JP5442284B2 - Pretreatment method for enzymatic hydrolysis treatment of herbaceous biomass and ethanol production method using herbaceous biomass as raw material - Google Patents

Description

  The present invention relates to a pretreatment method for enzymatic hydrolysis of herbaceous biomass and a method for producing ethanol using herbaceous biomass as a raw material.

  Biomass, which is an organic resource derived from living organisms, is a resource that can be renewed continuously because living organisms produce it from water and carbon dioxide using solar energy. Biomass ethanol produced from the biomass is a renewable natural energy, and its potential as an energy source is expected from the point that it does not increase the amount of carbon dioxide in the atmosphere by its combustion.

  Attempts to produce ethanol from biomass and use it as a fuel or chemical raw material are underway in Japan and overseas, and various types of biomass have been studied as raw materials. Biomass is forestry (sawmill waste, thinned wood, paper waste, etc.), agriculture (rice straw, straw, sugarcane straw, rice straw, coconut shell, vegetation, etc.), livestock (livestock waste, etc.), fishery ( Fishery processing residue, etc.), waste (garbage, garden trees, building waste, sewage sludge, etc.).

  Lignocellulosic biomass, such as woody biomass and herbaceous biomass, has been used as fuel as it is or discarded, but has attracted attention as a resource that can be used as a useful resource. Lignocellulose is the main component of plant stems and leaves, and is mainly composed of cellulose, hemicellulose and lignin, and fiber cells based on cellulose and hemicellulose are bound by an intercellular layer based on lignin. ing. Cellulose is a relatively stable polymer in which a large number of monosaccharides such as glucose are bonded in a straight chain, and has strong crystallinity. Hemicellulose is also a polymer in which a large number of monosaccharides are bonded in a straight chain, but the bond is not regular like cellulose and is easily decomposed. Lignin is an amorphous polymer mainly having a benzene nucleus.

  In order to produce monosaccharides from lignocellulose and ferment them to produce ethanol, it is necessary to decompose (saccharify) cellulose and hemicellulose to monosaccharides. Cellulose and hemicellulose are surrounded by a strong structure such as lignin, and since the crystallinity of cellulose is strong, it is not easy to decompose lignocellulose, and various decomposition saccharification methods have been studied.

  There is an enzymatic hydrolysis method as a method for degrading saccharification of lignocellulose. This is a method of hydrolyzing and saccharifying cellulose or the like with an enzyme such as cellulase under mild conditions, and can suppress the excessive decomposition of monosaccharides. In the enzymatic hydrolysis method, a pretreatment is required to effectively react the enzyme with cellulose or hemicellulose. That is, it is necessary to perform a pretreatment for decomposing and removing lignin binding cellulose and hemicellulose from lignocellulose and weakening the crystallinity of cellulose.

  A pulverization method may be mentioned as a pretreatment method for enzyme hydrolysis. (See Patent Documents 1 to 4) Patent Document 1 discloses a multi-stage pulverization method using a vibration ball mill in which a wood material is coarsely pulverized and then finely pulverized while adjusting to a specific moisture content. Patent Document 2 discloses a method in which wood is pulverized and saccharified by a ball mill pulverizer, and then a solid (saccharification treatment residue) obtained by solid-liquid separation is pulverized again. Patent Document 3 discloses a classification saccharification method in which a wood resource is pulverized and classified, and a classification residue is further pulverized. Patent Document 4 discloses a method in which woody lignocellulosic biomass is treated with pressurized hot water and mechanically pulverized before enzymatic degradation. In any pulverization method, wood-based lignocellulose is pulverized into single fibers and fibers are cut, and the crystallinity of cellulose can be weakened. The pulverization is effective as a pretreatment for enzymatic hydrolysis. It is said that.

  Other methods for the pretreatment of enzyme hydrolysis include an alkali method (see Patent Document 5) and a pressurized hot water method (see Patent Document 6). Patent Document 5 discloses pretreatment of waste mushroom beds mainly composed of wood sawdust with an alkaline solution having a concentration of 1% or more as an alkali method. Patent Document 6 discloses a pretreatment for steaming or steaming waste building materials as a pressurized hot water method.

JP 62-127000 JP-A-63-137692 JP-A-2-156894 JP 2006-136263 A JP2006-20603 JP 2004-89016 A

  Lignocellulosic biomass is divided into woody biomass and herbaceous biomass, and the constituents are different. Woody biomass such as wood chips and waste wood is composed of about 50% cellulose, about 15% hemicellulose, and about 30% lignin, and since the ratio of lignin is large, how to decompose and remove lignin is an enzyme. This is the point of pretreatment for hydrolysis. On the other hand, herbaceous biomass such as bagasse, rice straw, rice husk, oil palm empty fruit bunch is composed of about 50% cellulose, about 30% hemicellulose and about 15% lignin, and has a small amount of lignin and a high hemicellulose content. Therefore, weakening the crystallinity of cellulose and making hemicellulose available efficiently are the points of pretreatment for enzyme hydrolysis.

