JP2010159212A - Method for separating alcohol - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for separating an alcohol, by which the alcohol can efficiently be separated from a mixture comprising the alcohol (alkanol) and impurities having near boiling points, or an apparatus for separating the alcohol. <P>SOLUTION: The method for separating an nC alkanol [(n) is 1 to 3] from the first mixture comprising the nC alkanol, an n+2C aldehyde and an n+2C ketone comprises supplying the first mixture to a distillation tower 1, simultaneously supplying water to the distillation tower 1 from an upper position than a position for supplying the first mixture, distilling out the second mixture containing the n+2C aldehyde and the n+2C ketone from the distillation tower 1, and recovering the third mixture comprising the nC alkanol and water from the lower portion of the distillation tower 1. By such the method utilizing the extraction of the alkanol with the water, even impurities, such as the n+2C aldehyde and the n+2C ketone, having boiling points near to that of the nC alkanol can efficiently be separated from the alkanol. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for efficiently separating alcohol (or alkanol) from an alcohol mixture containing impurities (aldehyde, ketone, carboxylic acid ester, acetal, etc.) having a boiling point close to that of alcohol (or alkanol, etc.), in particular, ethanol dehydrogenation. The present invention relates to a method for efficiently separating ethanol from a reaction mixture (or an ethanol-containing mixture) obtained by the method.

  Acetaldehyde is a compound useful as an intermediate raw material for various materials and is used in various applications. As a manufacturing method of acetaldehyde, a manufacturing method by direct oxidation of ethylene is mainly used, but a method of manufacturing from acetylene and a method of manufacturing from ethanol by an ethanol dehydrogenation method or an ethanol oxidation method are also known.

  In the ethanol dehydrogenation method or oxidation method using ethanol as a raw material, acetaldehyde is produced by dehydrogenating or oxidizing ethanol using a metal catalyst. In addition, when utilizing such a reaction industrially, by recovering unreacted raw material ethanol and recycling it to the reaction system, it is possible to improve economy and reduce energy loss.

  However, in the dehydrogenation method and oxidation method, in addition to acetaldehyde, compounds such as butyraldehyde, methyl ethyl ketone, acetic acid, and ethyl acetate, which have a relatively close boiling point to ethanol, are by-produced. Therefore, when the mixture containing unreacted ethanol obtained by separating acetaldehyde is recycled to the reaction system, the metal catalyst is poisoned by the by-products, and the catalytic activity is lowered. On the other hand, in order to recycle ethanol into the reaction system while preventing poisoning of the metal catalyst, a step of removing by-products is required.

  For example, in “Manufacturing Process Diagrams”, Chemical Industry Co., Ltd., December 20, 1968, the first printing was issued, Volume 2, page 320 (Non-Patent Document 1), ethanol remaining after recovering acetaldehyde was recovered. It is described that ethanol sent to the tower and recovered is returned to raw ethanol.

However, the above-mentioned by-product has a boiling point close to that of ethanol, and it is difficult to separate by a simple process such as a distillation tower, and when separating with an extractant, it becomes necessary to separate the extractant, and the process is complicated. This is also economically disadvantageous.
Complete manufacturing process diagram Chemical Industry Co., Ltd.

  Accordingly, an object of the present invention is to provide a method for separating alcohol, which can efficiently separate alcohol from a mixture containing alcohol and near-boiling impurities.

  Another object of the present invention is to provide an alcohol separation method that can efficiently separate even an alcohol having a high latent heat of vaporization and can reuse the separated water for alcohol separation.

  Still another object of the present invention is to provide a method for separating alcohol that can maintain reaction efficiency without poisoning the reaction catalyst even when the separated alcohol (such as ethanol) is recycled to a reaction system for aldehyde production. It is in.

  Another object of the present invention is to provide an alcohol separation method capable of improving the alcohol recovery rate in a distillation column.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have supplied a mixture containing impurities such as aldehydes and ketones in addition to alkanol to the distillation column, while being higher than the supply position of the first mixture. Water is supplied to the distillation column from the section (in the distillation column, water is supplied from a supply port located above the supply position of the first mixture), a fraction containing impurities such as aldehyde and ketone, and alkanol And it discovered that it could isolate | separate efficiently into the fraction (bottom liquid) containing water, and completed this invention.

That is, the alcohol separation method of the present invention, _{C n} alkanol carbon number n is 1 to _3, from a first mixture comprising a _{C n + 2} aldehydes and _{C n + 2} ketones, a method of separating _{C n} alkanol, While supplying the first mixture to the distillation tower, water is supplied to the distillation tower from an upper stage than the supply position of the first mixture, and the second mixture containing C _{n + 2} aldehyde and C _{n + 2} ketone is added to the distillation tower. causes distilled from the distillation column, recovering a third mixture comprising the water C _n alkanol from the bottom of the distillation column. In such a method, even if the impurity has a boiling point close to that of C _n alkanol such as C _{n + 2} aldehyde and C _{n + 2} ketone, the extraction of alkanol with water (affinity between water and alkanol) is used, Alkanol can be separated efficiently.

In the above separation process, a third mixture comprising a C _n alkanol and water recovered from the bottom of the distillation column, and further supplied to an alcohol recovery column, stream comprising water (or flow amount) of the recovery column recovered from the bottom, and the purified C _n alkanol may be recovered from the top of the recovery column. A stream (or a stream) containing water recovered from the lower part of the recovery tower may be used as water to be supplied to the distillation tower. In such a method, water separated and recovered in the alcohol recovery tower can be used to separate alcohol from impurities in the distillation tower. Therefore, it is advantageous in terms of energy efficiency and economy.

In the separation method, the first mixture may contain C _n alkanol, C _{n + 2} aldehyde and C _{n + 2} ketone, and further contains C _n alkyl ester of carboxylic acid and di (C _n alkoxy) C _n alkane. You may go out. By supplying such a first mixture to the distillation tower, a third mixture containing C _n alkanol and water is recovered from the lower part of the distillation tower, and other components [C _{n + 2} aldehyde, C _{n + 2} ketone, carbon a second mixture comprising a C _n alkyl esters and di acid (C _n alkoxy) C _n alkane, etc.] may be distilled from the distillation column. Note that the second mixture also including C _n alkanol and / or water, usually contains.

