JP2642909B2 - Production method of purified ethanol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method capable of efficiently removing impurities in a crude ethanol aqueous solution obtained by a fermentation method or a synthesis method and producing a high-quality purified ethanol with a high yield. .

[0002]

2. Description of the Related Art Ethanol is produced by a fermentation method or a synthesis method. However, various impurities are contained in the obtained crude ethanol. Alternatively, it is necessary to increase the purity to a higher level. Examples of the impurities include ethyl acetate, acetaldehyde, acetone, methanol, n-propyl alcohol, i-propyl alcohol, butanol, i-amyl alcohol, and methyl ethyl ketone in the fermentation method, and acetaldehyde, diethyl ether, and the like in the synthesis method. Since acetone, n-propyl alcohol, butanol, etc. are contained in a considerable amount,
In order to use it as industrial purified ethanol, it is necessary to remove these impurities efficiently and to further concentrate to a predetermined ethanol concentration.

[0003] As a means for removing such impurities in crude ethanol, a distillation method has hitherto been widely used. In this method, a high-quality purified ethanol is obtained by removing various kinds of impurities as described above. Requires many distillation columns, a large amount of energy (such as steam) is required to operate each distillation column, the operation is complicated, and the recovery rate is considerably low. In addition, at least one of the distillation columns is an extractive distillation column, and the extractive distillation of ethanol is performed using a large amount of water.

[0004] As a relatively new purification ethanol production technique capable of solving these difficulties, impurities are extracted and removed using carbon dioxide in a high-pressure liquid or supercritical state as an extractant, and then extracted and distilled using water. A method for recovering ethanol has been proposed (Japanese Patent Publication No.
-35403). This method seems to be efficient at first glance because the extraction step and the ethanol recovery step can be made continuous. In addition to the problem that efficient operation cannot always be performed due to the adoption of a two-column split system, this method establishes an entire system to obtain high-quality ethanol that meets industrial alcohol standards. Not even doing that.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and its object is basically to utilize the above-mentioned high-pressure liquid or supercritical carbon dioxide. Utilizing the advantages of this extraction method, it is possible to extract it with carbon dioxide and recover ethanol with water in a single extraction tower, and to obtain purified ethanol of a quality that meets industrial alcohol standards with relatively simple equipment and operation. The aim is to establish a method that can be manufactured efficiently.

[0006]

Means for Solving the Problems The method for producing purified ethanol according to the present invention, which can solve the above problems, comprises using carbon dioxide in a liquid state or a subcritical or supercritical state under high pressure as an extracting agent, The extractant is brought into countercurrent contact with a crude ethanol aqueous solution obtained by a fermentation method or a synthesis method in an extraction column to extract and remove impurities in the crude ethanol, and to contact countercurrently with water supplied from the top of the extraction column. The gist lies in that the operation is performed by controlling the liquid level position in the extraction column according to the composition of the crude ethanol aqueous solution.

[0007] In carrying out this method, an ethanol aqueous solution is withdrawn from the bottom of the extraction column, subjected to a reduced pressure treatment to remove carbon dioxide, and then concentrated in a distillation column to produce 95% by volume or more of ethanol. A method of removing a component containing impurities such as n-propyl alcohol as a side cut fraction from any position of the distillation column in the concentration step, and further removing the side cut fraction from the liquid level of the extraction column. It is preferable to add a configuration for recycling above the position, because the recovery rate of purified ethanol can be increased and the removal rate of n-propyl alcohol as an impurity can be increased. In addition, if the carbon dioxide containing impurities discharged from the top of the extraction tower is configured such that the pressure is once reduced to remove the impurities, the carbon dioxide is purified at a high pressure in a carbon dioxide purification tower, and then recycled to the extraction tower, This is preferable because the carbon consumption can be significantly reduced.

Further, a step of introducing the ethanol-rich component extracted from the upper portion of the distillation column into a methanol removal column to remove methanol in the ethanol-rich component and extracting purified ethanol from the lower portion of the removal column may be added. If this is the case, it can be established as a continuous system for producing high-quality ethanol that is extremely effective industrially.

