JP5657915B2 - Methane fermentation method - Google Patents

Description

  The present invention relates to a methane fermentation method for fermenting a sugar solution with high efficiency.

  Faced with the depletion of petroleum resources and the problem of preventing global warming, research to create new energy using biomass as a raw material is being actively conducted. Among them, research on the production of bioethanol from sugarcane and corn as a raw material has become a global trend, but it may cause a food crisis and cause confusion. ing. Therefore, the development of new energy from forest resources has become an important issue.

  By the way, in order to extract an energy source such as methane gas from a wood raw material, a method of recovering methane gas by extracting cellulose-derived glucose from the wood raw material by hydrolysis with alkali or acid and further subjecting the glucose to methane fermentation in an anaerobic atmosphere. It has been known. This methane fermentation proceeds by a sequential reaction in which an organic acid such as butyric acid or caproic acid is produced from components derived from cellulose and further decomposed into acetic acid to methane gas. However, if the production of organic acid is significant during methane fermentation, the reaction will not proceed easily until the production of methane gas, and the methane fermentation technology developed so far is not sufficient to efficiently recover methane gas. there were.

  Under such circumstances, a methane fermentation method using anaerobic cellulolytic bacteria from wastes containing cellulosic organic materials has been disclosed for the purpose of efficiently using resources and converting organic matter to methane gas as energy. (For example, Patent Document 1).

JP 2005-254168 A

  However, in the method of Patent Document 1, it is necessary to provide a cellulose-degrading bacterium growth tank, and it is necessary to perform methane fermentation with great energy and cost. In addition, culture conditions that promote the growth of cellulose-degrading bacteria are required, and the operation is complicated for efficient methane fermentation. The present invention has been made to solve the above-described problems, and provides a methane fermentation method that enables methane fermentation with less energy and cost and that ferments a sugar solution with high efficiency. For the purpose.

  Therefore, as a result of repeated studies to solve the above-described problems, the present inventors have conducted methane fermentation from a sugar solution (cellulose waste solution) containing glucose monomers and / or multimers thereof in the sugar solution. The present inventors have found that the above-mentioned problems can be solved by adjusting the carbon concentration to 0.3 mol / L or less and causing methane fermentation to complete the present invention. That is, the present invention relates to a methane fermentation method in which the sugar concentration is adjusted to 0.3 mol / L or less and the sugar solution is methane-fermented in the sugar solution containing glucose monomers and / or multimers thereof.

  The present invention also relates to a methane fermentation method in which the sugar liquid is methane-fermented while maintaining the pH of the sugar liquid during methane fermentation at 6.4 to 7.0.

  In the present invention, it is preferable to maintain the pH of the sugar solution by neutralizing the sugar solution by adding an alkaline compound.

  The alkaline compound may be any one selected from the group consisting of aqueous ammonia, sodium carbonate, calcium carbonate, magnesium carbonate, magnesium oxide, sodium bicarbonate, sodium hydroxide, potassium hydroxide, and calcium hydroxide. preferable.

  According to the present invention, when a sugar solution containing glucose monomers and / or multimers thereof is subjected to methane fermentation by an anaerobic microorganism, methane fermentation can be performed with less energy and cost, and high The sugar solution can be fermented with efficiency.

It is a conceptual diagram of the fermentation system of the woody biomass concerning embodiment of this invention. It is a flowchart of the methane fermentation method concerning embodiment of this invention. It is a graph which shows the result of the methane fermentation experiment concerning an Example and a comparative example.