  The pretreatment method by the grinding | pulverization of patent documents 1-4 is a pretreatment method of woody biomass, and even if it applies to pretreatment of herbaceous biomass as it is, herbaceous biomass has a hemicellulose ratio compared to woody biomass. Since it is high, the sugar yield after enzymatic hydrolysis is low, and efficient pretreatment may not be realized. Moreover, it is desired to reduce the energy consumption required for pulverization, to be able to process in a short time, and to reduce the processing cost.

  Moreover, the pretreatment method by the alkali method of patent document 5, and the pressurized hydrothermal method of patent document 6 is also a pretreatment method of woody biomass, Comprising: When it applies to herbaceous biomass, the following problems will arise.

  When sugar is produced from herbaceous biomass such as palm palm empty fruit bunches, rice straw, bagasse, etc. by enzymatic hydrolysis, it is important to effectively use hemicellulose whose content is as high as 30% as described above. . Hemicellulose is weaker in crystallinity and different in degradability than cellulose. Hemicellulose, which is more easily decomposed than cellulose, decomposes hemicellulose under pretreatment conditions in which woody biomass is decomposed with an alkaline solution having a concentration of 1% or more. Since the sugar produced | generated by this will be excessively decomposed | disassembled, the recovery rate of the whole sugar will become low. On the other hand, if the pretreatment conditions are too gentle, the degradation of lignin and embrittlement of the crystallinity of cellulose remain insufficient, and thus there is a problem that enzymatic hydrolysis saccharification after pretreatment does not proceed.

  In addition, the pretreatment for steaming or steaming in Patent Document 6 requires a high-pressure apparatus for treatment at a high temperature and high pressure, and there is a problem that equipment costs and operating costs for the pretreatment are increased.

  The present invention has been made in view of such circumstances, and is a pretreatment method performed before enzymatic hydrolysis of herbaceous biomass, which consumes less energy, can be processed with good yield in a short time, and has a low It is an object of the present invention to provide a pretreatment method, particularly a pulverization method, of enzymatic hydrolysis of herbaceous biomass, which is a cost, and to provide an ethanol production method using herbaceous biomass as a raw material.

  In addition, even when the alkali method and hot water method are combined with the pulverization treatment, the excessive decomposition of the sugar produced from the hemicellulose by the pretreatment is suppressed, a high-pressure apparatus is unnecessary, and the sugar can be obtained at a low cost and in a high yield. It is an object of the present invention to provide a pretreatment method for enzymatic hydrolysis of herbaceous biomass that can be processed.

  According to this invention, the said subject is achieved as follows regarding the pre-processing method of the enzymatic hydrolysis of herbaceous biomass, and the ethanol manufacturing method which uses herbaceous biomass as a raw material.

<Pretreatment method for enzymatic hydrolysis of herbaceous biomass>
According to the present invention, the above-mentioned problems are related to the pretreatment method performed before the enzymatic hydrolysis treatment of the herbaceous biomass, a coarse pulverization step of coarsely pulverizing the herbaceous biomass raw material to an average particle size of 1 mm or less, Water is added to the pulverized herbaceous biomass to prepare a high-concentration mixture having a herbaceous biomass concentration of more than 10% by weight and 40% by weight or less, and the average particle size of the herbaceous biomass in the high-concentration mixture is adjusted to 100 μm or less. A first fine pulverization step for fine pulverization and a high-concentration mixture finely pulverized in the first fine pulverization step are added with water to prepare a low-concentration mixture having a herbaceous biomass concentration of 1 wt% to 10 wt%. And a second fine pulverizing step for further finely pulverizing the herbaceous biomass in the low-concentration mixture.

  According to the present invention having such a configuration, each process is performed as follows. In addition, in this invention, an average particle diameter is an average particle diameter calculated | required from the particle size distribution measured with particle size distribution measuring devices, such as a laser diffraction and scattering type particle size distribution measuring device.

(1) Coarse pulverization step The herbaceous biomass raw material is coarsely pulverized to a mean particle size of 1 mm or less by a dry process. By coarsely pulverizing, fine pulverization in the subsequent process can be performed efficiently.

