JPH0234329B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing anhydrous ethanol, more specifically, an economical method for producing anhydrous ethanol using a combination of distillation and pervaporation from an aqueous solution of ethanol with a water content higher than that of an azeotropic composition with water. , relates to a method for efficiently producing high quality absolute ethanol. Absolute ethanol is generally referred to as JIS-K.
-1505-54 or JIS-K-8101-61, refers to an ethanol content of 99.5% or more, but in the present invention it refers to a highly concentrated ethanol aqueous solution that does not have an azeotropic point. Anhydrous ethanol is used as a raw material for cosmetics, fuel, various chemicals, etc. Most of them are dilute aqueous ethanol solutions (for example, moromi) with a water content higher than the azeotropic composition with water.
It is produced by distillation method.

In this production method, the dilute aqueous ethanol solution is concentrated to near the azeotropic point of the ethanol/water system using a distillation column (mold tower or concentration column), and then dehydrated. There are methods such as dehydration using a dehydrating agent, dehydration by removing the azeotropic point by vacuum distillation, and dehydration by azeotropic distillation with the addition of an entrainer. However, the dehydration method using a dehydrating agent is not suitable for large-capacity processing due to its nature, and the dehydration method using vacuum distillation has the disadvantage of having to use low-temperature cooling water for condensation after distillation. Therefore, dehydration using an eletrainer is now common.

In this method using an entrainer, the dilute aqueous ethanol solution obtained by alcoholic fermentation, etc. is concentrated in a distillation column to near the azeotropic point of the ethanol/water system, and then fed to a dehydration column (azeotropic column). / Entrainer having the lowest azeotropic point in the ternary system (for example, the most commonly used one at present is benzene) is added, and this ternary system is azeotropically distilled, and the top of the dehydration tower is The azeotropic distillate is then coagulated and separated into an entrainer-rich layer and a water-rich layer by liquid-liquid equilibrium in a decanter, while the entrainer-rich layer is transferred to the dehydration tower. In this method, anhydrous ethanol is obtained from the bottom of the dehydration tower while the water-rich layer is treated in a recovery tower to recover entrainer.

However, the conventional method using this entrainer has the following drawbacks.

(1) Addition of entrainer, which is a third component other than the ethanol/water system, increases the size of the entire device, and the process is complicated due to the connection of a dehydration tower, decanter, recovery tower, etc.

(2) A large amount of extra thermal energy is required to azeotropically distill the ternary system of ethanol/water/entrainer and to recover the entrainer later.

(3) In the three-component system of ethanol/water/entrainer, selection of the entrainer having the lowest azeotropic point and adjustment of its usage amount are troublesome.

(4) There is a risk that entrainer, a third component, may be mixed into absolute ethanol, which poses a problem in relation to the intended use, especially if it is toxic.

In addition to the method described above, anhydrous ethanol can be produced by reducing the pressure in one of the two chambers of a cell divided by a polymer membrane, supplying a dilute aqueous ethanol solution to the high pressure side, and changing the pressure to the reduced pressure side by pervaporation. A method has also been proposed in which an aqueous ethanol solution with the same composition is generated and then the composition of the liquid in both chambers is further changed using separate distillation columns (Japanese Patent Application Laid-Open No. 1983-33279), but this method requires two or more distillation columns. There are many problems, such as the necessity of repeating distillation, and the complicated operation due to two systems of distillation.

The present invention provides an improved method for producing anhydrous ethanol that eliminates the above-mentioned drawbacks of conventional methods. that's all
The purpose is to concentrate it to less than 92.5% by weight, and then perform parvey evaporation as a means of dehydration. water/
At the azeotropic point of ethanol, the ethanol concentration is about 95% by weight, but the reason why it is kept at 89% by weight or more and less than 92.5% by weight is as follows. In other words, when purifying by distillation in a distillation column to near the azeotropic point, the number of stages required in the distillation column increases and the amount of reflux needs to be increased, resulting in higher equipment costs, but what is particularly noteworthy is the amount of steam used. On the other hand, unless it is concentrated to 89% by weight, the amount of ethanol with a high water content recovered in the parvey evaporation process will increase, which will place a burden on the distillation column. becomes.

