TW201439052A - Method for producing acetaldehyde - Google Patents

Abstract

The purpose of the present invention is to provide a method for producing acetaldehyde from acetic acid in an industrially efficient manner and with reduced energy consumption. The method for producing acetaldehyde from acetic acid according to the present invention is a method for producing acetaldehyde from acetic acid, and is characterized by comprising at least: (A) a condensation step of supplying a gaseous reaction product produced by hydrogenating acetic acid into a condenser to produce a condensed solution and an uncondensed gas; (B) an absorption step of bringing the uncondensed gas produced in the condensation step (A) into contact with an acetic-acid-containing solvent to cause acetaldehyde contained in the uncondensed gas to be absorbed in the acetic-acid-containing solvent; and (C) an acetaldehyde purification step of subjecting the condensed solution produced in the condensation step (A) and an acetaldehyde-absorbed solution produced in the absorption step (B) to distillation to separate acetaldehyde from unconverted acetic acid and water that is a byproduct.

Description

Method for producing acetaldehyde

This invention relates to a process for the manufacture of acetaldehyde from acetic acid. The present application claims priority to Japanese Patent Application No. 2013-015470, filed on Jan.

A process for producing acetaldehyde by hydrogenation of acetic acid is known. Patent Document 1 discloses a method for producing acetaldehyde, which comprises the steps of: hydrogenating a acetic acid by hydrogenating acetic acid to produce acetaldehyde and other products; and an absorbing step of using a solvent containing acetic acid from the steps described above. a part of the gaseous product of the obtained acetaldehyde absorbs acetaldehyde; the acetaldehyde purification step is carried out by distilling the acetaldehyde absorption liquid obtained in the above step, separating acetaldehyde from unreacted acetic acid and other products; The obtained unreacted acetic acid and a mixture with other products are subjected to azeotropic distillation to separate the acetic acid from other products.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 4094737

However, in the method described in Patent Document 1, the foregoing The load of the absorption tower in the step of absorbing acetaldehyde is large, and there is a problem that energy consumption is extremely high when acetaldehyde is separated by distillation.

Accordingly, it is an object of the present invention to provide a process for reducing energy consumption and industrially efficiently producing acetaldehyde from acetic acid.

In order to solve the above problems, the inventors of the present invention found that if the gaseous reaction product containing acetaldehyde obtained by the hydrogenation reaction of acetic acid is previously condensed to some extent by a condenser, the uncondensed gas is guided to the absorption. The column can be reduced in the amount of the acetic acid-containing solvent used in the absorption tower, and the load on the acetaldehyde refining column can be greatly reduced, and the present invention can be completed.

That is, the present invention provides a process for producing acetaldehyde, which is a process for producing acetaldehyde from acetic acid, characterized in that it has at least the following step: a condensation step (A) which is a gaseous reaction product obtained by hydrogenating acetic acid. Supply to the condenser to obtain condensed liquid and uncondensed gas; absorption step (B), which allows the uncondensed gas obtained in the condensation step (A) to be contacted with the solvent containing acetic acid, so that B in the uncondensed gas The aldehyde is absorbed into the solvent containing acetic acid; the acetaldehyde refining step (C) is carried out by distilling the condensate obtained in the condensation step (A) and the acetaldehyde absorption liquid obtained in the absorption step (B). The acetaldehyde is separated from the unconverted acetic acid and by-product water.

In the production method, the solvent containing acetic acid used in the absorption step (B) is preferably used in a mixture of water containing unconverted acetic acid and by-products separated by the acetaldehyde purification step (C).

Further, in the acetaldehyde purification step (C), in the absorption step (B) The feeding position of the obtained acetaldehyde absorbing liquid to the distillation column is preferably on the bottom side of the column than the feeding position of the condensate obtained in the condensation step (A) to the distillation column.

That is, the present invention relates to the following.

(1) A process for producing acetaldehyde, which is a process for producing acetaldehyde from acetic acid, characterized by comprising at least the following step: a condensation step (A) for supplying a gaseous reaction product obtained by hydrogenating acetic acid to condensation And absorbing the condensed liquid and the uncondensed gas; and absorbing the step (B), wherein the uncondensed gas obtained in the condensing step (A) is contacted with a solvent containing acetic acid, so that the acetaldehyde in the uncondensed gas is absorbed a solvent containing acetic acid; an acetaldehyde purification step (C), which is obtained by distilling the condensate obtained in the condensation step (A) and the acetaldehyde absorption liquid obtained in the absorption step (B), and acetaldehyde It is separated from the water of unconverted acetic acid and by-products.