  Hereinafter, the present invention will be described in detail. In the embodiment of the present invention, an acid and a phenol derivative are added to woody biomass to hydrolyze cellulose and hemicellulose in the woody biomass, and the resulting sugar solution (containing glucose monomers and / or multimers thereof) The case where methane fermentation is carried out by anaerobic microorganisms will be described. However, the sugar solution used in the present invention is applicable as long as it has a glucose component, regardless of the process extracted from the woody biomass. As a method of adding an acid and a phenol derivative to woody biomass, after adding a phenol derivative to woody biomass and impregnating it, an acid is added, and when the viscosity of the system decreases, a hydrophobic solvent described later is added, Furthermore, the method of performing stirring is mention | raise | lifted. By doing in this way, it becomes possible to isolate | separate into the layer which consists of a sugar component derived from a cellulose and hemicellulose, and a sulfuric acid, and the layer which consists of lignophenol, a phenol derivative, and a hydrophobic solvent.

  The woody biomass used in the present invention is a biological organic resource that can be regenerated and is composed of cellulose, hemicellulose, lignin and the like. Woody biomass refers to what is mainly made of wood, and examples thereof include wood flour and wood chips. Moreover, as wood to be used, any kind of wood such as conifers and hardwoods can be used.

  As the acid added to the woody biomass, either an inorganic acid or an organic acid can be used. The acid not only serves as a catalyst for hydrolyzing cellulose and hemicellulose, but also serves to break the bond between cellulose, hemicellulose and lignin that constitute the woody biomass. As the inorganic acid, any of sulfuric acid, phosphoric acid, hydrochloric acid and the like can be used. The acid concentration is preferably 60 to 90%. When the acid concentration is lower than 60%, the delamination reaction between cellulose and lignin does not proceed, and when the acid concentration is higher than 90%, the benzene skeleton of lignin and the additive p-cresol is easily sulfonated, There is a tendency for defects to occur. Of the acids, 60% or more sulfuric acid is preferred. Similarly, when the concentration of sulfuric acid is lower than 60%, the degrading reaction between cellulose and lignin does not proceed, and when the concentration of sulfuric acid is higher than 90%, the benzene skeleton of lignin and p-cresol, which is an additive, is reduced. Sulfonation tends to progress. As the organic acid, p-toluenesulfonic acid, trifluoroacetic acid, trichloroacetic acid, formic acid and the like can be used. However, the ion exchange resin and the ion exchange membrane may be swollen in the method for recovering the acid. Must. Among them, it is preferable to use sulfuric acid having a concentration of 60% by mass or more, more preferably 70% by mass or more from the viewpoint that cellulose and hemicellulose can be efficiently hydrolyzed. As usage-amount of the acid added to woody biomass, Preferably it is 200-3000 mass parts with respect to 100 mass parts of woody biomass, More preferably, it is 1000-2000 mass parts. When the amount of acid used is small, the woody material only swells and does not become liquid, making stirring difficult, and a new type of extrusion kneader is required. Moreover, when there is too much usage-amount of an acid, the burden to the recovery system of an acid will increase and economical efficiency will be impaired.

  The α-carbon of the phenylpropane unit in p-coumalyl alcohol, cinapyl alcohol, and coniferyl alcohol constituting lignin is chemically unstable, but by adding a phenol derivative, various uses such as molded articles Lignophenol which can be utilized in the process can be obtained. Here, lignophenol refers to a polymer containing a diphenylpropane unit in which a phenol derivative is bonded to the α carbon of the phenylpropane unit in lignin.

  Examples of the phenol derivative include a monovalent phenol derivative, a divalent phenol derivative, and a trivalent phenol derivative. Examples of monovalent phenol derivatives include phenol, naphthol, anthrol, anthrochiol and the like. These monovalent phenol derivatives may further have one or more substituents. Examples of the divalent phenol derivative include catechol, resorcinol, hydroquinone and the like. These divalent phenol derivatives may further have one or more substituents. Examples of the trivalent phenol derivative include pyrogallol. Pyrogallol may further have one or more substituents. The kind of the substituent which these monovalent to trivalent phenol derivatives have is not particularly limited, and may have an arbitrary substituent. Groups other than electron-withdrawing groups (such as halogen atoms), such as lower alkyl groups (such as methyl, ethyl, and propyl groups), lower alkoxy groups (such as methoxy, ethoxy, and propoxy groups), aryl groups (Phenyl group and the like), hydroxyl group and the like. Further, from the viewpoint of reactivity with the α-carbon of the phenylpropane unit constituting lignin, it is preferable that at least one of the two ortho positions of the phenolic hydroxyl group on the phenol derivative is unsubstituted.