Further, the second mixture distilled from the distillation column is condensed and phase-separated into a lower phase containing water and an upper phase containing at least C _{n + 2} aldehyde and C _{n + 2} ketone, The mixture may be refluxed (returned) from the upper stage to the distillation column from the supply position of the mixture. The upper phase may contain the following component (i), (ii) or (iii) according to the composition of the first mixture. Such a method can increase the recovery rate of alkanol in the distillation column.
(i) C _{n + 2} aldehyde and C _{n + 2} ketone,
_{(ii) C n + 2 aldehydes, C n} alkyl esters of _{C n + 2} ketones and carboxylic acids,
(iii) C _{n + 2} aldehydes, C _{n + 2} ketones, C _n alkyl esters of carboxylic acids and di (C _n alkoxy) C _n alkanes.

  The first mixture may contain ethanol, butyraldehyde, methyl ethyl ketone, ethyl acetate and diethyl acetal. While supplying the first mixture to the distillation column, the supply position of the first mixture In addition to supplying water from the upper stage to the distillation tower and extracting ethanol with water, a third mixture containing water and ethanol is recovered from the lower part of the distillation tower, butyraldehyde, methyl ethyl ketone, ethyl acetate And a second mixture containing diethyl acetal may be distilled from the top of the distillation column.

  In addition, the reaction gas containing acetaldehyde obtained by the ethanol dehydrogenation method or the ethanol oxidation method is condensed and / or absorbed by water, and this aqueous solution is supplied to the acetaldehyde separation tower to distill a fraction containing acetaldehyde. The ethanol-containing stream (or stream) may be recovered from the lower part of the separation column, and the ethanol-containing stream (or stream) may be supplied to the distillation column as a first mixture. In such a method, a by-product and ethanol can be efficiently separated from an ethanol solution containing a by-product generated in the production process of acetaldehyde as an impurity.

  In addition, a third mixture containing ethanol and water recovered from the lower part of the distillation tower is further supplied to the alcohol recovery tower to separate water and ethanol, and a stream containing water from the lower part of the recovery tower ( Alternatively, the purified ethanol may be recovered from the upper portion of the recovery tower, and the recovered ethanol may be recycled as a raw material ethanol for the ethanol dehydrogenation method or the ethanol oxidation method. In such a method, unreacted ethanol remaining in the aldehyde production process can be efficiently recovered, and this unreacted ethanol can be used as raw material ethanol for the reaction system. In addition, since unreacted ethanol from which reaction by-product impurities have been removed is recycled to the reaction system, the catalyst in the reaction system can be maintained in catalytic activity without the risk of being poisoned by impurities, and the reaction efficiency is maintained. It is also possible to do.

  In the present invention, in addition to the alcohol (or alkanol), a mixture containing impurities such as aldehyde and ketone is supplied to the distillation column, and the above-mentioned portion from the upper stage than the supply position of the first mixture (position of the supply port). Since water is supplied to the distillation column (that is, water is supplied from a supply port located above the supply port of the first mixture), a fraction containing impurities such as aldehyde and ketone, alcohol and water are supplied. The product can be efficiently separated into a fraction containing it (the bottoms), and alcohol can be efficiently separated and recovered from the mixture containing the impurities. Moreover, even an alcohol having a high latent heat of vaporization can be efficiently separated from impurities because extraction using water is used. Further, the aqueous alcohol solution obtained by the separation can be further separated into alcohol and water, and the obtained water can be reused for separation of the alcohol from impurities, which is advantageous from the viewpoint of energy efficiency and economy. On the other hand, the separated alcohol (such as ethanol) can be recycled as a raw material to the reaction system for aldehyde production, and since impurities are removed, the catalytic activity (and reaction efficiency) is eliminated without poisoning the reaction catalyst. ) Can be maintained. It is also possible to further improve the alcohol recovery rate in the distillation column by condensing the impurities separated in the distillation column, separating them into an aqueous phase and an organic phase, and refluxing the aqueous phase to the distillation column. is there.

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

FIG. 1 is a flowchart for explaining the alcohol separation method or separation apparatus of the present invention. In the example of FIG. 1, the alcohol separator is a mixture of a C _n alkanol such as ethanol and an impurity having a boiling point relatively close to that of the C _n alkanol (first mixture). And a supply means for supplying water to the distillation column from an upper stage part than the supply position of the first mixture in the distillation column 1. Supply line) 3. In the distillation column 1, in addition to C _n alkanol, C _{n + 2} aldehyde (butyraldehyde, crotonaldehyde, etc.), C _{n + 2} ketone (methyl ethyl ketone, etc.), C _n alkyl ester of carboxylic acid (eg ethyl acetate), di (C _n a first mixture containing an impurity such as alkoxy) C _n alkane (such as diethyl acetal), the supply line 2, is supplied to the distillation column, by the supplied water to the distillation tower 1 from the supply unit 3, the Separation into a second mixture (a fraction containing the aldehyde, ketone, carboxylic acid alkyl ester, di (alkoxy) alkane, etc.) and a third mixture (a stream (or stream) containing mainly alkanol and water) To do. The second mixture contains more impurities as described above than the third mixture, and usually contains components such as alkanol and / or water.

  The second mixture is distilled from the distillation column 1 (the upper part of the distillation column (including the top)) by the distillation line 4, and the third mixture is the lower part (or the bottom) of the distillation column 1. Is collected through a discharge line (or can line) 9B and a discharge line 8. Impurities contained in the first and second mixtures are less extracted by water than alcohol, and thus move upward in the distillation column to facilitate distillation from the top.

  And by such a separation apparatus or the separation method, an alkanol can be efficiently isolate | separated from the 1st mixture containing an alkanol and an impurity.

  In the example of FIG. 1, the separation apparatus further includes a condenser 5 a for condensing the second mixture containing impurities separated in the distillation column 1, and a second mixture condensed in the condenser 5 a, A reflux line 7A for refluxing the distillation column 1 and a discharge line 7B for discharging outside the system are provided. In this example, the position of the reflux port (supply port for supplying the second mixture to the distillation column 1) of the reflux line 7A is above (above or below) the first mixture supply position (supply port position). (Upper).

  Then, the second mixture containing impurities separated by the distillation column 1 is supplied to the condenser 5 a through the distillation line 4. Further, the second mixture condensed in the condenser 5a may be refluxed (returned) from the upper part of the distillation column 1 to the distillation column through the reflux line 7A, or may be discharged through the discharge line 7B.