(2) First fine pulverization step Water is added to the coarsely pulverized herbaceous biomass to prepare a high-concentration mixture having a herbaceous biomass concentration of more than 10% by weight and 40% by weight or less. In a state in which the coarsely pulverized herbaceous biomass is dispersed, the average particle size of the herbaceous biomass is finely pulverized to 100 μm or less, so that the herbaceous biomass is refined and the crystallinity of cellulose and hemicellulose is reduced to reduce enzyme hydrolysis. The decomposition reaction can be promoted. At that time, by increasing the concentration of the mixture, the time required for pulverization can be shortened, so that energy consumption for pulverization (power consumption of the pulverizer) can be reduced.

(3) Second fine pulverization step However, the pulverization treatment in the first fine pulverization step may not be sufficient to significantly improve the saccharification yield by the enzymatic hydrolysis reaction. In the herbaceous biomass pulverized in the first fine pulverization step, lignin is separated from cellulose or cellulose crystals are separated. Has been generated. In addition, herbaceous biomass that has not been crushed to the level of fine powder remains. If there are many such agglomerates and herbaceous biomass that has not been finely pulverized, this may cause a significant increase in the saccharification yield due to the enzymatic hydrolysis reaction. Therefore, after the first fine pulverization step, a second fine pulverization step is provided, water is added to the high concentration mixture to prepare a low concentration mixture of herbaceous biomass, and this low concentration mixture is further finely pulverized. As a result, the aggregate can be broken into fine powder, and herbaceous biomass that has not been finely pulverized can be pulverized into fine powder, and the saccharification yield can be greatly improved. Moreover, by setting it as a low concentration mixture, the load of a grinder can be made small and the energy consumption (electric power consumption of a grinder) for grinding can be reduced.

  In this way, by combining fine pulverization at a high concentration with fine pulverization by diluting to a low concentration, energy consumption is low, processing can be performed efficiently in a short time, low cost, and enzymatic hydrolysis reaction. It is possible to realize a pretreatment method for enzymatic hydrolysis of herbaceous biomass, which can greatly improve the saccharification yield.

  In the present invention, an alkali treatment or a heat treatment can be performed together with the pretreatment by the pulverization.

(I) herbaceous biomass in any one hydroxide aqueous solution of sodium hydroxide, potassium hydroxide and calcium hydroxide having an alkali-treated hydroxide ion concentration of 0.1 wt% or more and less than 0.5 wt% The alkali treatment for contacting is performed in any one of (1) to (5) below.
(1) Between coarse pulverization step and first fine pulverization step (2) First fine pulverization step (3) Between first fine pulverization step and second fine pulverization step (4) Second fine pulverization Step (5) During the solid-liquid separation step for solid-liquid separation of the reaction product of the second fine grinding step and the second fine grinding step

(Ii) Heat treatment The heat treatment for heating the herbaceous biomass to 60 to 100 ° C. is performed in any of the following (1) to (6).
(1) Before coarse pulverization step (2) Between coarse pulverization step and first fine pulverization step (3) First fine pulverization step (4) Between first fine pulverization step and second fine pulverization step (5) Second fine pulverization step (6) During the solid-liquid separation step of solid-liquid separation of the reaction product of the second fine pulverization step and the second fine pulverization step

<Ethanol production method using herbaceous biomass>
According to the present invention, the above-described problem is related to an ethanol production method using herbaceous biomass as a raw material, a pretreatment step performed by the above-described pretreatment method, and solid-liquid separation for solid-liquid separation of the reaction product of the pretreatment step. A step, an enzyme hydrolysis step in which a solid separated by solid-liquid separation in the solid-liquid separation step is enzymatically hydrolyzed to produce sugar, and a saccharide produced by enzymatic hydrolysis in the enzyme hydrolysis step is fermented And a fermentation process for producing ethanol.

  According to the present invention, water is added to the coarsely pulverized herbaceous biomass to finely pulverize the herbaceous biomass in a high-concentration mixture state, and then water is added to finely pulverize in the low-concentration mixture state. Therefore, pulverization is performed in two stages at different concentrations, so energy consumption required for pulverization is low, it can be processed efficiently in a short time, and costs are low. Saccharification yield by enzymatic hydrolysis reaction It is possible to provide a pretreatment method, particularly a pulverization method, of enzymatic hydrolysis of herbaceous biomass, which can significantly improve the above, and to provide an ethanol production method using herbaceous biomass as a raw material.

