JP5059650B2 - Method for producing monosaccharide or oligosaccharide from polysaccharide - Google Patents

Description

  The present invention relates to a method for producing a monosaccharide or oligosaccharide from a polysaccharide, and more particularly to a method for producing a monosaccharide or oligosaccharide by hydrolyzing the polysaccharide by a hydrothermal reaction.

  In recent years, the development of new energy resources to replace oil has been demanded due to the decrease in oil reserves and the increase in oil consumption due to the expansion of the economic scale of developing countries with large populations. In particular, due to the advantage of being recyclable, attention has been focused on biomass resources, and research and development of technologies for converting biomass resources into energy are actively conducted all over the world. At present, among various biomass resources, food resources such as starch are mainly used, causing food problems such as competition with food or increased crop prices due to conversion to crops that are raw materials for biomass resources. is there.

  Among biomass resources, if cellulose existing in large quantities in nature can be effectively saccharified (low polymerization degree), a wide variety of plant resources can be used as energy and feed by converting them into energy substances or feed as raw materials can do. For example, monosaccharides obtained by saccharifying cellulose are used as fermentation raw materials such as ethanol fermentation and lactic acid fermentation, and therefore can be converted into energy resources such as bioethanol. Monosaccharides and low-polymerization oligosaccharides can also be used as livestock feed. Furthermore, conversion from various chemical raw materials to fuel materials using monosaccharides or oligosaccharides as starting materials is also possible.

  Currently, there are a wide variety of waste materials containing cellulose or unused materials containing cellulose that are not effectively utilized. For example, forest resources such as wood, bamboo, herbs and ferns, rice, wheat, corn, stalks of grains such as straw, leaves, shells, etc. A large amount of cellulose is contained in food waste such as seafood such as foods, seaweeds, processing residues such as leftover rice and yakikuzu. A large amount of cellulose is also present in wastes such as algae, aquatic plants, and phytoplankton that have been propagated by eutrophication of lakes. In modern society, paper waste such as magazines, newspapers, OA paper, books, and packing paper is also discharged in large quantities. There is also a large amount of waste building materials. In this way, there are a lot of waste and unused substances containing cellulose, and if the cellulose contained in these can be efficiently saccharified into monosaccharides / oligosaccharides, energy resources will not occur without causing competition with food. Can be secured.

  In general, unlike polysaccharides such as starch, cellulose has a long fiber length and high crystallinity, so saccharification requires reaction conditions such as a higher reaction temperature or higher acidity than food polysaccharides such as starch. The On the other hand, the degradation product monosaccharides and low-polymerization oligosaccharides are amorphous and solubilized, so that the degradation products easily denature or undergo secondary decomposition under the above severe reaction conditions. Occurs. Among the secondary decomposition products, 5-HMF (5-hydroxymethylfurfural) in particular causes the fermentation to be inhibited. Therefore, considering that the hydrolyzed solution is used as a fermentation raw material as it is, it is desired to increase the yield of monosaccharides by reducing the generation of by-products as much as possible.

  Conventional cellulose saccharification methods include: (1) inorganic acids such as hydrochloric acid and sulfuric acid under relatively low temperature conditions (room temperature to about 100 ° C.), (2) enzymes, and (3) subcritical or supercritical. Critical water (for example, Non-Patent Document 1), (4) dilute inorganic acid (for example, Non-Patent Document 2) under high-temperature and high-pressure conditions, (5) high-concentration formic acid and hydrochloric acid (for example, Non-Patent Document 3) Hydrolysis using, etc. is known.

However, the conventional method described above has the following problems.
The acid hydrolysis method (1) is a method of decomposing using an acid such as hydrochloric acid or sulfuric acid. In this method, although it can be operated at normal pressure by heating near room temperature or slightly, the treatment time is relatively long and it is necessary to remove or neutralize the acid and desalinate after the treatment.

  The enzyme hydrolysis method (2) is costly because of the use of an enzyme, requires pH adjustment, and increases the treatment time. In addition, since cellulose has a high degree of crystallinity, the contact between the enzyme and the crystallized portion occurs only on the crystal surface, and therefore requires a significantly longer treatment time than polysaccharides having a low degree of crystallinity such as starch.

  The hydrolysis method using subcritical or supercritical water (3) is a method of performing high-speed hydrolysis in supercritical water in a state higher than the critical temperature of water (374 ° C.) or subcritical water slightly lower than the critical temperature. . However, this method has not yet been put into practical use at the experimental / research stage, and only a powder sample has been reported at this stage. In addition, although the reaction time is very short (on the order of seconds or milliseconds), it is difficult to control the reaction or to suppress secondary decomposition of the produced monosaccharide or low-polymerization oligosaccharide because of severe reaction conditions. In particular, natural cellulose has various fiber lengths, polymerization degrees, crystallinity, and shapes, so it is difficult to suppress further decomposition reaction of the product.

