JP2003238485A - Method and equipment for collecting (meth)acrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing (meth)acrylic acid by a catalytic vapor phase oxidation reaction while stably operating the process irrespective of e.g. the variation of atmospheric conditions. <P>SOLUTION: The method comprises the steps of producing a (meth)acrylic acid-containing gas by the catalytic vapor phase oxidation reaction, then bringing the gas into a collection column and collecting the (meth)acrylic acid as an aimed product in the form of a solution by using a water-based collection solvent, wherein the (meth)acrylic acid concentration of the bottoms discharged from the column is controlled by varying a water content of the gas discharged via the overhead of the column. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method and an apparatus for collecting (meth) acrylic acid. More specifically, by changing the amount of water in the gas discharged from the top of the collection tower, the concentration of (meth) acrylic acid in the bottom liquid of the collection tower discharged from the collection tower is controlled ( The present invention relates to a method and a device for collecting (meth) acrylic acid.

[0002]

2. Description of the Related Art A readily polymerizable substance such as acrylic acid or methacrylic acid is used as a raw material for manufacturing industrial products and is a chemical substance produced in large quantities in a large-scale plant. Generally, these compounds are manufactured through various collection and purification steps in order to obtain a highly pure product.

For example, in the process of producing acrylic acid, when propylene, propane, acrolein, etc. are catalytically vapor-phase oxidized with a molecular oxygen-containing gas in the presence of an oxidation catalyst, acetic acid, a low-grade compound, in addition to acrylic acid, which is a target substance, Low-boiling substances such as aldehyde and water and high-boiling substances such as furfural and maleic anhydride are generated as by-products. Therefore, the obtained mixed gas is introduced into an acrylic acid collection tower and brought into contact with an acrylic acid collection solvent to be absorbed and collected to obtain a solution containing acrylic acid and other by-products, and the solution is distilled and stripped. Acrylic acid is separated and purified by methods such as extraction, crystallization and the like to obtain a product.

As such a separation and purification method, Patent Document 1
The mixed gas obtained by catalytic vapor-phase oxidation of propylene or the like is introduced into an acrylic acid collection column and brought into contact with a collection solvent to form an acrylic acid aqueous solution (collection tower column bottom liquid). Is introduced into the azeotropic separation column to obtain acrylic acid.

In the collection of (meth) acrylic acid from such a (meth) acrylic acid-containing gas, it is relatively inexpensive and has a high ability to collect (meth) acrylic acid, and it is relatively easy to obtain a high concentration of (meth). Since an acrylic acid solution can be obtained,
It is common to use a collection solvent whose main component is water. Further, in the collection method, conventionally, no particular attention has been paid to the top pressure and the top temperature of the collection tower, so that the amount of water in the gas discharged from the top of the collection tower hardly changes. do not do.

However, as the molecular oxygen-containing gas in the catalytic gas phase oxidation step, air is usually used because of its low cost. However, when air is used, it may be added to the reactor due to changes in atmospheric conditions. Fluctuations in the amount of water brought in cannot be avoided, and the proportion of water in the acrylic acid-containing gas introduced into the collection tower also fluctuates. As a result, the concentration of (meth) acrylic acid in the liquid at the bottom of the collection tower is changed. This change in concentration causes a hindrance to stable operation of the (meth) acrylic acid separation and purification steps after the next step, and causes fluctuations in the amount of waste water.

As a solution to this problem, it is conceivable that the air used in the catalytic gas phase oxidation step is conditioned to a certain amount of water, but the equipment cost and utility cost for conditioned humidity are sufficient, and this is sufficient. Not a countermeasure.

As another solution, it is possible to change the supply amount of the collection solvent to the collection tower according to the amount of water brought into the reactor for carrying out the catalytic gas phase oxidation process, but the waste water is collected. When collecting and reusing as a solvent, the ratio of waste water to the amount of collected solvent supplied (hereinafter referred to as “collected solvent recovery rate”
, The amount of waste water to be recovered and reused must be changed with the change in the supply amount of the collecting solvent, and as a result, the change of the waste water to be discarded cannot be avoided.

When the fluctuation of the amount of waste water is to be adjusted by the recovery rate, the upper limit (100%) of the recovery rate is determined, so that it is necessary to set the recovery rate low as a whole.
As a result, the amount of waste water to be finally discarded increases.

As described above, conventionally, there have not been sufficient measures for ensuring the operational stability of the wastewater treatment facility including changes in atmospheric conditions.

