JP2005238032A - Membrane separation method for fermentation ethanol - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for directly and continuously producing a high concentration ethanol solution by a pervaporation separation method using an ethanol selective separation membrane in a method for obtaining a concentrated ethanol liquid from a diluted ethanol-containing fermentation solution. <P>SOLUTION: In the method, the concentrated ethanol liquid is produced from the diluted ethanol-containing fermentation solution by controlling pH within a range of 5 to neutrality and contacting it with the pervaporation separation membrane while controlling pH of the diluted ethanol-containing fermentation solution. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a method for membrane separation of fermented ethanol.

In the field of food, chemical industry, etc., the method of recovering and purifying target substances from multi-component systems in which multiple compounds coexist is an important separation and purification technique for taking out the final product, and various means have been adopted. It was.
Distillation is one of the methods widely used for recovery and purification of target substances. The distillation method is a method in which a solution of a substance is brought to its boiling point and components are separated by the difference in boiling points, and the advantage that reliable separation and purification of each component can be performed by the difference in boiling points is recognized as an effective separation means. It has been. In order to apply the distillation method, it is necessary to heat the target solution to be treated to the boiling point. This inevitably results in an energy intensive process.
The aqueous ethanol solution obtained by fermentation is obtained with a low ethanol concentration, but even in such a case, a distillation method has been adopted.
In addition, when an ethanol-water solution is concentrated by a normal distillation method, when the ethanol concentration is 95.6% by weight, the so-called azeotropic point is obtained, and as a result, the concentrations of the gas phase and the liquid phase coincide with each other. This is virtually impossible and limits appear in the concentration operation. In such a case, an azeotropic distillation method in which a substance such as benzene or cyclohexane is added to an ethanol-water system and distilled is used for further concentration and dehydration. If there is concern about air pollution or impact on the human body, the use of benzene is required to comply with strict environmental standards. Should be avoided.

  In consideration of these problems, in addition, when concentration of an aqueous ethanol solution is carried out by distillation, in an energy-intensive process that is said to consume about half the energy of ethanol produced. From the perspective of reducing the amount of energy required, it has been considered to develop a continuous process that avoids the distillation process.

As a method for taking out a specific component from a liquid mixture and separating and concentrating it, a method using a separation membrane other than the distillation method has attracted attention and is actually used industrially.
A method using a separation membrane has also been studied for selective separation and concentration of ethanol from an ethanol fermentation broth. Specifically, an aqueous solution (ethanol fermentation liquid) containing a specific substance to be treated (ethanol) produced by a microorganism such as yeast is supplied to one of the separation membranes having selectivity for ethanol, and the opposite (permeation) The ethanol selective hydrophobic permeable membrane which can take out the concentrated ethanol from the side) is utilized. At this time, an osmotic vaporization method in which the extraction side is kept at a reduced pressure is adopted, and as a separation membrane therefor, there is a method using a polyethylene, polypropylene, silicon rubber membrane (Patent Document 1), and polydimethylsiloxane or silicon rubber ( The use of non-patent document 1) is also well known.
In the case of using this separation membrane, the ethanol obtained by fermentation is concentrated to a concentration of about 20% to 30%. It has not become a thing. As an alcohol selective hydrophobic permeable membrane, a copolymer containing siloxane (Patent Document 2), and as a membrane having good alcohol permeability, a silyl compound polymer (Patent Document 3), substituted polyacetylene and polytrimethylvinylsilane are used. A method of recovering the performance of the separation membrane using the above membrane (Patent Document 4) is also known. Concentration of ethanol obtained by fermentation is not effective even when a membrane separation method is used, and the concentration is only concentrated to a concentration of about 20 to 30%.

