JPS6135834B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for continuous production of alcohol by mixed culture.

In recent years, fermented alcohol, which can be obtained without using petrochemicals, has been in the spotlight as an energy alternative to petroleum. It is produced by fermenting sugar cane, molasses, sweet potato, yam, corn, and other cellulosic or starchy materials through the action of bacterial cells. In this method, alcohol productivity is thought to depend on the bacterial cell concentration. Therefore, in order to increase the bacterial cell concentration, a method of circulating the bacterial cells and a so-called immobilized cell growth method in which yeast is encapsulated in a polysaccharide-based substance are being developed. However, in the former case, the centrifugal separator used to concentrate and separate the microbial cells becomes clogged or nozzles clogged by the solids present in the culture solution, making it increasingly difficult to circulate the microbial cells. Therefore, it is necessary to periodically clean the centrifuge, which makes the work extremely troublesome. In the latter case, there are many technical problems that are difficult to solve for mass production on an industrial scale.

In view of these circumstances, the present inventors have conducted extensive research to increase the bacterial cell concentration within the fermenter, and as a result, have completed the present invention.

The method for producing alcohol according to the present invention is a continuous method for producing alcohol by mixed culture, which is characterized by culturing bacteria with alcohol fermentation ability attached to a carrier and flocculating yeast in one fluidized bed fermentation device. .

The reason why a fluidized bed type fermentation device is used is that the power required to fluidize the bacterial cells attached to the carrier can be saved and wear of the carrier can be prevented.

As the carrier for attaching bacterial cells, crushed vermiculite, activated carbon, zeolite, etc. are preferably used from the viewpoint of fluidity of the carrier. As the bacteria having alcohol fermentation ability, Zymomonas mobilis is preferably used because it has excellent natural adhesion to the carrier. This bacterium produces alcohol by fermenting sucrose, glucose, and fructose, among the fermentable sugars contained in cane and blackstrap molasses. Bacteria having alcohol fermentation ability are not limited to the above-mentioned bacteria as long as they have good natural adhesion. By culturing carrier-attached bacteria under fluidized flow in a fluidized bed fermentation device, the concentration of bacterial cells in the tank can be increased and the productivity of alcohol from the fermentable sugar can be improved. On the other hand, the flocculating yeast may be any yeast having flocculating ability and alcohol fermentation ability. By culturing the flocculating yeast together with the bacteria in the same fermentation device under flowing conditions, unreacted fermentable sugars that have not been fermented by the bacteria are fermented to produce alcohol. and can improve the alcohol fermentation yield from sugar.

Since the alcohol production method according to the present invention is configured as described above, the following effects are achieved.

(1) Since a fluidized bed type fermentation device is used, the power required to fluidize the bacterial cells attached to the carrier can be saved, and wear of the carrier can be prevented.

(2) Since the carrier for attaching bacterial cells is fluidized, the solid surface area on which bacterial cells can attach can be increased, increasing the concentration of bacterial cells in the tank, and as a result, alcohol productivity can be greatly increased. can be improved.

(3) Since the flocculating yeast is fluidized, unreacted fermentable sugars that have not been fermented by the bacteria attached to the carrier can be fermented by the yeast, and as a result, the fermentation yield can be greatly improved. I can do it.

Comparative Example 1 Using a fermenter for static culture, Saccharomyces hormocensis was grown as a microorganism.
Formosensis) IFO Deposit No. 0216 (hereinafter referred to as microorganism A) was used as a fermentation raw material.
Diluted Cane molasses medium (yeast extract: 3g/
l, (NH ₄ ) ₂ SO ₄ : 1 g/l, KH ₂ PO ₄ : 1 g/l
and MgCl ₂ .6H ₂ O: 0.5 g/l), batch fermentation was carried out at a fermentation temperature of 30° C., and the fermentation characteristics were examined over time.