[0011]

[Patent Document 1] Japanese Patent Application Laid-Open No. 9-157213 (claim 1 etc.)

[0012]

Under the circumstances described above, the problem to be solved by the present invention is that the process for producing (meth) acrylic acid by catalytic gas phase oxidation reaction is performed regardless of changes in atmospheric conditions. It is to provide a method that enables stable operation.

That is, when air is used as the source oxygen source, the water content in the product gas introduced into the collection tower also changes due to changes in atmospheric conditions and the like. As a result, when the (meth) acrylic acid concentration of the bottom liquid from the collection tower changes,
The conditions of the subsequent purification process will have to be adjusted. In addition, if the amount of the collection solvent introduced into the collection tower is adjusted to suppress the change in the (meth) acrylic acid concentration, the amount of waste water used as the collection solvent must be changed one by one.

Therefore, an object of the present invention is to keep the concentration of (meth) acrylic acid in the bottom liquid of the collection tower without changing the amount of the collection solvent introduced into the collection tower, regardless of changes in atmospheric conditions. It is to provide a method for maintaining stable operation and enabling stable operation of the entire (meth) acrylic acid production process.

[0015]

[Means for Solving the Problems] The present inventor has taken measures for ensuring operational stability in the subsequent steps including a waste water treatment facility due to changes in atmospheric conditions, etc., regarding the amount of collected solvent supplied, the amount of waste water, and the amount of collected water. As a result of detailed examination of the changes in the (meth) acrylic acid concentration of the bottom liquid of the tower and the collection efficiency, it was found that all problems can be solved by changing the amount of water in the gas discharged from the top of the collection tower. I found it.

That is, since the conditions of the catalytic gas phase oxidation reaction are constant, the amount of (meth) acrylic acid and other by-products discharged from the reactor is also almost constant, but the amount of water is changed depending on atmospheric conditions and the like. Only changes. Therefore, when the amount of the collection solvent supplied is constant, maintaining a constant (meth) acrylic acid concentration in the bottom liquid of the collection column leads to the maintenance of the flow rate of the bottom liquid, which in turn stabilizes the amount of waste water. Becomes Moreover, surprisingly, the collection method of the present invention has less fluctuation in the collection efficiency as compared with the case where the supply amount of the collection solvent is changed.

Therefore, according to the method of the present invention, the loss of (meth) acrylic acid from the collection tower and the wastewater is minimized, and the operational stability of the subsequent steps including the wastewater treatment facility is ensured. can do.

The method of collecting (meth) acrylic acid of the present invention capable of exerting such effects is to produce a gas containing a target product by a catalytic gas phase oxidation reaction, and then introduce the gas into a collection tower. , A collection solvent whose main component is water (water concentration: 5
In the process for producing (meth) acrylic acid in which the target product is collected as a solution (0% by mass or more), the amount of water in the gas discharged from the top of the collection tower is changed to obtain a desired product from the collection tower. (Meta) of the bottom liquid of the collection tower that is discharged
It is characterized by controlling the concentration of acrylic acid.

In the above method, it is preferable that the amount of water in the gas discharged from the top of the collection tower is changed by the top temperature and / or the top pressure of the collection tower. This is because the amount of water in the exhaust gas can be adjusted relatively easily, and the equipment cost can be relatively low.

Further, it is preferable to reuse part or all of the waste water discharged from the (meth) acrylic acid production process as a collecting solvent. From the viewpoint of reducing the amount of wastewater, according to the collection method of the present invention, it is possible to reuse the wastewater very easily because stable operation of the entire process is possible without adjusting the amount of reused wastewater step by step. Also depends on

The water content in the gas discharged from the top of the collection tower may be changed according to the water content in the gas introduced into the catalytic gas phase oxidation reactor. The water content corresponds to the water content in the gas introduced into the collection tower after the reaction,
This is because if the method of the present invention is carried out according to the water content, the concentration of (meth) acrylic acid in the bottom liquid of the collection tower can be stably maintained. Further, the water content in the exhaust gas may be adjusted according to the water content in the air used as the molecular oxygen-containing gas. For the same reason.

Further, the (meth) acrylic acid collecting apparatus according to the present invention is a collecting tower for carrying out the above-mentioned method, and is a means for controlling a top temperature of the collecting tower and / or a top. It is characterized by having a means for controlling the pressure.