  The acid hydrolysis method (4) is a hydrolysis method in which hydrochloric acid or sulfuric acid, which is an inorganic strong acid, is added at a dilute concentration under high temperature and high pressure conditions. In this method, the hydrogen ion concentration in the reaction system is low, but it is difficult to say that it has a sufficient effect for suppressing side reactions.

  In the methods (1) to (4), powdered cellulose (crystallized cellulose having a low degree of polymerization) is often used as a sample, which is fibrous, has a high degree of polymerization, and has a high degree of crystallinity. There are few things that handled cotton cellulose. Powdered cellulose has a low degree of polymerization, a small particle size, and it is easier to control the decomposition reaction than fibrous cellulose, such as sample supply. However, naturally occurring cellulose has various fiber lengths, degrees of polymerization, crystallinity, and shapes. Therefore, artificially lowering the degree of polymerization is necessary to recycle naturally occurring cellulose. In many cases, the results obtained with powdered cellulose are not directly applicable. Therefore, for practical use, it is essential to demonstrate a fibrous cellulose sample having a high degree of crystallinity.

  The hydrolysis method (5) is a method of saccharifying cotton cellulose at a low temperature using a high concentration of formic acid and hydrochloric acid. This method requires a long treatment time, and the treatment requires an inorganic acid in addition to a high concentration of formic acid. It is considered that under low temperature conditions (100 ° C. or lower), formic acid alone cannot break cellulose crystals, and it is necessary to add hydrochloric acid. This method also has a low glucose yield because hydrochloric acid, which is a strong acid, promotes further decomposition of the decomposition products.

M. Sasaki, Z. Fang, Y. Fukushima, T. Adschiri, K. Arai, “Dissolution and hydrolysis of cellulose in subcritical and supercritical water”, Industrial and Engineering Chemistry Research, 2000, Vol.39, No.8, p.2883-2890. W. S. L. Mok, M.M. J. Antal, Jr., G. Varhegyi, “Productive and parasitic pathways in diluted acid-catalyzed hydrolysis of cellulose”, Industrial and Engineering Chemistry Research, 1992, Vol. 31, No. 1, p.94-100. Y. Sun, L. Lin, C. Pang, H.C. Deng, H. Peng, J .; Li, B. He, S. Liu, “Hydrolysis of cotton fiber cellulose in formic acid”, Energy & Fuels, 2007, Vol. 21, No. 4, p.2386-2389.

  The present invention provides a method for producing monosaccharides or oligosaccharides by suppressing side reactions and efficiently hydrolyzing polysaccharides (particularly fibrous cellulose having a high degree of crystallinity) in a short processing time. Objective.

  As a result of intensive studies on the hydrolysis (saccharification) of polysaccharides such as cellulose, the present inventors hydrolyze the polysaccharides by hydrothermal reaction in hot water containing weakly acidic organic acids. Thus, it was found that monosaccharides or oligosaccharides can be produced efficiently with a short treatment time. The present invention has been made based on this finding.

That is, the present invention
(1) A monosaccharide or oligo characterized by hydrolyzing a polysaccharide by hydrothermal reaction in hot water containing a weakly acidic organic acid and having a pressure of 0.2 to 100 MPa and a temperature of 120 to 300 ° C. A method for producing sugar,
(2) The method for producing a monosaccharide or oligosaccharide according to (1), wherein the polysaccharide is cellulose.
(3) The method for producing a monosaccharide or oligosaccharide according to (1) or (2), wherein the organic acid has a pKa at 25 ° C. of 1 to 6.
(4) The method for producing a monosaccharide or oligosaccharide according to any one of (1) to (3), wherein the organic acid is a carboxylic acid compound,
(5) The method for producing a monosaccharide or oligosaccharide according to any one of (1) to (4), wherein the concentration of the organic acid is 0.001 to 50% by mass,
(6) The organic acid is at least one compound selected from the group consisting of formic acid, acetic acid, oxalic acid, malonic acid, succinic acid, glycolic acid, lactic acid, cinnamic acid, and galacturonic acid. The method for producing a monosaccharide or oligosaccharide according to any one of (1) to (5),
(7) The method for producing monosaccharides or oligosaccharides according to (6), wherein the concentration of formic acid is 0.001 to 20% by mass, and (8) the polysaccharide as a raw material, A method for producing monosaccharides or oligosaccharides according to any one of (1) to (7), wherein an agricultural product containing cellulose, food waste, wood or paper is used. is there.

