JP2019088240A - Production method of organic substance - Google Patents

Abstract

To provide a production method of an organic substance excellent in productivity and capable of efficiently converging carbon monoxide in a synthesis gas in a specific composition into an organic substance.SOLUTION: There is provided a method for producing an organic substance by microbial fermentation of a synthetic gas including at least, carbon monoxide, carbon dioxide and hydrogen comprising: a synthetic gas supply step for supplying the synthetic gas into a fermentation tank including microbes; and a fermentation step for performing microbial fermentation of the synthetic gas in the fermentation tank. In the fermentation tank, carbon dioxide density in the synthetic gas is set to equal to or more than 0.1 volume% and equal to or less than 9 volume% to total density of the carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthetic gas.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of 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 synthesis gas.

  In recent years, from the viewpoint of global environmental problems such as concern for exhaustion of fossil fuel resources due to large consumption of oil and alcohol produced from petroleum as raw materials and increase of carbon dioxide in the atmosphere, various organic materials are used as raw materials other than petroleum. A method of producing a substance, for example, a method of producing bioethanol from an edible raw material such as corn by a sugar fermentation method has attracted attention. However, since the sugar fermentation method using such edible raw materials uses a limited farmland area for production other than food, there has been a problem such as a rise in food prices.

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

JP, 2015-53866, A

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 examined a method of producing an organic substance by microbial fermentation using waste-derived synthetic gas as described in Patent Document 1 as a raw material, and it was found that carbon monoxide is a synthetic gas having the same concentration. It has been found that the amount of production of organic substances produced by microorganisms differs depending on the gas composition other than carbon monoxide even if

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

  The present inventors have intensively studied methods for solving the above problems, and as a result, the concentration of carbon dioxide among various components in the synthesis gas is the assimilation rate of carbon monoxide and hydrogen by microorganisms, that is, the production of organic substances. It was found that the above problems could be solved by using the syngas for microbial fermentation after setting carbon dioxide in the syngas 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 microbially fermenting a synthesis gas containing at least carbon monoxide, carbon dioxide and hydrogen,
A synthesis gas supply step of supplying the synthesis gas into a fermenter containing microorganisms;
A fermentation step of microbially fermenting the synthetic gas in the fermenter;
Including
The concentration of carbon dioxide in the synthesis gas supplied into the fermentation layer is 0.1% by volume or more and 9% by volume or less based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthesis gas How to make organic substances.

[2] a raw material gas generation step of gasifying a carbon source to generate a raw material gas;
A pretreatment step of adjusting the carbon dioxide concentration in the source gas to obtain the synthesis gas;
The method according to [1], further comprising

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

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

[5] The method according to any one of [1] to [4], wherein the microorganism comprises Clostridia.

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

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

It is the figure which showed the production | generation pathway of ethanol by the fermentative action of microorganisms.

  Hereinafter, an example of the preferable form which implements this invention is demonstrated. However, the following embodiment is an illustration for describing the present invention, and the present invention is not limited to the following embodiment. In the present specification, the proportion of each component in the gas is based on volume, not weight, unless otherwise specified. Thus, unless stated otherwise, percentage% represents volume% and ppm represents volume ppm.

[material]
<Carbon source>
The carbon source used as the raw material of the synthesis gas used in the present invention is not particularly limited, and, for example, coke ovens in blast furnaces, blast furnaces (blast furnace gases), coal used in converters and coal-fired power plants, incinerators (especially gases) Various carbon-containing materials can be suitably used for the purpose of recycling, such as general waste and industrial waste introduced into the furnace and carbon dioxide by-produced by various industries.
More specifically, carbon sources include plastic waste, food waste, municipal waste (MSW), waste tires, biomass waste, household waste such as bedding and paper, waste such as building materials, coal, oil, etc. Petroleum-derived compounds, natural gas, shale gas and the like can be mentioned. Among them, various wastes are preferable, and unsorted municipal waste is more preferable from the viewpoint of separation cost.

<Source 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 source gas may further contain components such as soot, tar, nitrogen compounds, sulfur compounds, phosphorus compounds, aromatic compounds and the like.