In the apparatus, it is preferable to reuse part or all of the waste water discharged from the (meth) acrylic acid production process as a collecting solvent. This is because the amount of waste water can be reduced.

Also in this apparatus, the amount of water in the gas discharged from the top of the collection column is adjusted in accordance with the amount of water in the gas introduced into the catalytic gas phase oxidation reactor in the catalytic gas phase oxidation reaction. It is preferable to change. This is because the two water contents correspond to each other, and the (meth) acrylic acid in the bottom liquid of the collection tower can be stably maintained.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described with reference to FIG. 1 by taking a method for producing acrylic acid as a typical example.

First, a raw material component 1 such as propylene, propane, acrolein, etc., an inert gas 2 and a molecular oxygen-containing gas 3 such as air pressurized by a blower 4, and a catalytic gas phase filled with an oxidation catalyst. The gas is supplied to the oxidation reactor 10 and a catalytic gas phase oxidation reaction is performed to generate an acrylic acid-containing gas 20. The catalytic gas-phase oxidation reaction is not particularly limited as long as it produces acrylic acid in the presence of a catalytic gas-phase oxidation catalyst, but one using a multitubular reactor is superior in reaction efficiency. Preferably used. Specifically, using a reactor such as a multi-tube reactor, in the presence of an oxidation catalyst, starting materials 1 such as propylene, propane, acrolein, etc., an inert gas 2 etc., and a molecular oxygen-containing gas 3 such as air 3 A predetermined amount of the reaction raw material gas is supplied to perform the catalytic gas phase oxidation reaction. At this time, when propylene is used as a raw material component, acrolein is first produced, and this is further subjected to catalytic gas phase oxidation to obtain acrylic acid. The reaction steps adopted in the present invention may be either a one-step method in which these reactions are carried out in one reactor or a two-step method in which these reactions are carried out respectively in different reactors. Further, the oxidation catalyst to be used, and the reaction conditions such as the raw material components, the molecular oxygen, the gas concentration of the inert gas, the reaction temperature and the like may be applied to any condition of the conventionally known acrylic acid production reaction step. it can.

For example, as raw material components, propylene,
Any of propane and acrolein or a mixture of two or more thereof can be used, and these raw material components are
The amount of the reaction raw material gas supplied to the reactor is 6 to 20% by volume, preferably 8 to 15% by volume. In addition, the reaction raw material gas is used in an amount of 1 relative to the raw material components to cause the oxidation reaction.
~ 3 times (molar ratio) molecular oxygen, the rest is nitrogen,
It is an inert gas such as carbon dioxide or water vapor.

Further, for example, in the present invention, in order to produce acrylic acid by subjecting a propylene-containing gas to a catalytic gas phase oxidation reaction,
As a catalyst used in the first-stage reaction for producing acrolein by catalytic vapor phase oxidation of propylene, it is possible to use an oxidation catalyst generally used for producing acrolein by catalytic vapor phase oxidation of a raw material gas containing propylene. it can. Similarly, there is no particular limitation on the catalyst used in the second-stage reaction that produces acrylic acid by catalytic gas-phase oxidation of acrolein obtained in the first-stage reaction, and the reaction gas containing acrolein is subjected to catalytic gas-phase oxidation to produce acrylic acid. Oxidation catalysts commonly used in making can be used.

Generally, the acrylic acid-containing gas obtained by the catalytic gas phase oxidation reaction has a temperature of 200 to 350 ° C., and preferably 100 to 300 by the heat exchanger 21 before being supplied to the acrylic acid collection column 30. C., particularly preferably 130 to 270.degree. A known heat exchanger can be used as the heat exchanger 21 used for such cooling.
This cooling is necessary to ensure that the temperature of the reaction product gas mixture does not drop below its dew point. If the reaction gas is already in an appropriate temperature range, cooling is of course unnecessary.

The acrylic acid-containing gas obtained by this catalytic gas-phase oxidation reaction contains acrylic acid, molecular oxygen, unreacted raw material components, inert gas, and other by-produced water, acetic acid, propionic acid, It contains impurities such as maleic acid, acetone, acrolein, furfural, and formaldehyde.