According to the method of the present invention, polysaccharides such as cellulose can be hydrolyzed in a short time, and monosaccharides and oligosaccharides such as glucose can be efficiently obtained. And since it reacts on comparatively mild conditions, the secondary decomposition | disassembly of the produced | generated monosaccharide and oligosaccharide can be suppressed, As a result, a monosaccharide and oligosaccharide can be obtained with a high yield.
Furthermore, since a weakly acidic organic acid is used in the present invention, corrosion of the reactor can be suppressed. Further, as compared with the hydrolysis method using an inorganic acid, the acid can be easily separated and removed, the operation burden and the environmental burden are reduced, and the side reaction hardly occurs.
Furthermore, according to the method of the present invention, monosaccharides and oligosaccharides are efficiently produced in a short time from agricultural products containing cellulose, agricultural wastes, food wastes, wood resources and forest wastes or papers. Can be manufactured.
In addition, according to the present invention, cellulose-containing agricultural products, agricultural wastes, food wastes, wood or paper are converted to fermentation raw materials such as ethanol fermentation, lactic acid fermentation, and methane fermentation by reducing the molecular weight to glucose. It is possible to produce agricultural products, food wastes, agricultural wastes, woods or papers with excellent effects.

Hereinafter, the present invention will be described in detail.
The present invention provides a monosaccharide or hydrolyzed polysaccharide by hydrothermal reaction in hot water containing a weakly acidic organic acid and having a pressure of 0.2 to 100 MPa and a temperature of 120 to 300 ° C. This is a method for producing an oligosaccharide.
In the present invention, the “polysaccharide” refers to a polymer compound that generates a monosaccharide by hydrolysis, and specifically includes starch, agar, guar gum, cellulose, glucomannan, xylan, and the like. Of these, the present invention is preferably applied to cellulose.

In the present specification, “powdered cellulose” is cellulose having a non-fibrous amorphous particle shape made of crystalline cellulose having a substantially constant polymerization degree, and has a polymerization degree of about DP = 200 to 260, and is crystallized. Degrees: x _cr = about 70%. “Cotton cellulose” is made of fibrous cellulose and has a degree of polymerization and a degree of crystallinity higher than that of powdered cellulose, a degree of polymerization: about DP = 12000, and a degree of crystallinity: about x _cr = 80%. . According to the method of the present invention, cotton cellulose having a high degree of polymerization and high crystallinity can be efficiently hydrolyzed.

  In the method of the present invention, the hydrothermal reaction is carried out in the presence of a weakly acidic organic acid. By using a weak acid, the reaction can be allowed to proceed gently, preventing further decomposition of monosaccharides and oligosaccharides produced by hydrolysis, and as a result, side reactions such as 5-HMF that become fermentation inhibitors Generation is suppressed. In addition, since it is a weak acid, there is an advantage that corrosion of the reactor hardly occurs.

  In the present invention, “organic acid” refers to an organic compound that exhibits acidity. The organic acid used in the method of the present invention is preferably a carboxylic acid compound. In the present invention, the “carboxylic acid compound” refers to an organic acid having a carboxyl group and a salt thereof. Specific examples of the carboxylic acid compound that can be used in the present invention include monocarboxylic acids having one carboxyl group in the molecule (for example, formic acid, acetic acid, propionic acid, butyric acid, etc.), and dicarboxylic acids having two carboxyl groups. (Eg, oxalic acid, malonic acid, succinic acid, etc.), hydroxycarboxylic acid having a hydroxyl group in the main chain and having a carboxyl group (eg, glycolic acid, lactic acid, malic acid, citric acid, etc.), a carboxyl having an aromatic ring Examples thereof include acids (for example, cinnamic acid, benzoic acid and the like), uronic acids (for example, galacturonic acid and the like) which are carboxylic acids having a sugar skeleton, and the like.

  Further, in the present invention, “weak acid” means an acid dissociation constant pKa at 25 ° C. of 1 to 6. Specific examples include formic acid (pKa = 3.8), oxalic acid (pKa = 1.3), succinic acid (pKa = 2.2), lactic acid (pKa = 3.9), and cinnamic acid (pKa = 3). .9) and the like.

  The weakly acidic organic acid preferably used in the present invention is at least one compound selected from the group consisting of formic acid, acetic acid, oxalic acid, malonic acid, succinic acid, glycolic acid, lactic acid, cinnamic acid, and galacturonic acid. Among them, formic acid is particularly preferable.