Instead of the above microorganisms, baker's yeast manufactured by Kyowa Hakko Co., Ltd. (hereinafter referred to as microorganism B), Zymomonas mobilis IFO deposited No. 13756 (hereinafter referred to as microorganism C), and Zymomonas mobilis ATCC deposited No. 10988 (hereinafter referred to as microorganism The above operation was repeated using each sample (referred to as D).

Figure 1 shows the relationship between static culture time and ethanol concentration for each microorganism. As can be seen from the figure, microorganism A has the best alcohol fermentation ability (approximately 55 dl/on the second day), followed by microorganism B.
For microorganisms C and D, the alcohol concentration was only about 40 g/day even on the fourth day.

Comparative Example 2 An alcohol fermentation apparatus shown in FIG. 3 was used. This is mainly composed of a glass fluidized bed type fermenter 1 with an actual volume of 0.7, and is configured to be able to control temperature and pH. The fermentation raw material is supplied to the bottom of the tank 1 by a pump 2, and the reaction liquid is returned from the top to the bottom of the tank by a pump 3, and flows out from the carrier settling section 4 at the top of the tank. . In this fermentation device, we cultivated a congealing baker's yeast produced by Kyowa Hakko Co., Ltd.
The same sterilized 5-fold diluted Cane molasses medium as used in Comparative Example 1 was used as a fermentation raw material at a flow rate of 0.035/
Continuously supplied to fermenter 1 at 30°C and pH 5.
Continuous fermentation was carried out under the following fermentation conditions.

The ethanol concentration in the effluent reaction solution after the reaction was approximately the same as in the case of batch fermentation (Comparative Example 1), about 58
It was g/.

Example Using the alcohol continuous fermentation apparatus shown in Figure 3,
Zymomonas mobilis ATCC Deposit No. 10988 and flocculating baker's yeast manufactured by Kyowa Hakko Co., Ltd. were cultured in fermentation tank 1, and crushed vermiculite (60 to 80 mesh) was added to the same tank.
It was added at a concentration of 5wt/vol%. Next, the same sterilized 5-fold diluted Cane molasses medium used in Comparative Example 1 as the fermentation raw material was added to fermenter 1 at a raw material dilution rate (=raw material supply flow rate/total actual volume of the fermenter) = 0.05 h ^-1 . Continuous fermentation was carried out under fermentation conditions at pH 5 and temperature of 30° C. by continuous feeding. The ethanol concentration in the effluent reaction solution was 63 g/ml.

Next, the dilution rate was increased stepwise from 0.05 h ^-1 to 0.1 h ^-1 , 0.15 h ^-1 and 0.25 h ^-1 , and the ethanol concentration at each flow rate was measured. Figure 2 shows the relationship between raw material dilution rate and alcohol productivity. As can be seen from the figure, alcohol productivity is proportional to the dilution rate,
At a dilution rate of 0.25h ^-1 , alcohol productivity is approximately 16g/
・It reached a high value of h. Moreover, the ethanol concentration of the effluent reaction solution hardly changed.

As described above, high fermentation yield and high alcohol productivity could be obtained by culturing Zymomonas mobilis and flocculating yeast in a mixed manner using a fluidized bed fermentation apparatus. On the other hand, in the conventional continuous culture method that does not use a carrier for attaching bacterial cells, the ethanol productivity is reported to be 3 to 3 g/l·h. As described above, according to the present invention, it is possible to maintain a high alcohol fermentation yield and significantly improve productivity.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between culture time and ethanol concentration for various microorganisms in batch fermentation.
FIG. 2 is a graph showing the relationship between raw material dilution rate and alcohol productivity in an example of the invention, and FIG. 3 is a schematic diagram of a fermentation apparatus used in the example. 1...Fluidized bed fermentation tank.

Claims (1)

[Claims] 1. A method for continuous production of alcohol by mixed culture, characterized in that bacteria with alcohol fermentation ability attached to a carrier and flocculating yeast are cultured in one fluidized bed fermentation device.