(2) The method for producing acetaldehyde according to (1), wherein the solvent containing acetic acid used in the absorption step (B) is used in the acetaldehyde purification step (C) A mixture of converted acetic acid and by-product water.

(3) The method for producing acetaldehyde according to (1) or (2), wherein in the acetaldehyde purification step (C), the acetaldehyde absorption liquid obtained in the absorption step (B) is fed to the distillation column. The feed position is further to the bottom side of the column than the feed point of the condensate obtained in the condensation step (A) to the distillation column.

(4) The method for producing acetaldehyde according to any one of (1) to (3) wherein, in the condensation step (A), the condensation temperature of the condenser is 0 to 50 °C.

(5) The method for producing acetaldehyde according to any one of (1) to (4) wherein, in the condensation step, the pressure of the condenser is 0.1 to 10 MPa.

(6) The method for producing acetaldehyde according to any one of (1) to (5) wherein, in the absorption step (B), the content of acetic acid in the solvent containing acetic acid is 50 to 90% by weight.

(7) The method for producing acetaldehyde according to any one of (1) to (6), wherein, in the absorption step (B), a ratio of a solvent containing acetic acid to an uncondensed gas supplied to the absorption tower ( Weight ratio), the former / the latter = 0.1 ~ 20.

(8) The method for producing acetaldehyde according to any one of (1) to (7), wherein in the acetaldehyde purification step (C), the top pressure of the distillation column is 0.1 to 0.5 MPa.

According to the production method of the present invention, since the gaseous reaction product containing acetaldehyde obtained from the reaction system is supplied to the condenser in advance to condense a part of acetaldehyde, the solvent containing acetic acid used for absorbing acetaldehyde in the absorption step can be reduced. The amount of this can greatly reduce the distillation load in the acetaldehyde refining step. Therefore, it is possible to produce acetaldehyde from acetic acid without using bulk energy and industrially efficiently.

A‧‧‧reactor

B‧‧‧ heat exchanger

C‧‧‧Condenser

D‧‧‧ absorption tower

E‧‧ condensate heater

F‧‧‧absorbent heater

G‧‧‧ acetaldehyde refining tower (distillation tower)

H‧‧‧ reboiler

I‧‧‧Condenser

J‧‧‧ acetic acid recovery system

K‧‧‧Recycled absorption liquid cooler

L‧‧‧Compressor

1‧‧‧Reaction to generate gas pipeline

2‧‧‧Responsive reaction to generate gas pipeline

3‧‧‧Uncondensed gas pipeline

4‧‧‧condensate line

5‧‧‧ Condensate feed line

6‧‧‧Recovering hydrogen pipeline

7‧‧‧Acetaldehyde absorption line

8‧‧‧Acetaldehyde absorption liquid feed line

9‧‧‧ Finished acetaldehyde pipeline

10‧‧‧Refined Tata bottom product pipeline

11‧‧‧Recycled absorption line after cooling

12‧‧‧Recycled absorption line

13‧‧‧ acetic acid recovery system supply pipeline

14‧‧‧Hydrogen filled pipeline

15‧‧‧Acetic acid filling pipeline

Fig. 1 is a schematic flow chart showing an example of a method for producing acetaldehyde of the present invention.

Fig. 2 is a schematic flow chart showing a method for producing acetaldehyde shown in Comparative Example 1.

[Formation of the Invention]

The production method of the present invention is a method for producing acetaldehyde from acetic acid, which comprises at least the following step: a condensation step (A) of supplying a gaseous reaction product obtained by hydrogenating acetic acid to a condenser to obtain a condensate and a solvent. Condensation gas; absorption step (B), wherein the uncondensed gas obtained in the condensation step (A) is contacted with a solvent containing acetic acid, and the acetaldehyde in the uncondensed gas is absorbed into a solvent containing acetic acid; acetaldehyde a refining step (C) of distilling the condensate obtained in the condensation step (A) and the acetaldehyde absorption liquid obtained in the absorption step (B), and acetaldehyde and unconverted acetic acid and by-products The water is separated.

Hereinafter, the manufacturing method of the present invention will be described with reference to the drawings as needed.

[Condensation step (A)]

In the condensation step (A), a gaseous reaction product obtained by hydrogenating acetic acid is supplied to a condenser to obtain a condensed liquid and an uncondensed gas.

