JP3004509B2 - Method and apparatus for producing ethanol from microalgae - Google Patents

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 or a raw material for the chemical industry, using starch accumulated by microalgae as a raw material, and an apparatus therefor.

[0002]

2. Description of the Related Art Conventionally, ethanol is produced by using fossil resources such as coal and petroleum as raw materials and chemically synthesizing via ethylene, or by using biomass resources such as sugar cane sugar and corn starch as raw materials to mold, yeast, etc. It is manufactured by a fermentation method using microorganisms. Among biomass raw materials, microalgae, which are fine photosynthetic organisms represented by Chlorella, Donariella, Chlamydomonas, Scenedesmus, Spirulina, etc., contain a large amount of starch and glycogen (50% of dry weight) as alcohol raw materials.
The above is known, and there is a method for producing ethanol using these microalga starch as a raw material.
The production of ethanol from these microalga starches has been conventionally performed by the following method. (1) Microalgae are cultivated by a method such as photoautotrophic carbonation assimilation by photosynthesis in a light place and growth, or heterotrophic growth by providing organic substances such as sugars and organic acids in a dark place. Proliferate. (2) Since the grown microalgae mainly stores starch in the cells, the starch is exposed from the cells by mechanical means (such as ultrasonic crushing and explosion) or by using an enzyme or the like that dissolves the cell wall, and And extraction using an organic solvent. (3) Next, the extracted and separated starch is decomposed into glucose by an enzymatic saccharification method or the like, and is further fermented by adding alcoholic yeast to glucose and converted into ethanol.

[0003]

However, the above-mentioned conventional method has the following problems. (1) Although it is necessary to once extract and separate the starch in the cells, the cell walls of the microalgae are often strong, requiring a lot of power for mechanical crushing, and requiring expensive cell wall lysing enzymes. . In the process of starch extraction, a large amount of organic solvent and power for centrifugation are required. (2) Since the extracted and separated starch is in a raw state, a step of performing a heat treatment (referred to as gelatinization or α-starch) is required before it is decomposed into glucose by a saccharifying enzyme or the like. Is large. Usually, it is said that this heating energy accounts for 20 to 30% of the energy in the whole ethanol production process. Due to these problems, microalgae starch has not yet been put into practical use on a large scale, although it has many advantages over agricultural products such as potatoes and corn.
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and a method and an apparatus for efficiently producing ethanol by a simple process without using a large amount of energy or chemicals using microalgae that accumulate starch as a raw material Is to provide.

[0004]

Means for Solving the Problems In order to achieve the above object, the present inventors have been studying means for reducing a large amount of energy cost required for extraction and separation of starch from microalgae cells and heating of raw starch. Thus, it has been found that by effectively utilizing the alcoholization reaction of intracellular starch specific to microalgae, it is possible to produce alcohol without performing starch extraction and separation from cells and heat treatment.

That is, the present invention provides (1) a slurry obtained by culturing a microalga that accumulates starch in cells and concentrating a culture solution containing the cultured alga bodies, having a pH of 6.0 to 9.0.
A method for producing ethanol from microalgae, wherein ethanol is produced while maintaining a dark and anaerobic atmosphere while maintaining the range of 0, (2) culturing for culturing microalgae that accumulate starch in cells Means, concentration means for concentrating the culture solution, holding means for holding the concentrated algal slurry in a dark and anaerobic atmosphere, pH adjusting means for adjusting the pH in the holding means, and separation and concentration for separating and concentrating the produced ethanol Means for producing ethanol from microalgae.

[0006] Microalgae undergo photosynthesis under irradiation of sunlight or the like, and can accumulate starch in cells. In addition, there is also a substance that grows even under dark conditions and accumulates starch by using an organic substance such as sugar as a nutrient. On the other hand, when there is no light and no organic matter (nutrition), storage substances such as starch in cells are usually consumed, and life activity is maintained while oxidatively decomposing to carbon dioxide. No alcohol production occurs under these conditions. Here, when artificially provided with anaerobic conditions under dark conditions and no oxygen, the complete oxidation reaction of starch to carbon dioxide gas does not proceed, and depending on the type of microalgae, hydrogen gas, carbon dioxide gas, alcohol, lactic acid , Formic acid, acetic acid, etc. in various ratios have been found to exist. The present inventors have cultured and concentrated various types of starch-accumulating microalgae, and kept them in a dark and anaerobic atmosphere, and examined the productivity of ethanol from intracellular starch. It was found that by using such microalgae, it was possible to produce ethanol efficiently.

[0007] In the method of the present invention, the microalgae which can be used as a raw material for producing ethanol contains a large amount (preferably 50% or more by dry weight) of polysaccharides composed of glucose such as starch and glycogen in cells. Furthermore, it has the property of rapidly metabolizing the starch, glycogen and the like under a dark and anaerobic atmosphere and producing a large amount of ethanol. Examples of those satisfying these conditions include microalgae classified into green alga, prasino alga, crypto alga, and cyanobacteria, and further indicating the genus-level name, Chlamydomonas, chlorella and blue algae of the green alga Tropical spirulina, osylatoria, microcystis and the like can be mentioned.

