JP2009189250A - Method for saccharification of lignocellulose - Google Patents

Abstract

The present invention provides a method for saccharification of lignocellulose capable of obtaining a saccharide with high yield from lignocellulose as a raw material.
SOLUTION: A step of heating lignocellulose containing hemicellulose and cellulose with water vapor to saccharify the hemicellulose, and a step of saccharifying the cellulose by enzymatic treatment of the lignocellulose heated by the water vapor. Prepare. The enzyme-treated lignocellulose contains a sugar produced by saccharifying the hemicellulose. In the step of heating with water vapor, the lignocellulose is accommodated in a high-pressure boiler, water vapor having a temperature in the range of 200-220 ° C. is introduced into the high-pressure boiler, and the temperature is in the range of 180-200 ° C. Heat for 60 minutes maintaining time.
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Description

  The present invention relates to a method for saccharification of lignocellulose used for bioethanol production.

  In recent years, from the viewpoint of preventing global warming, it is required to reduce carbon dioxide emissions, which is considered to be one of the causes. Then, using the mixed fuel of liquid hydrocarbons, such as gasoline, and ethanol for automobile fuel is examined. As said ethanol, bioethanol obtained by fermentation of plant substances, for example, agricultural products, such as sugarcane and corn, can be used. Since the plant substance as a raw material has already absorbed carbon dioxide by photosynthesis, even if ethanol obtained from the plant substance is burned, the amount of carbon dioxide emitted is Equal to the amount of carbon dioxide absorbed by the plant itself. That is, it is possible to obtain a so-called carbon neutral effect in which the total amount of carbon dioxide emission is theoretically zero. Therefore, carbon dioxide emissions can be reduced by the amount of bioethanol used instead of liquid hydrocarbons such as gasoline.

  However, sugarcane, corn, and the like have a problem that the amount supplied as food decreases when consumed in large quantities as a raw material for ethanol.

  Therefore, a technique for producing ethanol using lignocellulosic biomass that is not edible as the plant substance instead of sugar cane, corn, or the like has been studied. The lignocellulosic biomass contains cellulose. The cellulose can be decomposed into glucose by enzymatic saccharification, and the obtained glucose can be fermented to obtain bioethanol. Examples of the lignocellulosic biomass include wood, rice straw, wheat straw, baros, bamboo, pulp, and wastes generated therefrom, such as waste paper.

  However, the lignocellulose contains hemicellulose and lignin as main components in addition to cellulose, and usually the cellulose is firmly bound to the hemicellulose and the lignin. Is done. Therefore, when the cellulose is subjected to an enzymatic saccharification reaction, it is desirable to remove the hemicellulose and the lignin in advance.

  Thus, a saccharification method is known in which lignocellulosic biomass is treated with pressurized hot water to separate the hemicellulose and lignin from the cellulose, followed by enzyme treatment to decompose the cellulose into glucose (for example, , See Patent Document 1).

However, the conventional lignocellulosic biomass saccharification method has a disadvantage that a sufficient yield cannot be obtained when the lignocellulose is enzymatically saccharified to obtain sugars such as glucose.
JP 2006-136263 A

  An object of the present invention is to provide a method for saccharification of lignocellulose, which can solve such disadvantages and can obtain saccharides in high yield from lignocellulose as a raw material.

  As a result of various studies, the present inventors have found that in the conventional lignocellulosic biomass saccharification method, xylose produced by saccharification of the hemicellulose separated from the cellulose when treated with the pressurized hot water. Was found to elute in the pressurized hot water. Therefore, in the conventional saccharification method, it is considered that when the pressurized hot water is removed prior to the enzyme treatment, the xylose is lost and the yield of saccharide is insufficient.

  Therefore, in order to achieve this object, the lignocellulose saccharification method of the present invention comprises heating a lignocellulose containing hemicellulose and cellulose with steam to saccharify the hemicellulose, and a lignocellulose heated with the steam. And a step of saccharifying the cellulose by enzymatic treatment of cellulose.