The concentration of the organic acid contained at the time of hydrolysis is not particularly limited. However, when a high concentration of organic acid is used, side reactions may not be sufficiently suppressed. It can also cause corrosion of the equipment. Therefore, as a density | concentration of the organic acid in this invention, Preferably it is 0.001-50 mass%, More preferably, it is 0.005-20 mass%, More preferably, it is 0.01-10 mass%.
In the present invention, the formic acid concentration when formic acid is used as the organic acid is preferably 0.001 to 50% by mass, more preferably 0.01 to 20% by mass, and still more preferably 0.05 to 10% by mass.

In the present invention, since an organic acid is used as a saccharification medium, treatments such as separation and removal of the acid from the reaction solution are easier than when hydrochloric acid, sulfuric acid, or the like is used as the saccharification medium. Organic acids such as formic acid, acetic acid and propionic acid have low boiling points (formic acid: 101 ° C., acetic acid: 118 ° C., propionic acid: 141 ° C.), and can be vaporized by distillation / evaporation and separated from the solubilized liquid. . Further, if distilled under reduced pressure, it is possible to separate the organic acid from the reaction solution at a lower temperature. In particular, when formic acid is used as the organic acid, the treated solution may be neutralized and desalted as in the case of the inorganic acid, but the boiling point is 101 ° C., which is close to the boiling point of water, and the solution is distilled and evaporated. It can be easily removed by operation. Further, the decomposition product of formic acid is carbon monoxide (CO) and water (H ₂ O) or carbon dioxide (CO ₂ ) and hydrogen (H ₂ ). Under reaction temperature conditions, side reactions due to these decomposition products are also relatively difficult to occur.
Therefore, in this invention, the burden of the acid treatment operation performed after reaction can be reduced, a process can be simplified, and cost and energy can be reduced.

In the method of the present invention, hydrolysis is performed in hot water. Water has a hydrolysis action by hydrogen ions and hydroxide ions, but in high-temperature and high-pressure water, the ion product indicating the amount of these ions becomes large and the hydrolysis action becomes intense.
In this specification, “hot water” means a pressure of 0.2 to 100 MPa, preferably 0.5 to 50 MPa, more preferably 1 to 30 MPa, and 120 ° C. or more, preferably 140 to 300 ° C., more preferably. Means water at 150 to 300 ° C. In this specification, “supercritical water” refers to water having a critical point (375 ° C., 22 MPa) or more, and “subcritical water” refers to a pressure of 8.5 to 22 MPa and 300 ° C. It means water under conditions of more than 375 ° C. Therefore, in this specification, hot water is clearly distinguished from supercritical water or subcritical water. In the case of polysaccharide degradation, the higher the processing temperature, the easier the polysaccharide and product monosaccharides and oligosaccharides denature. In the present invention in which hydrolysis is performed in hot water, the reaction temperature and pressure are lower than those of supercritical water and subcritical water, and therefore, there is an advantage that modification of polysaccharides and the like is less.
In the present invention, the reaction temperature during the hydrothermal reaction is preferably 120 to 300 ° C, more preferably 140 to 300 ° C, and even more preferably 150 to 300 ° C. When processing especially about cellulose, 180-300 ° C is preferred and 200-300 ° C is still more preferred.

  In the present invention, the pressure in the reactor during the hydrothermal reaction only needs to be maintained at or above the saturated vapor pressure of the solvent at each reaction temperature. If the pressure in the reactor is maintained at or above the saturated vapor pressure, the solvent becomes a liquid phase, and a stable flow rate is obtained, so that the hydrolysis reaction proceeds smoothly. The preferable pressure at the time of hydrothermal reaction is 0.2-100 MPa, More preferably, it is 0.5-50 MPa, More preferably, it is 1-30 MPa. In particular, when the treatment is performed on cellulose, 0.2 to 100 MPa is preferable, and 1 to 30 MPa is more preferable.

  Cellulose is a polysaccharide obtained by polymerizing glucose, which is the same as starch, but has a different chemical structure and has a strong hydrogen bond in the molecule. Therefore, it is crystallized, is thermally stable as compared with starch, is stable against acid or alkali, and hydrolysis of cellulose requires more severe reaction conditions than starch hydrolysis. In order to decompose such a crystallized cellulose sample, it is necessary to break the intramolecular hydrogen bond to make it non-crystallized and solubilized. Once cellulose is non-crystallized and solubilized, it can be easily hydrolyzed and saccharified. One method for breaking intramolecular hydrogen bonds is heating. When the treatment temperature is increased, the thermal motion of the cellulose molecules becomes active, the hydrogen bond strength becomes relatively weak, and a part of it is cut. Note that cellulose can be decomposed at about 320 ° C. or higher even in a vacuum or inert gas atmosphere in which no solvent such as water exists, but in such a thermal decomposition reaction, the secondary decomposition of the decomposition products further proceeds. Therefore, it is not suitable as a method for producing monosaccharides or oligosaccharides. Moreover, by adding a strong acid (inorganic acid) and performing acid hydrolysis, the hydrogen bond in a molecule | numerator can be cut | disconnected and also a glucoside bond can be cut | disconnected. However, even in this method, the secondary decomposition of the decomposition product further proceeds due to the strong acid, and the yield of monosaccharide (glucose) is low.