As an alcohol selective hydrophobic permeable membrane, a vaporization method using a membrane in which zeolite is placed in a silicon rubber matrix (by a pervaporation separation method) (Patent Document 5) has also been proposed. However, even with this method, satisfactory results cannot be obtained because the silicone rubber matrix affects the separation performance.
Silicalite which does not contain alumina in a crystal structure which is a kind of zeolite has very high hydrophobicity and is a porous substance. Focusing on this point, the present inventors invented Patent Document 6 as silicalite. Furthermore, the use of metal, ceramics, etc. as a film support for these silicalites was also examined. In addition, a separation membrane (Patent Document 7) made of a hydrophobic inorganic material such as zeolite containing high silicon or silicalite on a support such as porous ceramics, porous glass, and porous sintered body is also known.
These membranes are expected to be effective membranes in terms of their separation performance. This zeolite membrane has a dense and porous structure, and in the case of water and ethanol, the latter is more hydrophobic, so it is considered that silicalite has a higher affinity for ethanol.
Therefore, by using an alcohol-selective hydrophobic permeable membrane, and among these, using a silicalite membrane, a dilute ethanol solution can be concentrated to a high concentration and recovered as a high concentration of ethanol. The present inventors considered that.
By the way, when the concentration of fermented ethanol was actually continued using this silicalite membrane by the pervaporation separation method, it was found that there was a problem that the recovered concentrated ethanol concentration decreased with time (non- Patent Document 2). When this cause is examined, substances such as by-products are gradually accumulated due to influences such as reaction conditions changing in the fermentation process, and the above-mentioned unfavorable results. It is thought that it becomes.

I tried to prevent this change over time.
One method is to coat the silicalite separation membrane surface, which is in direct contact with the fermentation broth, with hydrophobic silicone rubber, so that concentrated (permeation through the separation membrane) ethanol can be made to a high concentration. The effect which can reduce deterioration significantly is recognized (nonpatent literature 3). However, even in this method, the present situation is that the deterioration of the separation membrane performance cannot be completely avoided. Such a large decrease in membrane separation performance is considered to be caused by the adsorption of the organic acid produced as a by-product during the ethanol fermentation process on the silicalite membrane surface.
In addition, in the case of a zeolite having a crystal structure including an alumina structure, it is also known to treat the membrane with silane and silicate (Patent Document 8), but even this cannot be expected to have a sufficient effect.

Inhibitory factors that cause such a decrease in separation membrane performance were further investigated. If this inhibitory factor can be removed, it is considered that ethanol can be concentrated and separated if the ethanol-containing liquid produced with the progress of the fermentation reaction is continuously operated stably.

JP 57-136905 A JP 61-242603 JP-A 61-174905 JP 62-250907 A JP-A-63-1116705 JP-A-6-99044 JP 63-287504 A Special table 2000-508231 Nomura et al., Abstracts of the 16th Autumn Meeting of the Chemical Engineering Society, p.540, 1982 BiotechnologyTechniques, Vol. 11, p. 921-924, 1997; Biotechnology Letters, Vol. 21, p.1037-1041, 1999 J. Chem. Technol. Biotechnol., Vol. 78, p. 1006-1010, 2003 J. MembraneSci., 30, p. 273-287, 1987

    An object of the present invention is to obtain a concentrated ethanol solution from a dilute ethanol-containing fermentation solution without using a conventional distillation method that requires a large amount of energy, and a pervaporation separation method using an ethanol selective separation membrane. To provide a method for producing a high-concentration ethanol solution directly and continuously.

When the present inventors are premised on the use of a separation membrane, ethanol is more hydrophobic than water in the selective recovery (concentration) of ethanol from an ethanol / water system. It is indispensable to maintain hydrophobicity using a hydrophobic material, and even in this case, organic acids produced as a by-product by fermentation reaction or related substances are adsorbed on the separation membrane. In the case of continuous operation, it is considered that an undesirable result is obtained. It is considered that the organic acid may exist as an organic acid molecule (non-dissociation type) or an organic acid ion (dissociation type) depending on the degree of dissociation. The presence of organic acid molecules in the solution is considered to result in the performance of the separation membrane being lowered as a result of being adsorbed on the separation membrane. Therefore, if the organic acid is maintained in a dissociated state (ions), adsorption to the hydrophobic separation membrane can be reduced.