  The separation device includes a decanter for phase-separating the second mixture condensed by the condenser 5a into an upper phase (organic phase) rich in impurities and a lower phase (water phase) rich in water. You may have. The condensed second mixture is supplied to a decanter, and is phase-separated into a lower phase (water phase) rich in water and an upper phase (organic phase) rich in impurities by the decanter. The gas may be refluxed from the upper part of the distillation column 1 to the distillation column through the reflux line. Moreover, the organic phase separated by the decanter may be discharged out of the system through the discharge line, and the discharged organic phase may be used as a fuel or the like as necessary, or may be incinerated.

  In addition, the supply position (position of the supply port or the return position) of the water phase in the distillation column 1 is lower than the supply position of the water from the supply line 3 (position of the supply port) as shown in FIG. The lower part or the lower part) and the upper part (the upper part or the upper part) of the supply position of the first mixture from the supply line 2 (position of the supply port) are preferable. When the aqueous phase is supplied to the distillation column 1, the alcohol contained in a trace amount in the aqueous phase and the alcohol contained in the first mixture from the supply line 2 are extracted from the water in the aqueous phase and the water supplied from the supply line 3. Due to the action, it moves to the lower part (lower part) of the distillation column (the concentration distribution in the lower part (lower part) becomes higher), so that it can be easily recovered from the lower part of the distillation column 1.

  In the example of FIG. 1, the third mixture containing alcohol and water discharged as bottoms from the bottom of the distillation column 1 through the line 9B may be discharged through the discharge line 8 and heated by the reboiler 5b. However, it may be returned to the lower part of the distillation column 1 through the line 9A.

  FIG. 2 is a flowchart for explaining another example of the alcohol separation method or separation apparatus of the present invention. In the example of FIG. 2, the separation device further includes a third mixture containing alcohol and water recovered from the lower part (or the bottom) of the distillation column 1 in addition to the distillation column 1 of FIG. 1. An alcohol recovery tower 11 for separating the stream (or stream) and the purified alcohol is provided. In FIG. 2, the same reference numerals are assigned to the units common to FIG.

  In the example of FIG. 2, the third mixture containing alcohol and water discharged from the lower part of the distillation column 1 through the discharge lines 9 </ b> B and 8 is supplied to the alcohol recovery column 11 through the pump 10.

  In the example of FIG. 2, the separation device separates the second mixture condensed by the condenser 5a into an upper phase (organic phase) containing a large amount of impurities and a lower phase (water phase) containing a large amount of water. A decanter 6 is provided. That is, the second mixture condensed in the condenser 5a is supplied to the decanter 6 through the line 7C. In the decanter 6, a lower phase (water phase) rich in water, and an upper phase (organic phase) rich in impurities, Phase separated. After the phase separation, the aqueous phase may be refluxed (returned) from the upper part of the distillation column 1 to the distillation column 1 through the reflux line 7D. The organic phase containing a large amount of impurities separated by the decanter 6 is discharged out of the system through the discharge line 7E. The discharged organic phase may be used as a fuel or the like if necessary, or may be incinerated. As described above, when the aqueous phase obtained by the decanter is refluxed to the distillation column 1, the alcohol recovery rate in the distillation column 1 can be improved. In particular, when the aqueous phase is refluxed to the distillation column 1 from a lower position (lower stage) than the supply position of water from the supply line 3 to the distillation column 1, the recovery rate can be further improved.

  Moreover, in the alcohol recovery tower 11 supplied with the third mixture, water and alcohol are separated, and a stream (or a stream) containing water is recovered from the lower part (including the tower bottom) of the recovery tower 11. On the other hand, the purified alcohol is discharged from the upper part (including the top) of the recovery tower 11 through a discharge line (distillation line) 12A. The discharged alcohol is condensed in the condenser 5d, and the condensed alcohol is recovered through the recovery line 12C. If necessary, the alcohol may be refluxed from the upper part of the alcohol recovery tower 11 into the tower through the reflux line 12B. .

  The water-containing stream (or stream) is supplied to the reboiler 5c from the bottom of the recovery tower 11 through a discharge line (canister line) 14B, heated by the reboiler 5c, and then through the line 14A. You may return in the tower from the lower part.

  Further, the stream containing water discharged from the bottom of the recovery tower 11 through the discharge line 14B is further supplied to the pump 15 through the line 13, and is discharged through the line (discharge line) 16 by the pump 15. Through the recycle line 17, it joins with a supply means (supply line) 3 for supplying water to the distillation column 1 and is used as water supplied to the distillation column 1.

  In such a separation apparatus or separation method, the water separated and recovered in the alcohol recovery tower 11 can be effectively used as it is as an extractant for separating alcohol from impurities in the distillation tower 1. It is advantageous in terms of sex.

  In the example of FIG. 2, the recycling line 17 is joined to the supply line 3, but is not necessarily joined to the supply line 3, and is a line different from the fresh water supplied from the supply line 3. Alternatively, it may be supplied to the distillation column 1. Further, it is not always necessary to supply fresh water, and only a stream containing water obtained from the alcohol recovery tower 11 may be used as a water supply source. Also, in the initial cycle of the separation method, when fresh water is used as a supply source and the stream containing water from the alcohol recovery tower is sufficiently recycled to the distillation tower 1, the fresh water is used. May be stopped.

[Impurity separation tower (distillation tower)]
The alcohol contained in the first mixture supplied to the distillation column is not limited as long as it can be extracted with water, and usually includes lower alkanols and the like, and is not limited to the above ethanol, but includes carbon atoms such as methanol, propanol, and isopropanol. n is _{C n} alkanol _{(C 1-3} alkanol), etc. can be used is 1-3. Preferred alcohols are _C2-3 alkanols such as ethanol and propanol.

  As the alcohol, in addition to various commercially available alcohols, synthetic alcohols obtained by conventional synthesis methods, bioalcohols obtained from plants and the like can be used, and industrial alcohols are usually used in many cases. For example, in ethanol, as a commercially available industrial ethanol, bioethanol produced by fermentation using sugar cane, corn, cassava lees, tapioca, etc., as well as direct ethanol hydration, ethylene is concentrated. Any of chemically synthesized ethanol produced by a chemical synthesis method such as a sulfuric acid method in which it is absorbed in sulfuric acid and hydrolyzed can be used.

  The first mixture includes impurities having a boiling point close to that of the alcohol, in addition to the alcohol. Examples of such impurities include aldehydes, ketones, carboxylic acids, carboxylic acid alkyl esters, and acetals. The first mixture may contain one or more of these impurities, but usually contains at least an aldehyde and a ketone in many cases. In addition to the aldehyde and ketone, the first mixture may contain at least one selected from carboxylic acid, carboxylic acid alkyl ester, and acetal.