As described later, the raw material gas is monooxidized by performing heat treatment (generally called gasification) to burn the carbon source (incomplete combustion) in the raw material gas generation step, that is, by partially oxidizing the carbon source. You may produce | generate as a gas containing 20 volume% or more of carbon.
In the above raw material gas production process, for example, burning wastes in a gasification furnace, heating by adding coal at the time of steel production (iron making process), carbon dioxide obtained by burning organic matter is reversed by metal catalyst Methods such as conversion to carbon monoxide by shift reaction may be mentioned.

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

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

  As described later, the synthesis gas used in the present invention generates a source gas by gasifying a carbon source (a source gas generation step), and then, from the source gas, carbon monoxide, carbon dioxide, hydrogen and nitrogen A gas obtained by the steps of reducing or removing the above-mentioned substances or compounds may be used as synthesis gas together with the concentration adjustment of each component.

The carbon dioxide concentration in the synthesis gas is, as described later, 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 synthesis gas More preferably, it is 0.5 volume% or more, more preferably 0.8 volume% or more, particularly preferably 1 volume% or more, and 9 volume% or less, preferably 8 volume% or less, more preferably 7 volume % Or less, more preferably 6% by volume or less, particularly preferably 5% by volume or less. The method of controlling the carbon dioxide concentration in the synthesis 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 adsorption capacity such as zeolite The carbon dioxide concentration in the synthesis gas can be reduced by bringing it into contact with a fluctuating adsorption method) or a TSA (thermal fluctuating adsorption method) device using an amine-based adsorptive solution, and control to be within the above range it can.
In the present invention, “to control” means to operate 95% or more of the conditions under the above conditions in the entire period from stably producing ethanol to stopping culture of the microorganism, It does not include the initial start-up step of growing the inoculum in the fermenter, and the end step of stopping the culture of the bacteria by stopping the supply of the culture medium and the syngas.

The concentration of carbon monoxide in the synthesis 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 synthesis gas. It is at least 50% by volume, more preferably at least 35% by volume and at most 45% by volume.
The concentration of hydrogen in the synthesis gas is usually 10% by volume or more and 80% by volume or less, preferably 30% by volume or more, based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthesis gas. It is volume% or less, More preferably, it is 40 volume% or more and 50 volume% or less.
Furthermore, the nitrogen concentration in the synthesis gas is usually 40% by volume or less, preferably from 1% by volume to 20% by volume, based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthesis gas. It is more preferably 5% by volume or more and 15% by volume or less.
The concentrations of carbon monoxide, hydrogen and nitrogen should be changed as appropriate by changing the CH-N elemental composition of the carbon source in the raw material gas production process, the combustion temperature, and the oxygen concentration of the supply gas at the time of combustion. By doing this, the predetermined range can be obtained. For example, if you want to change the concentration of carbon monoxide or hydrogen, change it to a carbon source with a high C-H ratio, such as waste plastic, and if you want to reduce the nitrogen concentration, supply a gas with a high oxygen concentration in the source gas generation process. There is a way to do it.

  The synthesis gas used in the present invention may contain a sulfur compound, a phosphorus compound, a nitrogen compound and the like in addition to the components described above. 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, more preferably Is less than 40 ppm. By making the content of the sulfur compound, the phosphorus compound, the nitrogen compound, etc. higher than the lower limit, there is an advantage that the microorganism can be cultured suitably, and by making the content lower than the upper limit, the microorganism was not consumed There is an advantage that the culture medium is not contaminated by various nutrient sources.

Sulfur compounds generally include sulfur dioxide, CS ₂ , COS and H ₂ S, and among these, H ₂ S and sulfur dioxide are preferable in that they are easy to consume as nutrient sources for microorganisms. Therefore, it is more preferable that the sum of H ₂ S and sulfur dioxide be included in the above range in the synthesis gas.
As a phosphorus compound, the point which is easy to consume phosphoric acid as a nutrient source of microorganisms is preferable. Therefore, it is more preferable that phosphoric acid be contained in the above-mentioned range in the synthesis gas.
Nitrogen compounds include nitrogen monoxide, nitrogen dioxide, acrylonitrile, acetonitrile, HCN and the like, and HCN is preferable in that it is easy to consume as a nutrient source of microorganisms. Therefore, it is more preferable that HCN be contained in the above range in the synthesis gas.

  In addition, the synthesis gas may contain 0.01 ppm or more and 90 ppm or less of an aromatic compound, 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 The content is more preferably 50 ppm or less, still more preferably 30 ppm or less. By setting the content above the lower limit, it tends to be possible to culture the microorganism suitably, and by setting the content below the upper limit, the culture medium is less likely to be contaminated by various nutrient sources that the microorganism did not consume. It is in.