  On the other hand, in the method of the present invention, partial hydrogen bonds in cellulose are broken by heating, or the bonds are weakened, and acid hydrolysis is performed by adding a small amount of weak acid. By using a weak acid, the hydrolysis reaction proceeds gently under weak acidic conditions, so that further secondary decomposition of the decomposed product can be suppressed.

According to the present invention, when the polysaccharide is hydrolyzed, the polymerization degree of cellulose can be adjusted from a polymer having a high polymerization degree to an oligomer or monomer (glucose) by appropriately adjusting the treatment time. Specifically, glucose as a monosaccharide and cellobiose, cellotriose, cellotetraose, cellopentaose, cellohexaose, celloheptaose, cellooctaose, etc. are produced as oligosaccharides. Even sugar is produced. In order to mainly produce glucose as a monosaccharide in the entire product, the reaction conditions are preferably a hot water temperature of 200 to 300 ° C. and a reaction time of 2 to 120 minutes. However, these reaction conditions vary depending on the concentration of the acid used. It is considered that the optimum reaction condition is that the reaction time may be short if the hot water temperature is high, and the reaction time is long if the hot water temperature is low.
In the present invention, the oligosaccharide is preferably one having a polymerization degree of about 30 or less, more preferably 2-6 monosaccharides subjected to condensation polymerization.

  When polysaccharides are hydrolyzed, products such as glucose are decomposed when they are present in the reactor after production, causing 5-HMF (5-hydroxymethylfurfural), which causes fermentation inhibition. According to the method of the present invention, since it is a hydrothermal reaction under the relatively mild conditions as described above, the secondary decomposition of the product can be suppressed.

  In the present invention, monosaccharides and oligosaccharides can be separated by chromatography (particularly gel filtration chromatography), crystallization using a difference in solubility, or membrane separation.

  In the present invention, the reactor may be a batch type or a continuous type, but a continuous type reactor is preferred from an industrial viewpoint. As a requirement of the reactor, a structure capable of suppressing side reactions so that further decomposition of the product does not occur is preferable. That is, the reactor can be quickly separated from the solvent, the sample and the product after the reaction, or the reactor having a function that the produced monosaccharide or oligosaccharide can be quickly removed from the reaction zone or rapidly cooled. A reactor having a structure is preferred. In the case of using a continuous reactor, water containing the sample and the organic acid are continuously supplied to the reactor at a predetermined flow ratio to carry out the reaction.

Next, a method for producing glucose using cellulose-containing agricultural products (agricultural waste), food waste, wood or paper as a raw material will be described.
Glucose and oligosaccharides thereof can be produced by performing the above hydrolysis method using cellulose-containing agricultural waste, food waste, wood or paper as a raw material.
Specific examples of cellulose-containing agricultural waste include, for example, stalks, leaves, shells, etc. of grains such as rice, wheat, corn, and straw, fruit peels such as apples and tangerines, and mushrooms. .

Utilizing the present invention, cellulose-containing agricultural waste, food waste, wood, or paper can be used as resources. Specifically, the obtained glucose and its oligosaccharide can be used in fields such as foods and pharmaceutical raw materials.
In addition, agricultural waste, food waste, wood or paper containing cellulose can be converted into glucose and its oligosaccharides and converted into fermentation raw materials. Specifically, raw materials for ethanol fermentation, lactic acid fermentation, and methane fermentation can be produced.

  In the case of ethanol fermentation, ethanol can be produced and used as fuel. Further, ethylene can be produced from ethanol, and various industrially useful compounds can be produced.

  In the case of lactic acid fermentation, lactic acid can be produced and used as a raw material for biodegradable plastics.

  In the case of methane fermentation, methane can be produced and used as fuel. Moreover, hydrogen can be produced from methane and can be used as a raw material for fuel cells.

  EXAMPLES Next, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these.