Next, the obtained acrylic acid-containing gas 20
Is introduced into a collection tower 30 in which a packed bed 31 and a disperser 32 are installed, is brought into contact with a collection solvent 33, and the bottom liquid discharged from the collection tower is an acrylic acid-containing solution (collection tower). As the bottom liquid 35, a part of the liquid is circulated in the acrylic acid collection column 30 while being cooled by the cooler 34, and the rest is withdrawn and dehydrated in the dehydration column 40.
And dehydration treatment is performed. The collecting solvent used here is not particularly limited as long as the main component is water, but a part or the whole amount of the waste water generated in the manufacturing process of acrylic acid and the vacuum generator waste liquid described later is collected. It is economical and preferable to reuse. In addition, depending on the case, a cleaning waste liquid or the like can be mixed and used.

A known contact method can be used for the method of contacting the acrylic acid-containing gas with the collecting solvent.
For example, cross flow contact using bubble cap trays, uniflux trays, perforated plate trays, jet trays, valve trays, venturi trays and any combination thereof; turbo grid trays, dual float trays,
Ripple trays, kittel trays, random packing, ordered packing and countercurrent contact with any combination thereof. Among them, the method of contacting the acrylic acid-containing gas and the collection solvent by countercurrent contact is advantageous, and in particular, in the collection column, a packing having a high absorption efficiency on the upstream side in the flow in the column of the collection solvent is used. It is advantageous to install packing and / or trays (trays) having a relatively low polymerization production capacity on the downstream side.

The dehydration treatment method in the dehydration tower 40 is not particularly limited, but an azeotropic distillation method using a poorly water-soluble azeotropic solvent is general. In this method, the target product (meth) acrylic acid is mainly obtained as the bottom liquid of the dehydration tower 40, but it may still contain impurities such as low-boiling substances and high-boiling substances. Transfer to 50 for further purification. On the other hand, impurities of (meth) acrylic acid contained in the (meth) acrylic acid-containing solution (collection tower bottom liquid) 35 are:
It is discharged as a distillate gas 41 together with a poorly water-soluble azeotropic solvent and separated from (meth) acrylic acid. The distillate gas 41 is condensed by a condenser 44 arranged at the top of the dehydration tower 40, and the condensed liquid is phase-separated into a solvent phase 42 and an aqueous phase 43.

The solvent phase 42 which has been phase-separated is returned to the dehydration tower 40 and is circulated for use. The aqueous phase 43 becomes waste water 46 together with the waste liquid of the vacuum generator 45, but contains a slight amount of (meth) acrylic acid. In some cases, it is economical to recover a part or all of the amount and use it as the collecting solvent 33, and it is preferable to reduce the amount of waste water. Waste water discharged from the next step 50 or waste liquid from the vacuum generator (recovered water 7
As for 0), a part or the whole amount thereof can be used as the collecting solvent 33. In some cases, it is also possible to mix the cleaning waste liquid of each device and use it as the collecting solvent 33.

Gas 36 discharged from the top of the collection tower 30
May treat all of them as exhaust gas 60,
It is advantageous to circulate a part of the recycled gas in the reactor 10 by using, for example, a blower 4 because the amount of the inert gas 2 supplied can be reduced.

In the present invention, in this collecting step, the amount of water in the gas discharged from the top of the collecting tower is changed to keep the supply amount of the collecting solvent 33 constant and the collecting tower 3
The concentration of (meth) acrylic acid in the bottom liquid 35 of the collection tower discharged from 0 is controlled, but the method of changing the amount of water in the gas discharged from the top of the collection tower is not particularly limited. For example, a method of changing one or both of the top temperature and the top pressure of the collection tower is preferable.

As an example thereof, when the water content in the air used as the molecular oxygen-containing gas in the catalytic gas phase oxidation step is large, the top temperature of the collection column is raised or the top pressure is increased. By lowering or adopting both means, the concentration of (meth) acrylic acid in the bottom liquid of the collection column discharged from the collection column can be kept stable. on the other hand,
When the water content is small, the reverse means may be adopted.

As a method of changing the top temperature of the collection tower 30, a method of changing the heat removal amount of the cooler 34, or a new cooler provided outside the cooler 34 is provided. Can be changed, the temperature of the trapping solvent 33 can be changed, the temperature of the acrylic acid-containing gas 20 can be changed, and these methods can be used alone or in combination of a plurality of methods. Good. Also, the collection tower 30
As a method for changing the column top pressure of, for example, a general method using a pressure control valve can be used.

The cycle for changing the amount of water in the gas discharged from the top of the collection tower may be set in consideration of the allowable fluctuation after the next step including the waste water treatment facility and the change in atmospheric conditions. There is no particular limitation such as setting for each second, minute, hour, day, month, and season.

