JP6943733B2 - Manufacturing method of organic substances - Google Patents

Description

The present invention relates to a method for producing an organic substance. In particular, the present invention relates to a method for producing an organic substance using a fermentation broth obtained by microbial conversion of a specific synthetic gas.

In recent years, various organic materials other than petroleum have been used from the viewpoint of global environmental problems such as the depletion of fossil fuel resources due to the mass consumption of oils and alcohol produced from petroleum and the increase in carbon dioxide in the atmosphere. Attention is being paid to a method for producing a substance, for example, a method for producing bioethanol from an edible raw material such as corn by a sugar fermentation method. However, the sugar fermentation method using such edible raw materials has a problem that the food price rises because the limited agricultural land area is used for production other than food.

In order to solve such a problem, various methods for producing various organic substances conventionally produced from petroleum by using non-edible raw materials which have been conventionally discarded have been studied. For example, Non-Patent Document 1 discloses the types of microorganisms and metabolic systems that convert synthetic gases containing carbon dioxide, carbon monoxide, and hydrogen into acetic acid and ethanol. Further, Patent Document 1 discloses a method for producing ethanol by microbial fermentation from steel exhaust gas, synthetic gas obtained by gasification of waste, and the like.

Japanese Unexamined Patent Publication No. 2015-53866

Michael Koepke et al., “Clostridium ljungdahlii represents a microbial production platform based on syngas”, Proc Natl Acad Sci USA, August 24, 2010, vol. 107, no. 34, 13087-13092

The present inventors have been studying a method for producing an organic substance by microbial fermentation using a synthetic gas derived from waste as described in Patent Document 1 as a raw material, and found that a synthetic gas having the same concentration of carbon monoxide. It was found that the amount of organic substances produced by microorganisms differs depending on the gas composition other than carbon monoxide, even if the above is used.

In view of the above circumstances, it is an object of the present invention to provide a method for producing an organic substance having excellent productivity, which can convert carbon monoxide in a synthetic gas having a specific composition into an organic substance with high efficiency.

As a result of diligent studies on methods for solving the above problems, the present inventors have determined that the concentration of carbon dioxide among various components in syngas is the assimilation rate of carbon monoxide and hydrogen by microorganisms, that is, the production of organic substances. It was found that it affects the sex, and that the above problem can be solved by using the synthetic gas for microbial fermentation after setting the carbon dioxide in the synthetic gas to a specific concentration range.

That is, the gist of the present invention is as follows.

[1] A method for producing an organic substance by microbial fermentation of a synthetic gas containing at least carbon monoxide, carbon dioxide and hydrogen.
A synthetic gas supply process for supplying the synthetic gas into a fermenter containing microorganisms,
A fermentation process in which the synthetic gas is microbially fermented in the fermenter,
Including
The concentration of carbon dioxide in the synthetic gas supplied into the fermentation layer is 0.1% by volume or more and 9% by volume or less with respect to the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthetic gas. A method for producing organic substances.

[2] A raw material gas generation process in which a carbon source is gasified to generate a raw material gas,
A pretreatment step of adjusting the carbon dioxide concentration in the raw material gas to obtain the synthetic gas, and
The method according to [1], further comprising.

[3] The method according to [2], wherein the carbon source is waste.

[4] The method according to [2] or [3], wherein the pretreatment step comprises treating the raw material gas with an absorption / desorption device.

[5] The method according to any one of [1] to [4], wherein the microorganism contains the genus Clostridium.

[6] The method according to any one of [1] to [5], wherein the organic substance contains ethanol.

According to the present invention, when a synthetic gas containing carbon monoxide, carbon dioxide and hydrogen is converted into an organic substance by microbial fermentation, carbon monoxide is increased by setting the carbon dioxide in the synthetic gas to a specific concentration range. It can be efficiently converted to organic substances, especially ethanol. In particular, from gasification of industrial waste or municipal municipal waste, or from raw material gases containing carbon monoxide, carbon dioxide and hydrogen obtained from the exhaust gas of steel mills and chemical plants, carbon dioxide by any pretreatment process. By using a synthetic gas having a controlled concentration, the productivity of ethanol obtained by microbial fermentation can be improved.

