JP2015015902A - Ethanol production method using cellulosic biomass as raw material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ethanol production method using cellulosic biomass as a raw material, in which saccharification/decomposition efficiency is improved and besides, a cost of a saccharification/decomposition process is suppressed.SOLUTION: The ethanol production method using cellulosic biomass as a raw material comprises: a first saccharification/decomposition step of performing hot water treatment on slurry of cellulosic biomass, whose pH is adjusted to 1.0 or more and 3.5 or less by strong acid, in a supercritical state or a subcritical state, and performing saccharification/decomposition on cellulosic biomass into C5 monosaccharide; a first solid-liquid separation step of performing solid-liquid separation on the slurry after the first saccharification/decomposition step; a second saccharification/decomposition step in which a dehydrated cake obtained in the first solid-liquid separation step is pressurized until it becomes a supercritical state or a subcritical state, and saccharification/decomposition is performed on cellulose contained in the cellulosic biomass into C6 monosaccharide; a second solid-liquid separation step of performing solid-liquid separation on the slurry after the second saccharification/decomposition step; a fermentation step of performing alcohol fermentation on saccharified solution obtained in the first solid-liquid separation step and the second solid-liquid separation step; and a distillation step of distilling the obtained fermentation liquid to concentrate ethanol.

Description

  The present invention relates to a method for producing ethanol (bioethanol) by hydrolyzing cellulosic biomass in a supercritical state or a subcritical state to produce saccharide, and then subjecting the saccharide to alcohol fermentation.

  As part of biomass energy utilization, there is an attempt to obtain ethanol by decomposing cellulose or hemicellulose which is a main component of a plant. There, it is planned that the obtained ethanol is partly mixed in automobile fuel mainly for fuel or used as an alternative fuel for gasoline.

  The main components of the plant are cellulose (polymer of glucose, a C6 monosaccharide composed of 6 carbons), hemicellulose (polymer of C5 and C6 monosaccharides composed of 5 carbons), lignin Starch is included, but ethanol is produced by fermentation of microorganisms such as yeast using saccharides such as C5 monosaccharides, C6 monosaccharides, and oligosaccharides that are complex thereof as raw materials.

  In order to decompose cellulosic biomass such as cellulose or hemicellulose into saccharides, 1) a method of hydrolyzing by the oxidizing power of a strong acid such as sulfuric acid, 2) a method of decomposing by an enzyme, 3) supercritical water or subcritical water Three types of methods that utilize the oxidizing power of are being industrially utilized. However, in the acid decomposition method of 1), since the added acid becomes an inhibitor for yeast fermentation, after the cellulose or hemicellulose is decomposed into saccharides, the saccharide is added before alcohol fermentation. Sum processing is indispensable, and it is difficult to put it to practical use in terms of processing costs. Although the enzymatic decomposition method of 2) can be performed at room temperature and constant pressure, no effective enzyme has been found, and even if it is discovered, the production cost of the enzyme is expected to be high. On the other hand, there is no prospect of realization on an industrial scale.

  As a method of hydrolyzing cellulosic biomass with supercritical water or subcritical water of 3) to obtain a saccharide, Patent Document 1 discloses that cellulose powder is hydrolyzed by contacting with hot pressurized water at 240 to 340 ° C. A method for producing a water-insoluble polysaccharide is disclosed. Patent Document 2 discloses a method of hydrolyzing a stripped biomass with hot water pressurized at 140 to 230 ° C. to a saturated water vapor pressure or higher for a predetermined time to decompose and extract hemicellulose, and then heated to a temperature higher than the decomposition temperature of cellulose. A method for decomposing and extracting cellulose by hydrolyzing with hot water is disclosed. In Patent Document 3, cellulose having an average degree of polymerization of 100 or more is contact-reacted with supercritical water or subcritical water having a temperature of 250 ° C. or more and 450 ° C. or less and a pressure of 15 MPa or more and 450 MPa or less and 0.01 seconds or more and 5 seconds or less, and then cooled. Disclosed is a method for producing glucose and / or water-soluble cellooligosaccharide, which comprises hydrolyzing by contacting with subcritical water at a temperature of 250 ° C. to 350 ° C. and a pressure of 15 MPa to 450 MPa for 1 second to 10 minutes. Yes.