The concentration of acrylic acid in the liquid at the bottom of the collection tower which is withdrawn from the bottom of the collection tower is not particularly limited, but is 60 to 85.
It is preferably set to mass%. This is because if it is less than 60% by mass, the amount of wastewater increases in addition to the facility cost and utility cost for the subsequent steps due to the separation of impurities. On the other hand, if the amount is higher than 85% by mass, the loss of acrylic acid from the top of the collection tower increases, and in order to suppress the loss, it is necessary to increase the theoretical plate number of the collection tower, which requires equipment costs.

The top temperature of the collection tower is not particularly limited, but is preferably in the range of 40 to 80 ° C. Four
If the temperature is lower than 0 ° C, equipment cost and utility cost for cooling are required, and in addition, condensation of a substance having a boiling point lower than that of acrylic acid is increased, and the liquid in the bottom liquid of the collection column is withdrawn from the bottom of the collection column. This is because the concentration of acrylic acid is reduced and the amount of waste water also increases.
On the other hand, if the temperature is higher than 80 ° C., the loss of acrylic acid from the top of the collection tower increases, leading to an increase in the cost of acrylic acid as a product, which is not preferable.

The top pressure of the collection tower is not particularly limited, but is preferably in the range of 0 to 30 kPa (gauge pressure). When the pressure is lower than 0 kPa (gauge pressure), a decompression device is required, which requires facility cost and utility cost. When the pressure is higher than 30 kPa (gauge pressure), it is necessary to enlarge the blower for supplying the raw material gas to the catalytic gas phase oxidation reactor. However, it is not economical because it requires facility costs and utility costs.

[0043]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

The collection efficiency of acrylic acid in the collection tower and the recovery rate of the collection solvent (the ratio of waste water contained in the supplied amount of the collection solvent) are calculated by the following equations.

Collection efficiency of acrylic acid = 1- (amount of acrylic acid in tower top exhaust gas / acrylic acid in tower inlet gas) Recovery rate of collection solvent = Waste water recovery water quantity / total collection solvent supply quantity ( Reference Example) A multi-tube catalytic gas-phase oxidation reactor filled with a catalyst was charged with 8.0% by volume of propylene, 14.4% by volume of oxygen, 5.2% by volume of water, 71.7% by volume of nitrogen, and others (propane). , CO _x , acrylic acid, acetic acid, aldehyde, etc.) 0.7
A reaction gas having a composition of volume% was introduced at a flow rate of 34,780 m ³ (standard state) / hour, and by a catalytic gas phase oxidation reaction, 7.1% by volume of acrylic acid, 14.5% by volume of water, and 73.5% of nitrogen.
An acrylic acid-containing gas having a composition of volume%, oxygen 1.4 volume% and others (propylene, propane, CO _x , acetic acid, aldehyde, etc.) 3.5 volume% was obtained.

This gas was supplied to an acrylic acid collection column, and a collection solvent having a water concentration of 92.8% by mass (flow rate 4.54 m ³ / hour) was used, and the top pressure of the collection column was 10.8 kPa ( Gauge pressure), the temperature at the top of the column is 62.8 ° C, and the recovery rate of the collected solvent is 0.
Acrylic acid was collected as No. 8.

The concentration of acrylic acid in the liquid at the bottom of the collection tower taken out from the bottom of the collection tower was 70.0% by mass, and the collection efficiency of acrylic acid was 0.987, which was discharged from the acrylic acid production process. The amount of waste water generated was 1.60 m ³ / hour.

Example 1 In the reference example, in the composition of the reaction raw material gas, water was 7.4% by volume and nitrogen was 69.5% by volume.
Except that the catalytic gas phase oxidation reaction was carried out in the same manner as in the reference example, acrylic acid 7.1% by volume, water 16.6% by volume, nitrogen 71.3% by volume, oxygen 1.4% by volume, other (propylene , Propane, CO _x , acetic acid, aldehyde, etc.) 3.6
An acrylic acid-containing gas having a composition of volume% was obtained.

This gas was supplied to the acrylic acid collection column, the top pressure of the collection column was 10.8 kPa (gauge pressure), and the flow rate of the collection solvent was 4.54 m ³ / hour as in the case of the reference example. Adjusting the temperature at the top of the collection tower so that the concentration of acrylic acid in the bottom liquid of the collection tower drawn out from the bottom of the tower is 70.0 mass% and the recovery rate of the collection solvent is 0.8. As a result of changing the amount of water in the exhaust gas from the top of the column and collecting acrylic acid, it was possible to satisfy the conditions at a column top temperature of 65.1 ° C.