The state of dissociation of organic acid molecules was investigated based on the data for these weakly acidic succinic acid, malic acid, acetic acid, lactic acid, and citric acid that are by-produced by fermentation. The result is as shown in FIG.
As is clear from this result, the dissociation state of the organic acid depends on pH. If the pH is maintained in the range from 5 to neutral, the organic acid is present in a substantially dissociated state. Therefore, under such conditions, it was considered that adsorption of by-product substances hardly occurred on the hydrophobic separation membrane, and as a result, it was possible to prevent a decrease in separation performance.
As will be described later, an experimental result supporting this content was obtained, and the present inventors were convinced that the idea of the present inventors was not an error.

The present inventors contain specific organic acids in the ethanol-containing aqueous solution that has been subjected to fermentation, and the dissociation state of these organic acids can be changed by controlling the pH. By finding that the pH can be adjusted to a weakly acidic to neutral range, it is possible to prevent adsorption of organic acids in the treatment liquid to the hydrophobic separation membrane, and to prevent a decrease in the performance of the separation membrane. The present invention has been completed by finding that it is possible.

In the conventional membrane separation of fermented ethanol, the adjustment of the pH of the feed solution and the maintenance of the pH at a specific condition were not performed, considering the following. it is obvious.
In ethanol fermentation, it has been practiced to maintain the pH at about 4.0 as a fermentation condition (Separation and Purification Technology 27 (2002) 59-66).
In general, it is well known that the growth of microorganisms is suppressed in an environment having a lower pH, and the pH of the fermentation process is carried out under acidic conditions from the viewpoint of preventing contamination by bacteria in the ethanol fermentation process.
The above conditions are adopted in consideration of these matters. A membrane separation step is installed subsequent to this fermentation reaction step, and no special operation is performed when introducing the treatment liquid into this step. Eventually, the pH of the membrane separation step is about 4 which is close to this. It is done. In this case, it is clear from the above discussion that the organic acid will be present as a non-dissociated organic acid molecule. In this case, the organic acid is separated by the separation membrane. As a result, it is impossible to prevent deterioration of the film performance.

According to the present invention, the following inventions are provided.
(1) In a method of obtaining a concentrated ethanol-containing liquid by a permeation vapor separation membrane separation method by contacting a dilute ethanol-containing fermentation solution with an ethanol-selective hydrophobic permeation vaporization membrane, ethanol selective while controlling the pH of the dilute ethanol-containing fermentation broth A method for producing a concentrated ethanol solution from a dilute ethanol-containing fermentation solution, which comprises contacting with a hydrophobic pervaporation membrane.
(2) The diluted ethanol-containing fermentation solution according to (1), which is brought into contact with an ethanol-selective hydrophobic pervaporation membrane while controlling the pH of the diluted ethanol-containing fermentation broth within a range of 5 or more and neutral. A method for producing a concentrated ethanol solution.
(3) The diluted ethanol-containing fermentation solution according to (1), which is brought into contact with an ethanol-selective hydrophobic pervaporation membrane while controlling the pH of the diluted ethanol-containing fermentation solution within a range of 6 or more and neutral. A method for producing a concentrated ethanol solution.
(4) The pervaporation membrane separation method is a method in which a diluted ethanol-containing fermentation broth and a separation membrane are brought into contact with each other under atmospheric pressure, and ethanol and water are taken out as a gaseous mixture while maintaining the opposite side of the membrane at a reduced pressure. The method for producing a concentrated ethanol solution from the diluted ethanol-containing fermentation solution according to (1), wherein ethanol and water liquefied and concentrated by a cooler are collected thereafter.
(5) The method for producing a concentrated ethanol solution from a diluted ethanol-containing fermentation solution according to (1), wherein the ethanol selective hydrophobic pervaporation membrane is a silicalite membrane.

