JPH0759532B2 - Method of quenching methacrylic acid production gas - Google Patents

Description

The present invention relates to a method for quenching a methacrylic acid-producing gas. More specifically, when one or more compounds selected from isobutylene, tertiary butanol, isobutyraldehyde and methacrolein are vapor-phase-oxidized to produce methacrolein and / or methacrylic acid, a high amount of gas flowing out from the gas-phase oxidation reaction part is produced. TECHNICAL FIELD The present invention relates to a method for recovering methacrolein and / or methacrylic acid by quenching a reaction gas containing a boiling byproduct in a quenching tower.

[Conventional technology]

Usually, a quenching tower is used to collect methacrolein and / or methacrylic acid from a reaction gas obtained by vapor-phase oxidizing one or more compounds selected from isobutylene, tertiary butanol, isobutyraldehyde and methacrolein. To be The gas-liquid contact method in the quenching tower includes both countercurrent contact and cocurrent contact. Liquids used for these contacts include a condensate of reaction gas, benzene, and a carbon number of 1 to 1.
A benzene derivative substituted with an alkyl group, an alkoxyl group or an alkoxycarbonyl group having 4 carbon atoms;
And aliphatic hydrocarbons or alicyclic hydrocarbons thereof.
However, in addition to the target components methacrolein and / or methacrylic acid, high boiling by-products such as benzoic acid, toluic acid, maleic acid, citraconic acid, terephthalic acid and tar-like substances are contained in the reaction product gas. Therefore, in the cooling process, these high-boiling-point by-products are deposited to cause a trouble of blocking the pipeline. Therefore, various proposals have been made as a method for preventing the duct blockage. For example, (1) a method for preventing clogging of pipes in which the temperature above the boiling point of maleic anhydride at the pressure of the reaction product gas is maintained and the average linear velocity of the gas is 5 m / sec or more (Japanese Patent Laid-Open No. 126605). ,
(2) Before condensing the reaction product gas, the temperature of the repaired portion in the repair device is set to 250 ° C or more, which is equal to or higher than the dew point of the gas at the internal pressure.
Method of introducing high boiling point by-products to a collector kept at ℃ or less (JP-A-58-52239), (3) Supplying the reaction gas to the quenching tower at a flow rate of 10 m / sec or more. , A method in which a reaction gas and a condensate are brought into parallel flow contact (JP-A-57-91944),
(4) A method of keeping the temperature of the reaction gas at the scrubber inlet at 130 ° C. or higher (JP-A-56-122327), (5) a part of a condensate liquid in which the gaseous reaction mixture is condensed and accumulated in advance, and 100 ℃
Direct countercurrent contact at the following temperatures (Japanese Patent Laid-Open No. 54-5205)
No. 7) etc.

[Problems to be solved by the invention]

However, although these methods have some effects as methods for preventing duct line obstruction, they are still far from the fundamental methods. That is, the methods (1), (3), (4), and (5) are common in terms of maintaining a gas linear velocity of a certain speed or more and / or a gas temperature of a certain temperature or more, and have a high boiling point. Although it is an excellent method for preventing the adhesion of heat, it causes local temperature drop due to heat transfer to the surrounding cooling section at the inlet to the quench tower of the supply pipe that supplies the reaction product to the quench tower. Alternatively, when the condensate is supplied in parallel flow, the droplet hits the tip of the gas outlet, and the droplet is concentrated there, causing the precipitation of high-boiling by-products. Once the precipitation of the high boiling by-product thus occurs, the high boiling by-product is impregnated with methacrolein and / or methacrylic acid which are the target components contained in the reaction gas in a large amount. Since they have poor thermal stability, they gradually polymerize there and eventually block the conduit.

In the method (2), in order to make up for the above-mentioned drawback, impurities having a high boiling point and a high melting point, which are contained in a gaseous state in the reaction product gas, are forcibly deposited and removed. However, since there are various kinds of precipitated impurities, it is extremely difficult to completely remove the impurities within a uniform temperature range, and in terms of taking out the deposited impurities that have adhered, it is difficult to operate continuously on an industrial scale. Then there are many practical problems.

Therefore, the present inventors, along with the condensate of the reaction product gas,
A method has been previously proposed in which ammonia gas or hydroxide of ammonia is brought into contact with a reaction product gas to rapidly cool the gas (Japanese Patent Laid-Open No. Sho 61-206).
62-438). This method is very effective in preventing the precipitation of polybasic organic acids such as terephthalic acid, which is a high boiling by-product, and the polymerization of methacrolein and / or methacrylic acid. However, the ammonium salt of the above organic acid is distributed to the raffinate side in the next extraction step and becomes a part of the drainage. In this case, the presence of ammonia in the effluent requires denitrification treatment by activated sludge treatment, and requires NOx countermeasures when incinerated, which is not necessarily a preferable method from a comprehensive viewpoint.