It is a figure which showed the production pathway of ethanol by the fermentation action of a microorganism.

Hereinafter, an example of a preferred embodiment of the present invention will be described. However, the following embodiments are examples for explaining the present invention, and the present invention is not limited to the following embodiments. In the present specification, the abundance ratio of each component in the gas is based on the volume, not the weight, unless otherwise specified. Therefore, unless otherwise specified, percentage% represents volume% and ppm represents volume ppm.

[material]
<Carbon source>
The carbon source used as a raw material for the synthetic gas used in the present invention is not particularly limited, and for example, a coke oven, a blast furnace (blast furnace gas), coal used in a converter or a coal-fired power plant, and an incinerator (particularly gas) Various carbon-containing materials can also be preferably used for the purpose of recycling, such as general waste and industrial waste introduced into incinerator), and carbon dioxide produced by various industries.
More specifically, carbon sources include plastic waste, garbage, municipal waste (MSW), waste tires, biomass waste, household waste such as futons and paper, waste such as building materials, coal, oil, etc. Examples thereof include petroleum-derived compounds, natural gas, shale gas, etc. Among them, various types of waste are preferable, and unsorted municipal waste is more preferable from the viewpoint of separation cost.

<Raw material gas>
The raw material gas obtained by gasifying the carbon source contains at least carbon monoxide, carbon dioxide and hydrogen as essential components, and may further contain oxygen and nitrogen. As other components, the raw material gas may further contain components such as sous, tar, nitrogen compounds, sulfur compounds, phosphorus compounds, and aromatic compounds.

As will be described later, the raw material gas is monoxide by performing a heat treatment (commonly known as gasification) that burns (incompletely burns) the carbon source in the raw material gas generation step, that is, by partially oxidizing the carbon source. It may be produced as a gas containing 20% by volume or more of carbon.
As the raw material gas generation process, for example, waste is burned in a gasification furnace, coal is added and heated during steelmaking (steelmaking process), and carbon dioxide obtained by burning organic matter is reversed by a metal catalyst. Examples thereof include a method of converting to carbon monoxide by a shift reaction.

When the raw material gas is derived from waste, the raw material gas usually contains 20% by volume or more and 80% by volume or less of carbon monoxide, 10% by volume or more and 40% by volume or less of carbon dioxide, and 10% by volume or more and 80% or less of hydrogen. It tends to contain 1 ppm or more of a nitrogen compound, 1 ppm or more of a sulfur compound, 0.1 ppm or more of a phosphorus compound, and / or 10 ppm or more of an aromatic compound. In addition, other substances such as environmental pollutants, dust particles, and impurities may be contained. Therefore, when supplying the synthetic gas to the microbial fermentation layer, substances unfavorable for stable culture of microorganisms, unfavorable amounts of compounds, etc. are reduced or removed from the raw material gas, and the content of each component contained in the raw material gas is contained. Is preferably in a range suitable for stable culture of microorganisms. In particular, since many aromatic compounds have cytotoxicity, it is preferable to reduce and remove them from the raw material gas.

<Syngas>
The syngas used in the present invention contains at least carbon monoxide, carbon dioxide and hydrogen as essential components, and may further contain nitrogen.

As will be described later, the syngas used in the present invention produces a raw material gas by gasifying a carbon source (raw material gas generation step), and then carbon monoxide, carbon dioxide, hydrogen and nitrogen from the raw material gas. A gas obtained by adjusting the concentration of each component and undergoing the steps of reducing or removing the above-mentioned substances and compounds may be used as a synthetic gas.

