JPH0817711B2 - Method for separating and concentrating fermentation products - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for efficiently separating and concentrating a useful low boiling point fermentation product in a fermentation liquor by utilizing a hydrophobic non-porous membrane. This method can be effectively used, for example, in continuous fermentation to continue fermentation while efficiently extracting the fermentation product, which is an inhibitor of fermentation, out of the system.

[Conventional technology]

Conventionally, as a method of separating and concentrating the low boiling point fermentation product in the fermentation liquid, a method of distilling after removing yeast and the like in the fermentation liquid is generally carried out, but recently, the fermentation liquid is utilized with a reverse osmosis membrane. Are also being studied, and research is being conducted on separation and concentration methods such as pervaporation using membranes.

In the fermentation, when the fermentation is continuously carried out, the fermentation product accumulates in the system, which acts as an inhibitor of the fermentation and the fermentation cannot be continued. As a continuous fermentation method which avoids this, there is known a method in which a hydrophilic ultrafiltration membrane is used and the fermentation is continuously performed while the fermentation product is separated from the fermentation liquid in the fermentation tank by the membrane.

[Problems to be solved by the invention]

However, in order to separate and concentrate the low-boiling-point fermentation product in the fermentation liquid, in the conventional distillation method, after the removal step of yeast and the like, it is necessary to distill and concentrate from a low-concentration liquid, and the equipment is complicated. It had the drawback of becoming larger and consuming a lot of energy. In the reverse osmosis membrane method, the concentration limit for practical concentration is low, and for example, in the case of ethanol, the concentration is about 15%, which is not sufficient. In the pervaporation method, the low boiling point fermentation product is concentrated as a result of selective permeation of water, so a yeast removal step is required before the pervaporation method, and a large amount of water is separated. The energy loss for is also large.

Further, in the continuous fermentation method using the ultrafiltration membrane,
Raw material for fermentation when water and low-boiling fermentation products are taken out of the system,
For example, glucose and inorganic salts also come out of the system, and the fermentation products must be separated from each other, and those separated in this way are usually economically disadvantageous because they are discarded except for the fermentation products. There is a problem in that the fermentation raw material and inorganic salts must be replenished in the fermentation tank only by the amount lost.

The present inventors have conducted intensive studies to improve the drawbacks of the above method, and the fermented liquid itself does not allow the hydrophobic porous membrane to pass through the fermented liquid, but it utilizes the ability to pass steam through the hydrophobic porous membrane. Japanese Patent Application No. 60-39408 proposed a method for separating and concentrating a low boiling point fermentation product in the fermentation solution by contacting one side of the membrane with the fermentation solution and keeping the opposite side under reduced pressure. Although this method can efficiently separate and concentrate low-boiling fermentation products, if the method is continuously carried out for a long time as in the case of applying this method to continuous fermentation, the pores of the separation membrane gradually become hydrophilic. It has been found that there is a drawback that the fermentation liquid may leak out. Therefore, the present inventors have completed the present invention as a result of investigating the development of a method capable of continuously separating and concentrating a fermentation product for a long time without deteriorating the permeation performance of the separation membrane.

[Means for solving problems]

That is, the method for separating and concentrating the fermentation product of the present invention has a step of contacting one side of the hydrophobic non-porous membrane with the fermentation solution, and maintaining a reduced pressure on the side not contacting the fermentation solution of the non-porous membrane. Characterize.

[Preferred embodiment for carrying out the invention]

In the present invention, as the fermentation liquid to be separated and concentrated, in the vapor-liquid equilibrium relationship between the low boiling point fermentation product and water at the temperature during the separation and concentration, the vapor composition of the low boiling point fermentation product is more than the liquid composition in equilibrium. Any fermentation liquid may be used as long as it has a higher gas permeation rate than the fermentation product having a lower boiling point than that of water with respect to the hydrophobic non-porous membrane. In particular, ethanol fermentation liquid, acetone-butanol fermentation liquid, etc. can be effectively used.

