JP2003135090A - Method and apparatus for producing high concentration ethanol by fermentation by pervaporation using silicalite membrane coated with silicon rubber - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To use fermented ethanol produced by yeast using sugars such as glucose as a raw material as an energy resource to replace fossil resources, it can be integrated with a fermentation system, and in parallel Provided is a method for producing high-concentration ethanol by a pervaporation separation method capable of separation and concentration. SOLUTION: By modifying the surface of silicalite, which does not contain alumina in the crystal structure and has a very high hydrophobicity, with a hydrophobic silicon rubber, a medium containing hydrophilic organic acids coexists. This is a method of selectively separating and concentrating ethanol to produce high-concentration ethanol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fermentation high-concentration ethanol production apparatus by a pervaporation method using a silica rubber membrane coated with silicon rubber.

[0002]

2. Description of the Related Art Energy production systems that depend on fossil fuels up to now continue to bring about an increase in greenhouse gases such as carbon dioxide on the earth. On the other hand, not only in Japan but also on the earth, biomass, which is an unused biological organic resource such as plants, is abundant and continues to be accumulated every year. Since plants absorb carbon dioxide, utilizing biomass as an energy resource can balance the carbon cycle on the earth and reduce the amount of fossil resources used, resulting in the reduction of greenhouse gases. Therefore, various developments are being actively promoted.

Energy resources obtained from biomass include methane gas, hydrogen gas, ethanol, butanol and the like. Among them, ethanol, which can be produced by fermentation reaction with microorganisms such as yeast at room temperature and atmospheric pressure, has a smaller amount of harmful substances in exhaust gas due to combustion as compared with gasoline, and is particularly useful as a liquid fuel alternative to petroleum. It is emphasized. However, since the concentration of ethanol produced by the fermentation method is as low as about 15%, a concentration step is indispensable in order to use it as a liquid fuel. A distillation method is generally used as a technique for this purpose. Furthermore, before concentrating dilute fermented ethanol by the distillation method, a solid-liquid separation step is required to remove yeast cells from the fermentation broth, and the distillation step requires about half the energy of ethanol produced. It is a process that consumes a lot of energy and is said to consume. Therefore, the competitiveness in production cost is very poor compared to petroleum, and biomass ethanol has not been put into practical use.

On the other hand, there is a method of concentrating fermented ethanol using a separation membrane as an alternative technique to the distillation method. The principle is as follows. By supplying the liquid mixture to one side through a separation membrane having selectivity for a specific substance and reducing the pressure on only the opposite (permeation) side, the vaporization of the liquid permeating through the membrane is facilitated. The method is to cool the vapor, liquefy it, and take it out. Instead of reducing the pressure on the permeate side, it is also possible to sweep vapor that evaporates from the film surface on the permeate side with an inert gas and guide it to a cooler to liquefy only the permeate vapor.
This method is a technique called pervaporation separation method.

In the pervaporation separation method, an alcohol aqueous solution (5 to 15% by weight) obtained by fermentation is subjected to a heat exchange operation on the supply side in a pervaporation apparatus provided with a pervaporation membrane,
Supply after heating. The heating temperature is determined by the type of alcohol. The alcohol pervaporated through the membrane is liquefied and taken out through the condenser on the permeate side of the membrane. The permeate side is kept under reduced pressure or vacuum by a pump. Such an operation is common (Japanese Patent Laid-Open Nos. 8-252434 and 8-252435). However, in such an operation, since the product is taken out from the reactor and then introduced into a newly installed pervaporation apparatus under a specific condition for processing, it is not rational from the viewpoint of the apparatus configuration. It is desirable that the obtained product can be concentrated with an alcohol-selective separation membrane without taking out the reaction product obtained in the reaction tank.

Conventionally, as alcohol separation membranes, separation membranes such as reverse osmosis membranes, hollow fiber membranes and pervaporation membranes have been known.
The material of the pervaporation separation membrane uses a membrane of a non-porous polymer compound, for example, polyolefin (JP-A-8-2
No. 52434), a silicone rubber film (JP-A-57-1).
No. 36905, Nomura et al., Proceedings of the 16th Autumn Meeting of the Chemical Engineering Society of Japan, p. 540 (1982)), poly (trimethylsilyl propane film) (JP-A-60-673).
No. 06), polyurea or polyamide membrane (Japanese Patent Laid-Open No. H5-
245345), perfluorinated olefin membranes (Japanese Patent Publication No. 2-502634), and the like are known. When these membranes are used, the ethanol obtained by the fermentation method is not effective because it is concentrated only to a concentration of about 20% to 30%. Also in the case of using these membranes, in any case, after the reaction product is taken out from the reaction tank, the product solution is permeated through the membrane to concentrate the solution (Japanese Patent Laid-Open No. 252434/1996).
JP-A-8-252435).