As will be described later, the carbon dioxide concentration in the synthetic gas is 0.1% by volume or more, preferably 0.3% by volume or more, based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthetic gas. , More preferably 0.5% by volume or more, further preferably 0.8% by volume or more, particularly preferably 1% by volume or more, and 9% by volume or less, preferably 8% by volume or less, more preferably 7% by volume. % Or less, more preferably 6% by volume or less, and particularly preferably 5% by volume or less. The method for controlling the carbon dioxide concentration in the synthetic gas is not particularly limited as long as it is a known method, but for example, in the pretreatment step of the raw material gas, PSA (pressure) filled with an adsorbent having carbon dioxide adsorbing ability such as zeolite. It is possible to reduce the carbon dioxide concentration in the synthetic gas and control it so that it is within the above range by contacting it with a variable adsorption method) device or a TSA (thermal variable adsorption method) device using an amine-based adsorption liquid. can.
In the present invention, "controlling" means operating under the above conditions for a period of 95% or more in the entire period from the start of stable ethanol production to the stop of culturing of microorganisms. It does not include the period of the initial start-up step of growing the inoculum in the fermenter and the end step of stopping the supply of the medium and synthetic gas and stopping the culture of the inoculum.

The carbon monoxide concentration in the synthetic gas is usually 20% by volume or more and 80% by volume or less, preferably 25% by volume, based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthetic gas. It is 50% by volume or less, and more preferably 35% by volume or more and 45% by volume or less.
The hydrogen concentration in the synthetic gas is usually 10% by volume or more and 80% by volume or less, preferably 30% by volume or more and 55% by volume, based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthetic gas. By volume or less, more preferably 40% by volume or more and 50% by volume or less.
Further, the nitrogen concentration in the synthetic gas is usually 40% by volume or less, preferably 1% by volume or more and 20% by volume or less, based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthetic gas. Yes, more preferably 5% by volume or more and 15% by volume or less.
For the concentrations of carbon monoxide, hydrogen, and nitrogen, the CHN element composition of the carbon source is changed in the raw material gas generation process, and the combustion conditions such as the combustion temperature and the oxygen concentration of the supply gas at the time of combustion are appropriately changed. By doing so, the range can be set to a predetermined range. For example, if you want to change the carbon monoxide or hydrogen concentration, change to a carbon source with a high CH ratio such as waste plastic, and if you want to reduce the nitrogen concentration, supply a gas with a high oxygen concentration in the raw material gas generation process. There is a way to do it.

The synthetic gas used in the present invention may contain a sulfur compound, a phosphorus compound, a nitrogen compound and the like in addition to the above-mentioned components. The content of each of these compounds is preferably 0.05 ppm or more, more preferably 0.1 ppm or more, still more preferably 0.5 ppm or more, and preferably 80 ppm or less, more preferably 60 ppm or less, still more preferably. Is 40 ppm or less. By setting the content of sulfur compound, phosphorus compound, nitrogen compound, etc. to the lower limit value or more, there is an advantage that the microorganism can be suitably cultured, and by setting the content to the upper limit value or less, the microorganism does not consume. It has the advantage that the medium is not contaminated by various nutrient sources.

Examples of the sulfur compound usually include sulfur dioxide, CS ₂ , COS, and H ₂ S, and among them, H ₂ S and sulfur dioxide are preferable because they are easily consumed as nutrient sources for microorganisms. Therefore, it is more preferable that the sum of H _{2 S} and sulfur dioxide are included in the above range in the synthesis gas.
As the phosphorus compound, it is preferable that phosphoric acid is easily consumed as a nutrient source for microorganisms. Therefore, it is more preferable that the synthetic gas contains phosphoric acid in the above range.
Examples of the nitrogen compound include nitric oxide, nitrogen dioxide, acrylonitrile, acetonitrile, HCN and the like, and HCN is preferable because it is easily consumed as a nutrient source for microorganisms. Therefore, it is more preferable that HCN is contained in the above range in the synthetic gas.

The synthetic gas may contain an aromatic compound of 0.01 ppm or more and 90 ppm or less, preferably 0.03 ppm or more, more preferably 0.05 ppm or more, still more preferably 0.1 ppm or more, and preferably 70 ppm. Below, it is more preferably 50 ppm or less, still more preferably 30 ppm or less. When the content is set to the lower limit or higher, the microorganisms tend to be suitably cultured, and when the content is set to the upper limit or lower, the medium is less likely to be contaminated by various nutrient sources not consumed by the microorganisms. It is in.