Examples of the aldehyde include saturated aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, and butyraldehyde, unsaturated aliphatic aldehydes such as crotonaldehyde, and preferably C _2-6 aldehyde. One or more of these aldehydes may be contained in the first mixture. The first mixture usually contains an n + 2 aldehyde (Cn _{+ 2} aldehyde) corresponding to the carbon number n of the alcohol.

Examples of the ketone include dialkyl ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, and methyl isopropyl ketone (di-C _1-4 alkyl-ketone, preferably di-C _1-3 alkyl-ketone). it can. One or two or more of these ketones may be contained in the first mixture. The first mixture usually contains a ketone having n + 2 carbon atoms (Cn _{+ 2} ketone) corresponding to the carbon number n of the alcohol.

Examples of the carboxylic acid include aliphatic carboxylic acids (such as C _1-6 carboxylic acid) such as formic acid, acetic acid, propionic acid, and butyric acid. The first mixture may contain one or two or more of these carboxylic acids. When the first mixture contains a carboxylic acid, the carboxylic acid contained usually corresponds to a carboxylic acid having about n−1 to n + 1 carbon atoms (C _{n−1 to n + 1)} corresponding to the carbon number n of the alcohol. Carboxylic acid) in many cases. For example, when the alcohol is ethanol, formic acid, acetic acid, butyric acid (particularly acetic acid) and the like are often included.

Examples of the alkyl esters of carboxylic acids, alkyl esters corresponding to the alcohol carboxylic acid (i.e., C _n alkyl ester of a carboxylic acid), but can be exemplified typically the carboxylic acid and esters of the alcohols (e.g., methyl acetate , C _n alkyl esters of C _{n-1 to n + 1} carboxylic acids such as ethyl acetate, and particularly C _1-3 alkyl esters of acetic acid. One or two or more of these carboxylic acid esters may be contained in the first mixture.

Examples of acetals include di (C _1-6 alkoxy) C _1-6 alkanes such as formaldehyde dimethyl acetal and diethyl acetal. One or two or more of these acetals may be contained in the first mixture. The first mixture typically corresponds to the number of carbon atoms n of the alcohol, di (C _n alkoxy) often contain C _n alkane.

  The first mixture preferably contains at least ethanol, butyraldehyde and methyl ethyl ketone, and more preferably contains ethanol, butyraldehyde, methyl ethyl ketone, ethyl acetate and diethyl acetal.

  In the first mixture supplied to the distillation column, the impurity concentration is, for example, about 0.0001 to 10% by weight, preferably about 0.0005 to 9% by weight, and more preferably about 0.001 to 8% by weight. May be.

  As such a first mixture, a component containing unreacted ethanol obtained by an ethanol dehydrogenation method or an ethanol oxidation method may be used. For example, a reaction gas containing acetaldehyde obtained by an ethanol dehydrogenation method or an ethanol oxidation method is cooled (or condensed) with a refrigerant such as water and / or absorbed in water, and ethanol obtained by separating acetaldehyde from this aqueous solution You may use the component containing. More specifically, an aqueous solution obtained by condensing and / or absorbing water containing the reaction gas containing acetaldehyde is subjected to an acetaldehyde separation tower described later to distill a fraction containing acetaldehyde, and the aldehyde separation. A stream (or a stream) containing ethanol is recovered from the lower part of the column, and this ethanol-containing stream may be supplied to the distillation column as a first mixture.

  As the impurity separation tower for separating the first mixture, a conventional distillation tower such as a plate tower (a perforated plate tower, a bubble bell tower, etc.), a packed tower, a flash distillation tower, or the like can be used. A preferred distillation column is a plate column.

  The number of theoretical plates of the distillation column is not particularly limited, but may be, for example, 2 to 60 plates, preferably 3 to 55 plates, and more preferably about 5 to 50 plates.

  The supply position (supply port position (height position)) of the first mixture in the distillation column is not particularly limited, and can be appropriately selected within a range in which impurities and alcohol can be efficiently separated.

  Further, in the distillation column, the water supply position may be an upper stage than the supply position of the first mixture. That is, the supply port for supplying water may be positioned above (or above) the position of the supply port for the first mixture in the distillation column. The water supply position (position of the water supply port) is, for example, in the height direction of the distillation tower (when the height of the distillation tower is 100%), and higher than the position 20% from the top of the tower. It may be a position (upper stage), preferably a position above 10% from the top, more preferably a position above 5% (particularly the top) from the top.

  Note that the water supplied to the distillation tower may be fresh water, or water discharged from the subsequent (following) or preceding process may be used. In particular, the water recovered from the subsequent alcohol recovery tower may be recycled. In addition, for example, recycled water may be combined with fresh water and supplied to the distillation tower, or fresh water and recycled water may be supplied to the distillation tower through separate lines. Good.

  The temperature in the distillation column is selected from the range of, for example, 15 to 200 ° C., preferably 30 to 190 ° C., more preferably about 35 to 180 ° C., depending on the type of alcohol and impurities, the amount of water supplied, and the like. it can.

  The pressure of the distillation column (top pressure) may be 10 to 1,100 kPa, preferably 20 to 1,000 kPa, more preferably about 30 to 900 kPa in absolute pressure, and in particular, distillation under atmospheric pressure. It is preferred to do so.

  The reflux ratio of the distillation column is, for example, 0 to 20 (for example, 1 to 20), preferably 0 to 18 (for example, 1.5 to 17), and more preferably 0 to 16 (for example, 2 to 15). It may be a degree.

  By distillation in the distillation tower, the impurities (second mixture) are separated and recovered from the distillation tower (upper part of the distillation tower) by distillation. The distillation position (position of the distillation outlet) of the second mixture is usually preferably a position (upper stage) above the supply position (position of the supply port) of the first mixture. In addition, since all the low boiling components in the distillation tower should just be discharged | emitted as a 2nd mixture, the distillation position of a 2nd mixture is usually a tower top. The second mixture discharged from the top of the column may be reused or discarded as it is, but is usually liquefied by cooling or concentration (condensation), and reused (for example, fuel) and / or discarded ( For example, incineration).

  In addition, since the liquefied 2nd mixture contains water, you may recycle to a distillation tower and utilize for isolation | separation of alcohol. When a solution such as a second mixture condensed in a distillate or a condenser is recycled to the distillation column, impurities can be concentrated.

