JP2571743B2 - Manufacturing method of absolute 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 for producing anhydrous ethanol from aqueous ethanol having an azeotropic composition.

[0002]

2. Description of the Related Art Since an ethanol / water mixture has an azeotropic point, it cannot be concentrated to an azeotropic composition (ethanol concentration of 95.3% by weight) or more by a normal distillation method.
As a method for producing anhydrous ethanol from water-containing ethanol having an azeotropic composition, a ternary azeotropic distillation method using an azeotropic agent has been widely performed. In the ternary azeotropic distillation method, the relative volatility of water is increased by the addition of an azeotropic agent, and anhydrous ethanol having a low water content of 99.5% by weight or more can be easily obtained. However, since the ternary azeotropic distillation method requires a large amount of reflux of the overhead liquid, it consumes a large amount of energy and has a drawback that the operation cost is high.

[0003] Recently, as a method for dehydrating alcohols, a membrane separation method which is more energy-saving, for example, a dehydration method by a pervaporation method (pervaporation method) or a vapor separation method (vapor permeation method) has been studied and proposed ( JP-A-63-175602, JP-B-2-343
No. 29). Membrane separation is a method that selectively separates water by using a high-performance separation membrane, which saves energy. However, the driving force for membrane permeation is increased through the separation membrane between the primary side (high-pressure side) and the secondary side. The activity difference on the (low pressure side), that is, the vapor pressure difference of each component in the case of the pervaporation method, and the partial pressure difference of each component in the case of the vapor permeation method, for example, a membrane separation method using isopropanol. In dehydration,
If an attempt is made to concentrate the isopropanol concentration to 99.0% by weight or more, the required membrane area increases exponentially, so that it is necessary to equip the membrane modules more. Of course,
It is known that the same tendency is exhibited in the case of dehydration of aqueous ethanol by a membrane separation method.

As a result, in the dehydration and concentration of water-containing ethanol by the membrane separation method, the ethanol concentration is 99.0% by weight.
Above, especially when trying to concentrate to 99.5% by weight or more,
There was a problem that the expensive membrane modules had to be increased exponentially. In addition, in the case of a membrane separation device, the processing amount and the required membrane area are in a proportional relationship, so the construction cost in the case of a large-scale treatment device is higher because there is no scale-up effect as in a distillation device. Because of the drawback, 99.
When producing anhydrous ethanol having a low water content of 5% by weight or more or in a large-scale industry, a membrane separation method is hardly adopted.

A method has also been proposed in which a liquid mixture having an azeotropic point is concentrated to an azeotropic composition or more by a pervaporation method and then concentrated by binary distillation without using an azeotropic agent (Japanese Patent Application Laid-Open No. Sho. 54-33279, JP-A-63-4
807, JP-A-63-4826). Since this method does not perform complete separation only by the membrane separation method, there is no need to equip a large number of expensive membrane modules, and there is an advantage that the construction cost is inexpensive and it is possible to cope with large-capacity processing. Not applicable to manufacturing. That is, as shown in FIG. 2, for example, the vapor-liquid equilibrium curve of the isopropanol / water system (broken line in FIG. 2) is apart from the diagonal line except for the vicinity of the azeotropic composition B, and the liquid composition and the corresponding vapor composition are the same. Since the specific volatility of water with respect to isopropanol is large because it is different, isopropanol and water can be separated by a two-component distillation method if concentrated by a membrane separation method to an azeotropic composition or higher. Vapor-liquid equilibrium curve of ethanol / water system (Fig. 2
(Solid line) indicates that when the ethanol concentration is lower than the azeotropic composition A, it is farther away from the diagonal line and is suitable for separation by distillation. This is because the vapor composition to be produced hardly changes, and the specific volatility corresponding to ethanol of water is almost 1, and therefore, in the case of ethanol, practically no concentration can be achieved by binary distillation.