Dehydrated fermented ethanol using a porous water-selective permeable membrane such as A-type zeolite,
It is also possible to produce concentrated ethanol. However, in this method, not only co-existing substances such as organic acids and fermentation raw materials dissolved in the fermentation liquor are also concentrated, but also the activity of yeast, which controls the fermentation reaction, is significantly reduced due to the increase in ethanol concentration. There is a drawback that
Therefore, the method of preferentially permeating ethanol from the fermentation broth by the pervaporation separation method using a hydrophobic membrane and concentrating it is more advantageous when considering the combination with the fermentation reaction. it is conceivable that. Development of such a device is desired.

Silicalite, which is a kind of zeolite and does not contain alumina in its crystal structure, has a very high hydrophobicity and is a porous substance. With water and ethanol,
Since the latter is more hydrophobic, silicalite is considered to have a higher affinity for ethanol. Therefore, the present inventors considered that it is possible to concentrate a dilute ethanol solution to a high concentration and collect it by using a silicalite film. However, it has been found that when the concentration of fermented ethanol is actually continued by the permeation vaporization separation method using this silicalite membrane, the concentration of recovered concentrated ethanol decreases with time ( Biotechnology Techniques Vol 11. No1
2 p921-924, Biotechnology letters 2
1: 1037-1041). If this change over time can be prevented, ethanol can be concentrated and separated without taking out ethanol produced as the reaction proceeds as a product solution. In particular, when ethanol is produced by a fermentation method, energy for recovery can be saved and its industrial value is extremely high.

[0009]

The object of the present invention is to enhance the ethanol solution obtained by ethanol fermentation by permeating through the ethanol selective separation membrane to the concentrated portion of ethanol without recovery. It is to provide a method for producing a concentrated ethanol solution.

[0010]

[Means for Solving the Problems] The present inventors have proposed a fermentation tank for producing ethanol by fermentation from a sugar as a raw material, and supplying one of them through an ethanol-selective separation membrane. Production of high-concentration ethanol by dividing the other part into the concentrated part of ethanol and making the ethanol solution obtained in the ethanol manufacturing part permeate through the ethanol-selective separation membrane and lead to the concentrated part of ethanol. The inventors have completed the present invention by finding that they can be achieved.

In ethanol fermentation, theoretically, 2 mol of ethanol and 2 mol of carbon dioxide are produced from 1 mol of glucose which is a fermentation raw material, but actually, organic acids such as succinic acid and malic acid are also by-produced.

The present inventors have conducted various studies on the effect of coexisting substances in the fermentation liquid on the membrane separation performance in the concentration of fermented ethanol by the pervaporation separation method using a silicalite membrane, and as a result, accumulated in the medium. The organic acids, which are by-products of fermentation, cause the hydrophobic silicalite membrane to become hydrophilic, resulting in a decrease in ethanol selectivity.Therefore, the surface of the silicalite membrane was modified with a hydrophobic material. It was found that it is possible to prevent a decrease in ethanol selectivity when used as a product, and the present invention has been completed based on this finding.

