JP2794332B2 - Acrolein production method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a production method devised to prevent polymerization of acrolein in a production facility during production of acrolein.

[Related Art] In the production of acrolein by catalytic gas-phase oxidation of propylene, in order to recover acrolein from a reaction product gas, generally, it is first cooled and separated into a condensate and an uncondensed gas. In order to recover the acrolein contained therein, the acrolein in the uncondensed gas is absorbed using an absorbing solution such as water.

Then, a method of concentrating and purifying the absorption solution containing acrolein to recover acrolein is known.

[Problems to be Solved by the Invention] However, acrolein is a substance that is very easy to polymerize, and a polymer of acrolein often precipitates in the system,
A problem that blocks the system occurs.

In particular, blockage problems often occur in the acrolein absorption tower. 3-3 in FIG. 1 is an acrolein water absorption tower.

As a countermeasure for the polymerization of acrolein, it is generally performed to add a phenolic stabilizer such as hydroquinone as a polymerization reaction inhibitor, but only by adding a phenolic stabilizer such as hydroquinone,
In particular, it is difficult to prevent polymerization when water is present.

The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method excellent in preventing polymerization in an acrolein absorption tower in an acrolein production process.

In view of the above situation, the present inventors have reached an acute opinion and arrived at the present invention.

[Means for Solving the Problems] A process for producing acrolein which prevents polymerization of acrolein according to the present invention comprises a process for producing acrolein by catalytic gas-phase oxidation of propylene with molecular oxygen in the presence of water vapor. A process for producing acrolein, characterized in that an aqueous solution having a pH in the range of 3 to 5.5 is used as an acrolein absorbing solution in a gas produced by a gas phase oxidation reaction.

A specific procedure for carrying out the present invention will be described based on the attached FIGS. 1 and 2 shown in block diagrams.

The arrows in FIGS. 1 and 2 indicate the direction in which the liquid or gas or the mixture of liquid and gas flows through each part.

1-1 is a reactor, which feeds a raw material gas consisting of propylene, oxygen, and a diluent gas such as water vapor or nitrogen supplied from the upper part in the presence of a catalyst at a normal temperature of 230 to 500 ° C. and a pressure of 0.2.
The reaction is performed in the gas phase under the conditions of 1 to 10 atm.

As the catalyst in this case, a general catalyst used in the synthesis reaction of acrolein, for example, a molybdenum or bismuth-based catalyst is used.

The oxidation product gas thus obtained usually contains 0.5
In addition to ~ 10% by volume of acrolein, water vapor, carbon monoxide, carbon dioxide, acetaldehyde generated during the reaction,
It contains carbonyl compounds such as propionaldehyde, organic acids such as acrylic acid and acetic acid, unreacted propylene and oxygen, and diluent gas.

Subsequently, the oxidation product gas is led to the cooling tower 2-2.

In the cooling tower, the oxidation product gas is cooled, and the oxidation product gas is separated into a condensate and a non-condensable gas.

The condensed liquid and non-condensed gas separated here are 5
It is sent to the condensate treatment tower of -5 and the acrolein absorption tower of 3-3.

The acrolein component in the non-condensed gas sent to the acrolein absorption tower is generally brought into contact with water to form an aqueous acrolein solution, and further sent to the 4-4 dehydration tower and further to the next purification tower.

However, this method has a drawback that the polymerization of acrolein described above is caused and a blocking problem is likely to occur.

Therefore, in the present invention, the acrolein component is absorbed by bringing the non-condensable gas into contact with an aqueous solution having a pH in the range of 3 to 5.5 in the acrolein absorption tower.

The acrolein absorbed in the liquid having a pH in the range of 3 to 5.5 in the acrolein absorption tower is sent to the 4-4 dehydration tower, passed through a distillation step, distilled as crude acrolein from the top of the dehydration tower, and subsequently formed. Sent to the process.

The following two methods can be used to adjust the pH of the acrolein absorbing solution within the range of 3 to 5.5.

One method is to adjust the pH of the acrolein absorbing solution by adding an acid.

When the pH of the acrolein absorbing solution is adjusted by adding an acid, the acid to be added is preferably an acid which can be easily separated in a dehydration tower or a purification step after the dehydration tower, that is, an acid having a large boiling point difference from acrolein.

Specific examples include acetic acid and propionic acid.
The boiling point of acetic acid is 117.
At 8 ° C, the boiling point of propionic acid is 141.4 ° C, and there is a sufficient difference in boiling points.

Another method is to adjust the pH by circulating a part of the bottoms of the dehydration tower 4-4 shown in FIG. 2 and using it as a part of the acrolein absorbing solution.

This method is described in, for example, "Production Process Complete Works", Chemical Industry Co., Ltd. (1987), pp. 264-265, the bottom of the cooler (corresponding to the 2-2 cooling tower in FIG. 2). A distillation column (corresponding to the 4-4 dehydration column in FIG. 2) is subjected to cooling water supplied from the top of the cooler and an absorption column (corresponding to the 3-3 acrolein absorption column in FIG. 2). This method is similar to the method of circulating and using as an absorption liquid supplied from the top of the above, but is clearly different in the following two points.

4-4 Only a part of the bottoms of the dehydration tower is used as the acrolein absorbing solution.