Therefore, if the concentration of ethanol distilled in the distillation column is within the above range, the thermal energy (hereinafter referred to as It was discovered that this method minimizes the heat load (referred to as heat load) and is economical and effective.

Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 1 is a schematic process diagram of the present invention. For example, the ethanol concentration obtained by alcoholic fermentation is 5 to 15
A dilute ethanol aqueous solution (moromi) of about % by weight is passed through the distillation column 1, which includes the moromi column, which is the distillation column recovery section, and the concentration column, which is the distillation column concentration section, as in the conventional method, in the direction of arrow A. Continuously supplied. Steam is supplied to the bottom of the distillation column 1 in the direction of arrow B, and while the dilute ethanol aqueous solution is heated in the distillation column 1, the ethanol concentration is 89% by weight or more and 92.5%.
It is concentrated to an ethanol concentration of less than 90 to 91% by weight, and is distilled from the top of the column in the direction of arrow C. This distillate, which is water-containing ethanol, is condensed in a condenser 2, and a part of it is returned to the distillation column 1 in the direction of arrow D in a distribution device 3, while the rest is supplied to the primary side 4 of a cell 4. . The cell 4 is separated into two chambers, a primary side 4a and a secondary side 4b, by a non-porous, uniform polymer membrane 5, and the secondary side 4b has a condenser 6 and a vacuum tank 7.
A vacuum pump 8 connected to the primary side 4 via
It is maintained at a lower pressure than a. The concentrated ethanol aqueous solution supplied to the primary side 4a of the cell 4 according to the connecting mark E passes through the molecular membrane 5 and is subjected to parvey evaporation to form ethanol vapor with a high water content on the secondary side 4b. As a result of being discharged, it is relatively concentrated and is continuously taken out from the tip of the primary side 4a in the direction of arrow F as anhydrous ethanol having an ethanol concentration of approximately 95 to 99.5% by weight and having no azeotropic point. On the other hand, ethanol vapor with a high water content discharged to the secondary side 4b is condensed in a condenser 6, and is returned to the distillation column 1 in the direction of arrow H via a vacuum tank 7 by a pump 9.

That is, the present invention does not involve the complicated method of performing parve evaporation without prior concentration and then repeating distillation as in the conventional method, but instead uses the distillation column 1 to distill the ethanol/water system from 89% by weight or more to 92.5% by weight. This method converts an aqueous ethanol solution concentrated to less than % by weight into absolute ethanol in one step.

FIG. 2 is an enlarged schematic vertical cross-sectional view of the cell 4. As shown in FIG. A plurality of tubular polymer membranes 5 are fixed at both ends at intervals inside the cylindrical body 10, and the cell 4 is connected to the primary side 4 by the tubular polymer membranes 5 as described above.
It is separated into two chambers: a and a secondary side 4b. While the water-containing ethanol supplied in the direction of arrow E passes through the primary side 4a, which is the inside of the tubular polymer membrane 5, part of the material is transferred toward the secondary side 4b, which is indicated by the small arrow in the figure. The substance is transferred in the form of ethanol vapor with high moisture content through the tubular polymer membrane 5 by pervey evaporation, and is then discharged in the direction of arrow G. As a result, it becomes relatively concentrated, and eventually the cell Anhydrous ethanol is continuously obtained from the end of 4 in the direction of arrow F. At this time, the ethanol solution supplied to the cell 4 in the direction of arrow E should be, for example, in the form of ethanol-containing vapor, taking into consideration in advance the heat loss due to vaporization to the ethanol-containing vapor discharged to the secondary side 4b. is also possible.

Although a polymer membrane is used in the present invention, pervey separation itself using such a membrane has been known for a long time. The materials used for polymer membranes include polyethylene, polypropylene, polyamide, polyester, polystyrene, cellulose polymers, and copolymers of these. Some are aminated or sulfonated. After all, these polymer membranes have properties that are appropriately selected in consideration of separation coefficient, permeation rate, strength, durability, etc., and the polymer membrane 5 of the cell 4 used in the present invention The material is not particularly limited, and its shape is, for example, a tube shape in the case of FIG. It is.

