JPS5871889A - Preparation of anhydrous ethanol - Google Patents

Abstract

PURPOSE:To improve the thermal efficiency in the preparation of anhydrous ethanol, by distilling and concentrating unrefined fermentation product in vacuum, adding an entrainer to the product, and distilling the mixture under pressure, wherein the vapor obtained from the top of the distillation column is used as a heat source. CONSTITUTION:The unrefined fermentation product is distilled and concentrated in the concentration column 12 under reduced pressure to obtain a composition near the azeotropic composition in an ethanol/water system. Toluene is added to the concentrate as an entrainer, and the mixture is distilled in the dehydration column 22 under pressure to separate anhydrous ethanol. The vapor obtained from the top of the dehydration column 22 is subjected to the heat exchange with the liquid contained in the concentration column 12 using the heat exchanger 33, and separated with a decanter 54 into the entrainer and water. The water-phase is sent to the concentration column 12 and the entrainer is introduced into the dehydration column 22. The objective anhydrous ethanol can be obtained from the bottom of the dehydration column 22.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a method for producing anhydrous ethanol by distillation from fermented mash obtained by alcoholic fermentation.

Anhydrous ethanol (JIS standard), which generally contains 99.5% by volume or more of ethanol, is widely used in pharmaceuticals, cosmetics, alcoholic beverages, etc., and has recently attracted attention as an energy source replacing petroleum.

Conventionally, many methods have been provided for producing such anhydrous ethanol, but most of them are methods for producing it by distillation from a dilute ethanol-containing material such as fermented mash obtained by alcoholic fermentation. In this conventional solution, the fermented mash is concentrated to near the azeotropic point of the ethanol/water system in a distillation column (a moromi column or a concentration column; hereinafter, this distillation column is collectively referred to as a concentration column), and the concentrated liquid is transferred to another distillation column. (Dehydration tower or azeotropic tower, hereinafter this distillation tower will be abbreviated as dehydration tower),
In the ternary system of ethanol/water/entrainer, azeotropic distillation is carried out with entrainer having the lowest azeotropic point (for example, benzene is commonly used at present), and the azeotropic distillate is extracted from the top of the dehydration column. After condensing the azeotropic distillate, it is separated into an entrainer-rich layer and a water-rich layer in liquid-liquid equilibrium, with the entrainer-rich layer being returned to the dehydration tower on the one hand, and the water-rich layer being returned to the dehydration tower on the other hand. The rich layer is further transferred to another distillation column (recovery column, in which case the above-mentioned concentration column may be substituted).
In this method, anhydrous ethanol is obtained from the bottom of the dehydration tower while recovering entrainer and ethanol.

However, such conventional methods have the following drawbacks. (1) The fermented mash obtained by alcoholic fermentation contains organic substances such as proteins, starches, sugars, etc., as well as inorganic substances such as calcium and magnesium. Contains a large amount of 9, and these adhere as strong schools to the inner surface of concentration towers (particularly moromi towers) and distillation shelves. As a result, pressure loss is large, efficiency is reduced, and in some cases, operation becomes impossible, forcing the extremely troublesome and time-consuming work of disassembling and cleaning the concentration tower.

(2) There are other impurities other than ethanol in the fermented moromi,
For example, it contains trace components such as fusel oil and fatty acid esters, and it is difficult to remove these impurities sufficiently in a concentrating column, so extra thermal energy is required for azeotropic distillation in a dehydration column. 0 (3) Since at least two distillation columns, a concentration column and a dehydration column, are used, a large amount of thermal energy is required for each.

In order to overcome these conventional drawbacks, the present invention operates the concentrator stage under reduced pressure and the dehydration tower stage under pressure, and uses the overhead vapor of the dehydration tower stage as a heating source for the concentrator stage. In particular, we will improve workability by preventing scale adhesion, improve the quality of anhydrous ethanol by sufficiently removing trace components, and save thermal energy by effectively using the steam at the top of the dehydration tower. The present invention provides an improved method for producing anhydrous ethanol.

By the way, recently, a new method for producing anhydrous ethanol has been proposed (Japanese Patent Application Laid-Open No. 16414/1983). This method also produces anhydrous ethanol by distillation from fermented mash, but at this time, a concentration column is used. One feature is that the dehydration tower is operated under pressurized pressure and the dehydration tower is operated under normal pressure. However, this method does not solve the conventional drawbacks (1) and (2), but rather tends to increase scale adhesion and difficulty in separating and separating trace components because the concentrating column is operated under pressure. Further, there are drawbacks such as the need to increase the reflux ratio in terms of gas-liquid equilibrium.