[0009]

As described above, in the present invention, a crude ethanol aqueous solution obtained by a fermentation method or a synthesis method is used as a raw material, which is converted into a liquid state under high pressure or carbon dioxide in a subcritical or supercritical state as an extracting agent. By countercurrently contacting in the extraction tower, impurities in the crude ethanol are extracted and removed, and water is supplied from the upper part of the extraction tower and countercurrently contacted to recover ethanol. By using the extraction column to remove impurities by carbon dioxide and recover ethanol by water in parallel, it is possible to simplify the equipment and operation and reduce the energy consumption required for the operation of the equipment. By appropriately controlling the liquid level of the extraction tower according to the composition of the crude ethanol aqueous solution as a raw material, the operation is carried out, so that high-quality purified ethanol can be recovered at a high level. It is those that succeeded in manufacturing under.

[0010] The aqueous ethanol solution extracted from the extraction column is then subjected to a reduced pressure treatment to remove carbon dioxide, and then concentrated in a distillation column to remove water, methanol, etc., so that a purified product having a purity of 95% by volume or more is obtained. Ethanol can be produced efficiently, and a series of steps from removal of impurities to purification can be performed extremely efficiently with simple equipment and operation.

FIG. 1 is a flowchart showing basic steps illustrating a manufacturing method according to the present invention. This process is roughly divided into five process systems and utility systems. The process system comprises an impurity removal system a composed of an extraction column, a low-pressure extractant recovery system b, an extractant recovery system c, an ethanol concentration system d, and a methanol removal system e. In addition to being composed of a single extraction column, the extraction column is provided with a liquid level control system x, and as will be described in detail later, the liquid level in the extraction column according to the composition of the crude ethanol aqueous solution as a raw material Although the method has a feature in controlling the position, it is desirable to put it into practice in a process system as shown in the figure in order to more effectively exhibit the feature in practical use. The utility system used in this process system is instrument air, high-pressure steam, low-pressure steam, and water.

The crude ethanol aqueous solution applied to this process contains various impurities as described above, and this raw material aqueous solution converts carbon dioxide into a supercritical state (or a subcritical state or a liquid state; hereinafter, a supercritical state). (Representative) is supplied from the middle of the extraction column set to a pressure that can be maintained. And while supplying supercritical carbon dioxide from the bottom of the extraction column, water is supplied from the top of the column, and the raw material aqueous solution is brought into countercurrent contact with the supercritical carbon dioxide in the extraction column, It is also brought into countercurrent contact with water supplied from above the tower. Then, impurities other than methanol and n-propyl alcohol among the impurities contained in the raw material aqueous solution are dissolved in supercritical carbon dioxide, and are discharged from the top of the column together with the carbon dioxide to the outside of the extraction column. Ethanol is recovered by coming into countercurrent contact with water flowing down from above the column, and is extracted from the bottom of the extraction column.

The supercritical carbon dioxide, which absorbs impurities and is extracted from the tower top, is depressurized in the low-pressure extractant recovery system b to remove impurities as fusel oil, and then pressurized in the extractant recovery system c. Is recycled to the lower part of the extraction column of the impurity extraction system a. Most of the ethanol-containing aqueous solution withdrawn as a raffinate from the bottom of the extraction column is ethanol, which contains n-propyl alcohol, methanol and carbon dioxide, which have higher water solubility than other impurities. Therefore, after evaporating and removing carbon dioxide under reduced pressure, the ethanol concentration system d
To concentrate ethanol. In this column, water having a boiling point higher than that of ethanol is separated at the bottom of the column, and n-propyl alcohol is extracted from the middle of the column by side cut and discharged to the outside or circulated to the impurity extraction system a. You. Since methanol having a lower boiling point than ethanol rises toward the top of the column together with ethanol, it is sent to a methanol removal system e to remove methanol and a small amount of remaining carbon dioxide, and the purified product ethanol is removed from the bottom of the column. Take out as.