  Patent Document 4 is a method for producing a saccharide from lignocellulosic biomass, in which a raw material mixture containing lignocellulosic biomass, weak acid (such as phosphoric acid), and water is heated (373-453K) in a nitrogen gas atmosphere. ) And a weak acid hydrothermal treatment process under pressure (0.1-5 MPa). The method of Patent Document 4 may further include an enzymatic saccharification treatment step of enzymatic saccharification of undegraded cellulose after the weak acid hydrothermal treatment step.

  Patent document 5 is used for hydrolysis treatment as a method for producing saccharides inexpensively and easily by reducing the amount of energy and water used for hydrolysis of polysaccharides in the production of saccharides from woody materials. Disclosed is a method for producing saccharides, characterized in that the treated water contains acidic water after the saccharides are recovered from the hydrolyzed extract containing the saccharide obtained by the hydrolysis treatment of woody materials. The pH of the treated water used for hydrolysis is preferably 2.6 to 2.9.

  When hydrolyzing or oxidatively degrading organic matter such as biomass with supercritical water or subcritical water, high-pressure water in which the organic matter is dispersed is rapidly heated to maintain the supercritical or subcritical state for a certain period of time to conduct the hydrolysis reaction. Wake me up. After completion of the reaction, the reaction system may be quenched to stop further chemical reaction. As an example of such a reactor capable of rapid heating and rapid cooling, Patent Document 6 discloses a reactor in which water vapor supplied from a boiler is pressurized with a piston to form supercritical water or subcritical water. .

JP 2000-186102 A JP 2002-59118 A Japanese Patent Laid-Open No. 2003-212888 JP 2009-22239 A JP 2008-43229 A JP 2002-263465 A

  The method of saccharifying (hydrolyzing) cellulose and hemicellulose, which are the main components of biomass, with supercritical water or subcritical water at high temperature and high pressure does not require acid neutralization compared to hydrolysis using strong acids Therefore, the processing cost is low and the processing method is friendly to the environment. However, even in a method using supercritical water or subcritical water, an acid may be added as a catalyst for the hydrolysis reaction in order to increase the decomposition efficiency of cellulose and hemicellulose.

  Here, in the invention disclosed in Patent Document 5, by recovering the acid produced as a by-product at the time of hydrolysis and extraction, neutralization is unnecessary, and polysaccharides such as cellulose contained in woody materials. The purpose of this is to improve the hydrolysis efficiency. However, the acid recovered in the present invention is an organic acid that is a weak acid, and its recovery amount is small, so that it is insufficient for improving the hydrolysis efficiency of the polysaccharide.

  On the other hand, in the method of saccharifying and decomposing cellulose and hemicellulose, which are main constituent components of biomass, with high-temperature and high-pressure supercritical water or subcritical water, first, hemicellulose in cellulosic biomass is hydrolyzed to C5 monosaccharide. The saccharified solution containing C5 monosaccharide is recovered by solid-liquid separation of the hydrolyzed slurry. Next, the solid content (dehydrated cake) as a residue is hydrothermally treated under higher temperature and pressure conditions, and cellulose in the cellulosic biomass is hydrolyzed to C6 monosaccharides. The saccharified solution containing C6 monosaccharide is recovered by solid-liquid separation of the hydrolyzed slurry.

  Patent Document 4 discloses that an enzymatic saccharification treatment step of enzymatic saccharification of undegraded cellulose can be performed after the weak acid hydrothermal treatment step. In this enzymatic saccharification treatment step, the slurry is added after the weak acid hydrothermal treatment step. Cellulase is added without performing solid-liquid separation, and the reaction is performed at a temperature of 45 to 55 ° C. so that the cellulase functions for 10 to 30 hours (paragraph 0043). Thus, in the enzymatic saccharification treatment step disclosed in Patent Document 4, acid does not function as a catalyst for saccharification and decomposition of cellulose to C6 monosaccharide, and high-temperature and high-pressure supercritical water or subcritical water. Compared with the technology for saccharifying and decomposing cellulose, the saccharifying and degrading of cellulose requires a long time.