The present invention operates the concentrating column stage under reduced pressure and at a relatively low temperature, thereby reducing scale buildup on the concentrating column inner surface and distillation rack, improving the removal of trace components, and lowering the effluent temperature. By operating the dehydration tower stage under pressure, it is possible to facilitate condensation of distillate, for example, while additionally using the dehydration tower stage overhead vapor as a heating source for the concentrator stage. These ultimately result in significant thermal energy savings.

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

FIG. 1 is a schematic diagram of an anhydrous ethanol production process according to a conventional method. According to the arrow A, the fermented mash exchanges heat with the bottom bottom of the concentrator 11 in the heat exchanger 31, and is supplied to the concentrator 11, where it is concentrated to near the azeotropic composition, and is then released from the top of the column according to the arrow B. During this time, organic substances such as proteins and fats, and inorganic substances such as calcium and magnesium in the fermented mash are entrained with the bottom liquid from the bottom of the concentrating column 11, and are also concentrated. Organic substances mainly consisting of schifusel oil (having a boiling point intermediate between that of ethanol and high-boiling substances) are separated from the middle part of the column 11, and separated by a fusel oil separator 51. In the dehydration tower M1, a three-component azeotrope of jetanol/water/entrainer (general entrainer nibenzene is used) is distilled from the top of the tower, and this is converted into diene by liquid-liquid equilibrium in a decanter 52 via a condenser 42. It is separated into a trainer-rich layer and a water-rich layer, and the former is returned to the dehydration tower 21 according to the arrow C, and the latter is returned to the concentration tower 11 (a separate recovery tower may be used in some cases) according to the arrow. Anhydrous ethanol is obtained from the bottom of the dehydration tower 21 while the entrainer and ethanol are being recovered.

During this series of treatments, heating steam is supplied in accordance with arrow E1F.

However, as mentioned above, such conventional methods have various drawbacks. FIG. 2 is a schematic diagram of the process for producing anhydrous ethanol according to the present invention. Heat exchanger 3 for concentration tower 12 and dehydration tower 22
2. The flow using fusel oil separator 53 and condenser 43 is similar to the conventional method described above in this limit. However, in the case of the present invention, the concentration column 12 is operated under reduced pressure and the dehydration column 22 is operated under pressure, and the overhead vapor of the dehydration column 22 is
Accordingly, the liquid is exchanged with the liquid in the concentrating column 12 in the heat exchanger 33 and used as part of its heating source, and then supplied to the decanter 54, where it is separated into an entrainer-rich layer and a water-rich layer. The following items are returned and collected in the same manner as in the conventional method.

As mentioned above, the gist of the present invention is that the concentrator stage is operated under reduced pressure and the dehydration tower stage is operated under pressure, and the overhead vapor of the dehydration tower stage is used as a heating source for the concentrator stage. It is in.

First, the advantages of operating the concentration column stage under reduced pressure will be specifically explained. FIG. 3 is a schematic vapor-liquid equilibrium curve in the ethanol/water system. As a typical example, 760o+Hg
A vapor-liquid equilibrium curve 10 at 150 wHg and a vapor-liquid equilibrium curve 2o at 150 wHg are shown, but as shown in the figure, as the pressure decreases, the vapor-liquid equilibrium curve becomes farther away from the 45 degree diagonal. This means that the separation of ethanol and water becomes easier, but in reality, according to the present invention, it is sufficient to lower the reflux ratio from 4.0 to 8.0 in the conventional method. can be concentrated to the same concentration as conventional methods,
This also leads to a reduction in thermal energy.

Furthermore, regarding the separation of fusel oils, fatty acid esters, etc., it is already known that the degree of separation can be greatly improved by operating under reduced pressure (Japanese Patent Publication No. 38-4319). The chameleon value (a value used to measure organic matter in ethanol), which is about 5 minutes in the conventional method, can be increased to 10 minutes or more.

Furthermore, according to this report, by operating the concentration column stage under reduced pressure, the temperature inside the column can be lowered compared to the normal pressure operation in the conventional method.
The adhesion of scale is extremely reduced, and therefore workability is improved and stable operation can be achieved.

In addition, according to the present invention, the bottom temperature of the concentrating column can be lowered by reducing the pressure of the concentrating column, so that the steam at the top of the dehydration column can be used as a heating source. In other words, in the normal pressure operation of the conventional method, it is almost impossible to connect the heat exchanger 33 in FIG. According to the present invention, which can reduce the heat exchanger 33, the adhesion of such scale to the heat exchanger 33 becomes negligible, and it becomes possible to use the heat exchanger 33 by connecting the heat exchanger 33.

