JP2007124933A - Pretreatment method of lignocellulose - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pretreatment method of lignocellulose which is used when enzymically hydrolyzing a lignocellulose raw material, and by which the treatment can be carried out at a low cost while keeping input energy low, and a sugar can be obtained at a low cost in good yield by suppressing the excess degradation of the sugar. <P>SOLUTION: The pretreatment method of the lignocellulose by enzymic hydrolysis comprises an acid-treating step for subjecting the lignocellulose raw material to acid treatment, a neutralizing step for neutralizing the reaction product of the acid-treating step, and a pulverizing step for subjecting the reaction product of the neutralizing step to wet pulverization treatment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pretreatment method for lignocellulose.

  In recent years, domestic and overseas efforts have been made to produce ethanol from natural resources such as bagasse, rice straw, and wood chips, which are renewable resources, and use them as energy and chemical raw materials. Various biomass is used as a raw material, but lignocellulose such as woody biomass has attracted attention as a useful resource in the future. Lignocellulose is a main component of plant stems and leaves, and is mainly composed of cellulose, hemicellulose, and lignin. Cellulose has a content of about 50% of wood and is a relatively stable polymer in which glucose is linearly bound. Hemicellulose has a content of about 20 to 30% of wood, and bonds are not regular like cellulose and are easily hydrolyzed. Lignin has a content of about 20 to 30% of wood and is an amorphous polymer mainly having a benzene nucleus.

In order to produce ethanol from lignocellulose such as woody biomass, hemicellulose is first hydrolyzed with acid or alkali to obtain a sugar solution derived from hemicellulose. The sugars constituting hemicellulose are mainly pentose sugars such as xylose and arabinose, and hexose sugars such as glucose, galactose and mannose, and the ratio of these amounts varies depending on the type of woody biomass.
Next, the residue after obtaining the hemicellulose-derived sugar is further treated with an acid or enzyme to obtain a cellulose-derived sugar. When dilute sulfuric acid is used for this treatment, the glucose yield is as low as about 40%. Sugar-degrading substances such as formic acid, levulinic acid and hydroxymethylfurfural (HMF) are likely to be produced, and these hyperdegrading substances have an adverse effect on fermentation to ethanol.
Hydrolysis with an enzyme has been studied as a method to replace the acid or alkali treatment described above, but it is necessary to select an appropriate method for the pretreatment for effectively carrying out the enzyme reaction depending on the raw material.

  One of the properties common to lignocellulose raw materials is that there is a difference in the hydrolysis conditions of hemicellulose and cellulose. Hemicellulose is relatively easily decomposed by acids and alkalis, and sugar can be obtained with a high recovery rate of 90% or more, whereas cellulose is decomposed under more severe conditions, and sugar overdegradation occurs at almost the same rate. As a result, the sugar recovery rate is low. Therefore, it is desirable to first recover the hemicellulose-derived sugar as much as possible by primary hydrolysis that also serves as a pretreatment for enzymatic hydrolysis.

The method of using an acid or alkali is well studied as a primary hydrolysis method.
All of the pretreatments for enzymatic hydrolysis are effective. However, when obtaining hemicellulose-derived sugars by primary hydrolysis, sugars tend to undergo excessive decomposition under alkaline conditions, so treatment with acid is advantageous. It is. As the primary hydrolysis treatment for the hemicellulose raw material, caustic soda cooking and lime treatment under oxidizing conditions have been reported, but the yield of sugars derived from hemicellulose is low.

On the other hand, in the primary hydrolysis treatment using an acid, sugar can be recovered, but depending on the raw material, it may be insufficient as a pretreatment for enzyme hydrolysis. For example, in wood, the residue after primary treatment of hardwood with acid or blasting is relatively easily saccharified by enzymes. When used, the enzyme hydrolysis rate is low.
Since waste building materials that are expected to be used effectively in Japan are mainly coniferous trees such as cedar, tsuga and pine, establishment of pretreatment methods for coniferous trees is particularly important in Japan.

  From such a viewpoint, a method of increasing the enzyme hydrolysis rate by performing a secondary treatment before subjecting the primary treated residue to enzyme hydrolysis has also been studied. For example, treatment with ozone, hydrogen peroxide, sodium chlorite and the like has been reported. However, the use of these chemicals is not only costly, but there is a concern that it may act to inhibit microorganisms in the subsequent fermentation, so it is necessary to provide a step for removal before fermentation.