<Pretreatment method for enzymatic hydrolysis of herbaceous biomass>
The pretreatment method performed before the enzymatic hydrolysis treatment of the herbaceous biomass includes a coarse pulverization step in which the herbaceous biomass raw material is coarsely pulverized to an average particle size of 1 mm or less, and water is added to the coarsely pulverized herbaceous biomass. A first fine grinding step of preparing a high-concentration mixture having a herbaceous biomass concentration of more than 10% by weight and 40% by weight or less, and finely grinding the average particle size of the herbaceous biomass in the high-concentration mixture to 100 μm or less; Water is added to the high-concentration mixture finely pulverized in the first fine pulverization step to prepare a low-concentration mixture having a herbaceous biomass concentration of 1 to 10% by weight, and the herbaceous biomass in the low-concentration mixture is prepared. Further, it is performed through a second fine grinding step of fine grinding.

  In lignocellulose of herbaceous biomass, fiber cells mainly composed of cellulose and hemicellulose are bound together by an intercellular layer mainly composed of lignin. After the coarse pulverization step of pulverizing the herbaceous biomass raw material to an average particle size of 1 mm or less, water is added to the coarsely pulverized herbaceous biomass so that the herbaceous biomass concentration is higher than 10% by weight and lower than 40% by weight. A concentration mixture is prepared, a first fine pulverization step in which the average particle size of the herbaceous biomass in the high concentration mixture is pulverized to 100 μm or less, and water is added to the high concentration mixture finely pulverized in the first fine pulverization step. Is added to prepare a low-concentration mixture having a herbaceous biomass concentration of 1% by weight or more and 10% by weight or less, and the herbaceous biomass in the low-concentration mixture is pulverized through a second fine pulverization step. As a result, cellulose is refined in a short time with low energy consumption, crystallinity is lowered, and lignin is separated.

  As a means for pulverization, mechanical pulverization is effective. Specifically, a grounder, a cutter mill, a vibration ball mill, a rotating ball mill, a planetary ball mill, a roll mill, a disk mill, a homomixer, and the like can be used. Also good. Hereinafter, each pulverization step will be described in detail.

(A) Coarse pulverization step In the coarse pulverization step, the herbaceous biomass raw material is pulverized dry to an average particle size of 1 mm or less. Any of the above-described pulverizers may be used, but a cutter mill is preferable for the herbaceous biomass material having a soft fiber system. Depending on the composition, shape, size, moisture content, etc. of the herbaceous biomass feedstock, the type of grinder and the optimum operating conditions are adapted.

(B) Fine pulverization step In the fine pulverization step, water is added to the coarsely pulverized herbaceous biomass, and the herbaceous biomass is finely pulverized by a wet process. By finely pulverizing herbaceous biomass, cellulose can be refined to reduce crystallinity, lignin can be separated, and as a result, an enzymatic hydrolysis reaction to saccharify herbaceous biomass raw materials can be promoted. , Sugar yield can be improved.

  In the present invention, this fine pulverization step is performed by adjusting the herbaceous biomass concentration as a high-concentration mixture having a herbaceous biomass concentration of more than 10% by weight and not more than 40% by weight, followed by pulverization in the first fine pulverization step and the first fine pulverization step. Water is added to the pulverized high-concentration mixture to adjust the herbaceous biomass concentration to a low-concentration mixture of 1% by weight to 10% by weight, followed by a two-stage fine pulverization step including a second fine pulverization step of pulverization. By carrying out separately, fine grinding can be performed efficiently, and the energy required for grinding can be greatly reduced.

  When high-concentration herbaceous biomass is pulverized for a long time in one fine pulverization step, it becomes excessively pulverized, and the loss of raw materials supplied to enzyme hydrolysis increases. In addition, energy consumption for pulverization becomes excessive. In addition, when low-concentration herbaceous biomass is pulverized in a single fine pulverization process, it takes a long time to obtain a fine powder of the desired size, and energy consumption is excessive until the desired pulverization target level is reached. .

  In contrast, in the present invention, in the first fine pulverization step in which the herbaceous biomass concentration is relatively high, the load on the pulverizer is large and the energy consumption per unit time is high. By performing the process in a short time, energy consumption can be significantly reduced. Further, in the second fine pulverization step, the aggregate in which the lignin and cellulose already separated in the first fine pulverization step are aggregated and the unpulverized portion is pulverized to obtain a desired pulverization target. The level can be reached efficiently and overgrinding can also be prevented. Further, since the herbaceous biomass concentration is relatively low in the second fine pulverization step, the load on the pulverizer is small and the energy consumption is small.

  Thus, a two-stage fine pulverization process consisting of a first fine pulverization process in which the herbaceous biomass concentration is relatively high and a second fine pulverization process in which the herbaceous biomass concentration is relatively low, By doing so, it can be finely pulverized efficiently, and the total energy required for pulverization can be greatly reduced.

  Further, in the second fine pulverization step, by adjusting the herbaceous biomass concentration to a relatively low concentration, the pulverized product can be easily discharged from the pulverizer. Furthermore, the concentration adjustment necessary for the subsequent enzyme hydrolysis treatment process can be performed, and the concentration adjustment step can be omitted.