At that time, the concentration of the collecting solvent water was 93.2% by mass, the collecting efficiency of acrylic acid was 0.982, and the amount of waste water discharged from the acrylic acid manufacturing process was 1.59 m ^3.
/ Hour.

Example 2 In the reference example, in the composition of the reaction raw material gas, water was 6.8% by volume and nitrogen was 70.1% by volume.
Except that the catalytic gas phase oxidation reaction was carried out in the same manner as in the reference example, acrylic acid 7.1% by volume, water 16.1% by volume, nitrogen 71.9% by volume, oxygen 1.4% by volume, other (propylene , Propane, CO _x , acetic acid, aldehyde, etc.) 3.5
An acrylic acid-containing gas having a composition of volume% was obtained.

This gas was supplied to the acrylic acid collection column, the top pressure of the collection column was 10.8 kPa (gauge pressure), and the collection solvent was supplied at a flow rate of 4.54 m ³ / hour as in the case of the reference example. Adjusting the temperature at the top of the collection tower so that the concentration of acrylic acid in the bottom liquid of the collection tower drawn out from the bottom of the tower is 70.0 mass% and the recovery rate of the collection solvent is 0.8. As a result of changing the amount of water in the exhaust gas from the top of the column and collecting acrylic acid, the conditions could be satisfied at the column top temperature of the collection column of 64.5 ° C.

At that time, the concentration of the collecting solvent water was 93.1% by mass, the collection efficiency of acrylic acid was 0.984, and the amount of waste water discharged from the acrylic acid production process was 1.59 m ^3.
/ Hour.

(Example 3) In Example 2, the conditions of the acrylic acid collection tower were the same as in the reference example except that the top temperature of the collection tower was 6
2.8 ° C, collection solvent supply flow rate 4.54 m ³ / hour, acrylic acid concentration in the collection tower bottom liquid withdrawn from the collection tower bottom is 70.0% by mass, collection solvent recovery The acrylic acid was collected by changing the amount of water in the exhaust gas from the top of the collection tower by adjusting the pressure at the top of the collection tower so that the ratio becomes 0.8. The conditions could be satisfied at a top pressure of 2.5 kPa (gauge pressure).

At that time, the concentration of the collecting solvent water was 93.1% by mass, the collection efficiency of acrylic acid was 0.984, and the amount of waste water discharged from the acrylic acid production process was 1.59 m ^3.
/ Hour.

(Comparative Example 1) In Example 2, the conditions of the acrylic acid collection tower were the same as in the reference example except that the top pressure of the collection tower was 1
Acrylic acid was collected under the conditions of 0.8 kPa (gauge pressure), column top temperature 62.8 ° C., collection solvent supply flow rate of 4.54 m ³ / hour, and collection solvent recovery rate of 0.8. As a result, the concentration of acrylic acid in the liquid at the bottom of the collection tower, which was withdrawn from the bottom of the collection tower, dropped to 66.5% by mass, and it was necessary to change the operating conditions of the subsequent steps.

At that time, the water concentration of the collecting solvent was 93.5% by mass, the collecting efficiency was 0.988, and the amount of waste water discharged from the acrylic acid production process was 2.19 m ³ / hour.

(Comparative Example 2) In Example 2, the condition of the acrylic acid collection tower was the same as in the reference example except that the top pressure of the collection tower was 1
0.8 kPa (gauge pressure), column top temperature 62.8 ° C., collection solvent recovery rate was 0.8, and acrylic acid concentration in the bottom liquid of the collection column was 70. As a result of collecting the acrylic acid by adjusting the amount of the collecting solvent so as to be 0.0% by mass, it was possible to satisfy the condition when the amount of the collecting solvent supplied was 3.95 m ³ / hour.

At that time, the water concentration in the collection solvent was 93.3% by mass, the collection efficiency was 0.982, and the amount of waste water discharged from the acrylic acid production process was 2.06 m ³ / hour.

(Summary) The results of the above examples are summarized in Table 1.