That is, the following inventions are provided. (1) A fermenter that produces ethanol by ethanol fermentation from sugar as a raw material is used as a part for producing ethanol by fermentation of sugar that supplies one through an ethanol selective separation membrane, and the other one is concentrated as ethanol. A method for producing high-concentration ethanol, characterized in that the ethanol solution obtained in the ethanol production section is permeated through an ethanol-selective separation membrane and led to an ethanol concentration section. (2) The method for producing high-concentration ethanol according to (1) above, wherein the pressure in the ethanol concentrated portion is kept lower than that in the ethanol produced portion. (3) The method for producing high-concentration ethanol according to the above (1) or (2), characterized in that the ethanol permeating the ethanol-selective separation membrane is taken out in a gaseous state by a pervaporation method. (4) A method for producing high-concentration ethanol, wherein the ethanol-selective separation membrane according to any one of (1) to (3) above is a silicalite membrane coated with silicon rubber. (5) In a fermenter that produces ethanol by fermentation using sugar as a raw material, through an ethanol-selective separation membrane,
A high-concentration ethanol production apparatus, characterized in that one is used as an ethanol production part by fermentation of sugars and the other is used as an ethanol concentration part. (6) The apparatus for producing high-concentration ethanol according to claim 5, wherein the pressure in the ethanol concentrated portion is kept lower than that in the ethanol produced portion. (7) The high-concentration ethanol production apparatus as described in (5) or (6) above, which uses a pervaporation membrane in which ethanol permeating the ethanol-selective separation membrane is taken out in a gaseous state. (8) A high-concentration ethanol production apparatus, wherein the ethanol-selective separation membrane according to any one of (5) to (7) above is a silica rubber membrane coated with silicon rubber.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Carbohydrates, specifically, monosaccharides such as glucose, maltose and sucrose, disaccharides and polysaccharides are used as a fermentation raw material for ethanol fermentation of the present invention. These can also be used as products obtained by previously hydrolyzing cellulose, starch and the like. A medium is used for the fermentation reaction. As the medium, a medium containing the above-mentioned sugar, for example, glucose in a specific amount is used. Generally, an aqueous solution containing 10 to 30% by weight is used. Yeast is used to drive the fermentation. Then, for example, yeast extract, peptone, potassium phosphate, magnesium sulfate are added. These media are used for fermentation after autoclaving.

The present invention will be described with reference to FIG. The fermenter (1) is divided into an ethanol production part (3) by fermentation through the ethanol selective separation membrane (2), and the other part is divided into an ethanol concentration part (4). In the ethanol production part, fermentation is carried out using the medium. After injecting a sterilized medium, yeast is added and fermented. Alternatively, yeast is previously grown in this portion and then fermented. At this time, 10 ^{8 in} 1 ml of medium
It is desirable that the number of yeast cells is on the order of individual pieces. There are many types of yeast that produce ethanol by fermentation, and any of them can be used, but Saccharomyces cerevisi
It is common to use ae and Saccharomyces ubarum. In addition, bacteria and the like can also be used. Also,
The fermentation reaction is preferably performed in the range of 25 to 35 ° C,
The most preferable temperature is around 30 ° C. The fermentation reaction is performed under atmospheric pressure. The ethanol recovery part is placed in a reduced pressure state so as to generate a pressure difference. The pressure in the ethanol recovery section should be under reduced pressure, for example 400 Torr or less, and
Maintaining a vacuum of 0 torr, more preferably 10 torr or less is effective in taking out alcohol by membrane separation. The product obtained by fermentation contains by-products and bacterial cells in addition to ethanol, and these are removed when they interfere with the use of ethanol-selective separation membranes. . A filtration membrane or a microfiltration membrane is used for these treatments. Which membrane to choose
It is selected according to the object to be removed.

As a portion for concentrating ethanol, a portion of a tubular body provided through a membrane with respect to a portion for carrying out a fermentation reaction is used. The tubular body has a mechanism for keeping the internal pressure reduced or vacuumed. The alcohol-containing substance that has permeated the separation membrane can be taken out as a liquid or a gas, but as mentioned above, the substance can be taken out in a gas while keeping it at a low pressure, specifically, a substance that permeates the membrane. A pressure lower than the vapor pressure of is effective in terms of separation efficiency and permeability. Specifically, it is carried out by maintaining a vacuum to reduce the pressure, or by flowing an inert gas to reduce the vapor pressure.