  In addition, in order to increase the concentration of water in the second mixture recycled to the distillation column, water and other impurities are separated by conventional means (such as the decanter), and the water-rich component is added to the distillation column. May be recycled. The supply position of the water-rich component (supply port position or return position) is usually a position (upper part) above the supply position of the first mixture from the viewpoint of separability between alcohol and impurities. In particular, it is the same as the first mixture supply position (the same number of stages) or above the first mixture supply position (upper stage) and below the water supply position from the supply means. The position (lower stage) is preferable. Depending on the return position, the water-rich component may be recycled by refluxing it to the distillation column. In addition, when a component containing a large amount of water is returned to the distillation column from the same position (the same number of stages) as the supply position of the first mixture or from the upper position (upper stage), the countercurrent contact between water and alcohol is efficiently performed. The alcohol is extracted and separated efficiently.

  By distillation in the distillation column, the third mixture containing alcohol and water is taken out from the lower part of the distillation column.

  The third mixture discharged from the lower part (preferably the bottom) of the distillation column may be recycled to the distillation column as it is, or if necessary, heated by a conventional heating means and then recycled to the distillation column. Good.

  Since the third mixture contains alcohol at a high concentration, it may be used as it is for applications using alcohol, but water and alcohol are separated by conventional separation means (eg, distillation tower, membrane separation, etc.). In addition, alcohol and water may be used separately.

[Alcohol recovery tower]
The third mixture recovered from the lower part of the distillation tower may be supplied to the alcohol recovery tower and separated into alcohol and water.

  As the alcohol recovery column, a conventional distillation column such as a plate column, a packed column, or a flash distillation column can be used.

  The theoretical plate number of the alcohol recovery column is not particularly limited, but may be, for example, 2 to 60 plates, preferably 3 to 55 plates, and more preferably about 5 to 50 plates.

  Further, the distillation temperature, pressure, reflux ratio and the like in the alcohol recovery tower can be appropriately selected according to the type of alcohol. The temperature in the tower can be selected from the range of, for example, 15 to 200 ° C, preferably 30 to 190 ° C, more preferably about 35 to 180 ° C.

  The pressure (column top pressure) of the recovery tower may be 10 to 1,100 kPa, preferably 20 to 1,000 kPa, more preferably about 30 to 900 kPa in absolute pressure.

  The reflux ratio of the recovery tower is, for example, 0 to 20 (for example, 0.1 to 20), preferably 0 to 18 (for example, 0.2 to 15), and more preferably 0 to 16 (for example, 0.1. It may be about 3 to 10).

  The alcohol separated in the alcohol recovery tower can be recovered by distillation from the upper part (for example, the top of the tower) of the recovery tower. The alcohol recovery tower may be composed of one tower or a plurality of towers (for example, two towers including a first alcohol recovery tower and a second alcohol recovery tower).

  Moreover, the water separated in the recovery tower can be recovered by canning or distilling from the lower part of the recovery tower. The water discharged from the lower part (preferably the bottom) of the recovery tower may be returned to the recovery tower as it is (recycled). If necessary, it is heated by a conventional heating means and then returned to the distillation tower (recycled). ) The water recovered from the recovery tower may be returned (recycled) to the distillation tower (impurity separation tower) as described above.

  The alcohol recovered from the alcohol recovery tower may be used as it is as a reaction raw material. Further, the water recovered from the recovery tower is further supplied to a dealcoholization tower (not shown), and separated into a stream (or a fraction) containing a large amount of water and a fraction containing impurities such as alcohol. However, the stream rich in water may be recycled to the distillation column.

  FIG. 3 shows separation of a component containing ethanol obtained by recovering an aldehyde from a reaction mixture obtained by an ethanol dehydrogenation method or an ethanol oxidation method by supplying it to a distillation column (impurity separation column) as a first mixture. It is a flowchart which shows the separation method or separation apparatus containing the series of processes to perform.

  In the example of FIG. 3, the separation device is for separating an aqueous solution containing an aldehyde obtained from an aldehyde formation reaction such as an ethanol dehydrogenation method or an ethanol oxidation method (using oxygen or air) into components such as an aldehyde and alcohol. The aldehyde separation tower 21, the impurity separation tower 1 for separating the component containing alcohol from the aldehyde separation tower 21 into alcohol and impurities, and the component containing alcohol from the impurity separation tower 1 are mixed with alcohol and water. And an alcohol recovery tower 11 for separation. Note that the separation device may further include a dealcoholization tower (not shown) for further recovering alcohol from the stream (or stream) containing water from the alcohol recovery tower 11.

  The aqueous solution containing alcohol supplied to the aldehyde separation tower 21 is a reaction gas containing acetaldehyde obtained in the aldehyde production reaction system 31 and a gas component such as hydrogen gas in a reaction gas condensation / absorption system (aldehyde absorption tower) 32. It is obtained by separating from The aldehyde generation reaction system 31 is supplied with ethanol gas obtained by evaporating and evaporating the raw material ethanol in the ethanol evaporation system 33.

  That is, in the example of FIG. 3, ethanol vaporized in the ethanol evaporation system 33 is subjected to an ethanol dehydrogenation reaction or an ethanol oxidation reaction in the aldehyde generation reaction system 31 to generate acetaldehyde. Then, the reaction gas containing acetaldehyde obtained in the reaction system 31 is supplied to the reaction gas condensation / absorption system 32, where the reaction gas containing acetaldehyde is cooled with a refrigerant such as water (or the like). Condensed) and / or absorbed in water and separated into non-condensed or absorbed gas components (such as gas components such as hydrogen gas) and aqueous solutions containing acetaldehyde. Further, the stream (aqueous solution) containing acetaldehyde separated by the condensation / absorption system 32 is supplied to the aldehyde separation tower 21, and in this aldehyde separation tower 21, acetaldehyde is recovered as a low boiling point component, and a stream containing ethanol. The stream containing the separated ethanol (or the stream) and the separated ethanol is supplied to the impurity separation column 1 as the first mixture. In the impurity separation tower 1, the stream containing ethanol from the aldehyde separation tower 21 is extracted and distilled with water supplied to the separation tower 1 from the upper stage than the supply position of this stream, and the stream containing ethanol ( Or a fraction) and a fraction containing impurities.