Therefore, in the ethanol production industry,
In the case of producing anhydrous ethanol having a low water content of 99.5% by weight or more, at present, a ternary azeotropic distillation method using an azeotropic agent is still employed. However,
In the ternary azeotropic distillation method, in designing the azeotropic distillation column, the capacity of the azeotropic distillation column (column diameter, column height, stage interval) is designed and manufactured with more margin than in the case of ordinary distillation column design. Therefore, the azeotropic distillation column has a drawback that the size and the construction cost increase. As described above, none of the conventional methods for producing anhydrous ethanol are still sufficiently satisfactory in terms of productivity, equipment construction cost, production cost, and the like.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has a low cost of equipment construction, meets the demand for energy saving, and has high productivity and large-scale production. It is an object of the present invention to provide a method for producing anhydrous ethanol having a low water content, which is also suitable for:

[0008]

Means for Solving the Problems The inventors of the present invention have studied in detail the chemical engineering reasons why the capacity of the azeotropic distillation column in the design of a ternary azeotropic distillation column using an azeotropic agent must be large. As a result, during the dehydration of ethanol, a remarkable bubbling phenomenon appeared near the raw material-containing ethanol supply stage of the ternary azeotropic distillation column, and it was found that this was the reason for increasing the capacity of the distillation column. As a method of suppressing this foaming, it is conceivable to inject an antifoaming agent, but since the product anhydrous ethanol is contaminated by the antifoaming agent, it cannot be used at all. Therefore, after various explorations, the size of foaming is related to the amount of water, especially the concentration of the raw water-containing ethanol at 95.5% by weight.
At the following feed concentrations, bubbling increased sharply, disturbing the balance in the distillation column.
Focusing on energy savings up to 9.0% by weight, it is possible to carry out energy saving and industrially without hindrance. By using the membrane separation method and the ternary azeotropic distillation method together, the construction cost is low and the demand for energy saving is required. It has been found that anhydrous ethanol having high productivity and low water content can be easily produced, and the present invention has been achieved.

That is, the present invention provides a method for producing anhydrous ethanol by concentrating aqueous ethanol having an azeotropic composition close to the azeotropic composition, wherein the aqueous ethanol is subjected to a membrane separation method using a water selective permeable membrane to have an ethanol concentration of 95.5% by weight or more. It is concentrated to less than 99.0% by weight, and the concentrated ethanol is further concentrated by a ternary azeotropic distillation method using an azeotropic distillation column, and the ethanol concentration is higher than 99.5% by weight, preferably 99.8%. It is characterized in that absolute ethanol is obtained in an amount of at least% by weight.

Next, the method for producing anhydrous ethanol of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing an example of the present invention. The raw water-containing ethanol near the azeotropic composition is introduced from the line 1, and the heat exchanger E1 and the heater E2
, And is supplied to the membrane module M. As hydrous ethanol near the azeotropic composition used in the present invention,
Hydrous ethanol having an ethanol concentration of 80.0% by weight or more and less than 95.3% by weight, preferably 90.0% by weight or more and less than 95.3% by weight is suitably used. These raw materials are
Generally, fuel grade or reagent grade hydrous ethanol concentrated by distillation is preferably used. Of course, a recently developed membrane separation method such as a membrane separation method using an ethanol selective permeable membrane or aqueous ethanol concentrated by a membrane distillation method may be used.

When the membrane module M is a pervaporation method, the aqueous ethanol is supplied as a heated liquid,
When the membrane module M is of a vapor-permeation method, it is supplied with heated steam. As the membrane module M, a series or parallel multistage membrane module is used depending on a desired degree of concentration.

The supplied aqueous ethanol is supplied to the membrane module M at an ethanol concentration of 95.5% by weight or more and 99.0% or more.
And less than 96.0% by weight to less than 98.5% by weight, and the ternary azeotropic distillation column T
1 Supply to the middle stage. If the concentration of ethanol supplied to the ternary azeotropic distillation column is less than 95.5% by weight, the required membrane area of the membrane module can be reduced, and the equipment cost of the membrane module is reduced accordingly. Since the bubbling near the supply stage of the component azeotropic distillation column becomes intense, the balance in the column is lost, and the desired anhydrous ethanol cannot be obtained. Since it is necessary to provide a boiling distillation column, the process does not end up being an inexpensive and energy-saving process, and the object of the present invention cannot be achieved. On the other hand, if the concentration of ethanol supplied to the ternary azeotropic distillation column is 99.0% by weight or more, the required membrane area of the membrane module becomes enormous, and there is no economical efficiency. .