[0008] When ethanol is produced by keeping the slurry containing these microalgae in a dark and anaerobic atmosphere, a small amount of organic acid is generated in addition to ethanol. Decrease.
Since the ethanol production reaction slows down when the pH falls below a certain value, in the method of the present invention, while maintaining the microalgae slurry in a dark and anaerobic atmosphere, the pH of the slurry is maintained.
Is adjusted to be in the range of 6.0 to 9.0, preferably 6.5 to 8.0. If the pH is less than 6.0, the production rate of ethanol becomes low, and if the pH exceeds 9.0 due to excessive supply of alkali for adjusting the pH, the production rate of ethanol also becomes undesirably low.

[0009] One of the ethanol production processes according to the present invention.
An example is shown in FIG. In the process of FIG. 1, the microalgae that accumulates starch in the cells is supplied to the microalga culture means 1 and cultured. In the case of the aforementioned photoautotrophic nutrition, the microalgae culturing means 1 is open at the top in a flowing water type culture tank having a water depth of about 10 to 30 cm, and receives sunlight while culturing by supplying inorganic nutrients such as nitrogen and phosphorus. A method can be used.
In the case of heterotrophic culture, irradiation with light is unnecessary, and the culture can be performed using a conventionally known general microbial fermentation tank after sterilizing the tank and the organic nutrient medium at 120 ° C. for about 15 minutes.

When the concentration of the microalgae in the culture solution becomes about 0.1 to 1.0 g per liter of the culture solution, the culture is stopped, and the microalgae is concentrated by the microalgae concentration means 2. In the microalga enrichment means 2, in the case of microalgae having a high sedimentation property, the microalgae is once concentrated by spontaneous sedimentation to a solid content of about 1%, and then the solid content is further increased to 10 to 20% by centrifugation, a belt filter or the like.
Concentrate to%. In the case of microalgae with low sedimentation, the solid content is directly 10-20% by centrifugation, belt filter, etc.
To concentrate. In this process, if the concentration is as high as possible (10 to 20%) within the range having fluidity, handling as a slurry and slow stirring in the subsequent stage are possible, and the ethanol concentration can be increased in the subsequent stage. Is advantageous.

The microalgae slurry thus obtained is led to a holding means 3 capable of holding a dark and anaerobic atmosphere to produce ethanol. The holding means 3 is provided with a slow stirring means such as a slurry pump or a stirrer.
Consists of a closed container with a monitor. Here, the dark atmosphere means a state where light is blocked to such an extent that photosynthesis is not performed. The slurry is introduced into the holding means 3 and ethanol is generated by holding the slurry in a dark and anaerobic atmosphere with gentle stirring. During this time, the pH of the slurry is monitored by a pH monitor, and the pH of the slurry provided with a means for supplying an alkaline solution such as NaOH or an acid solution such as HCl.
From the adjusting means 4, an alkaline solution or an acid solution is added to adjust the pH of the slurry to 6.0 to 9.0, preferably 6.5 to 9.0.
8.0. The pH adjusting means 4 works in conjunction with the pH monitor of the holding means 3,
It is also possible to adjust the pH of the slurry continuously. The residence time of the microalgae in the holding means 3 varies depending on the type of the microalgae, the holding conditions, and the like, but generally ranges from 5 to 50 hours.

The ethanol concentration in the slurry is 5 to 50 g
/ Liter (5,000 to 50,000 ppm), the liquid is led to the ethanol concentration means 5 to separate and concentrate ethanol. Ethanol separation / concentration means uses a distillation method, a concentration method using ethanol or a water separation membrane, or a supercritical extraction method using a solvent such as propane, etc., to condense to the desired concentration up to absolute ethanol. Can be. The residue after separating the ethanol can be disposed of by incineration or the like after drying.

[0013]

The method and apparatus of the present invention will be described more specifically with reference to the following examples. Example 1 Effect of pH on Ethanol Production Chlamydomonas rein
hardtii) UTEX2247 was mixed with mediums A to E having the composition shown in Table 1 in the proportions of A: 1 ml, B: 10 ml, C: 10 microliters, D: 100 ml, E: 6 ml, and water was added. The total volume was adjusted to 1 liter, and the cells were cultured using a culture solution adjusted to pH 8.0 with NaOH. 2 liters of this culture solution and 0.04 g of the above-mentioned Chlamydomonas culture were placed in a flat transparent container, and continuously irradiated with about 15,000 lux (lux) with a white fluorescent lamp, while air (5% CO ₂ added) was passed. After culturing at 25 ° C. for 3 days, a culture solution containing 1.5 g (as dry alga bodies) in 2 liters was obtained. Next, this liquid was concentrated by a centrifugal sedimentation method to prepare an algal slurry liquid containing 1.5 g of Chlamydomonas UTEX2247 in 16 ml of the liquid, and this liquid was divided into 2 ml × 8 samples. A universal buffer solution (Britton-Robinson buffer solution [H ₃ PO ₄ -acetic acid-boric acid-NaOH], pH _{4 to 11} , 8 steps) was added to each of the divided samples, mixed in 20 ml portions, and centrifuged. This was repeated twice to prepare one alga body slurry (0.19 g / 2 ml of alga bodies) at pH 4-11. 2 ml of this algal slurry was transferred to each 10 ml container, and nitrogen gas was injected into the slurry liquid for a short time to remove oxygen in the container.
The mixture was shaken (65 reciprocations / minute) while maintaining the temperature at ℃ to produce ethanol. After shaking for 48 hours, the concentration of ethanol formed in each slurry solution was measured. The result is shown in FIG. From the results in FIG. 2, it can be seen that the pH when producing ethanol from microalgae by the method of the present invention is preferably in the range of 6 to 9, and particularly preferably in the range of 6.5 to 8.0.