According to the present invention, ethanol that passes through an ethanol-selective hydrophobic permeation vaporization membrane is obtained by bringing a diluted ethanol-containing fermentation solution into contact with an ethanol-selective hydrophobic permeation vaporization membrane to obtain a concentrated ethanol solution by the pervaporation membrane separation method. Since the organic acid in the fermented treatment liquid is controlled by the pH value so that it is in a dissociated state, the organic acid does not adsorb to the separation membrane, so that ethanol concentration can be stably operated. As a result, the ethanol aqueous solution concentrated to a high concentration from the diluted ethanol aqueous solution obtained by the separation process fermentation can be stably and continuously recovered.
Further, since the organic acid molecules attached for some reason are led to dissociated organic acid ions when the pH is adjusted, the pervaporation membrane is regenerated as a result of desorption from the membrane. In this way, by adjusting the pH of the fermentation broth containing ethanol supplied to the separation membrane,
A concentrated ethanol solution can be produced stably.
Since membrane separation can be employed for the concentration of the ethanol solution obtained by the fermentation method, the distillation step can be eliminated, and a separation operation that does not require much energy is possible. Its industrial value is extremely high.

The feed solution in direct contact with the separation membrane used as an object of separation / purification in the present invention is a dilute ethanol-containing mixture obtained by a fermentation reaction with microorganisms.
For example, when ethanol is produced by a fermentation method, the ethanol concentration contained in the fermentation liquid is generally about 10 to 15%, and at most 20% or less. This contains microbial cells, water and various by-products.

In the present invention, a high-concentration ethanol aqueous solution is produced from the ethanol-containing aqueous solution to be treated.
In the present invention, the pervaporation membrane separation method, a method in which a dilute ethanol-containing fermentation broth and a separation membrane are brought into contact under atmospheric pressure, and ethanol and water are taken out as a gaseous mixture while maintaining the opposite side of the membrane at a reduced pressure. Is.
An ethanol-containing aqueous solution is supplied so as to come into contact with the ethanol-selective permeable membrane under atmospheric pressure, and the ethanol-selective permeable separation membrane is allowed to permeate in a state where the other side of the membrane is kept under reduced pressure. Since the permeation side of the separation membrane is maintained at a reduced pressure, ethanol and water are taken out as a gaseous mixture.
Thereafter, the gaseous mixture is led to a separate cooler, where the concentrated ethanol is liquefied and removed.
The shape of the ethanol selective permeable membrane is a flat plate shape or a cylindrical shape.
The state maintained at a reduced pressure is about 20 Torr to 1 Torr.
In order to reduce the pressure, a means for making a vacuum is employed. Specifically, a vacuum pump or the like is employed.
On the other hand, instead of reducing the pressure on the permeate side of the separation membrane, it is also possible to sweep the vapor evaporated from the permeate side membrane surface with an inert gas and guide it to the cooler to liquefy only the permeated vapor.

The present invention will be described with reference to FIG.
The ethanol pervaporation separation tank (1) (the separation tank 1 is composed of an ethanol supply liquid tank 2, an ethanol selective permeable separation membrane 3, and an ethanol recovery tank 4) is composed of an ethanol selective hydrophobic pervaporation membrane (3 ), One side is the feed liquid tank (2) where the fermentation broth containing ethanol is in contact with the separation membrane (3), and the other side is the separation membrane via the separation membrane (3). The permeation tank (4) is a part that preferentially permeates and collects ethanol vapor by concentration.
The ethanol supply liquid tank (2) is supplied with a fermentation liquid (5) containing ethanol from which fermentable microorganisms have been removed. Although it is possible to use a fermented liquid containing fermentable microorganisms as a supply liquid, from the viewpoint of preventing clogging of the ethanol selective hydrophobic pervaporation membrane (3), the fermentable microorganisms are removed in advance. It is necessary to keep.

In the ethanol fermentation broth, various organic acids such as succinic acid are generated as by-products other than ethanol, and they accumulate as the reaction proceeds, causing the pH of the fermentation broth to decrease. Further, since these are adsorbed on the separation membrane, it is considered that the separation performance is lowered when the fermented ethanol is concentrated and recovered by the pervaporation separation method.
It is thought that the degree of dissociation of these weakly acidic organic acids produced by fermentation, that is, the ratio of non-dissociated organic acid molecules and dissociated organic acid ions, will vary greatly depending on pH. That is, the change in pH in the ethanol fermentation liquid should be examined based on the degree of dissociation of the existing organic acid.
Therefore, the state of dissociation of organic acid molecules was investigated based on the data for succinic acid, malic acid, acetic acid, lactic acid, and citric acid. The result is as shown in FIG.

