JP2006246711A - Method for pretreating lignocellulose - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for pretreating lignocellulose when a lignocellulose raw material is enzymically hydrolyzed and to provide the method for pretreating the lignocellulose in order to suppress overdegradation of a saccharide and inexpensively obtain the saccharide in good yield. <P>SOLUTION: The method for pretreating the lignocellulose by enzymic hydrolysis is characterized as follows. The method comprises an acid treating step of treating the lignocellulose raw material with an acid, a solid-liquid separation step of carrying out the solid-liquid separation of a reaction product of the acid treating step and a pulverization treating step of subjecting the residue of the solid-liquid separation step to a wet pulverization treatment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 pentoses such as xylose and arabinose, and hexoses 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, even in wood, the residue after primary treatment of hardwood with acid or blasting is relatively easily saccharified by enzymes, but conifers have a structure containing lignin that is stronger than hardwood, so the residue after primary treatment remains as it is. 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).
Japanese Patent Laid-Open No. 55-9758 JP 59-91893 A JP-A 63-137690 JP-A-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.

  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 suppresses excessive decomposition of sugar and reduces sugar at a low cost and in a high yield. It is an object of the present invention to provide a method for pretreatment of lignocellulose to obtain the above.

  The inventors of the present invention have intensively studied to solve the above problems, and as a result, firstly lignocellulose raw material is subjected to acid hydrolysis treatment, and solid-liquid separation is performed to obtain a hemicellulose-derived sugar that can be recovered with acid relatively easily. After that, the inventors have found a pretreatment method that can increase the efficiency of the subsequent enzymatic hydrolysis by wet-grinding the solid residue.

  That is, the present invention is a pretreatment method for enzymatic hydrolysis of lignocellulose, an acid treatment step of acid-treating lignocellulose raw material, a solid-liquid separation step of solid-liquid separation of a reaction product of the acid treatment step, A lignocellulose pretreatment method comprising: a pulverization treatment step of subjecting a residue of the solid-liquid separation step to a wet pulverization treatment.

According to the present invention, the residue obtained by hydrolyzing hemicellulose with an acid can be pulverized to improve the yield of sugar in enzymatic hydrolysis at a low cost, and to improve the ethanol yield in subsequent fermentation. It becomes possible.
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.
Furthermore, since the pulverization step in the pretreatment method of the present invention 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 residue 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 can be greatly enhanced.

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 solid-liquid separation step for solid-liquid separation of a reaction product of the acid treatment step, and a solid-liquid separation step. And a pulverization treatment step of subjecting the residue to a wet pulverization treatment. 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 lignocellulose is first hydrolyzed mainly in the raw material hemicellulose in the acid treatment step, and then separated into a sugar solution and a residue in the subsequent solid-liquid separation step. The residue is pulverized in the pulverization process (pretreatment in the present invention), then hydrolyzed to sugar in the enzyme hydrolysis process, 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.

  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 separated into a filtrate and a solid residue in a solid-liquid separation step. The residue is subjected to a subsequent grinding process step. The filtrate contains hemicellulose-derived sugar, and ethanol is produced by fermentation as described below. As the solid-liquid separation method, filtration, centrifugation, or the like can be used, but it is preferable to use filtration with low energy consumption.

The solid residue in the solid-liquid separation process is wet pulverized in the pulverization process. This residue is softened by 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 of any type as long as it is a wet-type pulverizer, and a ball mill, stamp mill, and refiner are 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.
As described above, by pretreating lignocellulose, subsequent ethanol hydrolysis and ethanol production by fermentation can be efficiently performed at low cost.

As described above, the residue pulverized in the pulverization process 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 enzyme hydrolyzed solution contains glucose, which is a sugar derived from cellulose. A nutrient source containing nitrogen and phosphorus and an ethanol-fermenting microorganism are added to the sugar solution to convert the sugar into ethanol.

  On the other hand, glucose, xylose, arabinose, galactose, mannose, etc., which are sugars derived from hemicellulose, are included in the filtrate of the solid-liquid separation step. Furthermore, in the pre-treatment method of the present invention, the formation of sugar overdegradation products in the acid treatment step is suppressed, but this filtrate contains furfural, hydroxymethylfurfural (HMF), levulinic acid, formic acid, which are sugar overdegradation products. A certain amount is included. Since these inhibit fermentation by microorganisms, pretreatment is necessary. For example, a method of heating by adding lime is known as a method in which part of furfural and HMF is also removed. Nutrient sources containing nitrogen and phosphorus and ethanol-fermenting microorganisms are added to the filtrate neutralized with lime to convert sugar into ethanol.