The hydrogenation of acetic acid can be carried out by a well-known method. For example, acetic acid is allowed to react with hydrogen in the presence of a catalyst. Acetic acid reacts with hydrogen to form acetaldehyde and water. In addition, by-products such as ethanol, acetone, and ethyl acetate are usually produced.

The catalyst is not particularly limited as long as it is produced by hydrogenation of acetic acid, and examples thereof include metal oxides such as iron oxide, cerium oxide, tin oxide, vanadium oxide, and zinc oxide. Further, a noble metal such as palladium or platinum may be added to these metal oxides as a catalyst. In this case, the amount of the noble metal added is, for example, about 0.5 to 90% by weight based on the total amount of the catalyst. Among them, the preferred catalyst is Tim An iron oxide of a noble metal such as palladium or platinum is added. The catalyst may also be subjected to a reduction treatment in advance, for example, by contact with hydrogen gas before being used for hydrogenation of acetic acid. The reduction treatment is carried out, for example, at 50 to 500 ° C and 0.1 to 5 MPa.

The reaction temperature is, for example, 250 to 400 ° C, preferably 270 to 350 ° C. When the reaction temperature is too low, the formation of by-products such as ethanol increases, and if the reaction temperature is too high, the formation of by-products such as acetone increases, and in any case, the selectivity of acetaldehyde tends to decrease. The reaction pressure may be any of normal pressure, reduced pressure, and pressure, and is generally 0.1 to 10 MPa, and preferably 0.1 to 3 MPa.

The ratio of hydrogen to acetic acid to the reactor (mol ratio) is generally hydrogen/acetic acid = 0.5 to 50, preferably hydrogen: acetic acid = 2 to 25.

The conversion of acetic acid in the reactor is desirably below 50% (e.g., 5 to 50%). When the conversion ratio of acetic acid exceeds 50%, by-products (ethanol, ethyl acetate, etc.) are easily formed, and the selectivity of acetaldehyde is lowered. Therefore, it is desirable to adjust the residence time of the reactor and the space velocity of hydrogen so that the conversion ratio of the above acetic acid is 50% or less.

By reacting acetic acid with hydrogen, a gaseous reaction product mainly comprising unconverted acetic acid, unconverted hydrogen, acetaldehyde formed by the reaction, water, and other products (ethanol, ethyl acetate, acetone, etc.) can be obtained.

In the present invention, the gaseous reaction product obtained in this manner is not directly supplied to the absorption tower, but before that, it is supplied to the condenser to obtain a condensed liquid and an uncondensed gas. By setting up this condensation step, the amount of acetaldehyde supplied to the next absorption step (B) can be reduced, thereby enabling The amount of the acetic acid-containing solvent used in the absorption step (B) in order to absorb acetaldehyde is reduced. Then, along with this, the load of the distillation column can be alleviated in the acetaldehyde purification step (C). Therefore, the energy consumption of the entire purification system can be reduced.

The condenser is not particularly limited, and a condenser which is generally used for gas condensation can be used. The condensation temperature of the condenser is, for example, 0 to 50 ° C, preferably 0 to 20 ° C. The pressure in the condenser is not particularly limited, but is usually 0.1 to 10 MPa, preferably 0.1 to 3 MPa. The pressure at the condenser is the same as the reaction pressure, and preferably about the same.

By this condensation step (A), a condensate mainly comprising unconverted acetic acid, acetaldehyde and water (generally containing other products such as ethanol), and an uncondensed gas mainly comprising hydrogen and acetaldehyde can be obtained.

[Absorption step (B)]

In the absorption step (B), the uncondensed gas obtained in the condensation step (A) is brought into contact with a solvent containing acetic acid, and the acetaldehyde in the uncondensed gas is absorbed by the solvent containing acetic acid. This step is usually carried out by supplying the uncondensed gas obtained in the above condensation step (A) and the solvent containing acetic acid to the absorption tower, and bringing the two into contact in the absorption tower.

As the solvent containing acetic acid, a mixed liquid containing acetic acid and water which is separated for the acetaldehyde purification step (C) to be described later can be used. The mixed liquid containing acetic acid and water is obtained in the acetaldehyde purification step (C) from the bottom of the distillation column (acetaldehyde refining column) as, for example, a bottom product.

The content of acetic acid in the solvent containing acetic acid is, for example, 50 to 90% by weight, preferably 60 to 80% by weight. The ratio (weight ratio) of the solvent containing acetic acid to the absorption tower and the uncondensed gas is, for example, the former/the latter = 0.1 ~20, preferably the former / the latter = 1 to 10. The number of plates (the number of theoretical plates) of the absorption tower is, for example, 3 to 30, preferably 5 to 20.