Next, the liquid level control performed in the impurity removing system a will be described as follows. FIG.
FIG. 2C is an explanatory view showing a typical liquid level control position. When the liquid level position is almost controlled to the raw material supply position [FIG. 2A], the lower part of the raw material supply position, or Control in the upward direction is divided into [FIG. 2 (B) or (C): the liquid level control system is omitted in the figure]. These liquid levels are controlled, for example, by connecting a pipe communicating with the upper and lower portions of the extraction column A to a differential pressure gauge P as shown in the drawing, and by detecting a differential pressure between the upper and lower portions of the column detected by the differential pressure gauge P, the inside of the extraction column A is controlled. While controlling the opening of the flow rate control valve V to control the amount of ethanol-containing aqueous solution withdrawn from the tower A while detecting the liquid level position of the liquid. In this case, a viewing window may be provided in the extraction tower A, or a communication pipe may be provided to control the liquid level while directly detecting the liquid level.

The inventors of the present invention have studied the effect of the liquid level on the recovery rate of ethanol and the removal rate of impurities, and furthermore, n-propyl, which is a main impurity mixed into ethanol extracted from the extraction column. A study on the effect of alcohol on the extraction removal rate confirmed the following facts. That is, as shown in FIG. 2B, when the liquid level position in the extraction column is set below the raw material supply position (that is, the raw material supply position is a position where carbon dioxide is a continuous phase), the recovery rate of ethanol is increased. On the other hand, the contact area between the carbon dioxide and the raw material is shortened, so that the impurity removal rate is reduced. Conversely, as shown in FIG. 2 (C), the liquid level in the extraction column is set above the raw material supply position (that is, the raw material supply position). When the position is set to a position where water is used as the continuous phase), the contact area between carbon dioxide and the raw material becomes longer, so that the impurity removal rate increases, but the ethanol content that dissolves in carbon dioxide and rises toward the top also increases As a result, the ethanol recovery rate decreases.

In view of the above, in the present invention, it is desirable to appropriately control the liquid level so as to obtain the best ethanol recovery rate and impurity removal rate in accordance with the amount of impurities in the raw crude ethanol. Specifically, when a raw material having a relatively large amount of impurities is used, the liquid level position is set to be relatively high to relatively increase the impurity removal rate by carbon dioxide, and the contact efficiency between the carbon dioxide and the raw material is increased. On the other hand, when a raw material having a relatively small amount of impurities is used, it is desirable to set the liquid level lower to increase the alcohol recovery rate.

However, as is evident from the above, it is not preferable to excessively increase the liquid level because it is necessary to improve the ethanol recovery rate.
A considerable amount of n-propyl alcohol, which is particularly easily absorbed by water, is mixed in the aqueous ethanol solution extracted from the extraction column. Therefore, in the present invention, n-propyl alcohol and the like are removed in the ethanol concentration system d as described above. In the distillation column used for this concentration, a high concentration region of n-propyl alcohol and the like is formed at an arbitrary position. It was confirmed that if n-propyl alcohol was extracted from the high concentration region as a side cut portion, the removal could be performed extremely efficiently.

FIG. 3 is a graph showing the relationship between the height position (number of stages) in the distillation column used for ethanol concentration and the n-propyl alcohol concentration and the ethanol concentration. In this experiment, FIG. , Distillation column 2
A high-level n-propyl alcohol concentration position is formed at the position of 4 to 29 stages, and n-propyl alcohol can be efficiently removed by extracting n-propyl alcohol as a side cut component at this position. Thus, it can be understood that the quality of purified ethanol can be increased extremely efficiently.

This side cut component is n-
The propyl alcohol component is concentrated, but the main component is ethanol (for example, the ethanol concentration at the side cut position shown in FIG.
%), And releasing it as it is to the outside of the system leads to a decrease in the ethanol recovery rate. Therefore, in order to further improve the ethanol recovery rate, it is desirable to return the side-cut component to the extraction column and to recover the ethanol component well.
However, it is desired that the n-propyl alcohol contained in the side cut component is efficiently removed by the extraction column.