  As described above, when the lignocellulose pretreatment method of the present invention is used, sugar derived from hemicellulose can be efficiently recovered in the acid hydrolysis treatment step. The yield can be improved. Accordingly, the total sugar yield using lignocellulose as a raw material is increased at a low cost, whereby the yield of ethanol produced by fermenting sugar can be improved.

  According to the pretreatment method of the present invention, the amount of colored waste water can be reduced as compared with the conventional method using a chemical such as hydrogen peroxide in the secondary treatment after the primary hydrolysis. In addition, the amount of hemicellulose-derived sugar that was partially unreacted by acid hydrolysis, which is the primary hydrolysis, is larger than the method using chemicals in the secondary treatment, and the sugar contained in the raw material should be used more effectively. Can do.

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

(Examples 1-6)
Acid treatment process: Sugi material is used as a raw material, batch hydrolysis is used as a hydrolyzer (amount of treatment: 400 g / batch), sulfuric acid concentration is 1%, reaction temperature is 170 ° C., and reaction time is 10 minutes. As a result, 20 g of monosaccharide per 100 g of raw material (dry matter) was obtained. The solid content recovery was 75%.
Solid-liquid separation step: After primary hydrolysis, solid-liquid separation was performed by suction filtration. The obtained residue was thoroughly washed with water and used as a raw material for the pulverization process.
Crushing step: 80 g (wet weight) of the above residue was placed in a stamp mill (manufactured by Nippon Ceramics Co., Ltd., model: ANS143) and pulverized by changing the pulverization time. Table 1 shows the grinding time in each example.

  Enzymatic hydrolysis step: Into a 200 mL Erlenmeyer flask, 2.5 g of the pulverized residue was added as a solid substance, and a buffer solution and ion-exchanged water were added to the residue so as to be 50 ml together with the adhering moisture of the residue. As a buffer solution, 0.2 mol / L sodium acetate was used, and the pH of the reaction solution was adjusted to 4.5. Here, cellulase (SPEZYME GC 220, Genencor International Japan Limited) was added in an amount of 0.4 g to 1 g of the residual solid. This was shaken at a reaction temperature of 45 ° C. and 100 rpm to carry out enzymatic hydrolysis for a minute.

Analysis: Monosaccharides in the hydrolyzed solution after enzymatic hydrolysis were separated and quantified by HPLC. As the HPLC column, HPX-87P manufactured by BIO-RAD was used. The monosaccharide yield per 100 g (dry matter) of the substrate was calculated from the monosaccharide concentration in the hydrolyzate and the charged substrate concentration. Enzymatic hydrolysis was carried out at a total substrate concentration of 5 w / v%, so the monosaccharide yield S2 per 100 g of the substrate can be obtained from the following equation.
Monosaccharide yield per 100 g (dry matter) of substrate S2 [g] = Monosaccharide concentration in hydrolyzed solution [g / L] x (100/5) x (100/1000)
The monosaccharide yield S1 per 100 g (dry matter) of the raw material in the primary hydrolysis with dilute sulfuric acid was also calculated by the same calculation.
Furthermore, in order to convert the monosaccharide obtained by enzymatic hydrolysis per 100 g (dry matter) of the raw material, the total monosaccharide yield ΣS from the raw material is calculated in consideration of the solid content recovery rate R1 in the primary hydrolysis with dilute sulfuric acid. The following formula was used for calculation.
Monosaccharide yield per raw material (dry matter) ΣS [g / 100 g] = S1 + R1 × S2

(Comparative Example 1)
A monosaccharide was obtained in the same manner as in the above example except that the residue of primary hydrolysis was directly used in the enzyme hydrolysis step without being pulverized.
(Comparative Example 2)
The cedar log was treated with a stamp mill for 60 minutes, and an enzyme hydrolysis reaction similar to the above was carried out as it was without acid hydrolysis to obtain a monosaccharide.