Hereinafter, these drawbacks will be described in more detail with reference to the drawings while referring to the countercurrent and cocurrent contact quenching processes used for recovery of methacrylic acid and the like.

FIG. 1 is a schematic diagram showing an apparatus for carrying out the process of a conventional general countercurrent contact type quenching tower 8. In this process, the reaction gas enters the quench tower bottom through conduit 2 which is connected to conduit 1 and mounted at right angles to the tower wall. At that time, the reaction gas hits the collision dispersion plate 3 and is dispersed in the direction perpendicular to the paper surface, and rises in the column toward the top of the column. On the other hand, the condensate that has been pumped up and cooled in the heat exchanger 4 flows countercurrently with the polymerization inhibitor supplied from the conduit 7 through the tower top conduit 11 in a shower shape inside the tower and enters the tower. Upon contact, the reaction gas is rapidly cooled and condensed. Since the reaction gas is continuously condensed, the condensate is extracted so as to have a constant liquid level and sent to the next step through the conduit 5. The waste gas, which has been condensed, is discharged from the top of the tower through a conduit 6 to a waste gas treatment device.

Details of the gas blowing section are as shown in FIG. After being introduced into the conduit 2 through the conduit 1, the reaction gas collides with the collision dispersion plate 3 attached in a U-shape, and is dispersed and rises in the direction perpendicular to the paper surface. However, since the cooled condensate flowing down from above the dispersion plate 3 hits the dispersion plate 3 and cools it, the reaction gas collides with the cooled dispersion plate 3 and is cooled there. It causes condensation and solidification of high boiling by-products. The once-precipitated high-boiling by-product does not come into direct contact with the condensate containing the polymerization inhibitor in the dispersion plate 3, so that the condensation, coagulation and polymerization of the high-boiling by-product gas proceed at the tip of the conduit 2. , High boiling by-products 10
Due to this, the blockage progresses and finally the operation becomes impossible.

On the other hand, FIG. 2 is a view showing an apparatus for carrying out a conventional general co-flow contact quenching process. The reaction gas flowing out from the reaction part obtained by vapor phase oxidation of isobutylene or the like is
The condensate introduced from the top of the quenching tower 8'to the inside of the quenching tower and cooled by the heat exchanger 4'is fed from the conduit 11 'and brought into parallel flow contact to quench it. The gas phase containing uncondensed methacrolein and / or methacrylic acid is led to the next step through the conduit 6 '. At this time, details of the gas blowing portion are as shown in FIG. The reaction gas is kept warm by the heated gas blown into the heated gas blowing port 9'through the heated gas introduction pipe 3 ', so that condensation and solidification of the high boiling by-products are prevented. Therefore, the reaction gas conduit 2'is relieved of blockage at the tip of the conduit 2'because of the effect of the heated gas. However, at the same time, the wall at the top of the quenching tower is heated and the lower wall is also exposed to high temperature due to heat transfer, and when the condensate supplied from the conduit 11 'is scattered in parallel flow and adheres to the tower wall. The condensate is concentrated, leading to the precipitation of high boiling by-products and the polymerization of methacrolein and / or methacrylic acid. It gradually accumulates, and then it leads to clogging as it is, or it falls when it has grown to some extent, causing problems such as clogging of the lower pipe and clogging in the methacrylic acid extraction step which is the next step.

An object of the present invention is to prevent clogging of a nozzle of a quenching tower for methacrylic acid producing gas, and to provide a stable operation method of the quenching tower in which no tar-like substance is attached in the quenching tower.

[Means and Actions for Solving Problems]

As a result of various investigations by the present inventors as a measure for preventing the blockage of the pipe line, the reaction gas is supplied to the quenching tower, the heat transfer at the connection part between the supply pipe and the main body of the quenching tower is suppressed, and the splash of the condensate is the temperature. It has been found that the above object can be achieved by preventing the contact of the tip of the insertion portion of the high supply pipe, and the present invention has been completed.

That is, the present invention is directed to cooling a reaction gas containing methacrylic acid and a reaction gas condensate obtained by catalytically oxidizing isobutylene, tertiary butanol, methacrolein or isobutyraldehyde with a molecular oxygen-containing gas in the presence of steam. When the reaction gas is brought into contact with a liquid to quench the reaction gas, the reaction gas and the adiabatic gas are used as a reaction gas conduit penetrating the wall of the quenching tower as an inner tube and a heat insulating gas conduit is provided around the inner tube. Passing through each double tube arranged as an outer tube, discharging toward the liquid level at the bottom of the quenching tower, and spraying a part of the pre-cooled condensate toward the reaction gas discharging section, A part of the condensate is circulated to the top of the quenching tower, and the reaction gas and a part of the condensate are countercurrently contacted with each other through the filling material in the quenching tower. By way .