In all the examples, a semi-batch reactor (volume 3.5 mL) was used, but the effect of this method is not limited by the type and shape of the reactor. In all the examples, the reaction pressure is 10 MPa, but is not necessarily limited to 10 MPa.
In addition, absorbent cotton (Japanese Pharmacopoeia; polymerization degree DP = 12000; crystallinity degree x _cr = 80%) was used as the cellulose sample in the examples.

Example 1
(Comparison between aqueous formic acid and aqueous acetic acid)
A tubular reactor (internal volume: 3.5 mL) was used as a semi-batch reactor, and 0.5 g of a cellulose sample was gently charged into the reactor at room temperature. A molten salt thermostat bath that continuously supplies an organic acid aqueous solution having a concentration of about 0.1% by mass from a solvent tank to the reactor at a flow rate of 15 ml / min while maintaining the reactor at 250 ° C. (The temperature fluctuation is ± 1 ° C. or less) and the hydrothermal reaction was started. In addition, it was confirmed that the temperature inside the reactor reached the set temperature within about 30 seconds at any reaction temperature by measuring the change in temperature inside the reactor using the thermocouple inserted in the reactor. did. The pressure in the reactor was kept at 10 MPa (pressure fluctuation ± 0.1 MPa or less) by a pressure regulating valve set at the outlet of the flow path. The reaction solution was taken out at regular time intervals, quenched with a solvent cooling device to stop the reaction, and then collected from the outlet of the back pressure valve, and the saccharification yield and monosaccharide yield were measured by liquid chromatography.

  In the above experiment, the saccharification yield in the case of using a formic acid aqueous solution having a concentration of 0.1% by mass or an acetic acid aqueous solution having a concentration of 0.13% by mass as the organic acid, and when only water is supplied without adding the organic acid, Monosaccharide (glucose) yields were compared. The results are shown in FIG. 1 and FIG.

In the following examples, the saccharification yield (% by mass) and the monosaccharide yield (% by mass) are
Saccharification yield (% by mass):
(Carbon mass (g) in monosaccharide and oligosaccharide (degree of polymerization DP = 1-9) / carbon mass (g) of cellulose) × 100
(Here, the saccharification yield represents the total integrated yield of monosaccharides / oligosaccharides from monosaccharide to polymerization degree DP = 9 on a carbon weight basis.)
Monosaccharide yield (% by mass):
(Carbon mass of glucose (g) / carbon mass of cellulose (g)) × 100
It calculated | required from the numerical formula of.

  As apparent from FIGS. 1 and 2, when no organic acid was added, the saccharification yield was about 20% and the monosaccharide yield was 10% or less even after 60 minutes of reaction. Alternatively, when acetic acid was added, the saccharification yield was 50% or more and the monosaccharide yield was 20% or more, and it was found that the addition of organic acid significantly increased the saccharification yield and monosaccharide yield. In particular, the use of formic acid as an organic acid is more effective for saccharification of cellulose because both monosaccharide yield and saccharification yield are higher when formic acid is added than when acetic acid is added. I understood.

Example 2
(Effect of temperature)
In the same manner as in Example 1, 0.5 g of a cellulose sample was filled in a reactor, and a hydrothermal reaction was performed by continuously supplying a formic acid aqueous solution having a concentration of 0.1% by mass at a flow rate of 15 ml / min. The pressure in the reactor was kept at 10 MPa. The temperature of the reactor was set for each 20 ° C. in the range of 230 ° C. to 270 ° C. The reaction solution was collected at regular time intervals, and the saccharification yield and monosaccharide yield at each temperature were measured. The results are shown in FIGS. 3 and 4, respectively.
When reacted at 270 ° C, the saccharification yield 15 minutes after the start of the reaction is almost 85%, the monosaccharide yield has reached 40%, and a high saccharification yield can be obtained in a relatively short reaction time. I understood.

In the above experiment, the yield of by-produced 5-HMF (hydroxymethylfurfural) was also measured. 5-HMF is thought to be generated by further degradation of the product sugar. The results are shown in FIG.
Even after the reaction at 270 ° C. for 60 minutes, the yield of 5-HMF was approximately 1%, and the production amount was very suppressed. It can be said that it is very preferable from the viewpoint of fermentation treatment that 5-HMF, which is a fermentation inhibitor, is suppressed to a low concentration.

  Furthermore, the yields of sugars of each degree of polymerization contained in the reaction liquid obtained in the above experiment were compared. The results are shown in FIG. It was found that the ratio of the yield of sugar at each degree of polymerization was almost constant regardless of the temperature, and the decomposition reaction proceeded gently at any temperature. As shown in FIG. 3, the integrated yield after 60 minutes of each sample strongly depends on the temperature, but the ratio of the components in the reaction solution is almost constant at each temperature, and 45% of the generated sugar is a monosaccharide. 20% were disaccharides, and the yield gradually decreased as the degree of polymerization increased.