  The present invention is a method of saccharifying and decomposing cellulosic biomass in a supercritical state or subcritical state at high temperature and pressure, and further producing ethanol by alcohol fermentation, from the outside in order to improve the saccharification and decomposition efficiency of cellulosic biomass. An object of the present invention is to provide a method capable of avoiding an increase in processing cost by maximally effectively using the strong acid to be added while adding the strong acid.

  As a result of intensive studies to solve the above problems, the present inventors added a strong acid to a slurry of cellulosic biomass to saccharify and decompose hemicellulose into C5 monosaccharide, and then separated the solid-liquid separated dehydrated cake into a hydraulic cylinder type The present invention has been completed by finding that the strong acid added first can be effectively utilized for saccharification / decomposition of hemicellulose and cellulose by saccharification / decomposition to C6 monosaccharide in the reactor.

Specifically, the present invention
A slurry of cellulosic biomass adjusted to pH 1.0 or more and 3.5 or less by containing a strong acid is hydrothermally treated in a supercritical state or a subcritical state, and the hemicellulose contained in the cellulosic biomass is converted into C5 monosaccharides. A first saccharification / decomposition step for saccharification / decomposition,
A first solid-liquid separation step for solid-liquid separation of the slurry after the first saccharification and decomposition step;
In a pressurized reactor, the dehydrated cake obtained in the first solid-liquid separation step is mixed with steam and pressurized until it reaches a supercritical state or a subcritical state. A second saccharification step that saccharifies into C6 monosaccharides;
A second solid-liquid separation step for solid-liquid separation of the slurry after the second saccharification and decomposition step;
A fermentation step of subjecting the saccharified solution obtained in the first solid-liquid separation step and the second solid-liquid separation step to alcohol fermentation;
A distillation step of concentrating ethanol by distilling the fermentation broth obtained by the fermentation step;
The present invention relates to an ethanol production method using cellulosic biomass as a raw material.

  By containing a strong acid, the saccharification / decomposition efficiency of hemicellulose in the first saccharification / decomposition step is improved. Further, the present invention is characterized in that the dehydrated cake obtained in the first solid-liquid separation step is transferred into a pressure reactor and the second saccharification / decomposition step is performed. In the dehydrated cake obtained in the first solid-liquid separation step, strong acid remains at a sufficient concentration, so by pressurizing this dehydrated cake in a pressurized reactor until it becomes supercritical or subcritical. The saccharification / decomposition efficiency of cellulose can be improved by the catalytic effect of a strong acid.

  Since the temperature and pressure of the second saccharification / decomposition process are higher than those of the first saccharification / decomposition process, the rate at which the C6 monosaccharide is oxidized to an organic acid increases as the reaction time increases. However, the reaction time can be easily adjusted by performing the second saccharification / decomposition step in the hydraulic cylinder reactor. That is, in the present invention, the saccharification / decomposition efficiency of the second saccharification / decomposition step can be increased by the catalytic effect of the strong acid, and the by-product of the organic acid can be decreased.

  Specific examples of the strong acid used in the present invention are, for example, sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid, but other mineral acids or organic acids may be used. A strong acid is added to the cellulosic biomass slurry to be subjected to the first saccharification / decomposition step so that the pH is 1.0 or more and 3.5 or less.

  The second saccharification / decomposition step may be performed after further adding a strong acid to the dehydrated cake obtained in the first solid-liquid separation step and adjusting the pH to 1.0 to 3.5.

  The pressurization reactor is preferably a hydraulic cylinder reactor.

  When strong acid is consumed before the second saccharification / decomposition step, it is difficult to increase the saccharification / decomposition efficiency of cellulose in the second saccharification / decomposition step. Therefore, it is preferable to perform the second saccharification / decomposition step after adding a strong acid. . By adding a strong acid, the saccharification / decomposition efficiency in the second saccharification / decomposition process is improved, and the water content is adjusted by adjusting the water content of the slurry or adding a strong acid to the reactor. The heating efficiency in is improved.

  A strong acid is recovered from the saccharified solution obtained in the first saccharification / decomposition process and the second saccharification / decomposition process, and the recovered strong acid is used in the first saccharification / decomposition process and / or the second saccharification / decomposition process. preferable.