<Microbial>
The microorganism (species) which ferments the synthetic gas is not particularly limited as long as it can produce a desired organic substance by causing the synthetic gas to undergo microbial fermentation using carbon monoxide as a main raw material. For example, the microorganism (species) is preferably one that produces an organic substance from syngas by the fermentative action of gas-utilizing bacteria. Among the gas-utilizing bacteria, Clostridium (Clostridium) is more preferable, and Clostridium autoethanogenum is particularly preferable, but it is not limited thereto. The following further illustrates.

Gas-utilizing bacteria include both eubacteria and archaebacteria.
As the eubacteria, for example, a bacterium belonging to the genus Clostridium (Clostridium), a bacterium belonging to the genus Moorella, a bacterium belonging to the genus Acetobacterium (Acetobacterium), a bacterium belonging to the genus Carboxydocella, a bacterium belonging to the genus Rhodopseudomonas, a eubacteria (Eubacterium) bacteria, Butyribacterium bacteria, Oligotropha bacteria, Bradyrhizobium bacteria, aerobic hydrogen oxidizing bacteria Ralsotonia bacteria, and the like.

  On the other hand, as archaebacteria, for example, bacteria of the genus Methanobacterium, bacteria of the genus Methanobrevibacter, bacteria of the genus Methanocalculus, genus Methanococcus, bacteria of the genus Methanosarcina, bacteria of the genus Methanosphaera, bacteria of the genus Methanosphaera, bacteria of the genus Methanothrix, bacteria of the genus Methanoculleus, genus of the genus Methanofollisium Bacteria, bacteria of the genus Methanospirillium, bacteria of the genus Methanosaeta, bacteria of the genus Thermococcus, bacteria of the genus Thermofilum, bacteria of the genus Arcaheoglobus, etc. may be mentioned. Among these, as the archaebacteria, 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, bacteria of the Archaeoglobus are preferred.

  Furthermore, because of superior assimilability of carbon monoxide and carbon dioxide, as the archaebacteria, bacteria of the genus Methanosarcina, bacteria of the genus Methanothermobacter, or bacteria of the genus Methanococcus are preferable, and bacteria of the genus Methanosarcina or bacteria of the Methanococcus are particularly preferable. In addition, as a specific example of Methanosarcina genus bacteria, Methanosarcina barkeri, Methanosarcina mazei, Methanosarcina acetivorans etc. are mentioned, for example.

  Among the above-mentioned gas assimilable bacteria, bacteria having high ability to produce the desired organic substance are selected and used. For example, Clostridium autoethanogenum (Clostridium autoethanogenum), Clostridium ljungdahlii, Clostridium aceticum (Clostidium aceticum), Clostridium carboxidivorans (Clostridium carboxidirans) as a gas-utilizing bacterium having high ability to produce ethanol. And Moetella thermoacetica (Moorella thermoacetica) and Acetobacterium woodii (Acetobacterium woodii).

<Medium>
The culture medium used when cultivating the above-mentioned microorganism (species) is not particularly limited as long as it has an appropriate composition according to the bacteria. For example, the culture medium in the case of using Clostridia as a microorganism can be referred to, for example, "0091" of WO 2017-117309 pamphlet and "0097" to "0098" of US patent application publication 2017/260552. .

[Production method]
<Source gas generation process>
The source gas generation step is a step of generating a source gas by gasifying the carbon source described above. A gasifier may be used in the raw material gas generation step. The gasification furnace is a furnace which burns a carbon source (incomplete combustion), and examples thereof include a shaft furnace, a kiln furnace, a fluidized bed furnace, a gasification reforming furnace and the like. The gasification furnace is preferably a fluidized bed furnace type, because high hearth load and excellent operability can be achieved by partially burning the waste. The waste is gasified in a low-temperature (about 450-600 ° C) and low-oxygen atmosphere fluidized bed furnace to be decomposed into gas (carbon monoxide, carbon dioxide, hydrogen, methane, etc.) and char containing a large amount of carbon. Do. Furthermore, since incombustibles contained in wastes are separated from the bottom of the furnace in a hygienic and low oxidation state, it is possible to selectively recover valuables such as iron and aluminum in the incombustibles. Therefore, gasification of such wastes enables efficient resource recycling.