When used as acrolein absorbing solution, 4-4
The bottoms of the dehydration tower and water from outside the system are mixed so that the pH is in the range of 3 to 5.5.

Hereinafter, a procedure for circulating and using a part of the bottoms of the 4-4 dehydration tower will be described with reference to FIG.

In the 1-1 reactor, the same reaction as in FIG. 1 is performed, and the obtained oxidation product gas is led to the cooling tower 2-2.

In the cooling tower 2-2, the oxidation product gas is cooled by the cooling liquid and separated into a condensed liquid and a non-condensed gas.

The separated non-condensed gas is sent to a 3-3 acrolein absorption tower, and a part of the condensate is sent to the top of the cooling tower as cooling water, and the rest is sent to a 5-5 condensate treatment tower.

The non-condensable gas sent to the 3-3 acrolein absorption tower is
PH consisting of 4-4 dehydration column bottoms and water introduced from outside the system
Is adjusted to 3 to 5.5 and absorbed by the acrolein absorbing solution and sent to the 4-4 dehydration column. Then, the acrolein distilled in the 4-4 dehydration column is distilled as crude acrolein from the top of the dehydration column, and then sent to the production step.

On the other hand, part of the bottoms of the 4-4 dehydration tower is drained out of the system, but the rest is mixed with water from outside the system and supplied to the 3-3 acrolein absorption tower as an acrolein absorption liquid.

At this time, the mixing ratio of the 4-4 dehydration column bottoms and the water from outside the system is adjusted to be 5.5 from PH3 of the acrolein-absorbed liquid.

PH of aqueous solution used as acrolein absorbing solution is PH
If it is smaller than 3 or larger than pH 5.5, the effect of preventing polymerization is not sufficient.

The range of PH where the polymerization prevention effect is sufficiently seen is PH3 to PH
The optimum PH is between 5.5 and 4.2 on average.

The graph of FIG. 3 shows the relationship between the residual ratio of acrolein calculated by equation (1) and PH.

In the experiment, acrolein was added to acetic acid aqueous solution of various PH 1.7 times.
% By weight, and the solution was kept at 50 ° C. for 10 hours.

From the figure, when PH is in the range of 3 to 5.5, the residual ratio of acrolein is as high as 72% to 93%, but when PH is less than 3 and when PH is more than 5.5, the residual ratio of acrolein is 72%.
It can be seen that:

EXAMPLES Hereinafter, the content of the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Examples 1 to 4 Acetic acid was added to ion-exchanged water, and acrolein was added to a mixture whose pH was adjusted to the value shown in the table so as to be 1.7% by weight, followed by sealing in a glass sample bottle. This is immersed in a 50 ° C oil bath and left for 10 hours.

After 10 hours, remove the sample bottle and measure the concentration of acrolein using a gas chromatograph. The ratio of the thus obtained acrolein concentration after 10 hours to the acrolein concentration before the start of heating was defined as the residual ratio of acrolein.

Comparative Examples 1 to 5 Tests were performed in the same manner as in the Examples, except that the pH was adjusted to the values shown in Table 2.

As can be seen from the above table, when the pH of the solution is out of the range of 3.0 to 5.5, the residual ratio of acrolein decreases.

This means that the polymerizability of acrolein is increased.

Example 5 A test was performed in the same manner as in Examples 1 to 4, except that after adjusting the pH 3.1 solution, hydroquinone was added to the solution so as to have a concentration of 200 ppm.

It can be seen that a combination of controlling the pH of the solution and adding hydroquinone increases the effect of preventing acrolein polymerization.

Comparative Example 6 When acrolein was manufactured according to the flow shown in FIG. 1, a blockage trouble occurred once a month on average. Here, the acrolein absorbing solution (B) uses industrial water without pH adjustment.

Example 6 A part of the bottom liquid of the 4-4 dehydration tower shown in FIG.
The mixture was mixed with water (e) from the outside of the system, the pH was adjusted from 3 to 5.5, and the mixture was used as an acrolein absorbing solution, and the operation according to the flow used in the acrolein absorption tower was performed for half a year. No trouble occurred.

From the comparison between Comparative Example 6 and Example 6, prevention of polymerization of acrolein by adjusting the pH of the acrolein-absorbed solution to a value within the range of 3 to 5.5 by recycling a part of the bottoms of the 4-4 dehydration tower. The law can be said to be fully effective.

[Effects of the Invention] The present invention provides a device that is not complicated and large-scale,
It prevents acrolein polymerization in the acrolein absorption tower and the subsequent acrolein production process, and prevents troubles due to clogging.

Further, acrolein can be efficiently obtained by preventing a substantial decrease in acrolein yield.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are flow sheets showing an example of an embodiment of the present invention, and FIG. 3 is described in Examples 1-4 and Comparative Examples 1-5. It is a graph which shows the relationship between PH of a liquid and the residual rate of acrolein.

Claims (1)

(57) [Claims] In a process for producing acrolein by catalytically oxidizing propylene with molecular oxygen in the presence of water vapor, PH is 3 to 5.5 as an acrolein absorbing solution in a gas produced by the catalytic gas-phase oxidation reaction. A process for producing acrolein, characterized by using an aqueous solution in the range described above.