The ethanol supplied to the ternary azeotropic distillation column may be supplied to the ternary azeotropic distillation column after heat recovery using a heat exchanger if necessary. Water vapor is mainly separated on the secondary side of the membrane module M which is depressurized by the vacuum pump P. The vapor separated on the secondary side is cooled and liquefied in a condenser E3 through a line 3, collected in a permeate tank D1 and extracted from a line 4. Since a small amount of ethanol is contained in the permeate, the permeate is supplied to the recovery tower T2 or the decanter D2, and the ethanol is recovered. Of course, it may be recovered by a distillation apparatus or the like (not shown) for producing the raw water-containing ethanol supplied from the line 1. The method for recovering these ethanols is not particularly limited. The azeotropic agent is supplied from line 9 by decanter D
2. It is fed together with the reflux liquid to the top of the ternary azeotropic distillation column T1 through the line 6 to form an ethanol / water / azeotrope ternary azeotropic mixture at the top of T1. The azeotropic agent, for example, benzene, cyclohexane, methylcyclohexane, normal hexane, normal pentane, toluene,
Diethyl ether, methyl tertiary butyl ether and the like are preferably used. In the present invention, the azeotropic agent is not particularly limited.

The ternary azeotrope vapor at the top of the ternary azeotropic distillation column T1 is withdrawn from the line 5 and the condenser E5
And liquefied, and guided to the decanter D2. The organic layer (upper layer) and the aqueous layer (lower layer) are separated by the decanter D2, and the upper layer is refluxed through the line 6 to the top of T1. Depending on the type of the azeotropic agent, a part of the upper layer may be returned to the T1 raw material supply stage. The lower layer is led from line 8 to the middle stage of the recovery tower T2. Depending on the type of the azeotropic agent, a part of the lower layer may be refluxed from the line 7 to the top of the T1 column in order to stabilize the composition distribution in the T1 column. In the present invention, the method of extracting the upper layer and the lower layer of D2 is not particularly limited.

The bottom liquid of the ternary azeotropic distillation column T1 is heated and evaporated in a reboiler E4 to concentrate ethanol. T
1) A part of the bottom liquid is recovered from the line 10 by the heat exchanger E1 and, if necessary, cooled by a cooler (not shown).
A concentration of more than 5% by weight, preferably more than 99.8% by weight, of the product absolute ethanol is drained. The lower layer liquid of the decanter D2 led to the recovery tower T2 is concentrated at the top of the T2 column with the azeotropic agent and ethanol, cooled and liquefied from the line 11 by the condenser E6, and refluxed to the top of the T2 tower. Ethanol at the top of T2
When forming a ternary azeotrope of water / azeotrope,
A portion of the T2 overhead mixture is introduced from line 12 through condenser E5 to decanter D2. Depending on the type of the azeotropic agent, the T2 overhead mixture may become rich in ethanol. In such a case, the mixture is withdrawn from the line 13 and introduced into the T1 supply line 2. In the present invention, the method of extracting the T2 overhead mixture is not particularly limited.

Steam is directly blown from the line 14 into the bottom liquid of the recovery tower T2 to heat and evaporate it, thereby concentrating water at the bottom of the T2 tower. The method of heating the bottom liquid of the T2 column can also be performed by using a reboiler, but is not particularly limited in the present invention. The T2 bottom liquid is withdrawn from line 15 and discharged.
Depending on the type of the azeotropic agent, the T2 bottom liquid may be an aqueous ethanol solution containing no azeotropic agent. in this case,
Ethanol may be recovered by a distillation apparatus or the like for producing raw water-containing ethanol. In the present invention, the method for collecting the T2 bottom liquid is not particularly limited.