  The temperature of the gasification in the raw material gas production step is usually 100 ° C. or more and 1500 ° C. or less, preferably 200 ° C. or more and 1200 ° C. or less.

  The reaction time of gasification in the raw material gas production step is usually 2 seconds or more, preferably 5 seconds or more.

<Pretreatment process>
Before the synthesis gas supply step, this step is a step of removing or reducing specific substances such as various contaminants, dust particles, impurities, and an undesirable amount of compounds from the source gas. The pretreatment process includes, for example, scrubber (water soluble impurity separation device), gas chiller (water separation device), cyclone, fine particle (soot) separation device such as bag filter, desulfurization device (sulfide separation device), 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), removal 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 to remove contaminants and the like in the gas, and either a wet cleaning method or a dry cleaning method can be used depending on the purpose. Among them, a wet cleaning method in which particulate matter is brought into contact with a cleaning solution can be suitably used, and as an example, a cleaning method using a so-called water curtain can be used. When a wet cleaning method is used, the cleaning solution may, for example, be water, an acidic solution, an alkaline solution or the like, and is preferably water. The liquid temperature of the washing solution is usually 40 ° C. or less, preferably 30 ° C. or less, more preferably 25 ° C. or less, and still more preferably 15 ° C. or less.

  An adsorption apparatus should just have the ability to adsorb components other than carbon monoxide and hydrogen in source gas, and a desulfurization layer and a deoxidizing layer can be mentioned as an installation aiming at only adsorption, for example. Among these, the desulfurization layer is not particularly limited as long as it can remove sulfur content. If the sulfur content can not be sufficiently removed or reduced in the desulfurization layer and the amount of sulfur content remains high, the presence of the adsorption / desorption device in the subsequent stage may have an adverse effect.

  The oxygen removing layer is not particularly limited as long as it can remove the oxygen component. If the oxygen component can not be sufficiently removed or reduced by the deoxidizing layer, and the oxygen component remains high, the microorganism used in the present invention, in particular, the anaerobic microorganism may be killed.

  Further, an adsorption / desorption device may be provided, and in that case, any of PSA, TSA and PTSA can be suitably used. Furthermore, another device may optionally be provided to remove unnecessary impurities. As an adsorption-desorption material used for an adsorption-desorption apparatus, porous materials, such as activated carbon, a zeolite, and molecular sieves, and aqueous solutions, such as an amine solution, can be used. Among them, activated carbon or zeolite capable of adsorbing aromatic compounds and sulfur compounds is preferably used. As described above, since the adsorption and desorption material may be adversely affected if the amount of sulfur in the raw material gas is high, the adsorption and desorption device may be provided after the desulfurization layer.

<Syngas supply process>
The synthesis gas supply step is a step of supplying the synthesis gas obtained as described above into a fermenter containing microorganisms. The syngas to be supplied contains carbon monoxide and hydrogen, and the carbon dioxide content is at least 0.1% by volume based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the syngas. 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 synthesis gas to the above range, carbon monoxide in the synthesis gas can be converted to 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 subjecting synthetic gas containing carbon monoxide, carbon dioxide and hydrogen to microbial fermentation, the microorganism (for example, ethanol-producing bacteria) passes through acetic acid as disclosed in Non-Patent Document 1 etc. Is thought to produce ethanol. At this time, as shown in FIG. 1, not only carbon monoxide but also carbon dioxide forms ethanol via acetic acid. Therefore, no attention was paid to carbon dioxide in synthesis gas. For example, it is known that about 10 to 30% by volume of carbon dioxide is contained in the raw material gas after gasification of the steel exhaust gas and the carbon source, but for the above reason, the raw material gas is subjected to microbial fermentation It has been considered unnecessary to control the carbon dioxide concentration in the source gas.

  However, carbon dioxide and carbon dioxide have different energy levels, and carbon dioxide is lower in energy level than carbon dioxide and stable, so when carbon dioxide is produced from carbon dioxide via acetic acid It is believed that the energy required for is 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 carbon dioxide concentration contained in the synthesis 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, particularly preferably 5% by volume It shall be below volume%.