The molecular oxygen-containing gas used in the present invention is generally air, pure oxygen, or a mixed gas of nitrogen and oxygen,
Carbon monoxide, carbon dioxide, etc. may be contained in this.

The temperature of the reaction gas is generally in the range of 230 to 370 ° C. The temperature of the condensate in the quench tower is generally adjusted to 10 to 100 ° C, preferably 40 to 60 ° C.

The adiabatic gas is preferably one that has the greatest adiabatic effect without hindering product recovery, and generally air, nitrogen, or a mixed gas of nitrogen and oxygen can be used, but carbon monoxide, carbon dioxide, etc. are included in this. May be.

FIG. 5 is a schematic view of an example of an apparatus for carrying out the quenching method of the present invention. FIG. 6 is a detailed view of the gas blowing section of this apparatus, and FIG. 7 is a detailed view of the spraying section.

The reaction gas such as isobutylene, which is obtained by the gas phase oxidation and flows out from the reaction section, is introduced into the conduit 2 ″ through the conduit 1 ″. The reaction gas passing through the conduit 2 ″ is discharged from the tower bottom of the quench tower 8 ″ toward the bottom liquid level of the quench tower. When the condensate cooled by the heat exchanger 4 ″ is brought into cocurrent contact with the released reaction gas by the spray 12 ″, most of the reaction gas is adiabatically initially caused by evaporation of the condensate. The temperature is rapidly cooled to an intermediate temperature between the temperature and the condensate temperature, and a part of the condensed component is condensed.

Then, as the reaction gas changes direction and rises, the condensate from the overhead conduit 11 ″ is brought into countercurrent contact with the remainder of the condensed components to be cooled and collected almost completely. And the ratio of condensate distributed to the top of the column is 1: 5 to 1: 2
0 is preferable.

The gas phase containing uncondensed methacrolein and / or methacrylic acid is led to the next step by means of the conduit 6 ″. In this case, when the reaction gas is discharged into the cooling tower as shown in the detailed view of FIG. Has the following advantages because the heat insulating gas blown into the heat insulating gas outlet 9 ″ through the heat insulating gas introducing pipe 3 ″ creates a heat insulating gas atmosphere. The spray liquid does not come into direct contact with the hot conduit 2 ″ and is thus prevented from being concentrated and from having high boiling by-products and / or methacrolein or methacrylic acid polymerized. At the same time, the conduit 2 ″ is not cooled by the effect of the heat insulating gas even at the penetration portion where the introduction pipe 3 ″ penetrates a part of the side surface of the quenching tower 8 ″, and the high temperature inside the introduction pipe 2 ″ is maintained. Blocking is completely prevented without the precipitation of boiling by-products. At this time, it is preferable that the heat insulating gas discharged from the introduction pipe 3 ″ maintains a flow velocity of 0.3 to 5 m / sec.

Further, since the reaction gas is blown to the liquid level at the bottom of the column and the column wall is completely wetted by the condensate due to the dispersion effect of the packing material, the packing material is not partially exhausted by the hot gas flowing in, and the conduit 2 ″ is used. Not only does the clogging phenomenon occur in any part of the column, the polymerization inhibitor is supplied from the conduit 7 ″ and the condensate is withdrawn from the conduit 5 ″.
The ratio L / G between the reaction gas amount G and the condensate L from the top of the column is usually 0.3.
It is done in the range of ~ 2.0.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 In a methacrylic acid production apparatus by a catalytic gas phase oxidation method of isobutylene, isobutylene is oxidized in a first-stage oxidation reactor to methacrolein, and methacrolein is oxidized in a second-stage oxidation reactor. Then, the reaction gas discharged from the second-stage oxidation reactor was blown into the quenching tower of the type shown in FIG.

0.3 mol% methacrolein, 2.0 mol% methacrylic acid, water
36.0 mol%, non-condensable gas 61.4 mol%, other gases 0.
The reaction gas having a composition of 3 mol% is passed through the conduit 1 ″ to a temperature at which the high boiling point gas does not condense or solidify.
At 230 ° C and a pressure of 0.3 kg / cm ² , it was discharged toward the bottom of the quenching tower 8 ″. On the other hand, the room temperature air introduced from the conduit 3 ″ was blown out from the ring-shaped heat insulating gas outlet 9 ″ to react. The reaction gas flowing out from the gas conduit 2 ″ was kept adiabatic.