<Microorganisms>
The microorganism (seed) for microbially fermenting the synthetic gas is not particularly limited as long as it can produce a desired organic substance by microbially fermenting the synthetic gas using carbon monoxide as a main raw material. For example, the microorganism (species) preferably produces an organic substance from syngas by the fermentation action of gas-utilizing bacteria. Among the gas-utilizing bacteria, the genus Clostridium is more preferable, and Clostridium autoethanogenum is particularly preferable, but the gas-utilizing bacteria are not limited thereto. Hereinafter, further examples will be given.

Gas assimilating bacteria include both eubacteria and archaea.
Examples of eubacteria include Clostridium, Moorella, Acetobacterium, Carboxydocella, Rhodopseudomonas, and Eubacterium. Examples thereof include (Eubacterium) bacteria, Butyribacterium (Butyribacterium) bacteria, Oligotropha (Oligotropha) bacteria, Bradyrrhizobium (Bradyrhizobium) bacteria, and Ralsotonia (Ralsotonia) bacteria which are aerobic hydrogen oxidizing bacteria.

On the other hand, as paleobacteria, for example, Methanobacterium spp., Methanobrevibacter spp., Methanocalculus spp., Methanococcus spp., Methanosarcina spp., Methanosphaera spp., Methanothermobacter spp., Methanothrix spp. Examples thereof include bacteria, Methanospirillium spp., Methanosaeta spp., Thermococcus spp., Thermofilum spp., Arcaheoglobus spp. Among these, as archaea, bacteria of the genus Methanosarcina, bacteria of the genus Methanococcus, bacteria of the genus Methanothermobacter, bacteria of the genus Methanothrix, bacteria of the genus Thermococcus, bacteria of the genus Thermofilum, and bacteria of the genus Archaeoglobus are preferable.

Further, since the archaea are excellent in assimilation of carbon monoxide and carbon dioxide, the archaea are preferably Methanosarcina genus, Methanothermobactor genus bacterium, or Methanococcus genus bacterium, and Methanosarcina genus bacterium or Methanococcus genus bacterium is particularly preferable. Specific examples of Methanosarcina genus bacteria include Methanosarcina barkeri, Methanosarcina mazei, and Methanosarcina acetivorans.

From the above gas-utilizing bacteria, a bacterium having a high ability to produce a target organic substance is selected and used. For example, as gas-utilizing bacteria with high ethanol-producing ability, Clostridium autoethanogenum, Clostridium ljungdahlii, Clostridium aceticum, Clostridium carboxidivorans , Moorella thermoacetica, Acetobacterium woodii and the like.

<Medium>
The medium used for culturing the above-mentioned microorganisms (species) is not particularly limited as long as it has an appropriate composition according to the bacteria. For example, when the genus Clostridium is used as a microorganism, "0091" in the pamphlet of International Publication No. 2017-117309 and "0907" to "0998" in US Patent Application Publication No. 2017/260552 can be referred to. ..

[Production method]
<Raw material gas generation process>
The raw material gas generation step is a step of generating a raw material gas by gasifying the above-mentioned carbon source. A gasification furnace may be used in the raw material gas generation step. The gasification furnace is a furnace that burns (incompletely burns) a carbon source, and examples thereof include a shaft furnace, a kiln furnace, a fluidized bed furnace, and a gasification reforming furnace. The gasification furnace is preferably a fluidized bed type because partial combustion of waste enables a high hearth load and excellent operation operability. By gasifying the waste in a fluidized bed furnace with a low temperature (about 450 to 600 ° C) and a low oxygen atmosphere, it decomposes into gas (carbon monoxide, carbon dioxide, hydrogen, methane, etc.) and carbon-rich char. do. Furthermore, since the incombustibles contained in the waste are separated from the bottom of the furnace in a hygienic and low-oxidation state, it is possible to selectively recover valuable resources such as iron and aluminum in the incombustibles. Therefore, gasification of such waste enables efficient resource recycling.

The temperature of the gasification in the raw material gas generation step is usually 100 ° C. or higher and 1500 ° C. or lower, preferably 200 ° C. or higher and 1200 ° C. or lower.

The reaction time for gasification in the raw material gas generation step is usually 2 seconds or longer, preferably 5 seconds or longer.