  According to the lignocellulose saccharification method of the present invention, first, lignocellulose is heated with water vapor. If it does in this way, hemicellulose combined with the cellulose will be saccharified into xylose and separated from the cellulose, and lignin combined with the cellulose by the hemicellulose is also separated from the cellulose. At this time, since water vapor does not contain liquid water, the xylose remains in the lignocellulose heated by the water vapor.

  Next, the lignocellulose is saccharified by enzymatic treatment. Since the cellulose contained in the lignocellulose is separated from hemicellulose and lignin by heating with the water vapor, the enzymatic reaction of the cellulose is easily inhibited by enzymatic saccharification into glucose. Further, since the lignocellulose contains xylose produced by saccharification of the hemicellulose, the saccharide obtained by the enzymatic saccharification contains xylose together with the glucose. Therefore, according to the method of the present invention, saccharides can be obtained in high yield using lignocellulose as a raw material.

  In the lignocellulose saccharification method of the present invention, for example, the lignocellulose is accommodated in a high-pressure boiler, and steam having a temperature in the range of 200 to 220 ° C. is introduced into the high-pressure boiler, so that the temperature is 180 to 200 ° C. Heating with water vapor is performed by maintaining the temperature in the range for 15-60 minutes and heating.

  When the temperature of the water vapor introduced into the high pressure boiler is lower than 200 ° C, the temperature in the high pressure boiler may be lower than 180 ° C. On the other hand, if the temperature of the introduced water vapor exceeds 220 ° C, the temperature in the high-pressure boiler may become higher than 200 ° C. Moreover, when the temperature which heats the said lignocellulose is lower than 180 degreeC, saccharification of hemicellulose and decomposition | disassembly of lignin may not fully be performed. On the other hand, when the temperature for heating the lignocellulose exceeds 200 ° C., the hemicellulose may be excessively decomposed. Moreover, if the time for heating while maintaining the temperature is shorter than 15 minutes, saccharification of hemicellulose and decomposition of lignin may not be performed sufficiently. On the other hand, even if the time for heating while maintaining the temperature exceeds 60 minutes, no further effect is obtained.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a flowchart of a bioethanol production method using lignocellulose as a raw material, FIG. 2 is an explanatory cross-sectional view of a high-pressure boiler used in the present embodiment, and FIG. 3 is an inawara chip at the time of heating with water vapor in the present embodiment. It is a graph which shows the temperature change of.

  The lignocellulose saccharification method of the present embodiment relates to a heat treatment and a saccharification treatment with an enzyme, which are pre-stages of ethanol fermentation in a bioethanol production method using lignocellulosic biomass. Here, a general example of the bioethanol production method will be briefly described with reference to FIG.

  First, inawara is prepared as lignocellulosic biomass. Next, after heat-treating the prepared rice straw (STEP 1), water and enzymes are added to the heat-treated rice straw (STEP 2). Next, the rice straw is saccharified by enzyme treatment (STEP 3), and then solid-liquid separation is performed to separate the enzyme treatment liquid and the residue (STEP 4). The enzyme treatment solution is separated into an aqueous solution of the enzyme and sugar by ultrafiltration or the like (STEP 5). The enzyme is reused for the enzyme treatment of STEP3.

  Next, the bacterium is added to the aqueous solution of the sugar obtained in STEP 5 (STEP 6), and ethanol is produced from the sugar by performing an ethanol fermentation treatment (STEP 7). After completion of the ethanol fermentation, the solution is separated into an aqueous ethanol solution and the bacteria by ultrafiltration or the like (STEP 8). The aqueous ethanol solution obtained in STEP 8 is concentrated by, for example, a zeolite-based dehydration membrane (STEP 9), and becomes 99% by weight or more of ethanol. The bacteria isolated in STEP 8 are propagated by culture (STEP 10), and then reused as the bacteria to be added to the aqueous sugar solution in STEP 6 (STEP 10).

  As the inwara shown in FIG. 1, in the lignocellulose saccharification method of this embodiment, naturally dried inawara is pulverized with a cutter mill to form an inawara chip, for example, passed through a screen filter having a diameter of 3 mm.