  The separated ethanol-containing stream is supplied to the alcohol recovery tower 11 where it is separated into a fraction containing ethanol and a stream containing water. The fraction containing the alcohol (ethanol) separated in the alcohol recovery tower 11 is recycled to the ethanol evaporation system 33, and the stream containing water may be recovered as it is, for extracting ethanol in the impurity separation tower 1. It may be recycled as water. The stream containing water separated by the alcohol recovery tower 11 may be supplied to the dealcoholization tower, where it is separated into a stream containing water and a fraction containing impurities such as ethanol. A stream containing impurities may be recovered. The stream containing water separated in the dealcoholization tower may be recovered as it is or recycled as water for extracting ethanol in the impurity separation tower 1.

  In such a separation apparatus or separation method, unreacted ethanol remaining in the aldehyde production process can be efficiently recovered, and components containing the recovered ethanol are purified by the distillation column 1 and the alcohol recovery column 11. The purified ethanol can be used as a raw material ethanol for the reaction system. Moreover, since the impurities of the reaction by-product are removed from the ethanol recycled to the reaction system, the catalyst activity of the reaction system can be maintained without fear of being poisoned by the impurities.

  In the example of FIG. 3, the impurity separation tower 1 and the alcohol recovery tower 11 are the same as those in the examples of FIGS.

[Aldehyde separation tower]
In the aldehyde separation tower, a reaction mixture containing acetaldehyde obtained by an aldehyde production reaction such as an ethanol dehydrogenation method or an ethanol oxidation method is separated into a fraction containing acetaldehyde and a stream containing ethanol, etc., and a stream containing ethanol Is supplied to the impurity separation tower (distillation tower) as the first mixture.

  Although the form of the reaction mixture supplied to the aldehyde separation tower may be gaseous, it is usually preferable that the reaction mixture is a liquid (particularly, an aqueous solution containing acetaldehyde).

  As the aldehyde separation column, a conventional distillation column such as a plate column, a packed column, or a flash distillation column can be used.

  The number of theoretical plates of the separation column is not particularly limited, but may be, for example, 2 to 60 plates, preferably 3 to 55 plates, and more preferably about 5 to 50 plates.

  In addition, the distillation temperature, pressure, reflux ratio and the like in the aldehyde separation column can be appropriately selected. The temperature in the tower can be selected from the range of, for example, -35 ° C to 200 ° C, preferably -25 ° C to 190 ° C, and more preferably about -20 ° C to 180 ° C.

  The pressure (column top pressure) of the separation tower may be 50 to 1,100 kPa, preferably 80 to 1,000 kPa, and more preferably about 100 to 900 kPa in absolute pressure.

  The reflux ratio of the separation column is, for example, 0 to 20 (for example, 0.1 to 20), preferably 0 to 18 (for example, 0.2 to 15), and more preferably 0 to 16 (for example, 0.1. It may be about 3 to 10).

  The acetaldehyde separated in the aldehyde separation tower can be recovered as a product aldehyde by distillation from the upper part (for example, the top of the tower) of the separation tower.

  In addition, the ethanol-containing component separated in the separation tower can be recovered from the lower part of the recovery tower by canning or distilling. The recovered ethanol-containing component may be recycled as it is to the aldehyde separation tower, or may be recycled to the distillation tower after heating by a conventional heating means if necessary.

[Reaction gas condensation / absorption system (aldehyde absorption tower or aldehyde condensation / absorption tower)]
In the reaction gas condensation / absorption system (aldehyde absorption tower), the reaction gas containing acetaldehyde obtained by the ethanol dehydrogenation method or the ethanol oxidation method is condensed (for example, cooled with a refrigerant such as water) or brought into contact with water. To absorb acetaldehyde in water.

  The reaction gas supplied to the aldehyde condensation / absorption tower is not particularly limited as long as it is obtained by an ethanol dehydrogenation method or an ethanol oxidation method and contains acetaldehyde, and the reaction mixture obtained from the reactor is appropriately vaporized. However, from the viewpoint of energy efficiency and separation efficiency, the gas phase and liquid phase are separated by conventional gas-liquid separation means (condenser, cooler, etc.) It is preferable to use it. Gas-liquid separation may be performed a plurality of times.

  The aqueous solution containing acetaldehyde obtained in the aldehyde condensation / absorption tower is withdrawn from the lower part of the tower (preferably the bottom of the tower) and supplied to the aldehyde separation tower. Before use in the aldehyde separation tower, if necessary, it may be stored in a tank in order to make the composition and / or concentration of the contained components uniform, and the concentration may be adjusted by concentration or dilution. . The liquid phase component separated by the gas-liquid separation means may be supplied to the aldehyde separation tower together with the aqueous solution obtained from the aldehyde condensation / absorption tower.

  If necessary, a part of the aqueous solution containing acetaldehyde extracted from the lower part of the aldehyde condensation / absorption tower may be returned to the aldehyde condensation / absorption tower. The aqueous solution may be returned to the aldehyde condensation / absorption tower after concentration adjustment by concentration or dilution, if necessary.

  Further, exhaust gas components are discharged from the upper part of the aldehyde condensation / absorption tower. In the reaction mixture obtained by the ethanol dehydrogenation method, hydrogen is contained in the exhaust gas component. Therefore, if necessary, it may be purified by a conventional purification means to separate and recover hydrogen. The recovered hydrogen can be recycled as a reaction raw material if necessary.

  For the aldehyde condensation process (condensation system), conventional condensation means (condenser etc.) can be used. In the case of the dehydrogenation reaction, the condensation temperature may be, for example, 400 ° C. to −20 ° C., preferably 390 ° C. to −15 ° C., more preferably about 380 ° C. to −10 ° C. In the case of an oxidation reaction, the condensation temperature may be, for example, about 650 ° C. to −20 ° C., preferably 600 ° C. to −15 ° C., and more preferably about 600 ° C. to −10 ° C. Moreover, the pressure of a condensation process is an absolute pressure, for example, can be selected from the range of 1-1,100 kPa, Preferably it is 10-1,000 kPa, More preferably, it is about 50-900 kPa.

  As the aldehyde absorption tower, a conventional absorption means such as a plate tower, a packed tower, a spray tower, a wet wall tower and the like can be used.

  Moreover, the temperature, pressure, etc. in an aldehyde absorption tower can be selected suitably. The temperature in the tower can be selected from a range of, for example, about 0 to 30 ° C, preferably 1 to 25 ° C, and more preferably about 5 to 20 ° C. Moreover, the pressure in a tower | column is an absolute pressure, for example, a normal pressure-1,100 kPa, Preferably it is about 150-1,000 kPa, More preferably, about 200-900 kPa may be sufficient.