<Pretreatment process>
Prior to the syngas supply step, it is a step of removing or reducing specific substances such as various pollutants, dust particles, impurities, and unfavorable amounts of compounds from the source gas. The pretreatment step includes, for example, a scrubber (water-soluble impurity separation device), a gas chiller (moisture separation device), a cyclone, a fine particle (soo) separation device such as a bag filter, a desulfurization device (sulfide separation device), and a low temperature separation method ( Deep cooling type separation device, membrane separation type separation device, pressure swing adsorption type separation device (PSA), temperature swing adsorption type separation device (TSA), pressure temperature swing adsorption type separation device (PTSA), desorption The treatment can be performed using one or more of an oxygen device, a separation device using activated carbon, a separation device using a copper catalyst or a palladium catalyst, and the like. In the present invention, the pretreatment step may be a step of treating the raw material gas with a scrubber and / or an adsorption device.

The scrubber is used for removing pollutants and the like in the gas, and either a wet cleaning method or a dry cleaning method can be used depending on the purpose. Of these, a wet cleaning method performed by contacting a particulate substance with a cleaning liquid can be preferably used, and as an example, a cleaning method using a so-called water curtain can be used. When the wet cleaning method is used, the cleaning liquid includes, for example, water, an acidic solution, an alkaline solution and the like, and is preferably water. The temperature of the cleaning liquid is usually 40 ° C. or lower, preferably 30 ° C. or lower, more preferably 25 ° C. or lower, and even more preferably 15 ° C. or lower.

The adsorption device only needs to have the ability to adsorb components other than carbon monoxide and hydrogen in the raw material gas, and examples of equipment intended only for adsorption include a desulfurization layer and a deoxidizing layer. Of these, the desulfurization layer is not particularly limited as long as the sulfur content can be removed. If the sulfur content cannot be sufficiently removed or reduced in the desulfurization layer and the sulfur content remains high, there is a possibility that the desulfurization layer may have an adverse effect when the suction / desorption device is present in the subsequent stage.

The deoxidizing layer is not particularly limited as long as the oxygen component can be removed. If the oxygen component cannot be sufficiently removed or reduced in the deoxidizing layer and the oxygen component remains high, the microorganisms used in the present invention, particularly anaerobic microorganisms, may die.

Further, a suction / desorption device may be provided, in which case any of PSA, TSA and PTSA can be preferably used. Further, in order to remove unnecessary impurities, other devices may be optionally provided. As the suction / desorption material used in the suction / desorption device, a porous material such as activated carbon, zeolite, or molecular sieves, or an aqueous solution such as an amine solution can be used. Of these, activated carbon or zeolite capable of adsorbing aromatic compounds and sulfur compounds is preferably used. As described above, if the sulfur content in the raw material gas remains high, the suction / desorption material may be adversely affected. Therefore, the suction / desorption device should be provided after the desulfurization layer.

<Syngas supply process>
The synthetic gas supply step is a step of supplying the synthetic gas obtained as described above into a fermenter containing microorganisms. The supplied synthetic gas contains carbon monoxide and hydrogen, and the carbon dioxide content is 0.1% by volume or more with respect to the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthetic gas. It is characterized in that it is controlled to 9% by volume or less. In the present invention, by setting the amount of carbon dioxide contained in the synthetic gas within the above range, carbon monoxide in the synthetic gas can be converted into an organic substance with high efficiency. The reason for this is not clear, but it can be inferred as follows.

When an organic substance is obtained by microbial fermentation of a synthetic gas containing carbon monoxide, carbon dioxide and hydrogen, microorganisms (for example, ethanol-producing bacteria) pass through acetic acid as disclosed in Non-Patent Document 1 and the like. Is thought to produce ethanol. At this time, as shown in FIG. 1, ethanol is produced not only from carbon monoxide but also from carbon dioxide via acetic acid. Therefore, attention has not been paid to carbon dioxide in syngas. For example, it is known that the raw material gas after gasifying steel exhaust gas or carbon source contains about 10 to 30% by volume of carbon dioxide. For the above reason, the raw material gas is used for microbial fermentation. It was thought that it was not necessary to control the carbon dioxide concentration in the raw material gas.

