JPS5948427A - Preparation of anhydrous ethanol - Google Patents

Abstract

PURPOSE:To prepare anhydrous ethanol, by concentrating an aqueous solution of ethanol having higher water-content than the azeotropic water/ethanol composition by a distillation column to obtain the azeotropic mixture, and feeding the mixture in a cell separated into two chambers with a polymer membrane, and dehydrating by pervaporation. CONSTITUTION:A dilute aqueous solution of ethanol having a concentration of about 5-15wt% is supplied through the line A to the distillation column 1, and concentrated to an ethanol concentration of about 89-93wt% by heating with steam supplied through the line B. The concentrated ethanol is distilled off from the top of the column, and transferred to the condenser 2 and the distribution apparatus 3. A part of the ethanol is recycled to the distillation column 1 and the rest part is supplied to the primary chamber 4a of the cell 4. Since the ethanol vapor having high water content is discharged through the polymer membrane 5 to the low-pressure primary chamber 4b, the concentrated ethanol is further concentrated to anhydrous ethanol having a concentration of 96-99.5wt% and free from azeotropic point and, the anhydrous ethanol is discharged continuously from the line F. The ethanol vapor discharged to the secondary chamber 4b is condensed by the condenser 6, and recycled to the distillation column 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing anhydrous ethanol, more specifically, a method for producing anhydrous ethanol, and more specifically, a method for producing anhydrous ethanol by distillation and pervaporation from an aqueous solution of ethanol with a water content higher than that of the azeotropic composition with water.
), it relates to a method for economically and efficiently producing high-quality absolute ethanol.

Absolute ethanol is generally defined as JIS-1505-
54 or JIS-8101-61, which refers to an ethanol content of 99.5 parts or more as specified in JIS-8101-61, is referred to as a high-concentration aqueous solution of ethanol* that does not have an azeotropic point in the present invention. Anhydrous ethanol is used as a raw material for cosmetics, fuel, various chemicals, etc. Most of them are produced by distillation from a dilute aqueous ethanol solution (for example, moromi) with a water content that is much higher than the azeotropic composition with water.

In this production method, the dilute aqueous ethanol liquid is concentrated in a distillation column (a moromi column or a concentration column) near the azeotropic point of the ethanol/water system, and then dehydrated. There are methods such as dehydration using a solid or liquid dehydrating agent, dehydration by removing the azeotropic point by vacuum distillation, and dehydration by entrainer distillation. However, the method of dehydrating with a dehydrating agent is not suitable for large volume treatment due to its nature, and the method of dehydrating with vacuum distillation has the disadvantage of having to use low-temperature cooling water for condensation after distillation. Therefore, dehydration using an elm trainer 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 near the azeotropic point of the ethanol/water system, and this is fed to a dehydration column (azeotropic column) to form an ethanol/water solution. % of entrainer having the lowest azeotropic point in the ternary system of entrainer (for example, benzene is currently most commonly used) is added, and this ternary system is azeotropically distilled, and the column of the dehydration column is An azeotropic distillate is distilled off from the top, and then this azeotropic distillate is coagulated and then separated in a decanter by liquid-liquid equilibrium into an entrainer-rich layer and a water-rich layer; In this method, the water-rich layer is returned to the dehydration tower, and the water-rich layer is treated in the recovery tower to recover entrainer, while anhydrous ethanol is obtained from the bottom of the dehydration tower.

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 apparatus, and the process is complicated due to the connection of a dehydration tower, a tecanter, a recovery tower, etc.

(2) A large amount of extra thermal energy is required to azeotropically distill the ethanol/water/entrainer ternary system 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, which is a third component, may be mixed into anhydrous ethanol, which poses a problem in relation to the intended use, especially if it is toxic.

In addition to the methods described above, methods for producing anhydrous ethanol include
One of the two chambers of the cell divided into chambers is reduced in pressure, a dilute ethanol aqueous solution is supplied to the high pressure side, and an ethanol aqueous solution with a different composition is generated on the reduced pressure side by pervaporation, and then the liquid composition in the compartment is A method has also been proposed in which the composition is further changed by using distillation columns on each side (Japanese Patent Laid-Open No. 54-332).
79) has many problems, such as the need for two or more distillation columns, the need to repeat 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 drawbacks of sloping in conventional methods. It is concentrated to 93% by weight 1, and then pervenihalation is performed as a means of dehydration.

At the water/ethanol azeotropic point, the ethanol concentration is about 96% by weight, but the reason why it is kept at 89-93% by weight is as follows. That is, when purified by distillation at 1 near the azeotropic point,
The number of stages required for the distillation column increases, the reflux amount needs to be increased, and therefore the equipment cost increases or the amount of steam used increases, resulting in high energy costs.
If it is not concentrated to 9%, the equipment on the pervaporation side will be too large, and the amount of ethanol with high water content recovered in the barvaporation process will increase, which will place a burden on the distillation side. Become. It has therefore been found that it is most economical and efficient to purify anhydrous ethanol if the concentration of ethanol by distillation is within the above range.