  In the first fine pulverization step, water is added to the coarsely pulverized herbaceous biomass to adjust the herbaceous biomass concentration to a high concentration mixture of more than 10% by weight and 40% by weight or less, and then the average particle size of the herbaceous biomass. Is pulverized to 100 μm or less. If the herbaceous biomass concentration is 10% by weight or less, the pulverization efficiency is low, the time until the pulverization process is completed becomes long, and the required energy increases, which is not preferable. If the herbaceous biomass concentration is higher than 40% by weight, the load on the pulverizer increases, which is not preferable. The smaller the size of the coarsely pulverized herbaceous biomass, the higher the concentration, which is desirable because energy consumption can be reduced.

  The grinding time in the first fine grinding step is preferably 10 minutes to 60 minutes. Grinding is insufficient in a time shorter than 10 minutes, and saccharification does not proceed in the enzyme hydrolysis step as a subsequent step. Further, even if pulverization is carried out for longer than 60 minutes, the degree of degradation of lignin and the crystalline embrittlement of cellulose are not changed, and pulverization for longer than 60 minutes is not suitable because energy consumption increases.

  In the second fine pulverization step, water is added to the high concentration mixture finely pulverized in the first fine pulverization step to adjust the herbaceous biomass concentration to a low concentration mixture of 1 wt% to 10 wt%, The herbaceous biomass finely pulverized in one fine pulverization step is crushed to break up aggregates into fine powder, and the herbaceous biomass not pulverized is pulverized into fine powder. If the herbaceous biomass concentration is 1% by weight or less, the pulverization efficiency is low, the time until the pulverization process is completed becomes long, and the required energy increases, which is not preferable. If the herbaceous biomass concentration is higher than 10% by weight, it is not preferable because the concentration needs to be adjusted before the subsequent enzymatic hydrolysis treatment process. It is more preferable to adjust the herbaceous biomass concentration to 2 wt% or more and 5 wt% or less.

  The grinding time in the second fine grinding step is preferably 15 minutes to 5 hours. Shorter than 15 minutes is not preferable because the pulverization is insufficient. Further, even if pulverization is carried out for longer than 5 hours, the degree of degradation of lignin and the crystalline embrittlement of cellulose are not changed, and pulverization for longer than 5 hours is not suitable because energy consumption increases.

(C) Combined alkali treatment with pulverization treatment In the present invention, alkali treatment can be performed together with the above-described pretreatment by pulverization.

Alkali treatment in which the herbaceous biomass is brought into contact with any one hydroxide aqueous solution of sodium hydroxide, potassium hydroxide and calcium hydroxide having a hydroxide ion concentration of 0.1 wt% or more and less than 0.5 wt% Is performed in any one of (1) to (5) below.
(1) Between coarse pulverization step and first fine pulverization step (2) First fine pulverization step (3) Between first fine pulverization step and second fine pulverization step (4) Second fine pulverization Step (5) During the solid-liquid separation step for solid-liquid separation of the reaction product of the second fine grinding step and the second fine grinding step

  When alkaline treatment is used in combination, the herbaceous biomass is pulverized in the fine pulverization step, and the lignocellulose that binds cellulose and hemicellulose in the lignocellulose of the herbaceous biomass is decomposed by the aqueous hydroxide solution. The crystallinity of cellulose is embrittled. Due to the decomposition of lignin and the crystalline embrittlement of cellulose, cellulose and hemicellulose are easily hydrolyzed in the subsequent enzymatic hydrolysis step.

  When the hydroxide ion concentration of the aqueous hydroxide solution is less than 0.1% by weight, the decomposition of lignin and the crystallinity embrittlement of the cellulose do not progress, and when it exceeds 0.5% by weight, the sugar produced by the decomposition of hemicellulose is excessively decomposed. Therefore, it is not preferable. As the alkali agent, in addition to sodium hydroxide, an alkali metal hydroxide such as potassium hydroxide may be used, or an alkaline earth metal hydroxide such as calcium hydroxide may be used. Further, ammonia water, ammonium salts such as quaternary ammonium salts and ammonium carbonate may be used as alkali agents instead of hydroxides. In this case, the preferred concentration range is higher than the hydroxide.