In the present invention, an ethanol-selective separation membrane is used when the aqueous ethanol solution is concentrated. A conventionally known ethanol separation membrane can be used as the ethanol selective separation membrane. As a process using an ethanol-selective separation membrane, a method using a pervaporation membrane that concentrates and separates ethanol by utilizing vapor pressure difference is used. In the pervaporation membrane, a non-porous polymer compound membrane is used, for example, polyolefin membrane, silicone rubber membrane, polytrimethylsilylpropane membrane, polyvinyl alcohol membrane, polyurea or polyamide membrane, polyimide membrane,
Examples thereof include perfluorinated olefin film.
A silicalite membrane coated with silicone rubber is used as the ethanol selective separation membrane. The silicalite film is a film obtained by fixing silicalite on a porous sintered stainless steel substrate. The silicalite film is manufactured by a hydrothermal synthesis method. First, colloidal silica, an alkali metal hydroxide as an alkali metal source, and water are uniformly mixed to prepare an aqueous gel mixture. Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide and cesium hydroxide. Water is 30 to 1000 mol, preferably 50 to 250 mol, relative to 1 mol of silica. The ratio of colloidal silica and alkali metal is 0.1 mol of alkali metal hydroxide to 1 mol of silica.
The amount is 01 to 0.3 mol, preferably 0.1 to 0.15 mol. A crystallization modifier is added to the aqueous gel mixture. Tetrapropylammonium bromide, tetrabutylammonium bromide or the like is used as the crystallization modifier. The amount of the crystallization modifier used is 0.001 to 0.1 mol, preferably 0.002, relative to 1 mol of silica.
~ 0.01 mol. The aqueous gel mixture thus obtained is contacted with a carrier which has been previously coated with silica. Heat the aqueous gel mixture to prevent turbulence. The heating temperature is 80 to 250 ° C., preferably 1
It is 20 to 200 ° C. As a method for forming a silica film, a method for forming a silicalite film by one-time hydrothermal synthesis, a two-step method for forming a silicalite film by two hydrothermal synthesis reactions, and a seed crystal paste are used. There is a method to use.

The method of forming a silica film by one-time hydrothermal synthesis reaction is to form a silicalite film by one-time film formation. The specific conditions are as follows. Tetrapropylammonium bromide / SiO ₂ =
The values are 0.1, NaOH / SiO ₂ = 0.1, and H ₂ O / SiO ₂ = 60 to 90. The membrane obtained is washed with running water and dried at a temperature of 100 ° C. overnight.
300-40 in air to burn out template
The treatment is performed at 0 ° C. for 20 to 60 hours.

In the two-step method of forming a silica film by two hydrothermal synthesis reactions, in the first step, crystals are produced using a reaction solution having a high silica content, and then a reaction solution having a low silica content is used. Is used to perform a hydrothermal synthesis reaction at a temperature of about 170 ° C. to synthesize a membrane. Tetrapropylammonium bromide, the concentration of colloidal silica, caustic soda is the same as defined _above, carried out in a state silica content of H 2 O / _SiO 2 = 60 is large, _then, H 2 O / SiO
₂ = 90 or more The content is small. H ₂ O
With / SiO ₂ = 500, good results are obtained when it takes about 96 hours.

The method using a seed crystal paste is a method in which hydrothermal synthesis is performed using a substrate on which silicalite seed crystals (particle size: about 1 μm) are rubbed. H ₂ O / SiO ₂ =
It is desirable to set the value to about 300 to 700. Na
OH / SiO ₂ = 10, tetrapropylammonium bromide / SiO ₂ = 0.10, and a hydrothermal synthesis temperature of about 170 ° C. gives good results.

By using a porous substrate through which a gas or a liquid can easily pass as a carrier, it can be used as a gas or liquid separation membrane. The pore diameter is 1 μm or more, and usually in the range of 2 to 40 μm. The film is formed of silicalite, which has crystal growth in the form of an integral film having no grain interface.

The surface of the silicalite film thus obtained is coated with silicon rubber. Coating with silicone rubber is performed by immersing the silicalite film in a solution of silicone rubber. Examples of the silicone rubber include dimethyl silicone rubber, methyl vinyl silicone rubber, methyl phenyl silicone rubber and the like. These are crosslinked using a catalyst,
Alternatively, heat is applied to crosslink and then used. Better results can be obtained by heat-crosslinking. In the present invention, it is possible to obtain more effective results by using one having a larger molecular weight. Silicon rubber is generally used after being dissolved in a solvent. A non-polar solvent such as n-hexane or cyclohexane is used as the solvent. The concentration of the silicone rubber is appropriately adjusted according to the molecular weight of silicon and the like. A general concentration is 0.1 to 10%, preferably 1.0 to 5.0%. When the structure of the silicalite film coated with silicon rubber thus obtained was observed, the following differences were observed. FIG. 5 is a surface photograph of an untreated silicalite film and a silicalite film surface-treated with silicon rubber.