The quench tower is operated at a condensate circulation rate of 5000 / hr and a liquid temperature of 40-6.
Cool the condensate with a heat exchanger 4 ″ so that the temperature of the exhaust gas from the quenching tower is 41 ° C.
/ hr, 1000 / hr was sprayed toward the reaction gas outlet. The condensed and increased liquid was withdrawn by controlling the liquid level at the bottom of the column, and was sent to the next step via conduit 5 ″ and the gas phase via conduit 6 ″.

During this operation, no pressure rise was seen in the system for more than 6 months, and after the stop, the reaction gas and the inside of the tower were inspected.
Only the black substance leading to the nozzle portion was attached, and no other abnormality was observed.

Comparative Example 1 In a methacrylic acid production apparatus by the catalytic gas phase oxidation method of isobutylene, isobutyraldehyde was oxidized in the first stage oxidation reactor to methacrolein, and methacrolein was changed to methacrylic acid in the second stage oxidation reactor. The reaction gas exiting the stage oxidation reactor was blown into a quenching tower of the type shown in FIG.

0.3 mol% methacrolein, 2.0 mol% methacrylic acid, water
36.0 mol%, non-condensable gas 61.4 mol%, other gases 0.
The reaction gas having a composition of 3 mol% is passed through the conduit 1 ', at which the high boiling point gas does not condense or solidify.
It was blown into the top of the quenching tower at 230 ° C and a pressure of 0.3 kg / cm ² . Air heated to 230 ° C through conduit 3'mean gas velocity 1
Blow around the nozzle at 00m / sec. The specifications of the quench tower operation are as follows: the condensate circulation rate is 10 T / hr, the condensate temperature is 40-60 ° C, and the exhaust gas from the quench tower is 41 ° C. The condensate was allowed to flow in parallel from the top of the quench tower. The polymerization inhibitor was also placed in the condensate circulation line and dropped from the top of the tower. The liquid condensed and successively increased was withdrawn by controlling the liquid level at the bottom of the column and sent to the next step via the conduit 5'and the gas phase via the conduit 6 '. In this driving,
Even after 30 days, no pressure increase in the system was observed and the progress was good, but since the pressure increased gradually in the second month,
When stopped and inspected, condensate circulation line 11 ″
A black tar-like substance adhered and grew on the peripheral wall of the tower, and the flow path in the tower was reduced.

〔The invention's effect〕

According to the present invention, it is possible to prevent clogging of the circulating liquid insertion nozzle of the quenching tower for methacrylic acid producing gas, and also prevent tar-like substances from adhering to the inside of the quenching tower, which results in stable operation of the quenching tower for a long period of time. I can do it now.

[Brief description of drawings]

1 and 2 are schematic views of a conventional apparatus for carrying out a process around a conventional quenching tower, FIG. 3 is a detailed view of a gas blowing section in FIG. 1, and FIG. 4 is a gas blowing in FIG. FIG. 5 is a detailed view of a part, FIG. 5 is a schematic view of an apparatus for carrying out a process around a quenching tower to which the method of the present invention is applied, FIG. 6 is a detailed view of a gas blowing part in FIG. 5, and FIG.
It is a detailed view of the spray part in the figure. 1,1 ′, 1 ″, 2,2 ′, 2 ″ …… Conduit 4,4 ′, 4 ″ …… Heat exchanger, 5,5 ′, 5 ″ …… Condensate withdrawal conduit 7,7 ′ , 7 ″ …… Conduit for supplying polymerization inhibitor 8,8 ′, 8 ″ …… Quenching tower, 9 ″ …… Adiabatic gas outlet 12 ″ …… Spray

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuharu Yoguchi 4-7-4-411 Kamo, Takaishi City, Osaka Prefecture

Claims (1)

[Claims] 1. A cooling liquid of a reaction gas containing methacrylic acid and a reaction gas condensate obtained by catalytically oxidizing isobutylene, tertiary butanol, methacrolein or isobutyraldehyde with a molecular oxygen-containing gas in the presence of steam. When the reaction gas and the heat insulating gas are rapidly cooled by bringing the reaction gas and the heat insulating gas into contact with each other, the reaction gas conduit that penetrates the wall of the quenching tower is used as an inner tube, and the heat insulating gas conduit is removed around the inner tube. Pass the double pipes arranged as pipes,
It is discharged toward the liquid level at the bottom of the quenching tower, and a part of the pre-cooled condensate is sprayed toward the reaction gas discharge part, while a part of the condensate is circulated to the top of the quenching tower for rapid cooling. A method for quenching a methacrylic acid-producing gas, characterized in that the reaction gas and a part of the condensate are countercurrently contacted with each other through a column packing.