For the hydrophobic non-porous membrane used in the method of the present invention, since the vapor permeation rate increases in inverse proportion to the membrane thickness,
It is preferable to use a thin film as long as the strength and the separation characteristics allow, and a film thickness of 80 μm or less is suitable. As the material of the film, various kinds of materials can be used as long as they are hydrophobic, and silicon rubber, polycarbonate, polyolefin, polyfluorinated olefin and the like are exemplified as typical ones. Further, even when the material forming the membrane is hydrophilic, any material having a hydrophobic surface can be used. The form of the membrane may be a flat membrane, but it is preferable because the hollow fiber can have a large membrane area, the separation and concentration device can be made compact, and the maintenance and management thereof can be facilitated.

Note that the non-porous membrane here does not necessarily mean that all of the separation membranes are composed of non-porous membranes (homogeneous membranes). It may be a composite membrane that is supported or sandwiched from both sides. By using a hydrophobic non-porous membrane, only the mixed vapor of low boiling point fermentation products and water permeates the membrane, and at the same time, the bacteria resistance of the membrane is excellent, so that deterioration of the membrane due to bacteria almost occurs. Absent.

As for the degree of reduced pressure when carrying out the present invention, the higher the degree of reduced pressure, the faster the separation rate and the more convenient it is. However, 0.5 atm or less is usually sufficient, and it is not necessary to maintain a particularly high degree of vacuum. Further, as the temperature during operation, the higher the temperature, the higher the vapor pressure and the faster the separation rate, which is convenient, but considering the heat-resistant temperature of the membrane used, energy efficiency, the composition of the target fermentation liquid, etc. Just decide. When the low boiling point fermentation product is separated and concentrated at the same time while continuously fermenting the fermentation broth, the temperature during the operation is regulated by the heat resistance of yeast and the optimum fermentation temperature.

The method of the present invention requires an operation of maintaining a reduced pressure on the surface side of the non-porous membrane that is not in contact with the fermentation liquid, but this reduced pressure side simply maintains the reduced pressure, and thus the low boiling point fermentation product vapor and steam. The mixed vapor of the above may be recovered, but the pressure may be reduced while flowing an inert gas as the carrier gas of the mixed steam to be recovered. By flowing the inert gas, the mixed vapor that has permeated the non-porous membrane can be forcibly removed from the membrane surface, so that the permeation efficiency can be further enhanced.

The inert gas that can be used as the carrier gas may be any gas that does not react with the low-boiling fermentation product,
For example, nitrogen, carbon dioxide, sterilized air, etc. may be mentioned.

When the separation and concentration method of the present invention is applied to continuous fermentation, a part of the liquid in the fermenter is continuously extracted by a liquid feeding pump and sent to a separation and concentration device having a hydrophobic non-porous membrane for separation. The fermentation product and water are separated by a concentrator in a mixed vapor state in which the fermentation product is concentrated, and the liquid not separated by the separation concentrator is returned to the fermentation tank. In the method of the present invention,
Since the inorganic salt and the fermentation raw material in the fermentation liquor are not separated at all in the separation / concentrator, it is sufficient to replenish the system with only the fermentation raw material consumed by fermentation. When such an operation method is adopted, the system is agitated by extracting and returning the liquid, and thus it is not necessary to provide a stirring device separately.

Instead of pumping the fermented liquid to the separation / concentrator, the separation / concentrator may be immersed in the fermenter so that the fermented liquid contacts one surface of the hydrophobic non-porous membrane. . In this case, a means for stirring the inside of the fermenter is required.