  Preferred examples of the phenol derivative include p-cresol, 2,6-xylenol, 2,4-xylenol, 2-methoxyphenol (guaiacol), 2,6-dimethoxyphenol, catechol, resorcinol, homocatechol, pyrogallol and phlorog. Examples include lucinol, and p-cresol is particularly preferable. As a quantity of a phenol derivative, Preferably it is 200-3000 mass parts with respect to 100 mass parts of woody biomass, More preferably, it is 500-2000 mass parts. The amount of phenol derivative should be added in consideration of the stoichiometric amount necessary for masking the α-carbon of lignin, and the amount as an extractant necessary for phase separation. There must be.

  In the present invention, by adding an acid and a phenol derivative to woody biomass, it is separated into an aqueous layer composed mainly of acid, a sugar solution derived from cellulose and hemicellulose, and an oil layer composed of lignophenol and a phenol derivative. However, it is preferable to further add a hydrophobic solvent in order to separate the two layers in a shorter time. In addition, when a hydrophobic solvent is not used, a small amount of acid may be mixed in the oil layer, and a phenol derivative may also be mixed in the aqueous layer. This can be prevented by adding a hydrophobic solvent. I can do it. Examples of the hydrophobic solvent include n-pentane, n-hexane, heptane, octane, cyclohexane, decalin, and mixtures thereof. Of these, n-hexane is preferable. Since the hydrophobic solvent is separated into three layers when the dissolved amount of p-cresol or more is added, it is preferable to adjust appropriately according to the dissolved amount of p-cresol. When adding n-hexane, it is preferable to add 30-40 mass parts with respect to 100 mass parts of p-cresol. It is desirable to add the hydrophobic solvent at the same time when the lignin and cellulose are unraveled, but after separating the two layers roughly after the relaxation reaction, the upper layer (light layer) and the lower layer ( A hydrophobic solvent is added to each of the multiple layers), the aqueous sulfuric acid solution is separated and removed from the upper layer, and the p-cresol dissolved in a trace amount can be extracted and removed from the lower layer.

  In this invention, an acid is collect | recovered from the solution comprised after adding an acid and a phenol derivative to woody biomass, and the acid and the sugar component derived from a cellulose and hemicellulose. As a method for recovering the acid, a general method can be used, and examples thereof include an ion exchange chromatography method and an electrodialysis method. The concentration of the recovered acid is preferably 20% by mass or more, more preferably 30% by mass or more, and further preferably 50% by mass or more.

  The concentration of the acid in the sugar liquid obtained after collecting the acid is preferably 3% by mass or less. When the concentration of the acid in the sugar solution is higher than 3% by mass, the amount of acid remaining in the sugar solution increases, which causes fermentation to be inhibited when the sugar solution is fermented.

  In the present invention, the carbon concentration of the sugar solution is adjusted by diluting the sugar solution after collecting sulfuric acid with water. The carbon concentration of the diluted sugar solution is 0.3 mol / L or less, and preferably 0.15 to 0.3 mol / L. When the carbon concentration exceeds 0.3 mol / L, accumulation of organic acid is caused and methane fermentation tends to be inhibited. In order to set the carbon concentration of the sugar liquid to 0.3 mol / L or less, it is preferable to add water to the sugar liquid.