(D) Heat treatment combined with pulverization treatment In the present invention, heat treatment can be performed together with the pretreatment by pulverization described above.
The heat processing which heats herbaceous biomass to 60-100 degreeC is performed in either of following (1) thru | or (6).
(1) Before coarse pulverization step (2) Between coarse pulverization step and first fine pulverization step (3) First fine pulverization step (4) Between first fine pulverization step and second fine pulverization step (5) Second fine pulverization step (6) During the solid-liquid separation step of solid-liquid separation of the reaction product of the second fine pulverization step and the second fine pulverization step

  The temperature of the herbaceous biomass during the fine pulverization step or before and after the treatment may be normal temperature in terms of promoting the decomposition reaction of lignin and the crystalline embrittlement reaction of cellulose, but further promote the decomposition reaction and the embrittlement reaction. Therefore, it is preferable to heat-treat herbaceous biomass in a temperature range of 60 ° C to 100 ° C. It has been confirmed that when the herbaceous biomass temperature during the pulverization treatment is 60 ° C. or higher, the lignin decomposition reaction and the cellulose crystalline embrittlement reaction proceed remarkably as compared to the case of less than 60 ° C. Further, in order to perform the pulverization treatment in a state where the temperature of the herbaceous biomass exceeds 100 ° C., a high-temperature / high-pressure treatment apparatus is required, which is not preferable because equipment costs and operation costs increase.

<Method for producing ethanol from herbaceous biomass>
In this embodiment, a method for producing ethanol using herbaceous biomass as a raw material will be described. The production method includes the pretreatment step performed by any one of the above-described pulverization treatment, the pulverization treatment combined with alkali treatment, or the pulverization treatment combined with heat treatment, and the reaction product of the pretreatment step as a solid-liquid solution. A solid-liquid separation step to separate, an enzyme hydrolysis step in which a solid separated by solid-liquid separation in the solid-liquid separation step is enzymatically hydrolyzed to produce sugar, and generated by enzymatic hydrolysis in the enzyme hydrolysis step Fermented sugar is produced to produce ethanol.

  Next, each process of this embodiment is demonstrated.

  First, a pretreatment step is performed, but details are already described in (a) to (d), and thus will be omitted.

(E) Solid-liquid separation step After the herbaceous biomass is pretreated, it is subjected to solid-liquid separation to separate into solids containing cellulose or hemicellulose whose crystallinity is embrittled and liquids containing lignin degradation products. As a result, impurities such as lignin degradation products can be removed, and cellulose and hemicellulose, which are embrittled crystallinity, can be extracted. Examples of the solid-liquid separation means include filtration methods such as natural filtration, suction filtration, pressure filtration, and centrifugal filtration, and centrifugal separation methods, and any means may be used. When performing a pretreatment using an alkali treatment, wash the solid before the enzyme hydrolysis step after the solid-liquid separation step, and make the pH weakly acidic suitable for the enzyme hydrolysis reaction. Is preferred. It is preferable to perform a pretreatment for performing an alkali treatment in which the herbaceous biomass is brought into contact with an aqueous hydroxide solution having a hydroxide ion concentration of 0.1% by weight or more and less than 0.5% by weight. Even when the pretreatment is performed, since the pH is kept relatively low, a neutralization treatment is not particularly necessary, and the pH can be made weakly acidic suitable for the enzymatic hydrolysis reaction by washing.

(F) Enzymatic hydrolysis and saccharification step An enzyme is added to a liquid in which the solid matter obtained in the solid-liquid separation step is suspended, and the solid matter containing cellulose or hemicellulose is saccharified by enzymatic hydrolysis. Lignin is decomposed by pretreatment, and lignin decomposition products are removed by solid-liquid separation, and the crystallinity of cellulose is embrittled by pretreatment, so cellulose and hemicellulose in solids are hydrolyzed by enzymes. It has become easier. In the saccharification step by enzymatic hydrolysis, a separately produced enzyme such as cellulase or hemicellulase may be used, or a microorganism such as a mold that produces the enzyme may be used. Specifically, for example, cellulase is added to the liquid in which the solid is suspended, and the reaction is performed, for example, at pH 4 to 6 and 30 to 60 ° C. for 10 to 120 hours with stirring. The liquid hydrolyzed by cellulase contains glucose, which is a sugar obtained by decomposing cellulose, and glucose, xylose, arabinose, galactose, mannose, etc., which are sugars obtained by decomposing hemicellulose.

(G) Fermentation process A nutrient source containing nitrogen and phosphorus and an ethanol fermentation microorganism are added to the hydrolyzed sugar solution to convert the sugar into ethanol. As the ethanol fermentation microorganism, either yeast or bacteria may be used. Examples of yeast include Saccharomyces cereviciae, Shizosaccharomyces pombe, Zygosaccharomyces rouxii, and Pichia stipitis. Examples of bacteria include Zymomonas mobilis.

  You may perform the simultaneous saccharification fermentation process which advances a saccharification process and (g) fermentation process simultaneously, without passing through the solid-liquid separation process of (e) after a pre-processing process.