When water and ethanol are compared, it is natural that the latter is more hydrophobic. Therefore, in order to selectively recover ethanol by the separation membrane, the membrane is required to be hydrophobic.
Therefore, by maintaining the produced organic acid in an ionic dissociated state, adsorption to the hydrophobic separation membrane can be avoided, and the performance of the separation membrane can be maintained for the first time. It is considered possible.

Since the microbial cells responsible for ethanol fermentation and the separation membrane are physically unstable under alkaline solution, it is desirable to adjust the pH of the fermentation broth containing ethanol from weakly acidic to neutral. For this purpose, it is common to use 0.1 to 1M sodium hydroxide or potassium hydroxide as the alkaline aqueous solution.

The pH of the feed tank (2) should be controlled so as to contain ethanol that is subsequently adjusted to weakly acidic to neutral.
If the organic acid is maintained in a dissociated state (ions), the adsorption to the hydrophobic separation membrane can be reduced.
By adjusting the permeation vapor separation tank so as to meet the above-mentioned conditions, it is possible to avoid adsorption of organic acids to the ethanol selective hydrophobic permeation vaporization membrane, without reducing the performance of the separation membrane. , Can stably produce concentrated ethanol. In addition, even when the separation performance is reduced due to the adsorption of the organic acid to the ethanol selective hydrophobic pervaporation membrane, there is a method for washing the membrane surface with a neutral buffer solution under the above conditions. It can be said that it is effective. That is, the adsorbed organic acid molecule becomes dissociated and can be desorbed from the separation membrane.

  The ethanol-selective hydrophobic pervaporation membrane (3) includes a zeolite membrane or silicalite membrane supported on a known porous support, a silicalite membrane coated with silicon rubber, a known hydrophobic zeolite (inorganic). A separation membrane can be used. Examples include a membrane in which zeolite is contained in a silicon rubber matrix, ZMS-5, and a hydrophobic silicalite membrane developed by the present inventors. Furthermore, a film obtained by modifying the surface of these films with a hydrophobic material such as silicon rubber is also effective. Polyethylene, polypropylene, silicon rubber film, polydimethylsiloxane, silicon rubber, siloxane-containing copolymers, silyl compound polymers, substituted polyacetylene and polytrimethylvinylsilane films, and the like can be used.

The supply temperature of the ethanol fermentation liquid supplied to the main pervaporation separation tank is supplied at room temperature or about the reaction temperature of ethanol fermentation (25 to 35 ° C.). Even if the temperature is outside this range, it will not be served.

The fermentation liquor that cannot permeate the separation membrane is circulated and returned to the pervaporation separation tank or sent to a disposal step.

  The ethanol concentration finally recovered depends on the ethanol concentration in the supply liquid, the supply liquid temperature, and the performance of the ethanol selective permeable separation membrane (3) shown in FIG.

  As described above, a concentrated ethanol solution can be stably produced from an ethanol fermentation solution in which an organic acid coexists, using an ethanol selective permeable separation membrane.

EXAMPLES Next, the present invention will be described in further detail with reference to examples. The present invention is not limited by this example.

Example 1 Organic Acid Analysis of Ethanol Fermentation Solution Using glucose as a fermentation raw material, an 18% by weight glucose aqueous solution was autoclaved (121 ° C., 20 min), and then 150 ml was poured into a stainless steel container. 1.5 g of Saccharomyces cerevisiae (Oriental Yeast Industry) was added. Fermentation was performed at 30 ° C. (stirring speed: 600 rpm) and continued until all the glucose in the medium was consumed.
The organic acid composition in the obtained fermentation broth was analyzed by the bromthymol blue method using an organic acid analyzer (manufactured by Hitachi High-Technologies, L-7000 series). Hitachi gel C-610HS was used as the separation column, and UV-VIS detector (manufactured by Hitachi High-Technologies Corporation, model L-7420) was used as the detector.
The results are shown in Table 1.
The composition of the organic acids varies depending on the type of microorganism used for fermentation.
Further, in order to increase the concentration of ethanol produced, it is necessary to increase the concentration of sugar as a fermentation raw material. In such a case, the concentration of organic acids that are by-products also increases.