  Next, as STEP 1 in FIG. 1, 20 kg of the inwara chip passing through the screen filter is accommodated in the high-pressure boiler 1 shown in FIG. As the high-pressure boiler 1, one having a cylindrical reaction vessel 2, a water vapor blowing pipe 3 provided on the lower side of the reaction vessel 2, and a water vapor outlet 4 provided on the upper side of the reaction vessel 2 is used. it can. The water vapor blowing tube 3 extends in the longitudinal direction at the inner lower portion of the reaction vessel 2, and a water vapor outlet 5 is provided every 100 mm. Water vapor is ejected from the water vapor ejection port 5, and the Inawara chip is heated by the water vapor. The steam blowing pipe 3 is provided with an inlet valve 6 outside the reaction vessel 2 so that the amount of water vapor supplied to the reaction vessel 2 can be adjusted.

  A front door lid 7 is provided at one end of the reaction vessel 2, and a container of inwara chip, for example, a stainless steel cage 8 can be accommodated from the front door lid 7. The net cage 8 is disposed on a shelf spacer 9 installed on a shelf provided in the reaction vessel 2, and the shelf spacer 9 is arranged at the bottom of the reaction vessel 2 so that the inwara chip is not immersed in condensed water. It is installed with enough space. A condensate drip-proof hood 10 is provided above the shelf spacer 9, as shown in FIG. 2B, which is a cross-sectional view taken along line AA of FIG. Yes. A condensed water outlet 11 is provided below the reaction vessel 2, and condensed water generated in the reaction vessel 2 is discharged from the condensed water outlet 11.

  The high pressure boiler 1 is recommended to use alkaline boiler water having a pH of 10 to 11.8. By using the alkaline boiler water as water vapor, the effect of separating lignin from cellulose contained in lignocellulose is enhanced, and a beneficial effect can be obtained also in enzymatic saccharification.

  The inwara housed in the high-pressure boiler 1 is heated by supplying water vapor into the reaction vessel 2 from the water vapor blowing tube 3 after reducing the pressure in the reaction vessel 2 with a water-sealed vacuum pump. At this time, the pressure of the water vapor at the entrance from the water vapor blowing tube 3 to the reaction vessel 2 is approximately 2 MPa. By adjusting the opening of the inlet valve 6, the vapor pressure in the reaction vessel 2 is set to 1 MPa so that the saturation temperature of water in the reaction vessel 2 becomes 180 ° C., and then the inlet valve 6 is closed for 30 minutes. Maintain the temperature and vapor pressure. After a predetermined time elapses, the water vapor outlet 4 is opened and water vapor is discharged. When the pressure in the reaction vessel 2 becomes equal to the atmospheric pressure, the inwara chip is taken out from the reaction vessel 2. FIG. 3 shows the temperature change of the inwara chip in the net cage at this time.

  When the temperature change of the inawara chips accommodated in the three locations of the front door lid side net cage, the central part net cage and the rear wall side net cage during the heat treatment with water vapor is measured, as shown in FIG. It is apparent that the chip is heated to a predetermined 180 ° C. in about 15 minutes from the start of heating, and then maintained at a constant temperature at all three locations for 30 minutes until the water vapor outlet 4 is opened. is there. This is because the temperature in the reaction vessel 2 is maintained at the saturation temperature of water at the predetermined vapor pressure by maintaining the inside of the reaction vessel 2 at a predetermined vapor pressure.

  Next, the moisture content of the locust chip after the heat treatment with water vapor is measured, the wet weight of the locust chip is converted into a dry weight, and this is used as the substrate weight. A commercially available saccharifying enzyme (produced by Genencor Kyowa Co., Ltd., trade name: GC220, a mixture of cellulase and hermirase) is added to 10% by weight with respect to the substrate weight, and further an acetate buffer and ion exchange water are added The pH is adjusted to 4.5, and the substrate weight is adjusted to 20% (w / v) with respect to 1 liter of the resulting aqueous solution (STEP 2). The adjusted aqueous solution is placed in a saccharification reaction tank and stirred at a temperature of 50 ° C. for 24 hours to enzymatically saccharify the cellulose contained in the adjusted aqueous solution (STEP 3). After completion of the reaction, solid-liquid separation is performed using a filter press to obtain an aqueous solution of sugar.