Example 3
(Influence of formic acid concentration)
Using the same reaction apparatus as in Example 1, 0.5 g of a cellulose sample was filled, aqueous formic acid solutions of various concentrations were continuously supplied to the reactor at a flow rate of 15 ml / min, and hydrothermal reaction was performed at a reaction temperature of 250 ° C. Went. The pressure in the reactor was kept at 10 MPa. Changes in saccharification yield and monosaccharide yield over time are shown in FIGS. 7 and 8, respectively. The formic acid concentration of 0% by mass indicates distilled water.
With increasing formic acid concentration, saccharification yield and monosaccharide yield increased. With a formic acid concentration of 1% by mass, a saccharification yield of 90% or more could be obtained in a reaction time of 20 minutes, and the monosaccharide yield also reached 60%. Even with formic acid at a concentration lower than 1% by mass, the reaction proceeds uniformly with increasing time, and the treatment time becomes longer, but higher saccharification and monosaccharide yields can be obtained than when formic acid is not added. It was.

  In the above experiment, the yield of 5-HMF (hydroxymethylfurfural) was measured. The results are shown in FIG. As the formic acid concentration increased, the 5-HMF yield increased. Even when the formic acid concentration was 1% by mass, the 5-HMF yield was about 1.5% by mass at maximum. Considering that the saccharification yield after 20 minutes had reached 90% and the monosaccharide yield had approached 60% at the formic acid concentration of 1% by mass (FIGS. 7 and 8), 5-HMF at this point The yield of only 1% or less indicates that the further decomposition reaction of the produced monosaccharide / oligosaccharide is remarkably suppressed.

  Furthermore, the yields of sugars at various degrees of polymerization in the reaction solutions obtained in the above experiments were compared. The results are shown in FIG. The ratio of the sugar yield at each degree of polymerization was almost constant regardless of the formic acid concentration, and it was found that the decomposition reaction proceeded gently at any temperature. Of the produced sugars in the reaction solution, monosaccharides accounted for 50%, and disaccharides accounted for 20%, and the yield decreased successively as the degree of polymerization of the sugar increased.

Example 4
(Comparison with inorganic acid)
Using the same reactor as in Example 1, 0.5 g of a cellulose sample was filled, acid aqueous solutions of various concentrations were continuously supplied to the reactor at a flow rate of 15 ml / min, and hydrothermal reaction was performed at a reaction temperature of 250 ° C. Went. The pressure in the reactor was kept at 10 MPa. With respect to the case where the acid aqueous solution is sulfuric acid which is an inorganic acid of formic acid and strong acid, changes in saccharification yield and glucose yield over time at each concentration were compared. The results are shown in FIG. 11 and FIG.
In the case of 0.01 mass% (1 mM) sulfuric acid aqueous solution, it was observed that the solution was colored orange after 25 minutes, and the saccharification yield 40 minutes after the reaction was 80%. Here, the color change to orange indicates that the inner wall of the reactor is corroded. In addition, it was found that after 40 minutes, the total amount of total organic carbon in the solution was almost 100%, and the cellulose sample was solubilized by almost 100%. On the other hand, in the case of a 1% by mass (217 mM) formic acid solution, the solution was colorless and transparent even after 60 minutes, and a saccharification yield was 95.4%. Furthermore, as for the glucose yield, the yield after 40 minutes was about 40% in the case of the 0.01% by mass sulfuric acid aqueous solution, but the yield in the case of the 1% by mass formic acid aqueous solution was as high as 65%. . That is, in the 0.01% by mass sulfuric acid aqueous solution, although the cellulose sample was almost completely solubilized 40 minutes after the reaction, the saccharification yield and monosaccharide yield were low, and this was generated. This is probably because monosaccharides and oligosaccharides are secondarily decomposed by side reactions.
Furthermore, when the sulfuric acid aqueous solution was used, corrosion was observed inside the reactor even at a low concentration of 0.01% by mass. However, in the case of the formic acid aqueous solution, such corrosion was not observed, and the formic acid It was found that the corrosion of the reactor can be suppressed by using an aqueous solution.