  In the present invention, the pH of the sugar solution is maintained near neutrality by adding an alkaline compound to the sugar solution. As fermentation progresses, butyric acid, caproic acid, acetic acid, valeric acid, propionic acid, and lactic acid are usually generated, and the pH of the system is lowered and methane fermentation is suppressed. By adjusting so that it may be in the range of this value, suppression of methane fermentation can be prevented. The pH of the sugar solution is usually about 6 before methane fermentation, and is preferably maintained in the range of 6.4 to 7.0. When the pH is lower than 6, the organic acid accumulated in the sugar solution is not sufficiently neutralized, and methane fermentation is inhibited.

  The alkaline compound to be added to the sugar solution is not particularly limited as long as the pH of the sugar solution can be maintained in the range of 6.4 to 7.0 and exhibits alkalinity. Examples thereof include sodium, calcium carbonate, magnesium carbonate, magnesium oxide, sodium hydrogen carbonate, sodium hydroxide, potassium hydroxide, and calcium hydroxide. Among these, sodium hydroxide is preferable from the viewpoint of the efficiency of methane fermentation. These alkaline compounds may be used individually by 1 type, and may be used in combination of 2 or more type.

  Next, 50 mass parts of wood flour as a woody biomass raw material, 61 mass parts of p-cresol as a phenol derivative, 100 mass parts of 60% sulfuric acid, and 29 mass parts of n-hexane, a series of processes from release to fermentation. The case of processing will be described with reference to FIGS. FIG. 1 is a conceptual diagram of a woody biomass fermentation system according to an embodiment of the present invention. The fermentation system for woody biomass is a release tank 1 for producing sugar components and lignophenol from woody biomass as a raw material, and the sugar component and lignophenol produced in the release tank 1 into an aqueous layer and an oil layer, respectively. Separation tank 2 for separation, filter 3 for solid-liquid separation of lignophenol and solvent by filtering the solvent in the oil layer separated in separation tank 2, dryer 4 for drying lignophenol filtered by filtration machine 3, Resin chromatography column 5 for recovering acid from the aqueous layer (sugar solution) separated in separation tank 2, electrodialysis tank 6 for recovering acid from sugar solution obtained in resin chromatography tower 5, and electrodialysis tank 6 It is comprised from the fermenter 7 which ferments the sugar solution obtained by this.

  First, wood flour, p-cresol, sulfuric acid, and n-hexane are added to the relaxation tank 1 and stirred. Lignin in wood flour has high α-carbon reactivity and is chemically unstable, but is stabilized by p-cresol to form lignophenol. Cellulose and hemicellulose in wood flour are hydrolyzed using sulfuric acid as a catalyst. The saccharification treatment in the relaxation tank 1 is performed by applying a treatment time of 30 to 60 minutes at a temperature of 60 to 95 ° C. When the temperature of saccharification treatment is lower than 60 ° C., the efficiency of hydrolysis decreases, and when the temperature exceeds 95 ° C., the produced monosaccharide tends to be excessively decomposed. The sugar component derived from hydrolyzed cellulose and hemicellulose is present in a mixed state with monosaccharides such as glucose, dimers, oligomers and polymers thereof.

  In the release tank 1, decomposition of lignin and cellulose / hemicellulose in the woody biomass proceeds, and when the hydrolysis of cellulose and hemicellulose is completed, the obtained mixed liquid is sent to the separation tank 2. In the separation tank 2, the fed liquid mixture is divided into an oil layer (upper layer) composed of p-cresol, n-hexane and lignophenol, and an aqueous layer composed of a sugar component derived from cellulose and hemicellulose and sulfuric acid ( Separated into the lower layer). The oil layer is in the form of a slurry and includes 59 parts by mass of p-cresol, 29 parts by mass of n-hexane, and 17 parts by mass of lignophenol. The aqueous layer contains 20 parts by mass of a sugar component derived from cellulose and hemicellulose and 115 parts by mass of sulfuric acid.