  The concentration of glucose and xylose contained in the sugar aqueous solution was measured by high performance liquid chromatography (HPLC), and the yield of the sugar was determined from the measurement result (Example 1). The results are shown in Table 1.

  On the other hand, enzymatic saccharification was performed in exactly the same manner as in Example 1 except that heat treatment was performed using 180 ° C. pressurized hot water instead of the heat treatment with water vapor, and then the pressurized hot water was removed and enzymatic saccharification was performed. An aqueous solution of sugar was obtained. The concentration of glucose and xylose in the sugar aqueous solution was measured by HPLC, and the yield of the sugar was determined from the measurement result (Comparative Example 1). The results are shown in Table 1.

  Further, an enzymatic saccharification was carried out in the same manner as in Example 1 except that the heat treatment was not performed at all to obtain an aqueous solution of sugar. The concentrations of glucose and xylose in the sugar aqueous solution were measured by HPLC, and the yield of the sugar was determined from the measurement results (Reference Example 1). The results are shown in Table 1.

  From Table 1, according to the saccharification method of Comparative Example 1 in which heat treatment with pressurized hot water was performed, the yield of glucose was higher than that in Reference Example 1 in which no heat treatment was performed. It is clear that the yield of is almost equivalent to that of the saccharification method of Reference Example 1. On the other hand, according to the saccharification method of Example 1 in which the heat treatment with water vapor was performed, the yield of glucose was almost the same as that of Comparative Example 1, but the yield of xylose was the same as that of Comparative Example 1. It is clear that it is more.

  Therefore, according to the saccharification method of Example 1, it is clear that saccharides can be obtained with a higher yield than the saccharification method of Comparative Example 1.

  Next, except that the water content of the rice straw before heating with water vapor was changed, enzymatic treatment was performed in exactly the same manner as in Example 1 to obtain a saccharified aqueous solution. The water content of the rice straw before heating with the water vapor was 6.4% (Example 2), 30.3% (Example 3), 40.6% (Example 4), 48.9% (implemented) Example 5), 65.4% (Example 6), 75.0% (Example 7), 80.9% (Example 8), and 90.1% (Example 9). Next, the glucose and xylose concentrations of the aqueous sugar solution obtained at each water content were measured by HPLC, and the yield of the sugar was determined from the measurement results. The results are shown in Table 2.

  From Table 2, it is clear that the same high yield can be obtained if the water content before heating with water vapor is 75% or less (Examples 2 to 7). On the other hand, when the water content before heating with water vapor exceeds 75% (Example 8 and Example 9), the yield of the whole sugar may be reduced as a result. The reason that the yield of the whole sugar may decrease is that if the water content before heating with the steam is too high, water containing sugar (xylose) is dropped during the heating with the steam, It is thought that sugar is lost from lignocellulose.

The flowchart of the bioethanol manufacturing method. Explanatory sectional drawing of a high pressure boiler. The graph which shows the temperature change of the Inawara chip | tip at the time of the heating by water vapor | steam.

Explanation of symbols

1 ... High pressure boiler.

Claims (3)

Heating lignocellulose containing hemicellulose and cellulose with water vapor to saccharify the hemicellulose;
And a step of saccharifying the cellulose by enzymatic treatment of the lignocellulose heated by the water vapor.   2. The method for saccharification of lignocellulose according to claim 1, wherein the lignocellulose containing sugar produced by saccharification of the hemicellulose is treated with an enzyme. The lignocellulose is accommodated in a high-pressure boiler, water vapor having a temperature in the range of 200 to 220 ° C. is introduced into the high-pressure boiler, and maintained at a temperature in the range of 180 to 200 ° C. for a time in the range of 15 to 60 minutes. The method for saccharification of lignocellulose according to claim 1 or 2, wherein heating is performed.