[Aldehyde production reaction system]
(Dehydrogenation reaction system)
In the dehydrogenation reaction system, ethanol gas is dehydrogenated. In a dehydrogenation reactor, acetaldehyde is produced by dehydrogenating ethanol gas supplied to the reactor in the presence of a dehydrogenation reaction catalyst (such as a copper-based catalyst) filled inside, and hydrogen is added as a by-product. To be born.

  The temperature of the reaction system is, for example, about 100 to 400 ° C., preferably about 110 to 390 ° C., and more preferably about 120 to 380 ° C. (for example, 200 to 370 ° C.). The reaction pressure is preferably normal pressure or reduced pressure (slightly reduced pressure).

  The ethanol gas supplied to the dehydrogenation reaction system may be preheated to the temperature of the reaction system in advance. Moreover, you may heat and supply a part of ethanol gas with a heating furnace.

  The ethanol concentration in the supplied ethanol gas may be, for example, 80% by weight or more (for example, about 80 to 100% by weight), preferably 82% by weight or more, and more preferably 85% by weight or more.

  As a dehydrogenation catalyst, a copper-based catalyst, for example, a copper catalyst containing copper, a copper compound (oxide, hydroxide, salt, etc.), a catalyst system containing copper and other components (promoter or carrier, etc.) Etc. are used. As the catalyst system, for example, a copper-chromium catalyst or a copper-alkali metal catalyst (for example, a copper-silica-sodium catalyst) is used. The type of these catalysts is not particularly limited, but usually a solid catalyst containing constituent components, for example, a solid catalyst containing a copper component and, if necessary, other components (chromium component, silica component, sodium, etc.) is used. There are many.

(Oxidation reaction system)
When acetaldehyde is produced by the ethanol oxidation method, an oxidation reaction system (oxidation tower) is used instead of the dehydrogenation reaction system. In the oxidation reaction system, acetaldehyde is generated by oxidizing the ethanol gas supplied to the reaction system with air or oxygen in the presence of an oxidation catalyst (such as a catalyst containing metallic copper or silver) filled therein. In the oxidation reaction, hydrogen is not by-produced.

  The temperature of the reaction system is, for example, about 200 to 650 ° C, preferably about 250 to 600 ° C, and more preferably about 300 to 600 ° C. The reaction is preferably carried out at normal pressure or under pressure.

  The ethanol gas supplied to the oxidation reaction system may be preheated to the temperature of the reaction system in advance. The ethanol concentration in the supplied ethanol gas may be, for example, 80% by weight or more (for example, about 80 to 100% by weight), preferably 82% by weight or more, and more preferably 85% by weight or more.

  As the oxidation reaction catalyst, metallic copper or metallic silver is used, and usually a solid catalyst containing metallic copper or metallic silver is often used.

  Air or oxygen used for the reaction may be directly supplied to the reaction system, or may be mixed with ethanol gas in advance and supplied to the reaction system.

[Ethanol evaporation system]
In the ethanol evaporation system, ethanol supplied to the aldehyde generation reaction system is gasified. The evaporation system may be provided with a conventional evaporation means [for example, an evaporation tower (calandria, kettle, flash can, thermosiphon, thin film evaporator (WFE, FFE, etc.), etc., the above-mentioned distillation tower, etc.), etc.] A plurality of evaporation means may be combined.

  When the ethanol component recycled from the subsequent process is used as a raw material, it may be gasified and supplied directly to the reactor. Preferably, the reaction is conducted after gasification with fresh raw material ethanol in an evaporation system. Preferably it is supplied to the vessel.

  Further, the concentration may be appropriately adjusted in the evaporation system so that the ethanol concentration in the ethanol gas supplied to the reactor falls within the above-described concentration range.

  In the present invention, since alcohol is distilled from a mixture containing impurities such as aldehyde and ketone in addition to alcohol (or alkanol), the fraction containing impurities such as aldehyde and ketone, and alcohol and water are mixed. It can be efficiently separated into fractions containing it (bottom liquid). In addition, the separated alcohol (ethanol etc.) can be recycled as a raw material to the reaction system for aldehyde production, and since impurities are removed, the catalytic activity (and reaction efficiency) can be achieved without poisoning the reaction catalyst. ) Can be maintained. Therefore, for example, it is useful for industrially producing an aldehyde in combination with a reaction system obtained by an ethanol dehydrogenation method or an oxidation method.

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

Example 1
(1) Production and separation of acetaldehyde A 95 volume (vol)% concentration ethanol aqueous solution was evaporated and contacted with a solid catalyst (copper-silica-sodium catalyst) to produce acetaldehyde. The reaction gas containing acetaldehyde was condensed with a condenser and brought into contact with water to absorb the acetaldehyde in water. This aqueous solution containing acetaldehyde was supplied to the 45th stage from the top of the distillation tower (Oldershaw, 60th stage), and distilled at a reflux ratio of 1.5. A stream containing acetaldehyde was distilled from the top of the distillation tower, and an ethanol aqueous solution (hereinafter referred to as ethanol aqueous solution A) containing ethanol and the following impurities at the following concentrations was recovered as a bottoms.

impurities:
Butyraldehyde 0.4% by weight
Methyl ethyl ketone 0.1% by weight
1,1-diethoxyethane 0.1% by weight
(Diethyl acetal)
Ethyl acetate 0.5% by weight
Acetic acid 2.3 wt%
Crotonaldehyde 0.2% by weight
(2) Ethanol recovery (impurity separation)
The aqueous ethanol solution A obtained in the above (1) was distilled using a 30-stage Oldershaw tower.

  That is, while supplying water at the supply rate of 150 g / h from the top of the distillation column, the aqueous ethanol solution A was charged into the 10th stage from the top of the distillation column at a supply rate of 960 g / h, at atmospheric pressure and at a reflux ratio of 15 Distillation was performed. Then, a fraction containing impurities such as butyraldehyde, methyl ethyl ketone, diethyl acetal, and ethyl acetate is separated from the top (top) of the distillation column, and ethanol (ethanol and water containing stream) is taken out from the bottom of the column. (Or flow)) was collected.

Example 2
Ethanol was recovered in the same manner as in Example 1 except that the amount of water supplied was 180 g / h, the amount of aqueous ethanol solution A was 1150 g / h, and the reflux ratio was 5 (both the upper and lower phases were refluxed). It was.