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

FIG. 1 is a schematic process diagram of the present invention. For example, if a dilute ethanol aqueous solution (moromi) obtained by alcoholic fermentation with an ethanol concentration of 5 to 15% by weight is prepared by following arrow A,
As in the conventional method, it is continuously supplied to the distillation column 1, which includes the mashing column which is the distillation column recovery section and the concentration column which is the distillation column concentrating section. Steam is supplied to the bottom of the distillation column 1 in the direction of arrow B, and the dilute ethanol aqueous solution is supplied to the bottom of the distillation column 1.
While being heated, the ethanol concentration of 89-93% by weight is concentrated to an ethanol concentration of 90-91% by weight, and distilled from the top of the column according to 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 the arrow in the distributing device 3, while the other part is supplied to the primary side 4a of the cell 4. The cell 4 is separated into two groups, a primary side 14n and a secondary side 4b, by a non-porous uniform polymer membrane 5.
The secondary side 4b is maintained at a lower pressure than the primary side 4a by a vacuum pump 8 connected through a condenser 6 and a vacuum pump 7. Primary side 4 of cell 4 according to arrow E
The concentrated ethanol aqueous solution supplied to a is relatively concentrated as a result of ethanol vapor having a high water content being discharged to the secondary side 4b through the polymer membrane 5 by the perpetuating layer. Anhydrous ethanol having an ethanol concentration of about 96 to 99.5 weight coefficient and having no azeotropic point is continuously taken out from the tip of the side 4a in the direction of arrow F. On the other hand, ethanol vapor with a high water content discharged to the secondary side 4b is condensed in a condenser 6, passed through a vacuum tank 7 to a pump 9, and returned to the distillation column 1 according to the arrow H.

That is, the present invention does not involve the complicated method of performing barbe evaporation without prior concentration and then repeating distillation as in the conventional method, but instead concentrates the ethanol/water system in the distillation column 1 to near the azeotropic point. This method converts aqueous ethanol solution into absolute ethanol in one step.

FIG. 2 is an enlarged schematic vertical cross-sectional view of the cell 4. As shown in FIG.

Inside the cylindrical body 10, a plurality of tubular polymer membranes 5 are fixed at both ends with a gap between them. (111
It is separated into two groups with 14b. According to the arrow EK, while the supplied water-containing ethanol passes through the primary side 4a, which is the inner side of the tubular polymer membrane 5, there is some mass transfer toward the secondary side 41) indicated by the small arrow in Figure 1. , mass transfer in the form of ethanol vapor with high water content through the tubular polymeric membrane 5, which is then discharged as a result of relative concentration, eventually. Absolute ethanol is continuously obtained from the end of cell 4 in the direction of arrow F. At this time, the ethanol solution may be supplied to the cell 4 according to arrow E in the form of, for example, ethanol-containing vapor, taking into consideration heat loss due to vaporization to the ethanol-containing vapor discharged to the secondary side 41]. It is rrJ Noh.

Although a polymer membrane is used in the present invention, pervey evacuation itself using such a membrane has been known for a long time. The polymer membrane materials used here include polyethylene, polypropylene, polyamide, polyester, polystyrene, cellulose polymer materials,
There are copolymers of Konera, and more recently, there are also copolymers in which part of the molecule is aminated or sulfonated. Ultimately, these polymer membranes have a separation coefficient, permeation rate of 1
The material of the polymer membrane 5 of the cell 4 used in the present invention is not particularly limited, and its properties are appropriately selected in consideration of strength, durability, etc., and its shape, shape, For example, in the case of FIG. 3, the shape is a tube, but there are also sheet shapes, hollow fiber shapes, etc., and such shapes can be selected as appropriate.

As explained above, the present invention employs pervey separation as a dehydration means after moderately concentrating a dilute aqueous ethanol solution using a distillation column. By using a miniaturized one-step device that does not require distillation columns, dehydration columns, recovery columns, etc., and does not require repeated distillation, the conditions are ultimately economically efficient and energy-saving. It is effective in producing high-quality anhydrous ethanol without the problem of contamination with entrainer or its toxicity.

EXAMPLE According to the process diagram shown in FIG. 1 above, a dilute ethanol aqueous solution obtained by alcohol fermentation with an average ethanol concentration of 65% and a thickness of 50μ and an effective membrane surface of 150% was used.
The experiment was carried out as follows using a cell containing a polyester tubular polymer membrane of No. 7722.

While supplying steam at 108° C. from the bottom of the column, the dilute aqueous ethanol solution I was continuously supplied to the distillation column, and ethanol-containing vapor with an average ethanol concentration of 91% by weight was distilled out from the top of the column at a rate of 490 Kf per 4 U (!''). Next, this vapor is condensed in a condenser, and the condensed liquid is returned to the distillation column at a rate of 330 Kq/hour through a distribution device, while 1 hour is sent to the primary side of the cell.
60 Kq was supplied. At this time, in advance, the secondary side of the cell is
The ethanol condensate supplied to the downstream side was evacuated by suctioning to an absolute pressure of 300 m+n Hg using a vacuum pump connected through a condenser and a 1L tank. Ethanol-containing vapor with an average ethanol concentration of 75 times the maximum is discharged from the secondary side, condensed in a condenser, and returned to the distillation column in an amount of 60 kg per hour via a vacuum tank. Anhydrous ethanol with an ethanol concentration of 99.5% by weight was continuously obtained from the end of the reactor at a rate of 100 Kr/hour.

[Brief explanation of the drawing]

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.
...Reducing pressure tank, 8...Vacuum pump, 9...Pump, 4a...-Next side, 4b...Secondary side. Patent applicant Showa Denko K.K. agent Patent attorney Sei Kikuchi

Claims (1)

[Claims] (1) In the 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 concentrated to 89 to 93 M in a distillation column is divided into two chambers using a polymer membrane. Supplies the primary side of the separated cells,
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, while on the other hand, anhydrous ethanol is obtained from the terminal of the secondary side. A method for producing anhydrous ethanol.