[0017]

Next, an embodiment of the present invention will be described with reference to the drawings. Hydrous ethanol having an ethanol concentration of 94.0% by weight was supplied from the line 1 through the heat exchanger E1 and the heater E2 to the primary side of the membrane module M composed of 450 m ^{2 of the} polyvinyl alcohol-based water selective permeable membrane at a temperature of 95 ° C. for 438.
It was fed at 1 kg / h and concentrated to an ethanol concentration of 97.0% by weight. At this time, the amount of steam used for heating in the pervaporation was 687 kg / h. Membrane module M reduced in pressure to 15 mmHg by vacuum pump P
The vapor mainly composed of water permeated to the secondary side of the above was cooled and liquefied in the condenser E3, and was collected and collected in the permeated liquid drum D1. The ethanol concentration in the permeate was 3.21
% By weight and the permeation amount was 140.3 kg / h.

4240.7 kg of water-containing ethanol having an ethanol concentration of 97.0% by weight, which had flowed out of the primary side of the membrane module M, was fed from line 2 to the middle stage of an azeotropic distillation column T1 in which normal pentane had been previously charged from line 9. / H. 2.0kg / c pressure in reboiler E4 of T1
m ² G steam was supplied at 2451 kg / h to form a ternary azeotropic mixture vapor of ethanol / water / normal pentane at the top of T1. The azeotropic mixture vapor was introduced from line 5 to the condenser E5. After cooling, the mixture was led to a decanter D2 and separated into a normal pentane layer (upper layer) and an aqueous layer (lower layer). The entire upper layer liquid was refluxed from line 6 to the top of T1.
The lower layer liquid was supplied from line 8 to a recovery tower T2. The composition of the lower layer liquid was 62.04% by weight of ethanol, 33.13% by weight of water, and 4.83% by weight of normal pentane. T1
The bottom liquid was withdrawn from the line 10, cooled in the heat exchanger E1, and then discharged at 3777.6 kg / h as a product absolute ethanol having an ethanol concentration of 99.98% by weight.

At the bottom of the recovery tower T2, a pressure of 2.0 kg / c
m ² G steam was blown directly from line 14 at 67 kg / h and heated to form a ternary azeotropic mixture of ethanol / water / normal pentane at the top of T2 column, and the mixture vapor was condensed through line 11 Cooled in vessel E6 and T2
Refluxed to the top. Part of the T2 overhead vapor was introduced from line 12 to decanter D2 via condenser E5. T2
The bottom liquid was collected as an aqueous solution having an ethanol concentration of 55.03% by weight, flowing out from the line 15 at 430.1 kg / h.

In this operating state, the liquid in the azeotropic distillation column T1 was sampled, and the height of the foam formed was measured using a foaming tester. The measurement results are shown in Table 1 below. From this foam height, even if T1 is 97.0% by weight of ethanol, which is twice the amount of the normal ethanol ternary azeotropic distillation method, the foam height in the supply stage can be stably operated in the main distillation column. 3
It was found from the fact that there was a margin of not more than 00 mm and the amount of reflux to the top of T1 that a sufficiently stable operation was possible. At this time, the steam basic unit was 0.65 tons / kl, and the steam usage was reduced by 38% or more compared to Comparative Example 1 described later.

[0021]

Comparative Example 1 Hydrous ethanol was concentrated using only the ternary azeotropic distillation system used in the examples. Water-containing ethanol having an ethanol concentration of 94.0% by weight was added to line 1
Was supplied to the middle stage of the azeotropic distillation column T1 at 4381 kg / h via a heat exchanger E1 and a bypass line 16. T1
Steam at a pressure of 2.0 kg / cm ² G was supplied to the reboiler E4 at the bottom of the tower at 4740 kg / h to heat the T1 bottom liquid, and ethanol / water / normal pentane was added to the T1 top in the same manner as in the example. A component azeotrope was formed. T1
The bottom liquid was withdrawn from the line 10, cooled in the heat exchanger E1, and then discharged at 3630.3 kg / h as a product absolute ethanol having an ethanol concentration of 99.98% by weight.