Hereinafter, the method of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart showing an embodiment of the method of the present invention. Fermentation liquid storage tank 1 containing the fermentation liquid to be separated and concentrated
Is a constant temperature water tank 2 for maintaining the temperature of the fermentation liquid at a predetermined temperature.
It is arranged inside. The fermentation liquid in the fermentation liquid storage tank 1 is guided by a circulation pump 3 to a separation / concentrator 4 containing a non-porous membrane hollow fiber, where a fermentation product and water are fermented and produced via the non-porous membrane hollow fiber. After the substances are separated and removed in a concentrated state, they are returned to the fermentation liquid storage tank 1. The side of the non-porous membrane in the separation / concentrator 4 that is not in contact with the fermentation liquid is kept at a reduced pressure. The carrier gas and a mixed gas of the concentrated low-boiling fermentation product steam and steam are sucked into the cold trap 8 by the vacuum pump 7. The vapor and steam of the concentrated low boiling point fermentation product are liquefied and captured by the cold trap 8 kept at a low temperature. 9 is a manometer for measuring the degree of reduced pressure. As the separation / concentrator 4, for example, a hollow fiber module containing a non-porous hollow fiber 12 having a structure shown in FIG. 2 or 3 is used.

The non-porous hollow fiber 12 made of silicon rubber is used as the non-porous hollow fiber 12, and the ethanol separation / concentration method in the case of using the ethanol fermentation liquid as the fermentation liquid is further explained. The fermented liquid supplied from 10 flows through the inside of the separation / concentrator 4 while coming into contact with the outer surface of the hollow fiber 12, is discharged from the fermented liquid outlet 11, and returns to the fermented liquid storage tank 1.

The fermentation liquor cannot pass through the wall (separation membrane) of the hollow fiber 12 as a liquid, but ethanol and water flow into the hollow fiber 12 in the form of vapor in a reduced pressure. At this time, the vapor flowing on the separation membrane surface is
The composition has a concentration of ethanol that is higher than the concentration of ethanol in the fermentation broth. Furthermore, the vapor transmission rate in the silicone rubber membrane is
Since ethanol vapor is larger than water vapor, this causes ethanol to permeate the separation membrane as a more concentrated composition. Therefore, as compared with the case of using a porous membrane as the separation membrane, a more concentrated mixed vapor of ethanol is recovered. Hollow fiber 12 from carrier gas inlet 13
Carrier gas such as nitrogen gas is sent to the inside of the steam outlet
If sucked from 14 by the vacuum pump 7, this steam will come out from the steam outlet 14 together with the carrier gas. When a carrier gas is used, the pressure inside the hollow fiber is preferably 0.5 atm or less, and more preferably 250 mmHg or less. When the carrier gas is not used, it is preferably 100 mmHg or less. It is also possible to use the module having the structure shown in FIG. 3 as the separation / concentrator, and to suck only the mixed vapor from the fermentation liquid with the vacuum pump 7 without using a carrier gas.
This mixed vapor may be liquefied in the cold trap 8 cooled to, for example, −40 ° C. as shown in FIG. 1, or may be supplied to the ethanol distillation column without being liquefied.

When carrying out continuous fermentation, an ordinary fermentation tank may be equipped with the device used in the separation and concentration method of the present invention. In this case, the temperature in the fermenter and the temperature in the separation / concentrator may be different as long as they do not affect the yeast.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1 Using a hollow fiber made of silicon rubber having a film thickness of 80 μm, an inner diameter of 200 μm, and an effective length of 160 mm, a separation condenser having a structure as shown in FIG. ² having an effective surface area of 0.3 m ² was prepared. An apparatus having the configuration shown in Fig. 1 was assembled using this separation / concentrator, and continuous fermentation of ethanol was performed, and at the same time, ethanol, which was a fermentation product, was concentrated and separated from the fermentation liquid.

First of all, without operating the separation / concentrator, 2% by weight of glucose, 2.5% by weight of alcohol yeast, 0.3% of citric acid, 0.2% by weight of ammonium chloride and potassium phosphate were put in the fermenter.
When liquid 1 having a composition of 0.5% by weight, 0.01% by weight of magnesium sulfate, 0.1% by weight of sodium chloride and 0.001% by weight of calcium chloride was charged and fermented under normal conditions for 48 hours, the content of ethanol in the fermentation liquid was 10%. It became weight%.