However, carbon monoxide and carbon dioxide have different energy levels, and since the energy level of carbon dioxide is lower and more stable than carbon monoxide, when ethanol is produced from carbon dioxide via acetic acid. The energy required for carbon monoxide is thought to be greater than when producing ethanol from carbon monoxide via acetic acid. As a result, when the carbon dioxide concentration increases, the amount of acetic acid produced as a by-product increases, and the amount of ethanol produced is considered to decrease. Therefore, in the present invention, the upper limit of the concentration of carbon dioxide contained in the synthetic gas is 9% by volume, preferably 8% by volume or less, more preferably 7% by volume or less, still more preferably 6% by volume or less, and particularly preferably 5. The volume is not more than%.

Further, if the synthetic gas used for microbial fermentation does not contain carbon dioxide at all (that is, the carbon dioxide concentration is 0%), the amount of ethanol produced decreases. Conventionally, in the process of producing acetic acid or ethanol from carbon monoxide by microbial fermentation, as shown in FIG. 1, when the microorganism takes in carbon monoxide, it is converted into carbon dioxide, so carbon dioxide is intentionally supplied to the microorganism from the outside. It was thought that there was no need to. The present inventors have found that the productivity of ethanol is improved by using a synthetic gas containing a trace amount of carbon dioxide. It is considered that this is because the synthetic gas contains a small amount of carbon dioxide, which improves the balance of the microbial metabolism system, and as a result, the productivity of ethanol is improved. Therefore, in the present invention, the lower limit of the concentration of carbon dioxide contained in the synthetic gas is 0.1% by volume, preferably 0.3% by volume or more, more preferably 0.5% by volume or more, still more preferably 0.8. By volume% or more, particularly preferably 1% by volume or more.

As long as the component conditions of the synthetic gas are satisfied, the gas obtained through the raw material gas generation step and the subsequent pretreatment step may be used as it is as the synthetic gas. Alternatively, another predetermined gas may be added to the gas obtained through the raw material gas generation step and the pretreatment step, and then used as the synthetic gas. As another predetermined gas, at least one compound selected from the group consisting of, for example, a sulfur compound such as sulfur dioxide, a phosphorus compound, and a nitrogen compound may be added to obtain a synthetic gas.

<Fermentation process>
The fermentation step according to the present invention is a step of producing an organic substance by microbially fermenting the above-mentioned syngas. In the fermentation step, a fermentation tank containing the above-mentioned microorganisms (seed) is used. The fermenter may contain a medium (culture solution) in addition to the microbial species. It is known that certain anaerobic microorganisms produce organic substances that are valuable resources such as ethanol from substrate gases such as syngas by fermentation, and these gas-utilizing microorganisms are liquid. Is cultured in the medium of. For example, the culture solution and the gas-utilizing bacteria may be supplied and contained, and the synthetic gas may be supplied into the fermentation layer while stirring the culture solution in this state. As a result, gas-utilizing bacteria can be cultivated in the culture solution, and an organic substance can be produced from the synthetic gas by the fermentation action thereof.

The culture solution is a liquid containing water as a main component and nutrients (for example, vitamins, phosphoric acid, etc.) dissolved or dispersed in the water. The composition of such a culture solution is prepared so that gas-utilizing bacteria can grow well.

The fermenter is preferably a continuous fermentation apparatus. In general, a microbial fermenter having an arbitrary shape can be used, and examples thereof include a stirring type, an airlift type, a bubble tower type, a loop type, an open bond type, and a photobio type. , A known loop reactor having a main tank portion and a reflux portion can be preferably used. In this case, it is preferable to further include a circulation step of circulating the liquid medium between the main tank portion and the reflux portion.

The pressure in the fermenter may be normal pressure, but is preferably about 10 to 300 kPa (gauge pressure), more preferably about 20 to 200 kPa (gauge pressure). By setting the pressure in the fermenter within the above range, it is possible to further enhance the reactivity of gas-utilizing bacteria while suppressing an increase in equipment cost due to an excessive pressure load.