By this absorption step (B), an acetaldehyde absorbing liquid mainly containing acetaldehyde, acetic acid, water (generally containing other products such as ethanol), and an unabsorbed gas mainly including hydrogen can be obtained. The recovered hydrogen can be recycled to the reaction system.

[acetaldehyde refining step (C)]

In the acetaldehyde purification step (C), the condensate obtained in the condensation step (A) and the acetaldehyde absorption liquid obtained in the absorption step (B) are distilled, and the acetaldehyde and the unconverted acetic acid and by-products are distilled. The water (usually also containing other products such as ethanol) is separated.

The pressure at the top of the distillation column is usually 0.1 to 0.5 MPa, preferably 0.15 to 0.3 MPa, and the gauge pressure is usually 0.0 to 0.4 MPa, preferably 0.05 to 0.2 MPaG.

The condensate obtained in the condensation step (A) and the acetaldehyde absorption liquid obtained in the absorption step (B) are preferably preheated by a condensate heater or an absorption liquid heater to a boiling point or a boiling point near the distillation pressure, respectively. The heated condensate and absorption liquid are supplied to a distillation column. As the heat source for the heating, the bottom product from the acetaldehyde refining step (C) is preferably used.

When the condensate obtained in the condensation step (A) and the acetaldehyde absorption liquid obtained in the absorption step (B) are supplied to the distillation column, both can be fed at the same position (layer) of the distillation column, and It is preferred to feed at a position (layer) in accordance with the respective compositions.

In a preferred aspect of the invention, the acetaldehyde content is The feeding position (layer) of the condensate obtained by the aforementioned condensation step (A) which is relatively larger than the aforementioned acetaldehyde content in the feeding position (layer) of the acetaldehyde absorbing liquid obtained in the aforementioned absorption step (B) Also on the bottom side of the tower. In this way, by setting the feeding position (layer) of the condensate and the acetaldehyde absorbing liquid at the most appropriate position (layer), it is possible to efficiently separate and purify acetaldehyde without using unnecessary energy.

The number of plates (the number of theoretical plates) of the distillation column is, for example, 10 to 50, preferably 15 to 35. For example, if a distillation column having about 22 layers of theoretical plates is used, high purity acetaldehyde can be obtained. In the case where the number of theoretical plates of the distillation column is 22, for example, the condenser of the distillation column is set as the first layer, and then the feeding position of the condensate is preferably set to be the upper side. In the 14th layer, the feed position of the aforementioned absorbing liquid is set to the 17th layer from the top.

The product acetaldehyde can be obtained from the top of the distillation column by the acetaldehyde refining step (C). Further, a mixed liquid of acetic acid and water (generally including other components such as ethanol) can be obtained from the bottom of the distillation column.

A part of the mixture of acetic acid and water (usually including other components such as ethanol) obtained from the bottom of the distillation column can be used as the solvent containing acetic acid as the absorption step (B) as described above. The residue of the above mixture is supplied to an acetic acid recovery system where acetic acid is recovered.

The ratio of the amount of the recycled absorbing liquid supplied to the absorption step (B) (recycling rate) is, for example, 80 with respect to the amount of the mixed solution of acetic acid and water (usually including other components such as ethanol) obtained from the bottom of the column. About %, and the case where the condensation step (A) is not established (usually about 90%) can be greatly reduced. This is because the amount of acetaldehyde supplied to the absorption tower is small, and can be reduced. It is caused by the amount of the solvent containing acetic acid to be supplied to the absorption tower.

As described above, the mixed liquid of acetic acid and water (which usually contains other components such as ethanol) obtained from the bottom of the distillation column is supplied to the mixed liquid other than the absorption step (B) as the recycled absorbent. The acetic acid can be separated and recovered by being directed to an acetic acid recovery system.

The separation and recovery of acetic acid can be carried out by a method known in the art for separating and recovering acetic acid from an aqueous acetic acid solution containing water and acetic acid. For example, a solvent that azeotropes with water and is not mixed with water, by, for example, azeotropic distillation with ethyl acetate, can obtain acetic acid from the bottom of the column, and can obtain a mixture of water and azeotropic solvent from the top of the column (usually containing other product). The separated recovered acetic acid can be recycled to the reaction system. The water and the azeotropic solvent can be separated by, for example, liquid separation. The separated azeotropic solvent can be refluxed into the distillation column.