  As described above, when the pretreatment method for herbaceous biomass according to this embodiment is used, the energy required for pulverizing the herbaceous biomass can be reduced, and the sugar produced by the decomposition of hemicellulose contained in the herbaceous biomass can be reduced. By avoiding excessive decomposition, the yield of sugar after enzymatic hydrolysis can be increased. Therefore, the total sugar yield in saccharification by enzymatic hydrolysis using herbaceous biomass as a raw material is increased, and thereby the yield of ethanol produced by fermenting sugar can also be improved.

<Example>
EXAMPLES Hereinafter, although this invention is demonstrated further more concretely using an Example, this invention is not limited to these Examples.

  In this example, rice straw is used as a herbaceous biomass raw material, and is first finely pulverized by a ball mill in a dry manner with an average particle size of 1 mm or less, and then wetly pulverized by a ball mill to an average particle size of 100 μm or less. A pretreatment for performing the second fine pulverization was performed, the pretreated reaction product was suction filtered, and the pretreated solid of the filtered residue was subjected to an enzyme hydrolysis step. Enzymatic hydrolysis treatment was performed using a Meicelase solution as a cellulase enzyme and treated in 0.1 M acetate buffer (pH 4.5) at 40 ° C. for 24 hours. Then, the enzyme-hydrolyzed product was subjected to suction filtration, and the sugar in the filtrate was analyzed by the Somogene Nelson method to determine the sugar yield per gram of rice straw raw material.

  In Example 1, 6 times as much water as the first finely pulverized rice straw raw material was added to the rice straw to prepare a high concentration mixture having a rice straw raw material concentration of 14% by weight. , Ground for 30 minutes at a pot rotation speed of 400 rpm in a ball mill, and further added water 20 times the weight of the raw material as a second fine pulverization step, and a low-concentration mixture having a rice straw raw material concentration of 3.7% by weight was added. It was prepared and pulverized with a ball mill at a pot rotation speed of 200 rpm for 2 hours.

  In Example 2, water and sodium hydroxide were added to the coarsely pulverized rice straw raw material to prepare a high-concentration mixture having a rice straw raw material concentration of 14% by weight and a hydroxide ion concentration of 0.4% by weight, The first fine pulverization step was performed in combination with alkali treatment, and the same two-stage fine pulverization treatment as in Example 1 was performed.

  In Examples 3 and 5, the coarsely pulverized rice straw raw material was subjected to heat treatment, and then the same two-stage fine pulverization treatment as in Example 1 was performed. In Example 3, the heat treatment temperature is 80 ° C., and in Example 5, the heat treatment temperature is 100 ° C.

  In Examples 4 and 6, after heat treatment was performed to heat the coarsely pulverized rice straw raw material, water and sodium hydroxide were added to the coarsely pulverized rice straw raw material, and the concentration of the rice straw raw material was 14% by weight. A high-concentration mixture having an oxide ion concentration of 0.4% by weight was prepared, and the first fine pulverization step was performed in combination with alkali treatment. Further, the same two-stage fine pulverization treatment as in Example 1 was performed. . In Example 4, the heat treatment temperature is 80 ° C., and in Example 6, the heat treatment temperature is 100 ° C.

  For comparison with the examples, a comparative example in which the fine pulverization process was performed in one step was performed.

  In Comparative Example 1, 6 times the weight of the coarsely pulverized rice straw raw material was added to the rice straw to prepare a high-concentration mixture having a rice straw raw material concentration of 14% by weight. A one-stage pulverization process of pulverizing for 30 minutes was performed.

  In Comparative Example 2, a high-concentration mixture having a rice straw raw material concentration of 10% by weight was prepared and pulverized with a ball mill at a pot rotation speed of 400 rpm for 5 hours so as to increase the sugar yield.

  In Comparative Example 3, water and sodium hydroxide were added to the coarsely pulverized rice straw raw material to prepare a high-concentration mixture having a rice straw raw material concentration of 14% by weight and a hydroxide ion concentration of 0.4% by weight, The first fine pulverization step was performed in combination with alkali treatment, and the same one-stage pulverization treatment as in Comparative Example 1 was further performed.

  Table 1 shows the measurement results of the sugar yield (referred to as yield) per gram of rice straw raw material of each Example and Comparative Example.

  As shown in Table 1, in Example 1, which was finely pulverized in two stages, saccharification can be performed at a higher yield in each stage as compared with Comparative Example 1 that was finely pulverized in one stage.