A pressure of 2.0 kg / cm is applied to the bottom of the recovery tower T2.
The steam of ² G, directly from line 14 140kg / h
To form a ternary azeotropic mixture vapor of ethanol / water / normal pentane at the top of the T2 column, and the mixture vapor is cooled in the condenser E6 through the line 11;
Refluxed to the top of T2. Part of the T2 overhead vapor was introduced from line 12 to decanter D2 via condenser E5. The T2 column bottom liquid was collected as an aqueous solution of ethanol concentration of 54.81% by weight, which was discharged from the line 15 at 890.7 kg / h.

In the same manner as in the example, the liquid in the column at T1 was sampled in this operating condition, and the height of the foam formed was measured using a foaming tester. The results are shown in Table 1 below. From the foam height, it was found that the foam height in the supply stage was 290 mm, which is close to 300 mm at which the present distillation column can be stably operated, and that the apparatus capacity is almost full. At this time, the steam intensity was 1.06 tons / kl.

[0024]

[Table-1]

[0025]

Comparative Example 2 Hydrous ethanol was concentrated using only the pervaporation system used in the examples. Hydrous ethanol having an ethanol concentration of 94.0% by weight was supplied from line 1 through a heat exchanger E1 and a heater E2 to 450 m ^2.
Was supplied to the primary side of a membrane module M comprising a water selective permeable membrane. The effluent on the primary side of the membrane module M passed through the bypass line 17 and was heat-exchanged with the feed liquid in the heat exchanger E1, and was discharged as product anhydrous ethanol. Only when the supply amount of hydrated ethanol is reduced to 455 kg / h, is the absolute ethanol having a concentration of 99.98% by weight of 42
It was obtained at 4.9 kg / h. 30.1 kg of permeate having a concentration of 9.63% by weight on the secondary side of the membrane module
/ H. Pressure required for heating 2.0 kg / cm ² G
The steam consumption was 263 kg / h and the steam intensity was 0.50 ton / kl, but the production capacity of absolute ethanol was 11% of that of the example. In order to maintain the same production capacity as in the embodiment, the required membrane area of the membrane module needs to be about 4100 m ^2, and it is necessary to add 9.1 times more membrane modules than in the embodiment.

[0026]

According to the present invention, the foam height can be significantly reduced as compared with the conventional method for producing ethyl alcohol by the ternary azeotropic distillation method, so that the existing azeotropic distillation apparatus can be eliminated. In addition, the treatment capacity can be doubled with effective use, and a large amount of anhydrous ethanol having a low water content can be easily obtained.
The construction cost can be reduced to about 0 to 1/5, and the steam intensity can be reduced to about 1/2 to 2/3 compared to the conventional three-component azeotropic distillation method of ethyl alcohol. It has a remarkably remarkable effect as compared with a conventional method for producing this kind of anhydrous ethanol, such as a low cost.

[0027]

[Brief description of the drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 is an XY diagram of an alcohol / water system.

Claims (3)

(57) [Claims] 1. A method for producing anhydrous ethanol by concentrating water-containing ethanol having an azeotropic composition close to the azeotropic composition, wherein said water-containing ethanol is subjected to a membrane separation method using a water selective permeable membrane to have an ethanol concentration of 95.5% by weight or more and 99.0% by weight. % And then the concentrated ethanol is further concentrated by a ternary azeotropic distillation method using an azeotropic distillation column to obtain absolute ethanol having an ethanol concentration higher than 99.5% by weight. A method for producing absolute ethanol. 2. The concentration of the obtained absolute ethanol is 9
The production method according to claim 1, wherein the content is 9.8% by weight or more. 3. An ethanol concentration for concentration by the membrane separation method.
Is less than 96.0% by weight and less than 98.5% by weight.
3. The production method according to claim 1 or 2.