH0621102B2 - Method of condensing reaction product gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reaction product gas when producing methacrylic acid by a catalytic gas phase oxidation reaction of isobutylene, tertiary butanol, methacrolein or isobutylaredehyde. The present invention relates to a novel method for condensing a reaction product gas, which eliminates the troubles that occur during cooling and condensation.

[Prior Art] Isobutylene, tert-butanol, methacrolein or isobutylaldehyde is added with molecular oxygen in the presence of water vapor to give 1
Various impurities by-produced in the reaction are present in the condensate of the reaction product gas containing methacrylic acid obtained by catalytic oxidation in a two-stage or two-stage reaction by cooling and condensation. Examples of these impurities include aldehydes such as formalin, acetone, acetaldehyde and unreacted methacrolein, monobasic acids such as formic acid, acetic acid, propionic acid, isobutyric acid, acrylic acid, benzoic acid and toluic acid, or maleic acid. Dibasic acids such as citraconic acid and terephthalic acid or other polybasic organic acids, and tar-like substances are known.

These impurities, especially polybasic organic acids having a relatively high melting point, especially terephthalic acid, obtain a condensed liquid and a non-condensed gas of the reaction product gas in a cooling condensation step (generally, a quenching tower is used). At this time, since the solubility in the condensate is low, it precipitates on the pipe or tower wall and causes blockage, and when the reaction product gas is cooled, fumes are generated to separate it from the non-condensed gas. It causes difficulties and causes various troubles in the subsequent steps. On the other hand, terephthalic acid slightly dissolved in the condensate of the reaction product gas containing methacrylic acid,
Solubility decreases in the extraction process of methacrylic acid from the condensate using the following solvent and precipitates in the system, causing clogging of pipes and the like, and impeding continuous operation of the methacrylic acid production process including the extraction process. Has become.

As a solution to these problems, for example, an orifice scrubber is used, and the fume is dropped by increasing the gas flow velocity and hitting the collision plate (Chemical engineering, Volume 47, No. 6),
When the reaction product gas is cooled with water, a hydrophobic solvent is allowed to coexist therewith to dissolve and absorb the tar-like substance containing a polybasic organic acid such as terephthalic acid (JP-A-50-151815). For cooling, the gas and the condensate of the gas are brought into contact with each other in parallel flow at an inlet gas flow rate of 10 m / sec or more and a gas temperature of 200 ° C. or more (Japanese Patent Laid-Open No. 57-91944), alkali metal etc. in the condensate. A method such as adding the basic substance (JP-A-58-99434) has been proposed.

[Problems to be Solved by the Invention] However, these methods are mainly intended to prevent clogging of the reaction product gas in the cooling and condensation step, or are dissolved or precipitated in the condensate of the reaction product gas containing methacrylic acid. Impurities extracted as a slurry together with the condensate, that is, aromatic carboxylic acids, maleic acid, polymers, tar-like substances, etc. are efficiently separated and removed. In addition, the method of Japanese Patent Laid-Open No. 50-151805, which uses a solvent instead of water, also requires an operation for removing tar-like substances containing polybasic organic acids such as terephthalic acid that become solid when the solvent is separated and recovered. . However, since methacrolein and methacrylic acid are extremely easy to polymerize, even if a small amount of polybasic organic acid, especially terephthalic acid, is deposited, condensed methacrolein and methacrylic acid are impregnated in the deposited terephthalic acid, which facilitates It causes polymerization to occur and causes clogging inside the piping and the quenching tower. This phenomenon is especially terephthalic since it is unavoidable in the process that the already condensed methacrolein, methacrylic acid, etc. are exposed to a high temperature atmosphere in the transition region until the component to be condensed in the reaction product gas is completely condensed. It is considered that the presence of a polybasic organic acid precipitate such as an acid further promotes the polymerization.

The present invention has been made in view of the above points, and an object of the present invention is to block the occlusion mainly due to the polybasic organic acid such as terephthalic acid or methacrolein or methacrylic acid. It is an object of the present invention to provide a novel method for condensing a reaction product gas, which is capable of eliminating problems such as polymerization caused by cooling and condensing a reaction product gas and effectively removing the terephthalic acid or the polymer.

[Means for Solving Problems] As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that
When cooling the reaction product gas obtained by the catalytic gas phase oxidation reaction of isobutylene, tertiary butanol, methacrolein or isobutyraldehyde, by adding ammonia gas or hydroxide of ammonia, the metachlore in the transition region is added. In addition to being able to prevent the polymerization of rhein and methacrylic acid, polybasic organic acids such as terephthalic acid form ammonium salts and become water-soluble,
The present invention has been completed by finding that not only the above troubles in the cooling and condensation step are eliminated but also the step of separating the polymer and polybasic organic acid such as terephthalic acid in the subsequent step becomes unnecessary.