Example 2 Alcohol Production from Chlamydomonas reinhardtii Chlamydomonas rein
hardtii) UTEX2247 was mixed with mediums A to E having the composition shown in Table 1 in the proportions of A: 1 ml, B: 10 ml, C: 10 microliters, D: 100 ml, E: 6 ml, and water was added. The total volume was adjusted to 1 liter, and the cells were cultured using a culture solution adjusted to pH 8.0 with NaOH. 50 liters of this culture solution and the cultured species of Chlamydomonas (corresponding to 1.0 g as dry alga bodies) are placed in a flat transparent container, and the white fluorescent lamp is used for about 1500.
0 lux continuous irradiation, air (5% C
(O ₂ added) for 4 days at 25 ° C. with aeration.
A culture solution containing 38 g (as dry algal cells) of algal cells in a liter was obtained.

[0015]

[Table 1]

Next, this solution is concentrated by a centrifugal sedimentation method.
Chlamydomonas UTEX22 in 00 ml of liquid
An algal slurry solution containing 38 g of 47 algal bodies was prepared,
After transferring to a 00 ml Erlenmeyer flask and injecting nitrogen gas into the slurry solution for a short time to remove oxygen in the container,
The container was sealed and shaken under dark conditions (65 reciprocations / minute) to produce ethanol. During this time, 0.1N-NaOH and 0.1N-HCl were added to adjust the pH of the slurry to 6.
It was kept in the range of 5-8.0. On the other hand, ethanol was produced under exactly the same conditions except that the pH was not adjusted during shaking in a dark and anaerobic atmosphere using a separately prepared algal slurry. FIG. 3 shows how the concentration of ethanol in the slurry solution changes over time during both ethanol production steps. In FIG. 3, the solid line is the pH of the slurry liquid.
Is controlled within the range of 6.5 to 8.0, the dashed line indicates the pH.
The result when no adjustment is made is shown. From this, when the pH is not adjusted, the ethanol concentration is about 600 mg / liter, but this is because an organic acid (mainly lactic acid in the case of Chlamydomonas UTEX2247 of this example) is formed in the solution from the initial stage of the reaction, Is considered to be reduced to 5.5, which slows down the subsequent ethanol production.

On the other hand, when the pH was adjusted, the ethanol concentration reached 7,500 mg / liter, and it was found that ethanol production could be significantly increased by the pH adjustment. The above-mentioned nitrogen gas injection was performed in order to quickly provide an anaerobic condition. However, in practice, it is not necessary to take any means such as nitrogen gas injection for respiration of concentrated microalgae (oxygen consumption). However, it is possible to reach an anaerobic condition in a relatively short time (usually within 30 minutes).

[0018]

According to the present invention, after harvesting and concentrating starch-accumulated microalgae obtained by culturing, the pH of the concentrated algal slurry is in the range of 6.0 to 9.0 under a dark and anaerobic atmosphere. Ethanol production is possible only by gently stirring while keeping the inside. All of these operations require only a small amount of cost and energy, and the large cost and energy required for cell disruption after microalgae enrichment, extraction and separation of starch, and heating of starch in the conventional method can be greatly reduced (1/1). 10
In addition to this, it is possible to produce ethanol by a very simple process.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of an ethanol production process according to the method of the present invention.

FIG. 2 is a graph showing the effect of pH on ethanol production from microalgae in a dark and anaerobic atmosphere.

FIG. 3 is a graph showing a time-dependent change in ethanol concentration in a slurry liquid in an example.

──────────────────────────────────────────────────の Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) C12P 7/06 C12M 1/00 BIOSIS (DIALOG) CA (STN) WPI (DIALOG)

Claims (2)

(57) [Claims] 1. A microalga that accumulates starch in cells is cultured, and a slurry obtained by concentrating a culture solution containing the cultured alga bodies is darkened while maintaining the pH in a range of 6.0 to 9.0. A method for producing ethanol from microalgae, wherein ethanol is produced while maintaining an anaerobic atmosphere. 2. A culture means for culturing microalgae that accumulate starch in cells, a concentration means for concentrating a culture solution, a holding means for holding a concentrated algal slurry in a dark and anaerobic atmosphere, and the holding means. An apparatus for producing ethanol from microalgae, comprising: pH adjusting means for adjusting the pH in the means; and separation and concentration means for separating and concentrating the produced ethanol.