  If a strong acid remains in the saccharified solution, subsequent alcohol fermentation is inhibited. For this reason, the strong acid is usually neutralized or recovered before alcohol fermentation. In the present invention, after the second solid-liquid separation step, strong acid is recovered from the C6 saccharified solution and reused in the first saccharification / decomposition step and / or the second saccharification / decomposition step, thereby suppressing the consumption of strong acid. .

  According to the present invention, when cellulosic biomass is saccharolytically decomposed in a supercritical state or a subcritical state, the production cost of ethanol can be suppressed by improving the saccharification / decomposition efficiency and suppressing the consumption of strong acid. It becomes possible.

BRIEF DESCRIPTION OF THE DRAWINGS The conceptual diagram explaining Embodiment 1 of this invention is shown. The conceptual diagram explaining Embodiment 2 of this invention is shown. The conceptual diagram explaining Embodiment 3 of this invention is shown. FIG. 2 is a conceptual diagram illustrating a conventional technique for saccharifying and decomposing cellulosic biomass in a supercritical state or a subcritical state, in which a strong acid is recovered and reused.

  Embodiments of the present invention will be described below with appropriate reference to the drawings. The present invention is not limited to the following description.

<Embodiment 1>
(Preparation of slurry)
FIG. 1 shows a schematic flow diagram illustrating Embodiment 1 of the present invention. First, cellulosic biomass (for example, plant biomass such as bagasse, sugar beet or straw) is pulverized to several mm or less as a pretreatment. The pulverized cellulosic biomass is supplied to the mixing tank 1, added with water and strong acid, and stirred to form a slurry. The pH of the slurry is 1.0 or more and 3.5 or less.

(First saccharification and decomposition process)
Next, the slurry is preheated as necessary and then supplied to the hemicellulose saccharification reactor 2. A specific example of the hemicellulose saccharification reactor 2 is preferably an indirectly heated pressure vessel. In the hemicellulose saccharification reactor 2, the slurry is hydrothermally treated at a temperature of 140 ° C. to 200 ° C. and a pressure of 1 MPa to 5 MPa. Through this hydrothermal treatment, hemicellulose in cellulosic biomass is efficiently saccharified (hydrolyzed) into C5 monosaccharides by the catalytic action of strong acids.

  After the hot water treatment for a certain time, the slurry is supplied from the hemicellulose saccharification reactor 2 to the flash tank 3. By flash evaporation, the slurry is rapidly cooled to a temperature below the subcritical state, and the saccharification / decomposition reaction (hydrolysis reaction) of hemicellulose is completed.

(First solid-liquid separation process)
Next, the slurry is supplied from the flash tank 3 to the solid-liquid separator 4 and separated into the C5 saccharified solution and the dehydrated cake 1. Specific examples of the solid-liquid separator 4 are a drum filter, a belt filter, a disk filter, or a filter press. The C5 saccharified solution is supplied to the subsequent alcohol fermentation process. On the other hand, the dewatered cake (dehydrated cake 1) is supplied to the reaction chamber 6 of the hydraulic cylinder type pressure reactor 5. At this time, since the dehydrated cake 1 normally has a water content of about 70% by mass, the strong acid added to the slurry before the first saccharification / decomposition step remains.

(Second saccharification and decomposition process)
After the dehydrated cake 1 is supplied, steam is supplied to the reaction chamber 6 of the hydraulic cylinder type pressurized reactor 5 from an external steam generator (not shown) such as a boiler. The steam supplied from the steam generator is preferably 150 to 200 ° C. and 0.5 to 1.6 MPa. Thereafter, the reaction chamber 6 is pressurized by the hydraulic cylinder 7 until the temperature becomes 350 ° C. or more and 400 ° C. or less and the pressure becomes 18 MPa or more and 30 MPa or less. The treatment time for the second saccharification / decomposition step is generally 0.1 to 30 seconds, although it depends on the type of biomass.