The surface of the silicalite film thus obtained is coated with silicon rubber, and the film is placed between the reaction part and the reaction product recovery part in the reaction tank. The membrane is attached and fixed to the support.

In the reaction part, ethanol starts to accumulate in the medium at the same time as the addition of yeast. It is desirable to start the pervaporative separation of ethanol when the concentration reaches about 3% by weight. That is, the vapor permeated through the membrane can be recovered as a liquid by a cold trap by reducing the pressure on the permeate side of the membrane. As described above, the ethanol fermentation process and the pervaporation separation process can be integrated and the processes can be performed in parallel. Depending on the performance of the silicalite membrane used, ethanol concentrated to 50 to 70% by weight can be stably produced from a fermentation broth containing 10% by weight or less of ethanol.

[0025]

EXAMPLES The present invention will be described in more detail with reference to examples. The invention is not limited to this example.

Example 1 Preparation of Silicone Rubber-Coated Silicalite Film A silicalite film was prepared on a porous sintered stainless steel substrate by a hydrothermal synthesis method according to a previous report. Next, silicone rubber against hexane solvent (manufactured by Shin-Etsu Chemical, high molecular weight K
5% by weight of E45) or 3% by weight of silicon rubber (manufactured by Shin-Etsu Chemical Co., Ltd., low molecular weight KE108) is uniformly dissolved, and then the stainless steel substrate side is coated with cellophane to coat only the surface of the silicalite film. Covered with tape, the silicalite film was dipped for 10 seconds. Then, it was air-dried (room temperature) for 2 days. Table 1 shows the separation performance of this silicalite membrane using an aqueous ethanol solution.

[0027]

[Table-1]

Example 2 The ethanol pervaporation separation reaction tank obtained by the fermentation method was divided into two parts, and a medium containing glucose as a fermentation raw material was placed in the reaction part, and a commercially available dried baker's yeast (Saccharomyces cerevisiae, Oriental Yeast Co., Ltd.) was added. Fermentation 30 ℃ (rotation speed of stirrer; 60
0 rpm), and after the lapse of 12 hours from the start of fermentation, through the membrane (high molecular weight type KE45, 5% by weight coating) prepared in Example 1, the reaction portion and the concentrating portion side on the opposite side through the membrane The vapor containing alcohol that had permeated under reduced pressure (10 torr) was collected by a cold trap using liquid nitrogen. This cold trap was replaced regularly. The glucose and ethanol concentrations in the medium were measured by high performance liquid chromatography (JASCO, 880-PU), differential refractometer detector (JASCO, RID-300), sphere O.
It was analyzed over time using an A KC column (manufactured by Cica-MERCK).
In addition, the analysis of the ethanol concentration in the recovered liquid that permeated the membrane was performed by gas chromatography with a thermal conductivity detector (GC-8A manufactured by Shimadzu Corporation), Thermon-1000 packed column (3.0 mm × 2
m) over time. FIG. 1 shows the time-dependent changes in the concentration of ethanol recovered by the pervaporation separation method in the fermentation in which 1.5 g of dried baker's yeast was added to 150 ml of a medium having a glucose concentration of 20% by weight. The maximum concentration of concentrated ethanol is 70.2% by weight, and 63.4% by weight at the end of fermentation when all the glucose in the medium has been consumed.
Met. The ethanol concentration in all the collected products was 67.4% by weight.

Example 3 Silicon rubber (manufactured by Shin-Etsu Chemical Co., Ltd., low molecular weight type KE108) was uniformly dissolved in hexane solvent to a concentration of 3% by weight, and then a stainless steel substrate was used to coat only the surface of the silicalite film. The side was covered with cellophane tape and the silicalite membrane was immersed for 10 seconds. Then, it was air-dried (room temperature) for 2 days. The separation performance of this silicalite membrane using an aqueous ethanol solution is shown in Table 1 above. An experiment was conducted in the same manner as in Example 2 except that a silicalite film coated with silicon rubber (manufactured by Shin-Etsu Chemical Co., Ltd., low molecular weight type KE108) was used in place of the silicalite film coated with silicon rubber used in Example 2. I went. As a result, as shown in FIG. 2, the maximum concentration of the obtained concentrated ethanol was 59.3% by weight, and it was 50.2% by weight at the end of fermentation. The ethanol concentration in all the collected products was 55.4% by weight.