  In addition, a pretreatment method in which a pulverization treatment is performed before hydrolyzing a lignose raw material such as wood containing cellulose or hemicellulose has been reported (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). Similarly, a method has also been reported in which a lignose raw material is finely pulverized and then subjected to enzyme hydrolysis, and then a solid residue is pulverized again (for example, see Patent Document 4). In addition, a pretreatment method combining an alkali hydrolysis treatment and a mechanical pulverization treatment has also been reported (see Patent Document 5).

On the other hand, the inventors of the present invention have made extensive studies and first subjected to an acid hydrolysis treatment on the lignocellulose raw material to obtain a hemicellulose-derived sugar that can be solid-liquid separated and recovered relatively easily with an acid, and then a solid residue. The present inventors have found a pretreatment method that can improve the efficiency of the subsequent enzymatic hydrolysis by performing wet pulverization treatment on the surface of the material. In this pretreatment method, the raw lignocellulose is first hydrolyzed in the acid treatment step, mainly hemicellulose in the raw material, and then separated into a sugar solution and a residue in the subsequent solid-liquid separation step, and the residue is separated in the pulverization treatment step. It is pulverized (pretreatment method). Then, in an enzyme hydrolysis process, it is hydrolyzed to sugar and ethanol is produced by fermentation. On the other hand, ethanol is also produced from the sugar solution recovered in the solid-liquid separation process by fermentation after neutralization.
Japanese Patent Laid-Open No. 55-9758 JP 59-91893 A JP-A-63-137690 Japanese Patent Laid-Open No. 63-137692 JP-A-55-45306

  As described above, the pretreatment method in which the lignocellulose raw material is finely pulverized with a ball mill or the like requires fewer steps, but the effect as the pretreatment cannot be obtained unless the input energy is considerably increased. In addition, hydrolysis under an alkaline condition has a problem in that sugar excessive decomposition easily proceeds. Furthermore, little is mentioned about the yield of sugar derived from hemicellulose.

In the case of a pretreatment method in which a solid residue is pulverized after acid-hydrolyzed lignose raw material and then separated, hemicellulose-derived sugar and cellulose-derived sugar are separated and subjected to fermentation separately. In addition, since the number of processes is increased, the number of equipment, piping, and the like is increased, resulting in high costs and difficulty in equipment installation.
Further, when pulverization is performed in the pretreatment, it has been desired to use a pulverizer that can reduce power consumption from the viewpoints of cost reduction and environmental consideration.

    The present invention has been made in view of the above-mentioned problems of the background art, and is a pretreatment method for enzymatic hydrolysis of a lignocellulose raw material, which can be processed at a low cost with low input energy. It is an object of the present invention to provide a method for pretreatment of lignocellulose for suppressing sugar overdegradation and obtaining a sugar with high yield.

    The inventors of the present invention have made extensive studies to solve the above problems, and as a result, the lignocellulosic raw material is first subjected to an acid hydrolysis treatment, neutralized the reactants in the acid treatment step, and then subjected to a wet pulverization treatment. Thus, the present inventors have found a pretreatment method that can reduce the input energy for pulverization at a low cost and can increase the efficiency of subsequent enzymatic hydrolysis.

    That is, the present invention is a pretreatment method for enzymatic hydrolysis of lignocellulose, an acid treatment step of acid-treating a lignocellulose raw material, a neutralization step of neutralizing a reaction product of the acid treatment step, and the neutralization And a pulverization process step of wet pulverizing the reaction product of the process.

    According to the present invention, the reaction product obtained by hydrolyzing hemicellulose with an acid is neutralized and then wet pulverized to shorten the pretreatment process. Thus, it is possible to efficiently improve the yield of sugar in enzymatic hydrolysis at low cost and to achieve an increase in ethanol yield in subsequent fermentation. Since the process is shortened, compared with the case where the reaction product of the acid treatment process is solid-liquid separated, it is easy to operate in a closed system and it is easy to prevent contamination of bacteria and the like in the manufacturing process. In addition, when performing solid-liquid separation, it is necessary to add water for washing solids into the system. However, in the pretreatment method of the present invention, it is not necessary to add water, so that the sugar concentration can be increased. This can reduce the energy for separating the ethanol product.

According to the present invention, the amount of colored waste water can be reduced as compared with a pretreatment method using a chemical such as hydrogen peroxide in the secondary treatment following the primary treatment by acid hydrolysis. In addition, the amount of recovered sugar (such as xylose) derived from hemicellulose partially unreacted in the primary hydrolysis is larger than the method using a drug for the secondary treatment, and the sugar contained in the raw material can be used more effectively.
In addition, the reaction product is soft due to the elution of hemicellulose-derived sugar and the elution of part of the lignin in the reaction with an acid such as dilute sulfuric acid. The effect of hydrolysis can be greatly enhanced.
Furthermore, when a beater is used in the pulverization process, the pulverization power can be significantly reduced as compared with the case where a pulverizer such as a ball mill is used, so that cost reduction can be realized.