  In the second saccharification / decomposition step, the dehydrated cake 1 is heated and pressurized without adding water, so that strong acid remains at a sufficient concentration. The ratio of strong acid to cellulose in the second saccharification / decomposition process may be less than the ratio of strong acid to hemicellulose in the first saccharification / decomposition process. Therefore, even if the ratio of strong acid is small, it can be efficiently hydrolyzed to C6 monosaccharide.

  After heating and pressurizing treatment (saccharification and decomposition treatment) for a certain time, the treated slurry is supplied to the flash tank 8. At this time, the slurry contains a C6 saccharified solution. By flash evaporation, the slurry is rapidly cooled to a temperature below the subcritical state, and the hydrolysis reaction of cellulose is completed.

(Second solid-liquid separation process)
Next, the slurry is supplied from the flash tank 8 to the solid-liquid separator 9 and separated into the C6 saccharified solution and the dehydrated cake 2. A specific example of the solid-liquid separator 9 is the same as that of the solid-liquid separator 4. The C6 saccharified solution is supplied to the subsequent alcohol fermentation process. On the other hand, the dehydrated cake 2 is appropriately taken out of the system, but it is also possible to recover the C6 monosaccharide adhering to the surface by washing with water if necessary.

(Fermentation process)
Next, the C5 saccharified solution and the C6 saccharified solution are converted into ethanol using yeast in the fermentation process. A well-known fermentation method can be employ | adopted for a fermentation process. The C5 monosaccharide and C6 monosaccharide contained in the saccharified solution are converted into ethanol by the fermentation process. For the fermentation process, a known fermentation method in the brewing field can be employed.

(Distillation process)
Next, the alcohol fermentation liquid obtained by the fermentation process is distilled to concentrate ethanol. Components other than solids and ethanol are removed from the distillate obtained by the distillation step. In the distillation step, a known distillation method can be adopted as a method for producing distilled liquor.

(Washing process)
After the first solid-liquid separation step and the second solid-liquid separation step, the dehydrated cake 1 and the dehydrated cake 2 are washed with a small amount of water, and the first solid-liquid separation step and the second solid-liquid separation step are performed again. Monosaccharides and C6 monosaccharides may be recovered.

<Embodiment 2>
FIG. 2 shows a schematic flow diagram illustrating Embodiment 2 of the present invention. Since the basic flow of the present embodiment is the same as that of the first embodiment, only differences from the first embodiment will be described here. The same terminology is used for the same configuration as in the first embodiment.

  In this embodiment, the dehydrated cake 1 taken out from the solid-liquid separator 4 is supplied to the mixing tank 10 before being supplied to the reaction chamber 6 of the hydraulic cylinder type pressure reactor 5. As described above, the dehydrated cake 1 usually has a water content of about 70% by mass, but depending on the type of biomass or dehydration conditions, the water content is lower than 70% by mass and the solid content increases. There is also. In this case, if the dehydrated cake 1 is supplied as it is to the reaction chamber 6 of the hydraulic cylinder type pressurization reactor 5, the heat conduction to the dehydrated cake 1 is reduced, and the hydrolysis of cellulose in the second saccharification and decomposition step is not performed. It will be enough.

  Therefore, in the present embodiment, water and strong acid are added to the dehydrated cake 1 to form a slurry again, and this slurry is supplied to the reaction chamber 6 of the hydraulic cylinder type pressurized reactor 5. The strong acid concentration and water content of the slurry at this time are preferably adjusted in the same manner as the slurry used for the first saccharification / decomposition step.

<Embodiment 3>
FIG. 3 shows a schematic flow diagram illustrating Embodiment 3 of the present invention. Since the basic flow of the present embodiment is the same as that of the first embodiment, only differences from the first embodiment will be described here. The same terminology is used for the same configuration as in the first embodiment.

  In the present embodiment, the C5 saccharified solution taken out from the solid-liquid separation device 4 is supplied to the acid recovery device 11, and a strong acid is recovered. Similarly, the C6 saccharified liquid taken out from the solid-liquid separation device 9 is supplied to the acid recovery device 12, and a strong acid is recovered. Specific examples of the acid recovery apparatuses 11 and 12 are a reverse osmosis membrane apparatus or an electrodialysis apparatus. The deacidified C5 saccharified solution and C6 saccharified solution are supplied to the alcohol fermentation process. On the other hand, the recovered strong acid is supplied to the mixing tanks 1 and 10 and reused in the first saccharification and decomposition process. By recovering and reusing the strong acid, the consumption of the strong acid can be reduced.