Example 2 Adsorption behavior of succinic acid on silicalite crystal particles 0.5g of silicalite powder crystals hydrothermally synthesized from colloidal silica, sodium hydroxide and tetrapropylammonium bromide and 0.3% by weight adjusted with 1M NaOH solution 5 ml of an aqueous succinic acid solution was injected into an L-shaped test tube with a sealed stopper. The concentration of succinic acid after shaking for 24 hours at 30 ° C. (50 rpm) was measured, and the amount of succinic acid adsorbed on the silicalite powder was calculated from the decreased amount.
The result is shown in FIG. As the pH of the aqueous succinic acid solution increased, the amount of adsorption decreased sharply and was hardly adsorbed when the pH of the aqueous solution was adjusted to neutral.

Example 3 Effect of pH of Succinic Acid Aqueous Solution on Ethanol Separation Performance of Silicalite Membrane As the ethanol selective membrane, a hydrophobic silicalite membrane which is a kind of zeolite and does not contain any alumina in the crystal structure was used. This film was hydrothermally synthesized on a porous sintered stainless steel substrate by adding an aqueous gel mixture composed of colloidal silica and alkali metal hydroxide prepared in advance at a predetermined concentration and a crystallization modifier. The effective membrane area is 12.6 cm ² . Details of the film forming method were in accordance with a known report (Desalination, Vol. 144, p. 47-52, 2002). A 5 wt% aqueous ethanol solution containing 0.3 wt% succinic acid was supplied to one side through the membrane (30 ° C.). A 1M NaOH solution was used to adjust the feed solution to a predetermined pH.
The other side of the membrane was evacuated. The vapor that permeated through the membrane was condensed by a cold trap using liquid nitrogen and recovered as a concentrated ethanol solution. Analysis of the ethanol concentration in the recovered liquid that permeated through the membrane was performed using a gas chromatography equipped with a thermal conductivity detector (GC-8A, manufactured by Shimadzu Corporation) and a Thermon-1000 packed column (Φ3 mm × 2 m).
The result is shown in FIG. Here, the measured value in the case of pH 7 shows the separation performance in an ethanol / water system not containing succinic acid. The membrane separation performance decreased as the pH of the ethanol feed solution decreased. The membrane permeation ethanol concentration at pH 3.2 was 25% by weight, and the membrane permeation amount was only 49 g / m ² · h. Compared with the separation performance at pH 7, these decreased by 43 points in the membrane permeation ethanol concentration and decreased to 10% in the membrane permeation amount.
However, the membrane permeation ethanol concentration in the range of pH 5-7 was almost constant, and the amount of membrane permeation also showed a high ratio of 70% in the case of pH 7 in the case of pH 6.
As described above, even when an aqueous ethanol solution having the same succinic acid content was used as the feed solution, the decrease in the separation membrane performance could be remarkably reduced by adjusting the pH to near neutral.

Example 4 Influence of pH of Succinic Acid Aqueous Solution on Ethanol Separation Performance of Silicone Rubber-Coated Silicalite Membrane A silicalite membrane whose membrane surface was coated with silicon rubber was used instead of the silicalite membrane used in Example 3. The experiment was performed in the same manner as in Example 3 except for the above.
Here, the silicone rubber coating was performed as follows.
After silicon rubber (manufactured by Shin-Etsu Chemical Co., Ltd., high molecular weight type KE45) is uniformly dissolved in hexane to 7% by weight, the stainless steel substrate side is covered with cellophane tape to coat only the surface of the silicalite film. The membrane was immersed for 10 seconds. Thereafter, it was dried at 40 ° C. overnight.
The result is shown in FIG.
Although the membrane separation performance decreased as the pH of the ethanol feed solution decreased, no decrease in the membrane permeation ethanol concentration at pH 5 was observed compared to the separation performance at pH 7, and the membrane permeation amount was also 85%. % Showed a high ratio.