  Further, in order to saccharify with a yield of 0.4 or more by finely pulverizing in one step, a long pulverizing process is required as shown by the fact that the pulverization time is 5 hours as in Comparative Example 2. Become. For Example 1 and Comparative Example 2, the total power consumption required for pulverization was measured. Compared to the total power consumption required for pulverization in Comparative Example 2, in Example 1, the total power consumption was 1/2 or less of that. Thus, the energy for grinding can be greatly reduced by the present invention.

  As is clear from the results of Example 2, the yield can be increased by using an alkali treatment in combination with the fine pulverization step. In addition, when alkali treatment is used in combination with the fine pulverization step, in Example 2 in which fine pulverization is performed in two stages, saccharification can be performed at a higher yield in each stage than in Comparative Example 3 in which fine pulverization is performed in one stage.

  As is clear from the results of Examples 3 and 5, the yield can be increased by performing the heat treatment before the pulverization treatment, and the yield can be increased as the heat treatment temperature is higher. As is clear from the results of Examples 4 and 6, the heat treatment is performed before the fine pulverization treatment, and the alkali treatment is further used in the fine pulverization step, so that the yield can be further increased. The rate can be increased.

  A high concentration mixture was prepared by changing the hydroxide ion concentration of the high concentration mixture in Example 2 in the range of 0.05 to 1% by weight, and the first fine pulverization step was performed in combination with an alkali treatment. The same two-stage grinding treatment as in Example 1 was performed. When the hydroxide ion concentration is in the range of 0.1 wt% or more and less than 0.5 wt%, the sugar yield is 0.35 or more, which is an industrially efficient process. When the hydroxide ion concentration is less than 0.1% by weight, the decomposition of lignin and cellulose crystal embrittlement do not progress, and at a concentration of 0.5% by weight or more, the sugar produced by the decomposition of hemicellulose is excessively decomposed. It was confirmed that the sugar yield after the enzyme hydrolysis treatment was lowered. As described above, when the alkali treatment is used in combination with the two-stage fine pulverization treatment, the hydroxide ion concentration is preferably in the range of 0.1 wt% or more and less than 0.5 wt%.

  The present invention can be used in the industrial field where ethanol is produced using biomass as a raw material.

Claims (4)

It is a pretreatment method performed before the enzymatic hydrolysis treatment of herbaceous biomass,
A coarse pulverization step of coarsely pulverizing herbaceous biomass raw material to an average particle size of 1 mm or less,
Water is added to the coarsely pulverized herbaceous biomass to prepare a high-concentration mixture having a herbaceous biomass concentration of more than 10% by weight and 40% by weight or less, and the average particle size of the herbaceous biomass in the high-concentration mixture is 100 μm or less. A first fine pulverization step,
Water is added to the high-concentration mixture finely pulverized in the first fine pulverization step to prepare a low-concentration mixture having a herbaceous biomass concentration of 1 to 10% by weight, and the herbaceous biomass in the low-concentration mixture is prepared. A pretreatment method for enzymatic hydrolysis of herbaceous biomass, further comprising a second fine grinding step of fine grinding. Alkali treatment in which the herbaceous biomass is brought into contact with any one hydroxide aqueous solution of sodium hydroxide, potassium hydroxide and calcium hydroxide having a hydroxide ion concentration of 0.1 wt% or more and less than 0.5 wt% The pretreatment method for enzymatic hydrolysis of herbaceous biomass according to claim 1, wherein the step is performed in any one of the following (1) to (5).
(1) Between coarse pulverization step and first fine pulverization step (2) First fine pulverization step (3) Between first fine pulverization step and second fine pulverization step (4) Second fine pulverization Step (5) During the solid-liquid separation step for solid-liquid separation of the reaction product of the second fine grinding step and the second fine grinding step The pretreatment method for enzymatic hydrolysis of herbaceous biomass according to claim 1 or 2, wherein the heat treatment for heating the herbaceous biomass to 60 to 100 ° C is performed in any one of the following (1) to (6).
(1) Before coarse pulverization step (2) Between coarse pulverization step and first fine pulverization step (3) First fine pulverization step (4) Between first fine pulverization step and second fine pulverization step (5) Second fine pulverization step (6) During the solid-liquid separation step of solid-liquid separation of the reaction product of the second fine pulverization step and the second fine pulverization step A pretreatment step performed by the pretreatment method according to any one of claims 1 to 3;
A solid-liquid separation step for solid-liquid separation of the reaction product of the pretreatment step;
An enzyme hydrolysis step for producing a sugar by enzymatic hydrolysis of the solid separated by solid-liquid separation in the solid-liquid separation step;
A fermentation process for producing ethanol by fermenting sugar produced by enzyme hydrolysis in the enzyme hydrolysis process;
A method for producing ethanol using herbaceous biomass as a raw material.