  The oil layer separated in the separation tank 2 is solid-liquid separated by the filter 3 and separated into solid lignophenol, liquid p-cresol and n-hexane. Solid-liquid separation can be performed using a filter press or the like, and lignophenol is obtained in a cake form. The obtained lignophenol is dried by the dryer 4 and used as a raw material for various uses such as a molded article. Moreover, p-cresol and n-hexane contained in the filtrate are recovered and reused. n-Hexane is recovered from the top of the distillation column and p-cresol is recovered from the bottom.

  The solution containing sulfuric acid separated in the separation tank 2 is sent to the resin chromatography column 5 and sulfuric acid is recovered by ion exchange chromatography. In the resin chromatography column 5, sulfuric acid is adsorbed by the ion exchange resin, and about 92 to 97%, preferably about 95%, of the sulfuric acid contained in the solution is recovered. In this case, 109 parts by mass of sulfuric acid is recovered in the resin chromatography column 5.

  The recovered sugar solution still contains sulfuric acid, but the sulfuric acid is further recovered by the electrodialysis tank 6. Electrodialysis is performed so that the concentration of sulfuric acid in the sugar solution does not become lower than 0.5% by mass. When the concentration of sulfuric acid is lower than 0.5% by mass, current efficiency tends to deteriorate. In electrodialysis, a cation membrane that is a cation exchange membrane and an anion membrane that is an anion exchange membrane are used as partition walls. In the electrodialysis tank 6 of FIG. 1, a cation membrane exists on the anode side and an anion membrane exists on the cathode side. When a voltage is applied between the electrodes, sulfate ions move to the anode side and hydrogen ions move to the cathode side, but sulfate ions that are anions cannot pass through the cation membrane, and hydrogen ions that are cations. Cannot pass through the anion membrane, resulting in a liquid in which cations and anions are concentrated between the cation membrane and the anion membrane. Further, a liquid from which cations and anions are removed is obtained outside the cation membrane and the anion membrane. The concentrated liquid is mainly composed of sulfuric acid and is recovered and reused. In this case, 6 parts by mass of sulfuric acid is recovered. Therefore, a total of 115 parts by mass of sulfuric acid is recovered in the resin chromatography column 5 and the electrodialysis tank 6. In addition, in the electrodialysis tank 6 of FIG. 1, although it was set as the figure in which the cation membrane and the anion membrane were each installed for simplification, actually a some cation membrane and an anion membrane are installed alternately. .

  In addition, the liquid from which cations and anions have been removed, that is, the liquid from which sulfuric acid has been removed is recovered as a sugar solution. In this case, 20 mass parts of sugar solution is obtained by collecting sulfuric acid in the electrodialysis tank 6. The obtained sugar solution contains only about 0.5% by mass of sulfuric acid, and this sugar solution is fed to the fermenter 7.

  FIG. 2 is a flowchart of the methane fermentation method according to the embodiment of the present invention. When methane fermentation of cellulose waste liquid is started by anaerobic microorganisms, butyric acid 9 is first generated. Further, caproic acid 10 is produced from butyric acid 9, and acetic acid 11 is produced from caproic acid 10, and then methane 12 is produced from acetic acid 11. These reactions proceed sequentially. The sugar solution sent to the fermenter 7 is predicted to produce organic acids such as butyric acid and caproic acid as intermediates due to methane fermentation, which inhibits methane fermentation, so methane fermentation by anaerobic microorganisms Before performing, water is added and diluted so that the concentration of the sugar solution is 0.15 to 0.3 mol / L. The carbon concentration of the diluted sugar solution is 0.15 to 0.3 mol / L. Further, during the progress of methane fermentation, an alkaline compound is appropriately added to the sugar solution, and the pH of the sugar solution is maintained in the range of 6.4 to 7.0. When neutralizing the sugar solution, it is preferable to use a buffer solution. By doing in this way, it becomes possible to improve the yield of methane fermentation. The resulting methane is 16 parts by weight, leaving 4 parts by weight of residue. In addition, before performing methane fermentation, it is necessary to neutralize the sulfuric acid which remained in the sugar liquid by adding an alkaline compound. Moreover, it is preferable to perform methane fermentation at 25-50 degreeC.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1
(Methane fermentation experiment)
After adjusting yeast extract, ammonium chloride and dipotassium hydrogen phosphate to 1.0 mg / ml and resazurin sodium (redox indicator) to 1.0 mg / l respectively, sterilization with an autoclave makes the aqueous nutrient salt solution It was adjusted. 10ml of middle sea sediment (wet weight 13g, moisture content 78%) is taken in a 70ml vial, water is added to glucose solution (1.5M), and diluted to a sample concentration of 0.15M 40 ml of an aqueous nutrient salt solution (pH 7.0) was added.