In general, even with an inorganic acid that is a strong acid, a solution having a weak acidity can be obtained at a dilute concentration. However, at the same concentration, a strong acid has a higher acidity, and thus hydrolysis proceeds faster. In the case of this example, since sulfuric acid is a strong acid, the degree of ionization is considered to be 100%. Therefore, even with sulfuric acid having a concentration of 0.01% by mass, cellulose was almost completely solubilized in 40 minutes. On the other hand, formic acid is a weak acid and is not completely ionized (saturated aqueous solution of formic acid, pK _a = 3.8). In order to completely solubilize glucose, a higher concentration than sulfuric acid is required. . However, even if the concentration is high, since it is a weak acid, side reactions are suppressed, and as a result, almost 100% saccharification has been achieved. That is, it was found that higher saccharification yield and monosaccharide yield can be obtained by using a lower concentration organic acid than a lower concentration inorganic strong acid.

Example 5
(In the case of malonic acid)
Using the same reaction apparatus as in Example 1, 0.5 g of a cellulose sample was filled, and 0.226 mass% (21.7 mM) malonic acid aqueous solution was continuously supplied to the reactor at a flow rate of 15 ml / min. Hydrothermal reaction was performed at a temperature of 250 ° C. The pressure in the reactor was kept at 10 MPa. The time course of saccharification yield and glucose yield is shown in FIG. As a result, it was found that malonic acid is also effective for saccharification of cellulose.

It is the graph which showed the relationship between the addition of an organic acid and the saccharification yield in the hydrolysis of cellulose (Example 1). It is the graph which showed the relationship between the addition of an organic acid and the monosaccharide (glucose) yield in the hydrolysis of cellulose (Example 1). It is the graph which showed the relationship between reaction temperature and saccharification yield in the hydrolysis of cellulose (Example 2). It is the graph which showed the relationship between the reaction temperature and the monosaccharide (glucose) yield in the hydrolysis of cellulose (Example 2). It is the graph which showed the relationship between the reaction temperature and the 5-HMF yield in the hydrolysis of cellulose (Example 2). It is the graph which showed the relationship between the saccharide | sugar yield of each polymerization degree with respect to the reaction temperature and the saccharification yield in the hydrolysis of a cellulose (Example 2). It is the graph which showed the relationship between the formic acid concentration and the saccharification yield in the hydrolysis of cellulose (Example 3). It is the graph which showed the relationship between the formic acid density | concentration and the monosaccharide (glucose) yield in the hydrolysis of a cellulose (Example 3). It is the graph which showed the relationship between the formic acid concentration and 5-HMF yield in the hydrolysis of cellulose (Example 3). It is the graph which showed the relationship between the sugar yield of each polymerization degree with respect to the formic acid density | concentration and the saccharification yield in the hydrolysis of a cellulose (Example 3). It is the graph which showed the relationship between the formic acid concentration and the sulfuric acid concentration, and the saccharification yield in the hydrolysis of cellulose (Example 4). It is the graph which showed the relationship between the formic acid concentration and sulfuric acid concentration, and the monosaccharide (glucose) yield in the hydrolysis of cellulose (Example 4). It is the graph which showed the saccharification yield and the monosaccharide (glucose) yield in the hydrolysis of the cellulose using malonic acid (Example 5).

Claims (8)

Was contained weakly acidic organic acids, pressure 0.2～100MPa, in hot water at a temperature 120 to 300 ° C., a polysaccharide hydrolyzing the hydrothermal reaction, a process for the preparation of a mono- or oligosaccharide The method for producing monosaccharides or oligosaccharides, wherein the polysaccharide is cotton cellulose . The method for producing monosaccharides or oligosaccharides according to claim 1 , wherein the cotton cellulose is composed of fibrous cellulose, having a degree of polymerization of about 12000 and a degree of crystallinity of about 80% .   The method for producing monosaccharides or oligosaccharides according to claim 1 or 2, wherein the organic acid has a pKa at 25 ° C of 1 to 6.   The method for producing a monosaccharide or oligosaccharide according to any one of claims 1 to 3, wherein the organic acid is a carboxylic acid compound.   The method for producing a monosaccharide or oligosaccharide according to any one of claims 1 to 4, wherein the concentration of the organic acid is 0.001 to 50 mass%.   The organic acid is at least one compound selected from the group consisting of formic acid, acetic acid, oxalic acid, malonic acid, succinic acid, glycolic acid, lactic acid, cinnamic acid, and galacturonic acid. The manufacturing method of the monosaccharide or oligosaccharide of any one of 1-5.   The method for producing a monosaccharide or oligosaccharide according to claim 6, wherein the concentration of formic acid is 0.01 to 20% by mass. The production of monosaccharides or oligosaccharides according to any one of claims 1 to 7, wherein agricultural polysaccharides, food wastes, woods or papers containing cotton cellulose are used as the raw material polysaccharides. Method.

Images