The pretreatment method for enzymatic hydrolysis of lignocellulose of the present invention comprises an acid treatment step for treating a lignocellulose raw material with dilute sulfuric acid, a neutralization step for neutralizing a reaction product in the acid treatment step, and a reaction product in the neutralization step. And a pulverization process step for performing a wet pulverization process.
FIG. 1 is a flowchart showing an example of a method for producing ethanol using lignocellulose as a raw material and including the pretreatment method of the present invention.
The raw material lignocellulose first hydrolyzes hemicellulose in the raw material mainly in the acid treatment step, and the acid-treated reaction product is neutralized in the subsequent neutralization step. The reaction product in the neutralization step is wet pulverized in the pulverization step (pretreatment in the present invention), and then hydrolyzed to sugar in the enzyme hydrolysis step to produce ethanol by fermentation.

    Although the raw material lignocellulose used for this invention is not specifically limited, For example, wood, rice straw, rice husk, bagasse, etc. can be utilized. Particularly in Japan, it is desirable to use waste building materials that are generated in large quantities and have established collection routes. Waste building materials are mainly generated by the demolition of wooden houses, and the percentage of conifers such as cedar, pine, and oak is high.

    The lignocellulose raw material used in the present invention is preferably crushed in advance to a size of 1 to 20 mm, particularly 5 to 10 mm using a crusher. As the chip size after crushing is as small as possible, the efficiency of saccharification increases, but the energy required for crushing also increases. There is an appropriate chip size. This crushing process is different from the crushing process after acid hydrolysis, in order to facilitate the recovery of sugar from hemicellulose by improving the contact between the raw material and sulfuric acid or steam in the acid treatment process which is primary hydrolysis.

    Next, the lignocellulose raw material is acid-treated. Examples of the acid to be used include sulfuric acid, hydrochloric acid, nitric acid or a mixture thereof. Among these, sulfuric acid, particularly dilute sulfuric acid is preferable. Furthermore, the acid treatment in the present invention is preferably performed while heating. The sulfuric acid concentration used in the reaction is preferably 0.1 to 5%, particularly preferably 0.5 to 3%. The reaction temperature is preferably 140 to 230 ° C, particularly 160 to 210 ° C. The reaction time is preferably 1 to 20 minutes, particularly preferably 5 to 10 minutes. If the sulfuric acid concentration, reaction temperature, and reaction time are within the above ranges, hemicellulose can be efficiently hydrolyzed and sugar can be recovered in the acid treatment step.

    Next, the reaction product in the acid treatment step is neutralized in the neutralization step. Examples of the alkali used for neutralization include calcium hydroxide, calcium oxide, sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate, and calcium hydroxide is particularly preferable. The alkali concentration used for neutralization is preferably 0.5 to 5%, particularly 1 to 3%. The reaction temperature is preferably in the range of 10 to 100 ° C, particularly 40 to 70 ° C. The reaction time is preferably 0.1 to 10 hours, particularly 0.5 to 2 hours. When the alkali concentration, reaction temperature, and reaction time are within the above ranges, fermentation-inhibiting substances such as sugar hyperdegradation products generated in the acid treatment step can be appropriately removed. In addition, a part of the lignin in the residue is dissolved, and the hydrolyzability by the subsequent enzyme is improved. The pH of the reaction product after neutralization is preferably 8 to 11, particularly 9 to 10.

  The neutralization step can be performed after the pulverization treatment step, which is described later, before the enzymatic hydrolysis. However, when the pulverization treatment is performed at a low pH, for example, the beating machine needs to be acid-resistant. Since the cost increases, it is more preferable to perform neutralization before the pulverization treatment.

  The reaction product of the acid treatment step used for the neutralization step contains hemicellulose-derived sugars such as glucose, xylose, arabinose, galactose, and mannose. In the pretreatment method of the present invention, the formation of a sugar overdegradation product in the acid treatment step is suppressed, but this reaction product contains a sugar overdegradation product such as furfural, hydroxymethylfurfural (HMF), levulinic acid, formic acid and the like. Some amount is included. These require pretreatment in order to inhibit fermentation by microorganisms in the latter stage, but do not require special treatment because furfural and HMF are partially removed in the neutralization step.