  In addition, if the synthesis gas to be subjected to the microbial fermentation does not contain carbon dioxide at all (ie, the carbon dioxide concentration is 0%), the amount of ethanol produced decreases. Conventionally, in the process of producing acetic acid and ethanol from carbon monoxide by microbial fermentation, as shown in FIG. 1, when the microorganism takes in carbon monoxide, it is converted to carbon dioxide, so carbon dioxide is supplied to the microorganism from the outside. It was thought that it was not necessary. The present inventors have found that the productivity of ethanol is improved by using a synthesis gas containing a small amount of carbon dioxide. It is considered that the balance of the microbial metabolism system is improved by containing a trace amount of carbon dioxide in the syngas, and as a result, the productivity of ethanol is improved. Therefore, in the present invention, the lower limit of the carbon dioxide concentration contained in the synthesis 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 It is preferably at least 1% by volume, more preferably at least 1% by volume.

  As long as the component conditions of the synthesis 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 synthesis 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 synthesis gas. As another predetermined gas, for example, at least one compound selected from the group consisting of sulfur compounds such as sulfur dioxide, phosphorus compounds, and nitrogen compounds may be added to form synthesis gas.

<Fermentation process>
The fermentation process according to the present invention is a process of microbially fermenting the above-mentioned synthetic gas to produce an organic substance. In the fermentation process, a fermenter containing the above-mentioned microorganism (species) is used. The fermenter may contain a medium (culture solution) in addition to the microorganism species. It is known that some anaerobic microorganisms produce an organic substance which is a valuable material such as ethanol from a substrate gas such as synthesis gas by fermentation action, and this kind of gas-utilizing microorganism is a liquid It is cultured in the medium of For example, the culture solution and the gas-utilizing bacteria may be supplied and stored, and the synthesis solution may be supplied into the fermentation layer while stirring the culture solution in this state. Thereby, gas assimilable bacteria can be cultured in a culture solution, and an organic substance can be produced from syngas by the fermentation action.

  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 assimilable bacteria can grow well.

  The fermenter is preferably a continuous fermenter. Generally, the microorganism fermenter may be of any shape, and examples thereof include a stirrer type, an airlift type, a bubble column type, a loop type, an open bond type, and a photobio type. A well-known loop reactor having a main tank and a reflux can be suitably used. In this case, it is preferable to further include a circulating step of circulating the liquid culture medium between the main tank and the reflux part.

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

  When the culture medium (culture solution) is circulated in the fermenter, the circulation speed 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 preferably about 30 to 45 ° C., more preferably about 33 to 42 ° C., further preferably 36.5 It can be about 37.5 ° C. The culture time is preferably 12 hours or more, more preferably 7 days or more, particularly preferably 30 days or more, and most preferably 60 days or more in continuous culture, and the upper limit is not particularly set. From the viewpoint, 720 days or less is preferable, and more preferably 365 days or less. In addition, culture | cultivation period shall mean the period after adding an inoculum to a culture tank until the whole culture solution in a culture tank is discharged.

<Purification 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 subjected to a purification step for the purpose of purification thereafter. The purification step is a step of purifying a desired organic substance from the organic substance obtained in the fermentation step. The apparatus used in the purification step is, for example, a distillation apparatus, a processing apparatus including a pervaporation membrane, a processing apparatus including a zeolite dewatering membrane, a processing apparatus for removing low boiling substances having a boiling point lower than that of an organic substance, a boiling point higher than that of an organic substance The processing apparatus which removes a high boiling point substance, the processing apparatus containing an ion exchange membrane, etc. are mentioned. These devices may be used alone or in combination of two or more. As unit operation, thermal distillation or membrane separation may be suitably used.

  In thermal distillation, a desired organic substance can be purified with high purity using a distillation apparatus. Although the temperature in the distiller at the time of distillation of an organic substance (especially ethanol) is not specifically limited, It is preferable that it is 100 degrees C or less, and it is more preferable that it is about 70-95 degreeC. By setting the temperature in the distiller to the above range, the separation of the necessary organic substance from the other components, that is, the distillation (purification) of the organic substance can be performed more reliably.

  The pressure in the distillation apparatus at the time of 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 in the above range, the separation efficiency of the organic substance can be improved, and hence the yield of the organic substance can be improved. The yield (the concentration of the organic substance obtained after distillation) of the organic substance is preferably 90% by weight or more, more preferably 99% by weight or more, and particularly preferably 99.5% by weight or more.

  In membrane separation, a known separation membrane can be used as appropriate, and for example, a zeolite membrane can be suitably used.

