JPH0787986A - Process for producing ethanol from fine alga - Google Patents

Abstract

PURPOSE:To obtain ethanol useful as a fuel, etc., from a fine alga in a high yield by separating the ethanol from the culture slurry, treating the residual cells of the fine alga under specific conditions, and subsequently again supplying the treated cells to the ethanol-producing process for the reduction in the discharging volume of the solution containing organic components in high concentrations. CONSTITUTION:The method for producing the ethanol from the fine alga comprising culturing a fine alga accumulating starch in its cell, concentrating the culture slurry containing the cultured alga cells, holding the concentrated slurry in a dark and anaerobic atmosphere at a pH of 6.0-9.0 for producing the ethanol, separating the produced ethanol, returning the residual fine alga cells into the culture device, reaccumulating the starch by the photosynthesis reaction, and subsequently supplying the cells to the ethanol-producing process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing ethanol, which is useful as a fuel, a raw material for chemical industry, etc., by using starch as a raw material for microalgae.

[0002]

2. Description of the Related Art Conventionally, ethanol is a method of chemically synthesizing fossil resources such as coal and petroleum using ethylene, or a method of using biomass resources such as sugar cane sugar and corn starch as raw materials to mold, yeast, etc. It is manufactured by the fermentation method using microorganisms of. Among the biomass raw materials, a large amount of starch and glycogen (50% of dry weight), which are the raw materials for alcohol, are contained in microalgae, which are fine photosynthetic organisms represented by Chlorella, Donariella, Chlamydomonas, Senedesmus, and Spirulina.
The above) are known, and there is a method for producing ethanol from these microalgal starches as raw materials.

The production of ethanol using these microalgae starches as raw materials has been conventionally performed by the following method. (1) Microalgae are cultivated by methods such as photoautotrophic growth in the light by carbonic acid assimilation by photosynthesis, or heterotrophic feeding of organic substances such as sugars and organic acids to grow in the dark. Proliferate. (2) Since the grown microalgae mainly stores starch in the cells, the starch is exposed from the cells by mechanical means (ultrasonic crushing, blasting, etc.) or using an enzyme that dissolves the cell wall, Extract and separate with an organic solvent. (3) The extracted and separated starch is then decomposed into glucose by an enzymatic saccharification method or the like, and alcohol yeast is further added to the glucose for fermentation to convert it into ethanol.

The above-mentioned conventional method has the following problems. (1) It is necessary to temporarily extract and separate the intracellular starch, but the cell walls of microalgae are often strong, which requires a lot of power for mechanical disruption and requires expensive cell wall lysing enzymes. . In addition, a large amount of organic solvent and power for centrifugation are required in the process of starch extraction. (2) Since the extracted and separated starch is in a raw state, it requires a step of performing heat treatment (called gelatinization or α-starch formation) before it is decomposed into glucose by a saccharifying enzyme or the like. Is large (usually, this heating energy accounts for 20 to 30% of the energy in the entire ethanol production process), and there is a problem that an expensive saccharifying enzyme is required.

The present inventors have conducted various studies on means for reducing the large amount of energy cost required for extracting and separating starch from microalgae cells and heating raw starch, and culturing and culturing microalgae that accumulate starch. A slurry obtained by concentrating a culture solution containing algae is maintained in a dark and anaerobic atmosphere while maintaining the pH in a neutral to weakly alkaline region to generate ethanol, thereby producing a microalgae that accumulates starch. We found that ethanol can be produced as a raw material and filed a separate application.

[0006]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The method for producing ethanol utilizing the intracellular starch-alcoholization reaction peculiar to the above-mentioned microalgae uses a microalgae that accumulates starch as a raw material to produce a large amount of energy and drugs such as saccharifying enzymes. It is an excellent method that can efficiently produce ethanol by a simple process without the need for it. However, the microalgae-containing slurry after separating the produced ethanol contains a large amount of cell components other than starch. , A large-scale waste liquid treatment device was needed. An object of the present invention is to solve such problems and to provide a method for producing ethanol from microalgae in which the amount of waste liquid containing a high concentration of organic components is small and the burden of waste liquid treatment is small. .

[0007]

[Means for Solving the Problems] In the investigation of a method for producing ethanol from starch-containing microalgae, the inventors of the present invention maintained a concentrated slurry of starch-containing microalgae in a dark and anaerobic atmosphere to produce ethanol. The microalgae in the microalgae-containing slurry after the conversion reaction was performed and the produced ethanol was separated, although the starch content was low, re-proliferated by performing photosynthesis again in the culture device. It was found that starch is accumulated and can be reused as a raw material for ethanol production, and alcohol can be produced without producing a large amount of waste liquid as a by-product.