From this point of view, as a result of further research on a return position for more efficiently recovering ethanol from the side cut component and removing n-propyl alcohol, the return position was changed to carbon dioxide as a continuous phase. It was confirmed that the position should be set higher than the position of the extraction column, that is, the liquid level position of the extraction tower. Since n-propyl alcohol is mixed in the side cut component in a concentrated state, when this is returned below the liquid level in the extraction column, the n-propyl alcohol is immediately dissolved in ethanol. It will diffuse into the contained aqueous solution, and the purpose of reducing n-propyl alcohol cannot be fulfilled. However, when the side cut component is returned to the carbon dioxide continuous phase above the liquid surface, n-propyl alcohol in the side cut component is efficiently absorbed by carbon dioxide, and most of the n-propyl alcohol is absorbed together with carbon dioxide in the direction toward the top. It was confirmed that the flow down to the bottom was very small.

That is, if the return position of the side cut component is set as described above, it is possible to efficiently recover ethanol while removing as much as possible n-propyl alcohol therein. And quality can be improved together.

Thus, according to the present invention, the liquid level control in the extraction column, the side cut of n-propyl alcohol in the ethanol distillation column, and the return of the side cut component to an appropriate position to the extraction column are performed. The combination makes it possible to efficiently produce high-quality purified ethanol with a high recovery rate.

As described above, the most preferable embodiment for putting the present invention into practical use is an impurity extraction system a having a liquid level control mechanism.
However, the essential feature of the present invention is that, as described as the impurity extraction system a in FIG. 1, a crude ethanol aqueous solution is superposed in a common extraction column. By removing the impurities and removing ethanol by controlling the liquid level in the extraction column according to the composition of the crude aqueous ethanol solution as well as the countercurrent contact with both carbon dioxide and water in the critical state. It is characterized in that the collection of the above is performed simply and efficiently, so that for other process systems b to e, these may be replaced with other equipment or processed on another line. It is possible, and they are also included in the technical scope of the present invention.

The specific configuration and operating conditions of the impurity extraction system a, that is, the extraction column, are not particularly limited, and may be appropriately set in accordance with a known supercritical extraction method. (Liquid) In order to enhance the efficiency of removing impurities by carbon dioxide and the effect of collecting ethanol by water, it is preferable that the pressure be in the range of 5 to 20 MPa at 10 to 80 ° C, more preferably 6 to 12 MPa at 20 to 60 ° C. is there.

There is no particular limitation on the internal structure of the extraction column, but from the standpoint of enhancing the countercurrent contact efficiency, a tray type multistage structure type, a packed tower type in which the contact efficiency is enhanced by a filler such as Raschig ring, A spray tower type or those having various structures in which these are appropriately combined can be appropriately selected and applied. At this time, as described above, a liquid level control unit is provided at an appropriate position in the extraction tower, and the composition of the crude ethanol aqueous solution, the extractant ratio, the water ratio, the solubility of the ethanol component and the impurity component in the extractant and water, and the like are determined. By controlling the liquid level in the extraction column so that the optimum purification efficiency is obtained accordingly, it becomes possible to efficiently remove impurities and recover ethanol components in the extraction column.

Further, specific configurations and operating conditions of the other process systems shown in FIG. 1, such as the low-pressure extractant recovery system b, the extractant recovery system c, the ethanol concentration system d, and the methanol removal system e, are also described. There is no limitation at all, and known equipment and operating conditions may be applied substantially as it is or after being appropriately changed as needed.

[0027]

EXAMPLES Hereinafter, the structure and operation and effect of the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples and does not depart from the spirit of the preceding and following examples. All modifications within the scope are included in the technical scope of the present invention.

Using a specific crude ethanol production process as shown in FIG. 4, crude ethanol having a raw material composition shown in Table 1 was purified. In FIG. 2, A is an impurity extraction tower having a packed tower type gas-liquid countercurrent contact structure, X is a liquid level control unit, B is an extractant recovery tower main tower, C is an extractant recovery tower subtower, and D is fusel oil flash. Tank, E is a low-pressure extractant recovery tower, F is a low-pressure extractant compressor, G is an extractant condenser, H is an ethanol concentrate tower main tower, I is an ethanol concentrate tower subtower, J is an ethanol concentrate condenser, and K is methanol. The removal tower, L, indicates a methanol removal tower condenser, respectively.