That is, the present invention relates to isobutylene, tertiary butanol,
In producing methacrylic acid by catalytically oxidizing methacrolein or isobutyraldehyde with a molecular oxygen-containing gas in the presence of steam, a reaction product gas containing methacrylic acid obtained by the catalytic oxidation is a condensate of the reaction product gas. Along with, ammonium hydroxide or hydroxide of ammonia was added in an amount sufficient to neutralize 1N of the polybasic organic acid contained in the condensate and then rapidly cooled, and a condensate of methacrylic acid containing by-products was added. A method for condensing a reaction product gas, which comprises obtaining a non-condensed gas.

In the present invention, the amount of ammonia gas or ammonia hydroxide added together with the condensate is an amount sufficient to neutralize one part of the polybasic organic acid such as terephthalic acid contained in the condensate. To do. Although the pH of the condensate varies depending on the concentration of various acids contained in the condensate, it is usually about pH.
It is good to adjust in the range of 1.0 to 3.5. When a large amount of ammonia gas or hydroxide of ammonia is added in excess of the neutralization equivalent of polybasic acid, the target methacrylic acid is also neutralized and leaks to the aqueous phase side in the extraction step of extracting methacrylic acid from the condensate. When the amount of methacrylic acid is large, on the other hand, when the amount of methacrylic acid is small, the polybasic acid partially precipitates and the blockage cannot be completely eliminated.

The ammonia gas or the hydroxide of ammonia is generally adopted in cooling and condensing the reaction product gas.
No precipitation of contents in condensate below 150 ° C
It is desirable to add to the condensate in the temperature range of 10 ° C or higher.
The addition method is not particularly limited, but it is desirable to add the reaction product gas in a spray form in a cocurrent to the introduction part, or to add it to the condensate circulation line.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is an example of an apparatus used in the method for condensing a reaction product gas containing methacrylic acid according to the present invention.

In FIG. 1, a reaction product gas containing methacrylic acid obtained by a catalytic oxidation step (not shown) is introduced into a quench tower 7 through a conduit 1 and comes into contact with a condensate circulated through a conduit 3 through a cooler 2. Cooled and condensed. At this time, ammonia or a hydroxide of ammonia is supplied to the condensate circulated through the conduit 4 or the conduit 4'to the top of the column.
Preferably, these aqueous solutions are added. The uncondensed gas is sent to a non-condensed gas treatment system (not shown) through a conduit,
It is processed separately from the condensate. An amount of the condensed liquid corresponding to the condensed amount is sent to the next extraction step through the conduit 5. That is, the methacrylic acid aqueous solution, which is the condensate sent through the conduit 5, is supplied to the extraction tower 12 through the conduit 8 and the methacrylic acid is extracted by the solvent introduced through the conduit 9. The methacrylic acid extract is sent to the refining process through the conduit 10, and the raffinate is discharged out of the system through the conduit 11.

[Function] In the method of the present invention as described above, the mechanism by which the ammonia gas or the hydroxide of ammonia prevents the polymerization of methacrolein and methacrylic acid at the time of condensation is not necessarily clear, but it is probably It is considered that the presence of gaseous ammonia in the high temperature transition region due to high vapor pressure of ammonia suppresses radical polymerization of methacrolein and methacrylic acid. Further, this ammonia selectively forms an ammonium salt with a high-melting point polybasic organic acid containing terephthalic acid, which precipitates when the reaction product gas is cooled and condensed, and dissolves the high-melting point polybasic organic acid containing terephthalic acid in water. Therefore, these substances, which had been deposited and solidified on the pipes and tower walls in the past, are easily washed with the condensate and do not stay on the pipes and tower walls, and blockage during cooling and condensation. It seems that it has been resolved. Further, as described above, the polybasic organic acid containing terephthalic acid easily impregnates methacrolein and methacrylic acid, and the impregnated methacrolein and methacrylic acid are easily polymerized to cause pipe clogging, etc., Since these polybasic organic acids become ammonium salts and are washed away, methacrolein and methacrylic acid do not polymerize, and it is considered that the problems such as pipe clogging due to the polymer are solved.

Further, the polybasic organic acid dissolved in the methacrylic acid aqueous solution as an ammonium salt is not extracted into the solvent or precipitated in the next step of extracting methacrylic acid with the solvent, and is separated from the system as an aqueous phase. To be extracted. If necessary, this liquid is treated as waste water after recovering a small amount of entrained solvent. Therefore, in the method of the present invention, it is not necessary to particularly provide a facility for separating the polybasic organic acid containing terephthalic acid.