Fig. 1 is a schematic flow chart showing an example of a method for producing acetaldehyde of the present invention. In this example, the reaction product gas obtained by hydrogenating acetic acid in the reactor A is supplied to the heat exchanger B through the reaction product gas line 1, and after being cooled, it is supplied to the condenser through the reaction product gas line 2 C. The gas system which is not condensed in the condenser C is supplied to the absorption tower D through the uncondensed gas line 3, and the condensed condensate is guided to the condensate heater E through the condensate line 4, after which it is heated and passed through the condensate. The feed line 5 is supplied to an acetaldehyde refining column (distillation column) G.

In the absorption tower D, the uncondensed gas supplied through the uncondensed gas line 3 is in contact with the solvent containing acetic acid supplied through the recirculating absorbent line 11. The acetaldehyde in the uncondensed gas is absorbed into the above-mentioned solvent containing acetic acid, and the obtained acetaldehyde absorbing liquid is guided to the absorbing liquid heater F through the acetaldehyde absorbing liquid line 7, and after heating, passes through acetaldehyde. The absorption liquid feed line 8 is supplied to an acetaldehyde refining column (distillation column) G. The feed position of the acetaldehyde absorption liquid feed line 8 is more on the bottom side than the feed position of the aforementioned condensate feed line 5.

At the top of the column of the distillation column G, acetaldehyde is condensed by the condenser I, and is obtained as a product via the finished acetaldehyde line 9. The bottom liquid of the distillation column G is taken out through the refining bottom product line 10, and a part thereof is guided to the recirculating absorbent liquid cooler K through the recirculating absorbent liquid line 12, after which it is cooled and passed through the recirculating absorbent The line 11 is supplied to the absorption tower D. The residue of the bottom product taken out from the bottom of the distillation column G is sent to the acetic acid recovery system J through the acetic acid recovery system supply line 13. Wherein the symbol H is a reboiler.

In the absorption tower D, the hydrogen gas which is not absorbed into the acetic acid-containing solvent supplied through the recirculating absorption liquid line 11 is guided to the compressor L through the recovery hydrogen line 6, is pressurized, and passes through the heat exchanger B. Feed to reactor A. The hydrogen gas line 6 is recovered, and between the reactors A, a hydrogen filling line 14 and an acetic acid filling line 15 are connected, through which new hydrogen and acetic acid are supplied.

Among them, heat can be efficiently exchanged between the recirculating absorbent liquid cooler K and the condensate heater E and/or the absorbing liquid heater F to efficiently utilize heat.

[Examples]

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by these examples.

Example 1

Acetaldehyde was produced in the procedure shown in Figure 1.

Wherein, the hydrogenation of acetic acid is carried out using an iron oxide catalyst containing 40% by weight of palladium, a hydrogen/acetic acid feed molar ratio (hydrogen/acetic acid) = 7, a gas space velocity of 3,530, a reaction pressure of 17.2 bar (1.72 MPa), The reaction was carried out at a temperature of 300 °C.

In the refining system, the pressure of the condenser C was 17 bar (1.7 MPa), and the reaction product gas was cooled to 5 °C. The theoretical number of plates of the absorption tower D is 10 layers. The condensate heater E and the absorption liquid heater F are respectively heated to a saturation temperature (boiling point) of the top pressure of the distillation column G of 0.13 MPaG (gauge pressure). The number of theoretical plates of the distillation column G was 22, and the pressure at the top of the column was 0.13 MPaG (gauge pressure) as described above. The feed position of the condensate feed line 5 to the distillation column G is the 14th layer from the top, and the feed position of the absorption liquid feed line 8 to the distillation column G is the 17th layer from the top. The recirculating absorbent was cooled to 20 ° C in a recirculating absorbent cooler K.

The results of the refining system (material balance, etc.) are shown in Table 1. Here, the ratio (recycling rate) of the recycled absorbing liquid was 80% with respect to the amount of the bottom liquid (bottom product) taken out of the distillation column G.

Comparative example 1

Acetaldehyde was produced in the procedure shown in Figure 2. The flow shown in Fig. 2 differs from the flow shown in Fig. 1 in that the condenser C and the related devices and pipelines are not provided.

Among them, the hydrogenation conditions of acetic acid were the same as in Example 1.