When the medium (culture solution) is circulated in the fermenter, the circulation rate can be preferably about 0.1 to 10 m / s, more preferably about 0.5 to 1 m / s.

In the fermenter, the temperature (culture temperature) of the medium (culture solution) may be any temperature, but is preferably about 30 to 45 ° C, more preferably about 33 to 42 ° C, and even more preferably 36.5. The temperature can be about 37.5 ° C. The culturing time is preferably 12 hours or more in continuous culturing, more preferably 7 days or more, particularly preferably 30 days or more, and most preferably 60 days or more. From the viewpoint, it is preferably 720 days or less, more preferably 365 days or less. The culture period means the period from the addition of the inoculum to the culture tank to the discharge of the entire amount of the culture solution in the culture tank.

<Refining process>
In the method for producing an organic substance according to the present invention, the organic substance obtained through microbial fermentation in the fermentation step may be subsequently subjected to a purification step for the purpose of purification. The purification step is a step of purifying a desired organic substance from the organic substance obtained in the fermentation step. Equipment used in the purification process is, for example, a distillation apparatus, a treatment apparatus containing a permeation vaporization membrane, a treatment apparatus containing a zeolite dehydration membrane, a treatment apparatus for removing a low boiling point substance having a boiling point lower than that of an organic substance, and a treatment apparatus having a higher boiling point than an organic substance. Examples thereof include a processing device for removing a high boiling point substance, a processing device containing an ion exchange membrane, and the like. These devices may be used alone or in combination of two or more. As the unit operation, heat distillation or membrane separation may be preferably used.

In thermal distillation, a distillation apparatus can be used to purify the desired organic substance with high purity. The temperature inside the distiller during distillation of an organic substance (particularly ethanol) is not particularly limited, but is preferably 100 ° C. or lower, more preferably about 70 to 95 ° C. By setting the temperature in the distiller within the above range, it is possible to more reliably separate the necessary organic substance from other components, that is, to distill (purify) the organic substance.

The pressure in the distillation apparatus during distillation of the organic substance may be normal pressure, but is preferably less than atmospheric pressure, more preferably about 60 to 95 kPa (gauge pressure). By setting the pressure in the distillation apparatus within the above range, the separation efficiency of the organic substance can be improved, and thus the yield of the organic substance can be improved. The yield of the organic substance (concentration of the organic substance obtained after distillation) is preferably 90% by weight or more, more preferably 99% by weight or more, and particularly preferably 99.5% by weight or more.

In the membrane separation, a known separation membrane can be appropriately used, and for example, a zeolite membrane can be preferably used.

[Organic substances and their uses]
Examples of the organic substance obtained by the production method according to the present invention include methanol, ethanol, 2,3-butanediol, acetic acid, lactic acid, isoprene, butadiene, and the like, preferably alcohols or diols having 1 to 4 carbon atoms. Yes, more preferably ethanol is included. The use of the organic substance obtained by the production method of the present invention is not particularly limited. The produced organic substance can be used as a raw material for, for example, plastics and resins, and can also be used as various solvents, bactericides, or fuels. High-concentration ethanol can be used as fuel ethanol to be mixed with gasoline and the like, and can also be used as, for example, cosmetics, beverages, chemical substances, raw materials such as fuel (jet fuel), and additives for foods, etc. Very high quality.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples as long as the gist of the present invention is not exceeded.

<Analysis method>
In the following examples, the amount of ethanol produced and the amount of acetic acid produced were measured by liquid chromatography. The measurement conditions were as follows.
・ Analyzer: Agilent 7890B Series GC Custom
-Eluent: 0.005 mol / L sulfuric acid solution-Flow rate: 0.6 ml / min

[Comparative Example 1]
In a continuous fermentation device (fermentation tank) equipped with a main reactor, synthetic gas supply hole, medium supply hole, and discharge hole, inoculum of Clostridium autoethanogenum (microorganism) and liquid for culturing bacteria containing no sulfur compound It was filled with a medium (containing an appropriate amount of phosphorus compound, nitrogen compound, various minerals, etc.).
Next, a synthetic gas 1 composed of 30% by volume of carbon monoxide, 10% by volume of carbon dioxide, 35% by volume of hydrogen and 25% by volume of nitrogen is prepared in the continuous fermentation apparatus, supplied to the continuous fermentation apparatus, and cultured (microorganisms). Fermentation) was performed. While continuing the culture, the culture solution was collected regularly, and the amount of ethanol produced and the amount of acetic acid produced were measured by liquid chromatography. The amount was 100.