After the lapse of 48 hours, the fermentation liquor was continuously withdrawn from the fermenter at a flow rate of 0.3 l / min from the fermenter at a flow rate of 0.3 l / min, fed into the separation / concentrator from the fermentation liquor inlet, and contacted with the outer surface of the hollow fiber It was discharged from the fermented liquid outlet and returned to the fermented liquid storage tank. The inside of the hollow fiber was decompressed by a vacuum pump (20 mmHg in the manometer part), nitrogen was flowed as a carrier gas at a flow rate of about 150 Nml / min, and the ethanol mixed vapor permeated into the hollow fiber was cold at -40 ° C. Caught in a trap.

The average liquid capture rate in the cold trap is 27
It is g / hr, the liquid does not contain yeast, glucose and inorganic salts at all, and the concentration of ethanol is 68-76% by weight.
Therefore, it was possible to take out an extremely high concentration of ethanol.

An amount of glucose aqueous solution corresponding to the amount of ethanol aqueous solution collected in the cold trap was continuously added to the fermenter.

Example 2 Using the same apparatus as used in Example 1, the low boiling point fermentation product was separated and concentrated from the acetone-butanol fermentation liquid for about 20 hours. The composition of the fermentation product of the fermentation liquid is 0.4% by weight of acetone, 0.8% by weight of butanol and 0.1% by weight of ethanol, the temperature of the constant temperature water bath is 25 ° C, the vacuum degree on the decompression side of the separation condenser is 5 mmHg, and the carrier gas (nitrogen) flow rate is 100 Nml. It was carried out under the condition of / min. The average amount collected in a cold trap (temperature -40 ° C) was 22 g / hr, and the composition of the collected liquid was an aqueous solution containing 2% by weight of acetone, 8% by weight of butanol, and 20% by weight of ethanol. Yeast and inorganic salts were not included.

〔The invention's effect〕

According to the separation-concentration method of the present invention, yeast or fermentation raw materials directly from the fermentation broth, does not contain inorganic salts, and since it is possible to recover a low-boiling fermentation product significantly concentrated than the fermentation broth, yeast solution or From this, it is possible to reduce the energy cost as compared with the case of directly distilling from an aqueous solution from which solid substances such as yeast have been removed. Further, when the method of the present invention is applied to continuous fermentation, a conventional method for handling yeast, for example, a suspension batch method can be used as it is, an operation for immobilizing yeast in the fermentation layer and an apparatus therefor, for example, a bioreactor. The low-boiling fermentation product can be continuously removed from the system without the need for, and the concentration of the low-boiling fermentation product can be kept low, so that fermentation can be carried out continuously without inhibiting fermentation. it can.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of the separation and concentration method of the present invention, and FIGS. 2 and 3 are schematic cross-sectional views showing an example of a separation and concentration device containing a non-porous hollow fiber membrane. 1: Fermentation liquid storage tank (fermentation tank in the case of continuous fermentation), 2: Constant temperature water tank, 3: Circulation pump, 4: Separation concentrator, 5: Nitrogen cylinder 6: Flow meter, 7: Vacuum pump 8: Cold trap , 9: Manometer 10: Fermentation solution inlet, 11: Fermentation solution outlet 12: Non-porous hollow fiber, 13: Carrier gas inlet 14: Steam outlet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukinobu Sugimoto 2-3-19 Kyobashi, Chuo-ku, Tokyo Mitsubishi Rayon Engineering Co., Ltd. (56) References JP-A-61-199788 (JP, A)

Claims (3)

[Claims] 1. A hydrophobic non-porous membrane is contacted on one side with a fermentation solution,
A method for separating and concentrating a fermentation product, comprising a step of maintaining a reduced pressure on a surface side of the non-porous membrane which is not in contact with the fermentation liquid. 2. The method for separating and concentrating a fermentation product according to claim 1, wherein the fermentation liquid in contact with the hydrophobic non-porous membrane is a circulating fermentation liquid that is withdrawn from the fermentation tank and returned to the fermentation tank. . 3. The method for separating and concentrating a fermentation product according to claim 1, wherein the fermentation liquid in contact with the hydrophobic non-porous membrane is a fermentation liquid in a continuous fermentation tank.