In the operation of the process, the impurity extraction tower A is set at 20 to 60 ° C. and 6 to 12 MPa, and a crude ethanol aqueous solution 1 as a raw material is supplied to the impurity extraction tower A from the middle of the impurity extraction tower A. The supercritical carbon dioxide 2 is supplied from the lower side, the washing water 3 is supplied from above, and the crude ethanol aqueous solution 1 is supplied to the supercritical carbon dioxide 3 rising in the extraction column A and the extraction column. A is brought into countercurrent contact with washing water 3 descending in A, and a crude ethanol aqueous solution 1
The impurities contained therein are extracted and removed with carbon dioxide and washed with washing water 3. Then, from the top of the extraction column A, carbon dioxide in a supercritical state where impurities have been collected is extracted, and the bottom portion is sent to the flash tank D via the main column B for the extractant recovery column and the auxiliary column C for the extractant recovery column, and is sent to the fusel tank D. While recovering the oil, the decompressed carbon dioxide is recovered from the tops of the recovery towers B and C, and the carbon dioxide sent from the low-pressure extractant recovery tower E to be described later through the low-pressure extractant compressor F is removed. After being merged and sent to the extractant condenser G and pressurized to a supercritical state, it is recycled as the extractant 2 to the impurity extraction column A.

Since the ethanol-containing aqueous solution extracted from the bottom of the impurity extraction column A contains a small amount of carbon dioxide, methanol and n-propyl alcohol in addition to ethanol, it is first sent to the low-pressure extractant recovery column E. The liquid phase is removed by decompression and vaporization of carbon dioxide (this carbon dioxide is sent to the extractant condenser G via the low-pressure extractant compressor F), and the liquid phase is converted to the bottom part of the water in the ethanol condensing tower sub-column I. Separately, n-propyl alcohol is extracted as a side cut component from an appropriate position (for example, the middle abdomen) of the auxiliary column I, and this is returned above the liquid level of the impurity extraction column A as shown in the drawing, or as it is depending on the case. Discharge outside the system. The low-boiling components withdrawn from the top of the sub-column I are sent to the main column H of the ethanol concentration column, where components having a higher boiling point than ethanol are removed as much as possible and condensed in the condenser J. Most of this condensate is ethanol, but it contains a small amount of methanol and carbon dioxide whose boiling points are close to each other. Therefore, the condensate is sent to a methanol removal column K to remove methanol by distillation toward the top of the column. High-quality ethanol is recovered as a bottom component. At this point, the ethanol has been increased to about 95% by volume or more, and depending on the application, it can be commercialized as it is. Is also effective. On the other hand, the methanol fraction extracted from the top of the methanol removal tower K and condensed in the condenser L can be recovered as a by-product after further increasing the purity if necessary.

[0031]

[Table 1]

In accordance with the above process procedure, an ethanol recovery operation was performed under the following conditions. Conditions of impurity extraction column: Temperature: 20 to 60 ° C, Pressure: 6 to 12 MPa Carbon dioxide / raw material ratio (S / F): 1 to 5 wt / wt Wash water / raw material ratio (W / F): 0.1 to 0 0.5 wt / wt Liquid level control position: Raw material supply stage Extractant recovery tower main tower: 30 to 70 ° C, 6 to 8 MPa Extractant recovery tower subtower: 10 to 60 ° C, 6 to 8 MPa Low pressure extractant recovery tower: 10 to 10 150 ° C, 0.8-1.5M
Pa Extractant condenser: 50-70 ° C, 6-8MPa Ethanol concentration tower main tower: 70-100 ° C, normal pressure Ethanol concentration tower sub tower: 80-110 ° C, normal pressure Methanol removal tower: 60-80 ° C, normal Pressure