  The sample was sealed with butyl rubber and sealed with an aluminum cap, followed by stationary culture in a dark place at 25 ° C. Samples were fired every week for injection, the internal pressure was returned to atmospheric pressure, and the increased volume was measured. Then, 20 μl of the head space was measured for methane and carbon dioxide concentrations by gas chromatography. Methane is FID (column: Porapak Q, carrier gas: helium 20 ml / min, column temperature: 70 ° C., inlet detection temperature: 150 ° C.), carbon dioxide is TCD (column: silica gel column, carrier gas: helium 80 ml / min) Column temperature: 70 ° C., detection temperature at the inlet: 100 ° C.), and identification and quantification were performed using each standard gas.

(Methane production rate)
About the sample, the methane density | concentration after fermentation was measured and the methane production | generation ratio was computed using the following formula.

(Example 2)
About the adjusted sample, 0.5M sodium hydroxide solution was appropriately added dropwise until the fermentation of the sugar solution was completed so that the pH of the sugar solution during the methane fermentation was in the range of 6.4 to 7.0. The sample was statically cultured in the same manner as in Example 1.

(Comparative Example 1)
For the sample, the sample (concentration 1.5 M) was statically cultured in the same manner as in Example 1 except that the dilution with water was not performed, and the concentrations of methane and carbon dioxide were measured.

(Comparative Example 2)
For the sample, the sample (concentration of 1.5 M) was statically cultured in the same manner as in Example 2 except that the dilution with water was not performed, and the concentrations of methane and carbon dioxide were measured.

  FIG. 3 is a graph showing the results of methane fermentation experiments according to Examples and Comparative Examples. As shown in FIG. 3, in Example 1, the methane concentration increased after 35 days had passed and the methane production rate reached 24% when the culture time reached 115 days. In Example 2, the methane concentration increased after 21 days of culture time, and the methane production rate reached 31% when the culture time reached 115 days. On the other hand, in Comparative Example 1, the methane production rate was 0% even when the culture time was 35 days, and the production of methane was not confirmed. In Comparative Example 2, the methane concentration increased after 35 days, and the methane production rate reached 8% when the culture time reached 115 days.

DESCRIPTION OF SYMBOLS 1 Relaxation tank 2 Separation tank 3 Filter 4 Dryer 5 Resin chromatograph tower 6 Electrodialysis tank 7 Fermenter 8 Cellulose waste liquid (high concentration glucose)
9 Butyric acid 10 Caproic acid 11 Acetic acid 12 Methane

Claims (3)

The carbon concentration in the sugar solution containing glucose monomer and / or its multimer is adjusted to 0.15 to 0.3 mol / L, and the pH of the sugar solution during methane fermentation is adjusted to 6.4 to 7.0. A methane fermentation method in which sugar solution is methane-fermented while maintaining . Methane fermentation method according to claim 1, wherein maintaining the pH of the sugar solution by neutralization by adding an alkaline compound to the sugar solution. The alkaline compound is any one selected from the group consisting of aqueous ammonia, sodium carbonate, calcium carbonate, magnesium carbonate, magnesium oxide, sodium bicarbonate, sodium hydroxide, potassium hydroxide, and calcium hydroxide. 2. The methane fermentation method according to 2 .

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