<Conventional technology>
FIG. 4 is a conceptual diagram illustrating a conventional technique for saccharifying and decomposing cellulosic biomass in a supercritical state or a subcritical state, in which a strong acid is recovered and reused. The basic flow of the prior art shown in FIG. 4 is basically the same as that of the third embodiment except that a cellulose saccharification reactor 13 is used instead of the hydraulic cylinder type pressurization reactor 5. Only differences from the third embodiment will be described. The same terminology is used for the same configuration as in the third embodiment. A specific example of the cellulose saccharification reactor 13 is the same as the hemicellulose saccharification reactor 2.

  In the prior art shown in FIG. 4, after completion of the first saccharification / decomposition step, the dehydrated cake 1 taken out from the solid-liquid separation device 4 is supplied to the mixing tank 10 and water and strong acid are added. At this time, since the second saccharification / decomposition process is performed in the cellulose saccharification reactor 13, the dehydrated cake 1 needs to be adjusted to a moisture content comparable to that of the slurry supplied to the hemicellulose saccharification reactor 2. For this reason, compared with Embodiment 3, the amount of strong acid added before a 2nd saccharification decomposition process increases.

  The strong acid recovery rate in the acid recovery apparatuses 11 and 12 is the same as that in the third embodiment. However, since the amount of strong acid added to the dehydrated cake 1 in the mixing tank 10 is large, the amount of strong acid that cannot be recovered is greater than that in the third embodiment. There must be many. Since the second saccharification / decomposition step is a higher temperature and pressure condition than the first saccharification / decomposition step, the conventional technology using the cellulose saccharification reactor 13 in that the reaction can be stopped abruptly to suppress the production of by-products. Is inferior to the third embodiment in which the hydraulic cylinder type pressurized reactor 5 is used.

  The ethanol production method of the present invention is useful in the bioenergy field as a method for decomposing cellulosic biomass and producing ethanol.

DESCRIPTION OF SYMBOLS 1,10: Mixing tank 2: Hemicellulose saccharification reactor 3, 8: Flash tank 4, 9: Solid-liquid separator 5: Hydraulic cylinder type pressurization type reactor 6: Reaction chamber 7: Hydraulic cylinder 11,12: Acid recovery apparatus 13: Cellulose saccharification reactor

Claims (4)

A slurry of cellulosic biomass adjusted to pH 1.0 or more and 3.5 or less by containing a strong acid is hydrothermally treated in a supercritical state or a subcritical state, and the hemicellulose contained in the cellulosic biomass is converted into C5 monosaccharides. A first saccharification / decomposition step for saccharification / decomposition,
A first solid-liquid separation step for solid-liquid separation of the slurry after the first saccharification and decomposition step;
In a pressurized reactor, the dehydrated cake obtained in the first solid-liquid separation step is mixed with steam and pressurized until it reaches a supercritical state or a subcritical state. A second saccharification step that saccharifies into C6 monosaccharides;
A second solid-liquid separation step for solid-liquid separation of the slurry after the second saccharification and decomposition step;
A fermentation step of subjecting the saccharified solution obtained in the first solid-liquid separation step and the second solid-liquid separation step to alcohol fermentation;
A distillation step of concentrating ethanol by distilling the fermentation broth obtained by the fermentation step;
An ethanol production method using cellulosic biomass as a raw material.   The ethanol production method according to claim 1, wherein the second saccharification / decomposition step is performed after further adding a strong acid to the dehydrated cake obtained in the first solid-liquid separation step and adjusting the pH to 1.0 to 3.5. .   A strong acid is recovered from the saccharified solution obtained in the first saccharification / decomposition step and the second saccharification / decomposition step, and the recovered strong acid is used in the first saccharification / decomposition step and / or the second saccharification / decomposition step. Item 3. The method for producing ethanol according to Item 1 or 2.   The method for producing ethanol according to any one of claims 1 to 3, wherein the pressurized reactor is a hydraulic cylinder reactor.

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