[Effects of the Invention] According to the method of the present invention, not only the polymerization of methacrolein and methacrylic acid, which has been a great problem when cooling and condensing a reaction product gas in the past, is suppressed, but also a pipe and a tower wall are cooled and condensed. The polybasic acid containing terephthalic acid, which was deposited and adhered to methacrolein and methacrylic acid to promote the polymerization, can be further suppressed by the use of a water-soluble ammonium salt. Polybasic organic acids including terephthalic acid, which has caused various troubles such as blockages in the separation and purification process of methacrylic acid, can be effectively removed without installing a special separation device, so safe operation It is industrially very advantageous from the standpoint of achieving the above and also from the aspect of equipment and operation.

[Examples] Hereinafter, the present invention will be described more specifically with reference to Examples.

[Example 1] Methacrylic acid production plant by catalytic gas phase oxidation of isobutylene (methacrolein was produced in a first stage oxidation reactor,
Make methacrylic acid in the second stage oxidation reactor. ),
The reaction product gas containing methacrylic acid, which exited from the second-stage oxidation reactor, was introduced into the quench tower 7 illustrated in FIG. The composition of the reaction product gas is methacrolein 0.3 mol%, methacrylic acid
0.2 mol%, water 36.0 mol%, non-condensable gas 61.4 mol%,
The amount of other gases (including high-boiling point components) was 0.3 mol%.

The reaction product gas is passed through the conduit 1 at a temperature of 250 ° C at which the high boiling point gas does not condense or solidify, and the pressure is 0.5 kg.
/ cm ^2, were introduced from the top of the quenching column 7 in the gas average flow rate 15 m / sec.

The operating specifications of the quenching tower are the condensate circulation rate of 800 to 1000 / H.
r, condensate temperature 40 ~ 50 ℃, temperature of exhaust gas from quenching tower 5
The condensate was cooled by the heat exchanger 2 so that the temperature became 0 ° C., and the condensate was introduced from the conduit 3 to the top of the tower and circulated. Ammonia gas 22.4 / Hr was added to this circulation line together with the polymerization inhibitor through conduit 4.

The condensed liquid which was condensed and increased successively was withdrawn by the liquid level control device at the bottom of the column and transferred to the extraction column 12 through the conduit 5. The non-condensed gas was transferred to the gas treatment system through the conduit 6.

Condensate is supplied to the extraction tower from the top of the tower through conduit 8.
The extraction was carried out at a rate of 0.8 Kg / Hr, ethyl acetate was supplied as an extractant at a rate of 8.9 Kg / Hr from the conduit 9 at the bottom of the tower, and continuous countercurrent extraction was carried out. The extraction tower is 50 mm in total height.
A paddle type rotating disk tower with 1500 mm and 20 stages was used.

When continuous operation was carried out for one month under the above conditions, the operating state was good even after the lapse of one month, and the rise in gas pressure in the quenching tower 7 was slight. After the operation was stopped, the inside of the quenching tower was observed. As a result, almost no adhering matter was observed on the tower wall, and the inside of the tower wall was in a clean state without being contaminated by the precipitation of the polymer and terephthalic acid. The observation results are shown in Table 1.

The content of monoammonium terephthalic acid salt in the precipitation liquid was 5 ppm, and the content of ammonium terephthalic acid salt in the raffinate liquid was 550 ppm. Although a small amount of scum was observed at the interface of the extraction tower, precipitation of terephthalic acid particles was not observed in both the extract and the raffinate.

[Example 2] Example 1 except that the ammonia gas was changed to ammonia water
The same test was performed. The results are shown in Table-1.

[Comparative Example 1] The same test as in Example 1 was carried out except that ammonia gas was not added. As a result, the pressure in the quenching tower increased in about 2 weeks, and the operation became impossible. When the inside of the quenching tower was inspected, a considerable amount of blackish brown deposits were observed on the tip of the conduit 1 for introducing the reaction product gas into the tower and on the tower wall. This deposit was terephthalic acid containing a polymer of methacrylic acid and methacrolein. In addition, fine particles of terphthalic acid were precipitated in the condensate. After filtering this, extraction treatment was performed and the amount of terephthalic acid entrained in the extract was calculated to be 70 ppm.

[Comparative Example 2] Ammonia gas was added to a 10% aqueous solution of sodium hydroxide, 0.4 kg.
The same test as in Example 1 was performed except that / Hr was replaced. The results are shown in Table-1.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an example of an apparatus used in the method of the present invention. 7 ... Quenching tower, 12 ... Extraction tower

Claims (1)

[Claims] 1. When methacrylic acid is produced by catalytically oxidizing isobutylene, tertiary butanol, methacrolein or isobutyraldehyde with a molecular oxygen-containing gas in the presence of steam, the methacrylic acid obtained by the catalytic oxidation is included. The reaction product gas is added together with the condensate of the reaction product gas in an amount of ammonia gas or hydroxide of ammonia in an amount sufficient to neutralize one part of the polybasic organic acid contained in the condensate. A method for condensing a reaction product gas, which comprises quenching to obtain a methacrylic acid condensate containing a by-product and a non-condensed gas.