[Example 1]
Syngas 1 used in Comparative Example 1 was changed to Syngas 2 composed of 30% by volume of carbon monoxide, 5% by volume of carbon dioxide, 35% by volume of hydrogen and 30% by volume of nitrogen, in the same manner as in Comparative Example 1. , The amount of ethanol produced and the amount of acetic acid produced in the culture solution were measured, and the relative values with respect to the amount of ethanol produced and the amount of acetic acid produced (100) in Comparative Example 1 were calculated.

[Example 2]
The synthetic gas 1 used in Comparative Example 1 was changed to a synthetic gas 3 composed of 30% by volume of carbon monoxide, 1% by volume of carbon dioxide, 35% by volume of hydrogen and 34% by volume of nitrogen, in the same manner as in Comparative Example 1. , The amount of ethanol produced and the amount of acetic acid produced in the culture solution were measured, and the relative values with respect to the amount of ethanol produced and the amount of acetic acid produced (100) in Comparative Example 1 were calculated.

[Comparative Example 2]
Ethanol in the culture solution was the same as that of Comparative Example 1 except that the synthetic gas 1 used in Comparative Example 1 was changed to the synthetic gas 4 composed of 30% by volume of carbon monoxide, 35% by volume of hydrogen and 35% by volume of nitrogen. The amount of production and the amount of acetic acid produced were measured, and the relative values with respect to the amount of ethanol produced and the amount of acetic acid produced (100) in Comparative Example 1 were calculated.

The evaluation results of Examples and Comparative Examples are as shown in Table 1.

Generally, the carbon dioxide concentration in a gasifier or steel exhaust gas is 10 to 30% by volume, and although these raw material gases can be directly introduced into a continuous fermenter to produce ethanol, the carbon dioxide concentration in the raw material gas can be increased. The comparison between Examples 1 and 2 and Comparative Example 1 shows that the production of ethanol increases when the synthetic gas reduced by any means is supplied to the fermenter even if the carbon monoxide content is the same. Revealed by. It is considered that this is because when the carbon dioxide concentration is high as in Comparative Example 1, the path in which acetic acid is produced from carbon dioxide (see FIG. 1) is preferentially used, and as a result, the ethanol production amount is reduced. ..

On the other hand, it was clarified by comparison between Examples 1 and 2 and Comparative Example 2 that the ethanol production amount decreased when the synthetic gas did not contain carbon dioxide. It is considered that this is because when the carbon dioxide concentration in the synthetic gas is too low, the carbon dioxide consumed when producing ethanol from carbon monoxide is insufficient, and as a result, the amount of ethanol produced is reduced.

Claims (3)

A method for producing organic substances by microbial fermentation of a synthetic gas consisting of carbon monoxide, carbon dioxide, hydrogen, and nitrogen.
A raw material gas generation process that gasifies a carbon source derived from waste to generate a raw material gas,
By adjusting the concentration of the components in the raw material gas, the carbon monoxide concentration is 20% by volume or more and 45% by volume or less, and the carbon dioxide concentration is 0. A pretreatment step for obtaining a synthetic gas having a hydrogen concentration of 1% by volume or more and 9% by volume or less, a hydrogen concentration of 10% by volume or more and 50% by volume or less, and a nitrogen concentration of 1% by volume or more and 40% by volume or less.
A synthetic gas supply step of supplying the synthetic gas into a fermenter containing a microorganism containing the genus Clostridium, and
A fermentation process in which the synthetic gas is microbially fermented in the fermenter,
A method for producing an organic substance, including. The pretreatment step comprises treating the raw material gas by adsorption and desorption apparatus, a method according to claim 1. The method of claim 1 or 2 , wherein the organic substance comprises ethanol.

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