  The reaction product in the neutralization step is wet pulverized in the pulverization step. The water content of the reaction product to be pulverized is preferably 50 to 95%, particularly 60 to 90%. This reaction product is softened due to the elution of hemicellulose-derived sugar by hydrolysis with dilute sulfuric acid and the elution of a part of lignin. Therefore, the effect of subsequent enzymatic hydrolysis can be greatly enhanced even if pulverization is performed with a small amount of input energy. The pulverizer used in the pulverization process may be any pulverizer capable of obtaining a beating effect when wet, but a beating machine, a stamp mill, and a ball mill are preferable, and a beating machine is particularly preferable. Since this pulverization process is wet pulverization, there is no danger of dust explosion or fire, and part of the sugar component is hardly decomposed by heat denaturation.

The beating machine used in the pulverization process crushes when the raw material passes between the fixed blade and the rotary blade, selects the blade material and shape as appropriate, and controls the interval between the blades, the number of rotations, etc. Is a crusher capable of crushing wood and the like by freely changing the particle size from fine crushing to coarse crushing. When a beater is used, the power consumed during grinding can be significantly reduced compared to a grinding machine such as a ball mill or a stamp mill, so that the grinding process can be performed with high energy efficiency and low cost. The residue which has a particle size of about several micrometers-300 micrometers is obtained by the grinding | pulverization process using a beating machine.
As described above, by pretreating lignocellulose, subsequent ethanol hydrolysis and ethanol production by fermentation can be efficiently performed at low cost with low input energy.

The reaction product pulverized in the pulverization process as described above is subjected to enzymatic hydrolysis to produce sugar. Cellulase is used as the enzyme for enzyme hydrolysis. That is, cellulase is added to a liquid in which the pulverized residue is suspended, and the reaction is performed, for example, at pH 4 to 6, 30 to 60 ° C., for 10 to 120 hours with stirring.
The hydrolyzed solution by this enzyme includes glucose, which is a sugar derived from cellulose, and glucose, xylose, arabinose, galactose, mannose, etc., which are sugars derived from hemicellulose. A nutrient source containing nitrogen and phosphorus and an ethanol-fermenting microorganism are added to the sugar solution to convert the sugar into ethanol. As the fermentation microorganism, a microorganism capable of converting pentose may be used alone, or a microorganism capable of converting pentose and a microorganism capable of converting hexose may be used in combination.

  According to the present invention, the reaction product obtained by hydrolyzing hemicellulose with an acid is neutralized and then wet pulverized to shorten the pretreatment process. It is possible to improve the yield of sugar to be subjected to enzymatic hydrolysis efficiently at low cost, and to achieve an increase in ethanol yield in subsequent fermentation. Since the process is shortened, it is easier to operate in a closed system and prevent bacterial contamination in the production process than in the case of solid-liquid separation of the reaction product in the acid treatment process. In addition, when performing solid-liquid separation, it is necessary to add water for washing solid matter in the system when filtration is performed, but in the pretreatment method of the present invention, it is not necessary to add water. Can be increased. This can reduce the energy for separating the ethanol product.

    Further, according to the present invention, the amount of colored waste water can be reduced as compared with a pretreatment method using a chemical such as hydrogen peroxide in the secondary treatment following the primary treatment by acid hydrolysis. In addition, the amount of recovered sugar (such as xylose) derived from hemicellulose partially unreacted in the primary hydrolysis is larger than the method using a drug for the secondary treatment, and the sugar contained in the raw material can be used more effectively.

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

Acid treatment process: Waste building materials (chips for board raw materials) are used as raw materials, a continuous hydrolyzer (treatment amount: 120 kg / hour) is used as a hydrolyzer, a sulfuric acid concentration is 1%, a reaction temperature is 170 ° C., and a reaction time is 10 Primary hydrolysis was performed in minutes. The reaction product was a mixture of a sugar solution mainly containing 9% hemicellulose-derived sugar and a residue mainly composed of cellulose and lignin. The concentration of the residue as a solid was about 10%. The amount of the reaction product was 305 g with respect to 100 g of the raw material.
Neutralization step: Calcium hydroxide was added to the reaction product in the acid treatment step at a concentration of 1.8%, and neutralization was performed at a reaction temperature of 60 ° C. and a reaction time of 30 minutes.
Crushing step: 27 kg (wet weight, moisture content 90%) of the reaction product in the neutralization step was placed in a beater and pulverized for about 10 seconds. The particle size before pulverization was a distribution of several tens of μm to several mm, whereas after pulverization, the distribution was about several μm to 300 μm, and 50% D was about 60 μm.