According to the above-mentioned actual operation experiments, the influence on the recovery rate of ethanol when the supply amount (S) of the extractant and the supply amount (W) of the washing water with respect to the amount (F) of the crude ethanol aqueous solution were variously changed. Upon examination, the results shown in FIG. 5 were obtained. As is clear from this figure, it can be seen that the higher the ratio of the extractant used, the lower the ethanol recovery rate. However, if the use ratio of the extractant is reduced, the effect of removing impurities is naturally lowered and the product quality cannot be secured, so it is better to use a large amount of extractant within a range that does not adversely affect the recovery rate. From this point of view, it is understood that the preferable usage ratio (S / F) of the extractant to the crude ethanol is 5 or less, preferably 1 to 5, and more preferably about 2 to 4.

FIG. 6 shows fusel oil (lipophilic component) as a typical example of impurities contained in the crude ethanol aqueous solution.
The results of examining the relationship between the extraction ratio (removal ratio) of the extractant and the use ratio of the washing water (i.e., S / F, W / F) with respect to i-amyl alcohol exhibiting a behavior almost similar to that of FIG. From this graph, it can be seen that the amount of washing water used has no significant effect, but the ratio of the extractant used is i
-It has a remarkable effect on the extraction removal rate of amyl alcohol, and it is understood that the S / F ratio should be about 4 or more in order to obtain a sufficient removal rate. FIG. 7 shows the result of similarly examining the effect of n-propyl alcohol, which can be removed as a side cut component in the ethanol concentration tower, on the removal efficiency in the extraction tower. , By increasing the S / F ratio relatively,
The removal of n-propyl alcohol in the impurity extraction column can be carried out quite efficiently. From this, n-propyl alcohol (contains a considerable amount of ethanol) side-cut in the ethanol concentration tower can be returned to the impurity extraction tower and subjected to the re-extraction treatment as shown in FIG. It can be seen that this is effective in reducing ethanol loss.

Further, when the liquid level position of the impurity extraction column A was changed and the supply amount (S) of the extractant and the supply amount (W) of the washing water with respect to the amount (F) of the crude ethanol aqueous solution were variously changed, When the effect on the recovery rate of ethanol was examined, the results shown in FIG. 8 were obtained. As is clear from this figure, the ethanol recovery rate tends to decrease as the usage ratio of the extractant increases, and this tendency changes considerably depending on the liquid level in the extraction column. Below (the “CO ₂ continuous phase” shown in the figure) is above the raw material supply position (“H ₂ shown in the figure”).
O continuous phase ”). However, if the usage ratio of the extractant is reduced, the effect of removing impurities is naturally lowered and the product quality cannot be ensured. Therefore, it is desirable to use a large amount of the extractant within a range that does not adversely affect the recovery rate. As is clear from this graph, appropriate liquid level control is performed, the S / F ratio and W / F ratio are set appropriately, and particularly, the raw material supply position is continuously higher than the liquid level of the extraction column. It can be seen that a high ethanol recovery of 99% or more can be expected if the phase is controlled to a position where the phase is supercritical carbon dioxide (control at the bottom of the extraction column).

Based on the above basic experiments, the following operating conditions were set, and continuous operation was carried out for 20 days using the equipment shown in FIG. 4, during which the purity of the product ethanol and the composition of fusel oil were periodically investigated. 9 and 10 and Tables 2 and 3
Were obtained.

FIG. 9 is a graph showing the change over time in the purity of purified ethanol after the methanol removal treatment. The methanol content was always kept to a trace amount of 20 ppm or less, and the purity was a stable value of 94 to 95%. Is shown. FIG. 10 shows the result of examining the change in the composition of fusel oil extracted with supercritical carbon dioxide over time, and the composition of the crude ethanol aqueous solution as the raw material was sometimes stable during the test. However, a fusel oil having a very stable component composition was obtained.