Next, the advantage of operating the dehydration tower stage under pressure higher than normal pressure is that as the internal pressure of the tower increases, the proportion of water in the azeotropic composition per unit increases. 1st
The table exemplifies the content of each azeotropic composition when benzene is used as an entrainer and the dehydration tower is operated under four types of pressure conditions.As is clear from this table, according to the present invention, The amount of steam at the top of the column required to obtain the same amount of dehydration can be reduced, and in this case, the reflux ratio can also be reduced as the pressure increases. According to the method, a reflux ratio of 8.0 becomes sufficient even with a reflux ratio of 2.5, which leads to a reduction in thermal energy.

Table 1 It is also found that when toluene is used as an entrainer, the azeotropic temperature becomes higher and the proportion of water in the azeotropic composition increases compared to when benzene is used. Ta. Table 2 exemplifies the content of each azeotrope when the dehydration tower is operated under three types of pressure conditions using toluene as an entrainer. As shown above, in order to obtain the same amount of dehydration, toluene requires less pressure in the dehydration tower than benzene, and since the unit price of toluene is about half that of benzene, it is inexpensive. It is also possible to produce anhydrous ethanol.Table 2 Finally, regarding the degree of thermal energy savings in the case of the present invention explained above, a comparative example in the case of the conventional method is targeted, and a specific example is shown. List.

・Example According to the anhydrous ethanol production process diagram in Figure 2 above,
Absolute ethanol was produced under the following conditions.

The raw material is 155% fermented moromi containing 8% ethanol by volume.
0kg/hour. The product is 100kgZ hour of anhydrous ethanol containing 99.5% ethanol by volume.

The operation of the concentration column is 140wHg at the top and 47℃, and 3℃ at the bottom.
5 (80°C at la + temperature, reflux ratio 3.0°) The operation of the dehydration tower is 3350WHg at the top and 101°C, and 3540w at the bottom.
Hgte 125℃0 entrainer is benzene.

・Comparative example According to the anhydrous ethanol production process diagram in Figure 1 above,
Absolute ethanol was produced under the following conditions.

The raw materials, products, and entrainer are the same as in the example. The concentration column is operated at 760°C at the top and 78°C at the bottom, and at 105°C at the bottom.
0 cod 7, 110℃, reflux ratio 4. The operation of the O0 dehydration tower is 760 m at the top of the tower (65 °C in g, 84 g at the bottom of the column at 950 m).
℃.

・Results In the case of the example, under the above conditions, a total of 245 kg/hour of steam was required in the concentration column, 110 kg/hour and 135 kg/hour in the dehydration column, but in the case of the comparative example, under the above conditions, 360 kg/hour of steam was required in the concentration column. total of 55 per hour and 190 to 9 per hour to the dehydration tower
0 kg/hour of steam was required.

Therefore, according to the present invention, it was possible to save more than 50% of steam in comparison with the conventional method. Distill under reduced pressure to concentrate to near the azeotropic composition of ethanol, then distill the concentrated liquid under pressure with an entrainer to create anhydrous ethanol! By using the distillation column top steam during this dehydration as a heating source for the concentration, workability is improved by preventing scale adhesion, ensuring stable operation, and sufficient removal of trace components. In addition to improving the quality of anhydrous ethanol, it is also effective to save thermal energy by effectively utilizing the steam at the top of the dehydration tower.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an anhydrous ethanol production process according to a conventional method, FIG. 2 is a schematic diagram of an anhydrous ethanol production process according to the present invention, and FIG. 3 is a schematic vapor-liquid equilibrium curve diagram of an ethanol/water system. 11.12...Concentration column, 21.22...Dehydration tower, 31.32.33...Heat exchanger, 41.42.43...Condenser, 51.53...Fusel oil separation Vessel, 52.54...
... Decanter, 10.20 ... Vapor-liquid equilibrium curve Figure 1 Figure 2

Claims (1)

[Claims] ■ In a method for producing anhydrous ethanol by distillation from a fermented mash obtained by alcoholic fermentation, the fermented mash is distilled under reduced pressure to concentrate it to an azeotropic composition close to that of ethanol, and then the concentrated liquid is A method for producing anhydrous ethanol, which comprises distilling ethanol under pressure with an entrainer to dehydrate it to anhydrous ethanol, and using the vapor at the top of the distillation column during this dehydration as a heating source for the concentration. 2 Claim 1 in which the entrainer is toluene
A method for producing anhydrous ethanol as described in Section 1.