That is, according to the present invention, a slurry obtained by culturing a microalgae that accumulates starch inside cells and concentrating a culture solution containing the cultivated alga bodies is maintained at a pH of 6.0 to 9.0. However, in a method for producing ethanol that produces ethanol by maintaining it in a dark and anaerobic atmosphere and separates the produced ethanol, the microalgae after separating the ethanol-containing liquid are returned to the culture device and starch is re-accumulated by photosynthesis. The method for producing ethanol from microalgae is characterized in that it is supplied to the ethanol production step after the reaction.

An example of the ethanol production process according to the method of the present invention is shown in FIG. In the case of photoautotrophic, the microalgae culture means 1 is a method of culturing by receiving sunlight while giving inorganic nutrients such as nitrogen and phosphorus in a running channel type culture tank having a water depth of about 10 to 30 cm. Can be used. In the case of heterotrophic culture, light irradiation is not necessary, and it can be cultivated in a conventional general microorganism fermentation tank after sterilizing the inside of the tank and the organic nutrient medium at 120 ° C. for about 15 minutes.

With respect to the microalgae having a high sedimentation property, the microalgae concentrating means 2 can be concentrated to a solid content of about 1% by spontaneous precipitation and then further concentrated to 10 to 20% by centrifugation, a belt filter or the like. In this process, as high a solid content as possible (10 to 10
When concentrated to 20%), it can be handled as a slurry and can be slowly stirred in the latter stage and the ethanol concentration can be increased, and the concentration of ethanol in the latter stage is advantageous.

The holding means 3 in the dark and anaerobic atmosphere is a closed container with a pH monitor equipped with a slow stirring means such as a slurry pump or a stirrer. Here, since a large amount of carbon dioxide gas is generated in association with the ethanol production reaction, the carbon dioxide gas in the gas phase part can be transferred and introduced into the photoautotrophic microalgae culture means 1 and reused as nutrients. In the ethanol production reaction under such a dark and anaerobic atmosphere, the pH of the liquid gradually decreases with the progress of the reaction, and the progress of the ethanol production reaction slows. Therefore, the pH of the liquid during the reaction is 6. 0-9.0, preferably 6.5-8.
It is desirable to keep it in the range of 0.

The pH adjusting means 4 is provided with means for supplying an alkaline solution such as NaOH and an acid solution such as HCl, works in conjunction with the pH monitor of the holding means 3 in a dark and anaerobic atmosphere, and continuously operates in a tank. The pH inside can be adjusted. The solid-liquid separation means 5 separates the algal cells, whose volume has been reduced by the treatment in a dark and anaerobic atmosphere, from ethanol by centrifugation or membrane separation. In this step, ethanol remaining in the cells can be minimized by adding water and washing as necessary.

The ethanol-producing microalgae separated from the ethanol-containing liquid in the form of cake or slurry in the solid-liquid separation means 5 are microalgae-cultured by a microalgae returning means 6 equipped with a conveyor such as a belt conveyor. Return to means 1. The separated microalgae after ethanol production are re-grown by culturing in a culture tank, and starch is accumulated. By doing so, the waste can be reused and the amount of organic waste can be greatly reduced, resulting in a process with good productivity as a whole.

The ethanol concentrating means 7 is for concentrating and separating ethanol from the ethanol-containing liquid from which the microalgae after the production of ethanol have been separated. In addition to distillation, a method of concentrating with ethanol or a water separation membrane or a solvent such as propane It is possible to concentrate up to absolute ethanol to an appropriate concentration by a supercritical extraction method or the like.

[0015]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples. (Example 1) Alcohol production from the green alga Chlamydomonas reinhardy (Chlamydomonas rein
hardtii) UTEX2247 is mixed with the medium of A to E having the composition shown in Table 1 in the proportions of A: 1 ml, B: 10 ml, C: 10 microliter, D: 100 ml, E: 6 ml, and water is added. The total volume was adjusted to 1 liter, and the culture was cultivated using a culture solution whose pH was adjusted to 8.0 with NaOH. 50 liters of this culture solution and the above-mentioned Chlamydomonas culture seeds (corresponding to 1.0 g of dried algal cells) were placed in a flat transparent container, and a white fluorescent lamp was used for about 1,500.
Continuous irradiation of 0 lux was performed and air (5% C
O ₂ ) was cultivated for 4 days at 25 ° C. while aerating.
A culture solution containing 38 g (as dried algal cells) of algal cells in liter was obtained.