Further, Table 2 shows that 6 during the continuous operation period.
As a result of examining the quality of the product ethanol on days 11, 11, 16 and 18 by the general analysis method, Table 3 shows the result of similarly examining the product ethanol purity and the impurity content by gas chromatography analysis. As is clear from these results, according to the present invention, it is understood that high-quality purified ethanol can be stably and efficiently produced under excellent operability.

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

The present invention is constituted as described above. Carbon dioxide in a liquid state or a subcritical or supercritical state under high pressure is brought into countercurrent contact with an extracting agent and water in the same extraction column. By adopting a method for performing appropriate liquid level control, it has become possible to stably produce high-quality purified ethanol very efficiently with simple equipment and operation.

[Brief description of the drawings]

FIG. 1 is a basic flow chart showing a process for producing purified ethanol using the present invention.

FIG. 2 is a conceptual diagram for explaining an influence of a liquid level position in an extraction column for removing impurities on an ethanol recovery rate and an impurity removal rate.

FIG. 3 is a graph showing ethanol concentration and n-propyl alcohol concentration at a height position of a distillation column for ethanol concentration.

FIG. 4 is an explanatory diagram showing a purified ethanol production process used in Examples.

FIG. 5: Effect of extractant / raw material ratio (S
/ F) and the relationship between the washing water / raw material ratio (W / F).

FIG. 6 shows the relationship between the extractant / raw material ratio (S / F) and the wash water / raw material ratio (W /
It is a graph which shows the relationship of F).

FIG. 7 shows the effect of extractant / raw material ratio (S / F) and washing water / raw material ratio (W) on the extraction rate (removal rate) of n-propyl alcohol.
/ F) is a graph showing the relationship.

FIG. 8 shows the effect of the extractant / raw material ratio (S / S) on the ethanol recovery rate when the liquid level is controlled at the top of the extraction column.
It is a graph which shows the relationship between F) and washing water / raw material ratio (W / F).

FIG. 9 is a graph showing a change in purity of purified ethanol obtained by continuous operation using the equipment of the example.

FIG. 10 is a graph showing a change in the composition of fusel oil obtained by continuous operation using the equipment of the example.

[Explanation of symbols]

 a impurity removal system b low pressure extractant recovery system c extractant recovery system d ethanol concentration system e methanol removal system x liquid level control system A impurity extraction tower B extractant recovery tower main tower C extractant recovery tower sub-tower D fusel oil Flash tank E Low pressure extractant recovery tower F Low pressure extractant compressor G Extractant condenser H Ethanol concentration tower main tower I Ethanol concentration tower sub tower J Ethanol concentration condenser K Methanol removal tower L Methanol removal tower condenser X Liquid level controller V Flow control valve

Claims (5)

(57) [Claims] 1. Use of carbon dioxide in a liquid state or a subcritical or supercritical state under high pressure as an extractant, and the extractant is brought into countercurrent contact with a crude ethanol aqueous solution obtained by a fermentation method or a synthesis method in an extraction column. The impurities in the crude ethanol are extracted and removed, and the ethanol is recovered by contacting countercurrently with water supplied from the upper part of the extraction tower. A process for producing purified ethanol, characterized in that the operation is performed by controlling the liquid level. 2. An ethanol aqueous solution is withdrawn from the bottom of the extraction column, subjected to a reduced pressure treatment to remove carbon dioxide, and then concentrated in a distillation column to produce 95% by volume or more of ethanol. 2. The n-propyl alcohol is removed as a side cut fraction from the intermediate position of the above.
3. The method for producing purified ethanol described in 1. above. 3. The side cut fraction according to claim 2,
3. The method for producing purified ethanol according to claim 2, wherein the ethanol is recycled above a liquid level position in the extraction tower. 4. The process for producing purified ethanol according to claim 1, wherein the carbon dioxide containing impurities extracted from the top of the extraction column is purified under high pressure by a carbon dioxide purification column and then recycled. 5. The method according to claim 1, wherein the ethanol-rich component extracted from the upper portion of the distillation column is introduced into a methanol removal column to remove methanol in the ethanol-rich component, and purified ethanol is extracted from the lower portion of the removal column. 4. The method for producing purified ethanol according to any one of 4.