In the purification system, the number of theoretical plates of the absorption tower D was 10 as in the first embodiment. In the absorption liquid heater F, the absorption liquid is heated to a saturation temperature (boiling point) of the top pressure of the distillation column G of 0.13 MPaG (gauge pressure). The theoretical number of plates of the distillation column G is 22 layers, and the pressure at the top of the column is 0.13 MPaG (gauge pressure) as described above. . The feeding position of the absorption liquid feed line 8 to the distillation column G is the 15th layer from the top. The recirculating absorbent was cooled to 20 ° C in a recirculating absorbent cooler K.

The results of the refining system (material balance, etc.) are shown in Table 2. The ratio of the recycled absorbent (recycling rate) was 90% with respect to the amount of the bottom liquid (bottom product) taken out of the distillation column G.

The meanings of the English descriptions and abbreviations in Tables 1 and 2 are as follows.

Temperature: temperature

Pressure: Pressure

Vapor Frac: Vapor ratio

Mole Flow: Moir Flow

Mass Flow: mass flow

Volume Flow: Volume Flow

Mass Frac: mass fraction

AD: acetaldehyde

AT: Acetone

ETOH: ethanol

AE: ethyl acetate

AC: acetic acid

A comparison of Example 1 with Comparative Example 1 is shown in Table 3. In Table 3, the composition of the purification system feed is the composition of the fluid flowing into the reaction product gas line 1 in Figs. 1 and 2 . Comparing the total energy consumption of the condensate heater, the absorption liquid heater, and the distillation column reboiler, it is 7.14 Mcal/h with respect to Comparative Example 1, and Example 1 is 6.61 Mcal/h, and it can be seen that the condenser C can be provided by setting Reduce energy by about 9%.

[Industrial availability]

According to the production method of the present invention, the amount of the acetic acid-containing solvent used for absorbing acetaldehyde in the absorption step can be reduced, and the distillation load in the acetaldehyde purification step can be greatly reduced. Therefore, it is possible to industrially efficiently produce acetaldehyde from acetic acid without using a large amount of energy.

A‧‧‧reactor

B‧‧‧ heat exchanger

C‧‧‧Condenser

D‧‧‧ absorption tower

E‧‧ condensate heater

F‧‧‧absorbent heater

G‧‧‧ acetaldehyde refining tower (distillation tower)

H‧‧‧ reboiler

I‧‧‧Condenser

J‧‧‧ acetic acid recovery system

K‧‧‧Recycled absorption liquid cooler

L‧‧‧Compressor

1‧‧‧Reaction to generate gas pipeline

2‧‧‧Responsive reaction to generate gas pipeline

3‧‧‧Uncondensed gas pipeline

4‧‧‧condensate line

5‧‧‧ Condensate feed line

6‧‧‧Recovering hydrogen pipeline

7‧‧‧Acetaldehyde absorption line

8‧‧‧Acetaldehyde absorption liquid feed line

9‧‧‧ Finished acetaldehyde pipeline

10‧‧‧Refined Tata bottom product pipeline

11‧‧‧Recycled absorption line after cooling

12‧‧‧Recycled absorption line

13‧‧‧ acetic acid recovery system supply pipeline

14‧‧‧Hydrogen filled pipeline

15‧‧‧Acetic acid filling pipeline

Claims (3)

A method for producing acetaldehyde, which is a method for producing acetaldehyde from acetic acid, characterized in that it has at least the following step: a condensation step (A) for supplying a gaseous reaction product obtained by hydrogenating acetic acid to a condenser. Obtaining a condensate and an uncondensed gas; and absorbing step (B), wherein the uncondensed gas obtained in the condensation step (A) is contacted with a solvent containing acetic acid, and the acetaldehyde in the uncondensed gas is absorbed into the acetic acid containing Solvent; acetaldehyde refining step (C), which is obtained by distilling the condensate obtained in the condensation step (A) and the acetaldehyde absorption liquid obtained in the absorption step (B), and acetaldehyde and unconverted The acetic acid and by-product water are separated. The method for producing acetaldehyde according to claim 1, wherein the solvent containing acetic acid used in the absorption step (B) is an unconverted acetic acid and a subsidiary separated by the acetaldehyde purification step (C). A mixture of waters of the product. The method for producing acetaldehyde according to claim 1 or 2, wherein in the acetaldehyde refining step (C), the feeding position of the acetaldehyde absorbing liquid obtained in the absorbing step (B) to the distillation column is condensed The feed point of the condensate obtained in the step (A) to the distillation column is also on the bottom side of the column.