[0061]

[Table 1]

According to the results of Example 1, the water concentration in the reaction raw material gas used for the catalytic gas phase oxidation reaction was 7.4% by volume higher than that in the reference example (5.2% by volume). However, by adjusting the column top temperature, it is not necessary to change the amount of the collection solvent supplied to the collection column, and the collection amount discharged from the bottom of the column without significantly lowering the acrylic acid collection efficiency. The concentration of acrylic acid in the bottom liquid of the tower and the amount of waste water discharged from the manufacturing process could be maintained almost constant.

The results of Example 1 were the same as in Example 2 in which the water content in the reaction raw material gas was 6.8% by volume.

Example 3 is an example in which the adjustment was carried out under the same conditions as in Example 2 not by the column top temperature but by the column top pressure. In this case as well, acrylic acid production was similarly well carried out throughout the process. It became clear that it could be done.

In contrast to the above Examples, in Comparative Example 1, the tower top temperature and the tower top pressure were kept constant despite the fact that the water concentration in the reaction raw material gas was as high as 6.8% by volume. In this case, the acrylic acid collection efficiency can be maintained by making the supply amount of the collection solvent the same as in Reference Examples and Examples, but the concentration of acrylic acid in the bottom liquid of the collection column decreases, and the amount of waste water increases. did. As a result, it became necessary to change the operating conditions for the subsequent steps.

Further, Comparative Example 2 is a case where the acrylic acid concentration in the bottom liquid of the collection tower is maintained under the same conditions as in Comparative Example 1, but in this case, the amount of the collection solvent supplied must be reduced. However, it can be seen that the amount of wastewater increases.

[0067]

Industrial Applicability The method for collecting (meth) acrylic acid according to the present invention is a manufacturing process in which a (meth) acrylic acid-containing gas is introduced into a collection column and a target product is collected as a solution by a collection solvent. In the above, regardless of the amount of water contained in the reaction gas that is a manufacturing raw material, the supply amount of the collection solvent that collects the target product and the concentration of (meth) acrylic acid in the bottom liquid of the collection column, the collection efficiency, In addition, the amount of waste water discharged from the entire process can be kept stable, and the operation of the entire process can be stabilized, which is extremely useful in industry.

The above action and effect can be achieved by a very simple means of controlling the amount of water in the gas discharged from the top of the collection tower.

From the above, the method for collecting (meth) acrylic acid according to the present invention has an excellent feature that the production process of (meth) acrylic acid can be stably operated by a very simple means. , (Meth) acrylic acid is very effective as a method for collecting (meth) acrylic acid, and the apparatus of the present invention is industrially very useful because the method can be carried out.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a process of (meth) acrylic acid.

Claims (8)

[Claims] 1. A (meth) acrylic acid-containing gas is produced by a catalytic gas phase oxidation reaction, the gas is then introduced into a collection tower, and a target solvent is collected as a solution by a collection solvent whose main component is water. In the (meth) acrylic acid production process including the step of collecting, by changing the amount of water in the gas discharged from the top of the collection tower, the bottom liquid of the collection tower discharged from the collection tower is changed. A method for collecting (meth) acrylic acid, which comprises controlling the concentration of (meth) acrylic acid. 2. The method according to claim 1, wherein the water content in the gas discharged from the top of the collection tower is changed by the top temperature and / or the top pressure of the collection tower. 3. The method according to claim 1, wherein a part or all of the waste water discharged from the (meth) acrylic acid production process is reused as a collecting solvent. 4. In the above catalytic vapor phase oxidation reaction, the amount of water in the gas introduced into the catalytic vapor phase oxidation reactor is calculated as
The method according to claim 1, wherein the amount of water in the gas discharged from the top of the collection tower is changed. 5. In the catalytic gas phase oxidation reaction, the amount of water in the gas discharged from the top of the collection column is changed according to the amount of water in the air used as the molecular oxygen-containing gas. Item 4. The method according to any one of Items 1 to 3. 6. A collection column for carrying out the method according to claim 2, comprising means for controlling the temperature of the top of the collection column and / or means for controlling the pressure of the top of the column. A device for collecting (meth) acrylic acid. 7. The (meth) acrylic acid trapping apparatus according to claim 6, wherein a part or the whole of the wastewater discharged from the (meth) acrylic acid production process is reused as a trapping solvent. 8. The amount of water in the gas discharged from the top of the collection column is changed according to the amount of water in the gas introduced into the catalytic gas phase oxidation reactor in the catalytic gas phase oxidation reaction. Item 8. A (meth) acrylic acid collector according to any one of items 6 and 7.