FIG. 2 shows changes over time in the yield of monosaccharides S2 obtained by enzymatic hydrolysis in Examples 1 to 6 and Comparative Examples 1 and 2, that is, the yield of monosaccharides per substrate (grind residue) weight.
It was found that by performing the pulverization treatment on the primary hydrolysis residue as in Examples 1 to 6, the monosaccharide yield was significantly improved as compared with Comparative Example 2 in which the raw wood was pulverized. Moreover, compared with the case where a primary hydrolysis residue was not grind | pulverized like the comparative example 1, the monosaccharide yield improved. When the pulverization time was 30 minutes or longer as in Examples 2 to 6, the monosaccharide yield was increased by about 1.5 times compared to Comparative Example 1.

  Further, Table 2 shows the sugar yield S1 and the solid content recovery rate R1, the sugar yield S2 in the enzyme hydrolysis, and the total sugar yield ΣS in the acid treatment step of Example 2 and Comparative Example 1.

  When the pulverization treatment was performed for 30 minutes as in Example 2, the total sugar yield ΣS was reduced by about 20 as the monosaccharide yield S2 was significantly improved as compared with the case of not performing the pulverization treatment as in Comparative Example 1. % Could be improved.

(Examples 7 to 9)
Acid treatment process: Recycled board waste building materials are used as raw materials, a continuous hydrolyzer (treatment amount: 50 kg / hour) is used as a hydrolyzer, and a sulfuric acid concentration is 1%, a reaction temperature is 170 ° C., and a reaction time is 10 minutes. Hydrolysis was performed to obtain 21 g of monosaccharide per 100 g of raw material (dry matter). The solid content recovery was 70%.
Solid-liquid separation step: After primary hydrolysis, solid-liquid separation was performed with a tray filter (throughput: 18 kg / batch as a solid). The obtained residue was thoroughly washed with water and used as a raw material for the pulverization process.
Crushing step: The above residue 25 g / pot (wet weight) was put into a ball mill (CMT Co., Ltd., model: TI-200, capacity 50 mL / pot, number of pots 2), and pulverization was performed by changing the pulverization time. Table 3 shows the grinding time in each example.

Enzymatic hydrolysis step: Into a 200 mL Erlenmeyer flask, 2.5 g of the pulverized residue was added as a solid, and a buffer solution and ion-exchanged water were added to the residue so as to be 50 mL together with the adhering moisture of the residue. As a buffer solution, 0.2 mol / L sodium acetate was used, and the pH of the reaction solution was adjusted to 4.5. Here, 0.08 g of cellulase (SPEZYME GC 220, Genencor International Japan Limited) was added to 1 g of the residual solid. This was shaken at a reaction temperature of 45 ° C. and 100 rpm, and subjected to enzyme hydrolysis for 110 hours.
The analysis was performed in the same manner as in Examples 1-6.

(Comparative Example 3)
A monosaccharide was obtained in the same manner as in the above example except that the residue of primary hydrolysis was directly used in the enzyme hydrolysis step without being pulverized.

  Table 4 shows the sugar yield S1 and the solids recovery rate R1, the sugar yield S2 in the enzymatic hydrolysis, and the total sugar yield ΣS in the acid treatment steps of Examples 7 to 9 and Comparative Example 3.

  In any of Examples 7 to 9 and Comparative Example 3, 21 g of monosaccharide was obtained per 100 g (dry matter) of the raw material by primary hydrolysis, and the solid content recovery rate was 70%. By simply pulverizing with a ball mill for 10 minutes (Example 7), the yield of monosaccharides per substrate increased by about 1.8 times compared to the case without pulverization (Comparative Example 3). When compared with the sugar yield per raw material, the increase was about 37%. In Example 9, this increasing tendency was more remarkable.

  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 monosaccharide yield per substrate weight obtained by the enzyme hydrolysis in Examples 1-6 and Comparative Examples 1-2 is shown.

Claims (7)

  A pretreatment method for enzymatic hydrolysis of lignocellulose, comprising an acid treatment step for acid-treating a lignocellulose raw material, a solid-liquid separation step for solid-liquid separation of a reaction product of the acid treatment step, and a solid-liquid separation step A pretreatment method for lignocellulose, comprising a pulverization treatment step of subjecting the residue to a wet pulverization treatment.   The pretreatment method for lignocellulose according to claim 1, wherein the acid treatment is performed using dilute sulfuric acid.   The pretreatment method for lignocellulose according to claim 2, 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 1-3 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 1-4 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 1-5 characterized by the above-mentioned. The lignocellulose pretreatment method according to any one of claims 1 to 6, wherein the lignocellulose is crushed before acid treatment.

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