As explained above, the present invention uses parvey evaporation as a dehydration means after moderately concentrating a dilute aqueous ethanol solution in a distillation column, without using an entrainer or other means. By using a compact, so-called one-step device that does not require many distillation columns, dehydration columns, recovery columns, etc., and does not require repeated distillation, ultimately the distillation column can achieve 89% by weight or more.92.5
By performing parvey evaporation of an ethanol aqueous solution concentrated to less than % by weight, the heat load on the distillation column is minimized, so it is economically efficient and energy-saving, and it also prevents entrainer contamination and its toxicity. This method has the effect of producing high-quality anhydrous ethanol without any problems.

Example According to the process diagram shown in Fig. 1 above, a dilute ethanol aqueous solution with an average ethanol concentration of 6.5% by weight obtained by alcohol fermentation was targeted, and a polyester tubular polymer membrane with a thickness of 50 μm and an effective membrane area of 150 m ² was built in. The experiment was carried out as follows using a cell.

While supplying steam at 108° C. from the bottom of the column, the dilute aqueous ethanol solution was continuously supplied to the distillation column, and 490 kg/hour of ethanol-containing vapor with an average ethanol concentration of 91% by weight was distilled from the top of the column. Next, this vapor was condensed in a condenser, and 330 kg/hour of this condensate was returned to the distillation column using a distribution device, while 160 kg/hour was supplied to the primary side of the cell. At this time, the secondary side of the cell was previously suctioned to an absolute pressure of 300 mmHg by a vacuum pump connected via a condenser and a vacuum tank, and the ethanol condensate supplied to the primary side was parveyed. Ethanol-containing vapor with an average ethanol concentration of 75% by weight is discharged from the secondary side, condensed in a condenser, and returned to the distillation column at 60 kg per hour via a vacuum tank, while Anhydrous ethanol with an ethanol concentration of 99.5% by weight from 100% per hour
Kg obtained continuously.

Next, in the same manner as above, the reflux rate was increased from the top of the column so that the average ethanol vapor concentration was 92.5% by weight and 94% by weight, and 99.5% by weight of anhydrous ethanol was fed from the end of the primary side at a rate of 100% per hour.
Kg obtained, the heat load on the distillation column was 1.2 times and 2.6 times, respectively, compared to when the average ethanol concentration was 91% by weight.

Furthermore, the average ethanol vapor concentration from the top of the column is 89
When anhydrous ethanol was obtained using the same method and conditions as above, except that the reflux amount was reduced so that the average ethanol concentration was 91% by weight, the heat load on the distillation column was 1.19 times that when the average ethanol concentration was 91% by weight. .

From the above results, the heat load on the distillation column is minimum when the average ethanol vapor concentration distilled from the top of the column is about 91% by weight, and the average ethanol vapor concentration is less than 89% by weight, less than 92.5% by weight, or more than 92.5% by weight. In this case, the heat load on the distillation column increases.

[Brief explanation of drawings]

FIG. 1 is a schematic process diagram of the present invention, and FIG. 2 is an enlarged schematic vertical cross-sectional view of a cell that can be used in the present invention. 1... Distillation column, 2, 6... Condenser, 3...
Distribution device, 4... Cell, 5... Polymer membrane, 7...
...Reduction tank, 8...Vacuum pump, 9...Pump, 4a...Primary side, 4b...Secondary side.

Claims (1)

[Claims] 1 In a method of producing anhydrous ethanol by concentrating an ethanol aqueous solution with a water content higher than the azeotropic composition with water, an ethanol aqueous solution that has been concentrated to 89% by weight or more and less than 92.5% by weight in a distillation column is divided into two chambers using a polymer membrane. On the one hand, ethanol vapor with a high water content is discharged to the secondary side by parvey separation, and is condensed and returned to the distillation column. A method for producing anhydrous ethanol, characterized in that anhydrous ethanol is obtained from the side end.