[Organic substance and its use]
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, and preferably an alcohol or diol having 1 to 4 carbon atoms It is preferable to contain ethanol, more preferably ethanol. The application of the organic substance obtained by the production method of the present invention is not particularly limited. The manufactured organic substance can also be used as a raw material of, for example, plastics, resins, etc., and can also be used as various solvents, germicides, or fuels. High-concentration ethanol can be used as fuel ethanol to be mixed with gasoline etc. For example, it can be used as additives for cosmetics, beverages, chemicals, raw materials such as fuel (jet fuel), foods etc. Extremely high.

  Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

<Analytical method>
In the following examples, measurement of ethanol production and acetic acid production was performed 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
Seed of Clostridium autoethanogenum (microorganisms) in a continuous fermentation apparatus (fermenter) equipped with a main reactor, synthesis gas supply holes, culture medium supply holes, and discharge holes, and liquid for culture of bacteria that does not contain sulfur compounds The medium was filled with a medium (containing an appropriate amount of phosphorus compound, nitrogen compound, various minerals, etc.).
Next, the synthesis gas 1 consisting of 30 vol% carbon monoxide, 10 vol% carbon dioxide, 35 vol% hydrogen and 25 vol% nitrogen is prepared in the above continuous fermentation apparatus, supplied to the continuous fermentation apparatus, and cultured (microbe Fermented). While continuing the culture, the culture fluid is collected periodically, and the amount of ethanol and acetic acid produced are measured by liquid chromatography, and the amount of ethanol and acetic acid produced in the culture fluid when each production amount is stabilized The amount was 100.

Example 1
Comparative Example 1 is the same as Comparative Example 1 except that synthetic gas 1 used in Comparative Example 1 is changed to Synthetic gas 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. The ethanol production amount and the acetic acid production amount in the culture solution were measured, and the relative value with respect to the ethanol production amount and the acetic acid production amount (100) in Comparative Example 1 was calculated.

Example 2
Comparative Example 1 is the same as Comparative Example 1 except that synthetic gas 1 used in Comparative Example 1 is changed to 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. The ethanol production amount and the acetic acid production amount in the culture solution were measured, and the relative value with respect to the ethanol production amount and the acetic acid production amount (100) in Comparative Example 1 was calculated.

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

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

  Generally, the carbon dioxide concentration in gasification furnaces and steel exhaust gases is 10 to 30% by volume, and these raw material gases can be introduced as they are into a continuous fermentation tank to produce ethanol, but the carbon dioxide concentration in the raw material gases It is compared with Example 1, 2 and the comparative example 1 that the production amount of ethanol increases even if carbon monoxide content is the same if the synthetic gas reduced by arbitrary means is supplied to a fermenter. It became clearer. It is considered that when the carbon dioxide concentration is high as in Comparative Example 1, the path (see FIG. 1) in which acetic acid is produced from carbon dioxide is preferentially used, and as a result, the amount of ethanol production is reduced. .

  On the other hand, when the carbon dioxide was not contained in the synthesis gas, it became clear from the comparison between Example 1, 2 and Comparative Example 2 that the amount of ethanol production decreases. It is considered that when the concentration of carbon dioxide in the synthesis gas is too low, carbon dioxide consumed when producing ethanol from carbon monoxide runs short, and as a result, the amount of ethanol production decreases.

Claims (6)

A method of producing an organic substance by microbially fermenting synthesis gas containing at least carbon monoxide, carbon dioxide and hydrogen,
A synthesis gas supply step of supplying the synthesis gas into a fermenter containing microorganisms;
A fermentation step of microbially fermenting the synthetic gas in the fermenter;
Including
The concentration of carbon dioxide in the synthesis gas supplied to the fermentation layer is 0.1% by volume or more and 9% by volume or less based on the total concentration of carbon monoxide, carbon dioxide, hydrogen and nitrogen in the synthesis gas. , How to produce organic substances. A source gas generation step of gasifying a carbon source to generate a source gas;
A pretreatment step of adjusting the carbon dioxide concentration in the source gas to obtain the synthesis gas;
The method of claim 1, further comprising   The method of claim 2, wherein the carbon source is waste.   The method according to claim 2, wherein the pretreatment step comprises treating the raw material gas with an adsorption / desorption device.   The method according to any one of claims 1 to 4, wherein the microorganism comprises Clostridia.   The method according to any one of claims 1 to 5, wherein the organic substance comprises ethanol.