[0016]

[Table 1]

Next, this solution was concentrated by a centrifugal precipitation method to obtain 3
Chlamydomonas UTEX22 in 00 ml of liquid
An algal cell slurry liquid containing 47 g of algal cells of 38 g was added to 5
After transferring to a 00 ml Erlenmeyer flask and injecting nitrogen gas into the slurry liquid for a short time to remove oxygen in the container,
The mixture was sealed and shaken under dark conditions (65 reciprocations / minute) to generate ethanol. During this period, 0.1N-NaOH and 0.1N-HCl were added to adjust the pH of the slurry liquid to 6.
It was kept in the range of 5 to 8.0. On the other hand, using a separately prepared algal cell slurry liquid, ethanol was produced under exactly the same conditions except that the pH was not adjusted during shaking in the dark and anaerobic atmosphere. FIG. 2 shows the situation of the change over time in the ethanol concentration in the slurry liquid during the ethanol production process for both. In Fig. 2, the solid line indicates the pH of the slurry liquid.
When the pH is controlled within the range of 6.5 to 8.0, the broken line indicates pH.
The results are shown when the adjustment is not performed. From this, when the pH is not adjusted, the ethanol concentration is about 600 mg / liter, but this is because the organic acid (mainly lactic acid in the case of Chlamydomonas UTEX2247 of this example) is produced in the liquid from the initial stage of the reaction, It is thought that this is due to a decrease of 5.5, which slows down subsequent ethanol production.

On the other hand, when the pH was adjusted, the ethanol concentration reached 7500 mg / liter, and it was found that the ethanol production can be remarkably enhanced by the pH adjustment. Further, the results of culturing the microalgae after ethanol production in the medium shown in Table 1 are shown in FIG. 3, and it was found that the turbidity index (OD ₆₈₀ ) was increased and the microalgae after ethanol production were regrown. Next, FIG. 4 shows the ethanol production results when the microalgae were again held in a dark and anaerobic atmosphere. Fig. 4 shows the same pH as in the first ethanol production.
It is the result when the value is controlled to 6.5 to 8.0.
Ethanol of 00 mg / l was obtained, and it was found that the microalgae after ethanol production can be sufficiently used as a raw material for ethanol production.

[0019]

EFFECTS OF THE INVENTION According to the method of the present invention, a slurry obtained by culturing starch-accumulating microalgae and concentrating a culture solution containing the cultured algal cells is maintained at a pH in a neutral to weakly alkaline range. While maintaining a dark and anaerobic atmosphere to produce ethanol, in the method of producing ethanol,
It is possible to reduce the discharge amount of waste liquid containing a high concentration of organic components, and to significantly reduce the burden of waste liquid treatment. In addition, by reusing microalgae as a seed strain, the predominance of algal bodies in the culture tank is maintained, and it becomes possible to prevent contamination by other species that are of concern in microalgae culture. Has the following effect.

[Brief description of drawings]

FIG. 1 is a process flow diagram showing one embodiment of an alcohol production method of the present invention.

FIG. 2 is a graph showing changes over time in the concentration of ethanol in the slurry liquid in an example of the present invention.

FIG. 3 is a graph showing changes in the turbidity index (OD ₆₈₀ ) of the culture solution when the microalgae after ethanol production were cultured again.

FIG. 4 is a graph showing changes in the amount of ethanol produced from microalgae obtained by reculturing microalgae after ethanol production.

Front Page Continuation (72) Inventor Shin Hirayama 1-8-1 Koura, Kanazawa-ku, Yokohama-shi, Kanagawa Mitsubishi Heavy Industries, Ltd.

Claims (1)

[Claims] 1. A slurry obtained by culturing a microalgae that accumulates starch inside cells and concentrating a culture solution containing the cultured algal cells, while maintaining a pH in the range of 6.0 to 9.0 in the dark. And keep it in an anaerobic atmosphere to generate ethanol,
In the method for producing ethanol for separating produced ethanol, the microalgae after separating the ethanol-containing liquid is returned to the culture device, starch is re-accumulated by photosynthesis, and then supplied to the ethanol production step. A method for producing ethanol from microalgae.