Example 4 In order to repeatedly use the silicalite membrane coated with silicone rubber for the concentration of fermented ethanol, after the experiment of Example 2, the membrane surface was washed only with distilled water and then separated with an aqueous ethanol solution. It was confirmed that the performance was equivalent to that before fermentation. Next, the same experiment as in Example 2 was performed. As a result, as shown in FIG. 3, the maximum concentration of the obtained concentrated ethanol was 71.3% by weight, and 68.3% by weight at the end of fermentation. The ethanol concentration in all the recovered products was 69.7% by weight.

Comparative Example An experiment was conducted in the same manner as in Example 2 except that a silicalite film not coated with silicon rubber was used. As a result, as shown in FIG. 4, the maximum concentration of the obtained concentrated ethanol was 40.2% by weight, which was 24.3% by weight at the end of fermentation, which was 15 points or more lower. The concentration of ethanol in all collected products was 29.7.
% By weight.

[0032]

EFFECTS OF THE INVENTION According to the present invention, ethanol can be concentrated to a high concentration in parallel with the fermentation method using yeast and can be stably produced.

[Brief description of drawings]

FIG. 1 is a time-dependent change in the concentration of fermentation ethanol recovered by using a silicalite membrane coated with silicone rubber (manufactured by Shin-Etsu Chemical Co., Ltd., high molecular weight type KE45) as a separation membrane in Example 2.

FIG. 2 is a time-dependent change in the concentration of fermentation ethanol recovered by using a silicalite membrane coated with silicon rubber (manufactured by Shin-Etsu Chemical Co., Ltd., low molecular weight type KE108) as a separation membrane in Example 3.

FIG. 3 is a time-dependent change in the concentration of fermentation ethanol recovered by using a silicalite membrane coated with silicon rubber (manufactured by Shin-Etsu Chemical Co., Ltd., high molecular weight type KE45) as a separation membrane in Example 4.

FIG. 4 shows the time course of the concentration of fermentation ethanol recovered by using a silicalite membrane not coated with silicone rubber as a separation membrane in Comparative Example.

FIG. 5 is a diagram showing a state of a silicalite film and a silicalite film coated with silicon rubber.

FIG. 6 shows a device of the invention.

Continued front page    F term (reference) 4B029 AA02 BB07 CC01 DF05 DF07                       DG06 DG08 DG10                 4B064 AC03 CA06 CC08 CE06

Claims (8)

[Claims] 1. A fermenter for producing ethanol by ethanol fermentation from a sugar as a raw material is used as an ethanol production part by fermentation of a sugar to supply one through an ethanol selective separation membrane, and the other one is ethanol. Of the ethanol solution obtained in the ethanol production part.
A method for producing high-concentration ethanol, which comprises permeating through an ethanol-selective separation membrane and leading to a concentrated portion of ethanol. 2. The method for producing high-concentration ethanol according to claim 1, wherein the pressure in the ethanol-concentrating portion is kept lower than that in the ethanol-producing portion. 3. The method for producing high-concentration ethanol according to claim 1 or 2, wherein ethanol permeating the ethanol selective separation membrane is taken out in a gaseous state by a pervaporation method. 4. A method for producing high-concentration ethanol, wherein the ethanol-selective separation membrane according to claim 1 is a silicalite membrane coated with silicon rubber. 5. In a fermenter for producing ethanol by fermentation using sugar as a raw material, one is used as a part for producing ethanol by fermentation of sugar through an ethanol-selective separation membrane, and the other is used for ethanol production. A high-concentration ethanol production device characterized by being a concentrated portion. 6. The apparatus for producing high-concentration ethanol according to claim 5, wherein the pressure in the ethanol concentration portion is kept lower than that in the ethanol production portion. 7. The high-concentration ethanol production apparatus according to claim 5, wherein a pervaporation membrane is used, in which ethanol that permeates the ethanol separation membrane is taken out in a gaseous state. 8. An apparatus for producing high-concentration ethanol, wherein the ethanol-selective separation membrane according to any one of claims 5 to 7 is a silica rubber membrane coated with silicon rubber.