Example 5 Effect of pH of Succinic Acid Aqueous Solution on Ethanol Separation Performance of Silicalite Membrane Coated with Silicon Rubber In place of silicon rubber (manufactured by Shin-Etsu Chemical Co., high molecular weight type KE45) used for coating in Example 4, silicone rubber ( The experiment was performed in the same manner as in Example 4 except that Shin-Etsu Chemical Co., Ltd., low molecular weight type KE108) was used.
The result is shown in FIG.
Although the membrane separation performance decreased as the pH of the ethanol feed solution decreased, the membrane permeation ethanol concentration at pH 5 was not decreased compared to the separation performance at pH 7, and the membrane permeation amount was also 86. % Showed a high ratio.

Example 6 Effect of pH of Succinic Acid Aqueous Solution on Ethanol Separation Performance of Silicalite Membrane Coated with Silicone Rubber A silicalite membrane coated in the same manner as in Example 5 was further treated with silicone rubber (Shin-Etsu Chemical Co., Ltd.) in the same manner as in Example 4. The experiment was carried out in the same manner as in Example 4 except that a silicalite membrane manufactured by high molecular weight type KE45) was used.
The result is shown in FIG.
When the ethanol supply solution had a pH of 5 or higher, almost no decrease was observed compared to the membrane separation performance in ethanol / water system (shown as pH 7 performance in FIG. 6). Even at pH 4, as compared with the separation performance at pH 7, no decrease in the membrane permeation ethanol concentration was observed, and the membrane permeation amount also showed a high ratio of 70% or more.

It is a figure which shows the structure of the ethanol selective hydrophobic pervaporation membrane separation process for implementing this invention. It is a figure which shows the adsorption | suction behavior of succinic acid to a silicalite crystal particle. It is a figure which shows the influence of pH of the succinic-acid aqueous solution on the ethanol separation performance of a silicalite membrane. It is a figure which shows the influence of pH of the succinic-acid aqueous solution on the ethanol separation performance of the silicalite membrane coated with silicon rubber. It is a figure which shows the influence of pH of the succinic-acid aqueous solution on the ethanol separation performance of the silicalite membrane coated with silicon rubber. It is a figure which shows the influence of pH of the succinic-acid aqueous solution on the ethanol separation performance of the silicalite membrane coated with silicon rubber. It is a figure which shows the dissociation state which changes according to pH of various organic acids.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pervaporation separation tank 2 Supply liquid tank 3 Ethanol selective hydrophobic pervaporation membrane 4 Permeation tank 5 Supply liquid 6 Ethanol selective hydrophobic pervaporation membrane permeation vapor

Claims (5)

In a method in which a diluted ethanol-containing fermentation solution is brought into contact with an ethanol-selective hydrophobic pervaporation membrane to obtain a concentrated ethanol solution by a permeation-vaporization membrane separation method, the solution is brought into contact with the pervaporation membrane while controlling the pH of the dilute ethanol-containing fermentation solution. A method for producing a concentrated ethanol solution from a dilute ethanol-containing fermentation solution. The method for producing a concentrated ethanol solution from a dilute ethanol-containing fermentation solution according to claim 1, wherein the pH of the dilute ethanol-containing fermentation broth is controlled to be within a range of 5 or more and neutral, and is brought into contact with the pervaporation membrane. . 2. The method for producing a concentrated ethanol solution from a dilute ethanol-containing fermentation solution according to claim 1, wherein the pH of the dilute ethanol-containing fermentation broth is brought into contact with the pervaporation membrane while controlling the pH within a range of 6 to neutral. The pervaporation membrane separation method is a method in which ethanol and water are taken out as a gaseous mixture in a state where the dilute ethanol-containing fermentation broth and the separation membrane are brought into contact under atmospheric pressure and the other side of the membrane is kept under reduced pressure. 2. The method for producing a concentrated ethanol solution from a dilute ethanol-containing fermentation solution according to claim 1, wherein the ethanol aqueous solution liquefied and concentrated by a cooler is then recovered. 2. The method for producing a concentrated ethanol solution from a diluted ethanol-containing fermentation solution according to claim 1, wherein the ethanol selective hydrophobic pervaporation membrane is a silicalite membrane.

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