Comparative Example 1
Ethanol was recovered in the same manner as in Example 1 except that the amount of the aqueous ethanol solution A supplied was 1150 g / hour without supplying water from the top of the column.

Example 3
Ethanol was collected in the same manner as in Example 1 except that the amount of water supplied was 200 g / h and the amount of aqueous ethanol solution A was 1150 g / h, without reflux.

Example 4
In order to condense the distillate from the 30-stage Oldershaw Tower, using a device connected to the decanter, the lower-phase distillate separated by the decanter is returned to the second stage from the top of the Oldershaw Tower. The ethanol was collected in the same manner as in Example 2 except that the aqueous ethanol solution A was distilled.

Example 5
Ethanol was recovered in the same manner as in Example 1, except that the amount of water supplied was 200 g / hour, the amount of aqueous ethanol solution A was 1,520 g / hour, and the reflux ratio was 10.

Example 6
As the water supplied from the top of the tower, the bottoms extracted from the Oldershaw tower was further separated by an ethanol recovery tower, and the bottoms containing a large amount of water were used. Ethanol was collected.

  In addition, the above-mentioned bottoms from the Older Shower tower are supplied to the ethanol recovery tower and separated into a fraction rich in ethanol and a bottoms rich in water, and the fraction rich in ethanol is recovered. did.

  Table 1 shows the recovery rate of each component on the distilling side and the canning side in the examples and comparative examples (distilled or canned amount / preparation amount × 100) (%).

  As can be seen from Table 1, in any of the Examples, almost 100% of the impurities butyraldehyde, 1,1-diethoxyethane and ethyl acetate were recovered from the distillate side, and methyl ethyl ketone was 85-96%. Is recovered from the distillate side, whereas nearly 100% of ethanol is recovered from the can side. That is, in the Examples, it can be seen that the target alcohol is effectively separated from the impurities.

  On the other hand, in the comparative example obtained by distilling without supplying water from the top of the tower, the recovery rate of impurities from the distillation side is not so different from that of the example, but 30% ethanol is recovered together with impurities from the distillation side. As a result, the recovery rate on the can side decreased to 70%.

FIG. 1 is a flowchart for explaining the alcohol separation method or separation apparatus of the present invention. FIG. 2 is a flowchart for explaining another example of the alcohol separation method or separation apparatus of the present invention. FIG. 3 is a flowchart for explaining another example of an alcohol separation method or separation apparatus using a component containing ethanol obtained by an ethanol dehydrogenation method or an ethanol oxidation method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Distillation column 2 ... Supply line of 1st mixture 3 ... Supply line of water 4,12A ... Distillation line 5a, 5d ... Condenser 5b, 5c ... Reboiler 6 ... Decanter 8, 9A, 13, 14A ... Line 11 ... Alcohol recovery tower 21 ... Aldehyde separation tower 31 ... Aldehyde production reaction system 32 ... Reaction gas condensation / absorption system 33 ... Ethanol evaporation system

Claims (7)

C _n alkanol carbon number n is 1 to 3, from a first mixture comprising a C n _{+ 2} aldehydes and C _{n + 2} ketones, a method of separating C _n alkanol, supplying the first mixture to the distillation column However, water is supplied to the distillation column from the upper stage from the supply position of the first mixture, and a second mixture containing C _{n + 2} aldehyde and C _{n + 2} ketone is distilled from the distillation column, and C _n alkanol Separation method of alcohol which collects the 3rd mixture containing water and water from the lower part of the distillation column. The third mixture containing C _n alkanol recovered from the bottom of the distillation column and water, and further supplied to an alcohol recovery column, the water and C _n alkanol was separated and purified from the top of the recovery column C The separation method according to claim 1, wherein _n alkanol is recovered, a stream containing water is recovered from a lower part of the recovery tower, and the stream containing water is used as water to be supplied to the distillation tower. The first mixture comprises a C _n alkanol, a C _{n + 2} aldehyde and a C _{n + 2} ketone and may contain a C _n alkyl ester of a carboxylic acid and a di (C _n alkoxy) C _n alkane;
Feeding said first mixture to the distillation column, distillation of the third mixture comprising a C _n alkanol and water is recovered from the bottom of the distillation column, a second mixture comprising other components from the distillation column The separation method according to claim 1 or 2. The second mixture distilled from the distillation column is further condensed and phase-separated into a lower phase containing water and an upper phase containing at least C _{n + 2} aldehyde and C _{n + 2} ketone. A method of refluxing the distillation column from the upper stage from the supply position of the mixture,
The separation method according to claim 3, wherein the second mixture contains the following component (i), (ii) or (iii), depending on the composition of the first mixture.
(i) C _{n + 2} aldehyde and C _{n + 2} ketone,
_{(ii) C n + 2 aldehydes, C n} alkyl esters of _{C n + 2} ketones and carboxylic acids,
(iii) C _{n + 2} aldehydes, C _{n + 2} ketones, C _n alkyl esters of carboxylic acids and di (C _n alkoxy) C _n alkanes A first mixture containing ethanol, butyraldehyde, methyl ethyl ketone, ethyl acetate and diethyl acetal;
While supplying the first mixture to the distillation tower, water is supplied to the distillation tower from the upper stage than the supply position of the first mixture, and ethanol is extracted with water, and water and ethanol are contained. The mixture of (3) is recovered from the lower part of the distillation column, and the second mixture containing butyraldehyde, methyl ethyl ketone, ethyl acetate and diethyl acetal is distilled from the upper part of the distillation column. The separation method described.   The reaction gas containing acetaldehyde obtained by the ethanol dehydrogenation method or ethanol oxidation method is condensed and / or absorbed in water, and this aqueous solution is supplied to an acetaldehyde separation tower to distill a fraction containing acetaldehyde, The separation method according to claim 5, wherein a stream containing ethanol is recovered from the lower part of the separation tower, and the stream containing ethanol is supplied as a first mixture to the distillation tower.   A third mixture containing ethanol and water recovered from the lower part of the distillation tower is further supplied to the alcohol recovery tower to separate water and ethanol, and a stream containing water is recovered from the lower part of the recovery tower, 7. The separation method according to claim 6, wherein the purified ethanol is recovered from the upper part of the recovery tower, and the recovered ethanol is recycled as raw ethanol for the ethanol dehydrogenation method or the ethanol oxidation method.

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