  Enzymatic hydrolysis and alcohol fermentation process (hereinafter, simultaneous saccharification and fermentation process): To a 250 mL Erlenmeyer flask, 100 g of a pulverized reaction product containing about 10% of a solid residue was added. Subsequently, 5 g of corn steep liquor (manufactured by Nippon Food Processing Co., Ltd.) was added to adjust the pH to 6.5. Subsequently, 0.24 g of cellulase (GC 220, Genencor International Japan Limited) was added to 1 g of the residual solid. Furthermore, 5 g each of precultured solutions of ethanol-fermenting gene recombinant E. coli (strain name: KO11) and yeast (strain name: Saccharomyces cerevisiae TJ-1) were added. This was shaken at a reaction temperature of 35 ° C. and 100 rpm, and subjected to simultaneous saccharification and fermentation for 100 hours. In the case of recombinant Escherichia coli, the preculture was aerobically cultured for 12 hours in Luria-Bertani (LB) medium containing 4% xylose. In the case of yeast, it was cultured aerobically for 12 hours in a medium containing 5% glucose, 0.5% corn steep liquor, 0.08% urea, and 0.02% potassium dihydrogen phosphate.

Analysis: Ethanol in the fermentation broth before and after simultaneous saccharification and fermentation was separated and quantified by gas chromatography. CP-Wax 52CB manufactured by GL Sciences Inc. was used as a gas chromatograph column. In addition, monosaccharides before and after simultaneous saccharification and fermentation were separated and quantified by HPLC. As the HPLC column, HPX-87P manufactured by BIO-RAD was used. From the ethanol concentration in the simultaneous saccharification and fermentation broth, the ethanol yield per 100 g (dry matter) of the raw material was calculated. Considering that the above and sulfuric acid were added in the acid treatment step, calcium hydroxide was added in the neutralization step, and corn steep liquor and preculture were added in the raw material simultaneous saccharification and fermentation, the following equations were used.
Yield of ethanol per 100 g of raw material [g] = (ethanol concentration in fermentation broth [%] − ethanol concentration before fermentation [%]) × (305/100) × (118/100) × ((100 + 5 + 5 + 5) / 100)

(Comparative Example 1)
Ethanol was obtained in the same manner as in Example 1 except that the reaction product of the primary hydrolysis was directly used for enzyme hydrolysis without pulverization.
FIG. 2 shows the change over time in the ethanol concentrations of Example 1 and Comparative Example 1, and Table 1 shows the ethanol yield.

  From the result of ethanol yield obtained by the simultaneous saccharification and fermentation in Example 1 and Comparative Example 1, the reaction product of acid hydrolysis was neutralized and pulverized as in Example 1, thereby pulverizing as in Comparative Example 1. It was found that the ethanol yield was significantly improved as compared with the case of no treatment.

  The lignocellulose pretreatment method of the present invention is useful for saccharification and production of ethanol using woody biomass as a raw material.

An example of the manufacturing method of ethanol which uses lignocellulose as a raw material and includes the pre-processing method of this invention is shown with the flowchart. The time-dependent change of the ethanol concentration of Example 1 and Comparative Example 1 is shown.

Claims (8)

  A pretreatment method for enzymatic hydrolysis of lignocellulose, wherein an acid treatment step of acid-treating a lignocellulose raw material, a neutralization step of neutralizing a reaction product of the acid treatment step, and a reaction product of the neutralization step A pretreatment method for lignocellulose, comprising a pulverization treatment step of performing a wet pulverization treatment.   The pretreatment method for lignocellulose according to claim 1, wherein the wet pulverization is performed by a beating machine.     The pretreatment method for lignocellulose according to claim 1 or 2, wherein the acid treatment is performed using dilute sulfuric acid.     The pretreatment method for lignocellulose according to claim 3, wherein the concentration of dilute sulfuric acid is 0.1 to 5% in the acid treatment step.     In the said acid treatment process, reaction temperature is 140-230 degreeC, The pretreatment method of lignocellulose of any one of Claims 1-4 characterized by the above-mentioned.     In the said acid treatment process, reaction time is 1 to 20 minutes, The pretreatment method of lignocellulose of any one of Claims 1-5 characterized by the above-mentioned.     The said lignocellulose raw material is a waste building material, The pretreatment method of lignocellulose of any one of Claims 1-6 characterized by the above-mentioned. The lignocellulose pretreatment method according to any one of claims 1 to 7, wherein the lignocellulose is crushed before acid treatment.

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